REFLECTOR: Engine failure causes

[nmflyer1 at aol.com]

Brian, 

I shall print your notes/diagram and ponder it for a while. Did you happen to pull the plugs and see if you actually get a fuel starvation or over rich indication?? I plan on starting my first flight with fresh clean plugs, just so that I can double check that very issue. 

I too have injection and a return line. Airflow performance built my fuel pump setup (2 parallel electric pumps) but the return line does not go back to the sump. Instead it feeds right back in before the pumps. They say this keeps the flow up but avoids fuel frothing. 

I also have the backup fuel vent/valve inside the cabin... just in case. 

I recently went to an EAA meeting here at Mid Valley. The feature that night was a retired theoretical flight test engineer. He and his wife have built at least 10 homebuilts (and they still have them all). 
One of the things that came out of his experience probably relates well to your situation, mine, and many others. 
He suggests running the aircraft at takeoff power (tied down, with spotters) for at least 2-3 minutes. His experience suggests that this test will reveal items that may only raise their head on the first flight, in climb out... the worst time for a Gotcha to show up. 

I wondered how on earth I will manage to hold my beast still for that run, but your data and experience tell me that I NEED to do that somehow. 

I appreciate your continued openness on this and hope to hear of your discoveries. 

Best,? Kurt Winker


-----Original Message-----
From: Brian Michalk <michalk at awpi.com>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Sent: Mon, 6 Apr 2009 10:10 am
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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