On Tue, 6 Dec 2005 16:09:43 -0700 "sboese" <sboese@uwyo.edu> writes:
  As a separate test, I connected a fuel pressure
> regulator to the
> RX7 donor car’s fuel tank which was filled with fuel and had the
> original
> submerged fuel pump in it with a clean inlet sock.  Running the pump
> in this
> setup gave the same results:  bubbles in the return line, but
> nowhere else.

So cool that you are doing the real world tests! Keep it up!

> I don’t think there is a problem when the fuel is returned to the large
wing
> tank where it would be unlikely for the bubbles to get into the line
> supplying the pump.

I certainly agree. It seems reasonable to assume that the return line
always deposits bubbles into the tank. I'm told sock is effective at
removing them, obviously returning fuel some distance from inlet is
valuable. I have 2 gallon header, vented. Unable to get it close to vapor
lock. Only exception was brief moment on restart of overheated engine
(during my test phase years ago). That was only after 5 minute heat soak.
Pretty clear that was due to the 6" of tubing in engine compartment
getting too hot.

 It could be an issue, however, if the fuel is
> returned
> to a smaller header tank depending on how the header tank is
> constructed and
> vented.

I suspect you want it vented. Unvented opens you to new problems. Like
fuel sys that won't self prime.


>
> If the fuel is recirculated long enough, and if the bubbles are
> really air;
> the dissolved air should be eventually nearly eliminated from the
> system,
> but I didn't run the pump long enough to see if this is true.  I
> haven’t
> tried the tests with avgas, either.
>
> My apologies to the list if this is common knowledge.  

Don't apologize. This is valuable info that deals with one of the biggest
risk items our conversion have. Thanks for providing some science.


-al wick
Artificial intelligence in cockpit, Cozy IV powered by stock Subaru 2.5
N9032U 200+ hours on engine/airframe from Portland, Oregon
Prop construct, Subaru install, Risk assessment, Glass panel design info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html