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  #1  
Old 03-14-2017, 10:10 PM
n233va n233va is offline
 
Join Date: Jul 2014
Location: Prescott, AZ
Posts: 16
Default Power Loss Van's RV12 Rotax 912ULS

POWER LOSS VAN’S RV12 ROTAX 912ULS

Today 3/14/2017 a friend flew a RV12 to Williams Arizona, KCMR. Airport elevation 6691 ft. outside temperature was low 70’s. Flight in was normal. When he went to leave, just after becoming airborne the engine stumbled and lost significant power. An aborted landing was successful. An A&P from Prescott, AZ was contacted. The A&P had built this RV12 as well as a second one he flies. The A&P flew the second RV12 to Williams. He checked the carburetor bowls for debris on the first RV12 as well as doing a full run-up. All seemed normal and no debris was found. A second attempt to take off was made by the first RV12. Again the engine stumbled and failed to produce full power. The decision was to leave the first RV12 in Williams and fly the second one back to Prescott, planning on returning in the morning. The second RV12 did a run-up, which was normal, and started the take off roll. The second RV12 experienced a similar engine stumble and extreme roughness. The second RV12 could not develop take off power. Both aircraft are Rotax powered with 912ULS engines. Both are identical in the fuel system and carburation. Both also experienced fluctuating fuel pressure during the attempted takeoffs.

Both aircraft were burning 91-octane auto fuel with ethanol, purchased locally in Prescott Arizona at two different locations. It appears that both aircraft experienced vapor lock while applying full power for take off. The weather has been much warmer in Northern Arizona than usual for this time of year. We believe the fuel, which is in all probability, a winter blend, has too high a vapor pressure, thus causing the vapor lock.

For those of you RV12 drivers using auto fuel at high elevation airports in warm temperatures BEWARE. Both RV12’s will be flown out of Williams tomorrow morning when the temperatures are expected to be in the high 30’s to low 40’s.

Until or when we can determine that the refineries are producing summer blend auto gasoline, we will be changing to 100ll. And may continue with 100ll during the summer months to avoid the possibility of vapor lock at high elevation airports, regardless of the auto fuel blend.
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Old 03-14-2017, 10:30 PM
DHeal DHeal is online now
 
Join Date: Sep 2006
Location: Windsor, California
Posts: 520
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Thank you for the informative report. What kind of Fuel Pressure readings did you see (download flight data log?) during the climb-out and subsequent rough engine?
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  #3  
Old 03-15-2017, 07:53 AM
John-G John-G is offline
 
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Location: Northeast Ohio
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Quote:
Until or when we can determine that the refineries are producing summer blend auto gasoline, we will be changing to 100ll.
N233VA - I remember reading somewhere here in the forums where a gentleman did a little experimenting with the auto fuel/vapor lock issue and determined that by adding 30% 100LL to the auto fuel that it solved the vapor lock issue. This would save you the hassle of draining all the fuel in both aircraft.

Unfortunately, I can't put my mouse on that thread at the moment.
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Last edited by John-G : 03-15-2017 at 09:18 AM. Reason: typo
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Old 03-15-2017, 12:24 PM
mturnerb mturnerb is offline
 
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Location: Ponte Vedra, FL
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Is there a mixture adjustment on the Rotax? This sounds very similar to power loss when power is advanced with lean mixture...
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  #5  
Old 03-15-2017, 12:26 PM
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rv7boy rv7boy is offline
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Quote:
Originally Posted by John-G View Post
N233VA - I remember reading somewhere here in the forums where a gentleman did a little experimenting with the auto fuel/vapor lock issue and determined that by adding 30% 100LL to the auto fuel that it solved the vapor lock issue. This would save you the hassle of draining all the fuel in both aircraft.

Unfortunately, I can't put my mouse on that thread at the moment.
Would it happen to be post #9 in this thread?
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Old 03-15-2017, 12:37 PM
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DaleB DaleB is offline
 
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Location: Omaha, NE (KMLE)
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Quote:
Originally Posted by mturnerb View Post
Is there a mixture adjustment on the Rotax? This sounds very similar to power loss when power is advanced with lean mixture...
Nope. The Bing carb is (to whatever degree) self adjusting.
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  #7  
Old 03-15-2017, 12:37 PM
sergioam2009 sergioam2009 is offline
 
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Location: Brasilia, DF Brazil
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Default Installation?


I'll volunteer my dumb opinion. It must be some installation problem. I've been flying behind a Rotax 912ULS for the past two years. 100% of the time premium auto gas 91 octanes with 25% ethanol. Field at 3400 ft MSL, median temp around 25C/77F. Never experienced vapor lock. It's not a RV-12, it's a Paradise P-1, High wing.
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  #8  
Old 03-15-2017, 01:38 PM
John-G John-G is offline
 
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Location: Northeast Ohio
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Sergio,

I believe the bigger issue here in the states is EPA directed to strive for better emissions for automobiles, where by, there are two formulas used here ... one for winter and one for summer. The winter formulation is designed to improve the fuel evaporation during the cold temperatures of the winter months.

The vapor-lock issue is a real concern here when getting into spring and summer while still using the winter blend because it vaporizes much easier with the increase in ambient temperatures coupled with increases in altitude.
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Old 03-15-2017, 01:52 PM
boandrv7a boandrv7a is offline
 
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Location: denver
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Wow - There must be something unique to those fuel system setups. Hmmm. would love to hear a follow-up.

Jim
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Old 03-15-2017, 02:40 PM
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Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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Do both of these airplanes operate with electrical fuel pump running 100% of the time?
No switch to shutoff electrical fuel pump - correct?

Electric fuel pump in this application provides a vital function to reduce vapor lock. When engine is shut off the residual heat under the cowling can boil off the fuel in the carb bowls. If engine is warm for the restart it is best practice to allow electric fuel pump to circulate cool fuel for some period of time (maybe 5 minutes) prior to start and departure.

Note approximately 2 psi fuel pressure with electric pump running by itself and then about 5 psi when engine starts and mechanical pump is working in conjunction with the electric pump.
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Last edited by Piper J3 : 03-15-2017 at 02:53 PM.
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