REFLECTOR: Engine failure causes

[David Bertram]

The fuel shutoff sounds suspicious.  I ran a cable from the pilots side by
the seat back to the outlet of the sump tank.  I can shut the fuel off but
it does not open very well, but this is only used in emergency or
maintenance.  I also looked at foaming but found it as unlikely due to the
sump fuel outlet being at the bottom of the tank and I have a good vent
system.  When I had my engine fail everything and "everyone" thought it was
a fuel problem.  It was a ignition failure caused by my distributor gear. 
Dave Bertram
N350TX 
-------Original Message-------
 
From: Brian Michalk
Date: 4/6/2009 11:15:11 AM
To: Velocity Aircraft Owners and Builders list
Subject: REFLECTOR: Engine failure causes
 
I've been going through the possible theories as to why my engine failure
occurred.  I didn't want to post rampant speculation, but a week has passed,
and I need to bounce some ideas off the collective.

I am looking at fuel starvation as the reason for engine  failure.  I have
other ideas that excessively rich mixture might be a culprit, and a few
other oddball ideas, which I will explore as well.

Prime suspect #1: Fuel starvation due to fuel shutoff valve arrangement.
I placed a shutoff valve in the keel at the copilot's knee position.  This
is fed from the sump tank, and returns to an electric pump between the
firewall and gear bulkhead (fixed gear).  I still need to inspect the hose
for evidence of kinking.  The fuel return hose from the pressure regulator
did not have fuel in it during post crash inspection.  My theory is that my
aggressive climb at 90 kts resulted in the shutoff valve being higher than
the level of fuel in the strakes.  This could be a combination problem
coupled to other theories I have.  A vapor bubble might have gotten to the
fuel pump, and caused it to lose prime, and then cavitate when I lowered the
nose.

Theory #2: Foaming fuel in sump tank
The theory here is that never before had I run fuel flows as high as during
the first flight.  The electric pump, plus the mechanical pump at the
redline RPM caused a large volume of fuel to be bypassed back to the sump
tank.  I built the tank before I planned on fuel injection, and added a port
for fuel return very close to fuel inlet ports.  I need to go back and take
sump pictures to see the arrangement of the connectors, and also base that
in the context of high flows and takeoff angle.  It might be possible, but
unlikely that the sump tank became full of foaming gasoline.  diesel is much
worse, and avgas not so much, but it is a possibility.  I need to see if
foaming fuel could have been injested into the intake port and caused "prime
suspect #1" to happen.

Unlikely theory #3: Debris in the tanks clogging filters
I pulled the filters and inspected several weeks before flight.  They were
clean, and this is the first time since building the plane and doing all
taxi testing and ground runs that I had inspected the filters.  The tanks
were found to be very clean after the building process.

More unlikely theory #4: Water in fuel
Even though I did not check the sump before first flight, the tanks with
caps on are very tight, and the plane kept in a hangar.  Again, the high
angle from takeoff might have injested the water.  There should be evidence
of water in the main tanks if this theory is correct.  The dry fuel return
hose begins to rule this scenario out as a candidate.

More unlikely theory #5: excessive vacuum on vent line
It might be possible that the vent line exiting the plane is in a high
vacuum area.  I'll try to simulate with a leaf blower.

Discarded theories:
Clogged vent line

If anyone else has any theories, throw them out and I will entertain them. 
Please see my fuel diagram.



 
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