Arm Pain in High Performance Aircraft
Squadron Leader Nic Green, Royal Air Force Centre of Aviation Medicine, Henlow, UK
Arm pain has been reported experimentally and operationally by some aircrew exposed to high G forces, particularly in combination with certain cockpit configurations and anti-G systems. In this presentation, predisposing factors in the causation of arm pain are examined and a summary is given of the short-term and potential long-term consequences of regular exposure. Some possible strategies to reduce or remove the problem of arm pain are introduced.
An Investigation of Some Methods of Amelioration for High G Induced Arm Pain
Sqn Ldr Nic Green, Royal Air Force Centre of Aviation Medicine,
Henlow, UK
Dr Andy Prior, PDSL/QinetiQ, Farnborough, UK
The current Eurofighter anti-G system, Aircrew Equipment
Assemblies (AEA) and stick/throttle positions, in combination, are
anticipated to result in unacceptable levels of arm pain in aircrew
pulling more than approximately + 6 Gz. Whilst it is by no means
certain that arm pain will be a problem in operational flying, the
available evidence from previous centrifuge and Hawk investigations
indicates that the arm pain severity will effectively limit the
high G capability of the aircraft for the majority of aircrew. This
experiment was devised to investigate the effectiveness of three
different techniques expected to modify the occurrence of arm
pain:
a) the removal of Pressure Breathing for G
(PBG),
b) the addition of arm counterpressure,
using PBG pressures, to an existing chest counterpressure garment
(CCPS) and
c) the addition of a Swedish, upper arm,
counterpressure system (SUCS).
The latter device was developed by Colonel Jan Linder, Swedish Air Force, and has been well received by Gripen aircrew as a means of reducing arm pain.
Previous experience of centrifuge and Hawk high G induced arm pain suggests two facts:
a) once arm pain occurs, increasing +Gz
levels, and/or the number of G exposures, never results in a
lessening of arm pain severity within any particular set of
exposures and
b) inducing arm pain on one acceleration
exposure influences the appreciation of arm pain on immediately
subsequent exposures.
In respect of the latter, the duration of the effect is unknown although, from experience, it can be stated that an interval of seven days between exposures is sufficient to avoid such an influence. Using these principles, 8 high G experienced subjects, all of whom were familiar with high G induced arm pain, volunteered to complete 4 experimental conditions using the Farnborough man-carrying centrifuge. The conditions were as follows:
a) Full coverage anti-G trousers (FAGT)
with PBG,
b) FAGT without PBG,
c) FAGT with PBG and CCPS,
d) FAGT with PBG and bilateral SUCS.
Each subject, for each experimental condition, underwent centrifuge runs in sequence starting at +4Gz. If, at the end of the centrifuge run, the subject did not report unacceptable arm pain then the acceleration level was incremented by +1Gz. The process continued until arm pain was reported or +9Gz was reached. The G level at which the session was terminated was recorded. Each subject performed all experimental conditions within one day. Following an interval of at least 7 days, the session was repeated until each subject had completed 4 sessions. The condition order for each subject for each session was determined by a Latin Square.
The G level at which each subject experienced unacceptable arm pain, for each condition and for each session, was analysed for variance between condition, session and subject. These results will be presented and discussed in the context of a practical means of providing some amelioration of high G induced arm pain in Eurofighter.
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