Auto vs. Aircraft Engines - Some Musings

[AA5Bman]

I've been thinking lately about some of the similarities and differences between automotive engines and aircraft engines. Can anyone out there comment on my musings?



1. Efficiency: I can't quite get my head around why my old (now sold) O-360 burned 10 gallons an hour. It seems like an awful lot. It's only producing 180hp, about as much as my car. However, my car, at cruise, would go just over five hours between fillups, and only has a 13.5 gallon tank... total. What's the difference?

2. Horsepower: when we talk about horsepower, are we referring horsepower produced by the engine that is applied to the crankshaft? Is that "shaft" horsepower? When we say a O-470 produces 230 hp, we're not saying that the engine produces 230 hp of forward thrust, I imagine. Some of that energy must be lost due to inefficiencies in the props. How much is lost? For a typical engine, what is the horsepower rating actually referring to?

3. A typical car engine is going to produce its most horsepower at high(er) RPM - 6,000 or more(?). What exactly is it that allows aircraft engines to produce their best horsepower at much much lower RPMs?

4. If you think about truck engines, for instance, the 454 was considered a pretty dang beefy engine. But that was approximately 450 inches of displacement - not even as much as an O-470 in a 182, let alone the various configurations of the 520s, 540s, and 550s. However, that 454 had eight cylinders and the "big" aircraft engines only have 6. Why?

5. Following up on the question above, depending on the configuration, that 454 might produce between 270hp and 500hp, on less displacement. Why are the aircraft engines generally larger and less powerful?

6. Finally, is there a weight difference between an average automotive engine and a like-sized aircraft engine. Are aircraft engines considerably lighter?


Thanks in advance,

Mike

 

[SCCutler]

Apples and Alligators.

Car engines may be rated to produce more power, but they are rarely called-upon to do so for any extended period of time; the bigger power is used for acceleration, not steady cruise.

Look at the relative sizes of the crankshaft and the bearing journals - aircraft engines are vastly more stout, much more robust and mechanically simple.

They usually weigh less... but have no cooling system either.

 

[Areeda]

These topics have been discussed before, I suggest a search for more details but I'll take a stab at some of it.

Aircraft and car engines are very similar in efficiency or SFC specific fuel consumption defines as hp/fuel flow (actuall numbers are usually joules/gram per sec). The main reason your 180 HP airplane burns so much more fuel than your 180 HP car is that you run the a/c at 75% power and the car at an average of 10-20%.

HP is usually specified as BHP (brake horse power) which is what is produced at the crank shaft. Thrust horsepower is a measurement but it depends on speed and propeller efficiency so engine manufacturers don't use it.

Power is torque * rpm. So an aircraft engine would develop more HP at higher RPM. The red line is determined more by the propeller than the engine at least in direct drive props.

I think truck engines tend to run at higher RPM also to develop more horsepower.

I'll leave the other items to those more knowledgeable than me.

Joe

 

[sba55]

1. Efficiency: I can't quite get my head around why my old (now sold) O-360 burned 10 gallons an hour. It seems like an awful lot. It's only producing 180hp, about as much as my car. However, my car, at cruise, would go just over five hours between fillups, and only has a 13.5 gallon tank... total. What's the difference?

Your car engine - if your car was built in the last few decades - is much more sophisticated and thus much more efficient. Some engines these days have direct fuel injection (that's brand-new even for car engines), all of them are FADEC, which means they tend to be leaned much better than you can lean an engine manually, and they run lean of peak a lot (ie most of the time in cruise). With cars, the added complexity is ok, but it is more failure-prone just because it is more complex (at least in theory; in practice, modern car engines are extremely reliable since they are produced and tested much more than AC engines).

Most importantly, the aircraft engine might actually be running at 180 hp all the time. Your car cruises at maybe 1/5 that at highway speeds.

2. Horsepower: when we talk about horsepower, are we referring horsepower produced by the engine that is applied to the crankshaft? Is that "shaft" horsepower? When we say a O-470 produces 230 hp, we're not saying that the engine produces 230 hp of forward thrust, I imagine. Some of that energy must be lost due to inefficiencies in the props. How much is lost? For a typical engine, what is the horsepower rating actually referring to?

You're correct, but this is actually no different than for car engines. Many countries - like those in the EU for example - require that hp specs refer to the hp applied to the wheels. I don't believe that's the case in the U.S., which means that your 180 hp car is putting maybe 150 hp on the road.

3. A typical car engine is going to produce its most horsepower at high(er) RPM - 6,000 or more(?). What exactly is it that allows aircraft engines to produce their best horsepower at much much lower RPMs?

Lots of reasons for that. You can adjust the torque curve (ie how much hp the engine can deliver over its RPM range) in many ways. For example, one of my cars produces maximum power at 1200 RPM all the way to 7000 RPM. It's all adjustable.

4. If you think about truck engines, for instance, the 454 was considered a pretty dang beefy engine. But that was approximately 450 inches of displacement - not even as much as an O-470 in a 182, let alone the various configurations of the 520s, 540s, and 550s. However, that 454 had eight cylinders and the "big" aircraft engines only have 6. Why?

Lots of reasons for that, too. Mostly, though, car engines, including the 454, tend to have a much much higher compression ratio. That means you can get more power out of the same or less displacement. It also means that cyl pressures are higher (obviously) and that the engine will be more fuel efficient.

Btw., US made engines tend to get a miserable amount of power given their displacement. You can get >500 hp out of <250 cu in.

5. Following up on the question above, depending on the configuration, that 454 might produce between 270hp and 500hp, on less displacement. Why are the aircraft engines generally larger and less powerful?

Lower compressions, a need to be larger/lower compressions for cooling, weight, and reliability reasons.

6. Finally, is there a weight difference between an average automotive engine and a like-sized aircraft engine. Are aircraft engines considerably lighter?

Usually, yes.

 

[flyingcheesehead]

Lots of reasons for that. You can adjust the torque curve (ie how much hp the engine can deliver over its RPM range) in many ways. For example, one of my cars produces maximum power at 1200 RPM all the way to 7000 RPM. It's all adjustable.

Ummm... A flat torque curve from 1200 to 7000? I find that extremely difficult to believe. Not to mention, how do you know? I mean, car manufacturers don't just give out engineering information like that, do they?

 

[flyingcheesehead]

1. Efficiency: I can't quite get my head around why my old (now sold) O-360 burned 10 gallons an hour. It seems like an awful lot. It's only producing 180hp, about as much as my car. However, my car, at cruise, would go just over five hours between fillups, and only has a 13.5 gallon tank... total. What's the difference?

If you ran your car at 100% power for the first part of the trip and then 75% for the vast majority of the trip, it'd probably burn 10 gallons an hour too, while shedding parts as you get pulled over for doing well over 100mph.

2. Horsepower: when we talk about horsepower, are we referring horsepower produced by the engine that is applied to the crankshaft? Is that "shaft" horsepower? When we say a O-470 produces 230 hp, we're not saying that the engine produces 230 hp of forward thrust, I imagine. Some of that energy must be lost due to inefficiencies in the props. How much is lost? For a typical engine, what is the horsepower rating actually referring to?

Generally, in piston-powered aircraft engines they're referring to brake horsepower while in turbine engines it's shaft horsepower. In either case, it's the power applied to the prop, so the thrust that you actually get depends on the prop efficiency which, according to that article, is around 80% if it's done right.

3. A typical car engine is going to produce its most horsepower at high(er) RPM - 6,000 or more(?). What exactly is it that allows aircraft engines to produce their best horsepower at much much lower RPMs?

Oh, I bet if you ran an aircraft engine at 6,000 RPM's it'd develop significantly more power too - However, on an aircraft we're more concerned with the thrust from a particular engine-prop combo, and a prop that's spinning 6,000 RPM would have to be very small to keep the tips from going transonic. Aircraft engines, which tend to operate between 2400-2700 RPM max with the correct prop, probably operate there because it makes the most sense given all of the tradeoffs to make the engine-prop combo as efficient as possible.

4. If you think about truck engines, for instance, the 454 was considered a pretty dang beefy engine. But that was approximately 450 inches of displacement - not even as much as an O-470 in a 182, let alone the various configurations of the 520s, 540s, and 550s. However, that 454 had eight cylinders and the "big" aircraft engines only have 6. Why?

Oh, there is an 8-cylinder aircraft engine - The 400-horsepower Lycoming IO-720 - A beast that was used in the Piper Comanche 400, Beech Queen Air, and just a few other airplanes.

But, all else being equal, with aircraft engines the question might better be framed, "Why would you want eight cylinders?" An 8-cylinder engine in an aircraft leads to some cooling issues - Remember, we're talking air-cooled here - so the 2 cylinders in the back have trouble getting cool enough. You're also talking about special mags, four extra leads from the mags to the plugs, four extra plugs, and additional cooling fin surface area (read: weight).

The only real advantage I can think of to having extra cylinders is smoothness, provided you can make the power you want with reasonably-sized cylinders and the other engineering factors work out.

5. Following up on the question above, depending on the configuration, that 454 might produce between 270hp and 500hp, on less displacement. Why are the aircraft engines generally larger and less powerful?

See above - The engine itself could certainly make more power, but it's the engine-prop combo that matters in an airplane.

6. Finally, is there a weight difference between an average automotive engine and a like-sized aircraft engine. Are aircraft engines considerably lighter?

I can't say for sure, but I would imagine that aircraft engines are lighter. First of all, you don't have a liquid cooling system (yes, there are exceptions like the Thielerts and Rotaxes of the world, but I think the discussion here is centered on the average Lycs and Contis). You also don't have an engine block (big solid hunk of metal). There are certain things on aircraft engines (dual ignition, 1-2 vacuum pumps, sometimes dual alternators as well) that can cause them to be heavier in some aspects, but since weight REALLY matters a lot with aircraft engines, I think they're probably significantly lighter.

 

[Ted]

Your car engine - if your car was built in the last few decades - is much more sophisticated and thus much more efficient.

WRONG. As usual. Sophistication in no way means more efficient. It has been shown time and time again that aircraft engines are actually very efficient, and it's pretty hard to beat with an automotive engine that is comparable. The people who say that a new engine is inherently more efficient are making conjecture. Are some more efficient? Sure. All? No way.

1. Efficiency: I can't quite get my head around why my old (now sold) O-360 burned 10 gallons an hour. It seems like an awful lot. It's only producing 180hp, about as much as my car. However, my car, at cruise, would go just over five hours between fillups, and only has a 13.5 gallon tank... total. What's the difference?

Biggest one is that you're making a lot more horsepower in cruise in your 172 than you are in your Ford. Your car may run at, say, 10% power in cruise. Your airplane will run at, say, 65-75%.

2. Horsepower: when we talk about horsepower, are we referring horsepower produced by the engine that is applied to the crankshaft? Is that "shaft" horsepower? When we say a O-470 produces 230 hp, we're not saying that the engine produces 230 hp of forward thrust, I imagine. Some of that energy must be lost due to inefficiencies in the props. How much is lost? For a typical engine, what is the horsepower rating actually referring to?

Horsepower output at the crankshaft as read by a dynamometer, corrected for standard day conditions.

3. A typical car engine is going to produce its most horsepower at high(er) RPM - 6,000 or more(?). What exactly is it that allows aircraft engines to produce their best horsepower at much much lower RPMs?

Larger displacement which produces much more torque. Since horsepower is a function or torque and engine RPM, if you have more torque, you don't need engine RPM.

4. If you think about truck engines, for instance, the 454 was considered a pretty dang beefy engine. But that was approximately 450 inches of displacement - not even as much as an O-470 in a 182, let alone the various configurations of the 520s, 540s, and 550s. However, that 454 had eight cylinders and the "big" aircraft engines only have 6. Why?

Keep in mind that the big beefty truck engines like Kent drives mostly have 6 cylinders. More is not always better. The 6-cylinders ended up being very beefy and allowed for acceptable weight. Also they allowed direct drive for the propeller by making power at lower RPMs for operation and fewer parts (parts that aren't there can't break).

5. Following up on the question above, depending on the configuration, that 454 might produce between 270hp and 500hp, on less displacement. Why are the aircraft engines generally larger and less powerful?

Your 454 doesn't produce that power continuously, whereas an aircraft engine tends to need to. It comes down to reliability and efficiency for the most part. If you have a tiny engine that is wound up very tightly, it's difficult to make it reliable. If you make it reliable, it'll also be difficult to make it efficienct. Also keep in mind that in factory form, the 454s really didn't make more than about 250-300 hp at most. Using aftermarket engines as a comparison is not reasonable. I'd also argue that using comparisons from the various people who've turned the various Chevy V8s into engines used in aircraft is not a good comparison, either, because they don't end up meeting the same weight comparisons, and we don't know if they meet the reliability.

Now if you get into compression ignition engines (diesel) that's another matter, but remember that we're talking about spark ignition engines (gas).

6. Finally, is there a weight difference between an average automotive engine and a like-sized aircraft engine. Are aircraft engines considerably lighter?

Yes. Each of my Aztec's 540s weighs something aroudn 400-450 lbs. The 454 in my Suburban weighed a couple hundred pounds more than that. When you get into the geared pistons (GTSIO-520 and TIGO-541) then you can get close in weight.

 

[timwinters]

If you view your engines in terms of Horsepower per Cubic Inch instead of percent HP then you'll find that your auto engine is working just as hard cruising @ 75 mph down the highway as your airplane engine is working at 65-70% power. Auto engines are getting far more HP / CI than airplane engines do. My Toyota runs about 2500rpm at 78 mph (which is my typical cruise setting) No, it's not producing 70% of it's rated power but it IS producing just as many hp/ci as my 0-470 does @ cruise.

Airplane engines are limited by the speed a prop can be swung. To claim that my 0-470 is "working hard" at 70% power & 2300 RPM while only producing 160hp is very amusing.

 

[Henning]

I've been thinking lately about some of the similarities and differences between automotive engines and aircraft engines. Can anyone out there comment on my musings?



1. Efficiency: I can't quite get my head around why my old (now sold) O-360 burned 10 gallons an hour. It seems like an awful lot. It's only producing 180hp, about as much as my car. However, my car, at cruise, would go just over five hours between fillups, and only has a 13.5 gallon tank... total. What's the difference?

2. Horsepower: when we talk about horsepower, are we referring horsepower produced by the engine that is applied to the crankshaft? Is that "shaft" horsepower? When we say a O-470 produces 230 hp, we're not saying that the engine produces 230 hp of forward thrust, I imagine. Some of that energy must be lost due to inefficiencies in the props. How much is lost? For a typical engine, what is the horsepower rating actually referring to?

3. A typical car engine is going to produce its most horsepower at high(er) RPM - 6,000 or more(?). What exactly is it that allows aircraft engines to produce their best horsepower at much much lower RPMs?

4. If you think about truck engines, for instance, the 454 was considered a pretty dang beefy engine. But that was approximately 450 inches of displacement - not even as much as an O-470 in a 182, let alone the various configurations of the 520s, 540s, and 550s. However, that 454 had eight cylinders and the "big" aircraft engines only have 6. Why?

5. Following up on the question above, depending on the configuration, that 454 might produce between 270hp and 500hp, on less displacement. Why are the aircraft engines generally larger and less powerful?

6. Finally, is there a weight difference between an average automotive engine and a like-sized aircraft engine. Are aircraft engines considerably lighter?


Thanks in advance,

Mike

1) The airplane engine is more fuel efficient per HP being produced. When your care is at steady speed, you are only using a fraction of that HP. When calculating BSFC (Brake Specific Fuel Consumption) the old low speed big engines do better.

2) HP produced at the flywheel unless otherwise specified.

3) Displacement. Fuel Burned=Horsepower. The larger the engine displacement, the more fuel it can process per power stroke.

4) Because the O-470 operates at half the RPMs of the 454. This is because propeller efficiency requires we keep tip speeds below .92 Mach so in order to avoid gear reductions and their weight, cost and complexity, we build the engines large enough to process the fuel required for the HP we need at an RPM that is low enough that we can keep the prop tips slow enough.

5) See above, it's all about being able to get enough fuel (and air at the 13.7:1 ratio by weight) in the cylinder at the required speed without getting the ICP (Inner Cylinder Pressure) into areas which risk detonation which happens when we supercharge.

6) Yes, typically automotive engines are made of cast iron and have liquid coolant in them.

The reality is, you can use auto type engines, but by the time you get the power to weight ratios the same as well as the duty rating (the percentage of time it spends at specified HP out puts) you'll have as much or more money in it. It has been done before, Orenda used a BB Chevy and produced a 600hp recip aircraft engine, it isn't a hot seller to say the least. Toyota tried to develope one as well, they had a Revlon Red Aztec with it on one wing and a Lycoming 540 on the other. They gave up because they couldn't match the efficiency of the Lyc and had reliability issues.

 

[sba55]

Ummm... A flat torque curve from 1200 to 7000? I find that extremely difficult to believe. Not to mention, how do you know? I mean, car manufacturers don't just give out engineering information like that, do they?

You can find that information online or you can put the car on a dyno and find out for yourself (not very expensive). And I'm sure you will find that hard to believe since you haven't driven such a car before. Nevertheless, there are a few engines that can do that today - this particular one is completely flat all to way to 6000 and then tapers off as it approaches 7000 (although not much).

It's amazing what they can do these days.

 

[steingar]

Seems like every time I read about someone using an inexpensive auto engine to power their airplane they wind up spending as much in time and or money as they would have for an airplane engine. Between the cooling and reduction drives, there is a fair amount to work out. It seems like these issues have been pretty well dealt with for air-cooled auto engines like the Corvair and VW, but not so well for others. Just the impressions I've gotten from my readings.

 

[Steve Foley]

Auto engines are designed to run efficiently over a wide range of throttle settings.

Aircraft engines are not.

I really don't care how many gallons per hour I'm burning when I'm taxiing. I suppose I might if I was based at some ginormous airport where I had a six mile taxi from the hangar to the threshold.

 

[AA5Bman]

These topics have been discussed before, I suggest a search for more details

Sorry - didn't realize that.

By the way, I'm not looking at building a plane and putting in an automotive engine. Just curiosity here. Thanks for all the responses.

I pretty much guessed that the big difference in "perceived" fuel burn had a lot to do with how hard we run car vs. airplane engines. The only thing I'm still curious about is what kind of changes you would make to tweak the "torque curve" down towards the lower RPMs. Are there typical things you can do to make that happen (shorter/longer piston stroke or something?).

Also, what would be a typical automotive engine compression ratio?

 

[EdFred]

Run your car at 175mph and tell me what the fuel burn is.

 

[Capt. Geoffrey Thorpe]

Ummm... A flat torque curve from 1200 to 7000? I find that extremely difficult to believe. Not to mention, how do you know? I mean, car manufacturers don't just give out engineering information like that, do they?

With turbocharged auto engines, the torque curve tends to be pretty flat - the turbo is controled to give as much as possible as is consistant with durability.

Yes, they do give out hp and torque curves.

To the OP questions - as others have pointed out, if you ran your aircraft engine at the same 15% power...

Differences - auto engines do MUCH better at controlling fuel and spark for better efficiency. But, they operate in a much more transient enviornment spread out over a much larger speed / torque space. And they are tightly regulated, so we have to do a better job.

A lot of the things we (auto companies - I do powertrain controls for a living) do for fuel economy won't help much with aircraft engines because they are most effective at lower engine loads where you have a lot of losses due to throttling in a car.

Big / slow vs. smaller / fast for the same power is a design choice - aircraft engines tend to be direct drive and the speed is limited by the prop so cam timing, valve sizes, bore/stroke etc. are optimized for the lower speed operation. For a car with a transmission, it is easier to get more power by letting the engine rev faster...

Aircraft engines with gear reduction systems have been around a long time, but tend to be less popular for various reasons. I fly behind a Rotax with a gear reduction - I run up to 5500 RPM for takeoff and cruise at 4800...

Big cylinders have a lower surface to volume ratio which is good reducing heat lost to cooling. Two plug are a good thing also.

Auto engines run at the chemically correct ratio of air to fuel so the catalysts will be most efficient - this is near peak. Running rich of peak is throwing fuel out the exhaust system for the sake of cooling.

Things that could be done to improve aircraft engine efficiency:

Not running rich of peak.

Variable spark timing - this would be particularly effective if coupled with some kind of mixture measurement / control - as you go lean, you need to advance the spark to get the maximum result.

Positive crankcase ventilation - ok - not much for fuel, but it would significantly increase the life of engines that tend to be flown at infrequent intervals.

 

[zaitcev]

There was a guy who made a decent business adapting Subaru engines for experimentals. But he's switched to the 1.5L Honda engine due to its low cost and good durability when running at high power output for long periods. There is apparently some know-how here, e.g. how to minimize the amount of coolant because it's heavy.

I am still waiting for a small turboprop that would render the topic moot.

 

[flyingcheesehead]

You can find that information online or you can put the car on a dyno and find out for yourself (not very expensive). And I'm sure you will find that hard to believe since you haven't driven such a car before. Nevertheless, there are a few engines that can do that today - this particular one is completely flat all to way to 6000 and then tapers off as it approaches 7000 (although not much).

No, I only find it hard to believe because, well, it's a *curve* and to make curves completely flat in engineering is somewhat difficult.

Now, *very close* to flat, sure... But truly flat? Can you post it? I'd love to see it.

BTW, what kind of car is "such a car" anyway? And does it have a stock engine setup, or did you do something to it?

 

[flyingcheesehead]

Yes, they do give out hp and torque curves.

Hmmm... Know where I can get one for my car? 2001 Volvo S60 T5. After lots of googling, all I could find was a comment that it has a "broad-shouldered" torque curve, and some numbers that were rather questionable (as in, the wrong number of cylinders for the engine - Yeah, I know 5 is unusual, but still...)

 

[Clark1961]

No, I only find it hard to believe because, well, it's a *curve* and to make curves completely flat in engineering is somewhat difficult.

Naw, jus' put'er on a log scale and then run about three or four more cycles than you need. It'll look plenty flat to yer average manager type.

(stick with me on this and you'll go far, mark my words)

 

[Areeda]

This is what I found as a typical torque/power curve for a high performance engine
(http://www.corvetteactioncenter.com/tech/hp_torque.html)

 

[flyingcheesehead]

Naw, jus' put'er on a log scale and then run about three or four more cycles than you need. It'll look plenty flat to yer average manager type.

(stick with me on this and you'll go far, mark my words)

Nice!

 

[skidoo]

Ummm... A flat torque curve from 1200 to 7000? I find that extremely difficult to believe. Not to mention, how do you know? I mean, car manufacturers don't just give out engineering information like that, do they?

That is not what he said. He said maximum POWER from 1200 to 7000 rpm. That would mean that torque would have to fall off linearly as rpm increased above 1200 in order to keep the power flat. I find this even harder to believe... For example, torque would have to be half at 2400 rpm, then half again at 4800 rpm.

 

[Sac Arrow]

One of the problems with comparing the efficiency of automobile engines to airplane engines is that typically, if you compare operating BSFC's, you are measuring an automotive BSFC at a point where it will typically operate in cruise, which will be normally under 20% power, which is a very inefficient operational regime for any gasoline piston engine. An aircraft engine running 75% power at altitude is at, or very close to a wide open throttle position, at which all engines run most efficiently. If you do make an apples to apples comparison at the same operating conditions, which one will be more efficient? I suspect what you will find, is that aircraft engines will probably be more efficient than some car engines, and less efficient than others.

Regardless, they each have offsetting advantages. I'll list a few here.

1. Air cooled aircraft engines have less parasitic losses than automotive engines, due to the lack of a water cooling pump. And, generally, they have less engine driven accessories. (+)

2. Aircraft engines run at a lower RPM than automotive engines, which decreases gas frictional losses through the valves and exhaust system. It also decreases internal friction, which is in part a function of engine rpm. (+)

3. Aircraft engines typically operate within a 300 to 500 RPM range in flight, so that there is no requirement to make the induction system, spark, valving and valve timing operate over a very wide range of engine speed. (+)

4. Aircraft engines have less volumetric efficiency than most automotive engines due a reduced compression ratio. (-)

5. Aircraft engines must run a much higher octane than is optimal for power and efficiency to avoid detonation at high temperatures and altitudes. (-)

6. With the possible exception of GAMI equipped IO aircraft engines, aircraft engines normally do not have as even of a fuel distribution to the cylinders, compared with a modern multi port EFI automotive engine. (-)

7. Aircraft engine operating CHT's (and EGT's) are normally higher than that of automotive engines, resulting in better thermodynamic efficiency. (+)

8. With the exception of aftermarket Powerflow exhaust equipped aircraft engines, aircraft engines do not utilize tuned exhaust systems for exhaust gas scavenging. Many modern EFI car engines and most motorcyle engines do. (-)

9. Aircraft engines do not employ multiple intake and exhaust valves per cylinder, increasing gas frictional losses compared to modern automotive and motorcycle multivalve engines. The fact that they are pushrod actuated is unimportant at the RPM range in which they operate. (-)

10. Aircraft engines typically employ lower bore to stroke ratios (less diameter longer stroke) than most automotive engines, with the possible exception of some large truck engines. This is more mechanically efficient. (+)

Personally, I think the future of general aviation piston engines is the development of diesels, vs. modernized gasoline engines. Diesels are inherently more efficient than gasoline engines, and are well suited to typical aircraft operating requirements and conditions. Note the performance and range of the diesel equipped Diamond DA42's vs. the Lycoming 10 360 equipped option, which is a turd in comparison.

 

[sba55]

That is not what he said. He said maximum POWER from 1200 to 7000 rpm. That would mean that torque would have to fall off linearly as rpm increased above 1200 in order to keep the power flat. I find this even harder to believe... For example, torque would have to be half at 2400 rpm, then half again at 4800 rpm.

You're right, and I wasn't being specific enough. The torque curve is flat, which doesn't mean that the power curve is. Max power is around 6000 RPM.

Now, while some are having trouble believing, I'll just enjoy that amazing engine

 

[sba55]

This is what I found as a typical torque/power curve for a high performance engine
(http://www.corvetteactioncenter.com/tech/hp_torque.html)

Yes, that is somewhat typical. The one in question looks like that, except that the torque curve is much flatter. Which makes it even more fun!

 

[sba55]

No, I only find it hard to believe because, well, it's a *curve* and to make curves completely flat in engineering is somewhat difficult.

Now, *very close* to flat, sure... But truly flat? Can you post it? I'd love to see it.

BTW, what kind of car is "such a car" anyway? And does it have a stock engine setup, or did you do something to it?

I didn't do anything to it - it's just a very nice engine. Obviously, nothing is ever completely flat - that wasn't the point. Just that - on average - it is flat over the RPM range I mentioned, which is unusual. Of course, there are tiny variations over the RPM range, but nothing severe.

Btw., here's a torque curve for a 2001 S60. Obviously, that's not a HP engine as far as cars are concerned, and you can see that the curve is not flat at all (which is typical):

-Felix

 

[Capt. Geoffrey Thorpe]

Hmmm... Know where I can get one for my car? 2001 Volvo S60 T5. After lots of googling, all I could find was a comment that it has a "broad-shouldered" torque curve, and some numbers that were rather questionable (as in, the wrong number of cylinders for the engine - Yeah, I know 5 is unusual, but still...)

You typically find them in auto magazines. Sometimes in the propaganda at the dealer.

Finding the data afor a 2001 would take some effort.

 

[Doggtyred]

I've been thinking lately about some of the similarities and differences between automotive engines and aircraft engines. Can anyone out there comment on my musings?



1. Efficiency: I can't quite get my head around why my old (now sold) O-360 burned 10 gallons an hour. It seems like an awful lot. It's only producing 180hp, about as much as my car. However, my car, at cruise, would go just over five hours between fillups, and only has a 13.5 gallon tank... total. What's the difference?

Apples and oranges. You are using only a portion of your car's total HP at cruise. Your plane is using most of its total HP at cruise speed. If you ran a car engine at similar power settings, you would see similar but slightly better fuel economy at the drive shaft (liquid cooled engines have tighter tolerances than air cooled)

2. Horsepower: when we talk about horsepower, are we referring horsepower produced by the engine that is applied to the crankshaft? Is that "shaft" horsepower? When we say a O-470 produces 230 hp, we're not saying that the engine produces 230 hp of forward thrust, I imagine. Some of that energy must be lost due to inefficiencies in the props. How much is lost? For a typical engine, what is the horsepower rating actually referring to?

Shaft. The airplane loses HP converting it to thrust due to propellor inefficiency. An auto engine converted for airplane use would also lose efficiency in the same manner at the prop.

3. A typical car engine is going to produce its most horsepower at high(er) RPM - 6,000 or more(?). What exactly is it that allows aircraft engines to produce their best horsepower at much much lower RPMs?

If your airplane engine could SURVIVE rotating at those RPMS it likely would put out more HP.. Otherwise.. I'm gonna pass on this..

4. If you think about truck engines, for instance, the 454 was considered a pretty dang beefy engine. But that was approximately 450 inches of displacement - not even as much as an O-470 in a 182, let alone the various configurations of the 520s, 540s, and 550s. However, that 454 had eight cylinders and the "big" aircraft engines only have 6. Why?

6 larger cylinders, as opposed to 8 smaller ones. Cant tell you why. Pass

5. Following up on the question above, depending on the configuration, that 454 might produce between 270hp and 500hp, on less displacement. Why are the aircraft engines generally larger and less powerful?

Air cooled engines are slightly less efficient than liquid cooled do to the looser tolerances required for air cooled thermal expansion. An aircraft engine 0-470 could produce 500 hp if you turbocharged it, and turned it real fast. For a few minutes... until the cylinder heads exceeded redline and failed (perhaps catastrophically). The limiting factor here is heat.. and how you manage it. Air cooled engines have their limits. So do liquid cooled ones.. but liquid cooling can then be spread out in a large surface area radiator, where air cooled cylinder fins have their limits.

6. Finally, is there a weight difference between an average automotive engine and a like-sized aircraft engine. Are aircraft engines considerably lighter?

In flight configuration, with all necessary (and no unnecessary) accessories.... they can be pretty close, or the auto engine can weigh 50-100 lbs more. Depends on who engineers the install.


Thanks in advance,

Mike

Yer welcome

 

[N801BH]

I ain't gonna say a word.... :wink2::wink2::wink2:

I do love my V-8 in my plane though.....


Ben
www.haaspowerair.com

 

[flyingcheesehead]

I didn't do anything to it - it's just a very nice engine.

So... What's it in? I wasn't aware that Beech made a car.

Btw., here's a torque curve for a 2001 S60.

Not the one I have - Those numbers look like they're for the 2.4T, I have the T5. Where'd you find it?

 

[sba55]

Not the one I have - Those numbers look like they're for the 2.4T, I have the T5. Where'd you find it?

It is for the one you have. Keep in mind that your T5 only has about 220 HP at the wheels. Just google/image search and you can find these quite easily.

 

[jesse]

So... What's it in? I wasn't aware that Beech made a car.

Go look for yourself. You'll find it at his house in Hawaii, in the hangar/garage, between the p-baron and bonanza.

 

[Dan Thomas]

I can't say for sure, but I would imagine that aircraft engines are lighter. First of all, you don't have a liquid cooling system (yes, there are exceptions like the Thielerts and Rotaxes of the world, but I think the discussion here is centered on the average Lycs and Contis). You also don't have an engine block (big solid hunk of metal). There are certain things on aircraft engines (dual ignition, 1-2 vacuum pumps, sometimes dual alternators as well) that can cause them to be heavier in some aspects, but since weight REALLY matters a lot with aircraft engines, I think they're probably significantly lighter.

Ford 300 inline six, 130-150 hp @3400 RPM: Pushing 500 lb, not including exhaust manifolds. Add another 30 pounds or more for rad, plumbing, and coolant.

Lycoming O-320, 150 hp @2700RPM: 277 lb.

This sort of weight comparison is common enough. Auto engines are all heavier until we get into some of the newer aluminum engines that need reduction gearing to make their power useful, and that gearing (or belts or chains or whatever) is a real hassle in the homebuilt world. There are extremely few successful redrives, and many stories of those that have failed. The problem is that the engine delivers its power in big pulses but the prop wants a steady torque, and so those pulses have to be absorbed and delivered in a smoother fashion, requiring either some pretty snazzy engineering or simply massive overbuilding, ruining the power-to-weight ratio (and cost savings). I'd love to come up with a redrive that works but I'm old enough to realize that I'd probably never fly it. Takes a lot of time and money.

Dan

 

[N801BH]

Ford 300 inline six, 130-150 hp @3400 RPM: Pushing 500 lb, not including exhaust manifolds. Add another 30 pounds or more for rad, plumbing, and coolant.

Lycoming O-320, 150 hp @2700RPM: 277 lb.

This sort of weight comparison is common enough. Auto engines are all heavier until we get into some of the newer aluminum engines that need reduction gearing to make their power useful, and that gearing (or belts or chains or whatever) is a real hassle in the homebuilt world. There are extremely few successful redrives, and many stories of those that have failed. The problem is that the engine delivers its power in big pulses but the prop wants a steady torque, and so those pulses have to be absorbed and delivered in a smoother fashion, requiring either some pretty snazzy engineering or simply massive overbuilding, ruining the power-to-weight ratio (and cost savings). I'd love to come up with a redrive that works but I'm old enough to realize that I'd probably never fly it. Takes a lot of time and money.

Dan

To be accurate since we are comparing apples to apples posting the "true" weight is important. The 277 lbs figure is on the light side and that is for a stripped down 0-320. Add all the stuff that it takes for that 277+ lb 0-320 to run and post that figure. So, lets see. add the starter, intake tubes, carb, airbox, filter, exhaust system, mags, wiring harness, sparkplugs, brackets to hold on the alternator, alternator itself, all the cooling shrouds, baffles, oil filter, lord mounts, flywheel, ring gear, oil cooler, its brackets, and lines ...............................................

I have done it. I took a "complete" running 0-320 E2D off the nose of a Piper PA-28-151. When I say complete I mean all it took to start and run it was 12 volts to the starter. This is the "true" weight one needs to compare. :wink2: Using a very accurate scale and having the "complete" motor hanging off an engine hoist attached to this scale the REAL weight was..................................................... 359 lbs. Now, if you want to get realistic you can figure in a constant speed prop motors true weight. I believe there were a few very light certified twins made with this set up. Add 62 lbs for the prop, 24 lbs for the governor and related lines, linkage, etc and now you have a 150 HP light weight FAA certified
motor weighing in at 445 LBS..

Auto engine conversions will be heavier for the most part, but with advances in lightweight alloys, those numbers are falling pretty fast. I have lightened my auto engine conversion as much as I care to without compromising strength and safety and @ 330 HP and 437 lbs I would love to compare it to an aircraft engine of similar output. I did remove a 0-540, I believe was 260 HP, off the nose of a plane in its complete state to see the "real" weight. My scale is rated to 500 lb ... It was PEGGED.

In closing I will agree 60+ year old technology air cooled engines are lighter and made for the specific application, but progress moves on and evolution of engines is moving too. Just my humble opinion,,, again..

Tailwinds

Ben
www.Haaspowerair.com

 

[RotorAndWing]

Go look for yourself. You'll find it at his house in Hawaii, in the hangar/garage, between the p-baron and bonanza.

 

[Joe B]

4. If you think about truck engines, for instance, the 454 was considered a pretty dang beefy engine. But that was approximately 450 inches of displacement - not even as much as an O-470 in a 182, let alone the various configurations of the 520s, 540s, and 550s. However, that 454 had eight cylinders and the "big" aircraft engines only have 6. Why?

As previously discussed, the longer an in-line air-cooled engine gets, the harder it becomes to cool all the cylinders uniformly. The observation of the field suggests that 6 cylinders is the practical limit for a "big" engine.

However, big aircraft engines (without the quotes) certainly exist. They're round and come in multiples of 9 cylinders. Arranging the cylinders radially gives one a better shot at cooling them all. IIRC the largest radials got up to 4 stacked discs of cylinders.

 

[Ted]

However, big aircraft engines (without the quotes) certainly exist. They're round and come in multiples of 9 cylinders. Arranging the cylinders radially gives one a better shot at cooling them all. IIRC the largest radials got up to 4 stacked discs of cylinders.

Yes, but much like the horizontally-opposed 8-cylinder engines, they had problems cooling the rearmost cylinders. The majority of the big radials were double-stacked (R-2800 and R-3350 come to mind).

Ben's analysis covers it well. One question, Ben: does your 437 lbs include the cooling system with coolant in it?

 

[David]

Auto engine conversions will be heavier for the most part, but with advances in lightweight alloys, those numbers are falling pretty fast. I have lightened my auto engine conversion as much as I care to without compromising strength and safety and @ 330 HP and 437 lbs I would love to compare it to an aircraft engine of similar output. I did remove a 0-540, I believe was 260 HP, off the nose of a plane in its complete state to see the "real" weight. My scale is rated to 500 lb ... It was PEGGED.

In closing I will agree 60+ year old technology air cooled engines are lighter and made for the specific application, but progress moves on and evolution of engines is moving too. Just my humble opinion,,, again..

Tailwinds

Ben
www.Haaspowerair.com

Ben,
Here's the weight of a 300HP IO550 for comparison.
http://www.tcmlink.com/EngSpecSheetDocs/IO550B.pdf

 

[N801BH]

Here's the problem.....
You get the approximately thing.. The TCM should know the exact weight to the lb.

The IO-550-B engines have a 550 cubic inch displacement achieved by
using a cylinder design with a 5.25 inch diameter bore and a 4.25 inch stroke.
The engine enclosure is of the Permold series crankcase design. The dry
weight of the engine is 406.65 lbs. without accessories. The average weight of​

the engine with installed accessories is approximately 460 lbs.

They need to define "installed accessories".

Starter?
Prop Governor?
Cooling shrouds?
Oil cooler?
Filter?
Alternator?
Vacuum pump?
Flywheel?
Ring gear?

it goes on and on......

Just pull one off a flying plane and weigh it right then, the difference between TCM's docs and the REAL weight is astounding. !

Ben.

 

[tonycondon]

lol actually Beech did make a prototype car but it never got to production.

http://blog.hemmings.com/index.php/2007/09/09/sia-flashback-beechcraft-plainsman/