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Approval of specific airframes and engines through STCs (Supplementary Type Certificates) is slightly misleading. In the same way, regular unleaded gasoline is

Approval of specific airframes and engines through STCs (Supplementary Type Certificates) is slightly misleading. In the same way, regular unleaded gasoline is also approved through STCs for many airframes and engines. This isn’t the silver 1:1 bullet that replaces 100LL tomorrow. Nevertheless, I’m all for the 100LL alternatives efforts. If I was buying an aircraft, however, I would be more interested in a Jet-A burning piston (basically diesel). Unfortunately that market is currently limited to Diamond aircraft, which are fantastic if not for their tight grip on their service network.

jacobmarble 5y ago
I looked into using a diesel engine in an experimental aircraft (US/FAA definition). Unleaded car engines are fairly common in these planes. It turns out that Jet-A isn't necessarily good for a piston diesel engine, due to lubricity and cetane number. After enough reading, I decided to stick with unleaded/100LL until the day I can afford a proper turboprop. https://generalaviationnews.com/2011/03/17/jet-a-versus-diesel-fuel/ https://generalaviationnews.com/2011/03/17/jet-a-versus-dies... https://www.thedieselstop.com/threads/jet-a-vs-diesel.62296/ https://www.thedieselstop.com/threads/jet-a-vs-diesel.62296/ Having typed all this, when I was in Afghanistan with the US Army, the tactical trucks with diesel engines all ran on the same Jet-A that the aircraft used. I assume there was something different about that fuel, or the engines in those trucks.
- throwawayboise 5y ago
  All diesel fuels are lower lubricity than they used to be (due to changes for modern low-emissions diesel engines). If you have an older diesel engine, you can use additives to restore lubricity, but I don't know if they are approved for use in Jet/A for a piston diesel aircraft.
- wbl 5y ago
  Jet-A is Jet-A. It's the engines: the Army would like to avoid having to schlep around two kinds of fuel that can get confused to disastrous results.
  - jacobmarble 5y ago
    Yes, obviously. Safer to drive a diesel truck on Jet-A than a Chinook on diesel.
  - sokoloff 5y ago
    The Army is almost surely using JP-8, which is similar but not identical to Jet-A.
- selectodude 5y ago
  >I assume there was something different about that fuel, or the engines in those trucks. Nope, it's just that the operational lifespan of those trucks isn't long enough for the Jet-A to really matter. It's only a major issue for the fuel pump, anyway. Those can always be replaced.
  - gnopgnip 5y ago
    Yep, most up armored Humvee or MRAPs will last less than 10k miles.
briandear 5y ago
Diamond’s are fine unless you need an airplane equivalent to a Cessna T206 or a 421. Diamonds, are really competing with Cirrus or the Cessna 172. As someone flying a 310 horsepower turbocharged 206, using an unleaded AvGas is a scary proposition. The only way to operate these turbo engines on current unleaded technology fuels would be to significantly reduce the boost pressure of the turbo and massively de-rate the engines. Flying heavy or out of hot or high airports would be significantly more dangerous. On normally aspirated 172s with a 160 or 180 horsepower engine, it would be less of a big deal. On a turbo-high performance engine, getting the performance out of the fuel is something not likely (hence the STC only for 172 lycomings.) Detonation would be the main risk or you’d have to use significantly less power which defeats the purpose. There are already mogas STCs. Until those fuels work in high performance engines, this isn’t really a groundbreaking thing. And just a point of fact, just because lead is “scary,” the actual environmental impact of leaded AvGas is trivial — despite the flawed “studies” put forth by the anti-airport lobby. If we want to improve the environment, I am all for it, but targeting AvGas is like trying to swat a fly circling a dead elephant. One Chinese factory spits out enough toxins in a day than the entire AvGas fleet does in a year. That’s not to say we shouldn’t work for better and cleaner airplane fuels, but in terms of environmental impact, this isn’t doing much. Resources would probably be better spent on lead and asbestos remediation in old, low income housing — or in the water supply. Kids aren’t getting sick from AvGas exhaust.
- base698 5y ago
  How much are your annuals?
- wffurr 5y ago
  >> The EPA's own studies have shown that to prevent a measurable decrease in IQ for children deemed most vulnerable, the standard needs to be set much lower, to 0.02 µg/m3. The EPA identified avgas as one of the most "significant sources of lead". Atmospheric lead is pretty dangerous, more so than encapsulated lead paint inside a wall.
  - lazide 5y ago
    That’s an incredibly misleading quote - do you have anything that can correlate atmospheric lead concentrations at ground level with flight hours or take/offs and landings somewhere?
sidewndr46 5y ago
Given the heavy handed way that lead was removed from fuel for passenger vehicles, I'm still perplexed that a tiny lobby has managed to keep it around basically indefinitely. If I were to build an aerial vehicle that sprayed a toxic substance everywhere it went, the environmental groups would basically go nuts. But somehow because it is in a plane, nothing ever really happens about it. The logical thing to do with 100LL is to ban it, like was done with passenger fuels. Existing planes serving a public good (basically just bush planes at this point) can continue to operate on it indefinitely. No sales of new planes equipped with engines that operate on 100LL would be allowed either.
- jdhn 5y ago
  I'm willing to bet that the amount of lead that's put out by aircraft in a year pales in comparison to what was put out by cars, and as a result going after lead emissions from cars was deemed to be the best course of action by the EPA. Also, it's worth noting that leaded gasoline didn't go away overnight. It was still sold for awhile even after the EPA said that you couldn't make cars that ran on leaded gas.
- pc86 5y ago
  Can you not see how passenger vehicles, which are overwhelmingly for personal use, is a different category with a different economic impact than an entire class of public transportation?
  - lmm 5y ago
    Gasoline-engined planes are overwhelmingly for personal use.
GekkePrutser 5y ago
I've seen 172 conversions with diesel. In fact that young guy that flew around the world in this 172 last week used one.

jacobmarble 5y ago

I looked into using a diesel engine in an experimental aircraft (US/FAA definition). Unleaded car engines are fairly common in these planes. It turns out that Jet-A isn't necessarily good for a piston diesel engine, due to lubricity and cetane number. After enough reading, I decided to stick with unleaded/100LL until the day I can afford a proper turboprop. https://generalaviationnews.com/2011/03/17/jet-a-versus-diesel-fuel/ https://generalaviationnews.com/2011/03/17/jet-a-versus-dies... https://www.thedieselstop.com/threads/jet-a-vs-diesel.62296/ https://www.thedieselstop.com/threads/jet-a-vs-diesel.62296/ Having typed all this, when I was in Afghanistan with the US Army, the tactical trucks with diesel engines all ran on the same Jet-A that the aircraft used. I assume there was something different about that fuel, or the engines in those trucks.

throwawayboise 5y ago
All diesel fuels are lower lubricity than they used to be (due to changes for modern low-emissions diesel engines). If you have an older diesel engine, you can use additives to restore lubricity, but I don't know if they are approved for use in Jet/A for a piston diesel aircraft.
wbl 5y ago
Jet-A is Jet-A. It's the engines: the Army would like to avoid having to schlep around two kinds of fuel that can get confused to disastrous results.
- jacobmarble 5y ago
  Yes, obviously. Safer to drive a diesel truck on Jet-A than a Chinook on diesel.
- sokoloff 5y ago
  The Army is almost surely using JP-8, which is similar but not identical to Jet-A.
selectodude 5y ago
>I assume there was something different about that fuel, or the engines in those trucks. Nope, it's just that the operational lifespan of those trucks isn't long enough for the Jet-A to really matter. It's only a major issue for the fuel pump, anyway. Those can always be replaced.
- gnopgnip 5y ago
  Yep, most up armored Humvee or MRAPs will last less than 10k miles.

briandear 5y ago

Diamond’s are fine unless you need an airplane equivalent to a Cessna T206 or a 421. Diamonds, are really competing with Cirrus or the Cessna 172. As someone flying a 310 horsepower turbocharged 206, using an unleaded AvGas is a scary proposition. The only way to operate these turbo engines on current unleaded technology fuels would be to significantly reduce the boost pressure of the turbo and massively de-rate the engines. Flying heavy or out of hot or high airports would be significantly more dangerous. On normally aspirated 172s with a 160 or 180 horsepower engine, it would be less of a big deal. On a turbo-high performance engine, getting the performance out of the fuel is something not likely (hence the STC only for 172 lycomings.) Detonation would be the main risk or you’d have to use significantly less power which defeats the purpose. There are already mogas STCs. Until those fuels work in high performance engines, this isn’t really a groundbreaking thing. And just a point of fact, just because lead is “scary,” the actual environmental impact of leaded AvGas is trivial — despite the flawed “studies” put forth by the anti-airport lobby. If we want to improve the environment, I am all for it, but targeting AvGas is like trying to swat a fly circling a dead elephant. One Chinese factory spits out enough toxins in a day than the entire AvGas fleet does in a year. That’s not to say we shouldn’t work for better and cleaner airplane fuels, but in terms of environmental impact, this isn’t doing much. Resources would probably be better spent on lead and asbestos remediation in old, low income housing — or in the water supply. Kids aren’t getting sick from AvGas exhaust.

base698 5y ago
How much are your annuals?
wffurr 5y ago
>> The EPA's own studies have shown that to prevent a measurable decrease in IQ for children deemed most vulnerable, the standard needs to be set much lower, to 0.02 µg/m3. The EPA identified avgas as one of the most "significant sources of lead". Atmospheric lead is pretty dangerous, more so than encapsulated lead paint inside a wall.
- lazide 5y ago
  That’s an incredibly misleading quote - do you have anything that can correlate atmospheric lead concentrations at ground level with flight hours or take/offs and landings somewhere?

sidewndr46 5y ago

Given the heavy handed way that lead was removed from fuel for passenger vehicles, I'm still perplexed that a tiny lobby has managed to keep it around basically indefinitely. If I were to build an aerial vehicle that sprayed a toxic substance everywhere it went, the environmental groups would basically go nuts. But somehow because it is in a plane, nothing ever really happens about it. The logical thing to do with 100LL is to ban it, like was done with passenger fuels. Existing planes serving a public good (basically just bush planes at this point) can continue to operate on it indefinitely. No sales of new planes equipped with engines that operate on 100LL would be allowed either.

jdhn 5y ago
I'm willing to bet that the amount of lead that's put out by aircraft in a year pales in comparison to what was put out by cars, and as a result going after lead emissions from cars was deemed to be the best course of action by the EPA. Also, it's worth noting that leaded gasoline didn't go away overnight. It was still sold for awhile even after the EPA said that you couldn't make cars that ran on leaded gas.
pc86 5y ago
Can you not see how passenger vehicles, which are overwhelmingly for personal use, is a different category with a different economic impact than an entire class of public transportation?
- lmm 5y ago
  Gasoline-engined planes are overwhelmingly for personal use.

GekkePrutser 5y ago

I've seen 172 conversions with diesel. In fact that young guy that flew around the world in this 172 last week used one.