Page 3 - Combined_172_OCR

H. P. Bruns - 3 - November 11, 1969

Remedial action for this situation must begin with a better definition of the
vibration environment, i.e., data over the frequency range 1 Hz to 50 Hz recorded
at the input to the seat and the input to the driver. With this data an isolator can be
selected to attenuate the vibration transferred to the seat and driver. Without this
data attempts to design an isolator may result in shifting the seat resonance such that
it will couple with the input resulting in gross magnification (xlO) of the drivers vibra­
tion environment.

It must be noted that the accelerometers were located on the roll cage at seat
level just behind the driver and do not measure the actual inputs to the driver Ts spinal
column (the critical input) actual inputs may vary somewhat due to seat structural
characteristics. Also the accelerometer used was frequency limited to approximately
0-5 1/2 cps so that data above 5 1/2 cps may be distorted and could be at much higher
levels than indicated.

As indicated in Figure 1, the vehicle vibration environment falls in a range
severe enough to be unacceptable by USAF standards and can be tolerated for only a
few minutes. Severe performance degradation occurs in this environment according
to References 1,2,3 and 4 and coordination as well as other physical performances
are reduced. As stated by David E. Pettijohn, Reference 2, these performance degra­
dations are difficult to measure but some data has been accumulated in a simulated
pilots cockpit situation relative to flying maneuvers and reading gages, etc.

It is recommended that future tests include higher frequency accelerometers
located in the seat cushion to measure spinal column inputs.

/
.
2
(D
Wright
K
WPW:ck
cc:

CHO H. Bader, Jr.
J. E. Call
A. E. Douyard
G. Martin
CEO L. J. Rathgeb
R. M. Rodger
G. M. Wallace