REFLECTOR: Engine failure causes

Mon Apr 6 12:23:26 CDT 2009

Brian

When you test your aircraft, you need to run it on the ground for a
minimum of one to two hours (not continuous).   You also needed to have
tied it down and raised the nose to simulate climb and run it in that
position for 5-10 minutes (obviously make sure the propeller is clear).
It's amazing how much junk, water, resin, sanding grit,  gets in the
tanks, fuel lines, etc that doesn't show up until you fly and climb out.
Unless you have run the engine or drained the sump in a nose high (or
any unusual) attitude, you may never find the water that has accumulated
in your tank over the last few years.      Also, our local EAAs
recommend 15-20 high speed liftoffs at full power (pop it off the ground
and then land straight ahead).    This becomes very important if you
have changed the standard set ups and installations-this means you get
to be real test pilot flying a new design.

You also need to consider blocked vent lines.   I realize you had
minimum gas in the tanks, but if the main internal vents are plugged up
(with debris or gas) the system will not draw fuel.     This can bite
folks since they also check this with the plane level but not with the
plane in a nose high attitude.    After flying almost 500 hours in mine,
I filled my tanks to the max one day prior to a cross country and found
that one of the tanks would no longer feed fuel (I landed, popped the
cap and things equalized enough after about ten minutes to continue the
trip-I blew the system out when I returned home).    I apparently had
too much gas and totally plugged the vent system with gas.    

Good luck.

Bill Stockman, Senior Associate

Dayton Aerospace

(937) 369-4799 cell

(937) 426-4300 work

bill.stockman at daytonaero.com

________________________________

From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Brian Michalk
Sent: Monday, April 06, 2009 12:11 PM
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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