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Losing power during extreme heat conditions

M

Mauritz

Member
Today while I was busy with transition training (40 minutes in the flight) the Rotax engine started losing power at about 100ft AGL in the climb. I fly with 95 Shell Mogas. The engine has run for about 10 hours now, the tank was about half full, however the outside temp was 36.5⁰C or 98⁰F. As a result of the extreme heat in our part of the world I have moved the oil-cooler an inch forward which definitely help with the oil temperatures.

Did anybody experience this in extreme heat conditions? Is there a possibility that the fuel lines became too hot and resulted in the engine losing power? This was now the 2nd occurrence in extreme heat conditions and don?t want to fly any further until I have found the problem and or the solution.:confused:
 
Fuel flow

Assume pressure/flow were all in the green? If you are using Skyview you can chart all that data vs. RPM or MP.
 
Vapor lock? Was the electric fuel pump "On" at the time? Indicated Fuel Pressure at the time? Did you do a fuel flow check as specified in the PAP plans to verify adequate fuel flow? Fuel tank vent holes open? Restricted fuel flow orifice and hoses correctly installed per the plans? I assume you have the standard RV-12 fuel line installation with fire sleeving. As Brent mentioned, your SV data read-out might offer some clues.
 
Fuel flow vs power loss

Many thanks for your comments and thoughts. Yes the aircraft is Skyview equipped. The fuel pressure was in the green with the electric fuel pump on and has the standard RV12 fuel line installation with fire sleeving. Vapour lock was what I thought of also, maybe I will find something in the data.
 
Did you have a long taxi prior to your takeoff or did you have a short break to refuel before your takeoff or were you doing touch and gos when this occurred?:confused:
 
Mauritz said:
Today while I was busy with transition training (40 minutes in the flight) the Rotax engine started losing power at about 100ft AGL in the climb. I fly with 95 Shell Mogas. The engine has run for about 10 hours now, the tank was about half full, however the outside temp was 36.5⁰C or 98⁰F. As a result of the extreme heat in our part of the world I have moved the oil-cooler an inch forward which definitely help with the oil temperatures.

Did anybody experience this in extreme heat conditions? Is there a possibility that the fuel lines became too hot and resulted in the engine losing power? This was now the 2nd occurrence in extreme heat conditions and don’t want to fly any further until I have found the problem and or the solution.:confused:
Click to expand...

Sorry to hear that, Mauritz. I can imagine how unnerving that must have been for you.During the summer in Tucson we easily reach 100degF and more and I have not experienced any issues during touch-gos or extended climbs. I too have moved my oil cooler about an inch forward, away from the muffler, and I run on highest octane Mogas most of the time. I have a switched fuel pump and I never run it unless the tank level is below 8 gallons or to pressurize the system before engine start.
So even during the searing heat of the summer I was not actively pushing fuel through the system to avoid vapor lock during my flights. However, after a flight and some time on the tarmac I do need to flush the system with the pump on to ensure a proper engine restart.
Hope you find the culprit soon!
 
Last edited:
Spoke to Mauritz earlier and it seems that he has found the problem. Seems that the tank fuel vent pipe was pinched close. Apparently there is e new version out with a beefed up pipe.
 
Many thanks for all the comments and suggestions.
I will do a more comprehensive search (including float level checks) this coming weekend and report back on my findings.
@ Jetguy yes this happened during touch and gos and was already 40 minutes in the circuit when this occurred.
 
Power loss Rotax 912 on Mogas

Speaking on past experience with my Rotax 912, which was used on a Interplane Skyboy, I found that in summer months if I don't fly for a while the carby bowl dried out and a film of the additives used in mogas 98 Octane, would build up on the mixture needle causing it to jam. I cannot remember the exact procedure I used to lean it but vague memory is that would I flood the carby bowl and or physically clean the needle by wiping it with petrol (gas) soaked rag. Also memory creeping back is telling me that it wasn't so much a Rotax 912 issue but the Bing Carby it used. This engine & carby was exposed to the elements.

I hope my input helps and is a valid comment:confused:
 
Peter,

that is not an Additive??.it is a gum deposit from olefins.

Hence the reason Avgas has a very low limit on olefins.

Another reason why I personally do not like mogas. My Boat suffers this same problem.
 
(For the ELSA) Do you have a fuel recirculation line installed? It's a must for the new corona fuel pumps and the help reduce the chance of vapor build up.

Long idle times on the Tarmac or after a period of running then allowing it to sit for 30-40 min. then re-starting may have some vapor production, but this usually doesn't cause a power loss, but the possibility is certainly there. A piece of debris passing through the system could also cause this situation to crop up.
 
Report back on power loss during extreme heat conditions

I started by doing the float level tests and both carbs were within the required specs. I then weight both sets of floats and the two sets weight in at 5.7 grams also within specs. What I however found below the floats were paper thin flakes about 4mm long by 2mm wide too big to have passed through the VA-261 Fuel Strainer. The left carb had 3 flakes and the right carb had 5 flakes.

My engine was lying in the crate for over a year before installation. I must confess that after installation and initial ground test runs I have taken all precautions that no debris gets into the fuel system. I have cleaned the system up to and including the gascolator. I have never checked the carb bowls and I wonder if these flakes are not something that solidified in the carb bowls as a result of the prolonged crating time. Some folks have eluded to finding flakes in the carb bowls after a prolonged standing time. I think it was a coincidence that the power loss was during the heat of the day, it could have happened any time.

My proposal would be that after initial ground test runs the whole fuel system including the carb bowls be checked for any debris.

Now that I have found the problem I am going to enjoy this magnificent flying machine. Many thanks to all the folks on VAF forum and the technical people at Vans who had an interest in making our love of flying as safe as possible:)
 
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