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F-15-A

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RUDDER PEDAL OPERATION


PURPOSE

The purpose of these measurements is to determine the smallest leg length able to achieve full rudder pedal throw and brake operation with the carriage adjusted to its aft-most position. Leg length is expressed in terms of the combined values for ComboLeg, the sum of Buttock-Knee Length and Sitting Knee Height.  While this is not a conventional measure of leg length, it is a measure of total leg length and is directly related to the ability to reach and actuate rudder pedals. 

DISCUSSION

Because ejection rails are sloped up and aft, ejection seats typically move the operator away from foot controls when adjusted upward, and, of course, closer to foot controls when adjusted downward.  Since reach to the rudder pedals is so closely associated with seat position, access is examined at one-inch, or other small, intervals throughout the range of seat adjustment.

Subjects measuring as close as possible to the bottom of the accommodation range for the combined values for ComboLeg are used for this assessment.  The smallest combined leg length in the current USAF population is about 40.6".

This assessment is based on the following assumption. If maximum leg reach is necessary for one pilot to achieve full rudder depression when the rudders are adjusted to the full-aft position, another pilot with a one-inch longer ComboLeg will be able to achieve full rudder depression when the rudders are adjusted one inch forward from full-aft. 

The F-16 series of aircraft present a cockpit geometry in which the knee is usually not fully extended to obtain full rudder.  The seat pan in these aircraft is set typically at +30 degrees, potentially causing the underside of the thigh to press into the forward edge of the seat cushion when thrusting the feet forward.  Actual compression of the thigh and the seat is reduced, however, by the near-isometric nature of pedal operation.


PROCEDURE

Prior to examination, it is necessary to establish the position of the fully depressed rudder pedal with the carriage adjusted full-aft.  This is done by measuring its distance from a mark made on the outboard wall of the pedal well, aft and upward from the pedal toward the subject's hip joint as he/she sits in the seat. The location of neutral rudder is not used because of uncertainty as to its exact location.  By comparing this distance with a corresponding distance obtained when the subject adjusts the carriage to his/her maximum forward position, we can calculate the minimum combined leg length necessary to actuate the pedals in each seat position. The minimum leg length needed to fully actuate the pedals and attain braking with the carriage full-aft will be the minimum leg length that can safely operate the aircraft from any given seat position.

            1. The subject, wearing flight suit and appropriate flying boots, is seated in the cockpit.  The seat is raised to the full-up  position.

            2. The subject adjusts the rudder pedal carriage forward until he/she can just obtain full left rudder and actuate the left brake with the leg comfortably straight and knee extended, but without hip rotation.  After the subject has adjusted the pedal carriage, the left foot should be moved inboard while holding the pedal full down to make space for the measurement to be made.  Measure the distance between the contact surface of the depressed left rudder pedal aft and upward to the point marked on the outboard wall of the pedal well.  FIGURE illustrates a data form for these data.  

            3. Repeat at one-inch intervals through the range of seat adjustment. 

The minimum combined leg length needed to obtain full forward rudder throw and brake for a given seat position is equal to the subject's combined leg length minus the remaining aft carriage adjustment.  See the discussion at the beginning of this section.


ANALYSIS AND RESULTS

Analysis of the data consists of averaging values for ComboLeg required to actuate the rudder pedals and brake in the full-aft carriage adjustment, for each seat position.  The minimum combined leg lengths to obtain full forward rudder and brakes in the T-37B was found to be 41.9 inches, seat full-down, and 42.3 inches, seat full-up.

Since the smallest ComboLeg in the current USAF population is about 40.6 inches, some prospective pilots can expect to have difficulty obtaining full rudder throw in most seat positions in both cockpits of the T-37B.  These pilots would have to rotate their hips forward away from the seat back to fully depress the pedals.  The T-1A, F-16A, and C-141A all accommodate to the minimum 40.6" combined leg length.

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