Rules and methods for insuring safe structural strength of racing airplanes used in the major air meets in this country have recently been considered. Acceleration records made in racing airplanes during actual air races were therefore considered desirable, and the NACA undertook the measurement of acceleration of loads on airplanes during all conditions of flight. Accelerations were measured on four airplanes at the Miami All-American Races in January 1934 and January 1935. The airplanes were representative of the fastest limited and unlimited displacement racing airplanes in current use in this country. Records during two races, or flights, on the race course were obtained with each airplane. The maximum normal acceleration recorded was 6.2g and the minimum was -1.2g

Kirschbaum, H W

Scudder, N F

English

NASA Technical Reports Server

Abu lU 1935
To: ..<.-9.. ““’’-”-+..--—....” .“<. —.
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;. TEC3ti~CAL NOTES
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No. 537
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A PRELIMINARY DETERMINATION 03’ NORMAL ACC&TJNiATIOifS
6N RACING AIRPLANES
By X+ E. Scudder a~d H. W. Ki~*schbaum
Langley Memorial Aeronautical Laboratory
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NATIONAL ADVISORY COMMITTEE TOR AERONAUTIOS~
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TECHNICAL NOTE NO, 537 #’ “-
-..—.--—
A PRELIMINARY DET3RMIN.4TION Or NORMAL ACCELERATIONS
ON RACING AIRPLAIWS
By N. I?. Scudder and H. W, Kirsch%aum
Rules and methods for insuring safe structural
strength of racing airplanes used in,the ma~or,air meets
in this country have recently been considered. Accelerom-
eter records made in racing airplanes during actual air
races were therefore considered desirable, and the National
Advisory Committee for Aeronautics undertook the measure-
ment of accelerations during races as a part of an inves-
tigation of loads on airplanes during all conditions of ““
f light ,
Accelerations were measured on four airplanes at the
Miami All~American Air Races in January 1934 and Jqnuary
1935. The airplanes were representative of the fas~e~t
limited and unlimited displacement racing airplan8s in
current use in this country. Records during two races, ‘“
or flights, on the race course were obtainedwith each
airplaneQ The maximum normal acceleration recorde~ was
6=2G and the minimum was -1.2g.
-.
— .=-
INTRODUCE1ON
Within the past year there has been a movement toward
the adoption of regulations establishing minimum require-
ments for the structural strength of racing airplanes used
in the major air meets ii~ this. country. In order to cai%
ry this o%jective forward, the Professional Racing Pilotsf
Association, which includes in its membership all the ac-
tive racing pilots of the country, has been considering
recommendations regarding rules and methods for ips~rin~
safe structural strength adaptable to the conditions un-
der which racing airplanes are designed and built.
.
2 I?. A. C.A. Technical Note No. 537
.,
,.
One of the first requirements for formulating ration-
al design rules is + knowledge of the maxinum loads to
which the structure nay, pe gubjected in use, It would he
possible to set down load conditions that were both safe
and economical of structural weight as a result of an anal-
ysis of general :ioaii-factor measurements. The Nattonal
Advisory Committee for Aeronautics has been accumulating
data over a long period of time with regard to the loads
imposed on airplane structures both by the effects of at-
mospheric turbulence and %y all types of flight maneuvers,
Analysis of this work-alone would give a reasonable basis
upon which to formulate design rules~ but data oltained
hy direct measurements On racing airplanes during actual
races were considered desirable. At the suggest-ion of
representatives of the above-mentioned association and be-
cause the N.A,C,A, is interested in the general .subjoct of
airplane loads, steps were taken to get accelorometor rec-
‘ords during air races~
The first of these records was made in the lfedell-
Williams racer No. 44 during the Xiami ill-American Air
Races in January 1934; at the same races a ‘year later,
January 1935, rec”ords were ”tiade in three more racing air-
planes: the Keith Ryder San I?ranciscan, the Chester Spe-
cial$ and the Wittman Chief, The Wedell racer was of par-
ticular interest because it was the fastest landplane in
this countryO It held the worldls landplane maximum
speed record for some time and later exceeded that record
%Y 2 miles per hour, malting an average speed of 306.2
miles per hour on the 3-kilometer speed course at Cleve-
land, September 4$ 1934. The other three airplanes are
representative of the fastest specially built limlted
displacement racing airplanes now in use in this country,
APPARATUS ANrI METHOD
The four airplanes in which the records were obtainod
aro listed in the following table with the types and dis-
placements of the engi~es and the high speeds of the air-
planes--determined-on the3-kilompte.r. epe.ed course at
‘C15veland in September 1934. These speeds indicate the
maximnm, performance of the airplanes at the time the
Cleveland trials were made, The speeds at the time the
acceleration records were made are shown in the last two.
columns. These latter speeds were necessarily less bo-
cause of flying on a closed course, but they are reliable
N.A.C.A. Technical Note No. 537 3
‘1
‘1
values for the average flying speed while the records ~qre
made because timing was started. after the airplanes had
passed around the scattering pylon and returned to the
race coursec
-.
‘The wing loading of the Wedell racer could be esti-
mated from fairly reliable data to be 17 pounds per square
foot. Similar data for the other airplanes were.not avail-
able, but general practice would indicate that the wing
loading was nearly 20 pounds per square foot.
Airplane
lTedellNo. 44
Keith Ryder
Chester Special
l?ittmanChief
Engine
lta+ Jr.
Menasco
Menasco
Cirrus Hermes
Maximum
speed
Displace- on 3-km
ment course at
Cleveland
Cubic
inches M.p.h.
985 Not known
544 235.3
363 229.7
349 201.1
Average spseds
for races
First
acceler-
ateon
record
M.p.h.
236
225,5
221.5
189.3
Second
acceler-
ation
record
M.p.h.
Not a race
205.1
220.3
184,4
%06.2 m.p.h. with Wasp engine.
The accelerometers used in making the records were of
the maximum recording type. The usual prac;ice of setting
the scales of the instruments to read l.Og when th-e”a”ir-
.——
plane was in steady level flight was followed in these
tests. The instrument used in the Wedell racer was mount-
ed on the instrument panel and the others were attached to
the backs of the ~ilots! seats. In all cases the instru-
ments were properly oriented for measuring the normal coKL-
ponent of acceleration. In the case of the Wedell racer
the air speeds were recorded as well as the accelerations.
Damping was obtained by means of friction in these in-
str-urnents- The adjustnant was set as closely as possible
to critical damping in each case, but the damping was actu-
ally slightly less than critical~ No difficulty was ex-
yerienceii with three of the installations, but the instal-
4 N.A.C,J.. Technical Note Xo, 537
lation in the Chester racer was not entirely satisfactory
because for small deflections above and below that for
l,og the stylus cut through the Leavy paper of which the
record card was made. The. important part of the records
for these tests was the maximum reading; and, since the
stylus reached the ria~imtz~i deflections usually only once
in the time interval” corresponding to the width of the
stylus mark, the card was not cut and friction would have
been normal when the maximum aild minimum deflections were
recorded~
The instruments were calibrated both before and after
the tests.
PRECISION
The estimated limits of error were as follows: +0 , lg
for the instrument used in the Wed’ell racer, @.25g for
the instruments used in the Chester and Wittman racers’,
and =b3.5g for tf~e instrument used in the lIetth Ryder racer.
The calibrations made before and after the tests checked
almost exactly for the first three instruments mentioned
and showed a maximum difference of 0.5g in the case of the
instrument used in the Keith Ryder racer. “The records for
this instrument were read on the basl.s of a calibration
curve that waa a mean liae “oetween the calibration before
and the calibration” after the tests. Th8re was thus an
uncertainty in the calibration of ti.25g; the remaiuder of
the estimated possible error was allowance for vibration
effects on the instrument and errors of reading. The air-
speed readings on the Wedell racer” were undoubtedly in er-
ror by several miles per hour because the air-speed head
wa~ only 1 foot directly ahead of the nose of tho wing.
When examining the entries in the tabulated data, it
will be noticod that frequently an acceleration of less
than l.Og and one of considerably more than l.Og are en-
tered opposite the same time reading. ‘ This grouping occuru
only because the tine scale was so short that it was dif-
ficult to distinguish between events that may have occurrod
as much as 30 seconds apart~
#
..
#
N,A, C.A. Technical. Note Ho. 537
RESULT S
The following ta%le gives maximum and minimum values
of acceleration read over nest of the smeed range in the
5
Wedell racer.
Accelermaeter record
of January 13a
Indicated air I Accelerationspeed
M.p.h.
138 to 190
200
226
2’70
250 to 260
278 (-X.
ind.)
~
2.0
3.0
3.6 “
5.1
,
-. 1
1.0 to 3.5
Accelerometer re ord
~of January 14
Indicated air
speed
M.p.h.
147
160
200 .
216
23’7(max.
ind.)
296 to 208
Acceleration
g
3.2
3.6
5,3
4.3
2.0
0
%ace of 3 laps on 10-mile course; average speed of 236 m.p.h. for
race.
exhibition flight, 31apson 5-mile course.
Mr. T?edell reported that, as he was riot presses by the
other airplanes in the race of January 13, he aid not try
to turn closely around the pylons because he wanted to
keep out of the way. When he made the, second record, he
was alone on the course and pulled in close to the pylons.
The records taken in the Keith Ryder, Chester, and
Wittnan racers were read at the points where the deflec-
tions above or below that for log were greatest. The
reatiings are” tabulated in the following ta%le.
.
-.
Pilot: Roger Don We
Event 19
.Te.n.11
Av. epeed:
225.6 m.p.h.
T_lrJJ
4t&.5
4:25
4:26.5
4:%.5
4:27.5
4:28
4:29
4:30
4:30.5
4:31.6
4:33
LgQml .
~
5,2
4.9
3.5
5.2
6.2*
-.3
3.9
-.3
4.1
4.3
3.6
-.3
4’.4
-.4*
3.0
Event 19
J=. 12
Av. speed:
X)5.1 m.p.h.
T~e
425
4:25
4:27.5
4:26
4:29
4:29.5
4:31
4:31,.5
4:32
433
4:36
A~el.
~
3.7
-.6
4.5*
-1*O*
3.5
-.6
3.5
-.1
2.0
-.1
4.0
-.1
3.5
-.1
3.1
4.0
-.4
2.2
2*2
*.
Airplane: f.%egter 8pecl.al
PiloM Arthur C. @este~
Event M
Jan. 11
Av. e-peed:
221.4 m.p.h.
KT~e
u Zt
;:22.5
k:a
k:24.5
!:25
k:a.j
i.:2f3
%kchmnn or minimnm value for flight.
Ac.cel.
$
2.9
2.9
3.3*
2.7
-.2
2.9
0
2.9
-.4*
——
Svent 19
Jan. 12
Av. epeed:
2~.q m.p.h.
T*s
&30
4:33
4:36
4:38
A&ol .
g
4.5*
-.5*
4.3
-.2
4.5*
-*5*
4.1
Ah_cMne: Wittman Chief
Pil;ti S. J. Wlt%man
Event 18
Jm. 11 .,
Av. speed;
189.3 m.p.h.
T&e
::36
:37
:38
:39
:40
:41.5
:42
:43
:44.5
:46
:47*6
:49
:49.5
A~l .
g
4.0
4.7
-.3
5.0’
3.8
4.5
-.5
4.5
3.3
4.5
4.0
3.6
3.0
-.6*
3.3
3
;:5
Event 19
Jen- 12
Av. speed:
184.4 m.p.h.
WiIIJe
423
4:25
4:%
4:27
4:29
4:30
4:30.5
4:32
4:35
4:36
A-.
g
4.2
4.2
:::
-.6
4.7*
-.6
3.8
3.8
.;::*
3.6
3.8
m
N.A.C.A. Technical I?ote Ko. 537 7
?
i
,’
l
Th& deflections at times between those of– the readings
were not far enough above or below that for l.Og tb be of
interest . The number of readings shown is therefore indic-
ative of the number of times that large air loads occurred
during the flight.
DISCUSSION
The maxinum acceleration obtained in these records
was 6.2g recorded in the Eeitw Ryder racer. Maxima of l)e-
tween 4.5g and 5.Og occurred fairly frequently. The mini-
mun values obtained were -1.2g in the Keith Ryder and -1.Og
in the ‘Nittman racers, Th,ese values represent the invert-
ed-flight load factors since the accelerometer was set to
read l,Og when the airplane was in steady level flight.
The general appearance of the records showed. certain .
distinguishing characteristics between the different p~=
lots and airplanes. For example, the records made in the
Wittman racer showed noticeable regularity of occurrence
and uniformity of value of th6 maximum accelerations, -par-
ticularly in the first part of the record for event 19.
It is quite probable that tilis uniformity in handling the ‘“
airplane is due in a measure to the fact that the pilot
has used a simple indicating accelerometer mounted on the
dash of this airplane for a considerable amount of flying.
The value of such acceleration consciousness on the part
of the pilot is indicated also by the results from the
Chester racer. The pilot in this case had not used an in-
dicating accelerometer, but he had been trying to follow
the recommendations of reference 1 in which it was stated
the best racing turns should be made with a fairly defi-
nite value of maximum acceleration, about 4.75g for a 246
mile per hour airplane. He thus held to fairly uniform
accelerations, though of different values on different
days. The conditions of competition and his physical con-
dition may have led to the different a%solute values on the
two days.
—
These loads may be considered representative of the
loads that a racing type airplane experiences during a
race, They offer little information, however, On the ef-
fect of atmospheric turbulence as the pilots reported the
air.tO be comparatively smooth for all the flights during ‘--”~
which these records were made. In view of the large value
of the accelerations obtained, it seems that only the most
violent of atmospheric disturbances could produce air loads
8 i?.A, C’.A. Technical NO*B ‘53’7 .
c,ompara%le ~ith those experienced during race maneuvers
. .
CONCLUSIONS
The maximum acceleration recorded was 6.2g and the
minimum -lC2g0 Tizose accelerations occurred while the
airplanes were flying at near their maximum speeds~
Langley Memorial Aeronautical Laboratory,
National Advisory Committee for Aeronautics,
Langley Field, Vs., June 6, 1935.
REFERENCE
1. Jennings, W. 0,: I*Cornering lJat Yigh S~eeds.. R. &-M.
No. 1281, British A.R.C., 1930.
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A preliminary determination of normal accelerations on racing airplanes

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