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OPERATIONAL LEG CLEARANCE WITH CONTROL STICK/WHEEL MOTION ENVELOPES

PURPOSE

The purposes of these measurements are to identify areas of interference with control stick or wheel motion at the subject's preferred seat position, and to locate the highest seat position, if any, at which interference does not occur.

DISCUSSION

Interference with control stick/wheel motion appears to be associated with smaller values for Sitting Eye Height and larger values for Thigh Clearance or Circumference and Abdominal Depth.  Sitting Eye Height becomes important when the pilot has to raise the seat toward the top of its range to gain adequate vision out of the cockpit.  In raising the seat, the space available between the thighs for side to side stick motion is sometimes not adequate.  The upper seat positions bring the thighs closer to the base of the inverted cone of stick motion and increases the likelihood of interference.  Similarly, the thighs are also brought closer to the control wheel as the seat is raised and can interfere with its motion.

Short heavy subjects, particularly those with heavy thighs, are most prone to encroaching on stick and wheel movement. An example of wheel interference is presented below. 


AN EXAMPLE OF CONTROL WHEEL INTERFERENCE. 

Sometimes it is necessary to determine the accuracy with which the size and shape of the stick motion box, as specified in engineering drawings, has been rendered in the cockpit or mockup.

PROCEDURE

OPTION A, STICK CONTROLLED AIRCRAFT.

Before subjects are installed in the cockpit, measure the full range of side-to-side stick motion (in inches) from a convenient location on the stick, such as the tip of the trim button, to convenient locations on the right and left sides of the cockpit.  These locations should be marked to assure that they can be easily identified when subsequent measurements are made with the subject in the seat.  Measurements should be made at least at full-forward, at neutral, and at full-aft.  Also, measure full right and left aileron movement (in degrees) on the left wing, using an inclinometer.  (Aileron and pitch trim should be set at neutral for these measurements.)  These data will serve as baseline measurements from which potential interference is evaluated.  Click on FIGURE for a data form for baseline data.  

The subject, dressed in flight suit and boots adjusts the seat to the full-up position.  The rudder pedal carriage is adjusted to the most forward position that permits the subject full forward pedal throw, usually the balls of his feet, without squirming either hip forward.  It will be found in some aircraft, that, with the seat full-up, some small subjects cannot obtain full pedal throw, even with the pedal carriage adjusted full-aft.  In such a case, adjust the seat downward until full pedal use can be obtained in the full-aft pedal adjustment, record this seat position, and begin the examination there.

The subject moves the control stick side to side at full-forward, neutral, and at full-aft positions within its envelope, attempting to obtain full excursion - first with the feet on neutral rudders and again when holding full right or left rudder.  If interference is found between the control stick and the subject's legs at any seat position, the measurement(s) of stick positions (i.e., the distance between the points measured to obtain baseline measurements) and aileron angles are made and recorded.  The seat is then lowered in one-inch increments and the measurements are repeated until interference is no longer encountered or until the seat reaches full-down.  If and when a seat position is found at which no interference occurs, that position is recorded. 

Data are recorded on a form such as that in FIGURE

OPTION B, WHEEL CONTROLLED AIRCRAFT

The full and unimpeded range of control wheel rotation is measured with an inclinometer or other suitable measuring instrument.  Measurements are made in degrees right and left from neutral.

End points of full right and left aileron movement on the left wing are also measured in degrees.  These data serve as baseline measurements and are recorded on the data form.

The subject adjusts the seat to the full-up position.  The rudder pedal carriage is adjusted to the most forward position that permits the subject full forward pedal throw, using the balls of his feet, without squirming either hip forward.  The subject rotates the control wheel to the right or left, with the feet on neutral rudders and again toward the passive leg when holding full right or left rudder, whichever causes the greatest potential interference by the passive leg..  The object is to attempt full rotation.  Full forward and aft yoke positions are examined.

If interference is found at any column or leg position, measurements of wheel rotation and aileron angles are made.  Just as for control stick interference procedures, the seat should then be lowered in one-inch increments and the exercise repeated until the seat is full down or until interference is no longer encountered.  The seat position and interference data can be recorded on the form illustrated in FIGURE.


ANALYSIS AND RESULTS

Two wheel-controlled aircraft were examined.  Legs were found to interfere with wheel rotation in an early version of the T-1A.  Discovery resulted in correction prior to production.

 

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