Engine Failure on Take off

[John Moyer]

Input needed:

I have had two engine failures on take off in the past 60 days.  Very brief, maybe 1 to 2 seconds and then the engine continues to run.  It is as if the ingnition key was turned of and back on.

The first time we did the following:

• Drained and cleaned both fuel tanks
• disconnected all fuel lines and blew them out
• changed all filters
• changed fuel pump

 

We had no problems for 18 hours.

 

This morning at about 60 k and 300 ft the same thing occured.  Pulled power and landed. 

We taxed to parking and ran the engine up to 4900 and had the same thing occur 3 out of the 5 times we ran up  the power.

 

Note: Before taxing off the runway we did get a low amp  power warning.

 

All engine readings where in the green. 

• We check for fuel contamintation and found none. 
• Later when the mechanic tried to dublicate the problem on the ramp everything worked fine.

 

Anyone have this problem before?  It has me spooked.

John Moyer

[e-mail]

 

 FYI: TT aircraft: 130 hours

[Ben Fitzgerald-O'Connor]

Could this have happened due to fuel vaporisation?

 

In these instances, was the aircraft taking off from a cold start, or a warm turn around & how hot was it on the day?

 

If it is hot, it is a good idea to mix Avgas with Unleaded to get better stability and resistance from vaporisation which may well be the most likely reason for this.

 

Regards

Ben

[John Moyer]

Ben,

Thanks for the idea.

We had just returned form a long cross country and had been using 100% Avgass. 

Cold Start: we had taxied over a mile and then sat in the run up area for about 5 minutes.  I then did the pre take off run up and everything was in the green.  Out side temperature was about 70 F.  

 

I had wondered if sitting for a few minutes could have caused the problem, but I made sure  to do the full power to 4900 rpm before take off.

 

John 

[Ben Fitzgerald-O'Connor]

Thanks for the info - does not sound like it was a particularly hot day, and the fuel would have been flowing from the start. so coming through from the tank. Small chance I guess that there may still have been some water at the bottom of the tanks working through.

 

Unlikely to be ignition, as on the Rotax this is self sustaining (does not rely on the battery), and there are dual ignition circuits. There are also the dual carbs, so unlikely that one would have had a small blockage. The other thing that could possibly cause something like this is the air into the carbs - we have seen before the connection to the single air filter coming loose, and if not on the filter correctly; the tube can then vacuum itself onto the sidewall, which would restrict the engine of air while so court - however this should be obvious the moment you take the engine covers off. If this ever does happen, the solution is to engage carb heat pronto, as this bypasses the normal air source..

Sounds like this is still a bit of a mystery - there will be a good reason eventually found though. Has it happened again since?

 

Regards

Ben

[John Moyer]

Ben,

Thanks for the input.  We did find a gasket on carburetor bowl that has shrunk.  The mechanic (Jason) thinks that cause some air to be sucked into the carburetor. 

We have 3 hours on the engine and no further problems.

 

I will remember the carb heat suggestion.  That is one of my emergency procedure on engine failure.  Fuel pump, carb heat, change tanks. 

I will send your input to Jason.  He would like to see what you had to say.

 

Thanks, again

 

 

[Jonathan Trunz]

since you say it's like the key was turned off then on, has the ignition system been checked from key to modules?

[John Moyer]

Johnathan,

Good input.  We did this and everything check out.  We did find a cork gasket that had shrunk in one of the caburetor bowl and decided that it had allowed air into the fuel line.

 

Have flow it 10 hours and no further prob.em.

 

John

[daniel s dennison md]

I have had a similar problem three times and have drained tanks,changed fuel screens, changed fuel pump and fuel sensors. It turns out that the problem was vapor lock each time from the use of Mogas. I am now running avgas with the addition of TSP and have had no further problems whatsoever.

[Steve Posner]

John (and all others) -

Something to keep in back of your mind... I know at those low engine hours you have not done the 5 yr rubber change but of those that have there is a high percentage of engine failure on takeoff incidents that have occurred. The culprit has been tiny rubber particle contamination of the carbs from pushing rubber hoses on barbed connectors. This doesn't have to occur immediately...mine went 40 hours before 3 engine failures.

The important trick is just because you blow out the hoses, clean the carb jets and bowl etc. you are not out of the woods. The area to check is the fuel input chamber going into the carbs (fuel line is connected to a short metal stub that screws into a round chamber in the carb). You have to remove (unscrew) the metal line because in that chamber is a restriction (small hole) that the fuel must pass thru to get into the flow valve and carb bowl. This chamber traps the larger rubber pieces and blocks fuel flow causing the exact symptoms you had. On mine, after unscrewing this inlet, both chambers were found PACKED with rubber debris. All the carb and hose cleaning won't fix this problem without unscrewing this inlet tube from the carb.

Steve