Aircraft Engines vs. Auto Engines

LJS1993

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LJ Savala
Okay gents what's the overall differences between the two? I know quite a bit about auto engines but very little about aviation engines. Could high HP auto engines work in aviation applications? I assume back in the earlier days of aviation auto engines were used in aircraft applications due to ease of production. Are aviation engines much more heavy duty in terms of the metals used for the blocks, heads, pistons, cranks, etc?? I know cast-iron is out due to weight restrictions.
 
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Aircraft engines are built to fly.

Automobile engines are meant for cars.

Many have tried to build airplanes with auto engines, most fail, many have died.

Don't mix the two. ;)
 
Okay gents what's the overall differences between the two? I know quite a bit about auto engines but very little about aviation engines. Could high HP auto engines work in aviation applications? I assume back in the earlier days of aviation auto engines were used in aircraft applications due to ease of production. Are aviation engines much more heavy duty in terms of the metals used for the blocks, heads, pistons, cranks, etc?? I know cast-iron is out due to weight restrictions.
The requirements for auto engines differ considerably from those for aircraft engines. The biggest differences are that for aircraft you need something that has high HP/weight, small frontal area, develops full power below 2700 RPM, has limited complexity, and will run at high power settings continuously without overheating or wearing prematurely while automobiles need good efficiency running a small percentage of available power, rapid response to power changes, high HP/volume, and simple operation. None of the unique requirements for one application are by themselves undesirable for the other but they often result in very different design decisions. For example, high power at low RPM dictates large displacement while high HP/volume pushes for high revving small displacement engines.

Low weight/HP and high continuous power are compatible with air cooling while good efficiency at a small percentage of available power is more easily achievable with liquid cooling. The thermodynamics and combustion event behavior are very different between large bore slow turning engines and small bore high RPM engines. Much of the recent advances in auto engine design are aimed at limiting emissions while preserving performance and efficiency and that has never been a concern with aircraft engines. Things like variable cam timing, multiple intake and exhaust valves, overhead cams, and carefully shaped combustion chambers (heads and pistons) brings little if any benefit to aircraft engines and adds complexity and weight. The list goes on...
 
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In general an aircraft engine turns much slower than an auto engine due to the restriction of tip speed of the propeller. Tip speed above the speed of sound produces alot of noise and a lot of drag. Auto engines require a gear reduction which has proved to be a serious problem to overcome.

Auto engine are heavier, more complex, water cooled, and dependent on outside electricity to keep them running.

Aircraft ignition systems have dual systems, auto engines one, and a/c ignitions produce their own electricity, auto engines depend on ECMs that fail.

It certainly can be done, but history has shown many, many very smart people have failed, gone broke, or died trying.
 
Low weight/HP and high continuous power are compatible with air cooling while good efficiency at a small percentage of available power is more easily achievable with liquid cooling

I generally agree with you but liquid cooling allows a greater power output for a given displacement. Aircraft engines have relatively low power output for their displacements. Given that, air cooling works fine for GA engines and I don't think the complexity of liquid cooling adds anything although it is a more efficient way to cool the engine.

The big gripe I have with aircraft engines is electrical. EFI and stick coil ignition systems are fairly indestructible, and are more efficient than their mechanical counterparts.
 
The second video is an RV 10 with an auto engine that exploded after landing with 2 people on board. The pilot and his daughter. Both were seriously burned but fortunately survived. The plane was a total loss. :sad:

But, in the context of the thread, that didn't have anything to do with the auto engine..
 
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Auto engines are designed to run at 35% power maximum in a continuos static test. Any listed maximum horse power ratings are for short times. If you want to see a comparison of HP, take the HP rating for the engine and decrease it to 35%

Aircraft engines are designed to run at 100% power.

An aicraft engines TBO is developed by mounting the engine on a test stand with the correct prop and run none stop at 100% power till it breaks. even the worst aircraft engines would go 1200 hours.

When an auto engine has the same test, rarely does it make it past 300 hours.
 
The cause was undetermined, unless you know something I don't. ;)

Fuel fumes in the cockpit exploded. I don't know that the point of ignition or the source of the fuel leak (?) has been specifically identified, although the fuel plumbing in the cockpit is/was a distinct possibility for the leak.
 
How unique to the design of an aircraft engine is the need to tolerate the axial load of the propellor trying to pull the crankshaft out the front end of the engine? In a car engine the primary load seems to act perpendicular to the crankshaft and can be supported by the main bearings.

I guess if an auto engine has to be geared down to drive a propellor, the gearbox would support the propeller's load and not the crankshaft. So maybe this difference may not be so important in that case.
 
Fuel fumes in the cockpit exploded. I don't know that the point of ignition or the source of the fuel leak (?) has been specifically identified, although the fuel plumbing in the cockpit is/was a distinct possibility for the leak.

Agreed. The entire fuel plumbing was a deviation from the approved / proven Van's design according to what I have read, and been told by the owner of the plane.
 
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How unique to the design of an aircraft engine is the need to tolerate the axial load of the propellor trying to pull the crankshaft out the front end of the engine? In a car engine the primary load seems to act perpendicular to the crankshaft and can be supported by the main bearings.

I guess if an auto engine has to be geared down to drive a propellor, the gearbox would support the propeller's load and not the crankshaft. So maybe this difference may not be so important in that case.

Actually, the gear box is critical and a proven design seems to be very elusive. Lubrication, bearing loads, belts breaking. In flight failures are common. :eek:

The biggest problem with auto conversions is the snake oil salesmen that go with them. They promise the world and deliver 10%. They promise huge savings over conventional engines and rarely deliver that too. Delays, failures, no support in the field or from the factory, no mechanic will touch it. Rarely, if ever do they deliver. Stick with the proven reliable, time tested design. It will be cheaper in the long run.
 
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How unique to the design of an aircraft engine is the need to tolerate the axial load of the propellor trying to pull the crankshaft out the front end of the engine? In a car engine the primary load seems to act perpendicular to the crankshaft and can be supported by the main bearings.

I guess if an auto engine has to be geared down to drive a propellor, the gearbox would support the propeller's load and not the crankshaft. So maybe this difference may not be so important in that case.

You are correct about the forces imposed by the prop. In addition to the thrust (and drag) forces, a bigger issue may be the gyroscopic forces when you maneuver the airplane. That big gyroscope (err, propeller) out front really imposes some forces on the crank and associated bearings and whatever the bearings are inside.

Also, engines transmit torque pulses where the torque peaks partway through the combustion process, but reverses as the next cylinder is going through its compression stroke. That's rough on everything.
 
There are several in the Experimental world, VW, Porsche and Subaru are used quite often.
 
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There are several in the Experimental world, VW, Porsche and Subaru are used quite often.

VW, yes. Subie, some. Corvair - occasionally. Porsche? Not so much. In fact, I've never heard of anyone other than Mooney trying a Porsche engine in an airplane, and that one was considered a failure...

The guys who *really* put many hours on the VW and Subie engines are the exception rather than the rule. Neither appears particularly robust in the aviation environment.
 
I'd say Lance's summary is pretty much spot-on. It comes down to different design requirements that have caused differences in build. Ben has done a great job with his auto engine, but the majority of people who have tried putting an automotive engine in a plane have failed miserably.

The big gripe I have with aircraft engines is electrical. EFI and stick coil ignition systems are fairly indestructible, and are more efficient than their mechanical counterparts.

Many people believe that adding electronic controls to a piston engine will make them more efficient. Compared to a pilot operating a mechanical engine properly, that is not true.

An aicraft engines TBO is developed by mounting the engine on a test stand with the correct prop and run none stop at 100% power till it breaks. even the worst aircraft engines would go 1200 hours.

That is not how TBO is established. The FAR 33 endurance test, which is the pattern typically used, includes a good sum of time at maximum continuous power (with the appropriate intervals at takeoff power, if the two are different), plus a number of intervals at various cruise powers. The number of hours total is dependent on the specifics of the engine certification. Remember that most engines certified by Lycosaur or Chinesental are based heavily on another engine, and thus similarity can be used to reduce the hours required for testing. It is worth noting that many aircraft engines, while they can run at 100% power all the time, won't be happy or have long lives doing so. But unlike automotive engines, they are still happy in the 65-75% power range.

On a completely new engine design, historically the TBO has started relatively low - like the 1200 hour mark - and then increased with time and service history. However, this is negotiable and dependent on tests that are performed.
 
Modern automobile engines can be used in aircraft. Gearing their higher RPMs down is possible and has been done. For example, I've been following this recent effort:

http://www.vikingaircraftengines.com/

So far it looks like it is doing good - racking up several hundred hours on several flying machines.

They basically take the core of the Honda Fit/Jazz engine, remove stuff and add back their own machined parts. The Honda engine they are using can run at full power for extended periods; so even Honda used the same engine core for a marine engine:
http://marine.honda.com/Products/modeldetail/BF90EFI

Viking has a bunch of videos on Youtube:
http://www.youtube.com/user/eggenfellner
 
...develops full power below 2700 RPM...

Ha. Us Rotax drivers don't think so :).

I generally agree with you but liquid cooling allows a greater power output for a given displacement. Aircraft engines have relatively low power output for their displacements. Given that, air cooling works fine for GA engines and I don't think the complexity of liquid cooling adds anything although it is a more efficient way to cool the engine.

Which is why the Rotax is liquid cooled. One thing that liquid cooling should prevent is shock cooling (which I'll admit I don't understand terribly well).
 
Many people believe that adding electronic controls to a piston engine will make them more efficient. Compared to a pilot operating a mechanical engine properly, that is

Ted, I was waiting for you to chime in. I agree with you on that. I'm referring to the processes internally to the engine that the pilot would not have control over anyway. No leaning or fuel mapping algorithm works better than the pilot controlling it in an airplane, properly done.
 
Ha. Us Rotax drivers don't think so :).



Which is why the Rotax is liquid cooled. One thing that liquid cooling should prevent is shock cooling (which I'll admit I don't understand terribly well).

Only the top of the heads are water cooled. The sides cylinders are air cooled. :D
 
Conversions of 1.7l and 2.0l VW industrial engines have been used successfully in aircraft for 50+ years. They are however modified from the original by use of different cranks, pistons and magneto ignition.
 
Ted, I was waiting for you to chime in. I agree with you on that. I'm referring to the processes internally to the engine that the pilot would not have control over anyway. No leaning or fuel mapping algorithm works better than the pilot controlling it in an airplane, properly done.

Which processes internally to the engine are you referring to?

Don't get me wrong, I'd love to see electronic fuel injection and electronic ignition on aircraft engines. But my reasons have nothing to do with efficiency.
 
Ted, I was waiting for you to chime in. I agree with you on that. I'm referring to the processes internally to the engine that the pilot would not have control over anyway. No leaning or fuel mapping algorithm works better than the pilot controlling it in an airplane, properly done.

Which processes internally to the engine are you referring to?

Don't get me wrong, I'd love to see electronic fuel injection and electronic ignition on aircraft engines. But my reasons have nothing to do with efficiency.

Automotive fuel injection..... for all the expensive sensors and computing power is basically only controlling fuel and spark. Sure, there are cam phasers, variable valve lift, multi-length intake systems, etc, but these systems are all designed around transient torque. Airplanes have a built in slipper clutch that allows the engine to rev up, closer to peak power, and removes the need for rapid RPM transitions.

The big advantage of FI, is the ability to monitor the engine and run it right on the ragged edge of temperature / knock / combustion stability limits. Something a human controlling only load and AFR can't do. But.... that assumes an automotive type engine with a 10:1 CR or higher, and running at the edge of knock.

Yes, you could increase compression ratio in an airplane engine, add FI, and be more efficient during leaned cruise. Make more power at all altitudes. And probably protect the engine better.

But that's also the problem.... and why I think you don't see automotive systems making the transition. The ECU doesn't know you want peak power for climb, or maximum leaning for fuel economy, it just understands RPM. The strategy programmed into automotive ECU is very complicated, and relies on the transients to give the computer an idea of what the operator wants.

Long periods of partial power, fuel economy. Quick transitions of the accelerator pedal, full power. And over everything, if there is risk to the engine, it reduces power / adds fuel to cool it off. Which is fine on the road.... you just pull over.

If a company took the time to develop an aviation strategy, maybe incorporate altitude changes to determine if you want to climb (peak power) or cruise (peak efficiency), it would work. But that requires money..... lots of it. And to certify it :rofl:
 
Auto engines are designed to run at 35% power maximum in a continuos static test. Any listed maximum horse power ratings are for short times. If you want to see a comparison of HP, take the HP rating for the engine and decrease it to 35%

I keep hearing stuff like this being parroted as of all auto engines were designed and built equally. They are not.

Making 200hp continuous power out of a 360 cubic inch engine out of a purpose-built, clean sheet aero piston engine design using the latest auto engine technology would be trivial in anything but unit price.

If there is one thing I dislike about aviation, it's all the glorified 1930s technology that is no different than what you'd see in a Mercedes from the 1950s. It is the certification standards and perhaps the culture at Lycoming/Continental that stand in the way of evolution.
 
Automotive fuel injection..... for all the expensive sensors and computing power is basically only controlling fuel and spark.

Automotive engines can be efficient and powerful because the intricacies combustion is not only well understood, but completely engineered. Using supercomputers, we now do things like engineer a contra-rotating swirl pattern inside the cylinder and inject very precise amounts of fuel in a lean burning pattern at the right times in order to minimize heat being lost by absorption into the cylinder walls for greater thermodynamic efficiency.

why I think you don't see automotive systems making the transition. The ECU doesn't know you want peak power for climb, or maximum leaning for fuel economy, it just understands RPM. The strategy programmed into automotive ECU is very complicated, and relies on the transients to give the computer an idea of what the operator wants.

You would have to build a combined wind tunnel and altitude chamber from which to mount the engine and components on a test stand. From here you would map out all possible operating regimes and code that into the ECU.

The ECU could be "steered" towards operating behavior for takeoff, METO, cruise, and descent by push buttons or moving a lever into a certain detent.

But that requires money..... lots of it. And to certify it :rofl:

Money spent can only be justified if there is a corresponding market for the end product. Unfortunately, I don't think it will happen.
 
But that's also the problem.... and why I think you don't see automotive systems making the transition. The ECU doesn't know you want peak power for climb, or maximum leaning for fuel economy, it just understands RPM. The strategy programmed into automotive ECU is very complicated, and relies on the transients to give the computer an idea of what the operator wants.

Long periods of partial power, fuel economy. Quick transitions of the accelerator pedal, full power. And over everything, if there is risk to the engine, it reduces power / adds fuel to cool it off. Which is fine on the road.... you just pull over.

If a company took the time to develop an aviation strategy, maybe incorporate altitude changes to determine if you want to climb (peak power) or cruise (peak efficiency), it would work. But that requires money..... lots of it. And to certify it :rofl:

There are electronic ignitions which have been flying in the experimental world for 20+ years which use an RPM/MP map to determine spark advance. Electroair, Lightspeed, and now the eMag and pMag. Electroair, for one, has moved into the certified world.

They do work, give more power, give more power for less fuel, etc. The problem most introduce is that they are more complicated than a magneto (now you are dependant on electricity, a small computer, a manifold pressure transducer, a hall effect sensor, plumbing for the MP lines, etc.

So, we can make a more powerful and efficient engine. It just may not be as reliable...
 
If there is one thing I dislike about aviation, it's all the glorified 1930s technology that is no different than what you'd see in a Mercedes from the 1950s. It is the certification standards and perhaps the culture at Lycoming/Continental that stand in the way of evolution.

It just turns out, that the simplicity of 1930's technology, is still better than all auto conversions to date. Larger displacement auto engines are constantly suffering from over-heating problems. Just not enough radiator surface area in GA size airplanes without adding additional drag. Then you have the gear reduction unit problems, which have been significant. If you've muddled your way past those problems, you'll often find that the computer systems for auto-engines are far from compatible with aircraft use. Examples are modes, in which the computer senses a problem, and cuts the horsepower to half..........in limp mode. Works for cars, but won't keep the airplane airborne. This has been a serious problem, that's required some expert re-design. Auto engines, usually end up weighing more. In the end, that "old" technology still ends up being the one we trust.
 
Modern automobile engines can be used in aircraft. Gearing their higher RPMs down is possible and has been done. For example, I've been following this recent effort:

http://www.vikingaircraftengines.com/

So far it looks like it is doing good - racking up several hundred hours on several flying machines.

They basically take the core of the Honda Fit/Jazz engine, remove stuff and add back their own machined parts. The Honda engine they are using can run at full power for extended periods; so even Honda used the same engine core for a marine engine:
http://marine.honda.com/Products/modeldetail/BF90EFI

Viking has a bunch of videos on Youtube:
http://www.youtube.com/user/eggenfellner


Thanks for the link. I'd been doing some searching and for the most part either saw guys just talking about their conversions or running them with no wings in their backyard. I want to see one fly.
 
My point on electronic ignition is that it is simpler than a magneto system. A modern stick coil ignition system isn't mechanical, doesn't require high voltage distribution or wiring, isn't altitude sensitive, and timing doesn't drift. They are pretty bullet proof. More efficient? Probably not. Ever hear of these systems crapping out? I've never experienced it. Ever hear of magnetos crapping out? I've experienced that.

Similarly with EFI. The only real disadvantage is that these systems typically require a relatively high pressure boost pump compared to mechanical fuel injection. Otherwise fuel distribution is about perfect, and priming and hot starting issues go away. More efficient? Probably not except that a more even fuel distribution could allow LOP operation closer to the "box".

I don't view operation being any different. I don't see using fancy oxygen sensor loop control or fixed fuel mapping. Fuel flow would be proportionate to throttle setting and mixture lever position.
 
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Modern automobile engines can be used in aircraft. Gearing their higher RPMs down is possible and has been done. For example, I've been following this recent effort:

http://www.vikingaircraftengines.com/

So far it looks like it is doing good - racking up several hundred hours on several flying machines.

They basically take the core of the Honda Fit/Jazz engine, remove stuff and add back their own machined parts. The Honda engine they are using can run at full power for extended periods; so even Honda used the same engine core for a marine engine:
http://marine.honda.com/Products/modeldetail/BF90EFI

Viking has a bunch of videos on Youtube:
http://www.youtube.com/user/eggenfellner

This latest endeavor from Jan Eggenfellner, may be successful. I've heard mixed reports, when comparing this engine to the Rotax in an RV12. Prior Subaru installations from Eggenfellner, fit more into the disaster group.
Some builders gave up. Others replaced the engine with a Lycoming, while others were willing to nearly give away the firewall forward engine & prop components.

The following link makes for interesting reading...... a Subaru project..

http://www.meyette.us/engineJul05.htm

L.Adamson
 
This latest endeavor from Jan Eggenfellner, may be successful. I've heard mixed reports, when comparing this engine to the Rotax in an RV12. Prior Subaru installations from Eggenfellner, fit more into the disaster group.
Some builders gave up. Others replaced the engine with a Lycoming, while others were willing to nearly give away the firewall forward engine & prop components.

The following link makes for interesting reading...... a Subaru project..

http://www.meyette.us/engineJul05.h...osting them upwards of $30k is beyond reason.
 
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I agree. The Viking engine is heavier, less power, more complex, and you are a test pilot every time you fly.

Don't forget that the Viking is about half the cost of the Rotax. That counts for something if it turns out to be reliable. Whether your LSA cruises at 120 knots or 110, it isn't as if you got into that category of aircraft because it is optimized for high speed X/C work.
 
Don't forget that the Viking is about half the cost of the Rotax. That counts for something if it turns out to be reliable. Whether your LSA cruises at 120 knots or 110, it isn't as if you got into that category of aircraft because it is optimized for high speed X/C work.


That is a HUGE, unproven "if".

A fool and his money are soon parted. ;)
Resale on these planes remains to be seen, but I can assure you the money they thought was saved is long lost ( and then some) on resale value of the plane. Longevity of the gear box is suspect based on the Subaru fiasco. They supplied one, but made buyers buy the revised ones? :mad2:

It is money down the drain, watch and see. Time will tell, and history is on my side. ;)
 
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That is a HUGE, unproven "if".

A fool and his money are soon parted. ;)
Resale on these planes remains to be seen, but I can assure you the money they thought was saved is long lost ( and then some) on resale value of the plane. Longevity of the gear box is suspect based on the Subaru fiasco. They supplied one, but made buyers buy the revised ones? :mad2:

It is money down the drain, watch and see. Time will tell, and history is on my side. ;)

I tend to agree with your extrapolation about the Viking, but it isn't a *proven* failure yet. So I've got my fingers crossed that someone may have assembled a workable engine conversion for the 100 hp market.
 
Auto engines are designed to run at 35% power maximum in a continuos static test. Any listed maximum horse power ratings are for short times. If you want to see a comparison of HP, take the HP rating for the engine and decrease it to 35%

Aircraft engines are designed to run at 100% power.

An aicraft engines TBO is developed by mounting the engine on a test stand with the correct prop and run none stop at 100% power till it breaks. even the worst aircraft engines would go 1200 hours.

When an auto engine has the same test, rarely does it make it past 300 hours.

Let's not forget though that the aircraft engine running at "100% power" is limited by the prop, and not the engine's true capacity to make power. That engine would be able to produce more power if it was allowed to turn faster (i.e. O-300 = 145 hp, GO-300 = 175 hp)

I think it is a misnomer to state that these engines are running at 100% or 80%. Heck, they're barely breaking a sweat when cruising along at 2300 RPM.

I like to look at it in terms of HP/CI. When viewed from that perspective, a modern vehicle doing 75mph down the highway is working just as hard as my 0-470-L is when cruising at 2300RPM.

I'm in no way arguing for the use of automotive engines in airplanes. Just stating that the airplane engines aren't really working any harder or at least not as hard as people like to say they are.
 
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