January 2008 

NASA/TP-2008-215109 

A Piloted Simulator Evaluation of Transport Aircraft 

Rudder Pedal Force/Feel Characteristics 

Eric C. Stewart 

Langley Research Center, Hampton, Virginia 
 

The NASA STI Program Office . . . in Profile 

Since its founding, NASA has been 

dedicated to the advancement of aeronautics 

and space science. The NASA Scientific and 

Technical Information (STI) Program Office 

plays a key part in helping NASA maintain 

this important role. 

The NASA STI Program Office is operated by 

Langley Research Center, the lead center for 

NASA’s scientific and technical information. The 

NASA STI Program Office provides access to the 

NASA STI Database, the largest collection of 

aeronautical and space science STI in the world. 

The Program Office is also NASA’s institutional 

mechanism for disseminating the results of its 

research and development activities. These results 

are published by NASA in the NASA STI Report 

Series, which includes the following report types: 

x TECHNICAL PUBLICATION. Reports of 

completed research or a major significant 

phase of research that present the results of 

NASA programs and include extensive data 

or theoretical analysis. Includes 

compilations of significant scientific and 

technical data and information deemed to be 

of continuing reference value. NASA 

counterpart of peer-reviewed formal 

professional papers, but having less stringent 

limitations on manuscript length and extent 

of graphic presentations. 

x TECHNICAL MEMORANDUM. Scientific 

and technical findings that are preliminary 

or of specialized interest, e.g., quick release 

reports, working papers, and bibliographies 

that contain minimal annotation. Does not 

contain extensive analysis. 

x CONTRACTOR REPORT. Scientific and 

technical findings by NASA-sponsored 

contractors and grantees. 

x CONFERENCE PUBLICATION. Collected 

papers from scientific and technical 

conferences, symposia, seminars, or other 

meetings sponsored or co-sponsored by 

NASA.

x SPECIAL PUBLICATION. Scientific, 

technical, or historical information from 

NASA programs, projects, and missions, 

often concerned with subjects having 

substantial public interest. 

x TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientific 

and technical material pertinent to NASA’s 

mission. 

Specialized services that complement the STI 

Program Office’s diverse offerings include 

creating custom thesauri, building customized 

databases, organizing and publishing research 

results ... even providing videos. 

For more information about the NASA STI 

Program Office, see the following: 

x Access the NASA STI Program Home Page 

at http://www.sti.nasa.gov

x E-mail your question via the Internet to 

help@sti.nasa.gov 

x Fax your question to the NASA STI Help 

Desk at (301) 621-0134 

x Phone the NASA STI Help Desk at 

(301) 621-0390 

x Write to: 

 NASA STI Help Desk 

 NASA Center for AeroSpace Information 

 7115 Standard Drive 

 Hanover, MD 21076-1320
National Aeronautics and 

Space Administration 

Langley Research Center 

Hampton, Virginia 23681-2199

January 2008 

NASA/TP-2008-215109 

A Piloted Simulator Evaluation of Transport Aircraft 

Rudder Pedal Force/Feel Characteristics 

Eric C. Stewart 

Langley Research Center, Hampton, Virginia 
 Available from: 

NASA Center for AeroSpace Information (CASI) National Technical Information Service (NTIS) 

7115 Standard Drive 5285 Port Royal Road 

Hanover, MD 21076-1320 Springfield, VA 22161-2171 

(301) 621-0390 (703) 605-6000 
5

NOMENCLATURE 

V airspeed, knots 

h altitude above runway, ft 

E angle of sideslip, deg (positive to right) 

Pxy cross spectra (lb-deg/sec/Hz) of pedal force and heading 

Ef final steady crosswind component, knots 

\ heading relative to runway centerline, deg (positive for nose right) 

Eo initial steady crosswind component, knots 

ay _ ps lateral acceleration at pilot’s station, g units (positive to right) 

Y lateral displacement from runway centerline, ft (positive to the right) 

T pitch attitude, deg (positive nose up) 

G p rudder pedal deflection, inches (positive to left) 

Fp rudder pedal force, pounds (positive to left) 

E total crosswind (combined steady and random winds), feet/second 

(positive from right) 

 AGL above ground level 

B breakout force, (e.g. +/-10 pounds) 

bi coefficients of response surface equation, i=1,2,3....10 

CCD Central Composite Design (of experiments) 

C-H Cooper-Harper 

FAA Federal Aviation Administration 

h altitude at which the crosswind shear is initiated, ft 

IFD Integration Flight Deck (Langley Simulator) 

M maximum pedal force (force at maximum pedal travel, (e.g. +/-100 lbs, 

positive to the left) 

NTSB National Transportation Safety Board 

PIO pilot induced (or involved) oscillation 

PR pilot rating using Cooper-Harper pilot rating scale 

PS peak values of cross spectra for frequencies greater than 0.2 Hz 

r yaw rate, deg/sec (positive to the right) 

Stdev standard deviation 

X limits of pedal travel (e.g. +/- 2 inches), 

X1, X2, X3 Normalized axes of Central Composite Design 

ǻt time increment during wind shear, seconds 
6

ABSTRACT 

A piloted simulation study has been conducted in a fixed-base research simulator to 

assess the directional handling qualities for various rudder pedal feel characteristics for 

commercial transport airplanes. That is, the effects of static pedal force at maximum pedal 

travel, breakout force, and maximum pedal travel on handling qualities were studied. An 

artificial maneuver with a severe lateral wind shear and requiring runway tracking at an altitude 

of 50 feet in a crosswind was used to fully exercise the rudder pedals. Twelve active airline 

pilots voluntarily participated in the study and flew approximately 500 maneuvers. The pilots 

rated the maneuver performance with various rudder pedal feel characteristics using the CooperHarper rating scale. The test matrix had 15 unique combinations of the 3 static pedal feel 

characteristics. A 10-term, second-order equation for the Cooper-Harper pilot rating as a 

function of the 3 independent pedal feel parameters was fit to the data. The test matrix utilized a 

Central Composite Design that is very efficient for fitting an equation of this form. The equation 

was used to produce contour plots of constant pilot ratings as a function of two of the parameters 

with the third parameter held constant. These contour plots showed regions of good handling 

qualities as well as regions of degraded handling qualities. In addition, a numerical equation 

solver was used to predict the optimum parameter values (those with the lowest pilot rating). 

Quantitative pilot performance data were also analyzed. This analysis found that the peak values 

of the cross power spectra of the pedal force and heading angle could be used to quantify the 

tendency toward directional pilot induced oscillations (PIO). Larger peak values of the cross 

power spectra were correlated with larger (degraded) Cooper-Harper pilot ratings. Thus, the 

subjective data (Cooper-Harper pilot ratings) were consistent with the objective data (peak 

values of the cross power spectra).
7

INTRODUCTION

Directional handling qualities of transport airplanes have long been neglected compared 

to longitudinal and lateral handling qualities. As a result, the Federal Aviation Administration’s 

(FAA) quantitative certification requirements for rudder pedal feel characteristics are very 

limited [ref. 1]. For example, the maximum pedal force is limited to 150 pounds, but there is no 

requirement for breakout force or maximum travel. U.S. military handling qualities 

specifications [ref. 2], include a quantitative limit on the breakout force (no more than 14 

pounds). However, there are still no guidelines as to the optimum combinations of the 

quantitative parameters describing the rudder pedal feel characteristics or the sensitivity of the 

handling qualities to off-optimum combinations. The lack of comprehensive criteria was 

highlighted in a recent National Transportation Safety Board (NTSB) accident report on a fatal 

accident of a commercial transport that revealed the possibility that certain combinations of 

travel and breakout forces, while not specifically covered in the certification requirements, might 

help induce PIOs [ref. 3]. One of the recommendations of that NTSB accident report was for the 

FAA to include a certification standard for safe handling qualities in the yaw axis. To develop 

this new certification standard, a systematic handling qualities research program is needed. 

Recent studies [ref. 4 and 5], have begun to fill the need for data to base the certification 

standards on. However, more research is needed to develop criteria to apply to a practical 

system. Other work [ref. 6], has developed some simple indexes that define maximum limits of 

pedal feel characteristics. However, optimum characteristics and sensitivity to changes about the 

optimum are not specified. In addition, these indexes are demonstrated using the results from 

desktop simulations of limited realism. 

The present study is intended to be an additional step in the development of a directional 

handling qualities database and the production of preliminary estimates of acceptable pedal feel 

characteristics. Tests were conducted in a fixed-base simulator for a medium-sized commercial 

transport with two engines mounted under the wings. An artificial piloting task that required 

multiple rudder pedal inputs was developed specifically for the purposes of this research. 

Twelve volunteer airline pilots performed the artificial maneuver, which consisted of a simulated 

manual approach to a runway in a crosswind with random turbulence. A severe random lateral 

wind shear was introduced near the ground that ordinarily would cause the pilot to execute a goaround. However, the pilot was instructed to neither execute a go-around nor attempt a landing. 

Instead, the pilot was instructed to level off at about 50 feet above the ground, correct any lateral 

offsets from the runway centerline, and then track the remaining runway in a de-crabbed, crosscontrolled state. After each maneuver the pilot rated the airplane handling qualities using the 

Cooper-Harper (C-H) pilot rating scale. 

A simple and highly effective test matrix called a Central Composite Design (CCD) was 

used to minimize the number of simulation tests required. This design is efficient when used 

with a 10-term, second-order response surface equation with three independent research 

variables [ref. 7]. With this test matrix each maneuver was conducted with one of 15 unique 

combinations of maximum force, breakout force, and maximum travel. The maximum force was 

varied between 30 and 150 pounds; the breakout force was varied between 3 and 50 pounds, and 

the maximum travel was varied between +1 and +4 inches.

The ten coefficients of the response surface equation estimating the C-H rating as a 

function of the three research variables were determined in a least squares sense. The ten terms 
8

included a constant, the linear variations of the three research variables, their interaction terms, 

and their squares. The equation was then used to produce contour plots of constant pilot ratings 

as a function of two of the parameters with the third parameter held constant. These contour 

plots showed regions of good handling qualities as well as regions of degraded handling 

qualities. In addition, a numerical equation solver was used to predict the optimum parameter 

values (those with the lowest pilot rating). 

To supplement the subjective C-H pilot ratings, quantitative data such as tracking error 

and pilot inputs were recorded and analyzed. Various measures of pilot performance and Pilot 

Induced Oscillation (PIO) tendencies were explored. The most fruitful measure was the peak 

value of the cross power spectra between pilot input such as pedal force and airplane response 

such as heading. A response surface equation of the same form as that for the C-H ratings was 

used to produce contour plots and optimum parameter values using the same procedures used for 

the qualitative C-H ratings. The quantitative peak cross spectra data were in general agreement 

with the qualitative C-H ratings. 

Description of Simulator 

The Langley Integration Flight Deck (IFD) fixed-based simulator, shown in Figures 1 

and 2, was used for all tests reported in this paper. The simulator represented a medium size 

commercial transport with two engines mounted under the wings and a weight of approximately 

180,000 pounds. A conventional wheel and column control, rudder pedals, and twin engine 

throttles were provided. The simulation used a high fidelity, 6-degree-of-freedom, non-linear 

math model similar to that in a Level D commercial transport training simulator. Included in the 

simulation were non-linear models of the cable and hydraulic actuator systems for the pitch, roll, 

and yaw controls. In addition, a conventional yaw damper for transport airplanes was simulated 

to suppress the lightly-damped Dutch roll response. The entire simulation was solved on a 

digital computer in real-time at a rate of 50 times per second. A representative time history of 

the transient directional response to a ramped, full rudder input is shown in Figure 3. These 

responses probably have an effect on the results of this study and should be compared to the 

responses of other simulation studies of directional handling qualities. They can also be used 

with the pilot ratings obtained in this study to estimate proposed handling qualities indexes [ref. 

6].
9

 Figure 1. Exterior view of fixed-base Langley Integration Flight Deck (IFD) Simulator. 

Figure 2. Interior view of Langley IFD simulation cockpit. (Stereo) speakers were designed to 

provide a lateral acceleration cue. 
10

Figure 3. Transient response to a ramped, full rudder input at the test flight condition with 

Control Loader Combination #8. 

The out-the-window visual scene was driven by a computer-generated-image system with 

an approximate 200-degree field of view. The average pure transport delay in the visual channel 

was determined to be approximately 72 ms. The visual database of the scene represented the 

Dallas/Fort Worth airport and its surrounding terrain. The study utilized runway 36L, which is 

13,400 feet long and 150 feet wide. The visual database included all runways, taxiways, airport 

structures, and buildings. All tests were conducted in a simulated daylight environment with full 

visibility.

Hydraulic control loaders were provided for the wheel and column and varied the forces 

according to non-linear models of airspeed and other airplane and control system states. For the 

nearly-constant flight conditions of the present tests, the quasi-static control forces of the column 

and wheel are shown in Figures 4 and 5.
11

Figure 4. Quasi-static column forces. 

Figure 5. Quasi-static wheel forces. 
12

Hydraulically-loaded rudder pedals were used for directional control. The pedals were 

actuated through slots in the cockpit floor rather than from the side or from above as in some 

commercial transport airplanes. The floor under the pedals was covered with carpet. The slots 

and carpet presented a potential resistance to pedal inputs compared to the smooth metal floor 

underneath the rudder pedals in most commercial transports. The pilots were advised to place 

their feet high on the pedals to eliminate any interference. The maximum force, breakout force, 

and maximum travel of the rudder pedals were varied from run to run but, unlike the wheel and 

column, were constant during a given run regardless of changing airspeed and flight conditions.

The simulated pedal/rudder control system included a ratio changer to compensate for speed 

changes. The simulated mechanical gearing between the pedal and rudder ratio changer was 

modified so it changed whenever the pedal travel was changed in the course of the experiment. 

That is, the simulated mechanical gearing was programmed to change simultaneously with the 

changes in pedal travel so that the maximum rudder deflection normally attainable through the 

ratio changer was unaffected. In this way, only the pedal travel changed while the maximum 

rudder available at any given airspeed was a constant. 

In an attempt to compensate for the lack of motion cues, an experimental sound system 

using stereo speakers mounted on the pilot’s seat on either side of his/her head was installed, as 

shown in Figure 2. The sound level of a constant-pitch tone was made proportional to the lateral 

acceleration at the pilot’s station. For zero acceleration there was no sound; but when the 

simulated pilot’s station was accelerating to the right, the sound level increased in the right 

speaker; and when accelerating to the left, the sound level increased in the left speaker. 

Data recordings (e.g. control inputs, attitudes, etc.) were made at 10 samples per second. 

Video and audio recordings of the pilot’s actions and comments were also made. 

TEST SUBJECTS 

All the pilots who served as test subjects were volunteers who were paid a small stipend 

and expenses to participate. All were active airline pilots (either captain or first officer) with 

widely ranging levels of experience as seen in Table 1. The pilots were all currently flying 

airplanes with column and wheel controls similar to those in the simulator. 

Table 1. Test Subjects 

• All active airline pilots operating equipment with wheel/column controllers 

• 7 males and 5 females 

• 4 captains and 8 first officers 

• Individual Total Hours: 5,500 to 20,000, average = 11,000 

• Individual Hours in command: 500 to 18,500, average = 5,000 

• 6 with military flying experience and 6 without military flying experience 

Tests

Development of Research Maneuver: Several maneuvers were studied during 

extensive preliminary tests (data not shown). These maneuvers were flown by NASA research 
13

engineers who were qualified to fly transport airplanes. The goal was to develop a maneuver 

that required rudder pedal inputs and was amenable to pilot ratings. Standard, operationallyrelevant maneuvers such as engine failures did not produce much rudder pedal activity other than 

a steady input. An artificial, one-degree-of-freedom, yawing disturbance was studied and 

rejected because it was very unnatural. The selected maneuver, described below, was a 

compromise between an operationally realistic maneuver and a completely artificial maneuver. 

It became apparent during the tests that the C-H pilot ratings were dependent on the 

severity of the wind shears and whether the wind shears reversed direction. For consistency, it 

was decided to base the subjective C-H pilot rating analysis on only medium wind shears. 

However, it was feared that the pilots would learn to react in a mechanical (open-loop) manner if 

they were repeatedly exposed to only medium wind shears. Therefore, lower and higher wind 

shears were retained to prevent the pilots from learning how much input was needed for the 

medium wind shears. The result was that the test matrix size had to be doubled from 18 to 36 

data runs per pilot. Only the pilot ratings for the medium wind shears will be presented.

However, quantitative data will be presented for all the wind shears. 

Research Tests: All research test sessions were conducted from 8:00 am to 4:30 pm 

local time. The test session started with a 1-hour briefing covering the program background, a 

description of the simulator, the research variables, the maneuver, and the C-H rating scale. 

After the briefing, the test subjects were given a 1-hour familiarization/practice period in the 

simulator. All test subjects flew the simulator in the left seat regardless of whether they 

currently were a captain or a first officer. The first runs during this practice period were 

conducted with a nominal combination of rudder pedal characteristics. A combination is defined 

by three numbers (M, B, X) where M is the maximum force in pounds, B is the breakout force in 

pounds, and X is the maximum travel in inches. For the nominal combination, M = 90 lbs, B = 

26.5 lbs, and X= 2.5 inches or expressed as coordinates (90, 26.5, 2.5). A generic figure 

depicting the three research variables is presented in Figure 6.

Figure 6. Illustration of the three static pedal parameters  M ,B, X . Note that the slope around 

the origin has been greatly reduced for illustrative purposes. 
14

Approximately six practice approach and tracking maneuvers were performed starting 

with no steady winds or random turbulence, then adding winds and turbulence, and ending with a 

severe lateral wind shear described below. After the six practice maneuvers with the nominal 

pedal feel characteristics, the test subjects were given five additional runs with some of the most 

extreme pedal feel characteristics. However, for these five additional practice runs, a steady 

track angle maneuver at a constant altitude of 1,700 feet above ground level (AGL) was used 

rather than the research approach and runway tracking maneuver. For these maneuvers the test 

subjects were instructed to make slow, full-travel pedal inputs while keeping the wings fairly 

level. In this way, the test subjects experienced the full range of maximum pedal forces, 

breakout forces, and travel that would comprise the research test matrix. After the practice 

period, the actual research maneuvers were conducted. The test subjects were given a break after 

about one hour in the simulator or when they or the researcher felt tired.

Test Matrix: The test matrix for the independent variables is presented in Table 2. It was 

arranged according to a Central Composite Design (CCD) [ref. 7]. Fifteen unique combinations 

of rudder pedal feel characteristics were tested, but the nominal combination (90, 26.5, and 2.5) 

in the center of the matrix was used four times so that there were a total of 18 test conditions.

Measurements of the pedal characteristics for quasi-static inputs were made on the simulator for 

these 15 combinations and are shown in Figure 7. 

Table 2. Test Matrix 

(Control loader combinations are designated by the numbers in the shaded blocks) 

Figure 7. Measured quasi-static pedal forces for the 15 unique combinations tested. Coulomb 

friction = 1 lb and viscous friction = 1 lb/(in/sec). 
15

An explanation for the choice of the values in the test matrix is better understood by 

examining Figure 8. This pictorial representation of a generic CCD test matrix for three 

independent variables places the origin at the center of the selected range of each of the three 

independent variables—in this case at 90, 26.5, and 2.5. The coordinates are then normalized so 

that the normalized coordinates of the origin are 0, 0, and 0 and the extreme values are r1.4 .

The six extreme values are symmetrically placed on the plus and minus coordinate axes. The 

eight corners of the box are then placed at the appropriate combinations of r1. This test matrix 

is efficient for fitting the 10-term response surface equation shown later in the Data Reduction 

section.

Figure 8. Pictorial representation of a central composite design with 3 independent parameters 

(normalized). 

There were also 18 different combinations of wind shears, as shown in Table 3. These 

wind shears were selected during the maneuver development phase of the research (described 

above) because they were severe, but not unrealistic. The wind shear combinations were defined 

by three numbers: (1) the initial crosswind, Eo, (+15 kts or -15 kts), (2) the final crosswind, Ef,

(+15 kts, -15kts, +30 kts, or -30 kts), and (3) the altitude, ho, at which the transition from the 

initial to final crosswind began (100 feet, 125 feet, or 150 feet). The rate of change during the 

transition was a constant 15 kts/2 seconds. The wind shears are illustrated in the 6 time histories 

in Figure 9, which have generic time scales not related to the three altitudes at which the shears 

were actually initiated. Table 3 reveals that six wind shear scenarios had a 15 kts change in cross 

winds, six wind shear scenarios had a 30 kts change in the cross wind, and six wind shear 
16

scenarios had a 45 kts change in cross wind. The 30 kts-change wind shears are referred to 

herein as the “medium wind shears” and are used for the pilot ratings presented later. 

Table 3. Wind Shear Scenarios 
17

Figure 9. Lateral wind shear scenarios (Time scales are generic and not related to the actual time 

used in the tests). 

The 18 research variable combinations and 18 wind shear scenarios were randomly 

presented to the pilots so that they could not predict which combination was going to be 

presented for a given simulation run. In addition, each pilot was presented with a different 

combination of research variable combinations and wind shear scenarios so that any interaction 

due to the order of presentation would be averaged out for all 12 pilots. Each pilot flew a total of 

36 maneuvers (each pedal feel combination was flown twice, but with different wind shears). A 

typical run sequence for one pilot is shown in Table 4. The pilot rating (qualitative) data are 

presented for only the medium wind shear scenarios (+15 kts to -15 kts or -15 kts to + 15 kts).

The other wind shear scenarios were primarily intended as “fillers” to keep the pilots from 

recognizing the pattern of the medium wind shears. However, the quantitative data are presented 

for all the wind shear scenarios. 

Description of Research Maneuver: The maneuver started at an altitude of about 1,700 

feet AGL, stabilized with the wings level on the minus 3-degree glide slope to runway 36L, and 

yawed into the +15 kts initial crosswind. The airplane was in the landing configuration (flaps 

fully extended and the landing gear down) at an air speed of 130 kts. The yaw damper was on, 

but the auto throttles were off. The pilot was instructed to continue the approach as if to make a 

landing and to yaw out of the wind (“decrab” using cross controls) at an altitude of 400 feet 

AGL. Between 150 and 100 feet AGL the wind shear was introduced. Although, in general, the 

approach was no longer stabilized and would ordinarily have demanded a go-around, the pilots 

were instructed not to execute a go-around or to attempt a landing. Instead they were instructed 

to level off at about 50 feet AGL and correct any lateral offsets back to the runway centerline.

From that point on they were to continue tracking the centerline of the runway at 50 feet AGL 

and the nominal airspeed of 130 kts using column and throttle inputs. They were instructed to 

keep the airplane’s nose aligned with the runway centerline and keep the lateral displacement 

small so they could have made a landing if they had been required to (neglecting the fact there 

would not have been sufficient distance to stop on the runway after they landed). This maneuver 

required holding cross controls for several seconds while they transited the entire length of the 

runway after which the maneuver was terminated. The pilots were instructed to ignore the 

possibility of wing scrapes on the runway. Moderate random turbulence was constantly 
18

superimposed on the steady winds and wind shears. This turbulence required the pilots to 

constantly make small corrections that were especially important while tracking the runway 

centerline. 

Table 4. Typical Run Sequence 

(Shaded combinations were used for C-H ratings) 

Cooper-Harper Pilot Ratings: None of the pilots who participated in this study had any 

previous experience using the C-H rating scale, shown in Figure 10 [ref. 7]. Therefore, they 

were trained on the use of the scale during the initial briefing period. They were told to rate the 

total task including the longitudinal, lateral, and directional tasks but with emphasis on the 

directional task. It is recognized that rating the entire task can introduce scatter in the C-H 

ratings, but it was also important to account for the effects of the directional handling qualities 

on the other axes.
19

Figure 10. Cooper-Harper (C-H) pilot rating scale. 

The pilots were given a definition of “adequate performance” on the rating scale, i.e., “(1) 

returning the airplane back to the runway centerline (after the destabilizing wind shear) and 

stabilizing the lateral drifts and heading within the first half of the runway, (2) tracking down the 

second half of the runway close enough to the centerline so that a landing could have been made 

(without consideration of the runway remaining for stopping), and (3) maintaining the heading of 

the airplane aligned close enough to the centerline of the runway so that a landing could have 

been made.” Likewise, the pilots were given a definition of the words “satisfactory without 

improvement” on the rating scale, i.e.,: “an airplane that you, as a hypothetical chief test pilot in 

the development of this airplane, would recommend for production and operation for the 

complete life-cycle of the airplane.” The pilots were told to use their own judgment as to what 

was a “tolerable” workload and the correct adjective (“minimal,” “moderate,” “considerable,” 

etc.) to modify the words “pilot compensation.” 

For the purposes of this research, and due to the test subjects’ lack of experience with the 

C-H scale, the emphasis was not on the absolute pilot ratings, but rather on the sensitivities of 

pilot ratings to the pedal force-feel characteristics. The ratings that were given should be much 

more reliable in predicting relative merits between different combinations of the pedal feel 

parameters. Therefore, the ratings should be accurate in predicting optimum combinations of the 

parameters and the sensitivity to off-optimum combinations. 
20

Data Reduction 

The data can be analyzed and interpreted in different ways. For example, an analysis 

based on the highest C-H pilot rating for each control loader combination might be of interest.

Alternately, an analysis based on the largest variability in the C-H pilot ratings might be of more 

interest. For this report, the emphasis is on the average C-H pilot rating for each control loader 

combination. But this emphasis should not hide the fact that there were large variations in the 

pilot rating between pilots for the same control loader combination. The same comments apply 

equally well to the quantitative measurements of pilot performance and airplane response. 

One way to address the variation in pilot ratings is to fit an equation to the data. For 

example, the C-H pilot ratings for the medium wind shears were used to determine, in least 

squares, the ten coefficients of the following equation (referred to herein as the response surface 

equation)

2

10

2

9

2

1 2 3 4 5 6 7 8 PR(M ,B, X ) b  b M  b B  b X  b MB  b MX  b BX  b M  b B  b X (EQ. 1) 

A set of ten coefficients was determined from the pilot ratings of Pilot #1; the combined 

pilot ratings of Pilots #1 and #2; the combined pilot ratings for Pilots #1, #2, and #3; and so forth 

up to the combined pilots ratings for all 12 pilots. Comparisons of the predictions of pilot ratings 

( PR ) for these groups of pilots were made from these sets of coefficients to determine the 

number of pilots needed to converge on consistent estimates of PR(M ,B, X ).

An additional analysis was conducted on the quantitative performance data to measure 

the tendency toward a directional PIO. Cross spectra of the pedal force (pilot input) and the 

airplane heading (airplane response) were calculated. The peak value of these spectra for 

frequencies greater than 0.2 Hz was examined as a possible indicator of a PIO tendency. An 

equation of the same form as EQ. 1 was used to reduce these data. 

2

10

2

9

2

1 2 3 4 5 6 7 8 PS(M , B, X ) b  b M  b B  b X  b MB  b MX  b BX  b M  b B  b X (EQ. 2) 

However, in this case and explained earlier, the data from all wind shears and not just the 

medium wind shears were used. 

The response surface (EQ. 1 and EQ. 2) is versatile for interpreting and summarizing the 

data. The pilot ratings (PR) and peak spectra values (PS) can be calculated for any combination 

of the three independent variables M, B, and X. This makes it possible to construct contour plots 

as a function of any two of the variables M, B, and X while the third variable is held constant. 

The equations can also be used to find the combinations of M, B, and X that give the best 

(minimum) pilot rating or peak spectra values. That is, using an equation solver, the best 

combination of M, B, and X can be determined. If one (or two) of the parameters is constrained 

to a fixed value (or fixed values), the constrained optimum values of the other two (or one) 

parameters can be determined. For example, if X is constrained, the optimum values of M and B 

can be readily determined. Finally, the sensitivity of PR or PS to changes in M, B, and X about a 

design point can be determined by simply varying the parameter of interest while holding the 

other two parameters fixed. 
21

RESULTS AND DISCUSSION 

Time histories of a typical maneuver are presented in Figure 11, which shows little 

rudder activity before the wind shear at about 130 seconds. When the airplane was over the 

runway (after approximately 140 seconds), the pilot in this case was able to track the centerline 

fairly well. However, the pilot did not completely perform the decrab maneuver at 400 feet AGL 

(at approximately 100 seconds) as instructed, nor did the pilot perfectly align the heading with 

the runway after the wind shear when tracking the runway centerline. An examination of other 

time histories (not shown) showed this was a fairly typical response. That is, the pilots often 

failed to completely decrab the airplane while occasionally they decrabbed too much causing the 

nose of the airplane to be pointed slightly to the downwind side of the runway. The simulator, 

like a real airplane, lacked a positive visual cue of the heading making it difficult for the pilots to 

judge their actual heading. That is, the wide windshield field of view provided no ready 

reference for heading. Another possible reason for the partial decrab maneuvers is that in 

ordinary commercial transport airplane operations, the pilots can use a large crab angle at 

touchdown because of the strength of the landing gear on transport airplanes. 

Figure 11. Typical time histories of a research maneuver for control loader combination #8. 

In contrast, the view of the runway centerline provided a positive cue of the lateral 

position error, and operational landings have to be made near the runway centerline. When the 

pilots failed to completely decrab, their pedal forces were reduced. When they decrabbed too 

much, their pedal forces were increased over those required for a complete decrab in which the 

airplane was pointed directly down the runway. More important, the poor visual heading cues 

probably reduced the number of small corrective rudder inputs made by the pilots. An artificial, 

head-up, pointer on the horizon might have given the pilot the needed heading reference to more 

fully reveal any hidden tendencies to directional PIOs using the present evaluation maneuver. 

Pilot Ratings: The C-H pilot ratings for medium wind shears for all pilots are presented 

in Table 5 and plotted in Figure 12. There were wide variations in the C-H pilot ratings for a 

given control loader combination. For example, for control loader combination #6, Pilot #1 gave 

a rating of 1 and Pilot #9 gave a rating of 10. Control loader combination #6 had a breakout force 

of 26.5 pounds, but a maximum force of only 30, which Pilot # 9 said was too light. Pilot #9 was 

not able to stabilize the lateral position causing the pilot to make large pedal inputs in opposite 

a. Longitudinal parameters b. Directional parameters
22

directions as the runway centerline was overshot. At the same time, the airspeed got low and the 

angle of attack large so that the pilot actually touched down on the runway instead of 

maintaining the desired 50 feet AGL. Since the pilot could not control the lateral position and 

maintain altitude, combination #6 was given a rating of 10. 

Table 5. Cooper-Harper Pilot Ratings 

Note: Only pilot ratings for medium wind shears (wind shear scenarios 2, 5, 8, 11, 14, and 17 in 

Table 3) are shown. The shaded area is the center of the test matrix where M, B, and X are 

constant (90 lbs, 26.5 lbs, and 2.5 inches, respectively). 

Figure 12. Summary of pilot ratings showing the averages and variations about the average. 
23

The other control loader combination that was rated a 10 by Pilot #7 was control loader 

combination #5 (133, 43.3, and 1.43). Pilot #7 said this combination’s forces were too heavy 

and the travel was too short with the result so there was no indication where the rudder was 

located. The pilot also got high and fast with a large, unstabilized angle of attack, roll attitude, 

and lateral position error. Therefore, the pilot felt momentarily out of control and gave a pilot 

rating of 10.

Both combinations with a pilot rating of 10 demonstrate the coupling between the rudder 

pedals and the lateral and longitudinal tasks. That is, when the rudder pedals do not feel right, 

the pilot can become saturated with the directional task. As a result, the pilot momentarily 

ignores the lateral and longitudinal tasks causing large errors to develop in those axes.

The variation for a given pilot for the same control loader combination was also large — 

as much as 5 C-H rating units. This can be verified by referring to Table 5 for Pilots #3 and 9 for 

control loader combinations #8 through 11. Control loader combinations #8 through 11 were all 

M=90 lbs, B=26.5 lbs, and X=2.50 inches. Finally, there were large differences between pilots. 

For example, Pilot #1 had an average rating for all 18 control loader combinations tests of about 

2.4 while Pilot #3 had an average rating of about 6.0.

Many of these variations in pilot ratings were probably due to wide-ranging differences 

in pilot skill level and experience, shown in Table 1. But, as noted above, there were also 

substantial differences in the pilot ratings and performance for a given pilot for the same 

experimental condition. It appeared that many of these latter differences were due to the 

essentially open-loop pedal inputs to initially counter the wind shears. That is, when the wind 

shear was encountered, the pilot made a rather large step pedal input not really knowing what the 

pedal forces and travel were. After the large step input, the pilot needed to hold a steady pedal 

input and make small multiple inputs about that steady input. If the pilot’s first (open-loop) step 

input was close to the average value actually needed, the remaining task was much easier and the 

performance was better. Alternatively, if the pilot’s first step input was either too big or too 

small, the pilot often unsuccessfully searched for the correct input for the rest of the run.

Equation 1 for PR was fit to the ratings of different pilot combinations, and the resulting 

predictions are shown in Figure 13. In the upper left corner of Figure 13 the predictions for the 

ratings of Pilot #1 are compared to the predictions for the combined ratings of Pilots #1 and #2. 

As the data for more pilots are added, the difference due to each additional pilot gets smaller as 

can be seen from the other three plots in Figure 13. The change between consecutive pilots 

appears to be about the same for Pilots #1 through 7 compared to Pilots #1 through 8 (lower left 

plot) and Pilots #1 through 11 to Pilots #1 through 12 (lower right plot). 
24

Figure 13. Effect of additional pilots on response surface equation predictions and average C-H 

pilot ratings. 

Also, the worst control loader combinations were #4 and #5 as shown in Figure 13 

because they consistently had the highest values. The best combination was #18, but it was not 

much better than #16 or the nominal combinations #8 through #11. 

The estimated values of the coefficients for the combined data of all 12 pilots are 

presented in Table 6. These values were used to make the following predictions, but the 

fundamental information is included in these coefficients. That is, the equation can be used 

directly to calculate the pilot rating for any combination without reference to Figure 13 or the 

contour plots that follow. 

Table 6. Estimated Coefficients for Response Surface Equation for C-H Pilot Ratings 

b1 b2 b3 b4 b5 b6 b7 b8 b9 b10 

7.12966 -0.02491 -0.09033 -1.17499 5.79E-05 -0.01089 0.00348 0.00033 0.00197 0.27947
25

The cumulative average C-H pilot rating for all 18 pedal feel combinations is shown in 

Figure 14. As the data for more pilots are added to the average, the average effectively reaches a 

constant value of approximately PR 4.3 after 4 to 6 pilots. This result is consistent with the 

lower 2 plots in Figure 13 and indicates if the goal is to predict the average pilot rating — that 

six test subjects will be sufficient. 

Figure 14. Mean pilot ratings as more pilots are added to the calculations. 

Assuming that the C-H rating for all 12 pilots is the best estimate of the true handling 

qualities, the difference, or error, in using a smaller number of pilots is shown in Figure 15. For 

example, the error in the average pilot rating for the data of the first six pilots was less than 0.1 

C-H rating unit. The corresponding maximum errors in the average rating for all the individual 

pedal feel combinations were approximately +0.5 C-H rating units. These results suggest that 

ratings from only six pilots were needed to arrive at a consistent estimate of the handling 

qualities.

Figure 15. Errors in the predicted C-H pilot ratings assuming the predicted ratings for all 12 

pilots are correct. 
26

The response surface equation was used to populate the test matrix in Table 7. From this 

table, it is apparent that, in general, the pilots preferred longer travels, medium breakouts, and 

medium maximum forces. These observations will be confirmed in the contour plots that follow. 

Table 7. Predicted C-H Pilot Ratings 

The maximum force-breakout force contours of constant pilot rating are presented for 

three different values of maximum travel shown in Figures 16, 17, and 18. It should be noted the 

contours in the corners of these plots are extrapolations from the actual control loader 

combinations tested. The coordinates of the actual test points projected on the plane of the figure 

are plotted to illustrate the amount of extrapolation. The minimum (best) pilot rating decreases 

from 3.8 to 2.7 as the maximum travel increases from 1.5 to 3.5 inches. The breakout force at 

the minimum pilot rating is nearly independent of travel and has an approximate value of 18 to 

21 pounds. On the other hand, the maximum force at the minimum pilot rating increases from 

about 62 to 95 pounds as the travel increases from 1.5 to 3.5 inches.

Figure 16. Contours of C-H pilot ratings for a maximum travel of 1.5 inches. 
27

Figure 17. Contours of C-H Pilot Ratings for a Maximum Travel of 2.5 inches. 

Figure 18. Contours of C-H Pilot Ratings for a Maximum Travel of 3.5 inches. 
28

Figure 19 provides an alternate illustration of the effect of travel. For the nominal 

breakout force of 26.5 pounds, the minimum pilot rating occurs very near the high end of the 

travel tested. It would probably have been desirable to have tested to slightly larger travels than 

the current hardware was capable of producing.

Figure 19. Contours of C-H Pilot Ratings for a Breakout Force of 26.5 pounds. 

It is possible that during the initial practice runs with the fixed set of nominal pedal 

characteristics (M=90 lbs, B=26.5 lbs, and X=2.5 inches), the pilots developed a preference for 

this combination. An indication of this possible preference is the fact the optimum breakout 

force was 18 to 21 pounds while the maximum allowable breakout force is 14 pounds [ref. 2].

Further experiments will be required to determine the effect of the nominal practice conditions 

on the final result.

PIO Tendencies: Two time histories are presented in Figure 20. The time histories on 

the right show an oscillation at the same frequency in both the pedal force and the airplane 

heading while the time history on the left shows practically no oscillation in the pedal force and a 

turbulence induced oscillation in the heading. In both time histories the pedal force is divided by 

-150 and the heading by 20 to make them have approximately the same relative magnitude and to 

ensure positive values correspond to the same direction (nose right). The Dutch roll frequency 

was about 0.14 Hz and the observed oscillation frequency was about 0.4 Hz. Therefore, it 

appears that the pilot was inducing the observed oscillation although it was not a divergent 

oscillation.
29

 a) No pilot induced oscillations b) Pilot induced oscillations 

Figure 20. Time Histories Comparing Pilot Induced Oscillation (PIO) Tendencies. 

Cross power spectra between the pedal force and heading for the same two maneuvers are 

shown in Figure 21. A cross power spectra indicates a correlation between two parameters at a 

given frequency. Unless another factor was causing both the pedal force and heading to oscillate 

at the same frequency, it can be assumed that the pilot’s pedal force was causing the heading to 

oscillate—a PIO. The spectrum on the left shows practically no peak while the one on the right 

shows a definite peak at about 0.4 Hz indicating a tendency toward a PIO. A short program was 

written to capture the peak value of the spectra for frequencies greater than 0.2 Hz from the data 

files. The 0.2 Hz lower limit was imposed to eliminate large-scale, deliberate maneuvers. 

 a) No pilot induced oscillations b) Pilot induced oscillations 

Figure 21. Cross Power Spectra Comparing Pilot Induced Oscillation Tendencies. 

The program extracted the peak values for all research runs for all pilots. So, unlike the 

pilot ratings, the peak values were extracted for all wind shears and not just the medium wind 

shears used for the subjective pilot ratings. The results of this extraction process are presented in 

Table 8. The peak values are multiplied by 100 for better readability. An examination of this 

table indicates large variations similar to those for the pilot rating data. The reasons for these 

variations are probably the same as those discussed earlier for the pilot rating data. 

 The coefficients of EQ. 2 for PS were computed for the numbers in Table 8, and the 

results are shown in Table 9. These coefficients were used to make all the following predictions. 
30

Table 8. Peak Values of Cross Spectra 

Note: These peak values of cross spectra for frequencies greater than 0.2 Hz have been 

multiplied by 100. The shaded area is the center of the test matrix where M, B, and X are 

constant (90 lbs, 26.5 lbs, and 2.5 inches, respectively). 

Table 9. Estimated Coefficients for Response Surface Equation for Peak Values of Cross 

Spectra
31

For example, the equation was used to populate the test matrix as shown in Table 10. 

The results are, in general, consistent with the pilot ratings. The shorter travels generally have 

both higher pilot ratings (undesirable) and larger tendencies toward PIOs (undesirable).

However, the smaller breakout forces sometimes had lower pilot ratings but slightly larger 

indicated tendencies toward PIOs. 

Table 10. Predicted Peak Values of Cross Spectra 

Contour plots of constant peak power spectra values (PIO tendencies) are shown in 

Figures 22 through 25 for the same combinations of pedal feel characteristics as those in Figures 

15 through 19 for the pilot ratings. A comparison of the two sets of figures indicates that the 

indicated PIO tendencies are generally consistent with the pilot ratings. This consistency is 

examined in more detail in the next section. 

Figure 22. Contours of Peak Values of Cross Spectra for a Maximum Travel of 1.5 inches. 
32

Figure 23. Contours of Peak Values of Cross Spectra for a Maximum Travel of 2.5 inches. 

Figure 24. Contours of Peak Values of Cross Spectra for a Maximum Travel of 3.5 inches. 
33

Figure 25. Contours of Peak Values of Cross Spectra for a Breakout Force of 26.5 lbs. 

Sensitivity Analysis: The response surface (EQ. 1 and 2) can be used to determine the 

sensitivity to changes in M, B, and X about an initial combination or design point. To illustrate 

this capability, the initial combination was set to 90, 26.5, and 2.5, which is the center of the test 

matrix. However, any other initial combination could have been selected.

The sensitivity of PR and PS to changes in the force at maximum travel, M, is shown in 

Figure 26. Although the minimums in the two curves occur at different values of M due to the 

flatness of curves near the minimum, the shape and trends of the two curves are similar. The 

same observations are made for the sensitivity curves for B and X shown in Figures 27 and 28, 

respectively. Thus, it appears that the quantitative peak power spectra data are consistent with 

the qualitative pilot rating data. 
34

Figure 26. Sensitivity of pilot ratings and peak power spectra values to changes in the force at 

maximum travel. Breakout force = 26.5 lbs and maximum travel = 2.5 inches. 

Figure 27. Sensitivity of pilot ratings and peak power spectra values to changes in the break out 

force. Force at maximum travel = 90 lbs and maximum travel = 2.5 inches. 
35

Figure 28. Sensitivity of pilot ratings and peak power spectra values to changes in the maximum 

travel. Force at maximum travel = 90 lbs and breakout force = 26.5 lbs. 
36

SUMMARY AND RECOMMENDATIONS 

The rudder pedal static force feel characteristics of a medium-size commercial transport have 

been studied on a fixed-base simulator using active airline pilots as test subjects. The pilots 

assessed the handling qualities for an artificial research maneuver using the C-H rating scale. 

Pilot inputs and airplane responses were measured and analyzed. The following summarizes the 

results of this study: 

1. A test matrix based on a central composite design was effectively used to evaluate 

the effects of rudder pedal force breakout, maximum force, and maximum pedal 

deflection for an artificial research maneuver. 

2. A response surface equation was developed to predict the C-H pilot ratings for 

different combinations of three static rudder pedal force/feel characteristics. This 

equation is useful for constructing pilot rating contour plots, predicting 

combinations of pedal characteristics for minimum pilot ratings, and determining 

sensitivity to changes about a given combination of static rudder pedal force/feel 

characteristics.

3. An analysis of the cross power spectra of the pilot input and airplane response 

demonstrated a correlation of the peak values of the cross power spectra with 

PIOs. A response surface equation was developed to predict the peak values of the 

cross power spectra. This equation is also useful for constructing contour plots of 

the peak values, predicting combinations of pedal characteristics for minimum 

peak values, and determining the sensitivity to changes about a given combination 

of static rudder pedal force/feel characteristics. The predictions of the pilot ratings 

and cross power spectra are generally consistent with each other. That is, they 

show similar trends for the same combinations of pedal force/feel characteristics. 

4. Although the airline pilots who participated in this study had limited experience in 

the use of the C-H rating scale, the central-composite-design/response-surfaceequation methodology converged on a consistent average answer for about six 

pilots. This convergence was in spite of large variations in the individual pilot 

ratings and the peak values of the cross power spectra. 

5. An experimental stereo sound system designed to provide lateral directional cues 

in the fixed-base simulator was ineffective. 

6. It is recommended that future research determine the effects of: (a) simulator 

motion cues; (b) the research maneuver used; (c) the choice of the nominal pedal 

force/feel combination; (d) wheel force/feel characteristics; (e) column force/feel 

characteristics; and (f) the transient directional response to rudder inputs. 
37

REFERENCES 

1. Anon., “Part 25 – Airworthiness Standards: Transport Category Airplanes,” Department 

of Transportation, Federal Aviation Administration, 2002. 

2. Chalk, C.R., Neal, T. P., Harris, T. M., and Pritchard, F. C., “Background Information 

and User Guide for MIL-F_8785B (ASG), ‘Military Specification—Flying Qualities of 

Piloted Airplanes,’” AFFDL-TR_69_72, Air Force Flight Dynamics Lab, WrightPatterson AFB, OH, August 1969. 

3. Anon “In-Flight Separation of Vertical Stabilizer American Airlines Flight 587 Airbus 

Industrie A300-605R, N14053 Belle Harbor, New York November 12, 2001,” Aircraft 

Accident Report NTSB/AAR-04/04 National Transportation Safety Board, Washington, 

D.C.

4. Lee, B. “Criteria to Select Directional Control Sensitivity,” AIAA Paper 2005-6033, 

August 2005. 

5. Lee, B.; Rodchenko, V.; Zaichik, L.; and Yashin, Yu, “Effect of Pedal Feel System 

Characteristics on Aircraft HQ,” AIAA Paper 2005-6034, August 2005. 

6. Hess, Ronald A. “Certification and Design Issues for Rudder Control Systems in 

Transport Aircraft,” Journal of Guidance, Control, and Dynamics Vol. 29, No. 5, 

September-October, 2006. 

7. Montgomery, Douglas C. “Design and Analysis of Experiments,” Fifth Edition 2001 

John Wiley & Son, Inc; ISBN 0-471-31649-0; QA279.M66200 

8. Cooper, George E. and Harper, Robert P.: “The Use of Pilot Rating in the Evaluation of 

Aircraft Handling Qualities,” NASA TN D-5153; April 1969. 
REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing

data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or 

any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate

for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that

notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently

valid OMB control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.

1. REPORT DATE (DD-MM-YYYY) 2. REPORT TYPE 3. DATES COVERED (From - To) 

4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER 

5b. GRANT NUMBER 

5c. PROGRAM ELEMENT NUMBER 

6. AUTHOR(S) 5d. PROJECT NUMBER 

5e. TASK NUMBER 

5f. WORK UNIT NUMBER 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION

REPORT NUMBER 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSORING/MONITOR'S ACRONYM(S)

11. SPONSORING/MONITORING

REPORT NUMBER 

12. DISTRIBUTION/AVAILABILITY STATEMENT

13. SUPPLEMENTARY NOTES 

14. ABSTRACT

15. SUBJECT TERMS 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 

ABSTRACT

18. NUMBER 

OF

PAGES

19a. NAME OF RESPONSIBLE PERSON

a. REPORT b. ABSTRACT c. THIS PAGE

19b. TELEPHONE NUMBER (Include area code) 

Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. Z39-18 

01-01-2008 Technical Publication Jul 2005 - Jan 2008

A Piloted Simulator Evaluation of Transport Aircraft Rudder Pedal

Force/Feel Characteristics

457280.02

Stewart, Eric C.

NASA Langley Research Center

Hampton, VA 23681-2199 L-19330

National Aeronautics and Space Administration

Washington, DC 20546-0001

NASA

 NASA/TP-2008-215109

Publicly Available Availability: NASA CASI (301) 621-0390

Subject Category 08: Aircraft Stability and Control

A piloted simulation study was conducted in a fixed-base research simulator to assess the directional handling qualities for various

rudder pedal feel characteristics for commercial transport airplanes. Effects of static pedal force at maximum pedal travel, breakout

force, and maximum pedal travel on handling qualities were studied. An artificial maneuver with a severe lateral wind shear and

requiring runway tracking at an altitude of 50 feet in a crosswind was used to fully exercise the rudder pedals. Twelve active

airline pilots voluntarily participated in the study and flew approximately 500 maneuvers. Pilots rated the maneuver performance

with various rudder pedal feel characteristics using the Cooper-Harper rating scale. The test matrix had 15 unique combinations of

the 3 static pedal feel characteristics. This analysis found that the peak values of the cross power spectra of the pedal force and

heading angle could be used to quantify the tendency toward directional pilot induced oscillations (PIO). Subjective data

(Cooper-Harper pilot ratings) were consistent with the objective data (peak values of the cross power spectra).

handling quality, stability and control, experiment design, pilot-induced oscillation, pedal control forces and travel, directional

control

UU UU UU UU 38

STI Help Desk (email: help@sti.nasa.gov)

(301) 621-0390