Document
aircraft flew 3.8 billion miles and carried 90
Chapter I
million people.'
General aviation provides a wide variety of
GENERAL AVIATION
functions, varying from the actual transporta- tion of wuple and goods through charter,
COMPONENTS
cargo, mail, executive transport, and air taxi operations; to sports, recreational, and instruc- tional activities. Between these two poles lie a daVinci conceived it in his early sketches.
range of industrial and community services Popov claimed to have done it first. Langley's such as aerial photography, stock-herding, effort disintegrated over the Potomac River.
fish-spotting, advertising, corpse-flying. log- And on December 17. 1903, Orville Wright ging, law enforcement. fire fighting, environ- piloted man's first successful powered flight in mental management, health care delivery.
a heavier-than-air vehicle; a flight which if un- banking, and emergency services.
dertaken today could be completed within the Table 1-1 shows the number of vehicle- fuselage of a DC-10. His short 120 foot trip miles and passenger-miles travelled by general (0.02.3 of a passenger mile) marked the begin- av~ation, in comparison to other modes of ning of rqan's conquest of the sky, and the s!art transport. Table 1-11 presents some basic of a multi-million dollar industry, which in 197'i general aviation statistics. These show that it alone resulted in 120 billion passenger-miles. It includes 98 percent of all aircraft, 60 percent of freed man from the earth and darted him on his the total number of vehicle miles and 7 percent way to the moon in less than 66 years.
of all passenger miles flown.
The aviation industry has had a tremen- This report examines the relationship be- dous influence on the American way of life: in tween general aviation and community time, in mobility, in technology, in weaving our development. The first chapter discusses social fabric. Much of its influence, neverthe- general aviation and its components. Later less, remains highly misunderstood and unex- chapters will examine the environment in which plored. Although aviation has touched the lives general aviation operates, the process of of millions of people, most of their contact with analyzing community aviation needs, and it has been either through the Ilse, or the image, selected Virginia community aviation issues.
of scheduled air carriers in operation around The final chapter is a guidebook which will the world. Air carriers, however, represent only enable community decision-makers to deter- a small proportion of the total fleet of aircraft mine whether or not a general aviation service using the airspace, and serve only a small pro- is needed and how to go about satisfying such portion of the landing facilities available needs.
around the country. Exclusive of the military, The major components of the general wia- the other side of the civilian aviation coin is tion system discussed in this chapter are (1) the known as General Aviation, and is defined in- vehicle, (2) the air support facilities, (3) airways stitutionally as incorporating all operating and avionics, and (4) human factors. These civilian aircraft other than the air carriers, components combine to produce the dynamic which are certificated by the Civil Aeronautics category of General Aviation; ever moving Board.
toward increased safety and efficiency.
Today there are approximately 3,000 aircraft beirg used by air carriers, while in ex- THE VEHICLE cess of 130,MN) make up the general aviation Introduction fleet. Of the 13,000 airports in the United States, The purpose of this section is to present an only about 500 are served by air carriers in con- overview of selected aviation vehicles. The trast to total use by general aviation vehicles.
capabilities and performance of these vehicles General aviation employs thousands of persons are first presented, followed by a discussion of in this country in a wide variety of occupations, the aerodynamics, structures and materials, including aircraft crews, direct and indirect propulsion systems, noise, and configurations ground support personnel, and manufacturers.
of fixed-wing aircraft. Finally the discussion General aviation is assuming an in- focuses on the h~story, status, and future of at- craasingly important role in the national tempts to provide vehicles capable of short- transportation picture: in 1976! general av~ation field operations. Inclusion of the final section is due to the importance of such capabilities in ' "Non-Busmess Planes Carr~ed 90 tv.'l~on.' Newpon News De~ly Press, July 25. 1975. p 42 general aviation aircraft.
PRECEDING PAGE BLANK NOT m3
TABLE 1-1
PASSENGER AND CARGO TRAFFIC BY TRANSPORTATION MODE - 1971
Dommtic Only C.rgo T M i k s x l o ' Air Carrier Water Pipeline Rail Highway Truck Bus General Aviation Auto Total 2,216,676
- -
Note: NA may mean one of the following: 1) not available 2) not applicable 3) smaller than half the statistical unit used Source: "Summary of Natio!?al Transportation Statistics," DOT-TSC-OST-73-76, Washington, D.C., Novsmber, 1973.
TABLE 1-11 1971 GENERAL AVIATION STATISTICS General Aviation Category Vehicle Vehkle-miles Houn Flown Units % Units % Units % Business 33,314 25 1,130,000,000 36 7.100,000 29 Commercial 9,327 7 510,000,000 16 3,500,000 14 Instructional 19,750 13 650,000,000 2 1 6,400,000 26 Personal 68,475 52 794,000,000 25 7,200,000 29 Other 4,282 3 60,000,000 2 ~ , O O O 2 1. Total expenditures and revenues 21.4% of all air 2. Passenger miles 7% of all air 3. Number of fatalities 87% of all air 4. Total number of vehicles 98% of all air 5. Total vshicle-miles 60% of all air Source: "Summary of National Transportation Statistics," DOT-TSC-OST-73-76, Washington, D.C., November, 1973.
The airplane has been selected as the is at its center. The dimensions of the box (ac- specific aircraft to be discussed because it has, tually a rectangular figure) are variable in- dividually with p h a e of operation ',e.g., opera- since its invention, always been the dominant vehlcle on the aviation scene, and there are no tion in a termlnal area). The important point is reliable indicators that its status will cha~ge. that the airplane interdicts a sizeable airspace Other general aviation vehicles such as heli- and ground area, and this space may be, and copters, balloons, airships, and gliders are dis- sometimes is, the same for a small airplane as cussed briefly. For definitions of these and for a large one.
other terms, see the Glossary (Appendix E).
The airplane is a moderately constrained vehicle in terms of its freedom to move in Capabilities and Performance various directions relative to its own plane of symmetry. In flight its broadest-band The airplane is a specific type of flight capabilit~es are in that plane, and are those of vehicle or aircraft, propelled through the air by steady or nearly steady movement. These a powerplant which exerts ~ t s force prepon- capabilities are known collectively as its static derantly forward. It is sustained in the air by the performance, consisting of climbs, cruise forces created by differential pressures exerted flight, and descents.
on its exposed surfaces, mainly its fixed wlngs, due to its motion through the air. Straight and Level Flight The straight and level unaccelerated flight Fcr purposes of considering its incorpora- capability of an airplane may be portrayed by a tlon into an aviation system, the airplane can be considered as an imaginary box, the c,rnen- g r a p h s h o w i n g t r u e a i r s p e e d ( n o t groundspeed) against altitude. Figure 1-1 11- sions of which portray a volume of air around it lustrates the "flight envelope." The curved line which is forbidden to other aircraft; the airplane
TRUE AIRSPEED
CAPABILITIES: THE FLIGHT ENVELOPE FIGURE 1-1 which IS satisfactory for use in flight on air- at the left represents the trend of stalling ways. Emergency descents of 1,500 feet per speed, the speed below which the airplane can- not be flown straight and level, because of in- minute or even more can be made with reasonable pitch angle changes and within ac- sufficient aerodynamic lift. The long line is the stalling speed in "clean" (gear and high-lift ceptable limits of operation, though in devices retracted) configuration; the short lines unpressurized airplanes there is risk of damage give the stalling speeds for other configura- to passengers' ears.
tions; takeoff, segmented climb, and landing.
The "best approach" angle at which land- The horizontal line at the top of the figure ing approaches may be performed is that repre- represents the maximum altitude for which the senting a power-off (engines idling) glide at an airplane is certificated. It may be well below the airspeed about 30 percent above that for stall, with flaps fully extended and landing gear absolute ceiling of the airplane since reasons down. The angle may be anywhere from about 5 such as safety in event of a window blowout or oxygen requirements may govern the choice of to 9 degrees. Steeper approaches may be the highest altitude for which certification is made, but some pilots consider that safety sought. levels are reduced at the higher angles. The "ILS landing approach" angle of 2.5 to 3 The crooked line on the right represents degrees is established by the angle that the the highest speed or Mach number in normal glide slope beam of an instrument landing flight for which the airplane is certificated. The system transmitter makes with the ground. This symbol Vmo means "maximum operating shallow angle almost always requires that velocity" and Mmo means "maximum operat- engine power or thrust be above idle setting, ing Mach number." These speeds are usually and this increases the degree of control the very close to the top speeds the airplane can at- pilot has over the glide angle (since the throttle tain, and are set by a combination of structural is a climb and descent control).
and handling-qualities requirements.
Other Changes of FligM Path Climb and Descent The airplane is an awkward machine to Generally, an airplane does not climb with- turn; i t must be turned and banked out first pitching its nose up; at its maximum simultaneously, much as a car requires banked speed it has no climb capability at all. The max- curves on roads. A conventional airplane can- imum rate of climb is generally realized at an not move directly sideways at all except by slip- airspeed about 215 of the way between stalling ping, during which altitude typically must be speed and top speed.
lost because the aerodynamic drag (rearward) The maxium angle of climb is important for force on the airplane increases, and the takeoffs and for climbs which emergency con- airplane must either slow down or descend or ditions may necessitate performing near the do both, as a consequence. The slipping ground. Thls can vary with size and type of maneuver was popular years ago as a means of aircraft, and with speed and flight configuration steepening landing approach paths, but its of a given type. Small, slow airplanes may have capability is very limited. The advent of trailing clean-configuration maximum climb angles of edge flaps in about 1940 made it largely un- perhaps 14 degrees or so; the business jets may necessary, except as an aid in making achieve 40-degree angles.
crosswind landings. Recently Interest has revived in improving the ability of the airplane An airplane may be caused to descend to move sideways, this time as a means of mak- without pitching by retarding the throttle (the ing adjustments in the lateral position of the throttle is said by some flight instructors to be final approach path relative to a landing field the basic climb-and-descent control, though runway. This ability can be important for instru- this is oversimpli3tic). Except in air-carrier ment flight operations.
operation this is not an important maneuver. A more popular descent technique is to establish In turning flight, the measure is the radius some fixed vertical speed while retaining cruis- of turn, a function both of speed and of bank ing airspeed (approximately). In the cockpit of angle. As a general rule, the radius of a turn practically all modern airplanes there is an in- may be decreased (the turn made tighter) by in- strument called a Vertical Speed Indicator, and creasing the bank angle. At a given bank angle a popular vertical speed for descents out of a slow airplane is able to turn tighter than a fast ground proximity is 500 feet per minute, a rate one, so the minimum turning radii of small for which the apparent nose-down acgle of the airplanes are generally in the hundreds of feet, cabin is not disturbing to passengers, and while those of fast airplanes such as fighters are generally thousands of feet long. Power is place, will establish whatever relationships ex- required to make a level turn, in excess of that ist between field performance and other design required to drive the airplane straight. Conse- features.
quently, as the speed of an airplane is in- Three identifiable technological levels creased toward its top speed, its ability to turn have evolved into which marketed airplanes gradually deteriorates until at top speed it can- have been divided. (1) Conventional Takeoff not make level turns at all, but must slow down and Landing (CTOL) technology is typified by to do so. Passengers will begin to take notice, simple flaps, such as appear on most general and some will be disturbed if turns are made aviation airplanes. (2) Reduced Takeoff and with bank angles more than 30 to 45 degrees.
Landing (RTOL) incorporates complex flaps Historically, there has been a fairly close and leading-edge high-lift devices called slots, relationship between the size and the maxium slats, and Krijgers, and perhaps a little powered speed of airplanes marketed successfully in the lift. (3) Short Takeoff and Landing (STOL) United States. The smaller airplanes have max- airplanes use energy, in addition to that sup- imum speeds near 100 knots. As gross weight plied to ihe main propulsive means (e.g., prop) rises, maximum speed also rises, until at the to produce lift directly, through boundary layer top of the weight range for six-passenger control or lifting fans. Historically, STOL single-engine airplanes (about 3,800 pounds) airplanes have not found a market except with it is on the order of 200-220 knots. Larger the military. RTOL airplanes, slich as the Boe- ing 727, are in operation, but the only small piston-engine airplanes, the twins, are only a little faster than this, because of the airplanes in the category have beer, isolated unavailability of engines of more than about single examples because of the expense in- 350 horsepower. The turbin powered twins use volved in adopting the technology.
engines of 600 - 1,000 horsepower, and so are
Field performance data on specific considerably faster than piston twins of com- airplanes are given slsewhere, but it is instruc- parable size, with maximum spaeds on the tive to look at what corporate and utility order of 250 knots. This size-speed relationship airplane operators have considered to be ade- has not changed much in recent years.
quate field length requirements. Two surveys of such operators made some years ago, indicate The turbofan and turbojet airplanes, that all operators would be satisfied with 2,000- whatever their weights, have maximum speed foot-or-shorter field performance, but field of 350-450 knots. The lack of size-dependence length requirements of 5,000 feet or longer is due to the fact that the jet airplanes are would satisfy no one.
limited by the effects of the compressibility of air on their ability economically to achieve Range~Payload Tradeofis high-speed flight. The speeds of the jet Most airplanes, except very small ones, are airplanes are well above those of propeller weight-limited in such a way that full passen- airplanes of any size, though military propeller gers and f u l l f u ? l cannot be loaded airplanes during World War II were occa- simultaneously without exceeding the max- sionally flown straight and level at speeds just imum certificated gross weight. Figure 1-2 above 430 knots, during development pro- shows typical ranges for various types of grams.
aircraft starting with full tuel tanks. It also Little on the technological horizon has ap- shows one of the informative ways in which peared to indicate that the above relationships range-payload information can be portrayed will change much. New type piston engine graphically. The empty airplane occlrpies a development is moribund, the fuel economy of point at the origin of the graph, and eithei fuel the Wankel engine is not outstanding, and or payload must be loaded first. If, for illustra- there is a large region extending from about tive purposes, payload is considered to be Mach 0.9 to about Mach 1.5 in which efficient loaded first, the lefthand end of the top horizon- airplanes are difficult to develop.
tal line represents the airplane when loading is completed but fueling has not started; the Takeoff and Landing airplane can thus go nowhere. As fueling pro- Airplanes can be built which will take off and land in any given distance, including zero. ceeds, the capability of the airplane is indicated Takeoff and landing distances depend strongly by points on the horizontal line. Finally enough on stalling speeds, but in general, power is re- fuel has been added that the airplane is at its maximum certificated weight, and fueling must quired to fly slow, below a certain point, just as it is required to fly fast. This means that the stop whether the tanks are full or not (point A).
available technology, as well as the market If the tanks are filled before the payload is ad-
RANGE -
TYPICAL MAXIMUM RANGES (Nautical Miles)
General Aviation A i rcrafl
Light Airplanes 300 -990
Business Jets
Airliners
Trunk and International 4,000-@30
RANGE - PAYLOAD TRADEOFFS
FIGURE 1-2 ded, the airplane will be represented by points tion, with the occasiona! addition of major on the line between "Ferry" (the weight with nc jumps in tnnovatlon which nevertheless did not payload) and B (the point at which loading change the definitive outllne of the airplane it- payload must stop because the airplane has self.
again reached ~ t s certificated we~gh:). Between Aerodynamic Design A and B, fuel and payload must be traded to The general outline of the a~rplane as a set keep the gross wetght constant.
of wings with stabilizing and control surfaces was detinitive from the start. There were other concepts, but these disappeared rapidly.
The Fixed-Wing Aircraft Technologies Two changes took place within a decade after tha first flight. replacement of wing-warp- The history of the development of the ing by a~lerons. and settlement on the conclu- airplane has been that of technological evolu- sion that the tail-surface of an airplane tions of wings and bod!es, in accordance with- belonged behind it. Nothing basic has occurred the Whitcomb "transonic area rule."
since then in the area of general aerodynamic Aerodynamically, the modern airplane is configuration of small subsonic airplanes.
ar: extremely efficient device. Its propeller Combat airplanes underwent evolutionary delivers thrust horsepower at an installed effi- growth during World War I, with both sides pro- ciency, typically, of over 85 percent. The "in- ducing airframes using about the same tech- duced" drag which is an inherent theoretical nology until the Germans introduced the first penalty of the production of lift is exceeded by all-metal monoplane, near the end of the con- only about 10-15 percent in practice. The flict. General acceptance of the monoplane "parasite" drag which is the penalty for having waited until the appearance of aluminum i r ~ a useful load that occupies space, is little more than that which would be experienced by a thin sufficient quantities, and of acceptable proper- ties, made the aerodynamically superior in!er- flat plate, equal in exposed area to that of the nally braced monoplane technically feasible. In airplane's exposed skin, drawn through the air edgewise, at flight speed. This is approximately the meantime, during the decade of the twen- six times "cleaner" than a typical automobile ties, the biplane and strut-braced monoplane lived side-by-side, with no singular advance in (the above statements apply to "top-of-tho-art" aerodynamic technology. airplanes: unbraced-wing mono-planes with retractabls gear).
The next two significant improvements ap- peared almost simultaneously. The feasibility of On the low speed end of the flight envelope the airplane does not do so well. It cannot fly the internally-braced monoplar~e resulted in level at any speed below its "stalling" speed, higher wing loadings (thus higher stalling speeds) and In the Increasing significance for which can be compared roughly with the cruis- drag of items which previously were of minor ing speed of an automobi le. The safety implica- tions of having to toucn down no slower than importance. Flaps and retractable landing gear this are obvious and efforts to improve the appeared almost together, to make significant situation have been continual. The market extensions to both ends of the speed range.
The fighters of World War I could fly a little over place typically has called for speed and effi- ciency, however, and has accepted the risks of twice as fast as their stalling speeds; by the fast touchdowns.
1930's "twice as fast" had become "over three times as fast."
Indeed, striving for very low stalling speeds can be more dangerous than not. The At that point the major contriSut;ons to low reason lies in the fact that the aerodynamic subsonic aerodynamic art ceased. Slnce then force that a control surface (e.g., rudder) can there have been detail improvementsshaping exert, is proportional to the square of the speed refinements in ailerons, flaps. slats, airscoops, with whlch it moves through the air. So an and so on.
airplane configured for low speed handling can General aviation includes high-subsonic be oversensitive at high speeds 3r one con- airplanes, so the two most significant technical figured for high speeds too sluggish at low.
contributions to flight in the Mach-number Conventional general aviatlon airplanes of range from 0.6 to 0.9 should be ment~oned. The small-to-medium size are typically acceptable first of these was acc~dental. During the mid- on both ends of the speed range. One of the thirties specially shaped families of airfoils ways In which power requlred for cruise flight were developed in an attempt to reduce wing can be reduced. however, is by reducing wing skin-friction drag. Success in doing this was areas. The higher stallir~g spwds whlch result negligible for various reasons. Of interest, are undesirable, but can be lowered by increas- however, was the fact that the speclal airfoils ing the maxlmum wing lift capability. Thus the had better high Mach characteristics than their energy cris~s helps keep the pressure on for predecessors. Maximum opevating Mach num- fur!her development of high lift devices.
ber gains of more than 0.1, or about 15 percent.
were possible. The second development,that of Airfoil Development "Airfoil" refers to the shape and thickness the swept wing, wes German, and was not of a cross-section of a wing. Three forwclrd known to the United States until the collapse of Germany in 1945. High-subsonic airplane aero- surges in airfoil development can be identified.
dynamic deslgn coasted along on the strength First, the NACA low-speed programs of the 1920's and 1930's which resulted in the four and of these two developments untll the late 1950's.
whe.1 Boeing commenced utilizing a further five-d~git airfoil seric; (each digit of a designa- refined airfoil series and tailoring near the junc- tlon such as 2412 gives the magnitude of an air-
TABLE 1-111
EXAMPLES OF AIRFOIL DEVELOPMENTS
Romrrk8 Airtoll Cdigit mries NACA 24XX 5-dig~t series NACA 230XX (1 930's) " Larn~ner-tlow" NACA 63-4XX airfoi Is 4-digit airfoil with -- 2.0 NACA 6716 (1974) high-loaded trailing edge "Low-speed super- critical" thick air- foil Lift (Dynamic pressure) (Area) foil shape parameter). The entire series used a The gains being sought aro relatively type of thickness function based on only 2 air- small, and the cost of obtaining them %me- foils: one designed by Col. Virginius €. Clark, times seems excessive. Table 1-111 illustratesthe and one very similar designed at Gottingen.
evolution of high-lift airfoil technology. The The mathematical difinitions of thickness func- data are clouded by the fact that the later ex- tions and mean lines were sys:ematized, but not plorations have emphasized low test speeds.
on a theoretical physical base--!hey were ar- There has been much attenti011 devoted to bitrary, as were the Clark and Gottingen airfoils raising the maximum lift capabilities of airfoil that served as the point of departure.
sections. This has taken the forms ~f (1) devis- Second, the so-called "laminar flow" ing basic sections with high maximum lifts, and series, which as it turned out offered more to (2) dtwising slat and flap configurations to ap- high-Mach flight than to low. There were ply to these sections to produce high maximum several families of these, of which the survivors lifts in landing configuratioas (flap down, slat are the so-called "6" and "6A" series. Airfoil out).
contours were developed to match desired sur- Some of the recently-developed basic sec- face velocity dis!ribution.
tions have had lower drag at high lift than have Third, various programs seeking further older sections of the same thickness ratio relief from high-subsonic-Mach number limita- (thickness ratio is important because it indi- tions of thick airfoils developed. The names cates the depth of wing availabls for structure connected with these programs are Sinnott and and tankage). A conventionally corlfigured Pearcy in England, and 'Whitcomb in the United small airplane may be said to have "toc much" States.
wing for economical cruise, since the wing size Current work in the United States is of is determined by the requirement for low stall- three kinds: (1) theoretical and experimental ing speeds. The bensrit sought through use of work on multi-element (f:apped and slatted) air- the newer airloil sections is in that they allow foils; (2) theoretical and experimental work on smaller wings than usual, since their maxium high-lift basic airfoils, notable among which is lift capability is hiah. In climb and at cruise, the the GA(W) airfoil series to which Whitcomb's small wing omrates at higher lift per unit area, name has literally become attached; and, (3) and the shih: of maximum weightldrag ratios to continued wark on the "supercljtical" ;lasses higher lift values is therefore favorable to the new sections.
of airfoi Is.
The clas3ic approach to configuring multi- Second, in ona or two cases of note, element wings for takeof!, approach, and land- sopnisticated techn1que.i have produced solu- ing has been to start with a given basic airfoil, tions for airfoil shapes which obviously wwe no lay in flap and slat elements that will fit inside good, but were carried through wind tunnel the airfoil contour, and then explore what the tests despite the clarity with wnich the !ow settings of these elements should be for lift merits of the selections could be deduced from rnaximiz~tion. Powover, an airfoil designed for visual inspection of the airfoil contours.
high lifting capability with no flap will not Third, the orr~ibsions in the experimental necessarily be exceptionally good when a flap data provided for families of existing NACA air- system is added. This suggests that multi-ele- foils have been known to the industry for years.
ment airfoil research might be directed toward In some cases, filling in the data gaps and ex- finding airfoil sections and flap configurations tending the ranges of parameters in directions that are best when the flaps are down.
whose utility could easl ly be perceived, would have provided section geometries wh.ch are Most of the multi-element airfoil develop- ments of the past have been addrsssed to the only now being explored (an instance is the landing configuration, where flap deflections general correspondence betweel; th9 charac- are larg6 and maximum lifts high. The most teristics of the NACA 6716 section, only re- cently tested.$ and thcse of the GA(W)-1 sec- troublesome flight configuration remaining is that for climb, in particular the engine-out tions). In one notable case, that of the NACA c l i n h of twin-engine airplanes. Feder~l Avia- 230XX airfoils, a family c' sections with ob-
tion Regulatincs acknowledge the importance viously superior hlgh lie characteristics sat
atound for years, figuratively screaming for of climb performance by prescribing mi:iimum values of climb grse;;ents or rates, but implicitly more inquiry into just why they were so good.
acknowledge that trouble ex ats by setting the To many people there were good and suffi- minimum values very low.2 Gzvslopment of air- cient reasons for tt:a lack of attention to the foil systems tailoisd for the c l i ~ : ~ ; ~ regimes have
data gaps - World War II, the postwar funding
received little attfmtion.
crunch, the advent 3f diverting work (super- sonic flight, missiles, space programs). During Directions for Airfoil Research those periods, understandably, relatively little With the advent of automatic computation, work was done by NASA; general aviation it became possible to conduct theoretical ex- manufacturers took occasion to point out the plorations of airfoil characteristics which pre- lack; the larger alrplane companies such as viously tiad been too burder~some to undertake.
Douglas ar,d Boeing urldertook 10 remedy the The cllrrsnt nnalytical programs for single- and situation for their own benefit in their own multi . ,- 3nt airfoil shaping are cn facilities, and very little appeared in the public I Y ,d seem useful to apply such pro- domain.
gram, , tne problem of developing airroil and It ts suggested that benefit to general avia- flap systems together rather than separately, tion would result from a co~tinuing, long-range with specific appl~cation to climb performance.
program cf subsonic aercidynamic research While the& programs have merit, the which would include: following should be pointed out: (1) increased financial support for First, far cruder analyses, applied sensibly, NASA aeronautics research, to have provided important indications of what the ei:snt that not only could should be done to moke given modifications in NASA's cwn in-house and ,:on- airfoil characlsristics.
tractual research be augmented, but also close and coctinual technical monitoring could be I Federal Av~at~on .Tegulat~ons. Part 23. Par 23 65 el seo maintained over the manner in ' Hlcks. Raymond M , et e l , An Assessment ol Alrlo~l which governmenr: funds in Des~gn by Numer~cal Opt~m~zat~on." NASA 'TM X-3092 July. I974 general use are spent for aero- ' Barger. Raymond L and Brooks. Cuyler W Jr "A Streamline Curvature Method for Des~gn ot Supercrttlcal and nautical research.
Subcrltlcal Alrfo~ls." NASA TN 0.7770 September. 1974 (2) continuous liaison with univer- ' Blngham. Gene J . 'Low-speed Aerodynan~c Charac- ter~rtlcs of NACA 6716 and NACA 4.416 Alrlo~ls w~th 35-percent sities and with general aviation Clicrd Slngle Slotted Flaps." NASA TM X.2623. May 1974 manufacturers, using circuit.
' McG'ree. Robert J . ard Beasley. W ~ ! i ~ a m D "Low-Speed riders i f necessary, to determine A-rodynam~c Characterlstlcs of a 17-Percent Thlck A~rfo~l Secl~on in what ways NASA or cther Des~gned lor General Av~al~on Appl~cnt~ons. NASA TN-07428.
December. 197 7 govorcment agencier can be responsive to their research with low weights and low-strength materials needs. Coverage should not be dictated the use of wire-braced, thin-membered limitedto those of the public who trusses: the bridge-type fuselags framework have government contracb. A and the biplane wing celluk, which was essen- mechanism t o ensure the tially a repetition of the fuselage truss, disposed responsivness of the govern- laterally and with its horizontal panels covered ment agencies should be by secondary structure, the ribs and fabric en- devised. velopes. Some all-wood airplanes, their sur- faces made of spruce plywood bonded with ca- (3) "gap-filling" experirnen~al work.
sein glues, appeared during the war and The everyday problems of the throughout the 1920's. but they did not account small or medium-sized airplane for a major market share. Wooden airliners company are not those of push- were killed abruptly following the Knute i n g o u t t h e f o r e f r o n t of Rockne crash; the Fokker transport in which he knowledge. but rather are tho..
was killed was wooden-winged, aod the crash of obtaining detailed information was felt possibly due to the deterioration of the on items basically already well wing structure.
within the state of present art- such items as airfoil charac- Subsequently, wood for airliners was, in effect, regulated out of use, and the develop teristics, aerodynamics of ment of light-metal technohgy was thereby fuselage irregularities, inter- forced. Though unbraced-wooden-winged ference drag, engine cooling airplanes were bui It (Lockheed Vega, Fairchild drag, propeller performance, ex- PT-19), the development of light--metaltech- crescence drag, etc.
nology probably was a major factor in promot- (4) continued publication of com- ing aerodynamic improvements starting with pendia of data, of a higli order of the unbraced (internally braced wing. Cne completerless, with periodic might almost say it forced the aerodynamic revisions and reissues.
refinement, since duplicating w m o n struc- (5) revival of the pre-1958 NACA in- tural configurations typically leads to some dex sjstem. The current STAR weight increase, which must be offset by drag indexes are comprehensive, but decrease if installedengine power is not to ri.-e.
need supplementing to i. , , The 1930's were a period, then, of refine- the visibility of important NASA ment in all-metal design, culminating in the work. The old NACA index for- great combat air fleets of World War li.
mat was excellent in :his ragard, Immediate postwar developments included and far more usable than the the introduction of "sandwich" materials (a STAR indexes.
double skin of very thir layers prevec:ed from Elements of this program exist; some have buckling due to in-plane compressive loads by existed for a long time. The intent of the above a lightweight core of wood or metal suggestions is to express general concurrence honeycomb). but the impact of thls technology with the decisions which have produced the on general aviation has not been felt until re- present NASA general aviation aerodynamics cently. The delay was du2 in part to the programs, while citing areas in which addl- difficulty of inspecting sandwich structure tional funding seems desirable.
bonding using nondestructive techniques. a difficulty not surmounted until a very few years Structures and Materials ago.
Structural development h a beer1 paced historically by materials availability. The best The war product~on programs enabled utilizable weightistrengtti ratios in the pre- scme general aviation manufacturers to World War I period were possessed by various develop their all-metal technology at public ex- wocds (the u s of weightistrength ratio is a vast pense. The result was that production of oversimplification, which is why the word wooden, fabric-covered. general aviation "utilizable" has been inserted). Wrought airplanes rapidly subsidea after the war until at aluminum alloys were ?ot available ic temper present only a few mlt- ~r types are bemg pro- states that allowed use in primary structure, duced.
though secondary structure could use ~ t , and Sheet-me a! !ecbr !ogy of World War II did during the war.
level still dc .ninates rhe civil a1:plane field.
The necessity for building stiff structures Early attemp's tr* us.? plastics technology for secondary structures resulted in saving neither the requirements for structural strength, effi- weight nor cost. More recently a second cycle ciency, and low maintenenace. Wood, of attempts to use plastics technology was however, continues to be an acceptable begun. One certificated civil airplane, the Win- material for the construction of small airplanes.
decker Eagle, uses plastics almost altogether Fabric is a sort of natural companion of wood for skin. but the extent of plastics use in its pri- for this applicat~on. so along with thd program mary structure i s apparently lower. Other of resumed development of wood construction manufacturers have acquired or are acquiring technology which is suggested here, might well the capability to work major structural compo- go one of fabric application development.
nents in plastics.
The bugbears of the past have been: (1) in- sidious. invisible deterioration of the mechani- Military structural research has concen- trated most recently on the development of cal properties of wood structures; (2) non- destructive inspection of woods; (3) rot and in- composite structure with mono-filament load- festation; (4) deterioration of fabrics with ex- bearing members. This development has not yet reached the civil field. posuie i t sur. (hence pigmented dopes replac- ing the clear dopes of the first two decades of Sail plane structure has resched a new aviation); (5) palatability to field creatures of plateau with the replacement of composite cordage used in stitching; (6) resistance to ac- wood-and-fabric constn!ction by conventional tion of aviation fuels and lubricants; and. (7) fiberglasslepoxy layups aith foam filling. This bonding materials and techciques.
enables glassy-smooth exterior skin-surfacs Recent years have seen the introduction of to be built fairly easily.
synthetic aircraft cloths and long-life dopes.
Perhaps the most active area of structures which it is hoped will give finished fabric r e s e a r c u t least th& most visible at the mo- airplane coverings lifetime durability. However.
ment-is the analytical. The fairly simple sheet- work toward improving the characteristics of metal structure of 'No, Id War II could be stress- aircraft covering using renewable resources analyzed using closed-form methods. Very may yet be in order. This same constraint thick-walled structures such as landing gear should be considered for application to forgings could not be well dealt with using such resexch in any of the other areas.
simple methods, however. The availability of digital computer time has resulted in an explo- Propulsion sion of finiteelement methods for the analysis Propeller airplanes represent an over- of thick-walled structures of complex shape.
whelming percentage of the general aviation fleet, so perhaps starting with the propeller it- At the time of the disappearance of the wooden airliner, the technology of wooden self is appropriate.
airplane construction was fairly advanced.
Someone has said that only a real genius Throughout the years between then and 1941.
could design a poor propeller. Operating at its wooden airplane development struggled along, design point a typical wooden fixed-pitch pro- and it is now the property of sport aviation and peller of World War I vil age would show effi- one commercial manufacturer. The state of the ciencies in excess of ; 3 percent, and modern technology is practically the same as at the end techn3logy metal propellers can exceed 90 per- of the last major wooden airplane production, cent. Thus, aerodynamic refinements for tke Pi-19, left it.
design-condition operation yielded relatively small gains, the largest being experienced It would appear that there is riow reason for when aluminum technology permitted develop- taking it up again. While the state of availability ment of metal blades in the late 1920's.
of the major civil aircraft structural materials of the preserlt day-aluminum, magnesium, and The only major avenue of improvement, titanium-is better than that of petroleum fuels. then, was in the ~ r e a of off-designperformance.
still the refinement of these materials to aircraft and this problem was addressed in the early standards is energy intensive. In this regard 192C's, with controllable-pltch and constant- wood is attractive-a renewable resource, po- engine-speed propellers finally achieving wide tentially available in adequate supply to suppol: yse by the mid 1930's. The propeller technology small airframe production, and with small of general aviation tnda) is largely the tech- energy requirements to prepare ~t for aircraft rlology of that era, with detail refinements.
use.
Pract~cal piston engine development was Larger airplanes will u~doubtedly continue along two lines-aircooled and liquid-cooled.
to be built of more exotic materials because of Llquid-cooled engines are no longer used ex- cept for the World War Il :eftovers. and are not detail refinements, such as the introduct~on of produced at all. Aircooled engines got a rather fuel injection and turbo supercharging, both strange start with the "rotary" engine. whose spinoffs from military aviation. Minor types =J crankshaft was rigidly fixed to the airframe, the freaks have appeared now and then. such as pistons. cylinders, crankcase. and propeller all the Gui berson diesel radial, the six-cylinder whirling around at prop speed, which was then Curtiss radial (single-row radials have odd (WorldWar I) rather low. The rotary died a well- numbers of cylinders, so the Curtiss engine deserved sudden death after the war, its place was in essence two three-cylinder radials with a taken by the aircooled radial.
common crankcase), and the Herrmann cam engine.
The present horizontally-opposed con- figuration found in most general aviation Propulsion research has produced many airplanes dates back to the late 1920's: it and exotic configurations during the last twenty tne prevalent "lightplane" highwing configura- years-lift fans, tilting rotors. tilt-props, tilt- tion started together at thht time. a i d the family prop-tilt wings, tilting ducted fans. and so on.
resemblance remains until now. Improvements The main thrust h s been toward development since the 1920's have been in materials and of VTOL types other thar: the helicopter. With a NOW-
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single military exception, these devices have large, is a far less noisy device at the distances not been undertaken by any firm for production, at which it is typically encountered than is a although the present state ot documentation power lawnmover, a motorcycle or a "perfor- seems fairly good. Much of the information has mance" car. Experience has shown, however, been condensed into a reference work by Dr. that the airpicine's high visibility makes it Barnes W. McCormick of Pennsylvania State vulnerable, and that noise levels at major air-
University. ' Dr. McCormick has broadened the
ports generate an awareness of aircraft noise scope of his work to include powered boundary that "wipes off" on all airplanes. Also, an ob- layer control. essentially a part of STOL tech- jectionable noise need not be "loud." or have nology which also has found, to date, only mili- any specific frequency content, to generate tary applications.
complaints. There is experience to indicate that many complaints about "noise" are generated Piston engine development has simply in- simply by newness and unusualness. It all corporated old military engine technology into amounts to the fact that silencing airplanes is a civil engines, with one notable exception: response to a political fact of life, however ar- Teledyne Continental has produced an engine tificially generated, which did not exist as such with an altered internal power train and fairly years ago, but which we now ignore at our peril.
sophisticated dynamic damping devices.
Small piston engines are muffled, but not Dowty-Rotol has displayed a controllable- as effectively as automobile engines. There are pitch piston enginelshrouded propeller com- two probable reasons: (1) avery significant pro- bination in mockup form.
portion of the noise of an aircraft power plant is Turbine engine development in small sizes propeller noise--perhaps as much as 40 to 60 has utilized essentially military-funded tech- percent. The propeller noise therefore masks nology for civil engines of fairly conventional the exhaust noise at high prop speeds; and (2) form. Short-life turbine engines, based on weight is always critical, and the tendency is droneengine technology, have been proposed therefore to minimize the weight. as a percen- at various times as lift engiries (axis vertical) for tage of the total, of items that do not contribute STOL or VSTOL airplanes, but none has been to safety of flight or to sales potential.
adopted for production. Turbine engine tech- Propdler noise is predominantly due to air nology is very expensive to acquire, hence the compressibility effects at the blade tips. To get lack of civil funding for advanced research.
rid of the noise, then, demands that either the No engine produced to date for aviation, propeller be slowed to a tip speed where these excepr the diesel, has outshone the conven- effects will disappear (usually below Ms0.6) or tional gasoline piston engine from the stand- that blade profiles be reshaped. The "high- point of fuel economy. The shaft-gas-turbine speed supercritical" airfoils proposed by Dr.
enginc is lighter and its overhaul times typically Richard T. Whitcomb are designed for the longer; through intensive development its fuel specific purpose of delaying the onset of com- consumpt~cn has been hammered down to
pressibi lily effects by approximately .05 - 0.10
about the leve! of the wartime piston engine.
Mach. Along with this benefit go increases in Nevertheless, with little development since the loadings at which it is acceptable to drive 1945 except what the civil engine manufac- the blades, from a power-required standpoint .
turers could afford, the fuel consumption of the gasoline piston engine is now, after thirty years. Low tip speeds dictate increases in pro- about as far superior to that of the turbine as it peller "solidity" (number and width of blades) was when gas turbine development started, on to realize acceptable thrust power levels. Since a percentage basis.
thrust not only varies almost directly with solidity, but also with the square of propeller As long as flight speeds are below about speed, ground and low-speed engine cooling 325 knots, the propeller engine is superior to becomes a problem with slow turning pro- the only other two types in use. the turbofan and pellers, as was again demonstrated with the the turbojet. This superiority exists because of "spook" airplanes used in Vietnam.
propeller, rather than engine, characteristics.
The implication of this and the superior fuel Some persons have proposed L;se of economy of the basic piston engine is clear.
shrouded propellers to diminish noise output.
There is no present evidence to indicate that Noise the complicated tradeoffs involved in shrouded The general aviation airplane, taken by and propeller design will favor low-noise configura- - - -- tions of acceptable weight and efficiency. In- ' McCorm~ck. Barnes W Aerodyn~mrcsof V/STOL Flrght (New vork Academ~c Press. 1967) deed, the basic configuration generates noise machines in the air. This characteristic is the problems all its own at the low-loading end of the range of applicability. At the high end, the difficulty of "cleaning it up" after a single shrouded propeller becomes the secondary engine failure. The pilot must sort out which engine failed, shut it down, at the same time stage of the ducted fan engine. Here the trade- offs are considered vis-a-vis the turbojet conteracting the roll and yaw occasioned by engine, and are favorable to the fan because of the shutdown, then rapidly retract the gear and raise the flaps if they are extended. The its long shroud (not feasible at low loadings), difficulty of doing this is emphasized by the fact which can be acoustically treated.
that a large propocion of fatal accidents to It is surprisingly little understood that smsll twin-engined airplanes in which engine stop- propeller airplanes can now be silenced almost page played a part is sustained in training for to the lwel of the automobile at high speed engine failure emergencies.
cruise. Detail changes of configuration which must be made to do so include: (1) more effec- Attempts have been made to circumvent tive exhaust muffling; (2) overwing routing of the trouble by designing airplanes with "cen- exhaust stacks: (3) slow turning, wind bladed terline thrust," e.g., the "push-pull" Cessna propellers; and. (4) improvements in grol~nd 337. Such airplanes have their own problems, and low-speed cooling, perhaps with auxiliary notably those of detecting when an aft engine blowers or a reversion to liquid cooling. But the failure has occurred, and of providing adequate job can be done with111 the limits of present ground cooling for the aft engine. The cancept technology. An inspectionof the circumstances remains attractive, however, as a remedy for the surrounding the addition of noise certification basic problem, and if the conventional win requirements to the Federal Aviation Regula- cannot be rendered more tractable by the ep- tions would seem to be in order, to determine plication of advanced technology, the cen- whether. for any small airplane other than the terline thrust twin should be taken in hand and business jets, 2 real need exists for the regula- developed to the extent that it possesses less tions.
serious problems of its own than are possessed The changes listed above do not come by the conventional type.
. .
free. Each hasits cost in weight or efficiency, The Advanced Technology LigM Twin small though it may be. Whether this cost wi!!
(ATLIT). For several years a group under Dr.
be tolerable as fuel supplies grow scarcer can- David Kohlman and Dr. Jan Roskam has been not be predicted, but it is worth considering working at the University of Kansas in the area whether significant amounts of funds should be of the improvement of cruise and low speed spent on developing improvements which may performance of ?mall airplanes. The general in a very few years have to be discarded as the approach is to adopt high-lift airfoil technology last few percentage points of efficiency are to maintain low stalling speeds while improving sought.
cruise performance (range) and gust response by reducing wing area about 30 percent to cut Basic Configuration skin-friction-type parasite drag. Spoiler As pointed out previously, no definitive ailerons are adopted to maintain good roll per- changes in airplane configuration have taken formance at low speed.
place since aboct World War I. That war also generated the basic conventional twin, with At present this NASA-contracted program wing-mounted tractor-type powerplants, a type has modified a Piper airplane, an "ATLIT," for which survives and is popular today.
further experimental work. Their first airplane was a single-engined Cessna.
The conventional light twin represents the first step up in performance from the heavy Robertson Aircraft. While the aerodynamic single, largely due to the fact that there are no gains sought by the ATLlT project are worth engines on the market today in the 600 horse- achieving, quite a bit can be done toward im- power class except the Pratt and Whitney PT-6 provement of low-speed performance alone by turbine and the R-1340. Neither of these adopting less drastic measures. For many years engines is suitable for other than specialized the Robertson Aircraft Company has single-engine applications, the turbine specialized in modifying conventional produc- because of its cost, the R-1340 because of its tion airplanes for this purpose. The modifica- limited availabiiity. The twins, with their modern tions consist of sophisticated flap systems, opposed engines, fill the gap.
drooped-wing leading edges, vortex genera- The conventional twin as a type, unfor- tors, and lately full-span flaps and spoilers.
tunately. has one bad characteristic, which ren- Robertson's emphasis has been on keeping ders i t among the most potentially dangerous modification costs low and doing as little as possible that will affect the structural integrity down of the various field length performilnce of the basic airplane. targets advocated throughout the years, with a little information on each: Short Field Aircraft 1952: 500 feet; this was the point of (1) "Short-field Aircraft" is a catchall term departure for many discussions under which can be lumped all aircraft which among commercial manufacturers, use advanced technology to achieve shorter the Army, and the Office of Naval than ordinary takeoff and landing distances.
Research. In 1953, the Cessrla The term embraces short takeoff (STOL), Aircraft Company actually pro- reduced takeoff (RTOL). and vertical-or-short duced an airplane capable of tak- takeoff (V/STOL) types of machines.
ing off and landing over a 50-foot obstacle in 450 feet. The airplane RTOL and STOL was a heavily-modified L-19A. The There have been two definitions associ- "improvement" over CTOL was ap- ated with each of the names Reduced Takeoff proximately 25 percent.
and Landing (RTOL) and Short Takeoff and Landing (STOL), and much confusion has ex- 1959: 1,200-2,000 feet, developed in (2) isted because this fact was not appreciated.
part by technical studies growing The confusion existed because, while Conven- f r o m O N R t A r m y - s p o n s o r e d tional Takeoff and Landing (CTOL) airplane research performed at the Univer- technology and its associated performance sity of Wichita. The aircraft associ- were representedby existing types of airplanes, ated with these field lengths were as was VerticalIShort Takeoff and Landing
transports in the 30,000 - 60.000
(V/STOL) by the performance of the helicopter, pound class At this same time, no hardware and no steady performance Lockheed Aircraft started develop- targets existed for STOL. During the early years ment of a "BLC-130" with com- in the development of STOL technology, the parable performance.
typical argument was over what single fixed 1968: 1.000 feet. The FAA marked (3) takeoff and landing distances should be striven off 1,000-foot sections of runway at for through the application of the technology.
Washington National, Friendship, One of the early "definitions" of STOL was and LaGuardia airports and desig- "500 feet over a 50 foot obstacle." It was nated these as "STOL" strips. An surprisingly long in coming out that there were airline using Dornier "Sky Servant" actually two entities to define separately.
heavy twins (7,700 pounds) used The first was STOL technology, the ag- these strips. Though this airline gregation of technical developments that would operated only for a while, it pro- enable the design of an airplane with field vided information on tbe feasibility length requirements substantially less than of introducing STOL airplanes into those of a CTOL airplane, of the same payload, the mix of traffic at a heavily-used range, and speed.
airport.
The second was STOL airplane, and to its 1970: 2,000 feet. This was a relaxa- (4) definition no fixed field performance require- tion of the 1,000-foot "requirement" ment could be attached except arbitrarily. 5 ne above. Surveys of the larger com- field performance of successful airplanes muter operators at that time indi- designed to a given state of the art is size de- cated that they would have been pendent as shown in Figure 1-3. A STOL content with about 3,500-foot field airplane, then, is an airplane which utilized performance.
STOL technology effectively to produce some percentage improvement in performance, no 1975: 3,000-4,000 feet. This length (5) matter how short or long its field requirement is.
is associated with medium weight transport category airplanes Potential users, however, insist on thinking (146.000-206.000 pounds) in a in dimensional terms so here is a sample run- NASA-funded set of short-haul systems studies by Douglas, * Stalter. J L . and Wanson. Robert K . Jr . "Experimental In- vestlgatlon of a Means of Obtaln~ng Independent Control of Lift and Lockheed, Boeing, and others. Ad- Drag In Land~ng Approach." Unlverslty of Wlchlta Englneerlng Re- vanced ni-lift technology and port UWER-3155. Contract DA 44-177-TC-356. U.S Army Transpor- tatlon Research Command. April. 1959 materials were necessary at these