OT leaded aviation fuel

[J Tiers]

From ten years ago.....

OK, when they were newer. Sure.

The assertions I had seen were newer than that, possibly a couple years ago but I cannot turn them up with searches. The link was all I found that addressed the issue in any reasonable way.

Do you have any newer info either way?

[tom_d]

Apparently those Rotax engines are not all trouble free..... I saw some info on problems specific to them, which I need to find again. Just an example (perhaps) of another reason why engines for aircraft do not have radical new designs very often, too many new variables and unknowns.

You really do not want a lot of variables and unknowns when you are flying over territory which you do not want to have to try to land on (and get it right first try).

The 737 MAX was "certified" in its old form with the questionable MCAS behavior..... Something to remember with regard to "certified", even though "certification" is a necessary requirement. In that case, the "certified" version may not have had the exact same behavior of the shipped version with "minor and inconsequential" changes. It's those things that "won't screw up anything" which often bite you.

Not everyone agrees on the problems, and there is some evidence that they are not all really "Rotax" problems... for instance the following:

https://midwestflyer.com/?p=3412

Rotax engines are susceptible to problems just as any mechanical device. Overall they have a reputation for reliability when maintained and operated properly. This is true for both the four stroke and the two stroke models. Knowing that proper operation and maintenance procedures are in place, I have no worry about being held aloft with any of them. I've seen them both run well on 100LL. Many of the 4 stroke model operators prefer to use the highest octane ethanol free car gas locally available instead of using 100LL because they are running fully synthetic oil in the crankcase. Leaded fuel is not compatible with fully synthetic oil.

[A.K. Boomer]

Tom D just wanted to say you have incredible knowledge on aircraft engine details, and it's great to read this kind of insight on the board - we got experts in every walk and your one of them so kudos - great to learn, not my particular field but know enough about it to recognize someone who does...

[Tobias-B]

I use 100ll as a race fuel. It's incredibly stable compared to ethocrap you get out of the pump, and it's consistent. And it stores well.

As to how much lead is in it- I also use a wideband oxygen sensor, and although leaded fuel is supposed to kill them,
mine typically lasts hundreds of gallons of fuel (years, in race season terms.) I've replaced only one due to failure-
and that one had a bad heater, most likely from me smashing it into a curb.
I HAVE noticed that the 'lead' builds up a bit on exhaust valve stems, but not enough to matter.

As to aircraft- since buying a new light aircraft hasn't really been possible since 1986, it's not so surprising that the FAA
has kept the older fuel around, too. Fuel chemistry's a science, and more than one car manufacturer has
gotten it wrong (BMW's Nikasil, for example) so the FAA has some basis for their conservatism.

As to older engines running on unleaded- most can, and it's not difficult to update those that can't IF you're rebuilding.

I personally use 0% ethanol fuel in everything I don't use on the road- it's so much easier on the small
carbs it's not funny. The alcohol racers know not to leave alcohol in their cars, I figure I can learn something from that.

t
low horsepower

[J Tiers]

Rotax engines are susceptible to problems just as any mechanical device. Overall they have a reputation for reliability when maintained and operated properly. This is true for both the four stroke and the two stroke models. Knowing that proper operation and maintenance procedures are in place, I have no worry about being held aloft with any of them. I've seen them both run well on 100LL. Many of the 4 stroke model operators prefer to use the highest octane ethanol free car gas locally available instead of using 100LL because they are running fully synthetic oil in the crankcase. Leaded fuel is not compatible with fully synthetic oil.

Well then the issues must be due to not paying attention to what they want for maintenance. Would not be the first case of that.... blaming the engine for not running well when neglected. Gee, who'd a thunk it?

I assume they are certified for either fuel.

[strokersix]

Leaded fuel is not compatible with fully synthetic oil.

Please explain this. Why?

[Optics Curmudgeon]

OK, when they were newer. Sure.

The assertions I had seen were newer than that, possibly a couple years ago but I cannot turn them up with searches. The link was all I found that addressed the issue in any reasonable way.

Do you have any newer info either way?

The majority of problems have been in homebuilts, where the builder has latitude to use whatever prop, engine mount, cooling baffles, exhaust, etc. Some are good at this, most miss some critical factor. The inspectors that issue airworthiness certificates can't catch everything but eventually build up a database of stuff to look for. Rotax installations in certified aircraft have a lot fewer problems than the homebuilts. We had a fatal crash here a few years ago caused by a plastic fuel line leaking on a homebuilt, causing an in flight fire. The same line had leaked earlier, on the ground, but was simply replaced with the same material. Learning curve? The engine wasn't to blame, but went into the database as associated with the accident anyway.

[Optics Curmudgeon]

As to aircraft- since buying a new light aircraft hasn't really been possible since 1986, it's not so surprising that the FAA
has kept the older fuel around, too. Fuel chemistry's a science, and more than one car manufacturer has
gotten it wrong (BMW's Nikasil, for example) so the FAA has some basis for their conservatism.

You haven't shopped for a new single engine piston GA aircraft lately, I assume. There are plenty to choose from, just bring plenty of money.

[Optics Curmudgeon]

Here's an interesting and thorough study from OZ, from 2016: https://www.atsb.gov.au/media/576986...nal-report.pdf.

[Willy]

Please explain this. Why?

Fully synthetic piston engine aero oils do not exist to my knowledge due to the oil's inability to absorb the inherent lead combustion byproducts found in engines that use leaded fuel.
This can lead to lead deposits that are very prone to form in the piston's ring land area causing piton rings to stick.

Will be glad to see when lead is removed from avgas. It creates more issues than it solves. The FAA is however slow to to change.

I wonder what the trends are in other countries? I don't believe many other countries are still using leaded fuels in general aviation are they?

[strokersix]

Thanks. So is it something inherent to synthetic oils or do aero oils have some additive to absorb lead?

[tom_d]

Please explain this. Why?

Full synthetic oil is an excellent lubricant with a proven track record. Well worth the added expense if you want to use it in your automobile that uses unleaded fuel. While synthetics are an excellent lubricant they do not act as a solvent. Solvent, or dissolving, qualities are needed to handle the slow buildup of impurities in the oil. Some oils use dispersant additives to handle impurities from the combustion process that slip past the rings and accumulate in the crankcase. These additives alone are not able to handle lead byproducts that will accumulate in the oil. A regular mineral oil's solvent characteristics are required to handle the lead. Synthetic oil has been tried in engines burning leaded fuel and were shown to work well, initially. Over time, though, lead deposits will build up around the piston rings sticking them into place. Not good to see your engine cooked after only a few hundred hours of use.

[tom_d]

I use 100ll as a race fuel. It's incredibly stable compared to ethocrap you get out of the pump, and it's consistent. And it stores well.

As to how much lead is in it- I also use a wideband oxygen sensor, and although leaded fuel is supposed to kill them,
mine typically lasts hundreds of gallons of fuel (years, in race season terms.) I've replaced only one due to failure-
and that one had a bad heater, most likely from me smashing it into a curb.
I HAVE noticed that the 'lead' builds up a bit on exhaust valve stems, but not enough to matter.

As to aircraft- since buying a new light aircraft hasn't really been possible since 1986, it's not so surprising that the FAA
has kept the older fuel around, too. Fuel chemistry's a science, and more than one car manufacturer has
gotten it wrong (BMW's Nikasil, for example) so the FAA has some basis for their conservatism.

As to older engines running on unleaded- most can, and it's not difficult to update those that can't IF you're rebuilding.

I personally use 0% ethanol fuel in everything I don't use on the road- it's so much easier on the small
carbs it's not funny. The alcohol racers know not to leave alcohol in their cars, I figure I can learn something from that.

t
low horsepower

Yes. Incredibly stable. Just remember when you store it to keep it in a tight container. It's not going to turn rancid but it will evaporate if the container is vented in any way. Helps to keep it in a dark place too, so the temperature is more stable. That avoids high temperature pressure build up in the container, and condensation from temperature swings.

I can't speak to experience with oxygen sensors, but as to lead quantity in the fuel the last batch I purchased tested out at 1.73 g/gallon.

While most aircraft manufacturers gave in to product liability law suits back in '86, there was legislation passed to ease that burden. As an example, Cessna went back into production in the mid 90s and reintroduced their more popular 4 seat models. Production is far short of their peak years in the early 70s, but you can still buy a new airplane.......if you can afford it.