,

REFERENCES

1, Asmussen, E., and K, Heebol-Nielson: Isometric
Muscle Strength in Relation to Age in Men and
Women, ERGONOMICS, 5:167-169, January 1962.

2, Birmingham, H. P. and F. V. Taylor: A Human
Engineering Approach to the Design of Man-
Operated Continuous Control Systems, Naval Re-
search Laboratory, Report 4338, 1954.

8, Caldwell, Lee 8: The Load-Endurance Relationship
for a Static Manual Response, HUMAN FACTORS,
6:71-79, 1964.

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

5. Hertel, Heinrich: Determination of the Maximum
Control Forces and Attainable Quickness in the Op-
eration of Airplane Controls, T. M. No. 583, NACA,
1930.

6,"Hunsicker, Paul and George Greey: Studies in Hu-
man Strength, RESEARCH QUARTERLY, 28:102-
122, May 1957.

7. Hunt, Darwin P,: The Effect of Precision of Infor-
mational Feedback on’.Human Tracking Perform-
ance, HUMAN FACTORS, 3:77-85, 1961.

8. Karim, B, K. H. Bergey, R. F. Chandler, A. H.
Hasbrook, J. L. Purswell, and C. C. Snow: Prelimi-
nary Study of Maximal Force Capability of Female
Pilots, FAA Office of Aviation Medicine Report No.
72-27, 1972.

9. McAvly, William H.: Maximum Forces Applied by
Pilots to Wheel-Type Controls, NACA Tech. Note
No. 628, November 1937.

10. Monod, H.

1

p

12.

13.

14,

16.

17.

18.

. Rohmert,

Contribution a L'etude du traveul
Statique, Paris: These Medicine, 1956.

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

Morgan, C. T., J. 8. Cook, III, A. Chapanis, and
M. W. Lund: Human Engincering Guidé to Equip-
ment Design, New York; McGraw-Hill Book Com-
pany, Inc., 1963,

Paul, Richard: Evaluation of Control Forces, In-
terim Report, Project No. 69-524-160A, Federal
Aviation Administration, Oklahoma City, 1970.
Rogers, James C.: Discrete Tracking Performance
with Limited Velocity Resolution, HUMAN FAC-
TORS, 12:331-339, 1970.

W.: Ermittlung Von Erholungspausen
Fuer Statische Arbeit des Menschen, INTERNA-
TIONALE SEITSCHRIFT FUER ANGEWANDTE
PHYSIOLOGIE, 18:123-164(b), 1960.

Scheffer, J. C. and A. J. Marx: Measurements of
Forces Which Dependent on the Time of Exertion
Can Be Applied to the Controls of an Aeroplane by
a Pilot, Rept. V 1255 NARI, Reports and ‘Transac-
tions NLL, Amsterdam, Vol. XI, 1941.

VanQosterom, T.: 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, RCAF Rept. 63-RD-1, 1963.



nine trials were then given in a counterbalanced
order-as described earlier.

III. Results and Discussion.

The presentation of results has been divided
into four sections:

1. Recorded data from the test subjects.

‘2. Correlation analysis to determine the rela-
tionship between endurance time and anthropo-
metric and other variables.

3. Stepwise multiple linear regression to de-
velop prediction equations for endurance time
based on anthropometric and other variables.

4, Polynomial and exponential regression anal-
ysis for each control to examine the relationship
between force exerted and endurance time.

Recorded Data. Tables 2, 3, and 4 shown in
Appendix A present the data recorded for the
time each subject maintained each of the three
levels of force on the elevator, rudder, and
aileron trials, as well as a summary of endurance
times recorded for each of the nine test condi-
tions, From these tables some comparisons can
be made between the test data and the control
limits contained in FAR 23.148 now in effect for
general aviation aircraft,

The term “temporary” in FAR 23.148 has been
recently clarified by the Flight Test Branch as a
period of up to 20 seconds in control of pitch and
rol], and up to 30 seconds in control of yaw.
Because the ability of a pilot to exert force on a
control diminishes over time, the “temporary”
forces specified in FAR 23.143 should then be
compared to forces capable of being maintained
for a full 20 seconds in the case of pitch and
roll, and for a full 80 seconds in the case of yaw.

In the elevator strength endurance tests the
highest level of force maintained was 55 pounds,
compared to a force of 75 pounds specified in
FAR 23.143 for “temporary” application. In
these tests 14 of 24 subjects, or 58 percent, could
not maintain a 55-pound pull on the wheel’ for
20 seconds. This compares with data from
Karim (1972) in which study 7 of 25 subjects,
or 9 percent, could not maintain an elevator
push for 20 seconds at the 45-pound force level.
These studies suggéSt that this current control
limit is too high for a sizeable portion of female
pilots.

In the rudder strength endurance tests the
highest level of force maintained was 150 pounds,

the same as that specified in the regulation. In
these tests 5 of 94 subjects, or 21 percent, could
not maintain a 150-pound force on the right
pedal for 30 seconds. However, all 24 subjects
were able to maintain the 130-pound force for
30 seconds. These results compare to the results
from Karim (1972) in which study 3 of 25 sub-
jects, or 12 percent, could not maintain a left
rudder force of 105 pounds for 30 seconds. Sub-
jects who participated in both studies reported
that the seat in this study offered more support
than that used in the 1972 study. Also, subjects
in this study were allowed to lift the buttocks
from the seat while pushing on the rudder; this
was not allowed in the study by Karim.

In the aileron strength endurance tests the
highest level of force maintained was 22 pounds,
considerably below the force of 60 pounds speci-
fied in the regulation. In these tests 4 of 24, or
17 percent, could not maintain a 22-pound down-
ward puli with the left arm for 20 seconds. These
data compare with data from Karim (1972):
17 of 28 subjects, or 68 percent, could not main-
tain a 25-pound left aileron force for 20 seconds,
although all 25 subjects did maintain a 15-pound
force for 20 seconds. Since 17 percent of the
subjects in this study were unable to maintain
a force less than half the current control force
limit, this control force limit seems to be far too
high for a sizeable portion of female pilots.

Correlation Analysis. Correlation analysis
was used to determine what effect the anthropo-
metric and other parameters had on the data
obtained from the nine test conditions. Correla-
tion coefficients were computed for the time a
force was maintgined in each of the nine test
conditions versus the anthropometric parameters
of age, height, weight, elbow angle, angle of the
lower arm above horizontal, knee angle, foot
angle, seat-back height, and seat-bottom length.
The results of this analysis are presented in
Table 5 of Appendix A. A correlation coefficient
greater than 0.271 was required for significance
at the 10 percent level of confidence; a correla-
tion coefficient greater than .347 was needed for
significance at the 5 percent level of confidence.

It should be remembered that each subject in
this experiment adjusted her seated position in
the simulator to that closest to her normal flying
position. In most of the past research on maxi-
mum strength the subject’s seated position was

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In contrast the British Civil Air Regulation lists |

the following maximal contro! force specifications for

temporary application.

BRITISH CIVIL AIRWORTHINESS REQUIREMENTS
SECTION K SUB-SECTION K 2 - FLIGHT

K2-6 HANDLING ~ GENERAL

3.4 Excessive Control Forces. The assess-
ment of whether a control force is excess-—
ive, apart from a maximum figure which may
be prescribed, may be influenced by the ease
of applying it and the general level of con-
trol forces for the aeroplane. In the case
of the aileron and elevator control, forces
will, in any case, normally be regarded as
excessive if, at the specified air speed,
they cannot readily be applied with one

hand for the appropriate period without
retrimming.

NOTE: The maximum forces likely to be
accepted for short period application, with
the controls in a favourable position,
arei---

{a) for elevator control, 50 1b. for a
wheel control, or 35 lb. for a stick
control;

(b) for aileron control, 20 1b. for a
stick control, or 30 lb. applied at
the rim of a wheel control;

(c) for rudder control, 150 lb.

MIL-F-8785 B has four separate classifications of
aiypplanes. Class 1 airplanes are small light airplanes

similar to hose covered under FAR 23.143. The control

force specifications for military aircraft are listed

Th

cc

ur

according to class, flight maneuver and level of performance.

20



a

STUDY OF CONTROL FORCE

I, Introduction.

During flight a pilot experiences 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 perform 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 applications of very large forces 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 23.148, of the Federal Aviation
Regulations (FAR 23.143). This regulation
uses the words “temporary” and “prolonged” to
designate the two time periods of force applica-
tion, but does not specifically define them, nor
does the regulation state whether one or two
hands are to be used on the controls to maintain
the specified forces, Some critical flight situa-
tions 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 valid-
ity with respect to the physical capacity of the
general aviation pilot population or to a realistic
flight situation. .

Previous studies by VanOosterom (1959) have
shown that a pilot’s ability to exert force on an
aireraft control decreases with the amount of

gtime he is required to maintain that force. In a
previous study. of female pilot endurance by
Karim (1972), “temporary” forces were meas-
ured in terms of each subject’s maximal effort
on any given control. However, the term “tem-
porary” has since been clarified by a memoran-
dum (15 February 1972) from the Flight Test

LIMITS FOR FEMALE PILOTS

Branch, Flight Standards Service of the Federal
Aviation Administration as a period of up to
20 seconds for control of pitch and roll and up
to 80 seconds for control of yaw. In the present
study selected levels of force were presented to
each subject and the subject attempted to main-
tain the aircraft in a safe attitude for as, long
as possible. These levels of force were based on
the findings of Karim (1972) and chosen to pro-
vide periods of force application from several
seconds to seven minutes.

The lack of clarity and validity in the present
FAR 23.143 requirement was recognized by the
Flight Standards Service of FAA and the need
was expressed to develop a program of strength
tests that would accurately measure the strength
endurance capabilities of a pilot in flight. Data
from preliminary in-flight studies by Paul (1970)
and ground-based studies by Karim (1972) sug-
gested that maximal forces specified by FAR
23.143 were too high for most female pilots.
Paul compared FAR 23.143 with two similar
regulations: the British Civil Airworthiness
Regulation, BCAR K2-6 3.4, and the U.S. Mili-
tary Regulation, MIL-F-8785 B, “Flying Quali-
ties for Piloted Airplanes,” and found that the
control forces specified in FAR 23.143 are gen-
erally higher. The control forces specified by
BCAR K2-6 3.4 and MIL~F-8785 B are sub-
stantially lower than those specified by FAR
23.148 for aileron and elevator; rudder forces
are approximately equal for the three regula-
tions. All three regulations are shown in Ap-
pendix B of this report.

The need for a study of strength endurance
capabilities of pilots while maintaining an air-
craft in a.safe attitude has been recognized for
many years, However, most work specifying
control force limits used male subjects who were
tested for maximum static strength (no move-
ment of controls possible). This work is de-
scribed in reports by Hertel (1930), Gough and
Beard (1936), McAvoy (1937), Morgan and

Thomas (1945), and Watt (1963). Their results



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de du traveul
6.

homas: Control
ROYAL AERO-

Chapanis, and
Guide to Equip-
Hill Book Com-

‘ity, 1970.

ig Performance
HUMAN FAC-

Tholungspausen
len, INTERNA-
NGEWANDTE

leasurements of
eof Exertion
Aeroplane by
and Transac-

the Relation
Jd on the Rate
Achieved by
1D Report No.

ed on a Stick
‘RD-1, 1963.

APPENDIX A
TABLE 1

ANTHROPOMETRIC DATA

Seat Back Ht./

Seat Bottom Ln./

Tten Age Height Weight Shoulder Ht. Thigh Length
‘Subj. No. yrs. cm. in Tbs. % ba
1 42 159.0 62.6 19 89 70
2 42 169.7 66.8 131 82 61
3 35 161.1 63.4 134 96 63
4 55 152.0 59.8 104 66 60
5 42 166.3 65.5 132 87 64
6 64 161.2 63.5 140 90 66
7 28 166.7 65.6 Ww 94 64
8 33 167.3 65.9 134 or 63
9 42 169.6 66.8 205 83 63
10 37 171.6 67.6 150 87 63
u 26 167.1 65.8 160 84 63
12 29 174.4 68.7 154 89 60
13 32 165.5 65.2 133 89 66
4 29 163.4 64.3 125 93 64
15 31 165.7 65.2 92 94 63
16 45 157.1 61.9 334 2 67
7 2 161.2 63.5 122 95 64
18 25 156.5 61.6 102 91 60
19 24 154.9 61.0 308 83 62
20 20 165.6 65.2 109 88 64
2 43 165.1 65.0 4 83 60
22 29 167.2 65.8 124 84 65
23 28 165.7 65.2 127 94 64
24 24 153.3 60.4 114 87 64
Subj. Summary
Mean 34.4 163.64 64.2 128.5 87.9 63.5
Std. Dev. 10.8 5.81 2.29 23.2 6.3 2.4
Max. ‘ 64 174.4 68.7 205 96 70
Min, 20 152.0 59.8 92 66 60
Range 44 22.4 8.9 3 30 10
Item Foot knee Elbow Lower Arm Seat Position
Angle Angle Angle Angle Vertical Horizontal
Subj, No-
1 90° 13° 38° 27° 1 1
2 8s 120 7 4 14 2" cushion 3
3 93 125 106 18 1 4
4 88 131 94 30 1 1 + 2" cushion
5 34 128 98 a 1 4
6 4 131 94 23 1 3
7 al 138 95 3 } 4
8 88 116 84 29 4 1
9 92 130 no 16 1 3
10 88 118 94 27 1 3
n al 12 82 4 1 2
2 92 WW 79 34 1 3
3 9 133 108 25 1 3
4 1 7 85 32 1 2
15 90 122 8B 33 1 2
16 a9 18 0.86 33. 1 1
v7 80 WwW a7 33 1 }
18 84 121 72 7 1 } + 1s" cushion
19 84 126 72 32 1 1 + 14" cushion
20 90 125 95 28 1 3
a al m1 4 28 1 1 + 14" cushion
22 94 130 118 3 1 5
23 85 126 a7 3 1 3

+ 1K"

cushion



|

025
ce)
pli

pen
ght

bwn *

OO ft.
38 in.
50

54

30 knot

itial

1000 lbs.

Horizontal Distance--Seat back to wheel
Horizontal Distance-- Wheel to rudder pedal
Vertical Distance--Wheel to seat edge
Vertical Distance-- Seat edge to floor
Vertical Distance-- Rudder to floor
Angle--Seat back to seat bottom
Angle--Seat bottom to horizontal

oO7nnmooaw pb

Note: All dimensions from seat taken with
seat cushions uncompressed.

Figure 10. Seat dimensions and control placements.

28


RUDDER
po
————
Rained (secs.)

130 Ib. 180 Ib.
pete 180 Ib

ANCE TIME
PARAMETERS

APPENDIX B

COMPARISON OF CONTROL FORCE LIMITS

Excerpts from FAR 23.143, BCAR K2-6 3.4 and
MIL-F-8785 B are presented here for comparison of maximal
control force specifications. FAR 23.143 lists the fol-
lowing control force limits under the section on control-~
lability and maneuverability.

FEDERAL AVIATION REGULATIONS
PART 23, SUBPART B - FLIGHT

CONTROLLABILITY AND MANEUVERABILITY 23.143 General.

(c) If marginal conditions exist with regard to
required pilot strength, the "strength of pilots"
limits must be shown by quantitative tests. In

no case may the limits exceed those precribed (sic)
in the ‘following table:

Values in pounds of force
as applied to the control a

wheel or rudder pedals Pitch Roll Yaw
(a) For temporary applica-
tion .
Stick . 2 2. 4 ee ees 60 30 -
Wheel (applied to rim) . 75 60 -
Rudder Pedal . 2. « « « «© «© © © © © «© « « 150

(b) For prolonged applica-
tion 2. 26 6 © «© © © eo 10 5 20



quadratic, and cubic equations for each set of
data Points. Since there were only three levels
of the independent variable, the cubic equations
were not relévant and were therefore not cal-
culated. A linear regression on the logarithmic
transform of a negative exponential curve of the
form Y=ae—TM was also performed in an effort
to determine a prediction equation for control
force endurance times. For each control axis
studied the linear, quadratic, and exponential
prediction equations were compared on the basis
of variance explained by the regression divided
by variance unexplained by the regression. After
comparison of the effects of these three equations
the polynomial prediction equation containing
the significant term or terms and the exponential
prediction equation were plotted with the 72 data
points.

The prediction equations presented in this sec-
tion for each of the three control axes were found
to be significant at the 5 percent level. The
power of the tests and the probability of reject-
ing a false hypothesis were also calculated, with
the result that the tests based on the exponential
equations were much more powerful than those
computed for the linear and quadratic equations.
The results of the polynomial and exponential
regression analyses are presented in three parts:
one each for elevator pull, right rudder, and left
aileron.

All three prediction equations for elevator
pull were significant at the 5 percent confidence
level. They are presented below, with Y equal
to endurance time in seconds and X equal to
force maintained in pounds.

Linear Y=366.944—6.676 X

Quadratic Y=727,.968—26.595, X+0.249 X?

Exponential Y=1901.103 e—°%?*

Since the quadratic term in the polynomial
regression analysis was significant at the 5 per-
cent level (F=12.9), the quadratic prediction
equation and the exponential prediction equation
are plotted with the 72 elevator pull and data
points in Figure 7. It was determined that the
oxpppenti! curve fits the data better than the
quadratic equation in the range of tested values
from 25 to 55 pound¥

All three prediction equations for right rudder
were significant at the 5 percent level. However,
the quadratic term in the polynomial regression
was not significant (F=0.2). For this reason

14

only the linear and exponential prediction equa”
tions are presented below, with Y equal to endur-
ance time in. seconds and X equal to force
maintained in points.
Linear Y=229.486—3,944 X
Exponential Y=12677.754 e—.088*

These two prediction equations are plotted
with the 72 right rudder data points in Figure 8.
It was found that the exponential equation fits
the data slightly better than the linear equation,
but the difference in fit is quite small. However,
the levels tested in this study varied over a rather
small range of 110 to 150 pounds. By testing
rudder endurance at higher and lower force
levels the quadratic and exponential equations
would be expected to become more useful in pre-
dicting right rudder endurance times.

—— Exponential Equation
—— wodratic Equation

‘Control Force Exerted (pounds)
&

x
8

° $0 100 150, 200 250 300 380 400420
Endurance Time (seconds)
Ficvge 7. Plot of elevator pull endurance.

All three prediction equations for left aileron
were significant at the 5 percent level. The
quadratic term, however, was not significant in
the polynomial regression (F=0.5). Because of
this fact only the linear and exponential predic-
tion equations aré presented below, with Y equal
to endurance time in seconds and X equal to
force maintained in pounds.

Linear Y=878,128—15.516 X
Exponential Y=1714.61 e—776°*

These two prediction equations are plotted
with the 72 left aileron data points in Figure 9.
It was found that the exponential equation fits
the data considerably better than the linear
equation in the range of force levels tested. By
recording left aileron endurance times at a force
level above 22 pounds and at a level below 14
pounds, the authors believe the quadratic and
exponential equations would be more useful in
predicting left aileron endurance times.

8 5 g

Contre! Force Exerted (pounds)

3

Iv.

met
revi
rels
gre
of

tim

equ
dui



Ficcre 4, Plight instruments used for control of simulator; attitude indicator (left), turn and bank indicator
(right).

angle of about two degrees nose up, a roll angle
of about nine degrees to the left, and the turn
and bank pointer indicates a turn to the left at a
rate of about 114 degrees per second. To bring
these indicators to a null position the wheel
should be moved forward and turned clockwise,
and the right rudder should be pushed forward.

A clamp was attached at a point halfway from
the pivot point of the column to the center: point
of the grip. The spring scale and winch were
used to position the clamp precisely so that a
joad applied to the column at the point of the
cldmp was twice the force required at the center
of the grip to k&ep the column from moving
away from the subject. The load applied to the
column was in the form of lead weights sus-
pended from a low friction pulley in front of
the simulator. The amount of weight attached

to the cable equaled the load applied perpendicu-
lar to the column, Figure 5 shows 80 pounds
attached to the column, meaning the subject
would be requifed to pull the wheel toward her
with 40 pounds of force to keep it from moving
away from her and causing the aircraft to pitch
downward.

A similar cable and pulley arrangement was
attached to the left rudder pedal so that a load
applied to that pedal required an equal hori-
zontal force applied by the subject to the right
pedal to keep that pedal from moving toward
the subject.

A bracket and cable were attached to the co-
pilot’s wheel so that the load applied by adding
weights to the cable was half the force required
to be applied to the grips of the wheel to keep it
from turning clockwise.



Female Pilots (% of Population)

50

—-— U.S. Female Pilots
—— Test Subjects

O- 59- 6I- 63- 65- 67- 69- 7I&
58 60 62 64 66 68 70 over

Height (inches)

Figure 12. Height distribution curves.

29


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itor, and were
of the FAA
City, Okla-
analog sim-

as in a real
riable engine
pnditions, but
jt. capabilities
the cockpit.
re modified

pnvair-340 is

vas that nor-
A 8” thick
H board was

position ad-
s, based on
to the floor.

de adequate

maintain a
floor to the
edals, The
p” measured
vheel, again

Ficure 1. Cockpit interior of modified Convair-340 simulator.

representative of that dimension found in light
aircraft. The modified rudder pedal configura-
tion is shown in Figure 2.

The wheel used was a standard Beechcraft
Bonanza wheel from the current 1972 model.
This wheel was chosen because its grip and
diameter are typical of plastic molded wheels
used in current model general aviation aircraft.
It was mounted to the center of the Convair
wheel so the movement of the Bonanza wheel
caused a proportional movement of the control
linkage attached to the Convair wheel. When
the seat was in the most forward position, the
#vheel was 17’’ measured horizontally from the
cushion attachedto the seat back. The modified
seat and wheel are shown in Figure 3. All di-
mensions in the modified simulator were within
the range of dimensions found in five general
aviation aircraft measured by the experimenters.

Monitoring Equipment. Each subject’s per-
formance during the test was recorded on a
strip chart recorder. The recorder used was a
Sanborn 850, 6 channel recorder. The subject
performed tracking tasks on two instruments:
the artificial horizon (attitude indicator) and
the vertical pointer (needle) of the turn and
bank indicator. On the artificial horizon she
saw the two variables of pitch angle and roll
angle; and on the vertical pointer of the turn
and bank indicator she saw the variable of rate
of turn. During any one trial the subject tracked
on two of these displays while the third display
remained fixed in the null position. In this
simulator a change in the force applied to any
control surface caused an angular displacement
of the servo attached to that control. The re-
sultant change in voltage was viewed by the
subject as a movement on the appropriate dis-



are of rather small value here because the sub-
jects were not required to hold a force for any
extended time interval as would a pilot executing
@ maneuver in an aircraft. Others have tested
male subjects for static strength over varying
periods of time while the subject was required
to maintain the force he was exerting between
two force limits. This work is described in re-
ports by Scheffer and Marx (1941) and Van-
Oosterom (1959). These reports are discussed
in detail in a previous OAM report by Karim
(1972).

By testing the strength endurance of subjects
in a flight simulator, it was possible to give them
flight-related tasks to perform while they were
opposing a specific load on a specific control,
Birmingham and Taylor (1954) stated that in
piloting an aircraft the human acts as an error
detector, When an error is detected on a dis-
play, the human applies a force to one or more
controls to reduce that error. All displays used
in this study offered the subject continuous feed-
back information which should result in the least
tracking error and the most quickly stabilized
learning curve as reported by Hunt (1961).
Rogers (1970) reported that control operators
quickly learn the “feel” of a control; that they
balance its spring loading, damping, and inertia
against the excursion they wish to make. The
subjects in this study were given practice in
tracking with the displays and controls in the
simulator, and before the first strength endurance
trial began each subject was able to keep the dis-
play deviations to less than 50 percent of the
limits of a safe attitude as defined in this study.

At present there are approximately 29,000 fe-
male pilots: 7 percent of the total of U.S. gen-
eral aviation pilots. With thé exception of a
study by Karim (1972) no data have ever been
taken which would accurately represent the
strength endurance capabilities of female pilots,
yet they form a significant percentage of the
pilot population. In addition, none of the pre-
vious data applies to actual flight conditions or
reflects a pilot’s ability to exert large forces for

rolonged period of time. Further research
is definitely needed in order to specify realistic
control force limi¥s for light aircraft.

Il, Method.

A flight simulator and a strip chart recorder
were used as the basic equipment in this study

to monitor outputs from the simulator, and were
housed in the simulator building of the FAA
Aeronautical Center in Oklahoma City, Okla-
homa. The flight simulator was an analog sim-
ulator of a Convair-340, a twin-engine passenger
plane with a normal passenger capacity of ap-
proximately 40, The simulator, Manufacturer's
Serial Number 103, was built by Curtiss-Wright
and included all controls and instruments to
which a pilot and co-pilot are exposed in a real
aircraft. All controls and instruments were the
same size and in the same position as in a real
aircraft. The simulator included variable engine
sounds based on simulated flying conditions, but
did not provide cockpit movement capabilities
nor any visual cues from outside the cockpit.
The seat, wheel, and rudder pedals were modified
as explained below to put the subject in a posi-
tion similar to her normal flying position. The
cockpit interior of the modified Convair-340 is
shown in Figure 1.

Cockpit Model.

Pilot’s Seat. The subject’s seat was that nor-
mally found in a Convair-340. A 8” thick
cushion mounted to a 34’’ plywood board was
permanently installed against the original seat-
back to move the subject closer to the controls.
The seat allowed horizontal seating position ad-
justments in 1’’ and 14” increments, based on
its position on the tracks attached to the floor.
The subject was asked to adjust the horizontal
seat position before the practice periods of the
test to the position closest to her normal flying
position. Some of the smaller pilots found it
necessary to use cushions to provide adequate
seat adjustment as they normally do in the air-
craft they usually fly. The standard Convair-
340 lap safety belt and a shoulder harness were
used by each subject.

The floor of the simulator was raised 4’’ by
placing a wooden box under the rudder pedal
and the seat was raised 214” to make vertical
height from the floor to the top of the seat-
bottom and the top of the seat-bottom to the
center of the grip on the wheel representative of
those found in general aviation aircraft. The
rudder bars were also raised 4’’ to maintain a
typical 5’’ vertical distance from the floor to the
point of application on the rudder pedals. The
pedals were in a neutral position of 19” measured
horizontally from the plane of the wheel, again

a

Re Re A



are plotted
sin Figure 8
equation fits
ear equation,
ll. However,
over a rather

By testing
lower force
tial equations
useful in pre-
S.

ponent! Equation
posratic Equation

pu at ay
P 350 400420

Indurance.

r left aileron

level. The
significant in

Because of
ential predic-
with Y equal
X equal to

x

are plotted
in Figure 9.
equation fits
In the linear
Is tested. By

s

3

8

8g

Control Force Exerted (pounds)

—— Exponential Equation
—— Linear Equation

° SO 00180 200 250. 300, 380 400 420
Endurance Time (seconds)
Fievre 8 Plot of rudder endurance.

IV. Summary.

The correlation analysis between anthropo-
metric and other variables and endurance times
revealed, as expected, several significant linear
relationships. The stepwise multiple linear re-
gression analysis revealed the combined effects
of various anthropometric variables on endurance
times recorded at three force levels for elevator
pull, right rudder, and left aileron. Prediction
equations were also obtained for predicting en-
durance time based on control force exerted.

Polynomial and exponential regression analyses
were performed to calculate linear, quadratic,
and exponential equations to determine predic-
tion equations for control force endurance times
based on control force exerted. These equations
were then compared and the calculated negative
exponential regression equations were determined
to be the best predictors for endurance times.

The data showed that the current FAR 23.143
control force limits for general aviation aircraft
are too high for a sizeable portion of the U.S.
female pilot population.

24

—— Exponentiat Equation
— Linear Equation

Control Force Exerted (pounds)

0 80 100 150 200 250 300 380 400420
Endurance Times (seconds)

Fiovure 9. Plot of aileron endurance.


.
Fictre 3, Modified seat and wheel; note permanent seat cushion, shoulder harness and subject’s grip on Bonanza
wheel,

play, and was recorded on the appropriate chan-
nel of the strip chart. The resulting lines on the
individual channels recorded what the artificial
horizon and turn bank vertival pointer indicated
to the subject. The subject's task was to apply
enough force to the controls to center the two
active displays and keep them as close to center
as possible. .

The artificial horizon and the turn and bank
indicator were located on the control panel di-
rectly in front of the subject. The artificial
horizon showed an aircraft symbol which was
superimposed over a horizontal line when the
aircraft was aWzero degrees pitch and roll. When
the wheel was pulled toward the subject, the air-
craft symbol moved to a position above the hori-
zon, indicating a positive (nose up) pitch of the
aircraft. When the wheel was turned clockwise,

the horizontal line rotated counterclockwise, in-
dicating the right wing was lower than the left
and that the aircraft was in a roll to the right.
Scales over the aircraft symbol and at the top of
the indicator showed pitch in 5 degree increments
and roll angle in 10 degree increments. The
vertical pointer in the turn and bank indicator
showed the aircraft was on a straight course
when it was vertical and superimposed over the
center marker. When the right pedal was
pushed, the top of the pointer moved to the right,
indicating a right turn of the aircraft. When
the pointer was over one of the conventional
“doghouse” indicators, to either side of the center
marker, the aircraft was turning in that direction
at a rate of three degrees per second. The two
instruments used are shown in Figure 4. In this
picture the artificial horizon indicates a pitch


m lists

for The following excerpts from MIL-F-8785 B apply to similar

conditions as the control force specifications listed
under FAR 23.143.

ELEVATOR FORCES. For nose-wheel aircraft at take-
off, 20 pounds pull to 10 pounds push. For tail-
wheel airplanes at takeoff, 20 pounds push to 10
pounds pull; par. 3.2.3.3.2. Elevator force for
landing, 35 pounds pull; par. 3.2.3.4.1. For

spin recovery, 75 pounds; par. 3.4.3.

AILERON FORCES. For climb, cruise, and loiter,
ho pounds; for takeoff, approach, and landing,
20 pounds; par. 3.3.4.2. For spin recovery, 35
pounds; para. 3.4.3.

RUDDER FORCES. For speed change, go-around and
cross winds, 100 pounds; par. 3.3.5, 3.3.7.

For dives and assymetric thrust 180 pounds;
para. 3.3.8, 3.3.9. For spin recovery, 250
pounds; par. 3.4.3.

TABLE 6

CONTROL FORCE REQUIREMENTS FOR TEMPORARY APPLICATION
SPECIFIED UNDER FAR 23.143, BCAR K2-6 3.4
AND MIL-F-8785.B

Elevator <Aileron Rudder
FAR 23.143 75 lb. 60 150
BCAR K~26 50 30 150
3.4 . .
MIL-~8785B 10-75 20-40 100-250

»

ormance.



= ERALU. LIBCARY

23

, -————~$TUDY OF CONTROL FORCE LIMITS FOR
_ DNs FEMALE PILOTS

Robert C. Leeper
Howard A. Hasbrook
Jerry L, Purswell
FAA Civil Aeromedical Institute
P.O. Box 25082
Oklahoma City, Oklahoma 73125

‘Staves OF

December 1973

’

Availability is unlimited. Document may be released
to the National Technical Information Service,
Springfield, Virginia 22151, for sale to the public.

6 Prepared for
~ » DEPARTMENT OF TRANSPORTATION
FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine
Washington, D.C. 20591



The supplementary trim box included potenti-
ometers for varying the simulator’s force system
from zero to 150 pounds. The elevator potenti-
ometer provided force pulling the wheel toward
the subject, the rudder potentiometer provided
force pulling the left pedal toward the subject,
and the aileron potentiometer provided force
turning the wheel counterclockwise. There were
10 turn linear potentiometers which provided a
given force when turned to a specific point on
the revolution counter.

An AC digital voltmeter was used by the ex-
perimenter to ensure that all trim controls in the
simulator were in the same position at the start
of each trial. The voltmeter and the supple-
mentary trim box are shown in Figure 6.

Measurement. Previous studies by VanQos-

terom (1959), Caldwell (1964), Rohmert (1960),

and others indicate that the ability to exert force
on a control decreases with the amount of time
the force is required to be maintained. In order
to investigate this relation for pilots operating
aircraft controls, nine measurements were taken
for each subject.

Each subject was asked to keep two displays
as perfectly centered as possible while exerting
either a high, medium, or low level of force on
one of two controls, During a preliminary study
it was found that in most cases the subject could
keep the displays close to centered up to a certain
point, but at this point or shortly thereafter’she
released the control. Subjects reported that they
would attempt to keep the displays as perfectly
centered as possible in an actual emergency, and
reported little boredom in attempting to keep
both displays perfectly centered. These tests

Froune 6. Accessory equipment, AC voltmeter (left) and supplementary trim box (right).

8

em eRe Re



bank indicator

d perpendicu-
Ws 80 pounds
y the subject
el toward her
from moving
raft to pitch

Ingement was
o that a load
equal hori-
to the right
pving toward

Fiecre 5.

Equipment used to load controls.



50r

—-— U.S. Female Pilots
Test Subjects

a S
° °
T T

Female Pilots (% of Population)
N
3°
T mi

3
v

0-19 [ 5-29 35-39 45-49 | 55-8
+ 20-24 -30-34—40-44—50-54

Age (Years)

Frovre 11. Age distribution curves.

28



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Ficure 2, Rudder peaai mouincation; subject’s heel rested on wooden platform, ball of foot on horizontal bar.

ple
ne
inc
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TABLE 2

ENDURANCE DATA FOR ELEVATOR PULL

TABLE 3

ENDURANCE DATA FOR RIGHT RUDDER

Time Force Maintained (secs.)

Time Force Maintained (secs.)

Iten Item
25 Ib. 40 1b. 55 Ib. 0 Ib. 130 1b. 150 1b.
Subj. No. Subj. No.
2 Bm & i 2 Ss 0 "
3 123 a 24 3 420 320 ue
4 257 a 2 4 152 1
5 379 49 7 5 420 277 36
6 420 148 4s 6 420 420 420
7 185 6 Fl 7 205 272 208
H in ee R H io Hy S
10 420 101 34 10 420 420
n 259 55 4 n 39) 290 249
2 420 nz 6 it 420 420 420
B 216 59 4 3 420 420 134
i F: x i i e es 6
16 4 9 a) 16 268 18 we
v You 4 v an 88 39
8 18 219 Ww 66
19 203 58 2 19 170 64 3
20 65 36 to 20 238 59 Pi
21 184 62 32 21 95 62 25
22 278 98 26 22 420 420 165
23 157 5 28 23 420 22 420
a m av 4 5) 90 39 2
Subj. Summary , Subj. Summary
n 218.7 62.5 18.4 313.5
Std. Dev. 102.2 32.5 13.8 Std. Dev. 18,2 ite iE
Max. 148 cs) Max 420° 420° 20
Min. 65 8 2 Min. 90 B 0
Range 355 140 46 Range 330 382 a9
TABLE 5
TABLE 4 CORRELATION COEFFICIENTS FOR ENDURANCE TIME
ENDURANCE DATA FOR LEFT AILERON VERSUS WINE ANTHROPOMETRIC AND OTHER PARAMETERS.
Item Time Force Maintained (secs.) Elevator Pull
14 1b. 18 Ib. 22 1b.
25 1b. 40 1b. 55 1b,
Subj. No. n
ge A754e* -aggaee
} 199 2 & Height laz2see {2023
3 125 8 50 ene Te
Elbow Angle ira
4 109 74 39 Lower Arm Angle 21944
5 2s 164 a0 Lower Back He. £12505
7 n3 17 9
8 19 96 39
9 420 251 105 No 1. 150 1b.
10 124 2 52
oy oe a 2 Age 1645 1297
x 8 a 3 Hetgnt ‘sso7ee lass6e*
R is 5 5 Weight Sezeaee ator
i$ 3 ” i Knee Angle ‘osea 1
1% iw ad Hs Foot Angle * 12293
18 Hy He 3 Seat Back Ht. 12341 2992
v 8 3 R Seat Bottom Ln. ‘3783e* 1403
19 no 46 23
8 es 3 4
35 4b.
ay 00 ng a wie mie
23 227 59 u
2a 230, 64 3 Age 0999 1693 3520"
Netght 2987" lapeze ‘2034
Ketgnt 79708 craze ‘ezaaes
Subj. Spmmary Elbow Angle vee "2433 9
Mean 164.7 1.3 40.7 Lower Arm Angle 12208 =12769 15298"
Sea” bev. 37.8 58.2 23:0 Seat Back Ht. 1726 =0210 2952
Max. 420 251 19s
Min. 4 25 2
‘Significant at 10% level .271
Range 376 226 %3 oe Sgniticant at 5 level 247

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ACKNOWLEDGMENT

The authors wish to thank the many people at FAA who helped with
this study, and especially those in the FAA Flight Simulation Section who
constructed much of the equipment utilized in this research program.

Dr. Laverne Hoag, Department of Industrial Engineering, and Professor
Karl Bergey, Department of Aerospace, Mechanical, and Nuclear Engineering
at the University of Oklahoma also contributed much time and energy to
this study.



3 of 25 sub-
intain a left
pconds. Sub-
fies reported
ore support.
Also, subjects
the buttocks
rudder; this

r 20 seconds,
a 15-pound
reent of the
to maintain

s. Correla-
the time a
e nine test
parameters

significance
3 & correla-
needed for
confidence,
subject in
position in

osition was

‘a

adjusted- by the experimenter to achieve certain
predetermined angles at the elbow, knee, and
foot. Since the present study was conducted to
measure the strength endurance capabilities of a
pilot in flight, each subject in this study deter-
mined her own seated position which put her in
a different position relative to the controls than
that of any other subject. This means the sub-
jects had different strength endurance capabili-
ties in terms of the biomechanics of force exer-
tion. The data in this study represent the
strength endurance capabilities of female pilots
in the posture in which they normally fly and
not their capabilities in any given optimal or
minimal posture. It should be noted that all the
test subjects adjusted their seat position so they
could achieve full control of the rudder pedals,
their normal practice in the airplanes they fly.
Their arm position relative to the wheel was
determined by the seat position chosen for proper
rudder control. This position was often disad-
vantageous for force exertion on the wheel, es-
pecially for short subjects who used pillows
against the seat-back in order to reach the pedals
and then found the wheel, even when in the
neutral position was very close to their abdomen.
In response to a question on the personal data
form, all subjects replied that during the tests
they were in a seated position very similar to
that in which they normally fly. They also
stated that any problems of control placement
encountered in the simulator were similar to
those they encounter in general aviation aircraft.

Age, height, and weight all had a significant
effect on elevator pull endurance. Since age was
positively correlated with endurance for all three
trials, this means that older subjects maintained
a given force longer than yopnger subjects, This
result is contrary to the expected result that age
and endurance time would be negatively cor-
related since aging after the middle 20’s gener-
ally reduces muscular strength, as reported by
Asmussen and Heebol-Nielson (1962). In this
study no reason can be given for the observed
positive correlations. Height and weight were
positively correlated at the 5 percent level for
the low and the high force levels, meaning that
at these levely, taller and heavier subjects were
able to maintain a force longer than short and
light subjects.

The seated positions of the subjects placed
them in disadvantageous positions for exertion

of a large pull force on the wheel. With an
average elbow angle of 91 degrees and an aver-
age lower arm angle above horizontal of 27.8
degrees, the subjects’ biceps and latissimus dorsi
muscles were already partially contracted, mak-
ing exertion of a large force difficult. Hunsicker
and Greey (22) found that a subject with an
elbow angle of 90 degrees was weaker in pull
than’ with any other elbow angle except 60 de-
grees. In these tests elbow angle was not deter-
mined to be a significant variable in determining
elevator pull endurance, but lower arm angle was
significant for the highest force level. The nega-
tive correlation means that the greater the lower
arm angle the shorter the endurance time. A
large lower arm angle indicates a subject had to
grasp the wheel several inches above her elbow
height. This put more of the load on the biceps
and thereby shortened endurance time.

There were no significant correlations between
age and endurance time, although small positive
correlations were observed, Height and weight
were observed to be important variables in de-
termining how long a subject could maintain a
force. Knee angle and foot angle were not found
to be significant variables, probably because these
measured angles reflect. the subject’s seated posi-
tion while at rest. When a subject was exerting
a force, she often found an improvement in her
endurance by lifting the buttocks from the seat,
pushing the knee downward, and pushing the
heel forward, thus increasing the knee angle and
decreasing the foot angle. The height of the
buttock elevation was limited by the lap seat
belt, but the subjects were able to increase knee
angles to an approximate range of 130-170 de-
grees and decrease foot angles to an approximate
range of 70-90 degrees. These changes in knee
and foot angles occurred as subjects attempted
to “stand on the rudder,” as they would do in an
aircraft in an emergency which required the
exertion of a large force on the rudder. Data
presented by Morgan, et al. (1963) indicate a
knee angle of 135-150 degrees provides optimal
force application on a pedal. In an effort to
maintain a rudder force as long as possible, each
subject in this study found her endurance ca-
pability increased as she moved her knee toward
the locked position and then used her back
muscles against the seat-back to provide a push
force on the pedal. This technique on the part
of the subjects agrees with the suggestions of



pody, causing a
There was no

the wooden

e effect of this
Wheel could be
Subjects were
e aircraft level
hese trials, as
pft in an emer-
aintain an ab-
Many subjects
plane level in
were reduced.

orded in this
ic flying situa-
poden mock-up
closely reflect

pabilities of a

sion Analysis.
revealed the
thropometric
ime.

linear regres-
br pull endur-
force exertion
d weight and
f the variance
the 55-pound
ver arm above
2.4 percent;
d another 2.0
durance times
fined in terms
bles and must
it included in
equation for

and the standard error of the estimate was 11.89
seconds.

A similar analysis was performed for the right
rudder endurance data by using stepwise mul-
tiple linear regression to predict endurance time.
One subproblem was analyzed for each of the
three rudder force exertion levels (110, 180, and
150 pounds) used in the study. At the highest
force tested height explained 21.8% of the vari-
ance in right rudder endurance times for the
150-pound force level; foot angle and seat-
bottom length accounted for 13.5 percent; and
weight, seat-back height, and age explained an
additional 6.5 percent of the variance. A vari-
ance in right rudder endurance times of 58.2
percent was unexplained by the anthropometric
variables mentioned here. The final prediction
equation for right rudder endurance time at the
150-pound force level was:

(endurance time,
sees.) = — 2031.95

+ 244 (age, yrs)

+ 9.78 (height, cms)

+ 1.82 (weight, Ibs)

+ 5.98 (seat-back ht, %
of seated shoulder
ht)

6.65 (seat-bottom In, %
of seated thigh
In)
— 6.92 (foot angle, °)
and the standard error of the estimate was 133.16
seconds,

+

The stepwise multiple’ linear regression anal-
ysis for left aileron included one subproblem for
each of the 14-, 18-, and 22-pound force levels.
At the highest force tested weight and lower arm
angle explained 39.0 and 9.9 percertt of the vari-
ance in the endurance times recorded for the
22-pound left aileron test; height and elbow
angle accounted for an additional 6.0 percent of
the variance, A variance in endurance times of
45.1 percer® could not be explained by the an-
thropometric variables listed here and must be
attributed to the effects of other anthropometric
variables or to other factors which were not
studied here.

The final prediction equation for left aileron
endurance time at the 22-pound force level was:

(endurance time,
secs.) = +116.59
— 1.15 (height, cms)
+ 62 (weight, Ibs)
+ 49 (elbow angle, °)
— 45 (lower arm angle,
°
)
and the standard error of the estimate was 16.96
seconds.

Polynomial and Exponential Regression Anal-
ysis. One purpose of this study was to define
the relationship between contro! forces and the
time they can be maintained by a pilot flying an
aircraft. Polynomial and an exponential regres-
sion analysis were performed on each of the
three controls studies; elevator pull, right rud-
der, and left aileron. The independent variable
was the amount of force required and the de-
pendent variable was the length of time a force
could be maintained. On each control there were
24 subjects tested at each of three force levels,
resulting in 72 data points on each control axis.
Prediction equations were then obtained from
these analyses for endurance time in terms of the
force exerted for each of the control axes.

It should be remembered that the three levels
of force on each control in this study were abso-
lute values, not percentages of maximal force as
studied by Karim (1972). This means that a
given force might be very near one subject’s
maximal strength and yet might be a relatively
light force compared to another subject’s maxi-
mal strength. This explains some of the wide
variation in endurance times recorded for any
one force level. In some cases such as the highest
rudder force level, times ranged from 1 second
to 420 seconds. This is not unexpected since
Karim (1972) reported maximal rudder strength
ranged from 81 to 250 pounds in the aircraft
mock-up she used for testing the strength of
female pilots. The regression equations in this
study do not explain endurance times in terms
of maximal strength, but do reflect the capabili-
ties of a representative sample of female pilots
for maintaining a specific control force while
keeping an airplane in a safe attitude.

The polynomial regression program used in
this analysis was designed to compute linear,



| a

TECHNICAL REPORT STANDARD TITLE PAGE

T. Report No. 2. Government Accession No. 3. Recipient's Cotalog No.
FAA-AM-73- 23

7. Title and Subtitle 3, Report Date

STUDY OF CONTROL FORCH LIMITS FOR FEMALE PILOTS December 1973

6. Performing Organization Code

7. Author(s) 8. Performing Organization Report No.
Robert C, Leeper, A. Howard Hasbrook and
Jerry L. Purswell

9. Performing Orgonization Name and Address 10. Work Unit No.
FAA Civil Aeromedical Institute
P. 0. Box 25082 11. 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. T4. Sponsoring Agency Code
Washington, D.C, 20591

15. Supplementary Notes

Work was performed under Task No. AM-A-72-PHY-58

16. Abstract

The study described in this paper was the second phase in a ground-based
control force testing program conducted by the University of Oklahoma and the
Civil Aeromedical Institute of the Federal Aviation Administration located in
(Oklahoma City, Oklahoma. A Convair-340 simulator, modified to conform to a typical
civil aviation aircraft, was used for the study. Female pilots were used as
subjects,

The data show that the current FAR 23.143 control force limits for general
aviation aircraft are too high for a majority of U. S. female pilots. Data on
Istrength capabilities of women for operating aircraft controls are presented in
the form of prediction equations for level of control force versus time,

V7. Kay Words 18. Distribution Statement
Control Forces; Female Pilots; Availability is unlimited, Document may be
‘Aviation Safety released to the National Technical Informa-
. tion Service, Springfield, Virginia 22151,
for sale to the public.
19. Security Clossif. (of this report) 20, Security Classif, (of this page) 21. No. of Pages | 22, Price
Unclassified Unclassified 30 $3.00

Form DOT F 1700.7 1-69)



APPENDIX C

TEST CONDITIONS AND SEATING GEOMETRY

TABLE 7

TEST CONDITIONS IN CONVAIR SIMULATOR

Simulator Flying Conditions

Flight Engineer Controls
Gross Weight
Sound Volume
Center of Gravity
Turbulence
Wind Speed
Fuel

Cockpit Controls
Cowl Flaps
Panel Lights
Flap Position
Landing Gear
Altitude (locked)
Manifold Pressure
Engine RPM
Brake Horsepower
Indicated Airspeed (locked)

42,000 lbs.
225
225
to)
fo)
Full

Open
Bright

1i°* °
Down *
3000 ft.

38 in.
2350

154

130 knot

These values chosen to simulate an
phase of landing. .

aircraft

in initial



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50

BS
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a
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N
oO

3

r —-— U.S. Female Pilots
—— Test Subjects

O- 90- I10-130- 150-170 I90- 2I0&
89 109 129 149 169 189 209 over

Weight (pounds)

Ficure 13. Weight distribution curves.

30



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to exert force
ount of time
ed. In order
lots operating
its were taken

iminary study
subject could
ip to a certain
hereafter she
ted that they
p as perfectly
ergency, and
ting to keep

These tests

tT |

continued until the subject gave up or until the
display representing the control requiring the
subject to endure a specific force went outside
the limits of safe attitude. None of the sub-
jects succeeded ‘in bringing the aircraft back
within the defined limits once they had been ex-
ceeded. These limits were chosen to reflect an
aircraft grossly deviating from a straight and
level course, and were set at 10 degrees roll and
pitch, and a rate of turn of 2 degrees per second.
When the subject reached a deviation of half the
control limit, she was reminded to center the
display. At any time the display showed a
deviation of half the control limit or more, the
experimenter kept up a strong, verbal encourage-
ment to the subject to re-center the display. A
seven minute limit was used: two minutes more
than Monod (1956) and others have suggested
as the point where strength endurance can be
continued indefinitely.

Experimental Design. The test equipment was
designed to represent a typical general aviation
aircraft from the standpoint of dimensions and
placements of controls, Each control was kept
near the neutral position and each subject made
small movements, of the control around that. po-
sition to keep the appropriate displays centered.
A horizontal adjustment of the seqt was provided
to allow for differences in pilot size. Each sub-
ject was asked to adjust the seat to her usual
flying position. She used either the cushions she
brought or a 144’ thick cushion provided by the
experimenter to make adjustments, No attempt
was made to restrict a subject to any given posi-
tion because this would not have reflected her
actual flight posture.

Aileron strength endurance trials were con-
ducted using the left hand alone so that the
subject had the right hand free to activate the
throttles, radio, landing gear, and other controls
as she would do in flight. Elevator. strength
endurance testing was conducted with the right
hand only to avoid fatigue buildup resulting
from using the left hand in both aileron and
elevator trials. The right leg was chosen arbi-
trarily to test leg strength endurance on the
rudder pedals®

Each subject was showi the proper hand grip
on the wheel at the beginning of the session.
The Bonanza wheel had an inward projection
from the rim on which all subjects placed their

thumbs. This placed the fingers in the four
identations formed on the back of the wheel.
Each subject was asked to dry any perspiration
from the wheel and from her hand with a paper
towel before each trial. The subject was not
allowed to regrasp the wheel if it began to slip
out of her hand because the act of regrasping the
wheel required either temporary use of the other
hand to stabilize the wheel or a momentary loss
of contact between the wheel and the proper
hand, which allowed the airplane to go beyond
the limits of a safe attitude as defined in this
study. The subjects were aiso instructed to place
the ball of the foot on the steel pipe attached to
the surface of the pedal. This placed the heel
of the foot on the wooden box under the pedals.

Subjects. Previous anthropometric studies
have shown that strength is dependent on age,
sex, height and body type. The Aeromedical
Certification Branch, Civil Aeromedical Institute
of FAA has available data on age, height, and
weight for all active airmen including the female
pilot population. The sample of 24 female pilots
used in this study approximates the active female
pilot population closely for each of the three
parameters mentioned above. Age, height, and
weight statistics for the subjects tested are listed
in Table 1 of Appendix A, along with other
anthropometric data.

Each of the 24 subjects was tested on the three
control axes at the three levels of force. The
order of presentation of these nine trials was
counterbalanced so as to minimize the effects of
fatigue buildup in the data.

Experimental Routine. Experimental sessions
began at 9:00 a.m. or 1:00 p.m. and lasted from
2 to 21% hours. Upon arrival, the subject’s height
and weight were measured. She was seated in
the left seat of the simulator and the seat belt
and shoulder harness were adjusted to give a
snug comfortable fit. She was then asked to
slide the seat forward to the position closest to
her normal flying position, At this point the
purpose of the experiment was explained and the
proper grip on the wheel and proper foot posi-
tion on the rudder pedals were demonstrated.

Two short practice sessions were successfully
completed before the control force testing began.
These sessions allowed the subject to practice the
tracking task while applying a low force. The



Morgan, et al. on control placement. The work-
ing angles of these subjects reflect the true pos-
ture of a pilot required to maintain an abnormally
high rudder force; but since each subject varied
her knee and foot working angles over a wide
range of values during each trial, working angles
were not measured.

Seat-back height and seat-bottom length were
measured to determine what effect the support
characteristics of a seat have on endurance. Posi-
tive correlations between the height of the seat-
back, expressed in percentage of seated shoulder
height and endurance time, indicate that perhaps
taller seat-backs may give better support and
therefore increase endurance time since the only
significant correlation at the 10 percent level was
for the 150-pound force. Seat-bottom length, in
percentage of thigh supported, varied from 60
to 70 percent in this study and was positively
correlated with endurance time at the 5 percent
level for the 110- and 130-pound forces, although
the correlation was not significant for the 150-
pound force. This indicates that within the
range of 60 to 70 percent, a longer seat-bottom
gives more support to the thigh and this increases
endurance time.

Again the significant positive correlations be-
tween age and endurance times in this study
eannot be explained by any of the measured
variables. Height was an important variable in
aileron endurance at the low and middle force
levels, while weight was the most highly cor-
related variable with endurance time at all three
levels. These correlations indicate taller and
heavier subjects could maintain a force longer.
Elbow angle correlation with endurance time in-
creased as the required force increased and was
significant for the highest force level, indicating
that subjects with larger elbow angles maintained
the aileron force longer. Lower arm angle was
also increasingly important as the force require-
ments increased and was significant at both the
mhedium and high levels of force. The negative
correlations indicate that subjects whose elbows
were considerably below the level of the grip on
the gheel were able to maintain the aileron force
for a shorter time than those with higher elbow
positions. Seat-bacl¥ height was important at
the 22-pound level, indicating a higher seat-back
offered the subjects more support and thereby
increased endurance times.

It was noted during the aileron endurance
trials that when a subject tried to pull downward
on the left grip, she also had a strong tendency
to pull on the wheel toward her body, causing a
nose up attitude of the aircraft. There was no
way to record this tendency in the wooden
mock-up, but in the simulator the effect of this
incidental back pressure on the wheel could be
seen on the artificial horizon. Subjects were
continuously instructed to keep the aircraft level
in pitch as well as roll during these trials, as
they would have to do in an aircraft in an emer-
gency in which the pilot must maintain an ab-
normally high aileron force. Many subjects
reported that by keeping the airplane level in
pitch, their endurance capabilities were reduced.
The aileron endurance times recorded in this
study are based on a more realistic flying situa-
tion than those recorded in the wooden mock-up
of Karim (1972) and should more closely reflect.
the actual strength endurance capabilities of a
female pilot in an airborne aircraft.

Stepwise Multiple Linear Regression Analysis.
The previous correlation analysis revealed the
individual effects of each of the anthropometric
and other variables on endurance time.

The first three stepwise multiple linear regres-

sion subproblems predicted elevator pull endur-

ance at the 25-, 40-, and 55-pound force exertion
levels, At the highest force tested weight and
age explained 29.6 and 5.8 percent of the variance
in elevator pull endurance times for the 55-pound
force level; seat-back height and lower arm above
horizontal angle explained 3.2 and 2.4 percent;
and elbow angle and height added another 2.0
and 2.3 percent. A variance in endurance times
of 54.7 percent cpuld not be explained in terms
of these six anthropometric variables and must
be attributed to other variables not included in
this analysis. The final prediction equation for
right-hand pull strength at the 55-pound force
level was:

{endurance time,
sees.) = —.83.68
40 (age, yrs)
.48 (height, cms)
.20 (weight, lbs)
43 (seat-back ht, % of
seated shoulder ht.)
—  .84 (elbow angle, °)
—  .83 (lower arm angle, °)

+t

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