REFLECTOR: Engine failure causes

[Al Gietzen]

Prime suspect #1: Fuel starvation due to fuel shutoff valve arrangement.
 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.

Brian:  I don't like the idea of having that line come forward to the valve,
and back. Although normally not likely that the level of the valve getting
slightly above the level in the strake would result vapor bubble.  But how
big is the line? Pressure drop in that line and valve could result in vapor
lock when the pumps are drawing high flow rates. In addition, fuel returning
from the engine is warm, and warming the fuel in the sump. Now you have warm
fuel being pulled against a flow restriction.  Not good. You want minimal
restriction  between sump and pump  You might consider putting an emergency
shutoff back at the sump with a pull cable on a 90 degree ball valve.  Works
for me.

Theory #2: Foaming fuel in sump tank
 It might be possible, but unlikely that the sump tank became full of
foaming gasoline.

I think this very unlikely; that's a lot of foam.  Yes the flow is high, but
so is engine usage. I have FI pressure regulator bypass also returning to
the sump.  There was never enough foam to make the low fuel float switch
activate.  The fuel flowing in from the strake will force the foam out the
vent.  I did find evidence that some small amount foam was going out the
vent line, so I installed a small separator 'tank' replacing the vent
manifold - problem solved.

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.

Of course you'll check the filters.

All the best,

Al

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.tvbf.org/mailman/private/reflector/attachments/20090406/c93fb705/attachment.htm>