eRB No. L4E31
NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
WAl RTIMEl RE P0RT
May 1944 as
Restricted Bulletin L4E31
MAXIMUM RATES OF CONTROL MOTION QBTADIED
FROM GROUND TESTS
By De E. Beeler
Langley Memorial Aeronautical Laboratory
Langley Field, Va.
NACA WARTIME REPORTS are reprints of papers originally Issued to provide rapid distribution of
advance research results to an authorized group requiring them for the war effort. They were pre-
viously held under a security status but are now unclassified. Some of these reports were not tec.-
nically edited. All have been reproduced without change in order to expedite general distribution.
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NACA RB No. L4E31 RESTRICTED
I.ATIn1:AL ADVlTSOFY COT
I.14 -XIr RATES OF PCOTREDL 'CTICIT OBTAINED
FROi, GROUTJD TESTS
By De E. Beeler
Ground tests were conducted in a specially constructed
cockpit rig to determine the mraxinmr:rates of control-
ztick (elevator) motion and the corresponding maximum
stick forces that could be exerted, as based on results
obtained with a number of pilots.
The measurements indicate that the maximum rate of
push on the control stick is greater than the maximum
rate of pull; that the maximum rate of either push or
pull is less when a mental restriction is imposed upon
the pilot; and that the maximum rates at which the pilot
thought he would apply elevator control forces in flight
are considerably less than the rates at which he could
asrly these forces with the same stick stiffness.
The maximum rates of control motion as well as the
rmaxium. forces that a pilot can exert on the elevator
controls must be taken into account in the formulation of
rational design criterions for dynamic tail load computa-
tions. The maximum tail load consistent with the load
factor in vertical]-lane maneuvers results when an elevator
notion is specified in which the elevator is moved as
rapidly as possible to a ra;'ir-.. value and held there for
such a time that, when the controls are abruptly reversed,
FACA RB No. L4E31
the maximum alloWabli positive load factor is just reached.
Several investigations that have some bearing on this sub-
ject (references 1, 2, and 3) have already been completed,
but they do not yield sufficient data on the rate of
control motion. In references 1 and 2 the emphasis is
placed on the quickness with which a maximum force can be
develoc._d, whereas in reference 3 tests of the maximum
steady forces applied by a pilot in various positions was
The question of how the pilot actually moves the con-
trols depends on such unpredictable variables as the
physiological and ps-rchological makeup of the pilot, which
are in turn influenced by the "feel" of the airplane.
This subject is la-'r-ely outside the scope of the present
pape, which presents mainly the results of tests made
expressly to determine the effect of several variables on
the maximum possible rates of stick motion. Nine pilots,
varying in physical fitness and in flying experience,
participated in the performance of these tests.
The rig used in the tests (see fig. 1) consisted of
an adjustable bucket-type pilot's seat, a control stick,
and a rudder bar that were mounted on a heavy wooden table.
The relative positions of the seat, stick, and rudder bar
were similar to those used in present-day fighter air-
planes. A resisting force was applied to the stick by
means of two preloaded spiral springs, which were attached
at one end to a movable shelf that was installed under the
table top. The other ends of the springs were attached
to a collar, which could slide on a projection of the
stick that extended below the table top. Adjusting the
height of the shelP and of the collar permitted different
spring restraints to be imposed on the stick.
It was realized at the outset that general relation-
ships that would hold for 'll cases could not be estab-
lished between the force and the stick deflection. 'With
the type of control motion contemplated, an adjustment of
the springs such that an additional restraint would be
imposed during the return motion upr.ared necessary.
This adjustment would be in accordance with conditions that
would occur in flight when an angular velocity was present
and a convergent elevator was used. For this purpose, an
NACA RB No. LLE3i
adjustable nonreturn mechanism was attached to the spring
supplying the restraint in the pull direction. The
action of this apparatus is illustrated in figure 2, which
sho;js the time variation obtained for the stick position
and the stick force with the mechanism in operation. A
diagrammatic view of the stick system is also shown on
this figure. A strict interpretation of the results of
figure 2 in terms of the corresponding aerodynamic parame-
ters of the substitute elevator is not possible because
varying values of the parameters would be obtained for
different parts of the curve.
The position of the stick was recorded by a control-
position recorder mounted on top of the table. A timer,
also mounted on top of the table, was used to impress
timing signals on the control-position record in order
that accurate time histories could be obtained. The
relation between the stick position and the stick force
was obtained by separate calibrations for which the stick
was culled back slowly by a spring scale with the shelf
in each of the positions used during the tests.
A thigh belt was used to secure the pilot in the
seat. Although the belt restricted the reach of the
pilot, the results obtained by its use were believed to
be more consistent than would be obtained if no belt were
METHOD AND TES''TS
Three types of stick motion were investigated. For
each type, resisting forces of 55.5, 16.6, 8.5,
and 4.2 pounds per inch of control-stick displacement were
imposed on the control stick. For the first part of
the investigation, measurements were made of the maximum
rate and corresponding maximum force obtained when the
stick was pulled and then pushed as rapidly as possible
with no limitation as to either displacement or force.
In addition, one pilot was instructed to move the control
stick in this zame manner with no resisting force other
than inertia on the stick.
For the second part of the investigation, the pilot
was requested to use only one-half the displacement ob-
tained in the first part. This condition was thought to
simulate more nearly the flight condition inasmuch as the
NACA RB No. LLE51
pilot would generally be constrained as to amount of de-
flection by the knowledge that in flight he might obtain
larger accelerations th.,.n he could comfortably stand.
For the third part of the investigation, measurements
were made of the maximum rate and corresponding maximum
forces at which the subject pilot thought he would move
the control stick to pull out from a diving attitude if
forces similar to those applied to the cockpit rig were
experienced in the dive. These measurements are limited
in that they depended on the extent of flying experience
and imagination of each of the subject pilots.
The maximum rates for the tests of the three types
of stick motion were obtained directly from the record
films by measuring the maximum slopes thereon and the
rate of film travel at the midpoint of the maximum slope.
Maximum forces also were obtained from the film records
by reading the maximum deflections of the stick.
The measurements of the control-stick rates are
believed to be accurate to +10 inches per second,whereas
the measurements for maximum stick forces are accurate
to 5 pounds. These values are largely based upon the
accuracy to which the film records can be read.
RESULTS AND DISCUSSION
The results of the measurements made to determine
the maximum rates at which a pilot can move the control
stick with various restraints in the control system are
presented in figures 3 to 12. These figures show that
considerable scatter exists in the data. When this
scatter was first noted, consideration was given to
plotting the maximum rate of stick movement for each pilot
against the power exerted at the time of maximum rate in
order to reduce the scatter. The scatter, however, still
persisted and it was finally decided to plot the maximum
rates against either the maximum force or the maximum
stick displacement for a yiven run without distinguishing
NACA R3 'o. LL351 5
All the results given in figures 3 to 6 have one
thing in common; that is, with an increase in the maximum
stick f'rce there is a definite decrease in the maximum
rate of stick motion. This result contradicts results
of previous tests (reference 1), which report that forces
have little or no effect on the rate of control movements
provided they are within the pilot's capability.
Figures 7 to 10 show that the maximum rate also
increases w.ith stick displacement. This variation is to
be expected from the results in figures 3 to 6, however,
because with the system used the force is proportional to
the d jsplacement.
Comparison of the results shown in figure 11 and 12,
which represent the measurements made to determine the
maximum rates of stick motion during simulated dive pull-
outs, with results shown in figures 9 and 10 shows that
the maximum rates at which the pilots think they would
move the stick is considerably lower than the rate at
which they could move the stick. All the pilots were of
the opinion that the highest value of restraint used in
the tests was more than would be experienced with present-
day airplanes; however, records of such forces obtained
in flight on fighter-bomber airplanes indicate that re-
straints of this magnitude may exist.
A summary of the rates of stick motion given in
table I shows that the rate of motion is from 25 to
60 percent greater in the push direction than in the pull
direction. Factors that contribute to this difference
are: (1) the returning force introduced by the system
used effected the first part of the pushing motion,
(2) the distance the stick may be moved is greater in the
push direction, and (3) the pilot is in a more favorable
position for performing the pushing operation.
From the summary given in table I it may also be
seen that the maximum rates obtained in either direction
of motion with no restriction were from 20 to 50 percent
greater than those obtained with a restriction as to the
amount of travel. This difference in the rate seems a
reasonable one in view of the restrictions imposed. It
also seems reasonable that different results would be
obtained if a different restriction had been imposed on
UACA RB Do. LLE31
Tcsts conducted by means of a specially constructed
cockpit rig to determine maximum rates of control-stick
motion ind'cate the following conclusions:
i. The max.iwum rates of stick movement are greater
in the push direction than in ;'C)l whether there is a
mental restriction or no restriction imposed on the
pilot as to stick travel.
2. The maximum, rates of stick movement increase both
with a decrease in maximum stick force and with an in-
crease in )rsxinmum stick displacement.
3. The maxirrumn rate at which a pilot believed that
he iould. move the control stick is considerably lower than
the rate at which he could move the stick.
Langley I'.'orial Aeronautical Laboratory
National Advisory Committee for Aeronautics
Langley Field, Va.
1. Superintendent, Royal Aircraft Factory: Experiments
on the Possible Rate at Vhich a Pilot Can Pull
Back the Control Column in an Aeroplane. R. & ,.
No. 262, British A.C.A., 1916.
2. Yertel, Heinrich: Determination of the Laximum Con-
trol Forces and Attainable Quickness in the Opera-
tion of Airplane Controls. AIA T,, .: 5 1950.
5. o3ugh, 11. N., and Beard, A. P.: Liritations of the
Filot in Applyir.n Forces to Airplane Controls.
3'A:A TN o. 550, 19536.
NACA RB Io. LLE,3
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NACA RB No. L4E31
(a) Three-quarter front view.
(b) Side view.
Figure 1.- Cockpit rig used to obtain maximum rates of control
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A 2 4 & 2 1
Maximum rate of stick motion, in./sec (jul/)
Figure // VLriation of maximum rate of stick motion
maximum stick disp/ocement obtained in ground tests
during a simulated pull-out; p/ll/ Ace eAswrtd.
I NATIONAL ADVISORY
jo1 i --COMMITTEE FOR AERONAUTICS.
0 2 4 6 8 /0 /2 /4 /6
Maximum rate of stf/l' motion in./sec (push)
Figure /. Yar/af/on of maximum rate of stick motion wwth
maximum stick displacement obtained mr ground tests
during a simulated pu//-out; pw// force exerted.
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