8 ms·

I recall watching a YouTube video a little while back that went into the modern history of light aircraft engines, and how there have been several failed attemp

I recall watching a YouTube video a little while back that went into the modern history of light aircraft engines, and how there have been several failed attempts at redesigning existing technology over the past 20 (40?) years. Is it genuinely workable? Or is there some weird edge case that makes it completely impractical from a maintenance or reliability perspective?

sokoloff 4y ago
There were several failures from converted ex-automotive engines. Some of those were related to vibration; others to the much higher percentage of power that an airplane engine runs for hours on end. My engine might last for only 2000 flight hours between overhauls. In those 2000 flight hours, it's likely to burn ~30K gallons of fuel. Taking that as a proxy for the total energy generated, 30K gallons of fuel will take a typical car almost a million miles. How many cars reach 1 million miles without major engine work? There were also a bunch of (IMO misguided) attempts to fit liquid cooled engines into aircraft. What do you have absolutely no shortage of in flight? Fast moving, cool air. What do you have no tolerance for in flight? Loss of coolant. It's not impossible to improve upon them, but aircraft engines have gotten to a local maximum of sorts where they're pretty darn good at what they do and the maintenance needs and failure modes are pretty well understood.
- verelo 4y ago
  I’d agree with most of this but frankly when was the last time your car engine stopped on the highway? Or was hard to start because it was hot, or cold, or just because? These problems are solved in cars. The old Cessna 172 models I’ve flown all continue to have these issues, even a friends SR22 from the mid 2000s was a nightmare. Plane engines are well understood, but they are old and clumsy designs that could be drastically improved upon.
  - cush 4y ago
    I can't remember the last time I commuted and didn't see a car broken down on the side of the road.
    - TedDoesntTalk 4y ago
      Not necessarily engine problems.
    - elmomle 4y ago
      But thousands of cars pass that way each day, and one breaks down. The (admittedly anecdotal) issue rate described for planes sounded much higher.
      - iancmceachern 4y ago
        It's more to do with the relative consequences. A car engine goes out and you cal AAA, an airplane engine goes out and you have a serious problem.
        eru 4y ago
        If you have at least two engines on your plane, one failing ain't so bad?
        jabl 4y ago
        As the saying goes, when you have an engine failure in a twin, the remaining engine takes you to the crash site faster. ;)
        cush 4y ago
        I was responding to "when's the last time your engine gave out"
      - sokoloff 4y ago
        The anecdotes above I read as difficulty getting an airplane engine started, which is definitely true compared to a modern car engine. Even using proper technique, mine can be frustrating to get and stay started after a fuel stop. (It’s a vapor lock issue that arises from heat-soaking while stopped for fueling, not something that makes for a safety-of-flight issue.)
    - 4y ago
  - iancmceachern 4y ago
    When was the last time an issue with the car engine caused you to fall out of the sky?
  - code_duck 4y ago
    The most frequent problems I’ve had with cars in the last 20 years have been engine cooling systems and battery charging.
  - hef19898 4y ago
    Aircraft engines are running on full load for almost all the time, with added load during take off. Car engines are not, a modern car engine would blow up running under the same load patterns then aircraft engines. And sincr ICE engines are dying bread when it comes to aircraft, why bother if the current ones work perfectly fine for what they are supposed to do?
    - eru 4y ago
      > And since ICE engines are dying bread when it comes to aircraft, [...] Are they actually? I'd expect air-travel (and rockets) to remain the last holdouts for combustion engines for quite a while to come. Cars will definitely move to being electric. Big ships, maybe too?
      - jabl 4y ago
        Wouldn't surprise me if aviation engines would move to turbines (see TurbAero and Turbotech for turboprops designed for the GA end of the market), and electric for short range. Leaving little if any space for piston engines. Though of course existing planes aren't going away for a long time.
        eru 4y ago
        Turbines are internal combustion engines. But I guess the comment I originally replied to meant non-turbine ICE only?
        jabl 4y ago
        > But I guess the comment I originally replied to meant non-turbine ICE only? I would guess that yes, otherwise the comment would be pretty outlandish if the poster is predicting the imminent death of turbine powered aircraft.
        hef19898 4y ago
        Obviously claiming turbine powered aircraft are a dying breed would be outlandish. I wrote ICEs, and meant piston powered aircraft... my bad...
- scarier 4y ago
  Ooooohhh, the air-cooled vs. water-cooled argument is a great one. The mechanical simplicity of air-cooled engines is a very strong point in their favor, but it's arguably the only one. Water-cooled engines can be run leaner (i.e. more efficiently) because they don't need to run rich to keep cool, don't have uneven cooling issues, aren't susceptible to thermal shock when going to idle during a cruise descent, have better power-to-weight ratios, and don't have as big of a problem dealing with the dilemma of having the slowest/warmest airflow when the most engine power is needed (during takeoff and go-around conditions)--all for the relatively modest risk of a pump, radiator, or hose failure. In an alternate reality where we had seen the same amount of R&D go into general aviation piston engines as automotive ones, I wouldn't be surprised if nearly all light aircraft used hybrid-electric liquid-cooled engines with reduction gearboxes.
  - jabl 4y ago
    I don't know. If you look at the swan song of big aviation piston engines just before turbines took over (immediate post-WWII era), it was all air-cooled radials. If the WWII experience would have proved liquid cooled engines to be superior, I guess all those Convairs, Constellations, DC-6's etc. would be using Griffons, Sabres or such.
    - VLM 4y ago
      Classic scalability issue, those engines were HUGE compared to general aviation so all the rules about shock cooling and surface area to volume ratios don't apply unchanged to engines a thirtieth the size.
      - jabl 4y ago
        I'm not sure. Surface vs. volume is certainly and interesting thing that explains many scaling phenomena, but in this case, those huge radials had huge fins as well (correspondingly huger than fins on smaller engines in order to cool the much higher mass) to cool them under normal operations. So those same fins would equally rapidly cool the engine when descending quickly at idle power. So shock cooling is certainly an issue with big radials as well. Now I don't know the exact scaling relation, but I'd guess it's more similar to a smaller engine than a straightforward surface/volume scaling would imply. Or to put it another way, the surface area of the cooling fins is not proportional to the surface area of the cylinders without any fins, but to the power output of the engine.
- eru 4y ago
  > My engine might last for only 2000 flight hours between overhauls. In those 2000 flight hours, it's likely to burn ~30K gallons of fuel. Taking that as a proxy for the total energy generated, 30K gallons of fuel will take a typical car almost a million miles. How many cars reach 1 million miles without major engine work? I guess you could still take car engines, but overhaul them more often? Might still come out cheaper in the end?
  - wil421 4y ago
    If you wanted to use an auto engine it would probably be a truck engine. Most car engines aren’t designed to be run at lets say 5,000rpms for an hour or so at a time. It’s the same reason inboard/outboard engines in boats use big and small block GM designed truck engines (Merc and Volvo).
    - eru 4y ago
      Yes. I was being a bit lax when I said 'car engine'. I basically meant any land transport engine with a large production run. (Though looking at ship engines might also be interesting. I assume they are heavier and bulkier than car or truck engines, but they probably can also run at high load for a long time? I don't know anything about them..)
      - wil421 4y ago
        You wouldn’t want to run them wide open throttle for a long time but usually they give you a cruise RPM suggestion for optimal gas/speed. People make 20-30 miles runs offshore in smaller boats running them close to wide open for hours at a time. Yes I think they are heavier than their truck counterparts. Most are raw water cooled so they have intakes/risers and shoot water out the exhaust. The diesel ship engines are beasts, can take a beating, and run for 10x as many hours as a gas engine. It looks like they are too heavy for aircraft but there are some Diesel engine manufacturers listed on Wikipedia.
        cardiffspaceman 4y ago
- throwaway0a5e 4y ago
  >How many cars reach 1 million miles without major engine work? I can think of about a dozen engine platforms off the top of my head that would reliably get there or damn close if they got the same kind of maintenance/inspection schedule that a GA aircraft gets.
- Gordonjcp 4y ago
  > How many cars reach 1 million miles without major engine work? Every old Mercedes taxi. Every Skoda Octavia taxi.
bluGill 4y ago
Problem is it is a niche too small to support the customization needed. There are plenty of engines that are better in one aspect and we know that all needed aspects can be combined into one, but the engineering cost to do that is so high that you couldn't charge a reasonable price for the engine and still break even on R&D.
Scoundreller 4y ago
Maybe this guy's video: https://www.youtube.com/watch?v=_k1TQGK3mZI https://www.youtube.com/watch?v=_k1TQGK3mZI

sokoloff 4y ago

There were several failures from converted ex-automotive engines. Some of those were related to vibration; others to the much higher percentage of power that an airplane engine runs for hours on end. My engine might last for only 2000 flight hours between overhauls. In those 2000 flight hours, it's likely to burn ~30K gallons of fuel. Taking that as a proxy for the total energy generated, 30K gallons of fuel will take a typical car almost a million miles. How many cars reach 1 million miles without major engine work? There were also a bunch of (IMO misguided) attempts to fit liquid cooled engines into aircraft. What do you have absolutely no shortage of in flight? Fast moving, cool air. What do you have no tolerance for in flight? Loss of coolant. It's not impossible to improve upon them, but aircraft engines have gotten to a local maximum of sorts where they're pretty darn good at what they do and the maintenance needs and failure modes are pretty well understood.

verelo 4y ago
I’d agree with most of this but frankly when was the last time your car engine stopped on the highway? Or was hard to start because it was hot, or cold, or just because? These problems are solved in cars. The old Cessna 172 models I’ve flown all continue to have these issues, even a friends SR22 from the mid 2000s was a nightmare. Plane engines are well understood, but they are old and clumsy designs that could be drastically improved upon.
- cush 4y ago
  I can't remember the last time I commuted and didn't see a car broken down on the side of the road.
  - TedDoesntTalk 4y ago
    Not necessarily engine problems.
  - elmomle 4y ago
    But thousands of cars pass that way each day, and one breaks down. The (admittedly anecdotal) issue rate described for planes sounded much higher.
    - iancmceachern 4y ago
      It's more to do with the relative consequences. A car engine goes out and you cal AAA, an airplane engine goes out and you have a serious problem.
      - eru 4y ago
        If you have at least two engines on your plane, one failing ain't so bad?
        jabl 4y ago
        As the saying goes, when you have an engine failure in a twin, the remaining engine takes you to the crash site faster. ;)
      - cush 4y ago
        I was responding to "when's the last time your engine gave out"
    - sokoloff 4y ago
      The anecdotes above I read as difficulty getting an airplane engine started, which is definitely true compared to a modern car engine. Even using proper technique, mine can be frustrating to get and stay started after a fuel stop. (It’s a vapor lock issue that arises from heat-soaking while stopped for fueling, not something that makes for a safety-of-flight issue.)
  - 4y ago
- iancmceachern 4y ago
  When was the last time an issue with the car engine caused you to fall out of the sky?
- code_duck 4y ago
  The most frequent problems I’ve had with cars in the last 20 years have been engine cooling systems and battery charging.
- hef19898 4y ago
  Aircraft engines are running on full load for almost all the time, with added load during take off. Car engines are not, a modern car engine would blow up running under the same load patterns then aircraft engines. And sincr ICE engines are dying bread when it comes to aircraft, why bother if the current ones work perfectly fine for what they are supposed to do?
  - eru 4y ago
    > And since ICE engines are dying bread when it comes to aircraft, [...] Are they actually? I'd expect air-travel (and rockets) to remain the last holdouts for combustion engines for quite a while to come. Cars will definitely move to being electric. Big ships, maybe too?
    - jabl 4y ago
      Wouldn't surprise me if aviation engines would move to turbines (see TurbAero and Turbotech for turboprops designed for the GA end of the market), and electric for short range. Leaving little if any space for piston engines. Though of course existing planes aren't going away for a long time.
      - eru 4y ago
        Turbines are internal combustion engines. But I guess the comment I originally replied to meant non-turbine ICE only?
        jabl 4y ago
        > But I guess the comment I originally replied to meant non-turbine ICE only? I would guess that yes, otherwise the comment would be pretty outlandish if the poster is predicting the imminent death of turbine powered aircraft.
        hef19898 4y ago
        Obviously claiming turbine powered aircraft are a dying breed would be outlandish. I wrote ICEs, and meant piston powered aircraft... my bad...
scarier 4y ago
Ooooohhh, the air-cooled vs. water-cooled argument is a great one. The mechanical simplicity of air-cooled engines is a very strong point in their favor, but it's arguably the only one. Water-cooled engines can be run leaner (i.e. more efficiently) because they don't need to run rich to keep cool, don't have uneven cooling issues, aren't susceptible to thermal shock when going to idle during a cruise descent, have better power-to-weight ratios, and don't have as big of a problem dealing with the dilemma of having the slowest/warmest airflow when the most engine power is needed (during takeoff and go-around conditions)--all for the relatively modest risk of a pump, radiator, or hose failure. In an alternate reality where we had seen the same amount of R&D go into general aviation piston engines as automotive ones, I wouldn't be surprised if nearly all light aircraft used hybrid-electric liquid-cooled engines with reduction gearboxes.
- jabl 4y ago
  I don't know. If you look at the swan song of big aviation piston engines just before turbines took over (immediate post-WWII era), it was all air-cooled radials. If the WWII experience would have proved liquid cooled engines to be superior, I guess all those Convairs, Constellations, DC-6's etc. would be using Griffons, Sabres or such.
  - VLM 4y ago
    Classic scalability issue, those engines were HUGE compared to general aviation so all the rules about shock cooling and surface area to volume ratios don't apply unchanged to engines a thirtieth the size.
    - jabl 4y ago
      I'm not sure. Surface vs. volume is certainly and interesting thing that explains many scaling phenomena, but in this case, those huge radials had huge fins as well (correspondingly huger than fins on smaller engines in order to cool the much higher mass) to cool them under normal operations. So those same fins would equally rapidly cool the engine when descending quickly at idle power. So shock cooling is certainly an issue with big radials as well. Now I don't know the exact scaling relation, but I'd guess it's more similar to a smaller engine than a straightforward surface/volume scaling would imply. Or to put it another way, the surface area of the cooling fins is not proportional to the surface area of the cylinders without any fins, but to the power output of the engine.
eru 4y ago
> My engine might last for only 2000 flight hours between overhauls. In those 2000 flight hours, it's likely to burn ~30K gallons of fuel. Taking that as a proxy for the total energy generated, 30K gallons of fuel will take a typical car almost a million miles. How many cars reach 1 million miles without major engine work? I guess you could still take car engines, but overhaul them more often? Might still come out cheaper in the end?
- wil421 4y ago
  If you wanted to use an auto engine it would probably be a truck engine. Most car engines aren’t designed to be run at lets say 5,000rpms for an hour or so at a time. It’s the same reason inboard/outboard engines in boats use big and small block GM designed truck engines (Merc and Volvo).
  - eru 4y ago
    Yes. I was being a bit lax when I said 'car engine'. I basically meant any land transport engine with a large production run. (Though looking at ship engines might also be interesting. I assume they are heavier and bulkier than car or truck engines, but they probably can also run at high load for a long time? I don't know anything about them..)
    - wil421 4y ago
      You wouldn’t want to run them wide open throttle for a long time but usually they give you a cruise RPM suggestion for optimal gas/speed. People make 20-30 miles runs offshore in smaller boats running them close to wide open for hours at a time. Yes I think they are heavier than their truck counterparts. Most are raw water cooled so they have intakes/risers and shoot water out the exhaust. The diesel ship engines are beasts, can take a beating, and run for 10x as many hours as a gas engine. It looks like they are too heavy for aircraft but there are some Diesel engine manufacturers listed on Wikipedia.
      - cardiffspaceman 4y ago
throwaway0a5e 4y ago
>How many cars reach 1 million miles without major engine work? I can think of about a dozen engine platforms off the top of my head that would reliably get there or damn close if they got the same kind of maintenance/inspection schedule that a GA aircraft gets.
Gordonjcp 4y ago
> How many cars reach 1 million miles without major engine work? Every old Mercedes taxi. Every Skoda Octavia taxi.

bluGill 4y ago

Problem is it is a niche too small to support the customization needed. There are plenty of engines that are better in one aspect and we know that all needed aspects can be combined into one, but the engineering cost to do that is so high that you couldn't charge a reasonable price for the engine and still break even on R&D.

Scoundreller 4y ago

Maybe this guy's video: https://www.youtube.com/watch?v=_k1TQGK3mZI https://www.youtube.com/watch?v=_k1TQGK3mZI