2 rotary vs lycoming comparisons

Kestrel452 said:
Seriously, what is your obsession with the Renesis, an engine that is clearly NOT built to aircraft specs?
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I don't have an obsession with any engine. Unlike others I like to put information out there that shows there are two legitimate sides. Anybody can choose one way or the other but don't go dumping on one just because you are ill-informed.

Don't get it twisted, I'm not being emotional at all in case it is taken that way. These postings are in response to a few posts I put up before regarding my homebuild and those were two unanswered questions.
 
OhioStatePilot said:
Automotive engines may not be expected to run at constant throttle settings for extended periods, but that actually creates a lower amount of stress on the engine than continually changing throttle settings and varying loads. Regarding a propeller mounted on a Wankel, you seem to be neglecting the fact that any engine sees gyroscopic forces. Flywheels aren't light.

There is a key design feature of the Wankel that you're overlooking Killtron. You feel more comfortable with a reciprocating Lycoming than a Wankel rotary. The forces exerted inside any reciprocating internal combustion engine far exceed those inside a rotary engine. The rotor in a Wankel never reverses direction, which results in a drastic reduction in forces seen on the rotor when compared to a comparable piston engine. You can see this for yourself by calculating the piston velocity at any given power setting for a reciprocating engine, and then calculating the forces exerted by acceleration when the piston changes direction at the end of each stroke. This happens thousands of times per minute and the stresses are seen on the piston, wrist pin, rod, cap, rod bolts, crankshaft, etc.

I'm not attempting to knock the standard piston engines we use today, but merely trying to show you a mechanical comparison. In addition, I'd suggest looking at NTSB reports involving Wankel engines. You'll notice that there are a relatively small number of failures associated with the converted automotive engines. I feel safe behind a Lycoming, but even I believe it's more likely to suffer a mechanical failure than a Wankel engine.

Interesting notes:

Curtiss-Wright was one of the first to have license for the Wankel. You might know the name as being associated with aircraft. Their RC2-60 Wankel engine powered an experimental Lockheed aircraft for the military. The soviets also used the Wankel engine to power aircraft, including helicopters.
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I know when you're bumping around in turbulence the load on the propellar is changed with every climb and descent and there are hundred of small ones during every flight. The power setting is probably going to be high a mazda probably uses 50hp cruising down the highway but a cessna for example with 160hp engine at a conservative cruise setting of 65% is going to use 104hp.

A reciprocating engine is designed to handle those stresses. I'm sure there are thousands of G's on those pistons but they can sustain that. Airplanes also have flywheels and I would imagine the propeller being heavier and most of it moving faster than the flywheel has much greater forces exerted on it. I'm not saying the wankel will fail straight out of the gate but under some combination of wear and circumstances who knows what will happen. There are dozens of AD's out for every model of lycoming because even the engineers couldn't imagine every possible problem that might come up for even a purpose built aircraft engine.

Like I said before I can only think of a few problems with this I'm sure there are a lot more that I miss because I never tried to design an engine.
 
Killtron2000 said:
...I never tried to design an engine.
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There ya go:laff: Years of use and approval doesn't count for anything. Oh yeah, I forgot that airplane engines use that special metal, alloy-carbohydrate:)

P.S. - Any engine will fail with the right loads and stresses on it.
 
The advantage of the tried and true aviation piston powerplants is that they are just that- tried and true. What annoys me, is that when you buy a brand new Cirrus or Baron or whatever you are effectively getting a 1930's engine with 1950's fuel injection in a horribly underpowered application. 8:1 compression? Come on. Again, the advantage of this is that the engine is so understressed it can't hurt itself, but the downside is a lack of power, and even if you don't care about power and climb performance and going faster, it hurts efficiency.

Anyone who is mechanically inclined understands the difference between a road car, which may use 15% of its maximum rated power at normal cruise speeds (and is expected to last at least 100k miles) and an aviation powerplant (or a locomotive engine) that cruises at 50% to 70% of maximum rated power and is still expected to last 2000 hours. Race cars produce significantly more power than a road car, but the motor only has to last a few races, and even then, failure rates are pretty high when measured as a percentage.

However, an interesting argument to make here, would be to use a higher compression ratio in the cylinder to enhance efficiency, yet limit the throttle body from ever being wide open. Doing this, one could arrive at say a 360 cubic inch engine, running say 11:1 compression, that produced say 240HP at 25 inches manifold pressure, and yet could still give the same 120HP for cruise flight, at 50% power, in a more efficient manner, than the current engine (O-360 at 180HP) running 65% power to make the same cruise power setting. This would give better takeoff and climb performance, and allow more efficient operation.

In terms of piston development, I think we'll see aviation diesels burning Jet-A before we ever seen a modern Otto cycle engine. But, for an Otto cycle aviation engine, liquid cooling the jugs would make for far more consistent operating temps and get rid of the problem of shock cooling. A higher compression ratio would engine maximum power and improve efficiency. Modern, port fuel injection (or perhaps even direct injection) and digital ignition with the ability to advance spark would help power and efficiency.

I don't think a Wankel for aviation use is a bad idea, mainly because it is just that- a rotary engine that doesn't have the enourmous loads of the piston reversing direction thousands of times a minute, but I think the real milestone, if we ever get there, will be the availability of a turbine engine for under $50k.

For what it's worth on the price side of things, I think that to keep GA alive, something has to be done about the cost of certified aircraft and the parts to keep them flying.
 
My experience with modified auto engines in aircraft (Thielert) has been underwhelming to say the least. Not saying it's inherent in all auto engines, but it is what it is.
 
Kestrel452 said:
Rotary engines just are not as efficient at utilizing the most power per drop of fuel like a piston engine is. I will bet you dollars to donuts that the FAA is not going to like your proposed engine swap. You are sacrificing tons of safety for just the ability to say you swapped an engine. You said it yourself, you have to put a speed reducer in between the engine and prop, which says in itself that it will be even more inefficient since you are literally dumping a chunk of that power.

Seriously, what is your obsession with the Renesis, an engine that is clearly NOT built to aircraft specs?
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- That's a blanket statement with no basis except emotion.
- A speed reducer does NOT dump power. A speed reducer allows an engine to operate in it's ideal RPM range while also allowing the propeller to operate in it's ideal RPM range. It's also known as a geared engine, just like what you might find on a Cessna 421. There was also widespread use in WWII aircraft, and I wouldn't say those were lacking in power.

Killtron2000 said:
I know when you're bumping around in turbulence the load on the propellar is changed with every climb and descent and there are hundred of small ones during every flight. The power setting is probably going to be high a mazda probably uses 50hp cruising down the highway but a cessna for example with 160hp engine at a conservative cruise setting of 65% is going to use 104hp.
A reciprocating engine is designed to handle those stresses. I'm sure there are thousands of G's on those pistons but they can sustain that. Airplanes also have flywheels and I would imagine the propeller being heavier and most of it moving faster than the flywheel has much greater forces exerted on it. I'm not saying the wankel will fail straight out of the gate but under some combination of wear and circumstances who knows what will happen. There are dozens of AD's out for every model of lycoming because even the engineers couldn't imagine every possible problem that might come up for even a purpose built aircraft engine.

Like I said before I can only think of a few problems with this I'm sure there are a lot more that I miss because I never tried to design an engine.
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Did you read my statement about running engines at constant power settings in comparison to the stop and go abuse an automotive engine endures?

Did you also go look at the NSTB findings and compare?
 
Sprint100 said:
There ya go:laff: Years of use and approval doesn't count for anything. Oh yeah, I forgot that airplane engines use that special metal, alloy-carbohydrate:)

P.S. - Any engine will fail with the right loads and stresses on it.
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You haven't designed an aircraft engine either and there is probably a level of understanding you aren't even aware exists.
 
Killtron2000 said:
You haven't designed an aircraft engine either and there is probably a level of understanding you aren't even aware exists.
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...Or maybe not. I don't know what your credentials are, but airplane engines and the engineering behind them are pretty dang simple, especially compared to something like the V-TEC engine in your average Honda.
 
OhioStatePilot said:
There was also widespread use in WWII aircraft, and I wouldn't say those were lacking in power.
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Apples and oranges.



OhioStatePilot said:
Did you read my statement about running engines at constant power settings in comparison to the stop and go abuse an automotive engine endures?
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Yes but that doesn't necessarily mean the engine can handle being run at 65% of its power for hours and hours without a problem developing. There are all kinds of things you and I don't even know about that can wear parts out from some combination of vibration and heat or whatever that the part wasn't meant to handle.
 
Killtron2000 said:
Apples and oranges.
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How?



Yes but that doesn't necessarily mean the engine can handle being run at 65% of its power for hours and hours without a problem developing. There are all kinds of things I don't even know about that can wear parts out from some combination of vibration and heat or whatever that the part wasn't meant to handle.
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Fixed that for ya... ;)
 
Sprint100 said:
Any engine will fail with the right loads and stresses on it.
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Exactly so why use an engine that was meant to handle different loads and stress under different conditions. Do you really want to risk having your last conscious thought being "damn killtron was right"?
 
Killtron2000 said:
Because if you take a 1500 hp engine and the gear reduction rob a few horsepower it isn't noticeable but might be with a much smaller engine.
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You don't seem to understand how a gear reduction drive works. It does not rob horsepower. In fact, HP is a contrived number.

HP = (Torque (ft-lbs) x RPM)/5252
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In actuality, torque is the force exerted by the engine, and horsepower is work (force per time). When you use a gear drive, it allows the engine to run at a higher RPM, which allows for an increased HP output (as above), while still allowing the prop tips to run at subsonic speeds.
 
OhioStatePilot said:
You don't seem to understand how a gear reduction drive works. It does not rob horsepower. In fact, HP is a contrived number.
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And this gear drive operates with 100% efficiency? I know power is the rate at which you can do work. And I know what those terms mean and I know the BASICS of how all this stuff work just like you I suspect.
 
Killtron2000 said:
And this gear drive operates with 100% efficiency? I know power is the rate at which you can do work. And I know what those terms mean and I know the BASICS of how all this stuff work just like you I suspect.
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Well...no, but it's not really that bad. The benefits of the increased power available outweigh the slight decrease in efficiency.
 
No, nothing operates with 100% efficiency. But you realize your perspective has downgraded from "it's going to fail because it's not designed for it" to "well, it's being robbed of too much power!" You've spent a lot of time qualifying your statements with words such as might or suspect and that's representative of understanding the basics. However, don't presume to guess what I know.
 
OhioStatePilot said:
No, nothing operates with 100% efficiency.
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So it does rob horsepower?


OhioStatePilot said:
But you realize your perspective has downgraded from "it's going to fail because it's not designed for it" to "well, it's being robbed of too much power!" You've spent a lot of time qualifying your statements with words such as might or suspect and that's representative of understanding the basics. However, don't presume to guess what I know.
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Killtron2000 said:
Yes but that doesn't necessarily mean the engine can handle being run at 65% of its power for hours and hours without a problem developing. There are all kinds of things you and I don't even know about that can wear parts out from some combination of vibration and heat or whatever that the part wasn't meant to handle.
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and you responded with this:


OhioStatePilot said:
Fixed that for ya... ;)
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And you haven't really mentioned what you expertise in this area is. So I haven't backed down from my original point this gear reduction thing is just another tangent to the discussion.
 
My background is in building, modifying, and maintaining road race engines and for a short time and a lesser degree, drag race engines. How about yours?
 
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