Jjackh10 said:
There's basically 2 problems to solve.

1. Maintain detonation margin for high compression or forced induction engines.
2. Maintain compatibility with legacy GA fleet fuel systems (rubber).

The bureaucratic solution is to develop a blend of chemicals that is far more expensive, toxic, dangerous, and environmentally damaging then lead. And force you to use it.

A better solution would be to use ethanol, which any refinery can blend and ship much cheaper than the current 100ll (And cheaper still without fed and state road tax). Then remove the STC bureaucracy to make retrofit fuel systems affordable.

The right solution is to quit scaremongering and over stating the danger of leaded fuel. And remove the STC bureaucracy to make retrofit fuel systems affordable. This would let the market decide (how America is supposed to work).
Click to expand...
Can I offer another solution? The real, cowboy, pick yourself up by the bootstraps, get'r done, rugged individualistic, we don't need no stickin' badges, no whine and cheeze, gumbint out to get us solution?

Modify your fuel system to run car gas with any amount of ethanol, lower the compression if needed, and fly using gasoline you can get at the same pump you use to fill up your F-150. Done!

We've had over 50 years to solve this problem and we haven't. No one involved in aviation can say that they didn't see this day coming, yet they kept buying engines that only work with 100LL. Time to start a business converting all those Continental IO-550s to something that will burn car gas, or fix their fuel systems to not leak when exposed to a bit of aromatic fuels. As Braly has said a few times, the fuel he's developed is about the same as what they ran in the 1940s during WW2. Sure, those guys were smarter than us, and braver, but I guess we should be able to duplicate their fuel systems - ammirite?
 
rv8ch said:
Can I offer another solution? The real, cowboy, pick yourself up by the bootstraps, get'r done, rugged individualistic, we don't need no stickin' badges, no whine and cheeze, gumbint out to get us solution?
Click to expand...
Agreed, we're saying the same thing. And for the experimental world it's not a big deal.
rv8ch said:
Modify your fuel system to run car gas with any amount of ethanol, lower the compression if needed, and fly using gasoline you can get at the same pump you use to fill up your F-150. Done!
Click to expand...
the FAA induced costs of modifying the fuel systems of the certified fleet (think big engines and twins) would dramatically reduce the number of airworthy planes. And that's not good for anyone in GA, certified or experimental.
rv8ch said:
yet they kept buying engines that only work with 100LL.
Click to expand...
They kept buying them because the airframe designs required the compression to meet horsepower requirements. Aside from the costs of pistons and the labor to change them, dropping the compression enough to run 91 octane pump gas on say an SR22T, would put its performance more inline with an SR20.

So to maintain compression/hp without lead you need something else. the readily available option is ethanol. 103+ octane unleaded fuel already exists. It's pricey ($12/ gallon) because it's only used for racing. But IF the certified fleet could be converted economically, the market would be large enough for the major refineries to produce it cheaper than 100LL.
 
Jjackh10 said:
the FAA induced costs of modifying the fuel systems of the certified fleet (think big engines and twins) would dramatically reduce the number of airworthy planes. And that's not good for anyone in GA, certified or experimental.
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It's not just the big guys. It would be cost prohibitive for nearly every certificated aircraft out there to replace every single piece of rubber in the fuel system and verify the other components are ethanol safe. Tanks, fittings, fuel senders, gascolators, carbs, fuel pumps, fuel lines, flow meters, primers, bladders, etc all would have to be tested for compatibility and upgraded. Plus some airframes can't handle the current mogas stc and would never be compatible with the more volatile ethanol borne fuels.
 
jacoby said:
It's not just the big guys. It would be cost prohibitive for nearly every certificated aircraft out there to replace every single piece of rubber in the fuel system and verify the other components are ethanol safe. Tanks, fittings, fuel senders, gascolators, carbs, fuel pumps, fuel lines, flow meters, primers, bladders, etc all would have to be tested for compatibility and upgraded. Plus some airframes can't handle the current mogas stc and would never be compatible with the more volatile ethanol borne fuels.
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Exactly, agree 100%. In my head I was thinking about the lower compression planes, many with stc's already. They still cant run ethanol though. It's frustrating leaded fuel has been vilified. Other than extra oil changes there's nothing wrong with it.
 
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rv8ch said:
Modify your fuel system to run car gas with any amount of ethanol, lower the compression if needed, and fly using gasoline you can get at the same pump you use to fill up your F-150. Done!
Click to expand...
Plenty on this forum have done exactly that.
 
bertschb said:
Lycoming has approved 93 octane auto gas for almost all of their 360's (as well as several other engines) but not their 390. Where does that leave us 390 guys?
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The 360s on that list are 8.5:1 or less and parallel valve. The 360 Angle valves don’t make the MOGAS cut and of course the 390 wouldn’t make it either since it’s a modification of the 360 angle valve.
 
In the 1070 SB this looks a bit concerning

Automotive fuels usually have Reid Vapor Pressure (RVP) values between 7 and 9.3 psi (48 and 64 kPa) in summer seasons but specifications for the RVP can be as high as 15 psi (103 kPa) in the winter. In some geographic regions, there is no upper limit to RVP in the winter season. As vapor pressure increases, the tendency for vapor lock will increase as well as fuel “boil off” at altitude.
Click to expand...

Automotive ground transportation fuels available direct to consumers (e.g. “pump gas”) usually do not have labels with sufficient information to identify compliance with the requirements in Table 2. While indicated octane is generally necessary for display at retail points of sale, octane rating methods, fuel vapor pressure and oxygenate content can vary widely and are generally known only at the wholesale terminal
Click to expand...

so if we fill up with the "Super Plus" "No Ethanol" fuel I wonder how can we confirm that the vapor pressure is within the range recommended by Lycoming. I really don't like taking chances..

more from lycoming:

Unleaded Fuels Part 1

This article is the first of three that explains in more detail Lycoming Engines's position on automotive fuels. The bottom line is that it's possible to make automotive gasoline "fitfor-purpose" for aviation. However, in doing so, you deviate from "pump gas" and end up creating a low octane...
www.lycoming.com www.lycoming.com

Unleaded Fuels Part 2

Automotive fuel from the pump is NOT the same everywhere you go. There are summer blends, winter blends, geographical blends within the seasonal changes, varying levels and types of oxygenates (not just ethanol) and when tanks are switched over a mixture of "in between". The pump labeling is...
www.lycoming.com www.lycoming.com

Unleaded Fuels Part 3

Lycoming tests every engine that rolls off our assembly line. We take them into one of our test cells, attach a propeller and appropriate sensors, and then operate them through a range of tests. These tests can last from an hour up to four hours. We also use our test cells to evaluate components...
www.lycoming.com www.lycoming.com
 
Toobuilder said:
Plenty on this forum have done exactly that.
Click to expand...
The challenge of modifying the fuel system to work with ethanol-containing mogas is that there is not enough information about what components are compatible and what ones are not. For example, will my Tempest high pressure fuel pump for my fuel injected angle-valve 360 work with ethanol-containing fuel? I have not been able to get a straight answer to that.
What about the seals in the Bendix RSA-5? FM-150?
I'm guessing the ProSeal in my tanks is OK? given that so many are using mogas now, it probably is. I put Viton o-rings in my drain fittings, so those are ok. The fuel selector looks like teflon, so I think it is ok. The o-ring on my API fuel filter? I could replace that with Viton. What about my boost pump? My floscan flow meter?
??????????????

I can probably manage the detonation margin with operational techniques if I have to, but I just don't know how to know what to do with the fuel system components.

I guess I could take the GAMI approach - start using ethanol-containing mogas and when something fails, blame it on poor maintenance or old age.
 
scsmith said:
I guess I could take the GAMI approach - start using ethanol-containing mogas and when something fails, blame it on poor maintenance or old age.
Click to expand...
Love it!

All kidding aside, very good points made about the plethora of components with unknown compatibility. Theoretically if 100% compatibility was achieved what about the water attraction issue with ethanol and the resulting corrosion all about the system? We all know that a lot of aircraft sit A LOT. Yes i know there are folks running it but when applied to a fleet the issues start rearing as the sample size increases and more scenarios are encountered.
 
scsmith said:
Because of insufficient detonation margin.
Click to expand...
Detonation margin can be altered. It is willingly sacrificed by the E-AB crowd with the application of high compression pistons, for example. It can likewise be increased with other techniques. The angle valve already features significantly improved cooling architecture thanks to the head cooling fin configuration and the piston oil jets. Careful attention to cowling and most significantly, an appropriate advance curve schedule for those pro detonation regimes will go a long way toward improving that margin. Will we ever make it all the way to certification standards for detonation margin with these changes? Who knows, but I’ll bet we can get close enough to operate our airplanes safely in the real world.
 
scsmith said:
The challenge of modifying the fuel system to work with ethanol-containing mogas is that there is not enough information about what components are compatible and what ones are not.
Click to expand...
There are a lot of people who use car gas without any issues. My 1940 Taylorcraft has sat with a tank and carb full of the toxic chemical concoction that passes for auto fuel in California for the last 9 years. No issues yet. My Rocket has passed a few gallons of the stuff too. Admittedly, the Rocket is essentially an automotive fuel system at heart, but pro seal does not seem to mind the stuff. Lots of other RV people on this forum flying with it too.

Yes, testing is going to be required, but we do have the administrative freedom to do that and there is very likely a solution we can find much faster than the widespread rollout of unleaded “avgas”.
 
Jjackh10 said:
Exactly, agree 100%. In my head I was thinking about the lower compression planes, many with stc's already. They still cant run ethanol though. It's frustrating leaded fuel has been vilified. Other than extra oil changes there's nothing wrong with it.
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TEL has one major thing going for it: octane boosting power. IMHO it is bad in almost every other way. It cakes up on valves and pistons and gums up rings. It prevents the use of o2 sensors. It requires compatible oils. On top of that it has some pretty severe health and environmental side effects.

ATC_RV8OR said:
We all know that a lot of aircraft sit A LOT. Yes i know there are folks running it but when applied to a fleet the issues start rearing as the sample size increases and more scenarios are encountered.
Click to expand...

Even if you fly regularly there are scenarios where you can be down for extended times. ADs, prop strikes, ground events, medical events, natural disasters.

My 182 will likely be down for 1-2 years because of Helene. The case shops are backed up for months. I know of at least one case that’s been at the shop for 9 months now and still no eta on when it will be done.
 
Toobuilder said:
There are a lot of people who use car gas without any issues. My 1940 Taylorcraft has sat with a tank and carb full of the toxic chemical concoction that passes for auto fuel in California for the last 9 years. No issues yet. My Rocket has passed a few gallons of the stuff too. Admittedly, the Rocket is essentially an automotive fuel system at heart, but pro seal does not seem to mind the stuff. Lots of other RV people on this forum flying with it too.

Yes, testing is going to be required, but we do have the administrative freedom to do that and there is very likely a solution we can find much faster than the widespread rollout of unleaded “avgas”.
Click to expand...
Sure. Carbureted engines, yes. That's why there is even an STC for using it. (although I don't know if that allows ethanol-containing motor fuel?). So just because you keep saying, "Lots of other RV folks on this forum flying with it too" adds essentially no useful information. Not many people with Bendix FI using car gas (Any?).
There is just no info/experience base on long-term effects of ethanol on components specific to Bendix FI. Boost pump? Engine-driven fuel pump? etc.
 
lr172 said:
Yeah it is really sad how the faa has dealt with this. Swift 94 is a viable solution for a very large chunk of the fleet. Force the fbos to offer it and put a $2 premium on 100ll. Majority of problem solved. Jusy follow the cigarette model. Raise the taxes high enough and nobody uses it anymore. We can use sharp minds like braly to develop knock sensing technology to more safely use these fuels.
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It's thinking like this that will kill this hobby.
 
echostar7 said:
It's thinking like this that will kill this hobby.
Click to expand...
Let me guess, you think it is better that they discontinue 100ll and shove g100ul down our throats? I’m sure that would be great for our hobby. Fly for an hour and clean brown goo off your plane for 4 hours, assuming there is still enough proseal left to keep fuel in the tank. Sounds like fun.

What is your idea for a fix? Or do you just knock other peoples ideas? It is one thing to debate the options and the issues. It is another to offer nothing and call other peoples ideas bad.
 
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lr172 said:
What is your idea for a fix?
Click to expand...

The gov would have to ban production and overhauls of the engines not compatible with the existing UL fuels (listed in Table 2 SB 1070).
Then wait 30 to 50 years for the existing fleet to to age out. They could subsidize the upgrades to accelerate the timeline slightly. Other than that there does not seem to be an easy fix :(
 
ve0kog said:
The gov would have to ban production and overhauls of the engines not compatible with the existing UL fuels (listed in Table 2 SB 1070).
Then wait 30 to 50 years for the existing fleet to to age out. They could subsidize the upgrades to accelerate the timeline slightly. Other than that there does not seem to be an easy fix :(
Click to expand...
According to swift, their fuel is approved for use in about two thirds of the fleet (lyc says any engine that is approved for mogas). Therefore it seems reasonable to push this fuel force ably into the market (e.g. govt $s for adding third fuel at airport) and develop incentives for the eligible aircraft to use it. (Subsidies on swift or taxes on 100ll - mogas is already cheap). This, in theory, cuts 2/3 of current lead emissions. Just one idea. We are now decades into the 100% drop in replacement effort and each passing year it seems less and less likely to bear fruit. I am sure politics is playing a role in this, but the reason is irrelevant. It just isn’t going anywhere and maybe its time for more creative ideas. Not that anyone is listening to us. I believe there is a large population, myself included , that would use swift or mogas if they had somewhere to buy it, not counting a pick up truck full of 5 gal cans. Non ethanol fuel is tough to find in my state (corn belt state with a strong lobby). Ironically it is available at every marina, as the boat industry had issues. Most tanks were aluminum and fuel in boats can sit for months. The tanks were open air vented and the ethanol absorbed water and settled at bottom of tank. After several years, the tanks would spring leaks.
 
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scsmith said:
Not many people with Bendix FI using car gas (Any?).
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Plenty. That said, the basic engine architecture can handle auto gas without complaint. Evan assuming you go the full Monty and go to EFI, the overall dollar expenditure is essentially a wash. And even if it costs a few bucks more initially, there is a solution available now, today.

For those that want a drop in, zero cost solution…. NOT GONNA HAPPEN. But we will be able to fly our RV type airplanes on the junk car gas available today if we are willing to make the needed changes.
 
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Toobuilder said:
Plenty. That said, the basic engine architecture can handle auto gas without complaint. Evan assuming you go the full Monty and go to EFI, the overall dollar expenditure is essentially a wash. And even if it costs a few bucks more initially, there is a solution available now, today.

For those that want a drop in, zero cost solution…. NOT GONNA HAPPEN. But we will be able to fly our RV type airplanes on the junk car gas available today if we are willing to make the needed changes.
Click to expand...
Exactly my point. There are simple, and generally inexpensive solutions that can be applied to experimental aircraft today, and I'd argue to almost the entire fleet if the FAA and other 3 letter agencies get out of the way. The car guys were forced to figure this out in the 1970s. Last I checked they are making a lot of power on regular unleaded mogas, winter and summer blends, from sea level up to the highest peaks. These fixes are "expensive" for certified aircraft because the processes that the FAA has created in the name of safety are holding back progress. For experimental, as @Toobuilder said, good solutions are available now, and will allow you to be a spectator to the 100LL fiasco, not a participant or victim.
 
bertschb said:
What would you recommend for the IO-390?
Click to expand...
If I were installing an IO-390 today, I would strongly consider this solution: http://www.sdsefi.com/

There may be others that are as good, but this seems to be the "B&C" of programmable ignitions and fuel injection.

If I am not wrong, the IO-390 has only slightly higher compression than my IO-360, which happily runs mogas from the BP pump, UL91, and of course 100LL. I seem to have plenty of detonation margin even when running mogas. I'd discuss with Ross or one of the other ignition vendors to get their views. With the magic of EFI and electronic ignition timing you can increase your detonation margin.

I'm sure that someone with fixed timing and traditional fuel injection or carbs will chime in to explain how they are also running mogas.

Don't forget the other half of the issue of mogas - making sure that all your rubber is compatible, fuel tank sealant is compatible, and you do all you can to avoid vapor lock.

The car guys avoid vapor lock by putting the fuel pumps in the fuel tank and pushing the fuel to the engine, instead of sucking the fuel from the fuel tank. We don't yet have this solution as far as I know, but I guess if someone were looking for another great business opportunity...
 
bertschb said:
Thanks for sharing this but 279 pages?? Wow
Click to expand...
ChatGPT is your friend who can summarize this in a second to see if it’s probably gonna be a waste of your time…

The EASA Report No. EASA.2008.C51 primarily evaluates the safety and environmental impact of biofuels but does not provide specific technological solutions for immediate implementation. Instead, it discusses key concerns such as:


• Fuel Composition & Blending: The effects of ethanol admixtures on aviation fuel performance, including volatility and energy content.


• Material Compatibility: Potential degradation of aircraft fuel system components due to biofuel use.


• Operational Considerations: Engine performance, maintenance, and safety concerns related to biofuel adoption.





While the report outlines challenges and research areas, it does not offer a definitive technological roadmap for biofuel integration in aviation. It serves more as a feasibility and risk assessment study rather than a practical implementation guide. If you’re looking for current technological advancements in aviation biofuels, more recent research and industry developments would be necessary.
 
lr172 said:
According to swift, their fuel is approved for use in about two thirds of the fleet (lyc says any engine that is approved for mogas). Therefore it seems reasonable to push this fuel force ably into the market (e.g. govt $s for adding third fuel at airport) and develop incentives for the eligible aircraft to use it. (Subsidies on swift or taxes on 100ll - mogas is already cheap). This, in theory, cuts 2/3 of current lead emissions.
Click to expand...
No it does NOT! The 20% of the fleet that needs 100 octane consumes 90% of the fuel.

If what you said were true, then the government would have enacted exactly what you suggest. It was considered. But the reality that a small fraction of the fleet consumes the vast majority of the fuel, AND has made the case that they need the available performance, is why this has been such a stiff problem.
 
Toobuilder said:
Plenty. That said, the basic engine architecture can handle auto gas without complaint. ...
Click to expand...
rv8ch said:
Exactly my point. There are simple, and generally inexpensive solutions that can be applied to experimental aircraft today, and I'd argue to almost the entire fleet if the FAA and other 3 letter agencies get out of the way. The car guys were forced to figure this out in the 1970s. Last I checked they are making a lot of power on regular unleaded mogas, winter and summer blends, from sea level up to the highest peaks. These fixes are "expensive" for certified aircraft because the processes that the FAA has created in the name of safety are holding back progress. For experimental, as @Toobuilder said, good solutions are available now, and will allow you to be a spectator to the 100LL fiasco, not a participant or victim.
Click to expand...
You guys keep saying that, but do you mean ethanol-free mogas, or do you mean auto fuel with 10% ethanol? Until someone shows me a reference that says that the engine-driven fuel pump on my Bendix-Lycoming is compatible with 10% ethanol auto fuel, I still disagree with your assertions.

Yes, we could go to SDS (or other), and deal with all-electric engines. Yes, that is manageable. Some of us are not eager to accept that risk level and need for diligent risk mitigation. Not to mention that a retrofit would require essentially re-wiring my airplane. Yes, with smart timing maps, there is sufficient detonation margin, even with a CR 8.9:1 IO-390. Not all EFI's offer enough flexibility/access to the timing map to achieve that.
 
lr172 said:
Let me guess, you think it is better that they discontinue 100ll and shove g100ul down our throats? I’m sure that would be great for our hobby. Fly for an hour and clean brown goo off your plane for 4 hours, assuming there is still enough proseal left to keep fuel in the tank. Sounds like fun.

What is your idea for a fix? Or do you just knock other peoples ideas? It is one thing to debate the options and the issues. It is another to offer nothing and call other peoples ideas bad.
Click to expand...
You misunderstood, I was objecting to arbitrarily taxing 100LL to force market adoption of 94UL. You are aware I'm assuming that not everyone can run on 94UL? I think it's pretty clear now that g100UL is not going to work for most of the fleet either.
 
scsmith said:
You guys keep saying that, but do you mean ethanol-free mogas, or do you mean auto fuel with 10% ethanol?
Click to expand...
I think Greg ran a lot of e gas through his 9 before he went SDS. There are also others of the forum who will speak up from time to time and then there is that formation team that runs 100% alcohol exclusively. I don’t have all the details memorized but I feel like there are enough e gas success stories out there that it’s not really a concern with the soft bits in pumps and servos. Concerning pumps - the diaphragm units hanging off the back of most Lycoming are rooted solidly in the automotive world. Many of them are stamped “AC Delco”, in fact. The automotive world has been running concentrations of alcohol up to 100% for more than half a century and they figured it out. A bit of alcohol in our fuel should not be an insurmountable technical problem IMHO.

Just throwing out some wildly broad suggestions:

- Make sure your servo and pump was built in this century - but test it for compatibility with the junk that passes for car gas today
- consider the benefits of a purge system so you can flush the hot fuel back to the tank on a hot restart
- be methodical to the point of extremism in reducing 90 degree fittings and other flow reducing features in the suction side of the fuel system.
- consider boost pumps that “push” from the lowest and closest location to the tank
- and MOST IMPORTANT: pull out a LOT of ignition timing advance at high power settings like takeoff.
 
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scsmith said:
No it does NOT! The 20% of the fleet that needs 100 octane consumes 90% of the fuel.

If what you said were true, then the government would have enacted exactly what you suggest. It was considered. But the reality that a small fraction of the fleet consumes the vast majority of the fuel, AND has made the case that they need the available performance, is why this has been such a stiff problem.
Click to expand...
Thanks, i did not know all of that.

What makes up that 20% and why are they disproportionately consuming so much fuel? Is it some type of engines used in commercial applications?
 
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echostar7 said:
You misunderstood, I was objecting to arbitrarily taxing 100LL to force market adoption of 94UL. You are aware I'm assuming that not everyone can run on 94UL? I think it's pretty clear now that g100UL is not going to work for most of the fleet either.
Click to expand...
Yes, am aware. But many people can run 94 octane and will not do so without incentive. I wasn’t suggesting anything that isn’t already coming. I would place a good wager that g100 would have been $2 more per gallon than 100ll within 2 years of significant adoption. Not sure we have seen the accounting on the gami involvement. My guess is he can charge whatever royalties he wants. If he follows the current aviation trend over the last few years, that is raise the price every quarter until people stop buying. Lyc prices have doubled in 5 years and there is still a 2 year wait to get one. Appear there is little hope the supply demand economics stop this anytime soon. Once 100ll is gone, what is to stop gami from doing the same? Certainly hope i am missing something here. All of this is new territory. We pretty much know how a multi billion $ petroleum company handles this. We have no idea how a 1/2 million $ company will handle it. If he sees this as his retirement windfall, watch out!
 
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lr172 said:
What makes up that 20% and why are they disproportionately consuming so much fuel?
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twins like the Golden Eagle. They burn something 30-40 gph and often fly commercially. the tanks are near 200 gallons. so they dwarf the rec guys like us and they cannot use 94UL it sounds like.
 
lr172 said:
Thanks, i did not know all of that.

What makes up that 20% and why are they disproportionately consuming so much fuel? Is it some type of engines used in commercial applications?
Click to expand...
Mostly medium-sized twins I think, used in courier service, medical transport ,etc. Most are either turbocharged or high compression, and need the performance to accomplish their missions. And they burn a lot of fuel. That statistic I quoted has been cited frequently by all the players in the replacement programs.
 
Toobuilder said:
- and MOST IMPORTANT: pull a LOT of ignition timing advance at high power settings like takeoff.
Click to expand...
Just to clarify - I'd have thought you want less advance during periods of high power. Or perhaps you mean "pull" as in "reduce" your timing advance, so go from 20 degrees BTC down to 15 degrees BTC?
 
rv8ch said:
Just to clarify - I'd have thought you want less advance during periods of high power. Or perhaps you mean "pull" as in "reduce" your timing advance, so go from 20 degrees BTC down to 15 degrees BTC?
Click to expand...
Yes, pull “out” a lot of timing. Reduce. Sorry for the confusion. OP edited for clarity.
 
I don’t have a dog in this fight but I do have auto gas experience in my Piper for over 600 hours. I experienced an engine out due to vapor lock in a 172 while using it. I have also experimented with it in my RV7 with 9.0:1 compression mixing 100ll and Mogas. But I am no longer doing it. If you decide to try it yourself a good educational resource is :
Auto fuel in aircraft
There is more to consider than compression ratio. Vapor pressure, Mogas availability on cross country trips, fuel injection problems. Winter blend vs summer blend issues, Possible valve seat recession, etc. Many of these can be mitigated but it isn’t as simple as just changing pistons.
Go in with your eyes wide open. The above link has a section on suggestions for homebuilt aircraft. I suggest studying the entire site in detail.

If I sound like I am against using it, I am not. Be assured there is risk involved, some of it human factor related.

Be safe out there.

Joe

P.s. there is a difference in the octane rating numbers between automotive and aviation gasoline. They do not directly correlate.
 
scsmith said:
The challenge of modifying the fuel system to work with ethanol-containing mogas is that there is not enough information about what components are compatible and what ones are not. For example, will my Tempest high pressure fuel pump for my fuel injected angle-valve 360 work with ethanol-containing fuel? I have not been able to get a straight answer to that.
What about the seals in the Bendix RSA-5? FM-150?
I'm guessing the ProSeal in my tanks is OK? given that so many are using mogas now, it probably is. I put Viton o-rings in my drain fittings, so those are ok. The fuel selector looks like teflon, so I think it is ok. The o-ring on my API fuel filter? I could replace that with Viton. What about my boost pump? My floscan flow meter?
??????????????

I can probably manage the detonation margin with operational techniques if I have to, but I just don't know how to know what to do with the fuel system components.

I guess I could take the GAMI approach - start using ethanol-containing mogas and when something fails, blame it on poor maintenance or old age.
Click to expand...
Steve, Airflow Performance uses Fluorosilicone [generic Viton] seals and gaskets, so at least their products are safe for pump gas laced with moderate amounts of ethanol.
 
scsmith said:
Sure. Carbureted engines, yes. That's why there is even an STC for using it. (although I don't know if that allows ethanol-containing motor fuel?). So just because you keep saying, "Lots of other RV folks on this forum flying with it too" adds essentially no useful information. Not many people with Bendix FI using car gas (Any?).
There is just no info/experience base on long-term effects of ethanol on components specific to Bendix FI. Boost pump? Engine-driven fuel pump? etc.
Click to expand...
Steve, I've spent several hours in the past speaking with Mr. Petersen [of STC fame] about this subject. The issue preventing an STC for most parallel valve fuel injected Lycomings is due to the lack of a fuel return system to the fuel tanks. This is also why FI Lycomings have the reputation of being hard to restart when hot. He told me that if the air-frame manufacturers would modify the fuel systems to include a return, then the fuel tanks act as a fuel cooler, preventing vapor lock. For us as experimental builders, that simply requires adding an Andair duplex fuel selector valve and some extra plumbing.
 
All o-rings swell a little when exposed to something they don't like, but I never considered the case shown in the video where the o-rings are not always fully captured. Yikes. I wonder how Viton™ (FMK) o-rings would fare in this test.

The other thing that's very different between 100LL and other fuels is the change over time with exposure to air, light, moisture, and other things commonly seen in a fuel system. 100LL seems to be very stable, either by accident of it's composition, or by design. Not sure which.

The blend proposed by G100UL is very similar to what they burned in WWII GAMI said, but a little bit of leaking or paint bubbling was not considered a big deal when you are at war, and the lifespan of the machine is measured in weeks. We want our aircraft to last for decades.

A "drop in" replacement for 100LL is looking more and more difficult the more we learn.
 
rv8ch said:
A "drop in" replacement for 100LL is looking more and more difficult the more we learn
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At this point I'm thinking it's never going to happen. The aviation community seems committed to stand and die on the hill of "100% drop-in replacement no modifications required because everything must be reverse compatible forever". Meanwhile the last remaining producer of the lead additive may well just say "peace out" and end production in the next few years: https://www.avweb.com/air-shows-eve...vgas-can-become-too-expensive-to-be-worth-it/

I'm grateful I'm in the experimental world and can do things like add extra gas tanks to tanker fuel, and build to be ethanol-tolerant so I can run premium from the corner gas station. Now I just have to actually test that capability...
 
rmartingt said:
At this point I'm thinking it's never going to happen. The aviation community seems committed to stand and die on the hill of "100% drop-in replacement no modifications required because everything must be reverse compatible forever". Meanwhile the last remaining producer of the lead additive may well just say "peace out" and end production in the next few years: https://www.avweb.com/air-shows-eve...vgas-can-become-too-expensive-to-be-worth-it/

I'm grateful I'm in the experimental world and can do things like add extra gas tanks to tanker fuel, and build to be ethanol-tolerant so I can run premium from the corner gas station. Now I just have to actually test that capability...
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I don't think the community wants to demand a drop-in replacement. I think the cost of modifications to the certified fleet is the problem, and would likely push GA further out of reach for most people. And that's not good for anyone, including the exp world. If production stops, and an affordable solution isn't found, I believe the smaller municipal airports we use will go away. Cert GA and even experimental planes will be stuck following airline routes, or operating from personal strips.
 
Jjackh10 said:
I don't think the community wants to demand a drop-in replacement. I think the cost of modifications to the certified fleet is the problem, and would likely push GA further out of reach for most people.
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I just want a fuel that has been tested through an agreed upon industry standard with data available to all. Then we know what to expect. Getting a new fuel, 100LL disappears, and if after a few years we start finding issues (that could have been found now with standard testing) in manufacturing, transporting, or operations we are all screwed. We should not have to rely on some guy on YouTube to do the testing.
 
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when we first had alcohol added to our car gasoline, we started to have engine problems because the car plumbing wasn't compatible with the alcohol fuel. Car manufacturers improved the car design, ignition and engine management software to detect the alcohol content, and things became normal. The main difference to the car companies and aircraft companies is that they build millions of cars per year. They can make changes without waiting for decades for the FAA approvals. So if we find issues with either the GAMI fuel or Swift Fuel, we may end up living with the problems with no recourse. Lycoming isn't going to change, it won't add automation to improve manufacturing right now.
 
chaskuss said:
He told me that if the air-frame manufacturers would modify the fuel systems to include a return, then the fuel tanks act as a fuel cooler, preventing vapor lock. For us as experimental builders, that simply requires adding an Andair duplex fuel selector valve and some extra plumbing.
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Not necessary to have additional selector complexity. I have plumbed return lines directly to a fitting on the left tank, which is easy to manage on full tanks...just use the left one first. Just like an early model E-series powered Bonanza. They run well on mogas. My O360 RV-6 ran thousands of hours on 87 10% ethanol mogas no problem. But you have to be cognizant of 1. vapor lock and 2. the potential for preignition (NOT detonation.). I set up a RV6 I used to fly to run on mogas and unfortunately no matter how much I coached the owner to watch for signs of preignition he ignored them which caused problems on two cylinders. I keep one of the burnt pistons on my desk in the shop as a reminder.
 
PhatRV said:
when we first had alcohol added to our car gasoline, we started to have engine problems because the car plumbing wasn't compatible with the alcohol fuel. Car manufacturers improved the car design, ignition and engine management software to detect the alcohol content, and things became normal. The main difference to the car companies and aircraft companies is that they build millions of cars per year. They can make changes without waiting for decades for the FAA approvals. So if we find issues with either the GAMI fuel or Swift Fuel, we may end up living with the problems with no recourse. Lycoming isn't going to change, it won't add automation to improve manufacturing right now.
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The main difference in our case is that WE are the airplane manufacturers…. The Lycoming part of the fuel system is a very small part of the overall airborne system - and they aren’t going to help with that. Many will argue that Van’s is the manufacturer/designer of your fuel system - but so many builders modify the stock system, that there’s no way you can hold Van’s responsible…and legally WE are the manufacturers of the airplane….
 
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