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From: bxr307@csc.anu.edu.au
Newsgroups: sci.military
Subject: Re: Ejection seats
Message-ID: <1991Feb5.040420.4127@cbnews.att.com>
Date: 5 Feb 91 04:04:20 GMT
References: <1991Feb4.052511.15316@cbnews.att.com>
Sender: military@cbnews.att.com (William B. Thacker)
Organization: Computer Services, Australian National University
Lines: 44
Approved: military@att.att.com



From: bxr307@csc.anu.edu.au
In article <1991Feb4.052511.15316@cbnews.att.com>, voder!nsc!dtg.nsc.com!alan@decwrl.dec.com (Alan Hepburn) writes:
> 
> 
> 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.  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.  Does anyone out there
> have any real data on this?  Can a pilot survive a punch out through
> a canopy?

	Most modern, high-speed aircraft now have ejector seats which force
their way through the canopy.  This is necessary because at supersonic speeds
there is little time to wait for a canopy to be ejected clear from the aircraft
and then have the seat eject a second later.  It was deemed faster to simply
either destroy the canopy or to break through it.
	British aircraft are equipped with exploding canopies which have
detonating cord moulded into their clear plastic so that when the time to eject
comes this is exploded a split second before the seat is ejected from the
aircraft, clearing a way for it.  The det-cord appears as a thin black line in
the canopy and while partially obscuring vision for the pilot it is felt that
safety comes first (and anyway the argument runs, the pilot will be focusing on
objects in the middle and far distance and the det-cord will be nearly
invisible to him).
	Other nationalities tend to go for "canopy-cutters" atop the head rest
of the seat (basically a sharp edged structure which is designed to destroy the
canopy by brute force as the seat ejects) as they are uncomfortable with the
idea of several pounds of explosive within a few inches of the head of the
pilot.
	As to which is the better system, I think it is mainly horses for
courses.  Each airforce has its personal preference and believes its better
than the other's.  Both have disadvantages.  The det-cord has no backup if it
fails to destroy the canopy.  The canopy-cutters have the disadvantage that the
canopy has to be made weaker to allow them to work, and as such it is far less
resistant to other things, like birdstrike.


Brian Ross