RE: Franklin Fuel Pumps.

["Laurence W. Coen" <lwcoen@freewwweb.com>]

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From: 	James F. Agnew
Sent: 	Thursday, April 09, 1998 7:15 AM
To: 	Laurence W. Coen
Cc: 	'Reflector'
Subject: 	Re: Franklin Fuel Pumps.

Laurence W. Coen wrote:
> 
> I have a Pat Goodman installed fuel pump.  Between the recent article by Simon Aegerter and the recent tragedy that sounds like fuel starvation, I decided to dismantle my pump to see how it really works.  FYI, bypass valves are not used in diaphragm pumps because they are not needed.  They are an integral part of rotary vane pumps.  I have included a crude drawing of what's inside the automotive type pump.
> 
> The problem that Simon had sounds like one of the valves was defective and would only partly open.  This would explain why the electric pump couldn't deliver full volume through the engine driven pump.  As far as connecting the pumps in parallel, I own a Piper Cherokee that came from the factory that way and hasn't missed a beat in 30 years and 2400 hours.  The electric pump has been replaced 3 times but the engine driven (AC) pump was still working fine when it was replaced with a rebuilt when
> 
> The little information we have on the accident would lead me to believe that this was not a fuel pump failure but a fuel system failure, perhaps a clogged filter or a kinked line.
> 
> Larry Coen

Larry, I don't know what Cherokee you have, but my 1976 Piper Cherokee 6
manual shows the pumps in series as well as every other Piper manual I
have (6 models).
I have a Cherokee 180D that uses the parallel fuel arraignment.  I also have a Cherokee 140 manual that shows the same thing.


I work with Simon and there was not a piece of the system that wasn't
tested.  The boost pump worked fine and would pump through the engine
pump when the engine was not running it could not at high RPMs.

I'll say it again, would/should you trust their life to a 1960s
auto fuel pump designed for an engine with 45% of the displacement and
about half of the horsepower output.  Given the greater efficiency of
the auto engine the maximum fuel flow rate required was probably one
third that of the Franklin.  

I owned a 1960s Chevy with a 350 cu.in. V-8 and 1960s automotive engines were NOT more fuel efficient than aircraft engines.  In addition the fuel pump cam on the Franklin runs at 1.65 times crankshaft speed while the automotive version is run off the camshaft at half the crank speed.  The aircraft version of this pump has the identical stroke volume as the automotive.  The difference is that the aircraft version is built better not bigger.

Does the word "inadequate" come to mind?  I think the real question is
not will it fail but when.  All you have to do is picture Simon's engine
running smoothly at 2600 RPM then without any warning just shutting down
like the mags were turned off.

Jim
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