Unleaded Avgas

[dtw_rv6]

Originally Posted by roadrunner20

The last time I checked, they offer Swift fuel in Sebring Florida, KSEF, at the same price as 100LL.
No incentive for me to try it.

The incentive for me is the reduced valve guide wear and plug fouling. As a bonus, Swift fuel has a higher energy density than 100LL.

Don

[TXFlyGuy]

Originally Posted by dtw_rv6

The incentive for me is the reduced valve guide wear and plug fouling. As a bonus, Swift fuel has a higher energy density than 100LL.

Don

Do they not claim better specific fuel consumption?

[tspear]

Here is where I got the numbers:

AOPA webinar presentation on PAFI when established. A fair number of people asked about running autogas and 91UL. AOPA replaied that 80% of avgas is consumed by planes less then twenty years old. The planes by far run turbo or 8.5 or higher compression on engines that are maxed for HP. (Think of a new SR22 or Mooney, the engine is making 300+HP on a case originally designed for 260HP). The detonation margins are just not there to lower the octane.

FAA FAST day, PAFI was one of the topics. FAA claimed over 60% of the fuel was used by planes less then ten years old. Cirrus rep there backed the claim up; based on service records planes less then ten years averaged over 150 hours a year, from ten to twenty years Cirrus was seeing a decline down 50 hours a year. FAA also stated 8.5 or higher in summer months you have detonation problems for higher output engines. I believe the test case is rather brutal, something like 115 degrees at sea level. Basically think Death Valley or Houston in August. Again, this was always in reference to more modern planes.

I have not kept up with PAFI, or the 100LL debate, so I have no idea if there is newer/better data available; this all dates back to 2013 or so when I was paying close attention. It did not seem like they were making much if any progress so I stopped paying attention.

Tim

[roadrunner20]

Originally Posted by dtw_rv6

The incentive for me is the reduced valve guide wear and plug fouling. As a bonus, Swift fuel has a higher energy density than 100LL.

Don

Still unproven.
Once it is, I too will have the incentive to make the switch.

[rv7charlie]

Can't speak to Swift fuel, but with over a decade of experience, mogas certainly makes a huge difference in plug fouling, an the oil stays cleaner, too. Don't know if it actually reduces valve guide wear, but I'm at least hopeful that it will reduce valve sticking.

[Bugsy]

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We have swift 94UL at a couple airfields in Wisconsin. It is 75 cents cheaper than 100LL and the engine runs great on it. I usually just just fill Up
Mixing with whatever 100ll is in the tank but have run complete tank fills.

[paul330]

Well, dare I say, the "incentive" is to not push more lead into the atmosphere. I know it's not much in the big scheme of things and it's not something that keeps me awake at night but if an alternative is available I, for one, will use it.

Europe, of course, is ahead on this with UL91 and 91/96UL becoming more widely available. As far as I know, though, there is nothing on the horizon to replace 100LL. Africa, sadly, is still behind so only 100LL is available. MOGAS is a bit "iffy" given the high temperatures and, in any case, has just started to have ethanol added.

Given the VANS types, nothing more than 180hp is really necessary (or 260hp for the -10). If you do want more, the Aerosport IO375 gives 195hp with 7.8:1 pistons. That just leaves the -14 which, I suspect, would run quite happily with an IO375 up the front.

I realise that there are still legacy airframes that need consideration but I suspect many of those could convert to 8.5:1 pistons without a huge performance penalty (as has been alluded to above).

[rvsxer]

Here is what Lycoming says about fuels (at least for now): https://www.lycoming.com/sites/defau...%20Fuels_0.pdf
It looks like most of the standard-compression engines that specified 100 octane in the TCDS can use 94 and even 91UL avgas.

There is a note that Lycoming requires the oil additive LW-16702, or an oil that blends it in such as Aeroshell 15w50, if you use unleaded aviation fuel.

[Carl Froehlich]

Originally Posted by Bugsy

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We have swift 94UL at a couple airfields in Wisconsin. It is 75 cents cheaper than 100LL and the engine runs great on it. I usually just just fill Up
Mixing with whatever 100ll is in the tank but have run complete tank fills.

I wish I could get 94UL! This fuel is simply 100LL without the lead, so all the costs of special blending, segregated transport and storage are eliminated. My IO-360 and IO-540 are certified by Lycoming to run on it.

I've written to both the EAA and AOPA to promote this fuel. I get back the same noise on most fuel is burned by those needing 100LL so they only endorse a drop in replacement. What they don't discuss is how much this 100UL novelty fuel will cost.

I offered to them that if they promote some FBOs to carry the 94UL fuel, the market will decide. All those people wanting ~$10/gal 100UL might become a quickly evaporating pool as most will look again at engines that burn 94UL.

Carl

[rv7charlie]

Carl's post raises an interesting point. The fact that turbo'd and other high performance (typically business use) aircraft consume 60-80% of the avgas, means that they are timing out their engines a lot quicker, too. If they were given the option to use fuel that was even 5% cheaper, how long would it take for the vast majority to convert to lower octane engines at overhaul?