STATIC KNEE, LEG AND TORSO EJECTION CLEARANCES
purpose of these measurements is to determine the largest values of
Buttock-Knee Length and body breadth, usually at the shoulders, to clear
cockpit structures during ejection.
between the legs and torso and cockpit structures such as the main instrument
panel, controls and structures extending aft of the instrument panel, the canopy
bow, and cockpit side-sills and centerline canopy braces during ejection,
is associated almost
dimensions tell us little about leg and foot trajectories and submarining during
ejection and only very crudely approximate the violence of the ejection process.
The seat and its occupant are sometimes pulled up the ejection rails to
simulate the effects of knee depression and, to a minor extent, submarining. However, this also has not been shown to be a completely
adequate technique for simulating the ejection sequence, and will yield little
additional information beyond that obtained with the seat in the cockpit.
clearance subjects should be near the top of the range for Buttock-Knee
Length, Sitting Knee Height, and Bideltoid (Shoulder) Breadth.
Our procedure for examining ejection knee clearance assumes that the canopy has been blown off the aircraft. It is the first choice procedure and the easier procedure to measure since it can be done with the canopy open. A through-the-canopy ejection, however, represents the worst-case. We found that the most accurate measurements can be made directly to the forward transverse part of the canopy frame. This does not account for shards of canopy material remaining in the canopy frame in a through-the-canopy ejection.
The subject, dressed in full flight gear, including boots, is installed
in the seat. Using an inclinometer,
the thighs should be set at right angles to the ejection rails. To do this, the feet may have to be withdrawn aft and the
seat adjusted. An inclinometer can be used to set thigh angle.
If the seat adjustment and ejection angles differ, the seat should be
adjusted to either full-up or full-down, whichever causes the pilot to drift
farthest forward. The knees are set 12" apart - centerline to
A rigid straightedge (usually two sections of an anthropometer), equipped
with an inclinometer, is
held against the forward surface of the left knee (Typ.) in single cockpits (or
the outboard knee in side-by-side cockpits) and held in the vertical
(X-Z) fore-aft plane. By
viewing an attached inclinometer, the top end of the
3. Using a carpenter's retractable tape, the distance is measured
perpendicular from the aft surface of the straight edge to the nearest structure
or other threatening surface or edge forward of the knee, usually the canopy
bow, windscreen bow, or glare shield. The procedure is illustrated below.
Click on FIGURE for a proposed form for recording ejection clearance data.Shoulder/Elbow Width Clearance
1a. Single Crew Station. Measure
the distance across the crew station between the sills at the
shoulder-elbow station line forward of the seat back.
1b. Side-by-side Crew Stations.
Measure the distance between the outboard sills across both cockpits and
to the centerline of each cockpit at the shoulder-elbow station line.
Where there is a centerline longitudinal canopy brace, measure the width
of the brace. By calculation, the
extent to which the centerline brace may encroach into the ejection envelopes can be determined. Data
forms to record these measurements are not included in this report.
2. The subject, dressed in appropriate flight gear, is installed in the seat
and instructed to simulate hand and arm positions appropriate for ejection.
In the case of a D-ring, the subject should grasp the D-ring
with three fingers of each hand or by one whole hand with the second hand
grasping the first's wrist. In the
case of side seat-mounted ejection handles, the subject should simulate a
full hand grasp with the handles hinged upward.
3. Measure the distance from the most lateral body part, the shoulder, elbow
or hand to the inside of each side-sill. Clearance
with a centerline canopy brace between side-by-side cockpits can be
is a direct relationship between increases in Buttock-Knee Length and
reduced knee clearance with the glare shield and canopy bow during ejection.
It must be remembered, however, that this is a static measurement. While
it cannot be relied upon to pinpoint true clearances associated with ejection,
during which the total body is under severely dynamic loading, it is the only
technique available for general use in the field.
Buttock-Knee Length is the body dimension most closely associated with
ejection clearance, data analysis consists of adding the clearance between the
knee and canopy or windscreen bow and glare shield to the subject's
Buttock-Knee Length to obtain the threshold contact values.
Averages of such values were calculated. It is understood that,
should be made between canopy-open and canopy-closed ejections.
For the former we need be concerned with the potential interference
offered by the windscreen bow. Since
through-the-canopy ejection can be either the first or second
alternative, clearance with the canopy frame (and canopy shards remaining in the
frame) must also be considered - thus the measurement of the additional
potential interference offered by the canopy bow and frame.
The maximum static Buttock-Knee Length accommodated for ejection
clearance with the canopy bow in the T-37B (both cockpits) was found to be
clearance in the T-38A appears to be ample.
The T-37B has limited side-to-side clearance. On ejection, the pilot may experience interference between
the inboard hand and the centerline canopy brace.
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