REFLECTOR: Engine failure causes

Tue Apr 7 11:35:04 CDT 2009

I have a cable operated shutoff at the sump too- it only works to shut off
flow, because the cable can not push the valve back to open- I suppose a
wire could be fitted instead of the cable, but I only plan to use the valve
in emergency, and for maintenance, so it has not been an issue.

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Brian Michalk
Sent: Tuesday, April 07, 2009 10:42 AM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Engine failure causes

I am pretty sure it's not an ignition problem, because I have one magneto.
To answer a previous post, my runup test showed less than 50 RPM drop 
with mag off, and about 200 RPM drop with electronic off.
I was also able to briefly regain some power when I pulled back on the 
throttle, suggesting a lean condition.

I've heard several people talking about the remote shutoff valves being 
difficult to set to the open position with a cable attachment.  Is this 
because the torque is too high causing the cable core to bend?

David Bertram wrote:
> The fuel shutoff sounds suspicious.  I ran a cable from the pilots 
> side by the seat back to the outlet of the sump tank.  I can shut the 
> fuel off but it does not open very well, but this is only used in 
> emergency or maintenance.  I also looked at foaming but found it as 
> unlikely due to the sump fuel outlet being at the bottom of the tank 
> and I have a good vent system.  When I had my engine fail everything 
> and "everyone" thought it was a fuel problem.  It was a ignition 
> failure caused by my distributor gear. 
> Dave Bertram
> N350TX 
> /-------Original Message-------/
>  
> /*From:*/ Brian Michalk <mailto:michalk at awpi.com>
> /*Date:*/ 4/6/2009 11:15:11 AM
> /*To:*/ Velocity Aircraft Owners and Builders list 
> <mailto:reflector at tvbf.org>
> /*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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