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  #21  
Old 12-19-2021, 11:07 AM
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airguy airguy is offline
 
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My 2 cents, I don't think ANY fuel is going to meet ALL the specs for true drop-in replacement. If they keep waiting for the magic wand, we're all just going to keep waiting. There are simply too many different hooks in the spec, seeing as how the spec was written specifically for 100LL.

I fully expect a variety of fuels and STC's to cover different models, but I think I'll be comfortably dead and buried before a fully compliant drop-in replacement comes about.

Meanwhile I'll keeping running my 91E10 and smile about it. I'm sorry that some folks can't, but I am not able to solve all problems.
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2023 dues paid
N16GN flying 1,200 hrs and counting on 91E10; IO360, SDS, WWRV200, Dynon HDX, IFD440, G5
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
Repeat Offender - 10 empennage in process.
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  #22  
Old 12-19-2021, 11:46 AM
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rv6ejguy rv6ejguy is offline
 
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Location: Calgary, Canada
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Quote:
Originally Posted by N427EF View Post
I am not proposing a "drop in" replacement, just a solution for most of us who operate 8:5 to 1 Lycs. You really don't need 100 octane to operate that engine.
As Greg says, you can use mogas right now as he and others are, being aware of certain limitations and cautions.

This thread was really about unleaded avgas replacements though.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 462.1 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
https://www.youtube.com/channel/UCiy...g2GvQfelECCGoQ


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  #23  
Old 12-19-2021, 12:11 PM
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Fred.Stucklen Fred.Stucklen is offline
 
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Location: Brooksville, FL
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Default MoGas 93 Oct

Quote:
Originally Posted by rv6ejguy View Post
As Greg says, you can use mogas right now as he and others are, being aware of certain limitations and cautions.

This thread was really about unleaded avgas replacements though.
I am running 100% 93 Oct E10 Mogas in my IO-360 8.5:1 compression engine. The trick to defeat vapor lock is to have the fuel pressurized from the tank to the engine pump. Even 5PSI from a Fauset low pressure pump can do this from the wing root. I'm in Florida, and have yet to see any detonation issues on very hot days.
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Fred Stucklen
wstucklen1@cox.net
RV-7A N924RV Flying (2090 Hrs & counting)
RV-6A N926RV 875 Hrs (Sold)
RV-6A N925RV 2008 Hrs (Sold)
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  #24  
Old 12-19-2021, 04:07 PM
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rv6ejguy rv6ejguy is offline
 
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Quote:
Originally Posted by Fred.Stucklen View Post
I am running 100% 93 Oct E10 Mogas in my IO-360 8.5:1 compression engine. The trick to defeat vapor lock is to have the fuel pressurized from the tank to the engine pump. Even 5PSI from a Fauset low pressure pump can do this from the wing root. I'm in Florida, and have yet to see any detonation issues on very hot days.
Yes, I know many folks running Mogas with no issues and I run it in my turbocharged Subaru with 9.25 CR plus boost. It still doesn't provide the margins required to satisfy forced induction legacy aero engines though which was what this discussion is about- a drop in fuel to replace 100LL for all piston engined aircraft in use today.

Most RVs can safely use Mogas, no question as so many folks are doing it and have done it for a while. It just doesn't currently have the widespread airport availability to easily plan long cross country trips using it exclusively.

For the RV community, even if 100LL disappeared next year, we'd have some options with Swift, GAMI or Mogas.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 462.1 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
https://www.youtube.com/channel/UCiy...g2GvQfelECCGoQ



Last edited by rv6ejguy : 12-20-2021 at 01:33 PM.
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  #25  
Old 12-20-2021, 08:46 AM
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Quote:
Originally Posted by rv6ejguy View Post
Yes, I know many folks running Mogas with no issues and I run it in my turbocharged Subaru with 9.25 CR plus boost. It still doesn't provide the margins required to satisfy forced induction legacy aero engines though which was what this discussion is about- a drop in fuel to replace 100LL for all piston engined aircraft in use today.
And there's the rub - those folks running hotter engines "want" a drop-in replacement that they don't have to think about - just pump it and fly it. That may not be happening, sooner or ever. They may actually have to engage brain and modify their procedures (and possibly engines) to learn how to run a new fuel if they want to get away from lead.
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2023 dues paid
N16GN flying 1,200 hrs and counting on 91E10; IO360, SDS, WWRV200, Dynon HDX, IFD440, G5
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
Repeat Offender - 10 empennage in process.
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  #26  
Old 12-20-2021, 08:53 AM
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Quote:
Originally Posted by airguy View Post
And there's the rub - those folks running hotter engines "want" a drop-in replacement that they don't have to think about - just pump it and fly it. That may not be happening, sooner or ever. They may actually have to engage brain and modify their procedures (and possibly engines) to learn how to run a new fuel if they want to get away from lead.
Speaking for myself, I'm willing to engage my A&P to make whatever engine changes are necessary to run the fuel that they pump at my home airport, but it's going to have to be the entire infrastructure. They need to have that fuel at all the other airports I travel to as well. I don't want to have to plan my trips around the availability of the gas that my engine is set up to use.
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RV-9A, 2011, bought flying
IO-320D1A (factory new), C/S
Dual Pmags
IFR equipped
AFS 5400/3500, G5, IFD440 navigator,
bunch of other stuff
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  #27  
Old 12-20-2021, 09:36 AM
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airguy airguy is offline
 
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Quote:
Originally Posted by MacCool View Post
Speaking for myself, I'm willing to engage my A&P to make whatever engine changes are necessary to run the fuel that they pump at my home airport, but it's going to have to be the entire infrastructure. They need to have that fuel at all the other airports I travel to as well. I don't want to have to plan my trips around the availability of the gas that my engine is set up to use.
I don't plan mine around that fuel - I adjust to whatever is local. Granted I have extended range tanks, so I can make better than 1000nm without fuel if needed and frequently tanker my fuel in so I don't have to buy for the return trip - but I'm doing it mostly for price, not fuel quality. 91E10 is about $2/gal cheaper than 100LL. When I make a long trip and need fuel, I buy 100LL just like the rest of us.

If your engine is set up to burn 100LL, you'll always be able to burn 100LL. If you set it up to ALSO be able to burn a lower quality fuel like 91E10 or 93E10, it will happily burn that new fuel OR 100LL, or any mix between. You may need to modify your engine operations when burning just the lower quality fuel (I don't, but others might, test your setup yourself) but it will always be happy to burn a higher quality fuel.
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Greg Niehues - SEL, IFR, Repairman Cert.
Garden City, TX VAF 2023 dues paid
N16GN flying 1,200 hrs and counting on 91E10; IO360, SDS, WWRV200, Dynon HDX, IFD440, G5
Built an off-plan RV9A with too much fuel and too much HP. Should drop dead any minute now.
Repeat Offender - 10 empennage in process.
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  #28  
Old 12-22-2021, 09:52 PM
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Clostermann Clostermann is offline
 
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Quote:
Originally Posted by rv6ejguy View Post
It's pretty easy to obtain higher octane than 100LL exhibits by using aromatics however the specific gravity of these is generally around 17% higher than gasoline so if you put much in, fuel weight increases which will put you outside the spec. You need to find some other compound to spike octane rating without the extra weight.
Ross, you are getting warmer... There are other octane boosters that have densities closer to 100LL. They have been used in mogas for decades and have been evaluated by the FAA and others.

https://www.tc.faa.gov/its/worldpac/techrpt/ar06-27.pdf
https://www.tc.faa.gov/its/worldpac/techrpt/ct93-65.pdf
https://www.tc.faa.gov/its/worldpac/techrpt/ar96-42.pdf
https://www.hjelmco.com/pages.asp?r_id=14663
https://www.baylor.edu/mediacommunic...ory&story=1141

The key is to use them in the correct amounts to avoid over-leaning and increasing fuel flow, especially in turbocharged engines.

Last edited by Clostermann : 12-24-2021 at 12:42 PM.
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  #29  
Old 12-22-2021, 10:05 PM
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Clostermann Clostermann is offline
 
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Quote:
Originally Posted by rv6ejguy View Post
I think it's safe to say that vapor pressure of any drop in avgas replacement fuel will be an important spec to meet along with all the others. With STCs, which already exist for using mogas in certain aircraft, some fuel system changes or warnings may be required to comply, due to vapor pressure differences.
RVP is an important spec, especially on the high end to prevent vapor lock. Not so much on the low end. Some OEMS would like to see the D910 RVP spec tightened to avoid vapor lock.
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  #30  
Old 12-22-2021, 10:20 PM
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Clostermann Clostermann is offline
 
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Quote:
Originally Posted by rv6ejguy View Post
This wasn't GAMI but Swift: https://www.purdue.edu/newsroom/rese...iftRadial.html The main point- "Test results showed that 100SF produced a higher detonation onset threshold than 100LL. The engine was operated at 115-145 octane takeoff power settings and there were no indications of engine knock." This was a decade ago.

Seems the R2800s are being limited to around 52-54 inches on 100LL. Similarly on R3350s. I knew a pilot/ engineer on the Martin Mars water bombers in BC.

I suspect there is more testing going on than what is common knowledge. Purdue in particular has strong links to industry and some of the fuel companies going back to before WW2.
Thanks for the correction. I would have been surprised if the Wichita ACO had included the R2800 in the STC for non-turbocharged engines. This makes more sense. However, the Swift 100SF fuel is a long shot to be commercialized, for reasons I don't want to get into here.

Purdue NaTef is indeed a great research institution especially for materials compatibility. Not sure how much engine testing they are doing these days.
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