Taste 10—Correlation Coefficients for a Strength
Endurance Index, (% Max. Strength) x (Endurance
Time), Versus Seven Anthropometric Parameters

Elevator Push

Parameter 15 Ib. 30 Ib. 45 Ib.
. 0.2359 0.1194 0.0903
0, 2116 0, 4981** 0.3372
- 0,3463* 0, 4577** 0. 3795*
-~ —0,1606 —0,2186 — 0. 2890
Seat Back Ht.
(% Shoulder Ht.) —0.3663* 0. 5141** 0. 2953
Left Rudder
Parameter 35 Ib. 70 Ib. 105 Ib.
Age. 0. 3267 0. 5052** 0. 2264
Height. ~ —0,2548 —0,3001 —0,3314
Weight. - —0, 0048 0.3702* 0. 1026
Knee Angle_ 0.3192 0. 1248 0.0344
Foot Angle._ —0.3226 —0.0118 0, 2893
Seat Back Ht.
(% Shoulder Ht.) 0, 1452 0. 1234 — 0. 2981
Left Aileron
Parameter 10 Ib. 15 Ib. 25 Ib.
0, 2294 0.0491 0.2106
0, 2081 0. 1476 0. 3303
0.0559 0.1716 0.1370
Elbow Angle -__..- —0.4767** —0, 3338 — 0. 3546*
Seat Back Ht.
0. 2338. 0, 2208

0.3179

(%Shoulder Ht.)

*Significant at 10% level for r 0.338
**Significant at 5% level for r 0.398

(3) Multiple Linear Regression Analysis for
Maximal Strength Data. In addition to deter-
mining whether certain anthropometric variables
were correlated with maximal strength on an
individual basis, it is of interest to determine
how much of the variation in maximal strength
can be predicted, or explained by the set of these
variables (r?).

A multiple linear regression equation for right-
hand elevator push indicated that the variables
of elbow angle, height, seat-back height. weight
and age could explain 29 percent of the varia-
tion in maximal strength, where the variables are
again listed in decreasing order of importance.

(4) Regression Analysis for Load-Endurance
Data. As stated in the introduction, one of the

12

purposes of this study was to define the load-
endurance relationship for pilots operating air-
craft controls. A polynomial regression analysis
was performed for this purpose, using the time
a given level of force was maintained as the
dependent variable and the relative load as a
percentage of maximal strength as the independ-
ent variable. Three data points, corresponding
to performance of each of the three levels of
force on a given control axis, were obtained for
each of the 25 subjects giving a total of 75 data
points for each control axis tested. Prediction
equations were then obtained for endurance time
in terms of relative load for the three control
axes.

In interpreting the predicted curves for the
load-endurance relationships for the three control
axes tested, the fact must be kept in mind
that the subjects were all tested at the same levels
of force rather than at the same relative loads.
This design permitted a wide variation of rela-
tive loads among the subjects under any given
experimental condition and thus the shape of the
individual relative load-endurance curves also
varied, Most individual curves resembled some
type of exponential curve: but, some curves were
nearly linear. In certain cases the three standard
levels of relative load were high as compared to
a given subject’s maximal strength, since the
levels used were a compromise,

The polynomial vegression program used for
analysis was designed to compute linear, quad-
ratie and cubic equations for each set of 75 data
points. n analysis of variance for the regres-
sion equation as compared to the residual vari-
ance was computed for each curve fitted.

The plot of endurance time versus relative load
for elevator push is shown in Figure 8. Although
there is a wide dispersion of points, a definite
relationship between endurance and relative load
can be observed.

The wide dispersion of data points results from
the combining of endurance curves for 25 sub-
jects into one distribution. An evaluation of
the analysis of variance for the regression equa-
tion indicates that either a linear or cubic equation
can be fitted to the data. Since it has been
shown by other investigators that the relative
strength versus endurance function should ap-
proach an asymptote at 15 to 20 percent of maxi-
mal strength, the cubic equation was selected


were not made under conditions simulating actual
flight.

Extensive research has been conducted in the
past to determine the relationship between per-
centage of maximal static strength and endurance
for force exertions involving different muscle
groups. Kroemer (1970) cites E. A. Mueller’s
experiments during the 1930’s as initiating the
original idea of a maximal strength-strength
endurance relationship. Elbel (1949) investi-
gated the relationship between leg endurance
and the force applied to a pedal, while Tuttle,
Janey and Thompson (1950) measured grip-
strength. A decade later Rohmert (1960) per-
formed similar experiments, measuring endur-
ance at various levels of maximum response
strength for different muscle groups. In every
case it was found that, despite individual dif-
ferences in maximum strength, relative loading
eliminated any differences in endurance among

lOO F

756

25-r

RELATIVE LOAD
(Percent of Maximun Strength)
a
{e)

T

subjects. More recently, Caldwell (1964) studied
this relationship for a manual pull on an iso-
metric dynamometer handle and again found
that, with relative loading, individual differences
in endurance were unrelated to differences in
maximal strength. Similar work has also been
done on the relative-load-endurance relationship
by Molbech (1963) and Monod and Scherrer
(1967).

Kroemer (1970) reported that the relationship
between relative strength and strength endurance
had been definitely established by the work of
Elbel, Caldwell, Rohmert and others. This rela-
tionship is shown in Figure 1.

The many variables which enter into a study
of this nature, as demonstrated by the initial in-
flight pilot study, made it necessary to develop
a systematic research program with increasing
levels of sophistication, This study was the
initial step employing a static, ground-based

fe) 1 it
2 4

6 8 10

ENDURANCE TIME (Minutes)

Ficuxe 1,—Plot of Relative Load as a Percent of Maximal Strength Versus

3

Endurance Time in Minutes.



100 +
90

so +
70 3

50

404

30

20 3

RELATIVE LOAD (% of Maximum Strength)
ro)

O Elevator Push
O Left Rudder
AQ Left Aileron

O 30 60 90

4 n 4. 4
+ + +

120 150 180 210 240270 300 330

ENDURANCE TIME (Seconds)

Figure 6-—Polynomial Regression Functions for Strength Versus Endurance Data for Each Control Tested.

rent regulations, may be too high in relation to
the strength capabilities of a portion of the
female pilot population. here is also an indi-
cation that all present general aviation cockpits
do not accommodate the range of seat, wheel and
rudder control adjustment needed by many female
pilots. The use of biomechanical principles to
assess the adequacy of cockpit control layout for
force application is suggested for future aircraft
design. Further, the relative load versus endur-

16

ance curves of other investigators was found
to apply to the tests of endurance, although
there is the need to perform further testing to
explore low levels of relative load versus endur-
ance. Finally, on the basis of these preliminary
findings, it is recommended that more detailed
and comprehensive simulator and in-flight re-
search be conducted on the ability of female
pilots to safely control an aircraft during emer-
gency control conditions.


Tasty 4.—Maximal Static Contractions for Three Aircraft Controls

Elevator Rudder Aileron

Push (lbs) Push (Ibs) Pull Right Left Right Left

Subject No. L. Hand R. Hand (bs) (lbs) (Ibs) (Ibs) (Ibs)
67 74 72 126 175 30 24
59 65 56 178 150 42 30
69 88 71 160 170 27 34
66 50 50 130 120 26 28
69 63 63 192 137 30 30
84 70 87 198 150 -- 38
23 45 60 81 105 30 35
67 63 70 200 190 37 35
60 50 80 195 158 28 25
77 77 59 169 136 39 26
49 70 72 250 153 35 30
122 106 89 220 275 30 32
72 72 65 230 178 31 31
46 66 78 134 136 34 30
68 68 69 148 105 25 32
64 66 94 171 184 37 19
73 76 82 165 275 23 26
74 90 98 225 230 38 30
74 gl AT 120 225 39 41
69 78 80 225 215 36 30
81 110 80 164 250 29 30
88 68 60 160 275 36 45
70 59 59 150 168 23 23
69 57 57 225 182 26 20
66 104 104 230 182 42 29

mind off the arm or leg in use. Subjects were
told how previous subjects had done on this trial
and also how they were performing. An attempt
was made to instill some spirit of competition
among them in order to increase their motiva-
tion to apply force to the control as long as
possible.

During rest periods the subject was free to
move about, smoke, and have coffee or a coke.
Anthropometric data was also taken during these
periods and further discussion of the experiment
took place in order to interest the subjects and
increase their motivation.

IIL. Results and Discussion.

A. Distribution of Maximal Strength Data.

The maximal strength data for the test sub-
jects is listed in Table 4. Mean maximal forces,
standard deviations and ranges are given in
Table 5. The distribution of data was found
to follow a normal distribution for each con-
trol, using the Kalmogoroff-Smirnof test.

Taste 5.—Means,

Standard Deviations, Maxi

imum,

Minimum and Range of Maximal Control Forces

Mean Stand- Maxi- Mini- Range
Max. ard mum mum _— (Ibs)
Foree Dev. (Ibs) _ (Ibs)

Control Axis (bs) (Ibs)

Elevator

Push

(Left Hand) 69 17 122 28 94

Elevator

Push

(Right Hand) 73 18 110 36 74

Elevator

Pull 2 15 104 4787

Right

Rudder 177 43.250 81169

Left

Rudder 178 48.275 96 © 179

Right Aileron 33 6 42 23 19

Left Aileron 30 6 45 19 26



For the endurance trials subjects were presented
three levels of force to maintain for each of
three control axes. The nine experimental con-
ditions were randomized for each subject. Dur-
ing this phase of the experiment a five minute
rest period was allowed between each trial.
Astrand and Rodahl (1970) report that for
steady-state work of moderate intensity this re-
covery period is adequate for most people.

A. Cockpit Model. A wooden box frame con-
structed of 34’ plywood was used for the cock-
pit model. The box was fastened to a 4’ by 8’
base of 34’ particle board for added stability
during the tests. A drawing of the cockpit frame
is shown in Figure 2.

The pilot’s seat was constructed of 34’’ ply-
wood covered with a 2’ thickness of foam rubber
padding. Dimensions of the seat were chosen

Strain gauge mounting on moment arm fixed to frame or

Voltmeter to register rudder forces

Voltmeter to register
elevator and aileron forces

Strain gauge mounting on
rudder pedals

Tracks for aircraft seat

Ficure 2.—View of Cockpit Simulator Used for Strength Tests.

to conform with those of a standard aircraft
seat. The seat was bolted to a steel base fitted
with rollers, and mounted on standard aircraft
tracks fastened to the floor of the box frame.
Six horizontal position adjustments in 1’” incre-
ments were provided, with a distance of 18’
between the leading edge of the seat and the

rudder plates with the seat in the foremost posi-
tion. This distance was chosen to correspond
with that generally found in light aircraft.

A standard aluminum aircraft control wheel
of 10’ diameter was used. Since subjects had
trouble maintaining a proper grip on the wheel,
a layer of masking tape was added to the point



cockpit simulator. This study is to be followed
by studies in a ground-based simulator with full
motion capabilities, and ultimately an in-flight
test program.

In the present study an attempt has been
made to investigate the problem in terms of
maximal strength and strength versus endurance
with the objective of not only defining the
strength capabilities of the female pilot popula-
tion but also of confirming the load-endurance
relationship for this type of task. Once this
relationship is established, further studies of
the pilot strength problem would be greatly
simplified because it would only be necessary to
measure maximal strength for a given maneuver
in any particular aircraft. Endurance times
would be calculated directly from the relative
load-endurance curve and thus the test program
would be simplified considerably.

II. Method.

Maximal voluntary strength (in pounds) and
strength versus endurance (in seconds) for the
operation of rudder, elevator and aileron controls
were assessed.

In measuring the forces, it was necessary to
decide whether the elevator and aileron forces
would be measured for one hand or both hands
on the control wheel. After due consideration,
it was decided that the usual pilot routine of
operating the wheel with one hand would be
used as the task, since the other hand would be
used in operating other controls for many emer-
gency situations where control force is a con-
sideration.

The maximal static effort, usually called a
maximal voluntary contraction (MVC) in the
literature, was measured for the types of control
movement specified in Table 1, where the limb

Tasty 1.—Measures of Maximal Voluntary Effort
Obtained

Control Movement Limb Used

Elevator push Right and left arm separately

Elevator pull Left arm
Right aileron Left arm
Left aileron Left arm
Right rudder Right leg
Left rudder Left leg

used is also shown. Measurement of force Jevels
for both the right and left arms for elevator
push allowed a comparison of strengths to be
made for the two limbs. The trials for strength
versus endurance and the force levels chosen
are shown in Table 2.

Taste 2.—Measures of Strength Versus Endurance
Obtained

Control Movement Force Levels-lbs Limb Used

Elevator push 15
30
45

Right arm

Left rudder 35 Left leg
70
105

Left aileron 10 Left arm
15
25

For the first phase of the experiment, the
measurement of maximum strength was ‘accom-
plished. Each of the subjects was tested on all
control axes, and the order of presentation was
randomized according to the following scheme.
The series of controls to be tested involved four
tests using the left arm, one test using the right
arm and one test for each leg. The order of
testing was randomized separately for the trials
using the arm and the two leg trials. The leg
tests were then interspersed between the left arm
tests in the following patterns and the patterns
were alternated for successive subjects.

Pattern 1: Arm, Arm, Leg, Arm, Leg, Arm

Pattern 2: Arm, Leg, Arm, Leg, Arm, Arm
Using this scheme, no more than two left arm
tests in succession were required. “The measure-
ment for the right arm was made after the other
maximal strength tests had been completed for
each subject. No rest period was allowed be-
tween these tests, other than the time it took
to reset the equipment for the next trial (less
than one minute). Kroemer (1970) states that
fatigue is not a problem for maximal strength
exertions of less than ten seconds in duration
and maximal strength in these tests was exerted
for less than ten seconds in all cases.



a

10.

11.

| Damon, Albert:

REFERENCES

. Asmussen, E. and K. Heebol-Nielson: Isometric Mus-

cle Strength in Relation to Age in Men and Women,
ERGONOMICS, 5 :167-169, 1962.

. Astrand, Per-Olof and Kaare Rodahl: Textbook of

Work Physiology, New York, McGraw-Hill, 1970.

. Caldwell, Lee S.: The Load-Endurance Relationship

for a Static Manual Response, HUMAN FACTORS,
6:T1-79, 1964.

The Human Body in Equipment
Design, Cambridge, Harvard University Press, 1966.

. Dupuis, H., R. Preuschen and B. Schulte: Zweck-

mabige Gestaltung des Schlepper fuhrer Standes,
Max Planck Institutes fur Arbeitsphysiologie, Dort-
mund, Germany, 1955.

. Elbel, Edwin R.: Relationship Between Leg Strength,

Leg Endurance and Other Body Measurements,
JOURNAL OF APPLIED PHYSIOLOGY, 2: 207,
1949,

Gough, N. M. and A. P. Beard: Limitations of the
Pilot in Applying Forces to Airplane Controls.
(NACA-TR. No. 550), 1936.

Hertel, Heinrich: Determination of the Maximum
Control Forces and Attainable Quickness in the
Operation of Airplane Controls, (T.M. No. 583),
NACA: 1930:

Hunsiker, Paul and George Greey : Studies in Human
Strength, RESEARCH QUARTERLY, 28 :109~122,
1957.

Karim, Bonne B.: A Study of Female Pilot Control
Force Capabilities for General Aviation Aircraft.
Master’s Thesis, University of Oklahoma, 1971, Un-
published.

Kroemer, K. H. Eberhard: Human Strength: Termi-
nology, Measurement, and Interpretation of Data,
HUMAN FACTORS, 12 :297-313, 1970.

17

12,

13.

14,

15.

16.

18.

19.

McAvoy, William H.: Maximum Forces Applied by
Pilots to Wheel-Type Controls (NACA Tech. Note No.
623), November 1937.

Molbech, S.: Average Percentage Force at Repeated
Isometric Muscle Contractions at Different Fre-
quencies. Communication of the Danish National
Association for Infantile Paralysis, No. 16, 1963.

Monod, H. and J. Scherrer: The Work Capacity of a
Synergic Muscular Group, ERGONOMICS, 10:329-
388, 1967.

Morgan, M. B. and H. H. B. M, Thomas: Control
Surface Design, JOURNAL OF THE ROYAL AERO-
NAUTICAL SOCIETY, 1945,

Paul, Richard: Evaluation of Control Forces. In-
terim Report, Project No. 69-524-160 A. Federal
Aviation Administration, Oklahoma, City, 1970.

. Rohmert, W.: Ermittlung Von Erholungspausen fuer

Stati Sche Arbiet des Menschen, INTERNA-
TIONALE ZEITSCHRIFT FUER ANGEWANDTE
PHYSIOLOGIE, 18 :123-164(b), 1960.

‘Tuttle, W. W., ©. D. Janney and ©. W. Thompson :
Relation of Maximum Grip Strength to Grip Strength
Endurance, JOURNAL OF APPLIED PHYSIOLOGY,
2:663-670, 1950.

VanOosterom, .: Measurements on the Relation
Between Magnitude and Duration and on the Rate
of Application of the Control Forces Achieved by
Pilots in Simulated Maneuvers (AGARD Report No.
241), 1959.

. Watt, D. N.: Maximum Forces Exerted on a Stick

Type Control Column

1963.

(RCAF Report 63-RD-1),



average, 77% as strong as men. Since this figure
is also supported by several other studies, a
sample population consisting of women pilots
was chosen for this test.

The Aeromedical Certification Branch of the
Federal Aviation Administration has available
data on age, height and weight for all active

airmen. The overall pilot population and the
female pilot population were defined in terms
of these parameters, and an attempt was made
to secure a stratified sample of subjects to fit
the desired population as closely as possible for
each of the parameters. Age, height and weight
statistics for the test subjects are listed in Table 3.

TasLy 3.—Anthropometric Data for Test Subjects

Age Height Weight Upper Arm Lower Arm Upper Leg Lower Leg
Subject No. (yrs) (om) (tbs) (om) (em) (em) (om)
28 167.6 110 27.5 20.2 46.5 30.4
Ad 172.7 144 32.4 25.8 52.8 41.3
20 165.1 110 28.7 22.7 46.0 40.6
18 160.0 123, 32.0 18.1 36.1 39.4
28 177.8 140 34.1 24.8 51.3 45.7
41 167.7 190 30.4 22.8 46,2 43.2
b4 152.4 98 27.8 22.6 48.3 38.1
24 162.5 138 28.4 24,7 43.7 40.6
58 162.5 142 33.6 18.2 44.0 43.2
36 172.7 150 33.0 22.3 45.8 44.5
48 160.0 130 30.4 19.1 42.0 40.0
28 162. 5 115, 33.1 17.8 43.2 41.9
23 175.3 150 30.6 24.8 48.9 43.8
47 162.5 110 28.6 18.3 44,7 38.7
18 167.6 107 30.6 24.5 50.0 44,5
31 165.1 140 30.2 20.2 43.2 42.5
33 167.6 134 28.9 21.1 46.3 41.9
39 170.2 145 20.1 22.7 42.3 42.5
39 175.3 150 31.8 24.0 47.7 46.4
55 162.5 150 32.8 19.6 45.1 43.2
27 167.6 130 31.3 21.9 46.6 42.5
27 165.1 14 31.0 22.5 48.0 43.2
39 161.3 112 30.2 22.7 44.7 41.9
34 160.0 120 30.8 22.6 43.9 40.6
47 157.5 143 28.5 19.6 41.5 38.7

E. Feperimental Routine. Each experimental
session was conducted between the hours of
9:00 a.m. and 5:00 p.m. and lasted from one and
one-half to two hours. Upon arrival, the subject
completed a personal data sheet and then was
seated in the pilot’s chair. She was then asked
to adjust the seat to her normal flying position
and to fasten the safety belt. The purpose of
the experiment was explained and standard in-
structions were given for control operation and
to motivate subjects to perform at their highest
level.

The six trials were then administered in the
random order previously described. Subjects
were repeatedly asked the question, “Can you

do any better?” during the maximal strength
tests.

The procedure for the endurance tests was
explained during a five minute rest period and
then these tests began. After explaining the
voltmeter operation for monitoring force level,
the subject was told to push on the elevator with
her right hand, applying just enough force to
recenter the pointer and then to hold the pointer
steadily on center for a moment before releasing
the control. The subject then received standard
instructions which emphasized that the force
level was to be maintained for as long as possible.

During each trial the subject was engaged in
a running conversation in order to keep her



TECHNICAL REPORT STANDARD TITLE PAGE

T. Report No. 2, Government Accession No. 3, Recipient's Catalog No.
FAA-AM~72-27

4, Title and Subtitle 5. Report Date

A’ PRELIMINARY STUDY OF MAXIMAL CONTROL FORCE July 1972

CAPABILITY OF FEMALE PILOTS 6. Performing Organization Code

7. Author(s) Bonne Karim, M.S., Karl H. Bergey, M.S., 8B. Performing Organization Report No.

Richard F. Chandler, B.S.M.E., A. Howard Hasbrook,
Jerry L. Purswell, Ph.D., Clyde C. Snow, Ph.D.

9. Performing Organization Name and Address 10. Work Unit No.
FAA Civil Aeromedical Institute
P. O. Box 25082 TT. Contract or Grant No.

Oklahoma City, Oklahoma 73125

13. Type of Report and Period Covered

12. Sponsoring Agency Name and Address
Office of Aviation Medicine

Federal Aviation Administration
800 Independence Avenue, S. W. 14. Sponsoring Agency Code
Washington, D. C. 20591

OAM Report

15. Supplementary Notes

Work was performed under Task No, AM-A-72-PRS-52.

16. Abstract
The growing number of female pilots entering the field of civil aviation has

suggested the need for a study of the maximum allowable forces which should be
specified for operating aircraft controls. Therefore, a study was made of the
maximal voluntary forces which a sample of 25 female pilots could exert on each
flight control. Further, the percent of maximal strength versus endurance relation-
ship reported by other investigators was studied for this population in operating
each control. The percent of maximal strength versus endurance relationship was
established and compared with the results of other investigators. The results
obtained indicate a need for further study of the subject in simulated and actual
flight.

17. Key Words 18, Distribution Statement
Female pilots, Civil aviation, Control Availability is unlimited. Document may be
forces, Aircraft design released to the National Technical Informa-

tion Service, Springfield, Virginia 22151,
for sale to the public,

19. Security Classif. (of this report) 2. Security Classif. (of this page) Zi No. of Pages | 22. Price

17
Unclassified Unclassified $3.00

Form DOT F 1700.7 (8-59)



turning a wheel to the right with the left hand,
the arm is free to be fully abduced, while a turn
of the wheel to the left with the left hand allows
no room for arm abduction since the arm is
already at the subject’s side.

The review of maximal control forces allowed
by current regulations indicates that elevator
and aileron levels allowed are higher than 50
percent of the subjects could attain, while the
allowed force levels for rudder could be attained
by all but six subjects.

B. Correlation Analyses. (1) Maximal
Strength Data. The correlation of maximal
strength data with the set of anthropometric
parameters is shown in Table 6. No significant
correlations were obtained for the personal vari-
ables of age and height on any control axis. A
significant negative correlation (r=—0.52) was
obtained for weight versus maximal strength on
left aileron, and was not ‘correlated significantly
with forces on any other control axis.

TawuE 6.—Correlation Coefficients for Maximal Strength
Versus Seven Anthropmetric Parameters

Maximum
Push Maximum — Maximun
Parameter Right Hand Left Rudder Left Aileron
Age 0.273 —0.102  —0. 161
Height 0.279 0. 186 0.016
Weight 0.096 0.158 0. 519**
Elbow Angle 0.342% LL —0.170
Knee Angle -  0,4128*
Foot Angle - 0.192
Seat Back Ht
as % of
Shoulder Ht =0.125 0.377" = —0. 405

*Significant at 10% level-for > 0.338
**Significant at 5% level for > 0.398

A. significant correlation (r=0.34) was ob-
tained between elbow angle and maximal elevator
push, indicating better performance at the larger
angles (185-160 degrees). Knee angle also cor-
related significantly (r=0.41) with maximal
strength on left rudder.

The correlation between elbow angle and maxi-
mal strength was significant (r=0.34) for eleva-
tor push, but was insignificant for left aileron.

Knee angles from 89 degrees to 119 degrees
were measured for the test subjects and these

10

angles are in the range of increasing force
capability for leg extension given by Dupuis,
Preuschen and Shulte (1955). The correlation
between foot angle and maximal left rudder
strength was insignificant.

(2) Endurance Data. The data from the
endurance trials is presented in Tables 7, 8, and
9 for elevator push, left rudder and left aileron
respectively. The tables give the time in seconds
that each level of force was maintained and the
percentage of each subject’s maximal force
measured on the specified control represented by
this level of force. For example, referring to
Table 7, subject mumber four held a 15 pound
elevator push for 247 seconds. Her maximum
right-handed push is listed in Table 4 as 74
pounds, so the 15 pound force represented 20%
of this subject's maximum for elevator push.
Likewise she held 30 pounds (40% of maximum)
for 65 seconds and 45 pounds (61% of maximum)
for 14 seconds.

A strength endurance index was computed
for each subject and each experimental condition

Taste 7.—Strength Endurance Data for Elevator Push

15 Ib. 30 Ib. 45 lb.

Subj. Time % Time % Time %
No. (sec) Max. (sec) Max. (sec) Max.

247 20 65 40 14 61
300 34 120 51 85 68
145 17 60 34 18 51
213 30 28 60 21 90
300 24 136 48 30 72
300 21 163 42 63 63
239 33 58 67 17 99
166 24 15 48 17 72
126 30 90 60 54 90
300 19 185 39 43 58
300 21 64 43 25 64
300 14 300 28 103 42
300 21 187 42 78 63
169 23 22 46 29 68
193 22 62 44 38 66
300 23 70 44 61 66
300 20 59 39 3 59
300 17 107 33 61 50
300 16 190 33 51 49
300 19 105 38 61 58
300 14 120 27 59 41
205 22 67 44 60 66
117 27 73 54 39 80
103 15 94 29 10 44
300 21 61 42 i 63



The wide range of strength capabilities can
be attributed in part to the inherent strength
characteristics of the subjects, but a variation in
strength was also observed as a function of seat
position,

Past experiments in the field of maximal
strength measurement have generally been de-
signed so that all subjects were seated in the same
position relative to the point of force applica-
tion. Such a design required that the angles
at the subject’s elbow and knee be kept constant
at certain predetermined values. The seat posi-
tion was adjusted to achieve these angles, rather
than testing in the subject's preferred position.
Since the present study was conducted to predict
the actual strength capabilities of a pilot in
flight, it was decided to allow each subject to
adjust the seat to the position in which she nor-
mally flies. This design placed every subject
in a different position relative to the controls
and thus gave the subjects different strength
capabilities in terms of the biomechanics of force
exertion. In light of this fact, the maximal
strength data represents the strength capabilities
of female pilots in the posture in which they
normally fly and not what they might be able to
do in any given optimal or minimal posture.

The results of this study indicate that push
strength increases as the elbow angle increases
for the positions tested. This result agrees with
Caldwell (1964), who found that an elbow angle
between 135 and 160 degrees provided optimal
strength capabilities in arm extension against
an isometric dynamometer handle. Gough and
Beard (1936) and others have also found that
elevator push strength increases with increasing
distance between the elevator control and the
pilot’s seat.

While it might seem that a recommendation
should be made for seating pilots so that the
desired elbow angle is achieved, this study demon-
startes that other problems arise. All the test
subjects adjusted their seat position relative to
the wheel so that they could achieve full rudder
control, if possible. Since most general avia-
tion aircraft have fixed rudder pedals, the elbow
angle is determined by this seating position to
achieve rudder control. Some subjects were also
found to fly regularly with a pillow behind their
back in order to reach the rudder control, since
most general aviation aircraft do not provide

an adequate range of adjustment even when the
elbow angle is compromised.

No information is available reporting the opti-
mal elbow angle for maximal aileron strength;
however, Damon (1966) states that an elbow
angle of 90 degrees is most favorable for the
exertion of torque on a wheel control. Elbel
(1949) measured maximal leg strength capabil-
ities for the exertion of force on aircraft rudder
pedals and used knee angles between 106 and
116 degrees and foot angles between 55 and 65
degrees for his subjects. His assumption that
angles in these ranges were optimal was based
on extensive consultation with heavy bomber
pilots. More recently, Dupuis, Preuschen and
Schulte (1955) reported a knee angle of approxi-
mately 150 degrees as optimal for the exertion
of force on a pedal control.

Since the elbow and knee angles for force
application were not controlled, but allowed to
vary with the subject’s preference, a correlation
analysis as reported in the next section was per-
formed to investigate their relationship to maxi-
mal strength.

Maximal strength measurements for elevator
push were taken for both the left and right
hands and provide for an interesting comparison
of data, The mean maximal strength for the
left hand was 69 pounds with a standard devia-
tion of 17 pounds, while the mean right hand
push strength was 73 pounds with a standard
deviation of 18 pounds. Since one subject was
not right handed, the slightly higher value
for the right hand push agrees with Hunsicker’s
(1957) statement that right-handed subjects are
slightly stronger with the right hand than with
the left.

The rudder forces which were recorded for
both the left and right leg also provide an in-
teresting comparison of data. The mean maxi-
mal left rudder force was 178 pounds with a
standard deviation of ‘48 pounds, while the mean
force for right rudder was 177 pounds with a
standard deviation of 43 pounds. This similarity
between strength capabilities for the left and
right legs supports Watt’s (1968) contention
that there is no difference in leg strength between
the two legs.

The mean maximal force for right aileron was
slightly greater than that for left aileron due
to the biomechanics of the movement. When



of grip midway during the experiment. The
wheel was pinned to a control column which, in
turn, was fastened to a moment arm at the far
end of the frame. The moment arm provided
a mounting for the strain gauges used to measure
aileron and rudder forces. The wheel was aligned
in the neutral position during all tests and was
essentially immobile, although the elasticity of
the measuring system permitted some slight
deflection.

Two 6 x 8%” x¥’" steel plates, welded ver-
tically to horizontal 10’ x5’’x 14’ steel base
plates, were bolted to the floor to serve as rudder
pedals. Strain gauges mounted on the plates
were used to measure force levels. A 1’ steel
pipe mounted 114’” from the top of each plate
was used as the point of force application.
Again, only static loading conditions were
studied and the ‘two rudder pedals were im-
mobile. With this type of pedal arrangement
it was only possible to measure components of
force normal to the pedal surface. However,
with the type of pedal arrangement in an actual
aircraft, the only effective force on the pedal is
still that which is normal to the pedal surface.

B. Monitoring Equipment. Tn order to con-
duct the endurance testing, it was necessary to
provide a visual display for the subjects’ refer-
ence in maintaining the required force level. This
system was an addition to the usual chart record-
ing system and bridge circuits employed for
recording strain gauge data.

The visual display consisted of two voltmeters
connected in parallel with the chart recorder.
The subject was required to exert a given level
of force on a specified control axis by neutraliz-
ing a preset deflection on the appropriate meter.
The correct amount of deflection corresponding
to the desired force was determined prior to each
trial using the calibration system described under
Accessory Equipment. The meters were attached
to the cockpit frame as shown in Figure 2. The
left meter moved up and down registering: eleva-
tor forces, while the right meter moved right or
left registering aileron or rudder forces, depend-
ing upon which force was being measured. This
design was chosen so the direction of moyement
of the meter pointers would be consistent with
that of the equivalent aircraft instruments. Each
meter face was marked with a center point and
a linear scale. A third meter, also connected

in parallel with the chart recorder was attached
to the physiograph for use by the experimenter.
This meter was used for reference when deter-
mining the amount of deflection required for a
given level of force and for setting this deflection
on the subject’s meter.

C. Accessory Equipment. A winch was
mounted on a wooden platform with a height
adjustment provided to place it in line with
either the elevator or rudder controls. A spring
scale was then attached between the winch line
and the appropriate control. The scale was at-
tached directly to the end of the control column
for calibrating elevator forces and to cables con-
nected to the rudder pedals for calibrating these
forces. This arrangement enabled the experi-
menter to exert force on the desired control by
means of the winch and to read the force being
applied on the scale.

The spring scale was calibrated along its full
range using known lead weights and was found
to be accurate within one pound. Calibration
was performed before the test. program, midway
during the program and at the end of the pro-
gram. Calibration for elevator and rudder con-
trols was accomplished by matching deflections
on the recording paper with deflection made by
applying known forces with the winch-scale
arrangement described above.

Calibration for the aileron force was per-
formed prior to each test session by clamping
& moment arm to the control wheel and then
placing known lead weights on the beam. A
twenty inch moment arm was used, with a weight
of x pounds at this distance being equated to
4x pounds at the rim of the wheel. A range of
0-40 pounds was used for aileron calibration with
readings made on the recording paper for every
five pound increment of force.

A standard set of Gneupel measuring equip-
ment was used for the various anthropometric
measurements.

D. Subjects. Previous anthropometric studies
have shown that strength is dependent on age,
sex, height and body type. Hunsicker and Greey
(1957) report that body build is closely related
to strength. Asmussen has extended this study
to women in general, and reports that, after cor-
rection for gross body size, women are, on the


cially when it is noted that 12,000 female pilots
are now licensed, led to a joint study of pilot
control forces by the University of Oklahoma
and the Civil Aeromedical Institute of the Fed-
eral Aviation Administration, The study in its
entirety is covered in a Master's thesis by Karim
(1971). This OAM Report provides a condensa-
tion of that study.

A. Review of Previous Research. The need for
a study of the strength capabilities of pilots with
respect to aircraft controls has been recognized
for many years. However, little work has been
done in this field with the objective of produc-
ing results which could be used to specify maxi-
mum control force limits for general aviation
aircraft.

Early studies were concerned primarily with
testing the effects of different variables on a
pilot's maximal force exertion on aircraft con-
trols. Hertel (1930) investigated arm strength
for push and pull on stick controls, using 12
“athletic pilots and engineers” in a ground-based
aircraft cockpit. Measurements were taken with
both hands, with each hand alone and with or
without a restraing harness. An attempt was
made to study the influence of fatigue on a pilot's
performance, but measurements of force magni-
tude over a period of time were inaccurate. Two
additional studies were made by the National
Advisory Committee for Aeronautics in the
1930's, both using two male test pilots and a
ground-based cockpit mock-up. Gough and Beard
(1936) investigated the effect of control position
relative to the pilot’s seat and attitude of the air-
craft on the maximal forces exerted by subjects
on stick and rudder controls, Measurements were
taken for the right hand and right foot only with
the subjects restricted by a heavy aerobatic har-
ness; they concluded that the results of the test
were not valid for actual flight conditions be-
cause the accelerating forces normally encountered
in actual flight for the attitudes studied did not
exist in this ground-based test. McAvoy (1937)
made a similar study, looking at the effects of
wheel position relative to the seat, wheel size,
hand grip on wheel and use of a restraining
harness, on a pilot’s ability to exert force on a
control wheel. The results of both these studies
were not applicable to any general pilot popu-
lation since only two subjects were used. They
did establish optimal control positions for maxi-

mal force exertion but told nothing about the
amount of force a reasonable percentage of pilots
should be expected to exert.

A second series of tests was begun by the
National Aeronautical Research Institute (NLL)
in Amsterdam in the early 1940’s, The objec-
tives of this program were to test a statistically
valid sample of the pilot population and to
achieve reliable measurements for the magnitude
of forces exerted. This work is summarized in
a report of a 1958 NLL study by VanOosterom
(1959). VanOosterom measured optimal control
positions for maximal force exertion and maxi-
mal force exertion over four different time in-
tervals, using 27 civilian and military pilots
strapped into a cockpit model. Measurements
were made for the right hand only.

Only two sources were found (other than
regulations currently in use) which actually
recommend specific control forces that a certain
percentage of pilots can be expected to maintain.
Morgan and Thomas (1945) included a table giv-
ing data for the “greatest all-out effort the aver-
age pilot is capable of exerting with both hands
for a very short while,” “the maximum force
we can demand of him for a short while with
one or both hands,” and the “greatest force he
cares to exert for a short while with one or both
hands.” The paper states that these data were
drawn from flight tests of a wide variety of
airplanes; however, no information on these tests
is available. We know nothing about the physi-
eal characteristics of this “average pilot” or the
exact length of the time mentioned for force
exertion,

A study by Watt (1963) of the RCAF In-
stitute of Aviation Medicine, Toronto, recom-
mends control force limits supposedly applicable
to 90% of the American adult male population;
however, no justification is given for this figure.
Watt studied the push-pull forces exerted on a
control column by 20 male subjects strapped into
a pilot's seat mock-up. Measurements were taken.
for both hands and each hand alone. No data
are given for rudder controls.

It is evident that no accurate conclusions can
be made from the above studies about the physi-
cal capabilities of pilots in the exertion of force
on aircraft controls because the samples used
were not representative of any general pilot popu-
lation and accurate measurements of force exerted


6Ootf ss 4
40+ .
30F te “

20 4 .

10 4

RELATIVE LOAD (% of Maximum Strength)
a
{e)

0 30 60 90 120 150 180 210 240 270300
ENDURANCE TIME (Seconds)

Ficvre 3.—Plot of Relative Load Versus Endurance Time for Elevator Push.

as the most suitable function. The prediction
equation for elevator push versus time can be
expressed as follow:

time (sec.) =474.44—14.13647 (relative load,
% of max, strength) +0,14431 (relative load,
% of max. strength) *—0.00046 (relative load,
% of max, strength)*.

The five significant digits are shown because
of the small magnitude of the cubic term.

The predicted load-endurance relationship for
left rudder is plotted in Figure 4. It is apparent

13

that the relationship shown has a more constant
slope than for elevator push, which agrees with
the load-endurance relationship given by Cald-
well (1964). In this case, the linear equation
fitted and the cubic equation fitted are similar,
following a relatively constant slope.

The predicted linear equation for relative load
on left rudder is as follows: *

time (sec.) =41.880—3.228 (relative load, %
of max. strength)

The final predicted polynomial equation is as
follows:



=

Zio r

o .

wH 90T .

5 80

£ .° .

o 70T : ° :
= . .

S 60fr ° e ° ° e e
° e °
* sot - . ;
2 40 - .° -°

Oo e ee 4
— 304 . . ,
> j
E 20+ ° 3
<q

+ 10+

lJ

x . 1 4. . 1 4 + 2 rm rm

0 30 6

90 120 150 180 210 240270 300

ENDURANCE TIME (Seconds)

Fievre 5.—Plot of Relative Load Versus Endurance Time for Left Aileron.

ing that the force levels chosen for endurance
testing were not low enough to permit the sub-
jects to reach an asymptote, and thus the curves
do not reflect this segment of data. However,
the results are useful within the range shown,
and do demonstrate that an exponential relation-
ship does exist between relative load and endur-
ance, as shown by other investigators. The wide
dispersion in the data further indicates the
hazards of testing only a few subjects as has
been done in the past, without taking into ac-
count the range of performance which specifica-
tions of allowable force level must include.

15

IV. Summary.

This study was conducted to examine the con-
trol forces which could be produced by a small
population of female pilots. The control forces
were in terms of a few seconds maximal effort,
and a percentage of maximal effort which was
held as long as possible. A ground-based,
wooden “cockpit” equipped with strain gauges
to measure elevator, aileron and rudder forces
was used to test a selected sample of 25 female
pilots. The results obtained indicate that maxi-
mum allowable force levels, as permitted by cur-



A PRELIMINARY STUDY OF MAXIMAL CONTROL FORCE CAPABILITY
OF FEMALE PILOTS

I. Introduction.

During flight the pilot of a light aircraft ex-
periences a number of different conditions under
which he must apply forces to the aircraft
controls. In some instances an application of
force for only a few seconds is necessary to per-
form a maneuver or to bring the aircraft under
control. In others it may be necessary for the
pilot to exert forces over an extended period of
several minutes in order to maintain control of
the aircraft. These forces may be exerted on
one control alone or on various combinations of
controls simultaneously. At certain times they
may be small while in other situations applica-
tions of very large forces which are close to the
limits of the pilot’s maximal strength may be
required.

The present regulation specifying control force
limits for the type of light aircraft flown by
general aviation pilots is given in Part 23, Sub-
part B, Section 23.143, of the Federal Aviation
Regulations (FAR 23.143). This regulation uses
the words “temporary” and “prolonged” to
designate between the two time periods of force
application, but does not specifically define them.
Furthermore, the regulation does not state
whether one or two hands are to be used on the
controls to maintain the specified forces. Some
critical flight situations require the use of only
one hand on the controls. No information is
available concerning the origin of the control
force limits specified by this regulation, thus we
cannot judge their validity with respect to the
physical capacity of the general aviation pilot
population or a realistic flight situation.

Previous studies by VanOosterom (1959) have
shown that a pilot’s ability to exert force on an
aircraft control decreases with the amount of
time he is required to maintain that foree. As
mentioned above, in some instances a pilot is

required to exert force for only a few seconds
while in others force must be exerted for several

minutes, thus properly defined time limits for
force application are essential to the specification
of maximum allowable control forces. In a
recent study, Paul (1970) interpreted “tem-
porary” to mean less than 15 seconds and “pro-
longed” to mean a period “which is long, several
minutes, in comparison to a temporary, several
seconds period.” In the present study “tempo-
rary” forces were measured in terms of each
subject’s maximal effort on any given control.
“Prolonged” forces were measured by having the
subject maintain several predetermined levels of
force for as long as possible. These levels of
force were approximately 25%, 50% and 75% of
each subject’s maximum for any given control
axis.

Because of the lack of clarity of one or two
hand use and length of time for “temporary”
and “prolonged” force application in the present
regulations, a need was expressed to develop a
program of strength tests which would accurately
measure the strength capabilities of a pilot in
flight. Preliminary in-flight studies were con-
ducted by Paul (1970) using women pilots as
subjects. These studies seemed to indicate that
the forces specified by FAR 23.143 might be
excessive for some women pilots, as well as pos-
sibly for some male pilots over age 35. In addi-
tion, Paul compared FAR 23.143 with two
similar regulations, the British Civil Airworthi-
ness Regulation, BCAR K2-6 3.4, and the U.S.
Military Regulation, MIL-F-8785 B, “Flying
Qualities for Piloted Airplanes,” and found that
the control forces specified in FAR 23.143 are
generally higher than those specified by these
other regulations. In particular, the control
forces specified by BCAR K2-6 3.4 and MIL-F-
8785 B are substantially lower than those speci-
fied by FAR 23.143 for aileron and elevator.
Rudder forces are approximately equal for the
three regulations.

Recognition of possible inadequacies in the
present. standards for pilot control forces, espe-





TasBLe 8.—Strength Endurance Data for Left Rudder

105 Ib.

35 Ib. 70 Ib.

Subj. Time % Time % Time %
No. (sec) Max. (sec) Max. (sec) Max.

235 20 62 40 30 60
300 27 145 47 107 60
300 21 90 41 27 62
300 29 110 58 43 87
300 26 100 51 25 77
300 23 300 46 254 70
300 33 300 67 141 99
300 18 127 37 95 55
300 22 300 44 105 66
300 25 300 51 41 77
300 23 208 46 66 69
300 17 300 34 300 53
300 20 264 39 176 59
300 26 218 52 112 78
300 33. 300 67 3 99
300 19 300 38 85 57
300 13 300 25 82 33
300 15 78 30 161 46
300 16 192 31 105 47
300 16 300 33. 300 49
300 14 151 28 196 42
300 13 300 25 99 38
300 21 184 42 70 61
300 19 108 38 47 58
300 19 300 38 300 58

for use in the correlation analysis. This index
was eqaal to the product of endurance time
in seconds and the relative load (percent of each
subject’s maximum) represented by the level of
force maintained in each experimental condition.
Again referring to Table 7, the strength endur-
ance index for subject number four for a 15
pound elevator push would be 247 multiplied by
0.20, or 49.4. Likewise the index for 2 30 pound
push would be 65 multiplied by 0.40 or, 26.0.
Correlation coefficients’ were then computed for
the strength endurance index versus the an-
thropometric parameters of age, height, weight,
elbow angle, knee angle and foot angle. In
addition, another parameter called seat-back
height was correlated. The results of this an-
alysis are presented in Table 10. This parameter
is computed by expressing seat-back height as a
percentage of seated shoulder height.

Both weight and seat-back height were signifi-
cantly correlated with endurance for the 15
pound elevator push. For the 30 pound push,
height, weight and seat-back height all cor-

11

related significantly with endurance. The signifi-
cance of seat-back height can probably be ex-
plained by considering this parameter as a
measure of the torso support provided the sub-
ject during the endurance trial. Only weight
correlated significantly with endurance at the
45 pound level of force.

The endurance index for left rudder did not
correlate significantly with any of the anthropo-
metric parameters except age (r=0.51) and
weight (r=0.87) at the 70 pound of rudder
force.

The endurance index for left aileron correlated
significantly (r= —0.48) with elbow angle for a
10 pound aileron force. The data indicate that
subjects with smaller elbow angles were capable
of greater left aileron endurance at this level of
force than those with large elbow angles. Cor-
relations with other variables were significant
at this level of force as were all correlations at
the 15 pound left aileron force. The only signifi-
cant correlation at the 25 pound level of force
was again between elbow angle and the endur-
ance index (r=—0.35).

Taste 9.—Strength Endurance Data for Left Aileron
Subj. Time % Time % Time %
No. (sec) Max. (sec) Max. (sec) Max.

-- AT 19 25 57 9 96
295 30 85. 50 17 67
65 29 36 44 10 74

79 36 145 54 1 89
300 33 148 50 120 67
66 -- 23 -- 24 _
300 28 30 43, 7 71
70 29 40 45, 7 7
300 40 133 60 84 99
300 38. 55 58 7 96
300 33 26 50 17 83
121 31 64 AT 0 78

300 32 89 48 28 81
75 33 23 50 24 83

300 31 39 47 9 78
122 40 72 60 2 99
300 38 76 58 9 96
108 33. 52 50 22 90
7 24 58 37 24 61
202 33. 123 50 9 83.
122° 33 55 50 18 83
162 22 53 33 36 55
69 43 44 65 0 109
72 40 48 60 4 99
80 34 62 52 9 86



lOOT e

RELATIVE LOAD (% of Maximum Strength)

0 30 60 90 120!
ENDURANCE TIME (Seconds)

Ficure 4,—Plot of Relative Load Versus Endurance Time for Left Rudder.

time (sec.) =387.3550—5.55406 (reative load,
% of max. strength)
+0.02930 (relative
strength)?

—0.0007 (relative load, % of max. strength)*

load, 9% of

max,

The load-endurance relationship for left aileron
is shown in Figure 5.

The relationship is more similar to that ob-
tained for elevator push than for rudder force.

The final polynomial prediction equation for

the relative load-endurance relationship on aileron
is as follows:

14

50

° e
°, . ee
30 ° “. ° ° :
e? ° °
20 T e e ee
Iio+
+ + + + + + + + +

——
180 210 240270 300

time (sec.) =298.54698 —4.86167 (relative
load, % of max. strength)

+0,00330 (velative load, % of max,
strength)?

0.00017 (relative load, % of max.
strength)*

The predicted polynomial equation for each
control axis has been plotted in Figure 6. It
can be seen that the prediction equations for
rudder and aileron indicate an intercept, which
is not in keeping with the results of other inves-
tigators. This result can be explained by observ-