REFLECTOR: Engine failure causes

[Brian Michalk]

Al,

Good comments.  For prime #1, I envision three fixes.
First, would be as you point out to make the fuel shutoff valve a cable
operated valve.  Second, rather than pick up off the bottom of the sump,
and loop over the gear bulkhead, I would drill a hole near the bottom of
the bulkhead and route the fuel to the pump with little height change.
Third, I would ensure the fuel return flow doesn't compromise where I
pick fuel up to the pumps.

Al Gietzen wrote:
> 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
> 
>  
> 
> 
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