Requesting waiver on the "specialist" part. But concerning the fire
hazard, and while any opinion is reasonable given the implications,
the probability of winding up inverted, with insufficient damage to
rupture the fuel sys anyway, and having an ignition source back in the
area of the fuel vents, I think is extremely remote. For any
accident, about once in 10,000 hours, and then times the other
probabilities I cited, you'll have worse than State lottery odds. Our
anal-retentive FAA here does not require, on production aircraft
except aerobatic, prevention of fuel leakage while inverted. Not even
for airliners.
Maybe the rationale is that any no-spill system may cause more
problems than it ever prevents. I don't know about the Andair check
valve, but if it isn't fail safe when contaminated, it then needs
redundancy. Such as if the main vent clogged, then the vent for the
sight gauge takes over. You would need to be certain that sufficient
fuel will still flow to the engine while the system is attempting to
draw down the gauge level so as to suck air to relieve the vacuum in
the tank. Conversely, a problem with the sight gauge's check valve
could cause it to read high. Similar to immediate engine stoppage,
but only later....
Regards,
Fred F., A063
Alfred Buess wrote:
>
> Hi Europa fan community,
>
> The fuel tank ventilation design seems to have at least to main weaknesses:
>
> 1) In case of an accident with a plane flipped on its back, fuel runs out of
> the vent lines -> fire hazard.
>
> 2) Slow filling and spillage, spraying and vaporizing of fuel due to poor
> airing
> through the vent lines -> annoying and again fire hazard.
>
> In my XS I intend to modify the venilation system as follows:
>
> 1) To resolve the problem of loosing fuel when the plane is flipped on its
> back,
> I will add a bleeding check valve (Andair) in each vent line. They allow free
flow
> of air and fuel into the tank, but very slow and poor flow from the tank to
> the
> vent exit. It allows enough air to leave the tank on a hot day
> when fuel expands.
>
> 2) To improve airflow when filling the tank and to avoid spilling fuel, I will
> use a vent line (hose) from the tank with a larger diameter, add a T about a
foot
> above the tank's upper level, continue the vent line (small diameter) to the
check
> valve and to the vent exit. The T is connected to another hose of the large
> diameter, about three feet long, with a little faucet at the end. Before
> filling
> fuel into the tank, the end of the tube is taken out of the plane, the faucet
is
> opened and put into a small can on the ground. During filling, venting air and
> overflowing fuel go into the can. After filling, the hose is emptied, the
> faucet
> is closed and all is put back into the plane.
>
> This concept separates the venting during filling and the venting in normal
> operation. Any comments, ideas for impovements, warnings ... by the large
> number
> of specialists out there are welcome!
>
> Alfred
> (# 097 Mk I wing XS fuselage)
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