Warbird Information Exchange

To those Wixers that have deep knowledge about engines…
This past week-end, I meet some french warbird operators and the discussion veered toward 100LL AvGas soon to be phased out. So came the question about how our old engines, radials and V12, would fare on the long term with the new suposedly high octane fuels like GAMI G100UL or Swift Fuel 100R ?
People mentionned that an A-26 that flew with one engine fed with G100UL, but other added that one flight, or even 100 hours of test, can not be the gold rule to figure out the internal effects - if there are some – on an engine. It was also mentionned that it took the North Dakota University a couple thousands hours to "see" damages on the engines of its fleet and go back to 100LL from UL94 after citing an issue with "exhaust valve recession".
So, engine gurus, what is your take ?

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Paris, FRANCE

For reference, the A-26 was 44-35643 and the effort is covered in a short blog post on G100UL.com.

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Tri-State Warbird Museum Collections Manager & Museum Attendant

Warbird Philosophy Webmaster

Nobody wants to speculate on this. You know what happens to participants on this forum when they speculate.

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Dean Hemphill, K5DH
Port Charlotte, Florida

Speculate on what?

-The science of the fuel and any possible effects on the engines. I'm neither a chemist or engineer, so I won't guess. But there may be people here who are, and it would be interesting to get their opinions.

-Or speculate that even if there are tech issues involved with the use of the fuel, its adoption is a done deal so operators will have to learn to live with it.

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Remember the vets, the wonderful planes they flew and their sacrifices for a future many of them did not live to see.
Note political free signature.
I figure if you wanted my opinion on items unrelated to this forum, you'd ask for it.

The whole challenge is that they are trying to create a drop-in unleaded replacement for 100LL. If they manage that... we may not see any problems. As to how that would work out for large radials and V12s and such... I don't think anyone really knows. My crystal ball is as good as yours. From a more techy perspective, we may need to reduce the max TO and continuous power settings a bit, but many warbirds are flown below their full fighting weight and at lower power settings already.

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A Little VC10derness - A Tribute to the Vickers VC10 - www.VC10.net

I am by no means an expert, but, I do mess around with some cars stuff. And the way around no lead fuel is conversion to hardened valves seats.

Hopefully they have been doing that for a while, but if not, then I am sure it is coming. Lack of lead will lead to valves eating up the seats and possible valve guide damage.

Old car owners use lead additives to their gas if they're smart. Why can't wabird owners do the same?
Sure, I know it's a matter of volume for an airplane, but it's not impossible, especially if you have your own truck or tank to full from.

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Life member, 91st BG Memorial Association
Owner, 1944 Willys MB #366014
Former REMF (US Army, O3)

That might be a solution, but the challenge is going to be:
1. Getting the mix right.
2. Right now an aeroplane type will be certified using a specified type of fuel. Mixing your own fuel may invalidate that. Even for types on an experimental licence you will have restrictions on what you can put in the tank.
Just an example, a T-6 is certified on TC A-2-575 and the TCDS lists:

So anything that is not 'aviation gasoline' is not allowed to be used. If we want to start using additives, we need to get that mix certified as 'aviation gasoline'.

We will then run into another issue: the reason to do away with 100LL is that we don't want the lead to turn up in the emissions from the engine(s). If we add that lead back through additives, we will still have lead in the emissions. I don't know if that will satisfy the regulators, or more importantly, those lobbying for getting rid of 100LL.

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A Little VC10derness - A Tribute to the Vickers VC10 - www.VC10.net

It's important to note that both SWIFT100 and G100UL were run extensively by several big bore engine companies, including a 100 hour test on an R3350 that found no significant issues with use of unleaded fuels in the engine and, in fact, allowed for running at full 115/130 power settings without knocking or overheating, something not possible with 100LL.

Also, it's important to note that *most* large bore engines (both the radials and V's) have hardened valve seats already. In fact, if I remember the reports correctly, only Continental doesn't use hardened valve seats on their current engines and they're the only ones who've had any issues running unleaded fuel, and even then, the manufacturer's not 100% sure the seats were actually the problem in the issues.

Finally, remember that the issue with valve seat recession in cars is because engineers "used" the lead as a lubricant as a way to use lesser metal alloys and non-hardened seats for cost reasons since most of the time the engines weren't running at a high enough power setting to cause knock anyway. Aero engines, because they run at high power most of their lives, can't use TEL as a lubricant for that reason and weren't designed so poorly as car engines where cost was a major driving factor.

Going from AVGAS to Unleaded there are issues with fuel lines and seals, and the valves. They will have to replaced the lines and seals and then use hardened valves and seats. Apart from that it is ok.

Lead also reduces detonation, which is not something you want in an aero engine. Ever.
I believe this is one of the hurdles they are trying to clear with the unleaded fuel.

John Deakin had this to say about TEL: https://www.avweb.com/features/pelicans ... e-hogwash/
The column is quite old by now, so it is interesting to see how we have fared since he penned this. This 2020 article also includes some of GAMI's achievements: https://gami.com/future/_export_sites_k ... 6-2935.pdf
GAMI is able to offer their PRISM system, but they have also developed G100UL fuel that is on the market these days. John Deakin (may he rest in peace) was a huge fan of them, ran workshops with them, but I think that even without John rooting for them, this company has done a lot to push engine technology into the 21st century.
(This message has not been sponsored in any way and I have no direct experience with this company. I have enjoyed John's columns for many years though and have learned a thing or two from them.)

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A Little VC10derness - A Tribute to the Vickers VC10 - www.VC10.net

It'll work as long as the new stuff isn't corrosive or detrimental in chemical ways.

I have a P-40 manual that has two sets of power charts, one for the 100/130 in the operational theaters, and one for 90-octane used in the training environment in the USA.

You simply don't push the throttle up as high -- but in modern use, we almost never go near the max power setting anyway.

Dave

Lack of lead does not affect fuel lines and seals, ethanol in the fuel does, and that‘s another story.

Also, as I said, most of the large-bore engines already have hardened valves and seats due to the operating pressures. This is a red herring that keeps getting thrown up with no one actually reading the specs of these engines. Almost, if not all, of Lycoming's engines have hardened valves and seats.