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  #1  
Old 04-06-2021, 03:28 PM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
Join Date: Nov 2014
Location: Hinckley, Ohio
Posts: 2,376
Default Vapor Lock RV-12 Rotax 912ULS

I may be joining the ďSinker ClubĒ for 2nd time. Today I did several TO/Landing to full stop at a remote airport and on last TO had horrible stumble/vibration at about 500 AGL before turning crosswind. My first thought was I lost a tip of one propellor blade. Iím guessing power loss of about 10-20% - enough power loss to eliminate climb. I pulled throttle back to see if vibration would get better and it got a little better but not total solution. I checked both ignitions and they were working equally well. So, I keep power reduced and turned 180 degrees and landed on runway in opposite direction. Yeah, I know Ė donít do that. Engine ran and tested well on the ground, so I did a flight and stayed in traffic pattern, and once satisfied everything OK, I flew 30nm back to home airport. While all this was happening, I never experience fuel smell. I will weigh floats tomorrow and thinking about bumming Marvel Schebler floats from friend who is waiting to do installation in his own RV-12.

Running fresh 93E10 with 75F OAT, so possibility of Vapor Lock? Also, fuel purchased today may still be Winter Vapor Pressure...

A couple questions:

ē Is this normal "sinking float" failure mode that must folks are seeing?

ē Is everybody happy with the newest Marvel Schebler Floats MS80-430?

Thanks for listeningÖ
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Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 650

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H
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  #2  
Old 04-06-2021, 04:05 PM
mcems mcems is offline
 
Join Date: Apr 2008
Location: Salem SD
Posts: 171
Default

Jim

Your symptoms are exact to mine last May if you remember . It was indeed winter blend that cause exactly the same situation.

I though floats right away . It was not. It was winter blend vapor locking . You can go back and look at the old posts on this . about a year ago. When the weather started getting warm.

Brad Stiefvater
Salem SD
124BJ
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  #3  
Old 04-06-2021, 04:48 PM
Piper J3's Avatar
Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
Posts: 2,376
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^^^ Right ^^^

Now Iím wondering if removing the cylinder cooling shroud maybe increases under-cowling temperatures during ground operations. I just finished repairing a cracked engine mount, installed new high performance silicone coolant hoses, and changed out rubber engine mount isolators. While I was doing this work, I removed the fiberglass cylinder cooling shroud as per latest Vanís KAI. Maybe when doing a lot of TO/Landing/Ground ops the under-cowling temperatures get high enough to boil fuel in the carb float bowl?

Today was third shakedown flight with previous two flights still using last yearís fuel which Iím sure was summer vapor pressure. Todayís flight used newly purchased 93E10 Mogas which Iím quite sure is still being sold as winter blend.

I think lesson to be learned is reduce ground ops to a minimum when using winter vapor pressure fuel and OAT is +70ish...
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Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 650

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H
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  #4  
Old 04-06-2021, 05:48 PM
seagull seagull is offline
 
Join Date: Dec 2019
Location: San Bernardino
Posts: 289
Default

I removed my shroud 10/2/20, when I changed to silicone coolant hoses. That was 146 hours ago. I did not notice any temperature differences after the change.

The floats were changed to Marvel Schebler Floats MS80-430 on 1/9/21, 60 hours ago. The floats I had in it weighed good but I didn't want to have any future issues.

The plane is hangared in Southern California where it gets quite hot and we have EPA regulating our gasoline. Costco 91 octane is used exclusively.

One time before all the changes, my wife with an instructor experienced a power loss, it did not quit but had a power reduction on climb out. It was a 110 degree day and they had a long wait getting out. The instructor related the incident upon landing, he said he reduced power then came back up on it and it was running fine. They flew another .7 afterwards with no further problems. I pulled the Dynon logs and the oil temp was 180f on the takeoff roll and peaked at 256f. in the climb.

I personally have not had any running issues before or since but I do not let the temps climb that high.
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  #5  
Old 04-06-2021, 11:17 PM
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Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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I agree with above. My temps Ė (2) EGT, (2) CHT, and oil temp all same with/WO cylinder cooling shroud. Oil temps in green arc. My concern is with ground ops. It would be nice to have sensor to measure under-cowling temperature as indicator for prelude to vapor lock.

Iím really thinking my engine stumble/vibration problem was excess heat buildup from ground operations while using winter vapor pressure fuel. Today I will fly again with fresh winter fuel. I will fly early morning while OAT is cooler and I will keep ground ops to a minimum. I have ordered Marvel Schebler epoxy floats and will install soonest.

If my research is correct, winter fuel changeover doesnít occur until May 1 at fuel terminals and gas stations have until June 1 to complete the changeover to summer gasoline.
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Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 650

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H
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  #6  
Old 04-06-2021, 11:35 PM
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greghughespdx greghughespdx is offline
 
Join Date: Nov 2011
Location: Aurora, OR
Posts: 954
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What youíve described regarding running winter blend fuel and heat soaking on the ground is quite possibly the cause of your problem. Did you shut down and restart at all during these ground ops? Depending on the specific winter blend, OAT and heat soaking you could be boiling your fuel. The bigger the difference between winter temps and warmer present temps the greater the potential for problems.

Personally, I would not run in hot temps with winter blend fuel, ever. Especially winter fuel from northers states where it gets friggin cold and blends are made for the more extreme cold temps. Much better to put 100LL in the engine of summer fuel isnít available, to better ensure you donít have potential vaporization. The vapor pressures on winter blend fuels can be remarkably different than standard blend fuel in some locales. Fuel blended for cold-air ops just wonít perform in hot environments. Engines can potentially quit. Thatís definitely one of the potential risks one must actively understand and manage when running auto fuel. 100LL with a little Decalin scavenging agent added can bring a lot of Pearce of mind when an appropriate auto fuel isnít available.
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Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Building RV-8A since Sept 2014
Dual AFS 5600, Avidyne IFD 440, Whirlwind 74RV, Superior XP IO-360
VAF build thread - Flickr photo album - Project Facebook page
Aurora, OR (EAA Chapter 105)

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  #7  
Old 04-07-2021, 12:25 AM
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Piper J3 Piper J3 is offline
 
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Location: Hinckley, Ohio
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Thanks for your input Greg. I wonder if adding a series of louvers on the top cowling would keep temps in check?

As an experiment, Iím buying a two-channel digital temp sensor with type-K thermocouples for $19 on Amazon. Thermocouple leads will be long enough to measure temp of each carb float bowl to determine if fuel is near boiling point.

It would be really nice if my D-180 could input two additional temp sensors.
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__________________
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Jim Stricker - EAA #499867
PPL/ASEL 1970 - Sport Pilot since 2007
80 hrs Flying Aeronca Chief 11AC N86203
1130 hrs Flying 46 Piper J-3 Cub N6841H
Bought Flying RV-12 #120058 Oct 2015 with 48TT - Hobbs now 650

LSRM-A Certificate 2016 for RV-12 N633CM
Special Thanks... EJ Trucks - USN Crew Chief A-4 Skyhawk
MJ Stricker (Father & CFI) - USAAF 1st Lt. Captain B-17H
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  #8  
Old 04-07-2021, 12:36 AM
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greghughespdx greghughespdx is offline
 
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Location: Aurora, OR
Posts: 954
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Quote:
Originally Posted by Piper J3 View Post
Thanks for your input Greg. I wonder if adding a series of louvers on the top cowling would keep temps in check?

As an experiment, I’m buying a two-channel digital temp sensor with type-K thermocouples for $19 on Amazon. Thermocouple leads will be long enough to measure temp of each carb float bowl to determine if fuel is near boiling point.

It would be really nice if my D-180 could input two additional temp sensors.
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Louvers would allow a little more hot air to escape (like with the 12iS cowling). But it would not meaningfully impact the fact that winter blend fuel will boil/vaporize at a lower temperature (often MUCH lower) than summer blend or 100LL fuel will. I would not look to making physical changes to solve a problem that has a root cause in the actual fuel being used in an incorrect environment. Upper-midwest winter blend fuels made for very cold temps, for example, can have a VERY different vapor pressure than standard/summer-blend fuels. Fuels really need to be used in the ambient temperature environments they're blended for.

Opening the oil door (when shut down of course) can make a significant difference in reducing how hot the cowl gets as it heat soaks, and for how long. But it still gets hotter. Just physics.
__________________
Greg Hughes - Van's Aircraft - Director - Community, Media, Marketing, Support
Van's web site | Instagram | Facebook
Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Building RV-8A since Sept 2014
Dual AFS 5600, Avidyne IFD 440, Whirlwind 74RV, Superior XP IO-360
VAF build thread - Flickr photo album - Project Facebook page
Aurora, OR (EAA Chapter 105)


Last edited by greghughespdx : 04-07-2021 at 12:39 AM.
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  #9  
Old 04-07-2021, 09:02 AM
NinerBikes NinerBikes is offline
 
Join Date: Dec 2018
Location: Granada Hills
Posts: 1,131
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One of the flight schools in Boise, ID that posts here had the same problem in March or April of 2020, vapor lock and loss of power on take off.

Adding 10 to 20% of 100LL to the rest of the Mogas solved the problem.

Cammie Patch was the author of that comment, if you want to look it up, as they don't post that often.
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  #10  
Old 04-07-2021, 11:17 AM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
Posts: 3,168
Default THERMOCOUPLE

Piper J3, the Dynon D-180 has a thermocouple input on EFIS pins 27 & 28. If that input is free,
a type J thermocouple can be connected. Omega has part number WTJ-14-36 for $14.
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