Initial report on operational experiences of general aviation aircraft

d By Joseph W. Jewel, Jr.

NASA-Langley Research Center Langley Station, Hampton, Va.

Presented at the SAE National Business Aircraft Meeting GPO PRICE $ Wichita, Kansas April 3-5, 1968 CFSTI PRICE(S) $ Hard copy (HC)-

Microfiche (M F) -

ff 653 July 65 INITIAL REPORT ON OPERATIONAL EXPERIENCES O F GENERAL AVIATION AIRCRAFT

BY

Joseph W. Jewel, Jr.

ABSTFACT A n analysis has been made of 27,000 hours of VG and VGH data obtained from 62 general aviation a i r c r a f t based throughout the United States.

Comparisons are made between the actual f l i g h t loads experienced by a i r c r a f t engaged i n f i v e types of operations and the design f l i g h t envelopes fo& these a i r c r a f t . Gust and maneuver acceleration fractions, r e l a t i n g actual load factors t o design load factors, are indicated. Airspeed and a l t i t u d e are shown f o r the various a i r c r a f t . Landing impact operating practices a limited sample of accelerations measured acceleration distributions and during individual, practice, and competitive aerobatics a r e presented.

INITIAL REPORT ON OPERATIONAL EXPERIENCES OF G E N E R A L AVIATION AIRCRAFT .By Joseph W. Jewel, Jr.

INTRODUCTIOD About s i x years ago the National Aeronautics and Space Administration, at the request of the Federal Aviation Administration and upon recommendation of the N A S A Committee on Aircraft Operating Problems, commenced a data collection program on a i r c r a f t i n the g e n e r d aviation category.

The purpose of the program w a s t o update and reassess data on t h e f l i g h t loads and operating practices of l i g h t a i r c r a f t during t h e i r nomal usage, since l i t t l e or no data of t h i s type have been obtained over the past t h i r t y years.

The program has now progressed t o the point where preliminary r e s u l t s are available. I n t h i s paper, the scope of the program w i l l be indicated; and the r e s u l t s obtained t o date w i l l be discussed.

INSTRmmTION The data presented were obtained by NASA VG and VGH recorders which are described i n d e t a i l i n references ( 1 ) " and ( 2 ) , respectively.

A brief description of the recorders and the ty-pes of record obtained is given i n the following paragraphs.

VGH R E C O R D E R - A photograph of the VGH recorder i s

shown i n figure 1.

The recorder has three major components: the recorder base, an attached %umbers i n parentheses designate References at end of paper.

film recording d m , and the acceleration transmitter. m e transmitter is installed near the center of gravity of the airplane (usually within 2 feet), whereas the recorder base m y be mounted at any convenient location within the airplane. The installed weight of the recorder, drum, and acceleration transmitter is 20 to 23 pounds.

A n illustrative VGH record is shown in figure 2 . The record gives a time-history trace of the aircraft's indicated airspeed, pressure altitude,w+ , and normal acceleration. From the record, detailed counts may be made of the gust, maneuver, and landing impact accelerations and their associated airspeeds and altitudes.

VG RECORDER - A photograph of the VG recorder is shown in figure 3 .

This recorder weighs less than 5 pounds installed and is usually mounted

within 2 feet of the aircraft's center of gravity.

An illustrative VG record is shown in figure 4 . This record gives

an envelope of the maximum positive and negative accelerations experienced throughout the airspeed range during the period covered by the record.

The records were usually removed monthly and each represented from 10 to 60 hours of flight time.

SYMBOLS an incremental normal acceleration, g units incremental normal acceleration corresponding to the gust or

an^^^

maneuver limit load factor, g units f frequency of occurrence FM nautical flight miles 0 . 8 8 ~ ~

gust factor, 5.3 + pg

*Based on standard sea level pressure of 29.92 inches Hg.

m slope of l i f t curve per radian air density at sea level, slugs/cu f t Po S wing area, sq f t derived gust velocity, ft/sec,

K g Po ve m s

airplane mass r a t i o

%

design cruise speed, knots vC design dive speed, knots vD f p s equivalent airspeed, ' e m a x i m indicated airspeed, knots

vm

w airplane weight, lbs

PROGRAM DESCRIPTIOPJ In order t h a t a representative sample of general aviation operations could be obtained, f i v e types of operations were selected t o be covered i n the data collection program. These f i v e operations are: twin-engine executive, single-engine executive, personal, instructional, and commercial survey. Typical missions flown i n each of the operations are as follows: '?&in-engine executive:

Charter f l i g h t - cargo and personnel

Business flight - company and individual

Instrument check f l i g h t - training f o r instrument card

Instructional - check-out f o r multiengine

Single-engine executive:

Charter f l i g h t - cargo and personnel

Business f l i g h t - company and individual

Instrument check flight - training f o r instrument card

Instructional - check-out f o r heavier airplane

Personal :

Flying club - airplane flown by from 3 to 21 members. Used

f o r pleasure flying, instruction, or business

Individual - used f o r pleasure and business

Company awned - airplane rented t o individual f o r business

or pleasure flying, also a i r c r a f t used as check-out f o r heavier airplane Instructional : Training - a l l instrumented airplanes owned by flying schools.

Used as basic t r a i n e r s for private license. Also used by student a f t e r solo f o r cross country Commercial survey:

Pipeline p a t r o l - patrols flown from 250 t o 300 f e e t above

-ground-to check f o r leaks or breaks i n the pipeline

Forest p a t r o l - patrols flown 1500 feet above t e r r a i n f o r

f i r e spotting. When f i r e i s spotted, descents are made t o 200 t o 300 feet t o check condition of t e r r a i n around f i r e Fish spotting - patrols flown 1500 t o 2000 f e e t above water.

Occasional descents are made t o 300 t o 300 feet Generally, three VGH recorders and nine VG recorders a r e assigned t o a i r c r a f t i n each operation. The location of the instrumented a i r c r a f t i n i s shown on figure 5 . Aircraft selected for the program were the program based throughout the continentia1 United States t o avoid biasing the data as coming from any one geographical area.

The basic characteristics of the instrumented a i r c r a f t a r e l i s t e d on table I. Aircraft chosen f o r the program range i n s i z e from small, l i g h t training planes weighing l e s s than 1600 pounds t o twin-engine, jet-powered executive transports weighing 12,500 pounds. Owners of the a i r c r a f t were personally contacted, briefed on the purpose and aims of the program, and asked t o participate i n the program u n t i l 1000 or more hours of f l i g h t data were obtained over a period covering at least the four seasons.

Figure 6 shows the s t a t u s of the general aviation program i n terms of the number of a i r c r a f t instrumented, the hours recorded, and the average number of hours recorded per a i r c r a f t per year f o r each year the program has been i n existence. Data obtained i n 1967 are presented as half bars, since these data a r e f o r a 7-, rather than a 12-, month period. The progressive growth of the program i s readily apparent from the figure.

SCOPE O F DATA The data analyzed and discussed i n the following sections represent about 0.05 percent of all the general aviation flying t h a t was done i n the period during which t h e data sample w a s taken and about 60 percent of the

The largest sample - about 24,000 hours -

t o t a l data collected t o date.

w a s obtained from VG recorders. Data from VGH recorders were about one-sixth t h i s size, t o t a l i n g s l i g h t l y more than 4000 hours. Sixty-two a i r c r a f t , representing 15 different types of airplanes, were involved i n the data sample presented.

RESULTS AND DISCUSSION

G E N E R A L - The operating characteristics of the instrumented airplanes

a r e indicated on figure 7. This figure shows t h e average pressure altitudes, indicated airspeeds, and f l i g h t lengths recorded by a i r c r a f t i n the f i v e different operations. Turbine-powered a i r c r a f t , types 1 and 2, i n the twin- engine executive operations, were, as would be expected, flown at the highest average operating a l t i t u d e s and airspeeds. The lowest average operating a l t i t u d e s and airspeeds were recorded by a i r c r a f t used f o r instructional operations. The r e l a t i v e l y high average operating a l t i t u d e s exhibited by a i r c r a f t type 13 i n instructional operations and type 8 i n t h e single- engine executive and survey operations occurred because the a i r c r a f t were based a t f i e l d s having elevations of from four t o f i v e thousand f e e t .

The average f l i g h t lengths of a i r c r a f t i n all operations, with the exception of survey, were about one hour or l e s s . Average f l i g h t lengths i n survey operations ranged from s l i g h t l y more than two hours f o r f o r e s t p a t r o l work t o about four and a half hours f o r commercial f i s h spotting.

O m L L INFLIGHT LOADS - Composite VG records - t h a t is, a series of

h.

VG records from one type of a i r c r a f t t h a t have been superimposed, one on the other, so t h a t the 1.Og l e v e l f l i g h t l i n e s and zero airspeed positions

coincide - and design f l i g h t envelopes f o r a i r c r a f t i n the f i v e types of

are shown on figure 8. The solid and dashed outlines about the operations VG signatures represent the design f l i g h t envelopes based on the a i r c r a f t ' s maximum gross weight and minimum design weight, respectively.

The portions of the VG signatures t h a t exceed the design f l i g h t envelope i n the low-speed regime of the record are not considered significant since the exceedances were most probably caused by landing shocks. In general, the m a x i m u m load factors were about +3.O and -1.0 and were contained within the design f l i g h t envelopes. However, there are two notable exceptions.

The first, and probably most noticeable, w a s recorded by airplane type 1 4 i n instructional operations. In addition t o exceeding the design dive speed, t h i s particular a i r c r a f t also exceeded the positive and negative l i m i t load factors at the design dive speed. Inspection of the a i r c r a f t f a i l e d t o reveal any structural damage. It appears, then, t h a t although the design l i m i t loads were exceeded, the factor of safety used i n the design of the a i r c r a f t prevented a structural failure.

The second notable exceedance of the design f l i g h t envelope w a s recorded by airplane type 3 flown i n twin-engine executive operations. A n inspection of the a i r c r a f t by the owner a f t e r being notified of the exceedance indicated t h a t no structural damage had occurred. Discussions with the operator revealed t h a t the exceedance was gust induced when the a i r c r a f t w a s flown over t h e l e e side of a mountain range.

From the foregoing discussion, it i s evident t h a t atmospheric-induced, as w e l l as pilot-induced, loads i n excess of the design f l i g h t envelope may be encountered during normal operations of the general aviation fleet. It i s a l s o apparent from the data t h a t a l l a i r c r a f t types i n t h e f i v e operations were flm above the design cruising speed.

DESIGN SPEED EXCEEDARCES - Figure 9 indicates the percent time specific

a i r c r a f t types i n a given operation were flown above the design cruising speed. These data were taken from VGH records and were obtained by ratioing t h e time flown above the design cruise speed t o the t o t a l time of the data sample.

The r e s u l t s show t h a t the percent time flown above ranged from Vc 1 t o 21 percent of the f l i g h t time. Airplane type 1 4 i n instructional operations w a s flown above the design cruise speed 21 percent of the time; airplane type 8 i n single-engine executive operations, 16 percent of the time; and airplane type 4 i n twin-engine executive operations, 9 percent of the time. An examination of the VGH records indicated that Vc exceedances were most prevalent i n the following regimes of f l i g h t : m e 14 - Beginning of cruise. In l e v e l flight a f t e r descent.

In downwind position of t r a f f i c pattern during touch and go landing.

8 - During descent shortly after pushover.

m e

4 - During cruise and a l s o i n descent. m e airplane

Type apparently had sufficient power and w a s clean enough t o exceed VC during cruise. Most Vc exceedances w a s steepened.

i n descent occurred when descent While VGH data from a i r c r a f t types 10 and 1 1 i n personal operations have not been evaluated, a visual check of VGH records from these a i r c r a f t indicate that type 1 1 probably has a higher percentage of time flown above Vc than e i t h e r of the other two a i r c r a f t i n t h i s operation. Many excursions above VGH records from t h i s airplane during cruise and descent.

were noted on Vc It appears t h a t the a b i l i t y of the a i r c r a f t t o cruise a t or above Vc i n w a s a contributing factor.

l e v e l f l i g h t Aircraft i n commercial survey operations showed the lowest percent of time flown above Vc of the f i v e operations considered.

The data on figure 10 a l s o r e l a t e t o design cruise speed exceedances.

'kese data were obtained from VG recorders and represent a much larger data sample than t h a t from t h e VGH recorders. Because the design cruise and design dive speeds d i f f e r between a i r c r a f t i n a given operation, it w a s necessary t o nondimensionalize the airspeed data i n order t o compare the speed practices of the various a i r c r a f t . This w a s done by ratioing the difference between the maximum recorded airspeed and the design cruise speed t o the difference between the design dive speed and the design cruise speed.

The r a t i o , hereafter referred t o as the speed r a t i o , therefore, indicates the extent t h a t the speed regime between V c and VD w a s penetrated by the instrumented airplane. For example, a speed r a t i o of 1.0 indicates equaled VD. The speed r a t i o i s shown along the abscissa of the vNAx figures, and the probability per f l i g h t hour of the a i r c r a f t type reaching a given r a t i o i s indicated along the ordinate.

The results i n figure 10 show t h a t a l l the a i r c r a f t were flown i n the Vc and VD and t h a t the probability of exceeding speed regime between given values of the speed r a t i o varies significantly between different a i r c r a f t within a given operation. Aircraft i n instructional and personal operations appear t o be flown above more frequently than a i r c r a f t i n Vc This i s not unexpected since p i l o t s i n these two the other operations.

operations probably have the l e a s t f l i g h t experience of all the operations sampled.

The overspeed results based on the large samples of VG data shown i n figure 10 are, i n general, consistent with the results obtained from the

smaller sample of VGH data shown i n figure 9. For example, the a i r c r a f t

types showing the highest rate of exceedance are also t h e sane types

V c

the VGH records showed as flying t h e l a r g e s t percent of time above the design cruise speed.

ROUGH A I R - In order t o compare the r e l a t i v e turbulence environment

of a i r c r a f t i n different operations, the percent time a i r c r a f t i n the f i v e operations were flown i n rough air i s shown i n figure 11. The data were obtained from VGH records and rough a i r i s defined as turbulence containing derived gust velocities larger than 2 fps.

The results show t h a t the percent time spent i n rough air varied from 21 percent f o r a jet-powered twin-engine executive airplane t o 97 percent f o r an a i r c r a f t flown on pipeline p a t r o l i n commercial survey operations.

Single-engine executive, personal, and instructional a i r c r a f t operations experienced rough air from about 50 t o 80 percent of the f l i g h t time.

A s a general coqarison, commercial turbojet-powered transports experience rough air from about 3 t o 12 percent of t h e i r f l i g h t time.

G U S T ACCELERATION FRACTION - Figure 12 presents gust acceleration

fraction data f o r representative data samples from a i r c r a f t flown i n the

five types of operations. The gust acceleration fractions - obtained by

dividing the incremental (from 1. Og) gust accelerations by t h e incremental 1.0) gust limit load factor at Vc - are indicated along the abscissa.

(from The cumulative frequency per mile of the gust acceleration fractions are shown along the ordinate of the figure. Bands, indicated i n the figures by hatched areas, defining boundaries of gust acceleration fractions experienced by three types of short-to-medium haul jet transports are a l s o included i n the figures f o r comparative purposes.

Inspection of t h e data shaw, with the exception of airplane type 1, i n twin-engine executive operations and airplane type 15, a a twin j e t l i g h t single-engine piston a i r c r a f t used f o r f i s h spotting i n commercial survey operations, t h a t the general aviation a i r c r a f t experienced gust accelerations t h a t were closer t o the design gust load factor than did the a i r c r a f t i n commercial transport operations. The most severe gust acceleration w a s recorded by a i r c r a f t type 13 i n instructional operations.

This gust acceleration exceeded the design gust envelope by 34 percent.

It i s inferred from t h e data t h a t although the design gust load factors f o r general aviation a i r c r a f t are higher than those of transport a i r c r a f t , the margin between t h e gust load experience and t h e design gust load factor i s less than t h a t f o r the transport a i r c r a f t . It i s suspected t h a t the more severe gust acceleration experience of t h e general aviation a i r c r a f t may be due to: operations i n the lower atmosphere where more turbulence is present; operations of t h e general aviation a i r c r a f t at higher speeds r e l a t i v e t o the design cruising speed; and t o a s l i g h t l y lower design gust velocity f o r t h e general aviation a i r c r a f t .

GUST VELOCITIES - The derived gust velocity experience per f l i g h t

mile of a i r c r a f t i n t h e f i v e types of operations i s shown on figure 13.

The hatched bands i n t h e figures represent the derived gust velocity experience for three types of short-haul j e t transports and for four types of long-haul piston transports. Two of the general aviation operations, instructional and commercial survey, had a i r c r a f t t h a t encountered gust velocities of a given magnitude more frequently than the piston transports; commercial survey operations more frequently for gust velocities below 24 f p s and instructional operations more frequently f o r gust Velocities 24 fps. Both of these operations had one a i r c r a f t type t h a t l a r g e r than experienced gust velocities of a given value a t a significantly lower frequency than the other two a i r c r a f t types i n the operation. Aircraft i n twin-engine executive, single-engine executive, and personal operations experienced gust velocities t h a t were generally within or above the gust velocity experience of the short-haul j e t transport a i r c r a f t .

MANEUVER ACCELERATION FRACTION - The maneuver acceleration fraction

data from a i r c r a f t i n the f i v e types of general aviation operations and for short-haul j e t transport operations a r e shown i n figure 14.

Each figure indicates the emulative frequency per f l i g h t m i l e along the ordinate and the maneuver acceleration fraction along the abscissa. For these data the maneuver acceleration fractions were obtained by dividing the incremental maneuver accelerations by the incremental maneuver l i m i t load factor at Vc.

With t h e exceptions of a i r c r a f t i n twin-engine executive operations, a i r c r a f t type 7 i n single-engine executive operations and airplane type 15 i n commercial survey operations, the general aviation a i r c r a f t experienced maneuver loads t h a t for a given frequency of occurrence were closer t o the design maneuver l i m i t load factor than the maneuver load experience for short-haul j e t transport a i r c r a f t . Airplane type 13 used for pipeline p a t r o l i n commercial survey operations i l l u s t r a t e s the high rate of maneuvers required f o r t h i s type of flying. While the maximum maneuver acceleration fraction w a s only about .6, the frequency with which the lower maneuver acceleration fractions were experienced w a s from 10 t o 100 times t h a t f o r a i r c r a f t i n other types of operations. It therefore appears t h a t from a fatigue standpoint, a i r c r a f t engaged i n pipeline p a t r o l operations a r e subjected t o a more severe maneuver loading than any of t h e general aviation a i r c r a f t evaluated.

The probability of equaling o r exceeding

LANDING IMPACT ACCEI;ERCITIONS -

an i n i t i a l positive incremental acceleration during landing touchdown i s shown on figure 15. All of the landing accelerations from the three types of propeller-driven a i r c r a f t i n each operation were combined i n t h e figure t o show the r e l a t i v e relationships of the landing accelerations f o r the f i v e operations. The probability of three types of short-haul j e t transports equaling or exceeding a given landing acceleration i s a l s o given f o r comparison.

All general aviation a i r c r a f t , f o r a given probability, recorded larger landing impact accelerations than the commercial transport a i r c r a f t . The most severe landing accelerations, f o r a given probability of occurrence, were recorded by a i r c r a f t i n instructional operations, and the l e a s t severe by a i r c r a f t i n twin-engine executive and commercial survey operations. The highest landing acceleration, l . 5 g incremental, w a s recorded by an a i r c r a f t i n personal operations. The difference between the landing accelerations f o r short-haul comercial j e t transport and general aviation a i r c r a f t a r e

believed t o r e s u l t from two primary factors - the more sophisticated landing

gear systems used on t h e transport airplanes, and b e t t e r prepared surfaces the transport a i b l a n e s land on.

SAMPLE SIZE - Figure 16 indicates the e f f e c t of sample s i z e on maneuver

and gust acceleration distributions per f l i g h t mile f o r one airplane type.

For brevity, only the one data sample - obtained from airplane type 3 used

i n twin-engine executive operations - w i l l be discussed.

B The VGH records comprising the data sample were separated into two groups, one group containing roughly half the f l i g h t hours of the other group. In addition, e f f o r t s were a l s o made t o select f o r each group records t h a t were taken i n the four seasons. The cumulative frequency per f l i g h t m i l e the gust or maneuver accelerations were experienced f o r each of the sample groups, and f o r the t o t a l sample, were then determined and plotted on the figures f o r comparison.

Examining first the maneuver acceleration distribution, it appears t h a t the 291-hour sample provides basically the same distribution as the 447-hour sample. There is, i n f a c t , l i t t l e difference between the 447- hour sample and the 156-hour sample.

For the gust acceleration distributions, however, neither the 291- or the 156-hour sample i s close enough t o the 447-hour sample t o be considered representative, which indicates t h a t the data sample has not stabilized and more data should be acquired.

The significance inferred from these comparisons of sample sizes i s t h a t the data presented a r e as yet limited, are subject t o possible changes as more data are acquired, and should f o r the present be regarded as preliminary information.

AEROi3ATICS - Figure 17 presents VG and VGH data on a i r c r a f t involved i n

aerobatic operations. Since t h i s operation has only recently been included

i n the general aviation program, the data presented a r e limited - the VG

data represent four hours f l i g h t time and t h e VGH data represent eleven hours It was f e l t , however, t h a t because of the current i n t e r e s t i n f l i g h t time.

aerobatic f l i g h t and the significant r e s u l t s obtained from the VGH data, t h i s information should be presented.

J Figure l7(a) and l 7 ( b ) give VG signatures of 26 individual aerobatics The ordinate i s load factor, and t h e abscissa performed during the tests.

i s indicated airspeed. The various maneuvers have been grouped into f i v e at the top of the group as rolls, loops, reversements, basic types, identified

s t a l l s , and skids and s l i p s . All of the maneuvers were "positive" aerobatics -

no inverted aerobatics were performed. Negative load f a c t o r s were experienced primarily during rolls and one type of reversement, a s p l i t S, and generally d i d not exceed -1.Og. The highest positive load factors, less than 4.0g, were recorded i n a reversement ( s p l i t S) and a loop (square loop). These maximums were less than the c6.0g or -3.Og required f o r c e r t i f i c a t i o n i n the aerobatic category.

I n figure l 7 ( c ) peak acceleration data a r e shown f o r three types of The data indicated by the c i r c u l a r symbols are the peak aerobatic flying.

positive and negative accelerations recorded when one specific maneuver was performed. The data indicated by the square symbols are the peak positive and negative accelerations recorded during a complete f l i g h t i n which a

continuous s e r i e s of aerobatics - called an obligatory group - were

practiced. The diamond symbols indicate the peak positive and negative accelerations measured during a complete f l i g h t i n which obligatory groups of aerobatics were performed during aerobatic competition at a national air show. Airspeeds associated with the accelerations a r e shown along the bottom of t h e figure, and the design f l i g h t envelope f o r the a i r c r a f t performing the aerobatics is denoted by the s o l i d outline i n the center All p i l o t s involved i n the tests were experienced aerobatic of the figure.

p i l o t s .

Except f o r a few isolated points, the data a r e contained within the The load factor f o r the individual aerobatics design f l i g h t envelope.

varied, of course, w i t h the ty-pe maneuver performed; the square loop imposed

5.1, and the outside loop the highest

the highest positive load factor, negative load factor, 3.0.

It was thought that the maximum loads eqerienced during practice obligatory groups would be l e s s than those experienced during the heat of competition; however, the data did not indicate t h i s t o be true. The maneuvers causing the peak accelerations i n the practice and competition aerobatic f l i g h t s a r e not identifiable. However, it i s suspected t h a t the high accelerations occur when stall maneuvers, such as hammerheads

or t a i l slides, are followed by v e r t i c a l half rolls - which allow the

airspeed t o build up - and then by negative tuck unders t o outside loops

or snap rolls.

While individual aerobatics produced accelerations t h a t were within limits f o r aerobatic certification, the obligatory group the required aerobatics exceeded the negative l i m i t of t h i s requirement. Nineteen of the 28 practice and competition f l i g h t s contained negative accelerations i n excess of -3.Og. Three of the f l i g h t s registered negative accelerations larger than -4. Og.

Although the aerobatic data presented a r e limited, it does show rather severe exceedances of the minimum required negative maneuver l i m i t load factor and therefore suggests t h a t consideration should be given t o extending the minimum required negative load factor.

CONCLUDING FEMARKS Even though the r e s u l t s which have been obtained are i n some respects preliminary, they do provide an insight i n t o the operational experiences of r, general aviation a i r c r a f t and an i n i t i a l b a s i s f o r assessing some of the airworthiness requirements.

In general, t h e overall i n f l i g h t acceleration data from a i r c r a f t i n f i v e of the general aviation operations were contained within the design f l i g h t envelope. However, exceedances of the design f l i g h t envelope from gust and maneuver inputs were recorded by a i r c r a f t i n twin-engine executive and instructional operations.

A limited sample of data from aerobatic operations show significant exceedances of the minimum negative l i m i t load factor required by FAR-23 f o r c e r t i f i c a t i o n i n the aerobatic category when obligatory groups of maneuvers a r e performed.

The margin between the actual gust and maneuver load experience and the design gust and maneuver l i m i t load factor w a s generally l e s s f o r general aviation a i r c r a f t than f o r commercial transport a i r c r a f t .

Aircraft used f o r pipeline p a t r o l work i n commercial survey operations are subjected t o a more severe gust and maneuver loading, from a fatigue standpoint, than any of the general aviation a i r c r a f t evaluated.

The percent time flown i n rough air ranged from 21 t o 97 percent of the f l i g h t time. This compares t o a maximum of 12 percent f o r commercial transport operations.

Design cruise speeds were exceeded by a i r c r a f t i n a l l operations.

Specific types of a i r c r a f t appeared t o exceed t h e design cruise speed more often than other types. Aircraft used i n instructional and personal operations were flown above the design cruise speed more frequently than a i r c r a f t i n other types of operations.

All general aviation a i r c r a f t experienced higher landing accelerations than commercial transport a i r c r a f t used i n short-haul operations.

Aircraft i n instructional operations experienced the most severe landing impact accelerations.

REFERENCES 1. Taback, Israel: The NACA V-G Recorder. M C A TN 2194, 1950.

2. Richardson, Noman R.: NACA VGH Recorder. NACA TN 2265, 1951.

- Figure 3.- VG recorder.

v) * t . 2 d U COMBINED AIRCRAFT INVOLVED NO.

AIRCRAFT HOURS RECORDED

I

HOURS HOURS PER AIRCRAFT PER YEAR 4 r x lo2 COMBINED HOURS 2 61 62 63 64 65 66 67 63 64 65 66 67 61 62 63 64 65 66 67 CALENDAR YEAR Figure 6.- Status of general aviation program.

AVERAGE PRESSURE! ALTITUDE AVERAGE INDICATED AIRSPEED KNOTS AVERAGE FLIGHT LENGTH HOURS 8 13 15 1 2 3 4 6 7 8 9 12 13 14 SINGLE PERSONAL INSTRUCTIONAL SURVEY TWIN AIRCRAFT TYPE AND OPERATION Figure 7. - Typical mission characteristics of instrumented a i r c r a f t .

VGH data.

I I I I \ \ I k l 1 l o (0 , N O ^ : , P p : ' n o bG

c

c

R > &-" I E n o bG

“ 2

2 TYPE 8 COMPOSITE LOAD FOUR AIRCRA . FT FACTOR 14 RECORDS 570 HRS -2

-4 I I II I I

vD 4 r TYPE 13 COMPOSITE SIX AIRCRAFT LOAD 81 RECORDS FACTOR 6805 HRS -2 I I I I I I I 140 160 180 200 100 120 CATED AIRSPEED, KNOTS ( e ) Commercid survey.

Figure 8. - Concluded.

0 m m 0 m rl N

1 4

I I I I I I 10- TYPEA/C HOURS 0 13 6805 0 8 570 10- PROBABILITY 10- I I I I I I 1 , 0 .20 .40 .60 .80 1.00 1.20 Vmax - vc ' D - (e) CommerciaJ survey.

Figure 10.- Concluded.

U I - 0 N.

- 0 I I I I I I N.

4 N m

A 0 :: E 2

d m

d

k *rl a 3 k Io k rl TI

a

rl k

I ‘

I I @i rl d : Q) 0 0 cv W to rl

w“ IE

TPPEA/C HOURS 0 15 888

8 l 3 8 197

-- LIMITS SHORT 3,108

HAUL JET TRANSPORTS

P

( e ) Commercial survey.

Figure 12. - Concluded.

U W N W

E

COW* 3 m 5: V H \

000 I

I

I

I 1 I I I I I I I I 0 3 cy 0 m I I I I P 0 0 0 -I E) 3 E) E: W -* - c r V \ W k N -n

oooa I

I I

VI

- 2 -

+ ( a a " W - 4 H P XI * N m v1 N - .

" 8 W rl H m TYPEA/C HOURS

0 13 2 14

0 15 888

0 8 197

--

LIMITS SHORT 3,108 HAUL J E T TRANSPORTS LIMITS FOUR ENGINE 13,902 PISTON TRANSPORTS (e) Commercial survey.

Figure 13. - Concluded.

n P W m p1

I 1’

I n rd v

1: ?

7- n a v loo TYPE A/C HOURS LIMITS SHORT 3,108 10-1 HAUL J E T TRANSPORTS lo-2 Zf

-

FM

u

MANEUVER ACCELERATION FRACTION, A

"LLF ( e ) Commercial survey.

14. - Concluded.

Figure m cu I I E: rl E:

E

I4 PI n o 4:i- 5 % LL c m v I c3 - PI PI PI n o a 0 a b ai- o v 0 0 -1a -I< LL L L In c a e CK n o e n o <I- n o <I- O U aI- O U -I< O U --I< U --I< U U e CK e n o n o n o <+- a + <I- o u 2s Y U VI c 33 H

0 0 ' 0 1

P-

17 3 Fi 2 4 U ( I D "@.

8 0 0

N rl

2 -

0 rl C W *

d

N

, 0

- N - 3 W W * N

I I 1 NASA-Langley, 1968