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