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From: henry@zoo.toronto.edu (Henry Spencer)
Newsgroups: sci.military
Subject: Re: Ejection seats
Message-ID: <1991Feb5.040231.3928@cbnews.att.com>
Date: 5 Feb 91 04:02:31 GMT
References: <1991Feb4.052511.15316@cbnews.att.com>
Sender: military@cbnews.att.com (William B. Thacker)
Organization: U of Toronto Zoology
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From: henry@zoo.toronto.edu (Henry Spencer)
>From: voder!nsc!dtg.nsc.com!alan@decwrl.dec.com (Alan Hepburn)
>There's been talk recently about the injuries of the Allied POWs being
>caused by the act of ejecting from their planes...

Ejection injuries, up to and including fractured vertebrae, are not at all
uncommon.  Ejection is a very violent process, undertaken only when the
alternative looks even worse.

>Some people have
>said that some planes are designed such that the pilot must eject through
>a closed canopy.  It seems to me that a canopy designed to withstand
>air pressures of supersonic flight would be extremely difficult to
>punch through with a slow-moving seat, or head...

The typical approach taken in through-the-canopy-ejection aircraft is to
make the thick windshield on the front -- which has to contend with high
aerodynamic forces plus birdstrikes -- a separate piece from the relatively
thin overhead canopy.  This does mean putting a frame of some kind between
the two, which obstructs the pilot's vision somewhat.  On the other hand,
it permits truly instantaneous ejection, while jettisoning the canopy
before ejection involves a delay.  At low altitude that delay could be
fatal.

There are various intermediate approaches like putting detonating cord
in the canopy so it can be shattered as ejection begins.  I believe it
is also relatively normal for modern seats to be tall enough that they
hit the canopy before the pilot's head does.  Don't underestimate the
forces involved.

>... Can a pilot survive a punch out through a canopy?

Yes, definitely.  RAF combat aircraft are almost entirely eject-through-
canopy types, since the RAF stresses the low-altitude penetration role
and demands instantaneous ejection.
-- 
"Maybe we should tell the truth?"      | Henry Spencer at U of Toronto Zoology
"Surely we aren't that desperate yet." |  henry@zoo.toronto.edu   utzoo!henry