<<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
          <<  Lancair Builders' Mail List  >>
          <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
>>
Bill Gradwohl writes:

<< Why won't this work?
 What have I forgotten?
 Which one of my assumptions is incorrect?  >>

All your arguments are valid under "normal" circumstances. Unfortunately it is
the abnormal circumstances that kill people so lets discuss those.

The first problem I'll call "one dry all dry". Because of the low head
pressure (as you pointed out) and the relative location of the tanks and boost
pump, there is a slight negative pressure at the inlet of the boost pump
during operation. THIS IS BECAUSE THE FLOW LOSSES IN THE LINE BETWEEN THE TANK
AND THE PUMP EXCEED THE HEAD PRESSURE. Therefore when one tank runs dry air is
free to flow into the system and because the air has virtually no flow losses
it is AT A HIGHER PRESSURE THAN THE FUEL AT THE PUMP INLET. The boost pump
will try to pump air into the engine until the head pressure and flow losses
balance in the line that still has fuel at which point the boost pump will
pump a mixture of air and fuel to the engine. Check valves won't help here.

This brings us to a secondary problem of de-aeration. While aeration is good
for a fish tank it is bad for a fuel system, particularly a Continental fuel
system that relies on fuel pressure regulation for mixture control. A big gulp
of air in a Continental will likely cause a flameout. Also, one of the return
lines functions is to return air, and or fuel vapor, to the tanks but in your
system the air is returned to the fuel pump inlet. Can you say "VAPOR LOCK".
In your system on a hot day it would be easy to fill the entire system with
fuel vapor and have no way to purge it. This can also happen on hot start or
on climb out because the ambient pressure drops faster than the vapor pressure
of the hot fuel.

The third big reason is that the FAA or your DAR won't approve it. They are
particularly sensitive to fuel systems after the John Denver crash.

To review; with the system you describe you cannot predict when you will run
out of fuel, it has no provision to vent a vapor lock and it is not airworthy.

The KISS system IS the one described in the manual.

Just so you know that I am not making this up, I spent 12 years designing
hydraulic systems for robots, submarines and aircraft and I am the guy that
identified a fatal flaw in the factories prototype IV-P's hydraulic system.
The fix I engineered is in every IV flying today.

If I have not convinced you yet then go out to your shop, select a large
mallet from your toolbox, sit down on the floor and picture your fuel system
in your mind. While you are concentrating, strike your cranium repeatedly with
the mallet until you forget why you are doing it. Proceed with installing the
fuel system per the manual unhindered by foolish thoughts:)

Seriously though, I would hate for you to become another statistic. Please
don't implement your fuel system. My insurance rates can't tolerate another
increase.

Regards
Brent