REFLECTOR: Engine failure causes

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Hi Brian

I am trying to relate what you have discovered to how you described the 
incident - it may be useful.
/
As I taxied over to the fuel pumps, I saw the low fuel
light was on.  /(Do you think you were really that low on fuel or was it 
an indicator problem, or possibly air in sump tank?) /After taking on 
five gallons each side, I noticed the
warning light had turned off.  When the engine lost power after takeoff,
the light was on./

I favour your fuel starvation theory but the sooty plugs don't fit. Need 
to confirm the Mag plugs are working - what was the result of your 
run-up RPM drops prior to take-off? On mine - mag off - rpm drop hardly 
perceptable. EI off - rpm drop 300rpm.  This was normal on the Frank 
with one mag and one EI.

I know you have a modified Franklin. Can you measure the fuel flow thru 
your injectors? (or at least compare the cylinders near the firewall 
against those nearest the prop). This may help to understand the sooty 
Vs 'normal' electronic ignition plug findings.

Foaming fuel in sump tank . Why didn't it show up in earlier engine runs 
/ high speed taxi etc??? Maybe it did - /There's 4.9 gallons in that 
sump.  (The warning light was on) That's a lot
of time, and there is no way I could have emptied it.  /Something caused 
it to turn on or, its faulty. I would be looking closely at this!

The Franklin needs ~60 litres/hour at full power if memory serves: when 
you tested your fuel flow (are both pumps electric?) did you see 60 
litres/hr plus a good saftey margin? Did you take-off with both pumps 
running?

/The electronic injection system was
tuned out to 2250 RPM's, because that's the limit I could do in ground
testing.  I then extrapolated out to 3000 RPM's (red line at 2800), and
then richened up the whole table to be on the safe side./
What did you set the fuel flow to for max rpm?

Stupid question; any chance that backup injectors were also squirting juice?
Stupid question #2; any chance the fuel pressure regulator failed ?
And SQ#3; fuel drains (sump got one? how about those filters?) any 
chance you had a leaky one? Is there fuel in the sump now (post incident)?


I don't 'like' the fuel shut off valve up front (mine is push-pull cable 
operated and sits at the sump tank exit point) but still - just how nose 
high were you? and where does the air come from to give a vapour lock 
scenario? The sump tank would need to be full of bubbles to create an 
air lock right? and .... that warning light is still bothering me!

Vent line in a vacuum? is the suggestion that all the fuel got sucked out?

I think I would be looking a lot closer at the warning light - test it 
to buggery!
Hope some of these silly ramblings trigger something Brian.

Good luck
Steve

Brian Michalk wrote:
> 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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