Small V/STOL aircraft analysis, volume 1

N A S A C O N T R A C T O R

N A S A C R - 2 4 2 5

R E P O R T

fie:

SMALL V/STOL AIRCRAFT ANALYSIS

Volume I

by K. R. Smith, Jr., and F. W. Belina

Prepared by

THE AEROSPACE CORPORATION

El Segundo, Calif.

i<

Jor Ames Research Center

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION • WASHINGTON, D. C. MAY 1974

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

NASA CR - 2425 5. Report Date 4. Title and Subtitle MAY 19?U "Small V/STOL Aircraft Analysis Volume I 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No.

K. R. Smith, Jr., and F.W. Belina 10. Work Unit No.

9. Performing Organization Name and Address The Aerospace Corporation 11. Contract or Grant No.

El Segundo, California NAS 2-6473 13. Type of Report and Period Covered Contractor Report 12. Sponsoring Agency Name and Address Final Report National Aeronautics § Space Administration 14. Sponsoring Agency Code Washington, D.,C.

15. Supplementary Notes 16. Abstract A study has been made of the economic viability of advanced V/STOL aircraft concepts in performing general aviation missions. A survey of general aviation aircraft users, operators, and manufacturers indicated that personnel transport missions formulated around business executive needs, commuter-air service, and offshore oil supply are the leading potential areas of application using VTOL aircraft. Advanced VTOL concepts potentially available in the late 1970 time period were evaluated as alternatives to privately owned contemporary aircraft and commercial airline service in satisfying these personnel transport needs.

Economic analysis incorporating the traveler's value of time as the principle figure of merit vere used to identify the relative merits of alternative VTOL air transportation concepts.

Four representative advanced VTOL concepts were evaluated-compound helicopter, tilt rotor, tilt wing, and lift fan. Due to its low speed and short range characteristics, the compound helicopter was found to have little advantage over the conventional helicopter. Cost benefit analysis showed, however, that the tilt rotor, tilt wing, and lift fan could all compete favorably with currently used conventional aircraft and, for the higher time value passenger, the airlines. Specific comparison of these three advanced promising concepts showed the tilt wing slightly more advantageous than the tilt rotor due to the former's higher speed and lower cost characteristics. The higher speed lift fan was best suited to the longer range missions.

However, since there was little difference between these three advanced concepts, all three appeared promising to pursue.

17. Key Words (Suggested by Author(s)) 18. Distribution Statement General Aviation VTOL Aircraft UNCLASSIFIED-UNLIMITED Business Air Transportation r -> .-~. -•',"'•' , ••" .-.-«. CAT. 02 """"• -I':"' •-,;>. >,, .; ; . , - , . .

: 19. Security Classif. (of this report) 20. Security Ciassif. (of this page) 21 . No. of Pages 22. Price* UNCLASSIFIED .^'UNCLASSIFIED 86 4.00 *For sale by the National Technical Information Service, Springfield, Virginia 22151 SMALL V/STOL AIRCRAFT ANALYSIS Volume I ACKNOWLEDGMENTS This Small V/STOL Aircraft Analysis was performed for the Ames Research Center of NASA. Appreciation is extended to Mr. Elwood Stewart, the NASA Technical Monitor, and to Mr. T. W. Feistel and Mr. D. H. Hickey for their assistance and guidance during the study.

Many members of the technical staff of The Aerospace Corporation participated in the study. Particular acknowledgment for valuable contribu- tions is given to: John M. Lyons (Aircraft characterization) Suzanne C. Miller (Time value analysis) Joseph A. Neiss (Economics) CONTENTS INTRODUCTION 1 I.

SUMMARY AND CONCLUSIONS II.

GENERAL AVIATION MISSIONS

III. 5

Mission and Aircraft Characteristics A. 6 Comparison of Current vs. Desired Mission and B.

Aircraft Characteristics Criteria Definition 17 C.

D. VTOL Market Potential 20 AIRCRAFT CONFIGURATIONS AND CAPABILITIES IV. 23 Composite Current Aircraft A. 24 B. Advanced Aircraft Concepts Scheduled Airline Capabilities C.

V. AIRCRAFT COST BENEFIT ANALYSES A. Executive Transportation Mission Cost Benefit Analysis 45 B. Commuter Air Carrier Mission Cost Benefit Analysis 73 C. Offshore Mission Cost Benefit Analysis 77 VI. CONCLUDING REMARKS 83 VII. REFERENCES 85 VII

FIGURES

1. Desired Mission and Aircraft Characteristics 11

2. Comparison of Desired Mission and Current Aircraft Characteristics (Turbojet, Turboprop, and Helicopter) . . - . . , 13 3. Comparison of Desired Mission and Current Aircraft Characteristics (Large Twin Piston) 4. Comparison of Desired Mission and Current Aircraft Characteristics (Small Twin Piston) 15 5. Market Potential- -Fixed Wing Aircraft 21 6. Market Potential- -Helicopters . . 21 7. Advanced Small Aircraft Concepts '.'. 30 8. Passenger /Range Diagram Airline Trip Time (Block) 9.

10. Airline Trip Cost (Coach).

Scenario for Executive Travel 11. 44 12. Executive Mission- -Short Distance with Small Aircraft . . .

13. Executive Mission — Long Distance with Jet Aircraft 14. Two-Phase Time Value Diagrams for Small 15. Multiple -Phase Time Value Diagrams for Small . . 55 16.

17. Effect of Productive Work--Enroute Airline with Two-Phase Time Value Diagrams for Small VTOL 18.

. . 59 Vlll FIGURES (Continued) 19. Multiple-Phase Time Value Diagrams for Small VTOL/ and Contemporary Aircraft (AT = 1 hr) 60 : 20. Lift Fan Cost Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . 62 21. Small Lift Fan Extended Range Capabilities ;.. .,; . . 63 22. Advanced Large Aircraft Serving Executive Mission 65 23. Small Helicopter--CTOL Aircraft in Combination . . . . . . . . . 66 24. Definition of Fixed Distance Mission (Small" Aircraft) 69 25. Cost Savings of Small VTOL Relative to Small Turbojet 70 26. Cost Savings of Large VTOL Relative to Large Turbojet . . . . 72 27. Commuter Mission--Intercity Service with Large Aircraft • 75 28. Advanced Large Tilt Wing Aircraft in Commuter Mission 78 29. Offshore Mission--Crew Change with Large Aircraft 79 30. Offshore Mission--Supervisory Personnel Movement with Small Aircraft. . ; 81 IX TABLES I. General Aviation Current Aircraft Types and Mission Characteristics . . 8 II. Most Commonly Used Aircraft . 9 III. Potential Market for Improved Technology Aircraft 22 IV. Representative Current Aircraft 25 V. Small Composite Aircraft Descriptions . . . . ; . . . . 26 VI. Large Composite Aircraft Descriptions 27 VII. Composite Aircraft Cost Summary 28 VIII. Small Advanced Aircraft Descriptions 32 IX. Large Advanced Aircraft Descriptions . . . . . ' 34 X. Advanced Aircraft Cost Summary . 39 XI. Ground Rules for Scenario Development 45 XII. Executive Mission Time and Cost Parameters 47 XIII. Commuter and Offshore Mission Time and Cost Parameters . '74 I. INTRODUCTION In recent years the. possibility of providing air service into urban or industrial activity centers has received considerable attention. How- ever, vertical and/or short takeoff and landing (V/STOL) aircraft studies and flight test programs instituted to develop .and evaluate this service concept have been largely oriented toward large commercial airline applications. To date, there has been no significant examination of the applicability of V/STOL concepts to the needs of general aviation. Historically, general aviation acceptance of new aircraft concepts (e. g. , turbojets and helicopters) has, with some exceptions,followed widespread military and commercial applications.

The reasons for this delay are primarily economic, but also involved is the need for public familiarity with a concept prior to its broad acceptance. Thus the initial introduction of a new aircraft concept into the usually conservative general aviation field is essentially without precedent.

The objective of the present study was to investigate the applicability of V/STOL advanced technology to significant general aviation transportation needs and to assess the economic viability of V/STOL aircraft in those roles.

Identification of technology goals related to small aircraft applications was considered appropriate to provide further direction to V/STOL development activities. The study focused on the late 1970's, a period representing the earliest availability of advanced technology aircraft.

In performing the study, a. survey of general aviation users, manu- facturers, and trade associations was made first in order to identify the principal applications of the existing general aviation fleet. Based on the survey results, criteria for desired aircraft capabilities were then defined General aviation is a broad term applied by the Federal Aviation Adminis- tration (FAA) to those operations which are nonmilitary and outside of the Civil Aeronautics Board (CAB) regulated trunk and local service airlines.

More than 139, 000 aircraft are in use for a wide variety of purposes, ranging from air taxis and corporate personnel transportation to crop dusting and external load carrying.

for the principal mission areas. Preliminary performance and weight charac- teristics were defined for a number of advanced V/STOL concepts (compound helicopter, tilt rotor, tilt wing and lift fan) and conventional aircraft that satisfied the postulated mission criteria, and these concepts were then com- pared based on a cost-benefit measure related to the traveler's value of time.

The results of this analysis are presented in terms of the traveler's value of time, thereby permitting a wide range of comparisons to be made.

This report consists of two volumes: Volume I contains data and study results related to (1) General Aviation Missions, (2) Aircraft Configurations and Capabilities, and ,(3) Aircraft .Cost-Benefit Analyses. Volume II (Ref. 2) consists of appendices presenting the detailed results.of the survey activity, aircraft economics and cost-benefit analysis methodology, and other pertinent reference data. . .

/ 2) v 'The technology and operations of the small advanced V/STOL aircraft utilized in this study are discussed in greater detail in Ref. 1.

II. SUMMARY AND CONCLUSIONS A study has been made of the potential application of advanced V/STOL aircraft design concepts to general aviation missions. The advanced concepts considered include both small (8 to 10 passenger) and large (15 to 18 passenger) aircraft and reflect a state of the art applicable to the late 1970's. Whereas the evolution of general aviation aircraft has traditionally followed very conservative practices, there are significant advantages apparent for vertical takeoff and landing (VTOL) applications in personnel transport missions formulated around executive needs, commuter air service, and offshore oil supply. The VTOL capability appears most desirable from the standpoint of easy access to locations not served by,' or conveniently accessible to, scheduled airlines. Further, since most business activities are schedule oriented, the higher cruise speed advanced configurations appear to be of greater value. In view of these advantages, the economics of the advanced VTOL concepts appears favorable; however, such operational features as complexity and noise may become significant in the final choice.

The following specific conclusions can be drawn from the results of the study: • Advanced VTOL aircraft concepts have a potential application in executive, commuter, and offshore general aviation operations and can be competitive with current conventional takeoff and landing (CTOL) aircraft and helicopters.

• Based upon survey results and a city center access analysis, there appears to be less interest and advan- tages in advanced short takeoff and landing (STOL) aircraft in general aviation operations supporting business activities. Rather, advanced VTOL concepts giving maximum access capability appear favored within reasonable economic bounds.

Cost benefit analysis indicated that: a. The compound helicopter has little advantage over the helicopter and cannot compete with the longer range and faster VTOL concepts.

b. The tilt rotor, tilt wing, and lift fan concepts are roughly similar in their regions of economic operation and can compete favorably with con- : ventional aircraft and for many applications, the airlines.

c. Detailed comparisons indicate that the tilt rotor concept appears superior to both the helicopter and compound helicopter, but for long range applications lacks the higher speed advantages . .-..

of the tilt wing and lift fan concepts. The tilt wing concept, because of its speed and cost characteristics, appears to be the most viable of the advanced VTOL aircraft concepts con- sidered. The lift fan, offering high-speed capabilities, appears slightly better than the .

tilt wing for longer ranges and larger sizes.

However, since there was little significant difference among these three advanced concepts for most mission applications, all three concepts would appear promising to pursue.

While this study has identified preferred VTOL concepts based on mission performance and economic benefits, -.<• considerations of technological complexity and environ- mental impact may greatly affect concept preference.

The potential market for VTOL aircraft in executive, commuter, and offshore missions could utilize up to approximately 2200 large (16 passenger) aircraft and as many as 5500 small (8 passenger) aircraft by 1982.

Advanced aircraft concepts combining VTOL capabilities with good high-speed, long-range performance could significantly expand the utilization of aircraft for general aviation purposes, overcoming current access problems : : to new business locations, providing time savings to business travelers, and giving increased flexibility and improved utilization of the aircraft.

III. GENERAL AVIATION MISSIONS An initial effort was made to identify the general aviation activities that might be performed by small aircraft incorporating V/STOL technology.

The effort concentrated on the late 1970's--a period in which V/STOL con- cepts now in the design or development stage could be expected to be in service. In addition to identifying the possible applications, the study effort included an attempt to define the critieria by which users of small aircraft select their equipment. The combination of these two study activities was intended to provide a basis for evaluating the merits of alternative V/STOL concepts for satisfying the needs of the general aviation community.

The required data were obtained from the general aviation com- munity itself including aircraft manufacturers, commuter air carriers, and executive and commercial aircraft operators. These sources were sup- plemented by various aviation associations and governmental organizations that either use or administer the operation of such equipment. Appendix A in Volume II (Ref. 2) identifies the principal sources of the information on which this study effort was based and indicates the cross-section of the general aviation community from which the information was obtained.

In the following material in this section the results of these survey efforts are summarized in terms of (1) current and desired mission and air- craft characteristics, (2) comparison of current and desired mission and aircraft characteristics, and (3) the definition of criteria for identifying promising V/STOL applications and concepts.

The results of these efforts unavoidably include a degree of imprecision. In part this is due to the absence of complete statistics on general aviation activities. More importantly, the operators themselves in many cases tend to be specialized, serving highly constrained markets and consequently choosing their equipment for those applications based upon current aircraft capabilities. In other cases the operators are subjective in their equipment selection—placing emphasis on non-quantifiable factors such as aesthetics, furnishings, and prestige--and are therefore limited in providing precise criteria upon which their response to future aircraft devel- opments could be predicted. The study results are, however, based on a broad sampling of statistics and opinions of general aviation operators and equipment suppliers, and provide a consensus of the needs and requirements of the current general aviation community.

A. MISSION AND AIRCRAFT CHARACTERISTICS The general aviation community was divided into four mission categories for this study: 1. Air Taxi Commuter Air Carriers Intercity Service Central Business District (CBD) Service Non-Scheduled 2. Business Executive Transportation^) .

: Short Distance (< 100 miles) Medium Distance (100 to 500 miles) Long Distance (>500 miles) Business Transportation' ' . :": ; Short Distance • - ^ Medium Distance Long Distance 3. Aerial Application (Crop Dusting) /4\ 4. Industrial Special^ ' Any operator of small aircraft (30 passengers or less or 7500 Ib maximum payload) who performs, pursuant to a published schedule, at least five round trips per week between two or more points, or carries mail on contract.

Three of these categories received special emphasis: (1) Air Taxi (Commuter Air Carriers), (2) Business (Executive Transportation), and (3) Industrial Special (those applications dealing with p e r s o n n e l t r a n s p o r t ) .

It was judged that these categories would exhibit a high degree of commonality in requirements, would utilize professional flight crews with the skills neces- sary to adapt.to V/STOL operations, and would represent the greatest market potential in terms of numbers of aircraft operated and the capability of the users to meet the investment requirements.

1. CURRENT MISSION AND AIRCRAFT CHARACTERISTICS Table I shows the type of aircraft currently utilized for the four categories of general aviation missions and summarizes the characteristics of those missions. (The data in this table are predominantly from the sur- vey interviews.)

Table II summarizes the more popular aircraft and helicopter models employed in each mission category as a. function of hours flown as determined from R e f s . 3, 4, and 5. A more detailed basis for this deter- mination is included in Appendix B of Volume II ( R e f . 2). It is noted that in many missions relatively old models are heavily employed. This reflects the apparent desire for minimum investment costs consistent with mission requirements and the relatively prolonged use of an aircraft once purchased.

Only the most attractive of the newer models, those showing significant improvement over the older models, will thus appear in the top five air- craft for each mission category.

It appears from Table II that there is no single factor or group of factors that consistently govern the selection of equipment. Cost appears to influence the choice in many cases, but it is also apparent that the most Employee transport in company-owned aircraft by professional pilots.

(3 ) Use of an aircraft by an individual for business transportation purposes (not for compensation or hire).

(4) Use of an aircraft for specialized work allied with industrial activity (e.g., photography, patrol, exploration).

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A few significant observations may be drawn from Figure 1. First, it can be seen that the majority of general aviation activities are performed over stage lengths less than 300 miles. Nevertheless, the operators desire equipment having range capabilities on the order of four to six times greater than their "typical" stage lengths for operation. Secondly, with the exception of long-distance Executive Transportation, speeds in the range of from 150 to 350 mph are adequate--it appears that only the highest "time value" passenger requires (or can justify) speeds corresponding to jet equipment.

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(U !H ^ 00 UJ UJ rf Qj TRANSPORT DISTANCE SHORT DISTANCE LARGE AIRCRAFT SMALL AIRCRAFT INTERCITY SERVIC CBD SERVICE MEDIUM DISTANC LON6 COMMUTER AIR CARRI EXECUTIVE NON-SCHEDULED (PERSONNEL TRANSPORT ONLY) AIR TAXI INDUSTRIAL SPECIAL BUSINESS Most interesting, however, are the stated desires related to.balanced field lengths (i.e., the runway required for an aircraft accelerated to liftoff speed to brake to a stop or to continue take-off to 35 feet on one engine, which- ever is longer). These desires fall into three categories. The f i r s t involves long distance Executive Transportation, in which high block speed offers greater time-savings than the ability to use short, "close-in" airports. In these applications, balanced field length capabilities on the order of 3 to 4000 feet are acceptable. In the cases of medium distance operations (i.e., intercity service Commuter Air C a r r i e r s , non-scheduled Air Taxis, and medium distance Executive Transportation), block speed loses importance and operational accessibility becomes more important; hence, there is a short-term desire for balanced field length capabilities in the range of from 1500 to 3000 feet with a long-term VTOL, desired if cost is not a significant constraint. Finally, there are those operational categories in which direct access is the primary objective. These categories include Commuter Air C a r r i e r s providing CBD service, short distance Executive Transportation, and Industrial Special (personnel transport) operations'. In these cases, the desire is to have VTOL, capability, thereby providing the maximum flexibility for achieving close-in access.

B. COMPARISON OF CURRENT VS. DESIRED MISSION AND AIRCRAFT CHARACTERISTICS Figures 2 through 4 present comparisons of the performance charac- teristics of aircraft and helicopters currently being used to perform general aviation missions with the desired operational characteristics previously shown in Figure 1. Figure 2 displays this comparison for jet aircraft, turbo- prop a i r c r a f t , and helicopters; Figure 3 illustrates the characteristics of large twin piston aircraft; and Figure 4 presents similar information for small twin piston aircraft. These charts show the extent to which present air- craft satisfy the desired mission characteristics and also graphically dis- play the types of operational improvements desired by the general aviation community as discussed below.

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(() SERVICE INTERCITY SERVICE CBD SHORT DISTANCE MEDIUM DISTANCE LONG DISTANCE LARGE AIRCRAFT SMALL AIRCRAFT COMMUTER AIR CARRIERS NON- SCHEDULED EXECUTIVE TRANSPORTATION ONLY) (PERSONNEL TRANSPORT AIR TAXI BUSINESS INDUSTRIAL SPECIAL 1. JET AIRCRAFT As can be seen from Figure 2, current jet aircraft do not satisfy the desire for high-speed performance. Since this equipment is used to com- pete with commercial jet service, while offering privacy and departure-on- - demand, there is a strong desire for aircraft with comparable speed capa- bilities. Additionally, current jet aircraft have balanced field length charac- teristics somewhat longer than desired, 'but not to the extent that STOL capa- bilities are required. The operators generally believe that shorter field capability would compromise speed or cost, both of which are more dominant considerations in the selection of such equipment. This again reflects the opinion that block time (i.e., gate-to-gate aircraft-related trip time including taxi, take-off, descent, landing and air traffic delay) rather than access time is more important in those applications utilizing jet equipment, a belief that was confirmed by an example analysis of airport access times for 34 differ- ent metropolitan areas in the United States. The analysis [presented in Appendix C of Volume II (Ref. 2)] indicates that short field capabilities, and the corresponding flexibility to operate out of most existing general aviation airports, would'only reduce airport access time by fewer than 13 minutes.

2. TURBOPROP AIRCRAFT Some additional speed is desired for turboprop aircraft utilized in the Commuter Air Carrier category (Figure 2). Additionally, although a 2000-foot field length capability is desired, there was no stated require- ment for a true STOL, capability of less than 1500 feet. In the Executive Transportation category, the present turboprop aircraft characteristics essentially match the desired characteristics for:the medium distance mis- sions with the exception of a desire for some additional speed and the ability to carry more passengers. .

3. HELICOPTERS For helicopters (Figure 2), there is an apparent need for additional speed and range (especially for long-term needs); higher capacity is desired for the larger Commuter Air Carrier missions. The desire for more speed and range is not surprising considering the low speed and limited range of current helicopters. In the offshore petroleum industry, for example, large numbers of helicopters are used exclusively to transport personnel to and from offshore oil and natural gas rigs. These rigs are located up to 200 miles from shore.and are expected to be even further out in the future. The commercial operators presently servicing this industry are interested in a vehicle capable of making a maximum payload round trip of 400 to 500 miles (with reserves) without refueling. For the longer distances, additional speed also becomes an important factor.

Executive users of helicopters also appreciate its convenience but they would like to use it over greater stage lengths. Such a capability would have the additional advantage of eliminating intermodel t r a n s f e r s to the company jet or turboprop. Speed and range are thus limiting f a c t o r s for these missions.

4. TWIN PISTON AIRCRAFT For large twin piston aircraft (Figure 3), there w e r e no particular performance features of present aircraft that did not match the desired opera- tional characteristics except for a desire for more range and slightly more speed. This was also true for small twin piston a i r c r a f t (Figure 4).

C. • CRITERIA DEFINITION The preceding review of general aviation missions and equipment permits a number of conclusions to be drawn relative to operational needs and potential equipment developments. The following paragraphs summarize these conclusions in terms of CTOL modifications, and STOL and VTOL, requirements. These conclusions are then generalized into criteria that can be applied to the evaluation of new aircraft concepts.

1. C TOJL MODIFICATIONS The principal needs of executive and commuter operations are related to the reduction of trip time. For long distance operations utilizing • jet aircraft, the reduction of trip time is most effectively accomplished through an increase in block speed. Shorter field capabilities dp not produce significant reductions in ground access time and are consequently viewed as u n n e c e s s a r y compromises to equipment speed and cost. The executive and commuter operations presently utilizing turboprop and piston aircraft already have a reasonably short field capability (i.e., approximately 3000 feet), and the u s e r s of such equipment can presently operate into the majority of United States a i r p o r t s . Since the objective of this study was to identify potential applications for VTOL and STOL technology, rather than techniques for improving block speed, CTOL modifications were not considered f u r t h e r .

2 . STOL AIRCRAFT . . . ' • • . • . ' ' Based upon the survey results and the city center access analyses, [ Appendices A and C of Volume II ( R e f . 2)] the market for a new STOL air-, c r a f t for general aviation personnel transport missions appears limited. There was some limited interest in STOL aircraft with field length capabilities of about 1000 feet by some corporations with current large parking lots. However, the principal value in short field capabilities (on the order of 1500 to 2000 feet) was related to the potential of operating into general aviation airports close to the CBD or into separate STOL strips at hub airports. .Small aircraft cur- rently in use for commuter air carrier and executive transportation already possess satisfactory short field capabilities, and larger aircraft are primarily limited by noise rather than by field length capabilities. Thus, to the extent determinable f r o n t the e f f o r t s of this study, STOL technology does not appear to have a significant general aviation market potential and subsequent emphasis was applied to VTOL a i r c r a f t .

3. VTOL AIRCRAFT The most promising applications of V/STOL technology in general aviation operations appear in the VTOL category, particularly if such capabilities can be provided in combination with higher speed and longer range than that available with current helicopters. The combination of these features would find application both to the Commuter Air Carrier and to the short and medium distance Executive Transportation categories by offering significant improvements in access and block times. It would also appeal to operators of helicopter equipment performing Industrial Special (personnel transport) missions--particularly those involved in offshore personnel trans- port wherein large numbers of helicopters are used exclusively for such missions.^ ' The combination of these applications represents a significant market potential by 1982 as discussed below in Section D. For these reasons, the remainder of this study concentrates on the evaluation of alternative VTOL concepts and the definition of those VTOL systems most adaptable to these aviation missions.

4. CRITERIA FOR THE EVALUATION OF NEW VTOL CONCEPTS The following criteria were established for evaluating new VTOL concepts. These criteria are based primarily on a composite of the require- ments discussed above for the three general aviation missions: (1) Commuter Air Carrier, (2) Executive Transportation (short and medium distance), and (3) Industrial Special (personnel transport).

a. Range: 400 to 500 miles b. Speed: 200 to 300 mph c. Capacity: 8 to 10 passengers and 15 to 18 passengers d. Operating mode: VTOL For such equipment, costs must be comparable to those of current helicopters.

No special hovering capabilities are needed beyond those required for takeoff a n d landing. • . . - . .

Commercial operators that cannot justify exclusive use of a VTOL aircraft for personel transport alone will continue to favor the conventional heli- copter with its hover capability and more versatile application.

Similar criteria are appropriate for Long distance missions with the exceptions that speed must be equivalent to or better than that of existing jet a i r c r a f t , and range capability on the order of 1000 miles is required.

Whereas these criteria do not satisfy each and every interviewee's idea of an ideal a i r c r a f t for his needs, it is felt they do represent a good cross-section of desired characteristics as well as actual historical utiliza- tion in the noted mission categories.

D. VTOL MARKET POTENTIAL The market potential for new VTOL a i r c r a f t may be estimated from available projections of a i r c r a f t inventories in each of the general aviation mission categories. Projections through 1982 for each type of aircraft cur- rently utilized in these missions are shown in Figures 5 and 6. These data are based on FAA projections (Ref. 6) and the assumption of a constant fleet mix.

Table III, also based on FAA statistical data (Ref. 6), summarizes the mission potential for new VTOL a i r c r a f t in each of the general aviation mission categories of interest. The table identifies the 1969 fleets of large and small aircraft and the corresponding fleets projected for 1982. During this time period a demand is projected for approximately 1600 large aircraft and 3800 small aircraft for the shorter distance applications, with a grand total of approximately 2200 large and 5500 small aircraft if the long distance applications are included. Some fraction of this market can be satisfied by new VTOL aircraft concepts provided they possess the proper characteristics of speed, range, capacity, cost, and operating mode.

The remainder of this volume is concerned with the evaluation of new VTOL concepts that are potentially capable of satisfying that demand.

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J w ffi 5 O ^ ^ ^ ^ i f l O ^ C o x J. o -9 .2 2 C7 r7 U W M ft co Q O IV. AIRCRAFT CONFIGURATIONS AND CAPABILITIES This section describes the current and advanced aircraft concepts evaluated in the study and discusses the numerical parameters assigned to each for use in the comparative analyses presented in Section V. The pri- .

mary parameters needed for the analyses are related to the physical and economic characteristics of the aircraft under study. The physical parameters include size, speed, delay factor, and operational accessibility, which are defined below. The economic factors include development, investment, and operating,costs.

Two sizes of aircraft, corresponding to passenger-carrying capa- bilities of 8 and 16, respectively, were utilized in the comparative analyses.

These sizes conform to the desired mission requirements established in Section III.

In the comparative analyses, block time is used as the primary per- formance characteristic rather than cruise speed. Since block time cannot be stated without regard to a block distance, it is derived from two factors: the design cruise speed and a delay factor. The design cruise speed is the aircraft's cruising speed at a particular optimum altitude and throttle setting.

The delay factor refers to the time that the aircraft is operating but is not progressing, toward the .destination at design speed. This "non-productive" time includes taxi, takeoff, climb, descent, landing, and traffic delays.

When combined with cruise speed and distance, the delay factor produces the block time for a given flight distance. , .

The operational accessibility of an aircraft to a user is generally• . . - • . .

; related to its design concept. VTOL aircraft are considered more accessible than CTQL,aircraft since the latter require longer runways which are . , generally located at greater distances from the origin and destination points- ..

of the traveler. . • — 'Additionally, two crew seats are available for each aircraft except the small helicopter, which has only one.

23-

A. COMPOSITE CURRENT AIRCRAFT

The concept of a composite aircraft was introduced to permit meaning- ful comparisons between current and advanced aircraft. The characteristics of the composite aircraft were derived primarily from the features of the more popular aircraft currently performing general aviation missions. The characteristics also reflect the desired mission requirements, such as passenger capacity and range, as developed in Section III. Table IV sum- marizes the characteristics of aircraft in the current fleet from which the composite aircraft were developed. Performance and cost data shown on this table were derived from Refs. 4 and 5 and the equipment list of Appendix D< of Volume II ( R e f . 2). A more comprehensive tabulation of current aircraft characteristics is presented in Appendix B of Volume II ( R e f . 2).

1. SMALL AIRCRAFT CHARACTERISTICS Table V presents the primary characteristics for the small composite current aircraft. The three categories of aircraft shown--helicopter, turbo- prop, and turbojet—possess the characteristics required to perform the short, medium, and long distance Executive Transportation Missions, respectively.

Additionally, the small helicopter can satisfy the operational requirements of Offshore Missions in support of the petroleum industry's supervisory person- nel transport. The composite CTOL aircraft carries six passengers and the composite helicopter five passengers.

2. LARGE AIRCRAFT CHARACTERISTICS Table VI provides descriptions of the large composite aircraft.

Because of the different mission characteristics, the large turboprop is divided into two classes: the long and medium distance Executive Transpor- tation Missions and the intercity service Commuter Air Carrier Mission.

The large helicopter, like its smaller counterpart, performs a short distance Executive Transportation Mission and Offshore Mission (crew change); in addition, it is used for Commuter Air Carrier CBD service. Sizes range from the 12-passenger helicopter to the 18-passenger Executive Transpor- tation turboprop.

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3. INVESTMENT AND OPERATING COSTS The economic characteristics of the composite current aircraft dis- cussed above were determined by averaging the investment and operating costs of the aircraft currently performing the various general aviation missions. The investment costs are based on 1971 dollars. Spare parts were not considered in the investment costs but were assumed to be part of the : maintenance costs. Operating costs [described in detail in Appendix D o f Volume II (Ref. 2)] were divided into two basic portions: variable and fixed.

The variable costs are those directly related to cost per flying hour and typically consist of fuel, oil, and maintenance. Fixed costs, because of their independence of flying time, were computed on an annual basis and typically consist of crew, insurance, depreciation, etc. For convenience, the fixed costs were divided by the number of hours flown per year (utilization) and the quotient added to the variable cost to yield a total hourly operating cost.

Table VII summarizes the economic characteristics of the composite aircraft. The utilizations determined as a result of operator survey data for Table VII. Composite Aircraft Cost Summary Total Cos it ( S / h r ) Average Number Cost / P a s s e n g e r

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Small H e l i c o p t e r 150 1 52 2 4 4 < > 4 4 61 38 L a r g e H e l i c o p t e r 470 6 1 7 < > 363 238 8 6 10 103 40 -- 36 460 308 Small T u r b o p r o p -- -- -- • 4 -- -- 77 -- -- Large Turboprop 900 564 -- - - -- K -- - - 71 -- -- , Large Turboprop 480 142 8 18 -- -- -- -- -- -- -- Small T u r b o j e l 1. 130 620 4 156 -- - - -- -- . -- -- -- 2. 230 1050 Large T u r b o j e t S 131 -- -- -- -- -- -- -- (1) Executive type ( 6 ) Commuter M i s s i o n s (2) Commuter type ( 7 ) 1971 average (3) Executive M i s s i o n s (8) 40% load f a c t o r • (4) Small A/C O f f s h o r e . ( 9 ) . @ 4 0 0 - h r .utilization (5) Large A / C O f f s h o r e each mission are noted in the table, and their impact on the total hourly operating cost.can be seen in the cases of the helicopters which perform more than one mission.. The average number of passengers shown are those carried on a typical flight for the mission specified. The cost per passenger involves a prorated hourly operating cost, assuming that the average number of passengers are carried on each flight. This value is obtained by dividing total.cost per hour by average passengers per flight as determined from the user survey data.

B. ADVANCED AIRCRAFT CONCEPTS Advanced aircraft concepts for the general aviation personnel transport missions defined in Section in were required for comparison with the composite current aircraft. For practical reasons, only a limited, number of concepts could be examined. As explained in Section III, these concepts were limited to VTOL aircraft. In addition, only concepts which might be available in the late 1970's were considered, further eliminating some of the VTOL concepts requiring significant development effort. Noise was not a parameter for analysis in this study, but the nature of the missions and current environmental concerns suggested that noise could be used as a parameter to further limit concepts for consideration. The concepts finally selected for evaluation include compound helicopters, tilt rotors, tilt wings, and tip-driven pneumatic lift fans. While noise may be a problem (Refs.

7 through 9), the lift fan was retained as the most promising concept for com- parison with the current turbojets in accomplishing the long distance Executive Transportation Missions. (Direct lift concepts using turbojets and low by- pass turbofans were eliminated because of the noise consideration). Although there are additional VTOL, concepts that may prove promising for application to general aviation missions, the four selected a i r c r a f t design concepts were considered representative to fulfill specific missions of the late 1970's and may be related to the composite current aircraft.

Figure 7 presents sketches of the four concepts selected for evalua- tion. The compound helicopter shown in Figure 7a is a derivative of the 16H-3J design proposed by Piasecki ( R e f . 10). Sikorsky also has investigated b. Tilt Rotor a. Compound Helicopter d. Lift Fan.

c. Tilt Wing Figure 7. Advanced Small Aircraft Concepts compound helicopter designs and has flown a test version. The tilt rotor of Figure Ib is characteristic of the design work currently in progress at the Bell Helicopter Company (Ref. 11). Some experimental work has been spon- sored to date including the flights of the Bell X V - 3 ; however, this design has yet to reach a final prototype stage. The tilt wing in Figure 7c is related to the Canadair CL-84 ( R e f . 12) and the LTV XC-142. Both of these experimental aircraft have been extensively flight tested. Figure 7d is representative of current lift fan configurations. This concept has been flown in the Army XV-5A and the NASA XV-5B experimental configurations.

1. SELECTED DESIGN CONFIGURATIONS As in the case of the composite current aircraft, the salient physical and economic parameters associated with each of the new aircraft concepts ® •were defined to reflect the mission characteristics discussed in Section III.

For those mission characteristics expressed as a range of values ( e . g . , 6 to 10 passengers), the average value was chosen as the design point.

The following'design parameters were specified for each advanced VTOL concept: • .

a. Sizes: 8 and 16 passengers b. Crew: 2 , c. Range: 500 statute miles with maximum payload (10% fuel reserve} The additional ground rules and assumptions listed below were required to simplify the design effort: a. Engines were assumed available in any desired power or thrust f ff-'- range (i. e. , no development required).

'••• b.. Engine thrust (or horsepower) rating could be increased by 10% for no more than 2. 5 minutes to cover the contingency of an engine out on takeoff.

c. Takeoff could be continued with the loss of one engine at 2000 feet and 82°F.

d . Thrust t o weight ratios: . . .

T/W 2l. 05, with one engine out T/W 21. 25, normal operation e. Ten inches of clearance between the fuselage and the rotors or propellers.

•• f. P r e s s u r i z e d fuselage.

g. Circular fuselages of 6-foot d i a m e t e r .

h. • ^Approximate structural load factor of 4 g's.

i. Current state-of-the-art for airframe and propulsion technology.

The required physical and economic characteristics of the advanced VTOLi concepts were based on extrapolations or interpolations of existing experimental aircraft or conceptual designs proposed by various manufac- turers.

, The design p a r a m e t e r s of the small advanced VTOL concepts are summarized in Table VIII. The small compound helicopter, tilt rotor, and tilt wing were defined for application in the short and medium distance Except for the small compound helicopter which cruises at low altitudes.

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Executive Transportation Missions and the O f f s h o r e M i s s i o n s (personnel t r a n s p o r t ) . The lift fan was designed primarily to fulfill the medium and long distance Executive Transportation Missions as its speed and costs were^ c o n - sidered in excess of those desired for the O f f s h o r e Mission applications. Some comparative analyses for this mission are shown in Section V. .. Two lift fan configurations were considered. A basic design was defined in view of the general criteria of Paragraph C . 4 . To facilitate later comparisons of this basic design with a configuration d i r e c t l y suitable to longer range executive missions, a heavier extended range design incorporating higher thrust engines was also defined. Although the Extended Range Lift Fan has almost twice the takeoff weight of the small lift fan, it is still considered in the "small" category as'size is defined in terms of passenger load. The added -weight is a result of extra fuel required for the longer range plus the required added thrust and associated a i r f r a m e weight.

Table IX presents the physical parameters for the large advanced VTOL concepts. The missions envisioned for these aircraft correspond to those for the small concepts (i. e. , tilt rotor, tilt wing, and compound heli- copter for short and medium distance executive Transportation and Offshore Missions, and the lift fan for medium and long distance Executive Transpor- , tation Missions). Additionally, all four large aircraft are considered appli- cable to the Commuter Air Carrier Intercity Service and CBD Service Mis- sions, with the lift fan restricted from CBD operations due to noise consider- ations .

Figure 8 presents passenger load-range curves for the aircraft described above. In all cases, the range is at a constant gross takeoff weight and includes a 10% fuel r e s e r v e . To achieve ranges beyond that range associated with a full passenger load, fuel is substituted for p a s s e n g e r s .

2. DESIGN CONFIGURATION ANALYSIS The general arrangements of the small and large advanced aircraft concepts are quite similar except for the compound helicopters. Two prin- cipal problems existed in arriving at rotor and propeller design configura- tions: noise and engine-out capability. Operational experience with heli- o o o o o o 0 ^o o o S "^ m vO CO •»-' N -irH

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o U (M OO Sa39N3SSVd copters and analytical p r e d i c t i o n s by manufacturers have indicated; that the small rotor type .VTOL a i r c r a f t c o n s i d e r e d in this study will be able to s a t i s f y a noise c r i t e r i o n of 95 EPNdB at 500 f e e t . T h e r e f o r e the major problem in.the conceptual a n a l y s i s was the selection of an economic propul- sion system that would meet an engine-out requirement at 2000 feet and 82 F....

As an example., a typical two-engine tilt rotor would have to exhibit 64% more power per pound of weight to meet the engine-out design criterion-.(T/.W ,.= 1. 05.)

than would be required for T/W = 1. 25 at sea level on a standard day. The corresponding increase in power per pound for three- and four-engine air- craft would be 22% and 9%, respectively. Other cost and weight.factors tend...

to reduce the advantage of a large number of small engines, and the optimum power plant arrangement could only be selected by making detailed analyses beyond the scope of this study. Consequently it was assumed that all pro- peller and rotor aircraft would utilize two and four engines respectively for the 8- and 16-passenger sizes. This assumption for the large tilt rotor and tilt wing aircraft resulted in the incorporation of two engines per nacelle while the small VTOL concepts utilize only one engine per nacelle. Other significant features of each aircraft design are discussed in the following paragraphs. ' • a. Compound Helicopters The 8- and 16-passenger compound helicopters differ in their geometry. The small concept is based on the 16 H-3J design that has been proposed by Piasecki. It is powered by one Pratt and Whitney PT6T unit which consists of two PT6B engines driving a single gear box. The cruise thrust is provided by a 5. 5-foot diameter shrouded propeller while the anti- torque requirement is derived from vanes mounted in the propeller slip- stream. An engine-out capability is provided for takeoff.

The geometry, propulsion, lift, and control systems of the large compound helicopter are similar to those of the S-65-200 helicopter pro- posed by Sikorsky. One engine is mounted in each of two nacelles while the third engine is contained in the fuselage. All engines are cross-shafted to provide for an engine-out takeoff capability.

b. Tilt Rotor .

The geometry of the 8-passenger a i r c r a f t is essentially the same as the mockup of the Bell 300. However, the empty weight is 20% greater because of a c c e s s o r i e s , a p r e s s u r i z e d fuselage, and a 50% increase in powe r. • The 16-passenger aircraft configuration is similar but with slightly greater tail volume coefficients and four turboshaft engines, each pair driving a common' gear box (similar to the PT6T engine combination pro- duced by United Aircraft of Canada). The aircraft incorporates cross- shafting between the nacelles.

c. Tilt Wing . Similar geometry is employed for the 8- and 16-passenger tilt wing aircraft. The power plant arrangements in the 8- and 16-passenger versions are similar to the corresponding tilt rotor designs in that two engines are packaged in each nacelle for the large aircraft. The shaft horsepower per pound of the tilt wing aircraft is approximately 50% greater than that of the tilt rotor due to the higher disc loading.

A preliminary analysis was made to determine the propeller diameter, speed, and equivalent shaft horsepower (eshp) required to satisfy the takeoff c r i t e r i o n ( T / W = 1. 25) with a 4-blade propeller. A propeller diameter of" 17 feet and a rotation speed of 1000 rpm were selected. These parameters are also expected to result in acceptable noise levels. The engines, rated at 1420 eshp are also cros s-shafted. Individual engine power was determined by the engine-out criterion for an 82 °F day at 2000 feet.

In cruise f l i g h t , the propeller is slowed to 700 rpm.

d. Pneumatic T i p - D r i v e n Lift Fan The. 8- and ,1 6-pas senger lift fan a i r c r a f t are geometrically similar.

One lift fan is mounted horizontally in the aft portion of each nacelle, while one l i f t / c r u i s e fan is mounted vertically in the forward portion of each nacelle with a t h r u s t d e f l e c t o r . Pitch control is obtained by v a r y i n g the relative flow rates between the forward and aft fans. The four fans are powered b y . c r o s s - ducted gas g e n e r a t o r s , one in each nacelle and a third mounted in the f u s e - lage. During cruise flight, the two horizontally mounted lift fans and the fuselage-mounted gas generator are shut down. The extended range lift fan is similar" to the large lift fan except for modifications to provide for addi- tional fuel, and an 8-passenger configuration. Its range is thus significantly improved.

3. INVESTMENT AND OPERATING COSTS ' The advanced aircraft costs are presented in Table X. Investment costs were computed principally on the basis of aircraft empty weight, engine thrust (or eshp in the case of turboshaft engines), weight of the dynamic systems, and the anticipated development cost assumed for each ••.

a i r f r a m e concept. Development costs were a m o r t i z e d over an assumed production run of 700 units. Optional communication, navigation, and other electronics for IFR flight were then added to a r r i v e at the equipped invest- ment cost. Details of the cost estimating techniques and typical equipment assumed may be found in Appendix D of Volume II ( R e f . Z).

Total hourly cost of operation was computed in the same manner as for the current composite aircraft by determining the variable and fixed costs for each concept and size. Slightly different factors were used to determine .the cost elements depending on whether the aircraft was utilized r : -'"- ' '' ' '.' r' .' : * • in Executive Transportation or Commuter Air Carrier or Offshore (person- nel transport) service. The utilization columns reflect these differences.

The average number of passengers assumed per flight for the Executive Mis^sion.is equivalent to a 50% load factor. This is slightly lower than for current aircraft, but represents an owner desire (obtained from the surveys) to.hav.e the room available to allow flexibility in either the number of passengers or the working room in the cabin. Commuter Missions assume a 40% load, factor, while Offshore Missions in the large aircraft assume 10 passengers (e.quivalent to a typical crew change increment for an oil-drilling rig).

fable X. Advanced Aircraft Cost Summary / Total Cost ($/hr) Average Number Cost/Passenger of Passengers <$/hr) Annual Utilization ( h r ) Concept 600 421 341 276 4 Small Compound 319 4 105 85 -- -- Helicopter 1, 090 574 495 8 7 10 Large Compound 795 613 99 71 57 Helicopter Small Tilt Rotor 950 594 468 434 365 4 4 148 117 -- -- Large Tilt Rotor 1, 500 928 714 660 551 • 8 7 10 116 79 66 : Small Tilt Wing 920 562 422 322 4 4 140 105 389 -- -- Large Tilt Wing : . 1,490 . 899 664 610 502 8 7 10 112 72 61 Small Lift Fan 1, 520 795 504 394 4 - - • 4 198 -_ 140 ( 7 ) Small Lift Fan ( E R ) 2, 160 1176 830 752 596 4 -- -- 294 -- -- Large Lift Fan 2 , 3 0 0 1256 866 783 616 8 7 10 157 88 78 (1) Executive Missions (5) 1971 average .

(2) Small A/C - O f f s h o r e (6) 40% load factor (3) Large A/C - Offshore (7) Extended range (4) Commuter Missions G. SCHEDULED AIRLINE CAPABILITIES In addition to comparing advanced concepts against composite cur- rent aircraft, the analysis of Section V includes scheduled airline service as an alternative mode for satisfying the Executive Transportation Missions.

For this reason, a baseline set of time-and-cost characteristics was developed for scheduled airline service.

Figure 9 depicts the gate-to-gate time of typical airline service as a function of block distance. Data to develop this relationship were taken .

from the Official Airline Guide (Ref. 13). Several data points were obtained for each lO'O-mile increment and a straight line fitted to the points. At the shorter distances (less than 100 miles), Commuter Air Carrier service is assumed to follow the same relationship. (The slower cruise speeds of the Commuter Air Carriers compared with those of the larger airlines are hardly discernible owing to the latter s relatively greater traffic delays and higher altitude flight routing.) / Figure 10 is a similar representation of the airline fare vs.

distance ( R e f . 13). Coach fares were plotted for each 100-mile increment and a straight line fitted to the resulting points. Fares of Commuter Air Carriers tend to be slightly lower due, principally, to the lower boarding cost per passenger. The slope of the segment of the curve from 0 to 100 miles reflects this lower boarding cost.

Formulas are also provided for the relationships displayed in Figures 9 and 10, and were used as airline parameters in the comparative analyses. . "' "":' .:' , The usual limitations of airline services associated with available route structure (cities served), frequencies of schedules, or nonstop vs.

segmented vs. connecting flights were not generalized but are included in the comparative analyses in Section V.

'40 1.4 BLOCK TIME (hr) = 0 3 3 + 0.00206D ID = DISTANCE, STATUTE MILES) 1.2 I.'O 0.8 0.4 0.2 100 ' 200 300 400 500 .BLOCK DISTANCE, s.m.

Figure 9. Airline Trip Time (Block) COST ( $ 1 = 8 + O.I079D (FOR D < 1001 = 12 + 0.0679D (FOR D > 100) (0 = DISTANCE, STATUTE MILES) 100 200 300 400 BLOCK DISTANCE, s.m.

Figure 10. Airline Trip Cost (Coach) V. AIRCRAFT COST BENEFIT ANALYSES There are a variety of benefits that can be attributed to the introduction of new aircraft and operating concepts. However, many of these benefits --convenience, accessibility to unusual locations, flexibility of operation--are subjective. These subjective benefits are of varying importance to different users and do not readily permit a quantitative eval- uation. There are, however, cost benefits attributable to transportation systems which can form a basis for comparison of alternative air vehicle concepts. The present report is concerned with identifying these potential cost benefits when advanced aircraft concepts are used in selected general aviation missions. The advanced aircraft concepts will be compared only with other air transportation modes such as contemporary CTOL aircraft and scheduled airline service. A broader analysis of intercity short haul business passenger travel, including ground modes, is contained in Refs. 14 and 15.

Three different approaches are presented for assessing the cost benefits of the new aircraft concepts.when applied to the Executive Trans- portation, Commuter Air Carrier, and: Offshore Missions. The first is a simplified time line of the traveler's elapsed time from door to door includ- ing local travel and processing time (and associated significant costs). This analysis graphically illustrates the dollar cost and relative time savings of a given transportation mode. The second assessment of economic benefit compares the merits of alternative air transportation modes for various trip lengths in terms of the traveler's value of time. Both the performance and economic characteristics of a new mode enter into this analysis as well as the user's economic values. The third measure of cost benefit compares the potential saving resulting from the use of an advanced concept aircraft in place of today's turbojet aircraft. The mission scenarios used as well as each method of analysis is described in the following sections.

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cc CO CO CO z> OD A. EXECUTIVE TRANSPORTATION MISSION COST BENEFIT ANALYSIS , \- 1. MISSION SCENARIOS " .;,.. ::•< The development of a time line and the.'associated cost of travel is dependent on the use of scenarios which describe all of the steps in a trans- portation mode -which may affect either time or cost. In these analyses each trip is divided into three segments as shown in Figure 11. These segments consist of: the access segment (point of origination to the aircraft), the pri- mary segment of the trip (the flight), and the distribution segment (aircraft to the destination point). Access travel is considered to be by car on sur- face streets or, in selected instances, by small helicopter. The primary mode of transportation may be by scheduled airline; by company-owned helicopter, turboprop or turbojet CTOL aircraft; or by one of the company- owned advanced VTOL, concepts under consideration. The distribution trip from the a i r c r a f t to the destination is always assumed to be accomplished by car. Whereas the access and distribution portions' of a trip assume a common nominal ground travel distance, the primary mode considers dis- tance as the independent variable. ', »» In order to identify the significant differences, in the characteris- tics of the primary transportation modes a; number of scenario ground rules were developed and are presented in Table XI. A rationale for the use of each rule is also presented. Other ground'^rules peculiar to the individual missions will be presented along with the analyses.

A series of representative Executive Transportation Mission sce- narios are given in Table XII in terms of the time-and-cost increments for the door-to-door trip. The traveler is assumed to depart from his office using either a car or a private helicopter to access to the CTOLport. The primary segment of travel is then accomplished with an aircraft whose block time (gate-to-gate) is a function of cruise speed, distance, and nonproduc- tive flight time. Distribution from the airport to the local destination is assumed to be by car only. Processing times are scaled between modes to Table XL Ground Rules for Scenario Development Rule Rationale 1. All trips are one-way. Use of executive a i r c r a f t is not typically characterized by flights from A to B and return to A. They more often are multi-legged, A to B to C and return to A. By making trips one way, segments of any multi-legged trip can be analyzed separately and combined to provide total trip costs at will.

2. Aircraft are assigned a fixed time CTOL a i r c r a f t nonproductive time is 15 min- utes, consisting of taxi - 10 minutes, climb - delay for all nonproductive flight time and full operating expense is charged against his time.

3. Airline travel times are based on These schedules account for trip distance, current published airline schedules. a i r c r a f t performance, and current air t r a f f i c congestion.

4. All CTOL aircraft are assumed to This establishes a common access trip time.

operate from the same airport.

5. Processing times (access mode to Separate terminals and less formality are primary mode) are assumed less typical for this type of travel.

for executive travelers.

6. Average utilization for new VTOL's New VTOL's will be capable of combined VTOL will be greater than current execu* and CTOL missions, will be more expensive and,therefore, can only be justified by many tive VTOL or CTOL fleet.

customers if utilized more e f f e c t i v e l y .

7. Number of passengers per flight Load factors are derived from 1971 user sur- veys and show consistent patterns: vary with mission.

a. Executive A i r c r a f t : 50% load factor.

b. Commuter A i r c r a f t : 40% load factor.

c. Offshore: 4 passengers for a i r c r a f t seating 10 or less, 10 passengers in \ aircraft seating more than 10.

8. Costs are in 1971 dollars. Provides a standard base and avoids the u n c e r - tainties of future economic situations.

1971 airline coach fares are used. Since airline fares are continously changing it is necessary to select a point in time for ref- Commuter fares are used for dis- tances under 100 miles. erence. The use of 1971 fares is compatible with the use of 1971 d o l l a r s . Further, the commuter service has become more m a t u r e and its fares are, hopefully, r e p r e s e n t a t i v e of its costs.

Out of pocket car costs are relatively small 10. No cost increment for local travel by car. compared to the p r i m a r y mode costs. Fur- ther, in most scenarios several p a s s e n g e r s would use one car making insignificant the car cost per passenger.

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Access and distribution segments of the Executive Transportation Mission.are considerably simplified when advanced VTOL aircraft are used as the primary .mode o.f transportation,. . Tp take full advantage of their VTOL capabilities they are assumed to operate from -the immediate vicinities of both the origin and destination points. The gains thus realized by the elimi- nation of local travel and interface processing times are reflected in. reduced overall trip times. . . -.. ..

2. TIMELINE ANALYSIS FOR CURRENT AND ADVANCED .

AIRCRAFT ' / Results of the time line and cost analyses for Executive Transporta- tion Missions are presented in Figures 1Z and 13. Figure 12 compares the time lines for the small a i r c r a f t scenarios and their attendant costs over short and medium distances. The time advantages of the VTOL .concepts which do not require a conventional airport are clearly apparent over both the airline and turboprop aircraft which must use CTOLports. A further advantage accrues to the tilt rotor, tilt wing, and lift fan concepts due to their'-s'ignifi- cant speed capabilities, which provide real time savings out to distances of 500 miles. The helicopter is .attractive only at short ranges since it requires refueling for, ranges beyond 300 miles, nullifying its VTOL advantage. : Offsetting the time advantages of the VTOL concepts are the some- what increased costs of operation. These costs,- allocated on a per passen- : ger basis in Figure 12b, show only slight increases fo.r the tilt wing and.tilt rotor over today's popular turboprop aircraft. Their speed advantage over- shadows this small increase in cost as will be seen later in the time value analyses. . • . " The second class of.Executive Transportation Missions defined earlier was based on flying greater block distances for which jet-type air- craft may have more applicability. Figure 13 presents time line and equiv- alent .passenger costs for the lift fan VTOL compared with those for con- temporary turbojet general aviation aircraft and airline service. The MAXIMUM FULL FUEL RANGE [-*—TYPICAL STAGE LENGTH I CAR-TURBOPROP-CAR c CAR-AIRLINE-CAR e COMPOUND HELICOPTER

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b. Equivalent Passenger Cost Figure 13. Executive Miss ion--Long Distance with Jet Aircraft combination of jet speed and VTOL capabilities clearly shows up to advantage here, and also over the propeller and rotor concepts of Figure 12a.

The equivalent passenger cost increase is, however, just as apparent.

This timeline analysis shows a comparison of trip time and costs per passenger for different Executive Mission scenarios and aircraft con- cepts but does not include another key'factor pertaining to mode benefits,, i.e. , a traveler's time value. The next section includes a discussion of the integration of time value into the analyses.

3. TIME VALUE ANALYSIS OF COMPOSITE CURRENT AIRCRAFT The combined performance and economic characteristics for candi- date general aviation aircraft have been .analyzed by using "phase" diagrams to examine preferred modal choices for travelers of different time values as a function of distance traveled. By.using the scenarios previously described, total trip cost is determined for a given mode as the sum of the transporta- tion costs and the cost associated with the traveler's time for the given mode.

Lines of equal travel cost for two modes are created separating the areas of individual mode dominance. These phase diagrams can be made for two or.

more modes presenting areas of dominance of one mode over the others and have been developed for current and advanced aircraft in both the Executive Transportation and Commuter Air Carrier Mission scenarios described above.

A phase diagram analysis is less meaningful for the Offshore Mission due to (1) a lack of reasonable transportation alternatives for the longer distances under certain weather conditions and (2) less significant monetary values of time for the individual travelers. This mission was not addressed in the time value analysis.

a. Turbine-Powered Company-Owned CTOL Aircraft Phase diagrams displaying the preferred transportation modes from among current aircraft serving the Executive Transportation Mission are shown in Figure 14. The mission illustrated is the short distance Executive Mission for which both company.-owned turboprop and turbojet aircraft may be used as well as scheduled airline service. The dashed lines in the figure 5.1 AIRLINES DELAY •IAT; hri TURBOJET 160 160 I HELICOPTER

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a. Turbojet, Airline b. Helicopter, Airline 180 180 160 160 140 140 .= 120 -CO- ID TURBOJET 5 80 > 80 UJ UJ 5 60 P 60 40 40 200. 400 600 800. - 1 0 0 0 200 400 600 800 1000 DISTANCE, s.m. DISTANCE, s.m.

c. Turboprop, Airline d. Turbojet, Turboprop Figure 14. Two-Phase Time Value Diagrams for Small Contemporary Aircraft represent airline delay times (AT) attributable to the fact that a scheduled airline flight may not be precisely scheduled at the desired time of depar- ture by the executive. Lines showing a zero delay, a one-hour delay, and- a three-hour delay are illustrated in the figure and compared with'.ea-ch com- " '" i • ^ * posite current aircraft concept. It should be noted the airline delay referred to is in addition to the aircraft delay times and access and distribution seg- ment times identified in the mission scenarios. . . '..

Such delay times are considered appropriate as the survey of users ; o'f executive aircraft indicated in general that their aircraft are not custom- ;•- arily used in direct competition with the airlines. Companies that operate their own aircraft normally utilize them for trips to point's where, airline schedules are incompatible with the purpose of the trip, or into points hot served by airlines. Examples of incompatibility include: (1) business con- cluded early, (2) time between planned conclusion of business and next airline flight departure exceeds-the- time required to access arid board the airline, and (3) a nonstop flight is not available or additional access time is required for the airline since the executive may be able to fly in his own aircraft to an air- port closer to his destination. These incompatibilities are felt to be realistic of most airline schedules with the possible exceptions of the services offered between Los Angeles-San Francisco and New York-Washington, where very frequent service is offered. As can be seen in Figure 14, the relatively low - cost and high speed of the airline is such that airline travel dominates all; but the very high time value range at short distances, if no airline delay time is considered (AT = 0). As airline delay times are considered, however, both the turbojet and the turboprop become more favorable at lower time values.

The helicopter, due to its limited range, is able only to favorably compete : with a scheduled airline up to a trip distance of approximately 300 miles.

In general, ' the "break-even" value -of -time 'increases as the distance increases for any AT since the airlines are the more efficient mode at long distances. Also-, the business turbojet becomes iricrea/sirigly more competitive as the airline penalty time becomes greater. For example, if 5 3',-3 we assume an airline penalty time of one hour, Figure 14a shows that at $100/hr time value and 500-mile trip distance, both;modes would have equal: costs. This 'distance is about the median value for,executive trips with company-owned jets. For an airline penalty time of;|three hours and a 1000- : mile trip distance, the turbojet is more economical at time values greater than $77/hr. These results seem in the neighborhopd of consistency with existing usage of business jets. , . ; ' ) . - Ohe of the primary uses for executive aircraft is to provide service to airports'where there is no airline service available. In this application the choices of current turbine CTOL aircraft are between small turbojet or turboprop aircraft as illustrated in Figure 14d. The,economy of the turbo- prop aircraft dominates the lower time values even to distances as great as 1000 miles. The higher time value passenger, however, clearly benefits from the turbojet speed capabilities. - ' • • ; : .

As a further comparison, multiphase time value diagrams have been constructed. Figure 15a, b, and c compares .current executive air- craft with each other as well as to the airline at airline delay times (AT) of zero, one, and three hours. As can be seen in Figure 15a, b, and c, the.

helicopter dominates the very short distance missions through almost the entire range of time values. The turboprop becomes more attractive for the 250- to 500-mile range missions, with the turbojet dominating for the higher time values and the longer missions once airline delays are con- sidered. Again, however, even with delay times of three hours, the airline will dominate for longer range missions up to time values of approximately $60/hr. A further comparison for the case where .airline service is not available is shown in Figure 15d. As can be seen again, the helicopter dominates for shorter distance trips, the turboprop dominates for the lower time value traveler for longer distance trips, and the turbojet dominates for long distances and time values in excess of $60/hr.

180 — _. ' - HELICOPTER I / ! 140 HELICOPTER / AIRLINE £. 120 ~ 1 <ry -C/> - 100 / UJ UJ / O rD I 80 " / UJ p 60 ^TURBOPROP / / NOTE: TURBOJET, TURBOPROP - ' 1 . ' DOMINATED 40 AIRLINE 20 - / 1 1 1 - • ' 1 1 Q 0 200 400 600 800 1000 0 200 400 600 800 1000 DISTANCE, s.m.

DISTANCE, s.m.

a. 4 Modes (AT = 0 hr) b. 4 Modes (AT = 1 hr) HELICOPTER TURBOJET £ 120 -c/> - 100

400 600 1000 400 600 soo 1000

DISTANCE, s.m. DISTANCE;, s.m.

c. 4 Modes (AT = 3 hr) d. 3 Modes Figure 15. Multiple-Phase Time Value Diagrams for Small Contemporary Aircraft b. Effect of Varying Aircraft Utilization The previous examples assumed a fixed utilization for the executive aircraft at 500 hours per year. Although the survey and other available data show this to be a reasonable average there are applications in which lesser or greater annual utilizations occur. The effect of varying utilization of the turboprop and turbojet aircraft on their break-even economics with the air- line is shown in Figures l6a and I6b, using the optimum (zero delay) airline schedule. (The executive aircraft are always to the left of the utilization line s e l e c t e d . ) Increasing utilization to 800 hours per year causes the break- even passenger time value to decrease and, thereby, almost doubles the area of the phase diagram in which the turboprop and turbojet are favored over air- line service. However, the ranges over -which they are preferred are still limited to ZOO to 300 miles.

Productive Work En Route c.

A further cost benefit associated with the use of executive aircraft is that productive work can be accomplished en route by the passengers. For simplicity the scenarios and phase diagrams shown here have assumed transit time as nonproductive time. Figure 17 illustrates the change in break-even distances for executive travelers conducting productive work en route (assumed to occur during one-half of the block time) in an executive aircraft as opposed to nonproductive transit time in an airline with optimum schedule.

Although the passenger time values for which a turbojet is attractive do not significantly decrease, the range is greatly extended over which the execu- tive turbojet can be effective. This capability to accomplish productive work en route decreases the effective cost of executive travel in corporate aircraft and can be a valuable consideration in the decision to operate an executive airplane.

TURBOPROP 800 UTILIZATION (hf/yr) AIRLINE 200 400 600 800 DISTANCE, s.m.

a. Turboprop and Airline with Optimum Schedule (AT = 0 hr) f-SMALL TURBOJET 800 UTILIZATION (hr/yr) - 120 •V* uilOO r> AIRLINE _J UJ S >- 60 200 400 600 800 1000 DISTANCE, s.m.

b. Turbojet and Airline with Optimum Schedule (AT = 0 hr) Figure 16. Effect of Varying Aircraft Utilization TURBOJET WITH WORK DURING FLIGHT 400 600 800" 1000 DISTANCE, s.m.

Figure 17. E f f e c t of Productive Work-Enroute"' Airline with Optimum Schedule (AT = 0 hr) 4. TIME VALUE ANALYSIS OF ADVANCED AIRCRAFT , .

A selection of the principal, time value phase diagrams is presented here, illustrating potential areas of economic application for advanced aircraft concepts competing against each other as well as against current air modes.

a. Small Aircraft The potential areas of application for advanced small aircraft con- cepts serving the Executive Transportation Mission are illustrated in Fig- ure 18. This figure identifies each advanced concept and compares it against an airline, again with optimum scheduling and one- and three-hour delay times. The compound helicopter appears most efficient at shorter distances over almost all time value ranges. The tilt rotor and tilt wing dominate even further due to their higher speed and longer range capabilities. The lift fan, the fastest of all concepts, dominates throughout distances approaching 1000 miles; however, it does this at slightly higher time values due to increased costs compared to the tilt'wing and tilt rotor.

A further comparison of each of these advanced concepts with current a i r c r a f t as well-as the airline can be seen in Figure 19, with ,an airline delay time of one hour assumed. As can be seen in Figure 19a, the helicopter and AT, hr 150 160 COMPOUND TILT ROTOR 140 140 HELICOPTER JE 120 .£ 120 </> -co- . 100 - 100 UJ Ijj => o 5 80 § 80 UJ UJ p GO 5 60 40 40 20 20 0 0 200 400 - 600 800 1000 0 200 400 600 800 1000 DISTANCE, s.m. DISTANCE, s.m.

a. Compound Helicopter, Airline b. Tilt Rotor, Airline 180 180 140 140 TILT WING LIFT FAN .£ 120 ^ 120 -V> •CO- I0 ui 100 u; ° ;D =D 5 80 § 80 LU L i J i 60 P 60 40 40 20 20 0 0 400 600 800 1000 200 400 600 800 1000 DISTANCE, s.m. DISTANCE, s.m.

# MAXIMUM RANGE AT 50% LOAD FACTOR Wing, Airline d. Lift Fan, Airline c. Tilt Figure 18. Two-Phase Time Value Diagrams for Small VTOL Aircraft and Airlines 180 180 TURBOJET- COMPOUND " HELICOPTER 140 140 £ 120 ^ 120 TILT. ROTOR -co- I0 u; ° => ZD 5 80 § 80 UJ L i J p 60 p 60 20 20 0 0 0 200 400 600 800 1000 0 200 400 600 800 1000 DISTANCE, s.m. -DISTANCE, s.m.

a. Compound Helicopter b. Tilt Rotor 200 400 600 800 400 600 800 1000 DISTANCE, s.m.

DISTANCE, s.m.

c. Tilt Wing d. Lift Fan Figure 19. Multiple-Phase Time Value Diagrams for Small VTOL and Contemporary Aircraft (AT = 1 hr) compound helicopter predominate in the shorter ranges for higher time values with the higher cost compound helicopter requiring time values in excess of approximately $60/hr. Thus the compound helicopter does not appear to have any significant time value advantages over the conventional helicopter. From Figure 19b, c, and d the tilt rotor, tilt wing, and lift fan all appear to have significant advantages over conventional company-owned aircraft (see Figure 15b). They also compete favorably with the airline at passenger time values above $15/hr at the shorter distances and increasing almost linearly with the longer'distances out to approximately 800 miles. If the three advanced concepts are compared in more detail, the tilt wing aircraft appears slightly better for the shorter range executive missions. This is due to slightly lower cost and higher speed of the tilt wing when compared to the tilt rotor. For the longer range missions, the lift fan appears preferable for the higher time value passenger. However, there is litte significant d i f f e r - ence between.,these three concepts and all three appear promising to pursue f u r t h e r .

b. Lift Fan Cost Sensitivity During the course of establishing the economic base for the advanced VTOL aircraft some cost areas were difficult to estimate with any reasonable degree of certainty. Authorities on the subject differed to a marked degree, and confidence in some cost numbers was limited. One such area concerned the cost of the lift fan mechanisms for the lift fan aircraft. Estimates varied as much as +100% and -50% from nominal. In order to assess the sensitivity of the results to these cost variations, the aircraft unit costs were adjusted to reflect fan cost uncertainty and a time value diagram made up as shown in Figure 20. The small lift fan is compared to the airline with optimum schedule and the break-even curve represents nominal lift fan costs. Dou- bling the cost of the lift fan mechanism results in a 6% increase in the 400 600 800 1000 DISTANCE, s.m.

Figure 20. Lift Fan Cost Sensitivity aircraft hourly cost and raises the break-even curve to time values approximately $5 to $10 per hour higher than for the nominal case, which is felt to be within the accuracy of this type of analysis.

c. Extended Range Missions for Small Aircraft The design criteria previously developed were weighted toward the average 1970 missions as reported by current users of executive.and com- muter aircraft. This raised some concern about the potential for long range missions using advanced VTOL concepts. A small lift fan (Extended Range Lift Fan) was designed for longer ranges to determine if a design incor- porating extended range capability significantly affected its time ,value application. The Extended Range Lift Fan design had a full load. (8 passenger) range of 1420 miles as compared to the 600-mile range of the basic lift fan design with the same passenger load. The resulting impact on time values is compared in Figure 21 using the Executive Mission scenario parameters shown in Table XII. This figure compares the basic lift fan and the Extended Range Lift Fan to the small turbojet, all at a 50% load factor. As can be seen, there is a definite advantage in u s i n g the basic lift fan configuration and offloading passengers and adding fuel for range extension in comparison to using the Extended Range Lift Fan.

[ ^ M A X I M U M RANGE OF BASIC LIFT FAN 50% LOAD FACTOR ^- «- .JlOO —I .tj s - 60 40.0 600 800 200 1000 DISTANCE, s.m. .

Figure 21. Small Lift Fan Extended Range Capabilities At a range of 950 miles the Extended Range Lift Fan configuration r e q u i r e s passenger time values of approximately $160 per hour for economic utilization while the basic lift fan competes with the turbojet at $30 per hour time value. If $100-per-hour time value passengers are assumed, the basic l i f t 1'an could lose one hour refueling at 950 miles and still be more economical than the Extended Range Lift Fan configuration. The apparent large penalty i n c u r r e d in range extension through design rather than offloading appears p r o h i b i t i v e when weighed against a stated requirement for average mission riinges of about 500 miles and average load f a c t o r s of 50%.

d. Large Aircraft Regions of potential economic viability for the large advanced aircraft concepts.in the Executive Transportation Mission are shown in Figures 22a through d. In general large VTOL aircraft follow the.same pattern as the .

previously discussed small aircraft with only minor exceptions. The heli- copter has been eliminated in the larger sizes due to its increased cost per passenger. Also, the tilt rotor is "dominated" in turn by the tilt wing (Fig- ure 22b) and the lift fan (Figure 2 2 c ) . The large tilt wing is effective to approximately 1000 miles, which exceeds the range of the large lift fan (Fig- ure 2 2 c ) . The airline has been added in Figure 22b'and "dominates" the low time value segment of the diagram, displacing the turboprop.

Generally the lift fan seems most advantageous in serving the Executive Transportation Mission requiring large aircraft. The lift fan is followed closely" by the tilt wing concept. The tilt rotor is less advantageous in this economic performance analysis because of its lower speed. However, there is little significant difference when comparing these three concepts; other measures of acceptability such as technical risk and noise may have a significant impact.

e. Combined Company -Owned Helicopters and CTOL Aircraft Missions The previous sections examined the attractiveness of advanced design concepts combining VTOL capabilities and significant speed in com- petition with current turbine aircraft. To circumvent the need for an advanced VTOL concept an operator could use a helicopter for access to a CTOLport from which a turboprop or turbojet aircraft could be utilized.

Two scenarios were developed to analyze this case .(see .summary in Table XII). By using these scenarios the time value diagrams of Figure 23 were created. Figure 23a shows that, when compared to the compound heli- copter, the combination turboprop-helicopter is more economical than the turboprop-car only at the shorter ranges. Hence, in general, the added expense of the helicopter is not made up by time savings'and the small ; NOTE TILT WING DOMINATES COMPOUND HELICOPTER, HELICOPTER. TURBOJET, AND TILT ROTOR • 100 rioo I TILT WING 60 60 TURBOPROP 20 20 TURBOPROP I I 0, 400 600 800 1000 200 400 600 800 1000 DISTANCE, s.m.

DISTANCE, s.ffl.

a. Compound Helicopter Dominant b. Tilt Wing Dominant 180 - ISO - 160 - 160 - 140 - 140 - NOTE : LIFT FAN DOMINATES ALL [ ,; MAXIMUM RANGE OF LIFT FAN ^120 OTHER AIRCRAFT 2 0 ~ | V AT 50% LOAD FACTOR

s 5'

uTlOO - * ~ioo -- _' _ 3 80 - 2 8 0 UJ . UJ z 0 ' „ •- 60 •= 60 LIFT FAN ^ ^"^^ 40 40 LIFT FAN : ^ — ^AIRLINE WITH ONE HOUR ^ 20 20 ^^^^^ CONNECTION DELAY £ ^_____ — j ' TURBOPROP — -^ 1 1 1 \ I. \ °C 200 400 600 800 1000 "0 200 400 600 800 1000 DISTANCE, s.m. DISTANCE, s.m.

c. Lift Fan Dominant d. Lift Fan with Airlines Available Figure 22. Advanced Large Aircraft Serving Executive Mission WITH CAR ACCESS COMPOUND .

HELICOPTER ) WITH HELICOPTER ACCESS TURBOPROP 400 600 800 1000 DISTANCE, s.m..

a. Small Compound Helicopter 180 — 160 - 140 - £ 120 - .jioo - • L i J s WITH - HELICOPTER ACCESSy - 60 ' 40 / WITH CAR ACCESSy L.

~ LIFT FAN J""'^-''^^' I • .f ^^-| TURBOJET n 200 •400 600 800 1000 DISTANCE, s.m.

b. Small Lift Fan Figure 23. Small Helicopter--CTOL Aircraft in Combination compound helicopter continues to be more desirable. The situation is slightly improved for the small lift fan -when compared with the combination t u r b o j e t - helicopter, as shown in Figure 23b. Since the lift fan dominates the turbojet at such low time values, the use of helicopter a c c e s s results in a further advantage for the lift fan. The analyses generally indicate that a helicopter - CTOL combination has only limited advantage as compared to advanced a i r - craft concepts having both VTOL and reasonable speed capabilities.

A further advantage accrues through using a VTOL concept such as a lift fan that is capable of performing a long range mission competitively with a turbojet in that a single vehicle can replace both the helicopter and the turbojet. Such would be the case, however, only for a company that uses its helicopter predominantly to access the turbojet.

5. COST SAVINGS ANALYSIS CONSIDERING AIRCRAFT ALTERNATIVES The trip scenarios for the Executive Transportation Mission given in Table XII assumed a fixed annual utilization for all a i r c r a f t concepts under consideration. By using this assumption the number of miles flown per year is a function of the block speed and the mission distance. Where a i r c r a f t of widely v a r y i n g speed capabilities are being compared it is also of interest to examine their capabilities for conducting a fixed number of annual missions, which results in a variable utilization for the d i f f e r e n t concepts. This fixed mission approach is more applicable to the case where a company operates a particular a i r c r a f t and is c o n sidering a replacement. In this case the com- pany has (initially) fixed mission requirements and the p r e s e n t a i r c r a f t flies a specified number of hours annually to satisfy these missions, while a faster a n d / o r less delay-prone a i r c r a f t ( V T O L ) may fly fewer hours while accom- plishing the same annual mission r e q u i r e m e n t s . While operating costs per hour of, the f a s t e r a i r c r a f t may be g r e a t e r , since the fixed portion of the cost is spread over fewer hours, they also fly fewer hours to satisfy the mission requirement. Hence, their aggregate variable costs are generally less for the year. The net result is a potential decrease in the total annual o p e r a t i n g costs for the more advanced concepts and a possible cost saving.

The following cost savings analyses are made on the basis of satis- fying a fixed number of annual Executive Transportation Missions, and cost savings of the advanced aircraft concepts are developed relative to the composite turbojet aircraft.

a. Comparison of Cost Savings for Small Aircraft • The scenarios used in the cost savings analyses are those defined as the primary segment of travel in Table XII. As a reference case it is assumed that a corporation now uses a turbojet to accomplish its nominal annual mission. This mission is defined in Figure 24. The utilization is 500 hours per year as indicated in Figure 24a, and the yearly miles flown and the number of flights per year are indicated in Figures 24b and 24c as a function of trip distance (all the trips made in accomplishing the yearly mission are assumed to be a constant distance).

Since the VTOL aircraft have different speeds, their required utili- zation to accomplish the same nominal annual mission as the turbojet •will vary as shown in Figure 24a. The utilization of the tilt rotor and tilt wing aircraft is either greater or less than 500 hours per year depending on trip distance. The lift fan utilization never exceeds 450 hours per year, while the slower compound helicopter varies from 700 hours per year to over 1000 hours per year depending on trip distance.

Figure 25 is a result of savings computations for the four concepts under study using the utilization data of Figure 24a. The effect of varying utilization on operating costs has been included in the analysis. The savings shown in Figure 25 represent the total difference in yearly costs (including time value as well as aircraft operating costs) between the turbojet and the VTOL aircraft while making the same number of trips and carrying the same number of passengers. Three different time values, $50, $100, and $150/hr are shown parametrically. The greatest savings for all four concepts are in the short ranges. Here many business jet flights are required to accumulate 500 hours and each is inefficient with respect to the traveler's time. Conse- quently the CTOL concept is penalized accordingly. As mission range increases, the savings for all the VTOL aircraft decrease. At approxi- mately 400 miles, it is seen in Figure 25a that the slow speed and high cost COMPOUND HELICOPTER MAXIMUM RANGE AT 50% LOAD FACTOR TURBOJET REFERENCE AIRCRAFT LIFT FAN -• 200 200 400 600 800 1000 1200 DISTANCE, s.m.

a. Utilization ,o '§ 100 0 200 400 600 800 1000 1200 DISTANCE, sm b. Total Miles (All A i r c r a f t ) g 2000 UJ ^ 1000 0 200 400 600 800 1000 1200 DISTANCE, s.m.

c. Number of Flights (All Aircraft) Figure 24. Definition of Fixed Distance Mission ! , (Small Aircraft) MAXIMUM RANGE AT MAXIMUM RANGE AT 50% LOAD FACTOR 50% LOAD FACTOR TIME VALUE, $/hr jj I TIME VALUE, $/hr I •0 200 400 600 800 1000 200 400 600 800 , 1000 DISTANCE, s.m. DISTANCE, s.m.

a. Compound Helicopter b. Tilt Rotor MAXIMUM RANGE AT MAXIMUM RANGE AT 50% LOAD FACTOR 50% LOAD FACTOR _TJME VALUE, $/hr T[ME VALUE, $/hr 150, J I 400 600 800 1000 200 400 600 800 1000 0 200 DISTANCE, s.m. DISTANCE; s.m.

c. Tilt Wing d. Lift Fan Figure 25. Cost Savings of Small VTOL Relative to Small Turbojet of operation of the compound helicopter puts it at a disadvantage with respect to the turbojet 'and, instead of saving money, it begins to cost more. It is seen in Figures 25b and 25c that despite higher operating costs and lower speeds, the tilt rotor and tilt wing exhibit savings to their respective maxi- mum ranges for almost all values of traveler's time. However, the higher costs associated with the lift fan (Figure 25d) result in savings only for v travelers whose time value exceeds $100/hr. These savings result at any trip distance within the maximum range shown.

-•";. For the nominal Executive Transportation Mission distance of 500 miles, yearly cost savings of $200,000 to $300,000 per aircraft may be realized using tilt rotor, tilt wing or lift fan concepts. The results of Fig- ure 25 indicate that the tilt rotor and tilt wing concepts could produce the greatest" sayings as'a replacement to the small turbojet Executive Aircraft.

The curves in Figure 25 also answer the question of how much more economical bn'e'VTOL concept might be than another in a given region of the phase diagrams. For example, although the tilt wing indicates an economic superiority, over the tilt rotor in the phase diagrams of Figures 18 and 19, it can be seen by comparing Figures 25b and 25c that the economic differ- ence is small. For this reason a choice between these two concepts may be based on other considerations such as noise, ride quality or aesthetics.

b. Comparison of Cost Savings for Large Aircraft A similar cost savings analysis was conducted for the large (16 passenger) advanced VTOL concepts in comparison with the large turbojet aircraft. The results.obtained, by using similar procedures given previ- ously for. the small aircraft, are illustrated in Figure 26. It can be seen that all of the advanced aircraft have a significant potential for cost savings over the composite turbojet. The large compound helicopter (Figure 26a) produces cost,savings to greater mission distances than did the small com- pound helicopter. Since the costs associated with large aircraft operations are higher than those of small aircraft operations, the corresponding sav- ings available through the use of large VTOL concepts are also significantly greater. • • ...

n TIME VALUE, $/hr TIME VALUE, $/hr 6 MAXIMUM RANGE AT r 150 I50 ^ 50% LOAD FACTOR

j

0 200 400 600 800 1000 0 200 400 600 800 1000 DISTANCE, s.m. DISTANCE; s.m. •: -...

a. . Compound Helicopter .

b. Tilt Rotor '•• • 2nr I50VTIME VALUE; $/h, 0 . - • 200 - 400 600 800 1000 0 200 400 600 800 ' 1000 DISTANCE, s.m.. DISTANCE, s.m..

c. -Tilt Wing d. Lift Fan Figure 26. Cost Savings of Large VTOL Relative to Large Turbojet In general the following conclusions on potential cost savings for equal missions using large aircraft are: 1. For trips below 500 miles all four concepts can produce a significant cost saving as a replacement for the turbojet.

2. For trips beyond 500 miles the tilt wing and lift fan appear to have the best cost saving potential compared to the other concepts.

3. The large tilt wing concept appears to provide the best cost ' . saving potential for low time value passengers; for high time value passengers the large lift fan appears best.

B. COMMUTER AIR CARRIER MISSION COST BENEFIT ANALYSIS 1. MISSION SCENARIOS Selected scenarios for Commuter Air Carrier Missions are devel- oped in Table XIII. These missions assume that a traveler starting from home or office travels to the nearest commuter port by car, boarding the primary^mode with minimum processing time. Large, advanced VTOL air- craft are assumed to operate from VTOLports which are more conveniently located to the traveler, resulting in shorter access and distribution times than for airline service.

2. TIME LINE ANALYSIS Results of the time line and cost analyses for Commuter Air Car- rier Missions as described in the foregoing scenarios are given in Figure 27.

Again the advantage of VTOL aircraft operating from a multiplicity of neigh- borhood VTOLports becomes evident in minimizing access and distribution segment time. The Commuter Mission is generally short (typical stage length approximately 100 miles); hence, all VTOL aircraft—whether rotor, propeller or fan--have significant time advantages over CTOL aircraft oper- ating from today's few air carrier ports. The operating cost per passenger of the lift fan concept (Figure 27b) is only slightly in excess of that of the airline, even though the scenario indicates the cost per hour per passenger CM (M r>J (NJ M (-0

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a. Time Line I ^MAXIMUM FULL FUEL RANGE | -w-240 of » 200 UJ CAR-COMPOUND CO HELICOPTER-CAR g 160 CAR-TILT ROTOR-CAR o: CAR-TILT WING-CAR CO CAR-LIFT FAN-CAR o CAR-AIRLINE-CAR 0 100 200 300 400 500 600 700 BLOCK DISTANCE, s.m.

b. Equivalent Passenger Cost 27. Commuter Mission--Intercity Service with Large Aircraft Figure is much greater, reflecting its increased speed over slower commuter airline aircraft. The rotor craft show up as least desirable in this anal- ysis because of their lower speeds which are not offset by lower cost per passenger.

It should be noted that all of the new, large VTOL concepts are over 12,000 pounds in gross takeoff weight. They are, however, all under 30 passengers and 7500 pounds in maximum payload. Thus they could be operated by commuters in accordance with changes to the CAB's jruling per- taining to Part 298 operations. The FAA, however, has yet to relieve the requirement that all aircraft over 12, 500 pounds in gross takeoff weight be operated under Federal Aviation Regulation (FAR) Part 121 rather than the less stringent FAR Part 135 under which most commuters presently operate.

Thus direct comparison of the new VTOL concept operating costs with present commuter Part 135 costs (as reflected by their fares) can only be valid if the FAA adopts criteria similar to the CAB and thus permits operation of the larger aircraft under Part 135. '»-""— 3. TIME VALUE ANALYSES OF ADVANCED AIRCRAFT A complete analysis of the role of advanced VTOL aircraft in the Commuter Air Carrier Missions was beyond the scope of the present study.

However, the previous section showed favorable time savings at relatively small increases in cost for some of the concepts. Since the Commuter Air Carrier Mission is generally short (under 200 miles) full advantage cannot be taken of the speed of the lift fan concept. Therefore, the next most attrac- tive candidate is the tilt wing which also showed up favorably in the executive mission analyses. Consequently a time value analysis has been made for the Executive Transportation Mission (considering airline, small helicopter, and small tilt wing alternatives) and the large tilt wing in the Commuter Air Carrier Mission.

Here the cost of operation includes both direct operating costs and indirect operating costs, but not a return on investment, and can be thought of as the commuter "break-even" fares.

Figure 2 8a compares a company-owned small tilt wing a i r c r a f t , ' an executive small helicopter, and current CTOL commuter fares. Fig- ure 28b then adds'a large tilt wing commuter application to the scenario.

As can be seen, Figure 28b shows that a tilt wing aircraft utilized in the Commuter'Air 'Carrier Mission would be attractive for executive travelers with time values up to approximately $10 per hour for the nominal commuter distance of i 00 miles.' For greater distances conventional commuter airline service becbme^s"more attractive, and for greater traveler time values a company-owned small tilt wing concept in the Executive Transportation Mis- sion would be'more cost effective to the traveler. Fares for the CTOL and VTOL commuter aircraft are also shown in Figure 28. Although the tilt -wing may be competitive'with the CTOL commuter for the executive traveler, the required fare for a commuter tilt wing may be too high to attract lower time value classes of commuters.

C. OFFSHORE MISSION COST BENEFIT ANALYSIS , • . .

One of the .more, significant Industrial Special, applications .of the helicopter is the delivery of personnel on routine schedules to offshore oil drilling sites (platforms). The helicopter typically operates between a land base and drilling sites approximately 100 miles offshore. VTOL capabili- ties are required and hence the scenarios shown in Table Xlllb incorporate only the primary segment of travel. The four advanced aircraft concepts are shown along "with conventional helicopters as now used. Both small and large configurations are shown in the scenario and these are not generally interchangeable in the Offshore Mission since the large helicopters are used for scheduled crew changes while the small vehicles are used for movement of supervisory personnel.

Results of the time line and cost analyses for the two Offshore Mis- sions are shown in Figures 29 and 30. It appears from Figure 29 that the efficiency of crew change could be enhanced through the use of advanced VTOL aircraft, with the lift fan concept leading the candidates both in improved delivery time and cost per passenger. All of the advanced 0 0 0 f op «) rO OO O> CM o u.

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MAXIMUM FULL FUEL RANGE I TYPICAL ROUND TRIP DISTANCE :240 E- • 160 _ COMPOUND HELICOPTER TILT ROTOR < •' TILT WING LIFT FAN •: .40 0 100 200 300 400 500 600 BLOCK DISTANCE, s.m.

a. Time Line MAXIMUM FULL FUEL RANGE cc UJ g .200 UJ CO CO g 160 cc UJ COMPOUND HELICOPTER °- 120 i— TILT ROTOR <j~> TILT WING LIFT FAN 500 600 TOO 0 100 200 300 400 BLOCK DISTANCE, s.m.

b. Equivalent Passenger Cost Figure 29. Offshore Mission--Crew Change with Large Aircraft :79 concepts have significant advantages over today's helicopter for this purpose.

Further, limited range of the current helicopter precludes safe use for longer stage lengths as offshore distance requirements increase. The advanced VTOL aircraft can safely operate at round trip ranges over 400-500 miles.

The time line and cost analysis for the Offshore Mission of trans- porting supervisory personnel presented in Figure 30 also shows the advanced VTOL concepts to be time saving in operations over the helicopter. The heli- copter, however, has a small cost advantage. In general the tilt wing and lift fan concepts appear the most attractive for this mission. The two Offshore Missions require the use of different-size vehicles; hence, the operator would most likely make his choice within a given size and not between sizes. There- fore a direct comparison of large and small aircraft time and cost is not presented herein.

•& U.S. GOVERNMENT PRINTING OFFICE: 1974—739-160/133 MAXIMUM FULL FUEL RANGE I p*—TYPICAL ROUND TRIP DISTANCE c e • COMPOUND HELICOPTER J 160 TILT ROTOR TILT WING LIFT FAN 0 100 200 300 400 500 600 BLOCK DISTANCE, s.m.

a. Time Line MAXIMUM FULL FUEL RANGE COMPOUND HELICOPTER TILT ROTOR LIFT FAN TILT WING 500 600 700 100 300 400 BLOCK DISTANCE, s.m.

b. Equivalent Passenger Cost Figure 30. Offshore Mission--Supervisory Personnel Movement with Small Aircraft VI. CONCLUDING REMARKS This study was intended to delineate broad areas of economic viability in order to identify the advanced VTOL concepts worth pursuing.

For this purpose, the level of aircraft design detail used was considered sufficient to compare the concepts by a cost-benefit analysis. Further in- vestigation of the promising VTOL concepts would require more detailed configuration design tradeoff studies to identify those potential problem areas that might further influence the choice of VTOL concepts or suggest worth- while areas of research. These analyses, as well as the investigation of other influencing factors such as noise, technical risk, and technical com- plexity were beyond the scope of this study.

v . There are a number of VTOL concepts that may be applicable to general aviation missions. This study evaluated the four representative advanced VTOL concepts that appear to be typical of the technology of the late 197O's. Due to the rapid advancement of VTOL technology, however, it is possible that the most appropriate VTOL aircraft for application to general aviation missions one to two decades from now may incorporate a concept or combination of. concepts not yet recognized.

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VII. REFERENCES 1. Feistel, T. W. ; Stewart, E. C. ; Gerdes, R. M. ; Smith, K. R. , Jr.: A Look at V/STOL For Business Aircraft. Society of Automotive Engineers, Inc.; Transactions, 1972, Volume 81, Section 8, pp 1259-1272.

2. Smith, K. R. ; Belina, F. W.: Small V/STOL A i r c r a f t Analysis, Volume II, Ames Research Center, NASA CR-114629, June 1973.

3. Office of Management Systems, Federal Aviation Administration: National Summary of General Aviation Aircraft and Hours Flown.

1969.

4. Flying Annual and Pilot's Guide. Ziff-Davis, 1971 5. Taylor, J. W. R. : Janes All The World's Aircraft. 1968-69.

6. Office of Aviation Economics, Federal Aviation Administration: Aviation Forecasts Fiscal Years 1971-1982. January 1971.

7. Benzakein, M. J. ; Volk, L. J. : Study Program for Lift Fan Noise Reduction and Surpression, General Electric Company, February 1969.

8. Dugan, J. F. : Airbreathing Propulsion System Trends, Astronautics and Aeronautics, Volume 9, Number 11, Page 37, November 1971.

9. Sternfeld, H. ; Hinterkeuser, E. : Effects of Noise on Commercial V/STOL Aircraft Design and Operation, Journal of Aircraft, Volume 7, Number 3, Page 8, May 1970.

10. Taylor, J. W. R.: Janes All The World's Aircraft 1970-71, B. P. L. Publishing Ltd., London, England.

11. Anonymous: Advancement of Proprotor Technology, Task I - Design Study Summary, Bell Helicopter Company Report 300-099-003, 3 September 1969.

12. Bernstein, S. : CL-84 Tilt Wing Applications, ICAS Paper No. 68-45, Sixth Congress of the International Council of Aeronautical Sciences, Munich, Germany, September 1968.

13. Official Airline Guide, Quick Reference - North American Edition, July 1971.

14. Drake, H. M. ; Kenyon, G. C. ; and Galloway, T. L. : Mission Analysis for General Aviation in the 1970's. AIAA paper 69-818, 1969.

15. Kenyon, G. C. jjjalloway, T. L. ; and Drake, H. M. : An Economic Analysis of Future Short-Haul Transportation, NASA TM X-2Z28, March 1971.

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