RESEARCH MEMORANDUM

ANALYSIS OF V-g DATA OBTAINED FROM

SEVERAL NAVAL AIRPUNFS

By James 0. Thornton

Langley Aeronautical Laboratory Langley Air Force Base, Va.

CLASSIFICATION CANCELLED

NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS

WASHINGTON

NacA RM L9Ll3

.

By James 0. Thornton

Carnposite envelopes of V-g records obtained in training an& oper- ational f l ights with the F8F-1, SB-, .Fa+, F4-, and TBM3 a 3 r p h s a m given and ccnnpmed mith the design envelopes. In addition, the records from the F8F-1, SB2C3, and F6F3 a t r p l m e e m e analyzed statis- t i ca l lg t o show a variation of lmge values of acceleration and airspeed

The loads encountered in f l i gh t mmt be h o r n before an efficient airplane desi@ is possible. For maneuverable akglanee, these loab vary with the aerodynamic chamxteristice and type of operation. Since V- data can furnish the exprience of previoua airplanes on similas missions, the possibility is suggested that fLtght loads may be predicted fram the malysis of such records. W c r k of this nature hae been carried on f o r the last few yeme in th i s country and abroad, a recent example of which is given in reference 1.

V-g records supplied the NACA by the Bureau of Aeromutfcs i n 1948 and 1949 have prwided additional material. These recorda me analyzed etat ie t ical ly in this report t o show the frequency of large values of acceleration end airspeed, and results are campared with the design requirements.

\

2

SYMBOIS

WlCA RM L9U3

e a m x maximum podtive or negative acceleration lncramsnt on V"g recmd, g d t s

indicated airspeed at wUch marrimurn positive negative acceleratian increment on V-g recmd is experienced, miles per hour

ma~cFmum indicated airspeed on V- record, milee per hour

Q atandwd deviation of frequency dietribution, reference 2

% acceleration increment correspording t o V-, g unite - - V-, &, 8, average value6 of frequency dietributiona of V-,

&, and Vo, respectively probablli- that maxFmum acceleration increment

- on V-g record will exceed a given value

pan probabili- that value of maximum acceleration incre- ment 0 n V - g record will occUr in a given interval

= pv probability that mximum indicated airapeed an V-g record will exceed a given value probability that value of l aa~~ imum indicated airapeed

on V"g record w i l l occm i n a given interval

7 average flight time ger record, h o u r B

a3 coefficient of lskewneee of frequency distribution, reference 2 . . .. . "

"4 cwfficient of Imrtoeie of frequency distribution, reference 2 . .. MID* midpoint of class interval of frequency Ustribution

k Ilumber of cLassee in frequency distribution I

c

NACA RM L9Ll3 3

The data available far analysis coneisted of V-g records obtained with the F8F-1, Fa+, Fk-, sBC2C-5, and a3rglanes. The F8F-1, F6F-5, and F4- airplanes m e Singl0-pke fighters; the SEiX-5 is a t-lace, l o e d w i n g dlve bomber; asd the amlane is a tbree- place, midwing torpedo boniber. pu1 airplanes are s ing le engine and are cmrier+aeect -0s. A f e w pertinent details are listed in the following table :

Airplane Average take-off

w e i g h t

Sufficient records were available an the Fa-1, SB20-5, and F 6 F j airplanes t o make a s ta t ie t icd ana lys i s . The distribution of f lying hours s?n these records is shown i n figure 1 where the flying time per record is plotted against number of records. In addi t ion to the data of figure 1, 35 records yere furniehed on t h e F4U4 airplane and 45 r e c o d on t he -3 airplane.

Postwar f l e e t squadron operatiom of Attack C m i e r Air Grw ll provided 9 cormon 6ource of records obtained with the Fa-1, sSX-5, F6F-5, and -3 alqplanes. Operatiom carried out by each airplane were . a s follows: F8F--1, diving and dive pull-outs, gunnery ~~218, routine squadron operations; SB2C-5, diTe bcanbing, rocket rune, b-ing and simulated attack; TB"-3, night operations a& glide babing; asd Fa-, banibhg rocket runs and simulated attacks. Same S B 2 C 3 and F4Ulf recar- were obtained f r a m the Maval A i r Training Station at Jacksonville, Fla.

W & i m e operatione were Umited t o 76 recorda f r o m the F6Fq airplane and 8 records from the F 4 w airplane obtained in the Pacffic mea in 1945. Operations carried out were as follows: Fa+ , ccubat air patrol, gunnery, and simulated combat; F4U4, strafing enemy installations, guzvlerg practice, and simulated combat.

4 RACA RM L9Ll3

* Comgosite diagram, or overlays of the V-g records by awplane +ne, a m given by t h e imp@ solid lines in figures 2 t o 6. Since it waa not possible t o determhe the airplane weight at which these acceleratiom occurred, the assumflion made that they apply t o an average weight at talre-off. The dashed-line ll?nit-lo&+actor curves shown in these figures were based on this assmugtion.

Although f'urther' study of the T- records frm the F4U-4 and "+ airplases wae prevented by l imited data, an analysis of records f'rm the F8F"l, SBX-5, and Fa+ airplanes w&8 made t o determine V-g "flight" envelopes and the frequency of large valuee of accelera- t ion and airspeed, ' Figures 7 and 8 are sample V-9 recorda shoxing the values which were read. For the SB2c-5 airplane, seven values were read fraa each record: these were the maximum positive acceleration increment and the airspeed at which it occurred Yo; the macirmun indIca6ed airspeed V- and the acceleration at which it occurred &+; and the maximum negative acceleration increment % and the airspeed at which it occurred Vo; and the flying time repre- sented by the record 7.

Records . f r o m the F8F-1 and Fa-5 airplanes differed f r a m those of the SBX3 airplane in having two peaks of positive acceleration. The l o m p e e d peak was caused lq m&~~8uvers starked below the maximum level- f l igh t speed of the airplane, w h i l e the high-lpeed peak was cawed ky diving t o sane exce88 of speed 8n.d pulling out of the dive. In order t o t r e a t these peaks separately, nine values were read, the last two being the maxinm acce lera t ion incremt in hfgh-apeed f l igh t and the airspeed at which it occurred.

Tables I t o 111 &ow each value of acceleration and airepeed arranged i n a frequency distribution. In order t o amooth and 'extend these data to obtain the'accelerations and airspeeds expected BE flying tFme increases, Pearson type probability curve8 were chosen by the methods of reference 4. Essentially, thi8 comiste of computing the f i rs t four moments of the data about the m e a s and matching these momente with the moments of a Pearson frequency distribution. The parameters involved are the mean value, the standard deviatim 6, md the 8tatis- t ical coeff ic ients 3 and %. These curves give the probabili- of exceeding a given value of acceleration or airspeed on a V-g record and are used in drawing V- flight envelopes..

Details of the construction of the f l ight envelope shown in fig- UT08 6 t o 8 are discussed in references 5 etnd 6. These envelopes are

.

NACA REiI L9Ll3 5 L

= . composed of segments which will be exceeded, on the average, once i n the stated number of hours with equal chance of befng exceeded in agp range of the e e p n t . In figures 4 ~ t n d 6, four s e p n t s are used t o enclose the area: low-speed positive maneuvers, high-peed positive Maneuvers, ma~rimMl airspeed, and negative acceleratione. Each emelope

j is broken off on Intersection with the curve of C % l a x o

The construction of an emelape e e p n t of maclmum airspeed i s parallel t o that of the other s e p n t e . In table IV, the occurrence of a maximum value of &speed on a V-g record and the fact that the value occurs a t a p&icular acceleration m e considered t o be independent events. As such, t h e probabiliw P of a mascFmum value of airspeed occurring in a given interval of aqceleration ie the poduct of the separate probabilities md is equal t o T / k as explained in reference 5. In symbols, t h i s is

c

c

where all values are available except CP,. The correspondln@F T- is found by reference t o the probabili- distribution of V-.

Figures 9 t o 12 are probability curves tramformed by multiplying the reciprocal of the probabili- by T t o give the average tFme required t o exceed maximum values of airspeed and accelera$ion. In these figures the probability is that the given value will be exceeded once i n the specified interval of time. The ordfnates of these curves are the average numbers of flying hours in which an airplane w i l l exceed the stated value once; o r i f large nuibers of airplanes are considered, the ordinates become the sum of the flying hours of a group of airplanes i n which, on the average, one airplane w i l l exceed the stated value once. The design l d a d factors in these figures are based on an average weight a t take-off. Negative ultimate load factors were not included since they were not c r i t i ca l . Crude s t a t i s t i ca l t e s t s show that in most cases the error due to sampling is less than 5 percenk of the airspeed and 10 percent of the acceleration.

Figures 10 .and 12 coqmre the loading obtained i n l o w p e e d maneuvers with that obtained in high-speed maneuvers. A more general curve givhg the time t o exceed a value of acceleration rega3.dless of the maneuver in which it waa obtained waa found in the f ollo%ing m e r : Since a raaximm value of acceleration increment on a V-g record m q occur i n a high- or lo-pmd range (but not both), them events me exclwlve, and the 10- due t o either were obtained by taking the sum of the separate probabilities. In term of time, this is

6 EIACA RM L g u

T = T1T2 TI + T2

where the subscripts refer t o high- and l owpeed m8neuver8, reepectiveu.

The average r a t i o of airplet;nes which wiLl exceed the design ultimate load factor to all afrplaneEi flying is shorn f o r given periode of time in figures 10 t o 32. Theae r a t io s are f i x e d by T/h, where h is the average time t o reach ultimate load factor, aml. m e a result of the failure rate set by the choice of ultimate load factm. Losees m e not exactly determbed, of course, became finding h iwOlve8 extending the original data t o the ultimate load, and became airplanes m g not fail at the design ult+te load.

Accelerations and l o a d factore baaed on the norml gross weight axe shown in figure 13 Fn order to carqpese t h e F&F-L, SB2C-5, and Fa+ airplanes.

DISCUSSION

Since a V-g record obscures values of acceleration and airspeed tha t are not a maximum, a total count of these obscured values cannot be made. Figures 9 t o 13 therefore give the average time fn which maximum ValueF on a V-g record are exceeded rather than a t o t a l fre- quency of exceeding given values. The difference is not significant f o r large values, and results given in these figures are said to apply t o individual OccurrenceEI of the large values. The results, however, represent a set of operational conditions tha t o n l y existed when the records were taken. The effect of small changes in these conditions has not been determined, but a gross change would, i n all likelihood, give different results.

The applicatian-of statist ical me%hods t o maneuTierable flight data is somet-lmes objected to on the grounds that maneuvers are arbitrary. The data in figures 9 t o 1.3, however, show regular trends with time, indicating that while the intent of an individual maneuver may be arbi- trary, the accelerations and airspeed6 obtained i n practice are random, and consequently respond t o statistical, treatment.

Since the events are random, the frequency of an event does not t e l l when it may occur. It i s noted i n figure 4 tha t the maxim values of the composite diagram exceed the predicted envelopes or any reasonable extension thereof. Figure 10, for example, indicates that the Large acceleration in figure 4, which has occurred i n some 5000 hours of flight, is only exceeded on the average every 20,000 hours. Apparently

NACA RM LgL13 7

c

then, 811 airplane can obtain the largest loads in i t s early hours of flight. In this connection it is sham that the position of these events within a given period of time is not fixed; and that the event may occur first, las t , o r in the middle of 8 period of time, depending on the starting point from which t i m e i s measured. The thing that does not change is the average f'requency which in this case is one.event i n 20,000 hours.

Although the average time in uhich limit load factor is exceeded has been used on occasion as a measure of the l i fe of transport air- planes, the average time i n which ultimate load is exceeded is a more appropriate measure f o r maneuverable airplanes. It is seen in figure 13 that a maneuverable airplane can exceed i t s limit load quite e8zI.y with- out exceeding i ts design ulthnate load i n a reasonable time. For pur- poses of discussion, therefore, a figure which may be taken t o compare the safety of maneuverable airplanes' i s the average time i n which the design ultimate load i s exceeded. On th i s basis, figures 10 to 12 indicate that the ~ 8 ~ 4 and SBX-5 airplanes have practically identical service lives while the F6F-5 airplane has a shorter service life by a factor of approximately 50.

Ordinarily the loading experienced by a maneuverable airplane would be expected to depend on i ts maneuverability as measured by st ick force per g. However, other factors beside stick force per g are evidently important. This f ac t i s indicated by the F~F-I and F6F-5 airplanes which obtain accelerations and airspeeds with different frequencies, although they have about the same stfck fo rce per g.

The analysis of V-9 data obtained i n maneuvers indicates thht large values of acceleration and airspeed are randm w d can be subjected t o 8 s t a t i s t i ca l analysis. Since the limit load factors of maneuverable airplanes are exceeded in a relatively short period of time, the design ultimate load factor i s a more appropriate level on which t o base the safety of maneuverable airplanes than the limit load factor. It appears f r o m the data that other factors beside stick force per g have an hportant bearing on the accelerations that are experienced.

Langley Aeronautical Laboratory R a t i o n a l Adviemy Committee f o r Aeronautics

Langley A i r Farce Base, Va.

8 NACA FM L9LI-3

1. Reynolds, LaWence B. : A S m m a t y of Flight Load Data Recorded i n Tactical and 'Ilraining Operatiana d u r a the Period of Wmld W a r x. Preprint No. 235, Inst. Aero. Sci., Inc., July 1949.

2. Kenney, John F. : Mathamtics of Statistics. R. I, pp. 60-75, and Pt. Il, pp. 4 H 1 . D. Van N o e t r d Co., LC., 1939.

5. Pelem, A. M., and WiUrerson, M.: A Method of Analyeie of V-G Recarde *am Transport Operations. NACA Rep. 807, 1945.

6. Wilkereon, M., md B e n n e t t , S. A.: Analysie of V-G Records Frau the SNJ-4 Airplane. WCA MR ~ 5 ~ 0 6 , 1945.

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.. NACA RM L9n3 9

I t €-CY

I 3 3 8 8 21 - 13 22 21 18 12 . 7 . 9 4 3 . 6 1

Fre- w=w

4 1 6 8 12 3-3 14 12 21 52 20 10 5

l l 7 3 I

4.12 1.44 -0.02 2.38

I 7

v, = 427.4

.

.

h (d

0.0 - 0.1 .4 - .s .2 - .3 .6 - -7 .8 - .9

L O - 1.1 1.2 - 1.3 1.4 - 1.5 1.6 - 1.7 1.8 - 1.9 2.0 - 2.1 2.4 - 2.5 2.2 - 2.3 2.6 - 2.7 2.8 - 2.9 3.0 - 3.1 3.2 - 3.3 .L I

I - v, - 271.1 u * 6g.b

’5 = 0.92 ”4 - 3.70

velooity

$re-

a- 1

1 0

0 1

1 3 2 0 9 ,u 9

5 23 19 32 24 6 8 3 1 0 0 0 1

24 1

4 16 ee

15 13,

6 !u u 4 lo 6 4 1 1 1

1

i

& = 2.ll

% - 9.35 u - 1.46

= 0.42

. . . .. . . . . . . . . . I

. . . . . . .

XACA RM L9Ll-3 t

Positive accelezations in level flight

lb" 9 m 3

1 0 0 1 1

10 9

21 17 25 6 22 12 7 9 3 4 2 0 1

Be- lU83lC: -

1 0 3 0 3 9 6 7

13 10 13 13 5 6 7 5 3 1 2 3 1 1 0 0 1

LO - 1.3 1.4 - 1.7 1.8 - 2.1 2.2 - 2.5 2.6 - 2.9 3.0 - 3.3 3.4 - 3.7 3.8 - 4.1 4.2 - 4.5 4.6 - 4.9 5.0 - 5.3 5.4 - 5.7 5.8 - 6.1 6.2 - 6.5 6.6 - 6.9

8 4 4 9

13 15 13 19 22 - 13 11 7 8 2 3

0.5 - 0.7 08 - 1.0

1.1 - 1.3 1.4 - 1.6 1.7 - 1.9 2.0 - 2.2 2.3 - 2.5 2.6 - 2.8 2.9 - 3.1 3.2 - 3.4 3.5 - 3.7 3.8 - 4.0 4.1 - 4.3 4.4 - 4.6 4.7 - 4.9 5.0 - 5.2 5.3 - 5.5 5.6 - 5.8 5.9 - 6.1. 6.2 - 6.4 6.5 - 6.7 6.8 - 7.0 7.1 - 7.3 7.4 - 7.6 7.7 - 7.9

1 0 I 6 4 7 6

13 5 8 5 15 13 12 8 5 1 2 0 0 1

235 - 249 250 - 264 265 - 279 280 - 294 295 - 3w 310 - 324 325 - 339 340 - 354 355 - 369 370 - 384 385 - 399 4-00 - 414 415 - 429 430 - 4-4-4 445 - 459 460 - 474 475 - 489 490 - 504 505 - 419 520 - 534 535 - 549

.

c

c

. .

0.Q - 0.3 .4 - .5 -6 - .7 .a - .9 1.0 - 1.1 1.2 - 1.3 1.4 - 1.5 1.6 - 1.7 1.8 - 1.9 2.0 - 2.1 2.2 - 2.3 2.4 - 2.5 2.6 - 2.7. 2.8 - 2.9 3.0 - 3.1 3.2 - 3.3 3.4 - 3.5 3.6 3.7

Fre- quency

1 0 2 1 5 5 16 17 2Q 14 16 4 8 9

12

S 2

4 3 1 1 1 2

5 (-0.4) - (-0.1) 0 - .3

.4 - .7 a 8 - 1.1

1.2 - 1.3 1.6 - 1.9 2.0 - 2.3 2.4 - 2.7 2.8 - 3.1 3.2 - 3.5 3.6 - 3.9 4.0 - 4.3 4.4 - 4.7 4.0 - 5.1 9.2 - 9.5 5.4 - 5.9 6.0 - 6.3 6.b - 6.7 6.8 - 7.1

1 94 15 2-2

3 15

16 9 10 8 u. 3 2 3 0 0 0 1

1

, I

', i ' * !

. " . . . 8

KACA RM L9n3 13

r 1 negative acceleration Positive acceleratim 0.9 - 1.1 1.2 - 1.4 1.5 - 1.7 1.8 - 2.0 2.1 - 2.3 2.7 - 2.9 3.0 - 3.2 3.3 - 3.5 3.6 - 3.8 3.9 - 4.1 4.2 - 4.4 4.5 - 4.7 4.8 - 5.0 5.1 - 5.3 5.4 - 5.6 5.7 - 5.9 6.0 - 6.2 6.3 - 6.5 6.6 - 6.8 6.9 - 7.1 7.2 - 7.4 7.5 - 7.7 7.8 - 8.0 8.1 - 8.3 8.4 - 8.6

2.4 - 2.6

I 1 0 2 2 0 1 4 3 7 6 6 5 II 6 0 2 1 2 4 0 0 0 0 0 1

260 - 266 274 - 281 - 287 280 - 294 302 - 308 309 - 315 316 - 322 323 - 329 330 - 336 337 - 343 344 - 350 351 - 357 358 -364 365 - 371 372 - 3-ca 379 - 385

267 - 2g 295 - 301

0.0 - 0.2 03 - .6 - :f .g - 1.1

1.2 - 1 .4 1.5 - 1.7 1.8 - 2.c 2.1 - 2.3 2.4 - 2.t 2.7 - 2.5

1

8 4 10 14 13 7 4 1

2 0 3 0 3 4 2 7 6 6 6 5 9 3 4 3 1 1

1% - 162 163 - 18 176 - 1 1% - 201 202 - a4 a 5 - 227 228 - 240 241 - 253 254 - 266 267 - 279 280-292 293 - 305 306 - 3x3 319 - 331 332 - 344 343 - 357 358 - 370

2 1 1 1 3 1 6 3 7 5 9

1 5 2 1

L

8, = 327.30 u = 27.10 a3 = -0.34 Q= 2.65

v, = 271.6 Q = 49.00

= 3.91 9 = -0.58

14 mAcA RM L9Ll.3

Maximum velocity

270 - 3 9 280-29 2 9 - 299 300 - 309 310 - 319 320 - 329 330 - 339 340 - 349 350 - 359 360 - 369 3 0 - 379 390 - 399 3L - 389

1 0 2 3 1 7 1 ll 9 15 8 4 3

Fr6-

2 1 2 7 4 2 6 1 7 5 14 2 5 4 0 1 2

% = 2.49 a = 1.16 3 = -0.06

= 2.33

1 .. .

. . "

mcA RM L g n 3 . .. . c

15

-1

0

1

2

3

4

5 6 -

Mid- X

-0.5

-5

1.5

2.5

3.5

4.5

5.5

-r

"

i

.630

.3@

.170

.062

0175 . 044 -0504 491

5000, Hours

16 NACA RM L9U3

record

Figure 2.- A 292-hour V-g composite o f records obtained with Pkr-4 &?planes.

. . . .

L "_" """- -

t

F i w e 3 . - A 453-hour V-g composite of record6 obtained with TBM type airplanes.

. . . . . . . . . . . . . . . . . . . . . .

.. .. I b

I ,"- 5OOO-hour envelope

5000-hour enve lop 2000-hour envelope

I L """"""_ / -* t

I W

speed

h3 0

Figure 5.- A comparison of predicted 2OOO-hour envelopes with a 7 8 0 - b ~ V-g C a m p O S i t e of records s obtained with the S E - 5 airplane. G

F W

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

-hour envelope

- -8 .-hour envelops

1"

Figure 6. - A comparison o f predicted 2000- and .5OOO-hour envelopes with a $O-hour V-g cmposite of records obtained with the P6F-5 airplane.

. . .. .

6 -

c -

e -

0 -

-2 - -

100

Figure 7.- Sample Y-g recora from the SBX-5 airplane.

. . . . 4

.. . ...

. . 1 I

8 -

6 -

4 -

2 -

8

6

4

2

0

- L

Do . 300 466

0

- L

Figure 8.- Sample V-g r e c o r d from the F8F-1 airplane,

. .

24 NACA RM L9Ll.3

Figure 9.- Average time required t o exceed a given value of maximum indicated airspeed.

.

JACA RM L9L13

. -- 0

Figure 10. - Average time required to exceed a given value of maxirmrm acceleration increment on a V-g record from the F8F-1 airplane.

26

a

NACA RM L9Ll.3

Figure 11. - Average time required t o exceed a given value of maximum acceleration increment on a V-g record from the SEX-5 airplane.

I

F i g r e 12. - Average time required to exceed a given value of maximum acceleration increment on a V-g record f’rom the F6F-5 airplane.

28 ETACA RM ~ 9 ~ 1 3

Figure 13.- A comparison of the average time required t o exceed gfven values of maximum acceleration increment on V-g records from the F8F-1, SBX-5, and F6F-5 airplanes.

NhCA-Lnnplw - 7-7-W -17s

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i

8