On Wed, 19 May 2004 19:46:43 +0000, Pete Schaefer wrote:

Hey Jim-Ed:


"Jim-Ed Browne" wrote in message
om...
Is this because none of the ones available as designs currently have
any, or because you feel it's not feasible, or because....exactly why?

I've never looked at any airplane designs that have such features. There is
a huge price to pay in terms of weight, required power and such to provide
pilot protection. Drives up cost a ton, and makes operations more
expensive.

Most paraglider pilots have a harness that includes some 'crushables' to
protect their backs if their canopies collapse at low-level. Recently the
tide has turned against rigid harnesses with carbon-fiber backplates.
These used to be popular on the grounds that they would reinforce the
backbone - now people believe that they are so rigid they can concentrate
the forces on small sections of the spine (typically the lower lumbar
vertebrae) and _increase_ the risk of spinal injuries. Now people prefer
airbags that let the air out gradually through the seams during an impact
(to prevent recoil). Alternatively some harnesses use foam to spread
impact forces over the whole area of the back. There's little consensus
about how well they work, but little doubt that they can provide an 'edge'.

This is just a longwinded way of saying 'I don't see why passive safety
should necessarily be heavy and expensive' It might be as little as 2" of
foam and a more ergonomically shaped seat.

To put it another way, I weigh 20kg less than average. I wonder how much
energy that weight of intelligently positioned crushable foam could
absorb? Or even a small fraction of that weight.

Keep in mind that crumple zones are only really for front impact, too.

No reason why. Actually, I'd have thought it should be easier to design
passive protection into an aircraft because side and rear impacts are
probably less common.

I have heard something in the New-Scientist about weakened floors in
airliners that could crumple and save people's backs when planes crash
with too high a descent rate. I also heard that in one frontal collision
in an airliner, many lives were needlessly lost because many people's legs
swung forwards under the seat infront and fractured around the shins. This
meant that they couldn't leave the accident site, even though there was
time. Now, most airline seats have soft edges around the relevant parts of
the seats.

None of this directly applicable to GA.

AC