Brian Rauchfuss - PCD wrote:
> My concern with this setup is that the electric pump side is very vunerable to
> vapor lock - while the pump is off there will be fuel sitting in the fuel
> lines on the hot side of the firewall (since you merge the two lines after the
> mechanical pump) getting hotter and hotter. After a while the line will be
> filled with vapor. Will this cause vapor lock? Some of my reading on the
> subject implies that it can.
True, but vapor lock is much more serious on the suction side of the
system. One method of attacking pressure side vapor lock is a
restricting orifice and check valve in a return line to the tank.
This allows a small am't of cooling fuel to flow whether the engine
needs it or not. Problem is engineering the orifice size and thus
ground/flight testing complications. The 912 mech pump is not
adequate for merely the 914, hence you're up against its limits in
critical climb config with no fuel feedback. Plus add'l periodic
inspection hassle.
Nigel's system looks pretty cool, with only quibble of a LearJet
flavor to it, requiring continuing understanding of it to deal with
emergencies, but jet drivers are ordinary mortals like us.
EAA Sport Aviation (March '01) has an excellent article discussing
above and about everything else, including parallel vs. series boost
pump systems. For any non-member thus not subsidizing our expensive
Oshkosh habit, I can email the article. Scanned at lousy "Web Page"
resolution, it's still 6 x 120K jaypeggers, but color needed for the
pix and diagrams. Lemme know!
Regards,
Fred F., A063
|