Another reason not to run G100UL…

[Tusayan]

@hindsight2020 my job is within a group doing engineering development of new design, geared reciprocating aero engines. Given the issues that exist in the real world, my own propeller driven plane won’t be equipped with a geared engine.

A few weeks ago I ran into one of our metallurgists sitting at a picnic table outside the office, staring at a damaged reduction gear in bright natural light as part of a customer funded sustaining engineering effort. A nice conversation followed, always enjoyable and happily not involving a reduction of my personal bank balance. The cost for each of these engines is BTW several times what my plane is worth. The resulting revenue indirectly pays my salary and bills, including amply covering those associated with my plane.

When considering my own expenses, I’m very happy with my carbureted low compression Lycoming that has and will still run on almost anything after 5 decades without disassembly. I’d prefer 80/87 AVGAS but 100LL is fine. It’s quality fuel, and would be even better for my purposes if the lead was removed from the fuel I’m buying and everything else was left the same.

 

[Skyrys62]

I would not be willing to swap bladders.

Maybe once they are aged out, but are approved ones even available?

 

[tspear]

@Tusayan

Rotax has run with reduction gears for decades and done very well. PSRUs are viable, you just have to do the engineering on them.
As you have implied, the labor to design and implement a PSRU is rather expensive.

Tim

 

[SebIp]

If it was up to the FAA, oil companies, and pilots, 100LL would be available forever.

But you have the Karens riled up and worried about their kids.

And add in that there is ONE company making TEL.

100LL could go away in a couple of years. And then where would we be??

Mogas for some, value proposition to make new engines based on automotive ones?

Who knows. Mine can use mogas which is a comfort.

 

[455 Bravo Uniform]

Maybe once they are aged out, but are approved ones even available?

No such thing as approved that I am aware of. The new fuel was supposed to be ok with the original designs of many planes.

 

[SoonerAviator]

@Tusayan

Rotax has run with reduction gears for decades and done very well. PSRUs are viable, you just have to do the engineering on them.
As you have implied, the labor to design and implement a PSRU is rather expensive.

Tim

The marine industry has been doing it for almost 3/4 century with inboard-outboards, in an arguably much harsher environment. Obviously not apples-to-apples since an outdrive on a boat weighs a ton, but the challenges of recips and reduction gearing aren't new science. It's being able to put that tech into a really light-weight package that poses most of the problem.

 

[Mikey52]

Any data on the octane rating of 100LL, without any lead in it? Is it equivalent to the 91 octane non ethanol MoGas? Would it stay as stable without the lead in it. Just curious?

 

[tspear]

Any data on the octane rating of 100LL, without any lead in it? Is it equivalent to the 91 octane non ethanol MoGas? Would it stay as stable without the lead in it. Just curious?

No. Mogas and Avgas use different methods to calculate octane. Swift 94UL is effectively 100LL without the TEL.
There are a lot of other differences between mogas and avgas. Mogas needs to be stable for 30 days or 60 days, I forget which. Avgas needs to be stable for 6 months. Avgas has much higher vapor pressure requirements...

Tim

 

[455 Bravo Uniform]

Let all who wanna run G100UL also get to opt in to Experimental if they wanted. That way they wouldn’t have to suffer the other cost consequences (oring, bladders, paint) and the baked-in costs of certified plane compliance. Give em an option, with all the good and bad that comes with it.

 

[Sierra_Hotel]

Let all who wanna run G100UL also get to opt in to Experimental if they wanted. That way they wouldn’t have to suffer the other cost consequences (oring, bladders, paint) and the baked-in costs of certified plane compliance. Give em an option, with all the good and bad that comes with it.

Yeah but that makes too much sense.

 

[flyingron]

Reduction gearing has been around in aircraft for over 75 years. My Navion came from the factory with the gopher35 engine in 1950. There ain't no free lunch. The efficiency and other improvements you get from the slower turning prop (the gearing was 120:77 if I remember) you lose with the fact that the gearbox was heavy.

 

[Pinecone]

IEspecially if it's in the interest to use a "better" fuel. My brain says you lose the better fuel argument when it requires work of that magnitude.

It will come down to, at some point, use a new fuel or park your plane for many people.

Whatever that fuel is, it will be better than no fuel at all.

 

[Kiddo's Driver]

...Avgas has much higher vapor pressure requirements...

Tim

And automotive Mogas formulation changes throughout the year. Higher Reed Vapor Pressure rating during the winter when it is cold, Lower when it is hot. Worst case that they make the Mogas STC process test for is winter fuel running at summer temperatures without causing vapor lock.
Back to my earlier comment, I would love to be able to be blessed by the FAA to run 50/50 mix of AvGas & mogas without having to do the STC testing. I know the engine can hack 100% mogas, but I'm a low wing and would probably have to add fuel pumps from the tanks to pass 100% mogas on the airframe.

-Jim

(Edited to correct that I had Higher & Lower backwards on RVP. Low RVP is good.)

 

[Dana]

The marine industry has been doing it for almost 3/4 century with inboard-outboards, in an arguably much harsher environment. Obviously not apples-to-apples since an outdrive on a boat weighs a ton, but the challenges of recips and reduction gearing aren't new science. It's being able to put that tech into a really light-weight package that poses most of the problem.

An aircraft reduction drive can be a much more difficult engineering task because of the inertia of the large heavy propeller which leads to torsional resonance issues. The smaller boat propeller, which much more damping due to water's viscosity (compared to air), is much susceptible to resonance.

 

[SoonerAviator]

An aircraft reduction drive can be a much more difficult engineering task because of the inertia of the large heavy propeller which leads to torsional resonance issues. The smaller boat propeller, which much more damping due to water's viscosity (compared to air), is much susceptible to resonance.

Sure, that has been an issue, as well as the diesel engines with stronger power pulses. Although aircraft don't require a neutral/reverse option, turboprops/beta notwithstanding.

 

[kyleb]

So I'm wondering something about octane... my IO-540-k15d has a compression ratio of 8.7:1 according to what I'm able to look up.

I know automotive engines with higher compression than that can run 87. Even automotive engines pushing 11:1 ratios can run on 91 octane. I know it's not a total apples to apples comparison but what gives? Is it a different octane scale, vastly different timing curves, the continual operation at high power?

A lot of it is cylinder volume vs flame front speed. Those high revving small cylinders in a bike can use very high compression because the cylinder volume is small. The flame front burns all the fuel in the cylinder quickly, which avoids the problem of compression, heat, and time breaking down the fuel molecules in the corners of the combustion chamber into something that detonates. We have BIG cylinders and low RPM. Meaning our engines are very detonation prone. That's why we need higher octane than higher revving engines with smaller combustion chambers.

Ever notice when an old technology (points ignition, fixed timing, carburetor) engine pings? Low RPM, high engine load. That's the state our aircraft engines live in all the time. Even those old technology engines (thinking of you, Dad's F-100) didn't ping once you wound them up just a little, regardless of load.

 

[kyleb]

An aircraft reduction drive can be a much more difficult engineering task because of the inertia of the large heavy propeller which leads to torsional resonance issues. The smaller boat propeller, which much more damping due to water's viscosity (compared to air), is much susceptible to resonance.

That and gyroscopic loads.

 

[AV8R_87]

An aircraft reduction drive can be a much more difficult engineering task because of the inertia of the large heavy propeller which leads to torsional resonance issues

I wonder why giubos are not a thing on props driven through reduction gearboxes.

 

[pfarber]

It is a question of unknown state of the fleet, along with the labor required to inspect and address each plane and part. Never said not solvable, just that it is not practical to solve in a short timeframe. The FAA should have set the stage to solve the TEL problem in 1970. Now, the ship has sailed, and owners (pilots to a lesser degree) are effed.

Tim

We just did theirs with ADS-B with the same level of teeth gnashing... and overall ADS-B has been wildly popular. we can't let aircraft live in the 1940s and 50s forever. These aircraft are old and out of date and simply need updating. The use of ultra low lead fuel is just another step in the evolution of these dinosaurs

If you don't want to go through the pain, then build or buy an experimental amateur built and be done with it. If you want to fly an old dinosaur then be prepared to make the necessary changes to keep it alive in the modern world.

 

[kyleb]

We just did theirs with ADS-B with the same level of teeth gnashing... and overall ADS-B has been wildly popular. we can't let aircraft live in the 1940s and 50s forever. These aircraft are old and out of date and simply need updating. The use of ultra low lead fuel is just another step in the evolution of these dinosaurs

If you don't want to go through the pain, then build or buy an experimental amateur built and be done with it. If you want to fly an old dinosaur then be prepared to make the necessary changes to keep it alive in the modern world.

ADSB was a very simple upgrade. Rip out one box, install another. Hook up an antenna or two and you're done. Even better, if it doesn't work properly, it is an inconvenience, not an existential threat to safety.

Implementing a replacement fuel is a whole 'nother level of difficulty unless it is truly a drop-in replacement. Experimental or not, the challenges are the same. If it eats seals, paint, sealant, bladders, and/or hoses, figuring that out and replacing or updating the impacted items can be a huge and expensive undertaking. For instance, if it eats fuel tank sealant and paint, now you have the problem of developing a sealant that is compatible, then retrofitting the fleet at thousands of dollars a tank plus downtime, plus paintwork. You're looking at 10-20K/airplane if there is a sealant that is compatible. On the engine side, if the fuel doesn't perform as well as 100LL, you're looking at derating engines via piston (compression) changes, timing changes, etc. De-rating engines means rewriting all of the performance charts and probably recertifying the airplanes. It is a nightmare.

 

[Bob Noel]

ADSB was a very simple upgrade. Rip out one box, install another. Hook up an antenna or two and you're done. .

not so simple if there wasn't a suitable GPS installed first.

 

[Bell206]

I would love to be able to be blessed by the FAA to run 50/50 mix of AvGas & mogas without having to do the STC testing.

You could. Put your aircraft under Experimental Exhibition and mix away. They might require your 1st 30-60 days under Exp R & D but this is how a number of possible ideas or upgrades are tested out before attempting any certification routes. If you want to follow a more structured route, prior to going Exp Exh, sit down with your DAR and work out a plan to include your anticipated results and possible goals like pursuing an approval method for your mix? And keep your A&P/IA in the loop from the beginning as you'll still need a yearly condition inspection plus if you ever want to go back to a Standard AWC.

 

[kyleb]

not so simple if there wasn't a suitable GPS installed first.

Mine came with an internal gps. It was simple.

 

[tspear]

not so simple if there wasn't a suitable GPS installed first.

Simple in comparison to potentially derating engines, swapping engines, or working through material compatibility of the fuel system.

Tim

 

[Randomskylane]

And how often? Twice a year I have to repaint the areas around my fillers and sumps? At what cost?

Sorry, I was joking.

 

[pfarber]

It is a question of unknown state of the fleet, along with the labor required to inspect and address each plane and part. Never said not solvable, just that it is not practical to solve in a short timeframe. The FAA should have set the stage to solve the TEL problem in 1970. Now, the ship has sailed, and owners (pilots to a lesser degree) are effed.

Tim

Cheap, easy, fast.

Pick 2.

 

[Kenny Phillips]

I wonder why giubos are not a thing on props driven through reduction gearboxes.

They are in some. There's always some way to absorb torsional vibration. It can be a shaft that allows twist, a coupling, or simply an overbuilt drive.
Most of the failures seen in experimentals seem to derive from a designer not taking into account how damaging torsional vibration can be over a long time period. Death by 1,000 tappy-taps.

 

[Salty]

I really wish the industry would invest in getting modern engine swap STCs to the market instead of wasting the money keeping 1930s tech running. I could give a rats patootey about the lead, but my way solves more problems with less effort.

 

[Half Fast]

I really wish the industry would invest in getting modern engine swap STCs instead of wasting the money keeping 1930s tech running. I could give a rats patootey about the lead, but my way solves more problems with less effort.

I hear ya, but when I think of how much cash I'm dumping into overhauling my O360, I'd kinda like to be able to use it for a while.

 

[TCABM]

I really wish the industry would invest in getting modern engine swap STCs to the market instead of wasting the money keeping 1930s tech running. I could give a rats patootey about the lead, but my way solves more problems with less effort.

Are you talking LS modern swap or are you talking Rotax modern for an O-470 swap? Or are you talking a mogas STC for all my friends kind of swap?

 

[Michael Luvara]

It would be really cool if someone who has access to G100UL and some old o-rings/bladders and painted parts to soak in it would do some tests and post the results. I would but I don't know where I'd get the former and I don't really have much in terms of the latter.

It would seem easy enough to just get some jars or something with G100UL and put these different parts in them for a period of time and document what happens.

For some reason, I didn't see @nauga's tag for me, so sorry for the delay.

The photo that started this thread is very familar to what I've seen on the west coast.

I have done a series of videos and testing on materials, based on issues we were seeing in California. You can find it here: Paint and Materials Testing

Michael

 

[Michael Luvara]

I might be wrong on the valve recession, could have sworn I heard something about it but maybe it was just speculation based on the 94UL issues.

As for the paint issue- is it possible simply using a different paint would fix it? If nothing else just adjusting our fueling procedures and being more sensitive to seeps/leaks might make things viable. I'm not enthusiastic about any of this and I'm content to keep using 100LL but should that turn out to not be possible, it's not a bad idea to have a plan B.

There is a recent interview with the Swift CEO where he addressed this. UND was running at Peak EGT. See this video

 

[StraightnLevel]

Are you talking LS modern swap or are you talking Rotax modern for an O-470 swap?

Which Rotax has a 250+ hp output?

I'm not seeing any that would be viable replacements for any IO-470 variant.

 

[Sierra_Hotel]

None, they're talking hypotheticals, a Rotax-like modern engine capable of replacing an O-470.

 

[Racerx]

There is a recent interview with the Swift CEO where he addressed this. UND was running at Peak EGT. See this video

Scott Perdue- "Didnt mean to **** you off"
Chris d'costa- "This is how I am"

Not a good look for swift.

 

[ragedracer1977]

I liked what DAcosta had to say so much, in the face of obvious misinformation and puppetry from Perdue, that I immediately bought the swift STC.

 

[schmookeeg]

I prefer the shark to the eel in this ridiculous drama. I have no use for a swift STC though. Yet.

 

[WDD]

CEO's can be great at running processes, but that doesn't mean they should be the company spokesman. I'd say that's amplified if the personality/industry is engineering. Engineers already start with a "people skills" challenge.

If I had to bet $1 on which unleaded we'd end up with, I'd put it on Swift 100R. Then again, might change next month.

 

[Racerx]

CEO's can be great at running processes, but that doesn't mean they should be the company spokesman. I'd say that's amplified if the personality/industry is engineering. Engineers already start with a "people skills" challenge.

If I had to bet $1 on which unleaded we'd end up with, I'd put it on Swift 100R. Then again, might change next month.

The problem with 100r is it won't be able run the engines that require 100ll without derating.

 

[Half Fast]

Engineers already start with a "people skills" challenge.

I beg your pardon, but I have excellent people skills. It's my idiot skills that aren't so hot.