Bob Darrah wrote:

With the specific intent of stirring up controversy, I will present the Darrah
Theory (untried, unproven) on header tanks.  Also keep in mind, I have
never learned anything from someone with whom I agreed!

1. A header tank that is unvented is unneeded.

2. Using an engine that requires an electric fuel pump to be operating
continusly in order to run does not need a vented  header tank.

Now that ought to stir up some of you.

Bob Darrah

That's a real good point Bob.

Your wing tank vent could be plugged and if it feeds into
an unvented header tank there goes your fuel supply.

If you see the level going down in your unvented header tank it is time
to land even if you just took off with full wing tanks.

A gravity feed header tank is best.

An unvented gravity feed header tank is an excellent back up.

Use a float switch if neccessary to control the wing tank pump 
to maintain the fuel  level in the header tank.

The wing pump should last longer as it is not running
all the time. The EFI high pressure fuel injection pump feeding
from the header tank must run all the time of course.
A back up is called for there.
 
Cessnas have far fewer fuel interruption problems than
all the low wing airplanes. There are no fuel pumps in
my O-470 (carb) powered 182. The only time I ever had a forced
landing was when flying a Mooney. The boost pump went
out and the broken carbon vane parts jammed the engine
mechanical pump valves. 

Pump current drain is an issue when your electrical system
goes out. You will fly further if you can dump some electrical 
power load. I would have an on and off switch on every pump.
I would have dual pressure pumps and run only one at a time.
A preflight check should be to test both pumps.

I would also use a sealed or high vented center sump tank  near 
the floor with both wing tanks feeding it. In fact a 
transparent vent line mounted vertically on the side of the cockpit
will make an excellent, low cost, very simple  and
very reliable fuel gage.

I would then have a back up mechanical wobble pump 
to fill the header tank if necessary. This too will extend 
your alternator-out flying range.
  
Paul Lamar
 
The Aircraft Rotary Engine Newsletter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org