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Brent,
It does seem that doing
something to prevent the fuel from spewing out of the fuel lines would be useful
for some crash scenarios. Do you know of some kind of automatic valve or
limiting device one could put at the wing root without screwing up the fuel
pressure for normal operation?
I'm also wondering how those
discriminating valves work. Are they active or passive?
Colyn Case
----- Original Message -----
Sent: Sunday, May 15, 2005 5:31 PM
Subject: [LML] Re: Crash Safety
Terrance brings up an interesting point. Post
crash fires are apparently responsible for many fatalities. I suspect that the
exact number of fatalities that can be attributed directly to the post crash
fire is difficult to determine as a crash survivor may be fatally injured but
alive at the time of the fire. I do not think there is an effective
solution for fuel carried in the wings but, armoring fuel carried in the
passenger compartment may be desirable.
Race cars achieve fuel safety
by limiting the amount of fuel on board, holding the fuel in a foam filled
rubberized fuel bladder, placing that bladder within the protective structure
of the car and (in the case of formula cars) adding energy absorbing material
(aluminum honeycomb) to the nose of the car. Race car fuel vents are typically
large diameter as rapid fueling is usually a requirement. The fuel vents
feature a Discriminator Valve that will allow air to pass but will close in
the presence of fluids. In human physiology this functionality is provided by
the anal sphincter.
Implementing effective race car type fuel safety
in an airplane is problematic because it would involve one or more of;
increased cost, increased weight, reduced range and increased
maintenance. In a IV or ES you would need roughly 22 unique fuel
bladders that would require interconnections (fuel and vent) and be removable
via access hatches for maintenance. Since wings are sometimes "removed" during
accidents, the individual bladders would need to maintain their integrity and
the fuel and vent lines would need to seal. Bladders have been used in
aircraft applications. Many spam cans use them and, in one Lancair case, I was
involved in the design of a bladder tank that was installed in the back seat
of a IV to provide additional fuel for transoceanic flights.
Back in
the 1970s and '80s research was conducted to investigate adding aluminum foam
to the fuel tanks of airliners. The foam would limit the vaporization rate of
the fuel and therefore limit the fire expansion rate. This research
culminated in the radio controlled crash of an airliner in the desert.
Unfortunately, because of poor controllability, one of the jet's engines
struck the "wing rippers" installed on the runway and the hot
engine parts defeated the foam suppression. A spectacular fireball ensued.
Bummer.
My gut tells me that adding fuel bladders to the wings will
have only a limited effect on safety and be prohibitively expensive to install
and maintain. The increased opportunity of a fuel leak (and loss) may actually
increase the probability of an accident even if decreasing the probability of
a post crash fire.
The header tank is another matter altogether. I
don't think it is ever a good idea to have large quantities of flammable or
hot fluids in the passenger compartment. If you must have fuel in the
passenger compartment then armoring against taking a 100LL shower is a good
thing.
Regards
Brent Regan
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