What an excellent analysis. Assume failures others have
had will happen to you, design accordingly.
Subject: [FlyRotary] Re: SPAM-LOW: [FlyRotary] Re: Fw:
Rotary Engine & Fuel Valves
If you are going to use a
common feed system, the best way to do it is via a
Left/Right/Both/Off type selector valve.
With that system if you are
running on “Both” and you have an uneven feed, it’s easy
to resolve, just switch to the fullest tank.
More important is the missing
fuel cap scenario. Most aircraft have a vent tube that
is situated is such a manner that it works like a little
ram air scoop to force air into the vent system.
Most pilots think that when
you loose a fuel tank cap, the fuel is sucked out …..
not so. What happens is the fuel tank without the cap
fails to pressurize the way the fuel tank with the cap
does. As such (in a “T” or common feed system) the
higher pressure tank begins to push the fuel into the
lower pressure tank. Of course with no fuel cap, the low
pressure tank overfills an the excess fuel goes
overboard.
Once the last of the fuel
passes the common junction, you have fuel starvation and
one full tank of fuel that you cannot access. In a
system with the described selector valve, selecting
between individual tanks would make this a non-event. If
you were running on “Both” you could empty the high
pressure side but once it started sputtering you could
be back in business by switching to the full tank (with
no cap) and would still be able to access that fuel.
Just something to consider. I
just picked up n airplane this past spring that had a
common sump system. The first thing I did was convert it
to the system I described above. The owner said it
didn’t feed from the wing tanks evenly and he would have
to land sometimes to let the fuel settle out to an even
level then press on. This selector valve setup allows
you to correct the issue in the air.
T Mann