100LL

[KSCessnaDriver]

Excellent post, and all absolutely correct information, except for this. 8.5:1 is absolutely NOT "high compression." My Porsche street car runs 12.8:1 and is absolutely happy on junk pump gas. And yes, I drive it hard The race car runs 12.5:1 on 100 octane (R+M/2) unleaded race gas, and it stays wide open all afternoon and doesn't blow up. Plenty of tuner kids are running 25 lbs of boost on Supras and making 600HP out of 3 liters (in cubic inches that's only 190 cubes kids) at the wheels, and their motors don't blow up. The secret? Modern engine design. Modern engine management. Which means: no magnetos, and no manual fuel control.

So they make some power for a little bit. How long would a 600hp peak Supra run making 75% power all day long. My bet is not very long. It's just too tough to compare car engines (which make gobs of power for short periods) to airplane engines (which make quite a bit of power for a long, long time).

Plus, all the innovation is great, but the economies of scale just aren't there for GA. Why does Lycoming/Continental want to pour tons of money into new technology? They pour that money in, they've got to cover their costs somehow. The market just isn't big enough to spread the costs to the point that consumers would buy the things. Couple that with the reputation that Thielert go going for the diesels, and its going to be tough to make them sell.

Edit: Its not like they haven't tried different engines. The PFM engine was a horrible flop on the Mooney. Probably the only modern, widely selling aircraft engine is the Rotax 912, and even it is still carburetated.

 

[z987k]

There is. It's called 1930's engine design. Look at where cars were at way back when, and then wonder why you still have the same thing powering your airplane today.

Which brings up another point. Why the hell are we still using air cooled engines? We could run much tighter tolerances and make significantly more power with a much smaller engine. There would be no such thing as shock cooling, and the weight gain from the added components could be more than offset by a massive reduction in engine size.
Why no EFI? This stuff has been around for decades and requires no research other than implement it and test to make sure you didn't mess something up.

All this ancient garbage they pass off in aircraft makes me think the only reasonable airplane to own is experimental.

 

[Barty]

if a 8.5:1 engine needs 100 octane or 115 r+m/2 as you said, then something is seriously wrong with that engine design. Did they put pointy carbon spikes in the combustion chamber from the factory?
If vehicle manufacturers can produce engines that run on 87-93pump at 11:1. I think it's reasonable that an aircraft engine can run on 100 at 8.5:1.

Variable valve and ignition timing have a lot to do with that. Even still, auto engines at 8.5-9:1 compression have been running on 87 octane fuel for decades.

Aircraft engines run fixed ignition timing, which in my opinion is what holds back these engines the most in terms of performance and fuel selection.

 

[mshunter]

Edit: Its not like they haven't tried different engines. The PFM engine was a horrible flop on the Mooney. Probably the only modern, widely selling aircraft engine is the Rotax 912, and even it is still carburetated.

I woulden't exactly call the 912 modern. It's still a box (opposed) 4cyl. It borrows from a bunch of other technologies that also aren't so modern. Nikisil(the cyl. plating) has been in motorcycle engine for decades. All they really did was take a proven desgine, water cool the heads and build better cylinders. You could Nikisil Lyc. cylinders and get the same leakdowns. Hardly modern, just re-vamped. And you have to spin the crud out of them to make the same power, and hang a gearbox on it to make the prop work.

It'd be like calling the MDS(Multi Displacment Sys.) of a Hemi "modern." Hardly. It's still a pushrod V-8. Heck, it's still the same 2nd gen Hemi that Dodge introduced a few years back. They just stop the actuation of some lifters with a soleniod to shut down four cylinders.



P.S. Diesels are for trucks!

 

[Richman]

A couple of things:

1) Tuner cars aren't going to run 2000 hours at near %75 of their rated horsepower most of the time. Nor are they subjected to variable air cooling with significantly reduced air density.

2) Liquid cooling. VERY important. Maintains a VERY constant cylinder head temperature and provides even cooling with no hotspots. Sure, water cooling is great. Till you figure out what it does to your cruise performance. Oh, yea, and what happens when you bust a water pump? Or spring a coolant leak?

3) Variable ignition and value timing. Also huge in reducing detonation. Have a computer run the ignition. Super deluxe. What happens when the ignition power supply croaks? Ooops, no fire.

Aircraft engines are they way they are for a reason. Stone simple. Nothing fancy to break. You can lose EVERYTHING, and still have a running motor.

Oh, yea, and maintainable, forever. Ever try to find parts for a 1978 Cadillac with the fancy 8-6-4 cylinder fuel control? Good luck with that. Now go find a carburator for a 1943 Cessna 140, and I bet you can find a least a dozen places to buy one.

Continental tried the liquid cooling thing ages ago. Not compelling enough to make it worth while.

Diesels? Sure, but no panacea if you talk to Theilert. Not only that, %80, if not %90 of the GA fleet would be sent to the boneyard before the owners would spring for a $50k new engine for an airframe hardly worth that. Without the fleet numbers, you have no GA. Which will push the price for everything else into orbit.

Richman

 

[ASpilot2be]

According to BP, they are going to stop producing 100LL in ten years.

 

[KSCessnaDriver]

I woulden't exactly call the 912 modern. It's still a box (opposed) 4cyl. It borrows from a bunch of other technologies that also aren't so modern. Nikisil(the cyl. plating) has been in motorcycle engine for decades. All they really did was take a proven desgine, water cool the heads and build better cylinders. You could Nikisil Lyc. cylinders and get the same leakdowns. Hardly modern, just re-vamped. And you have to spin the crud out of them to make the same power, and hang a gearbox on it to make the prop work.

If you look at it that way. Compare a Rotax 912 to a comparable aviation engine (O-200) and it is much more modern (Water cooled, much lower displacement for similar horsepower, etc). They've been working on putting fuel injection on them, but from what I've heard, all it does is increase the fuel burn. At least the 912 can run on Mogas with ethanol in it. I'd just like to see them build something that is in the 160-200 hp range, ala O-320/360. Could be sold with an STC for tons of airplanes.

 

[Patrick]

A couple of things:

1) Tuner cars aren't going to run 2000 hours at near %75 of their rated horsepower most of the time. Nor are they subjected to variable air cooling with significantly reduced air density.

2) Liquid cooling. VERY important. Maintains a VERY constant cylinder head temperature and provides even cooling with no hotspots. Sure, water cooling is great. Till you figure out what it does to your cruise performance. Oh, yea, and what happens when you bust a water pump? Or spring a coolant leak?

3) Variable ignition and value timing. Also huge in reducing detonation. Have a computer run the ignition. Super deluxe. What happens when the ignition power supply croaks? Ooops, no fire.

Aircraft engines are they way they are for a reason. Stone simple. Nothing fancy to break. You can lose EVERYTHING, and still have a running motor.

Oh, yea, and maintainable, forever. Ever try to find parts for a 1978 Cadillac with the fancy 8-6-4 cylinder fuel control? Good luck with that. Now go find a carburator for a 1943 Cessna 140, and I bet you can find a least a dozen places to buy one.

Continental tried the liquid cooling thing ages ago. Not compelling enough to make it worth while.

Diesels? Sure, but no panacea if you talk to Theilert. Not only that, %80, if not %90 of the GA fleet would be sent to the boneyard before the owners would spring for a $50k new engine for an airframe hardly worth that. Without the fleet numbers, you have no GA. Which will push the price for everything else into orbit.

Richman

1. Correct. I was never insinuating that we put a 600HP at 7000RPM 3.0 liter engine on an airplane. However, an IO-550 with 10:1 pistons and modern management would easily make 400 some HP without a turbo, and would cruise MUCH more efficiently in terms of fuel burn and would still go to TBO just fine.

2. Liquid cooling is the answer. Even Porsche realized this eventually.

3. You don't need variable valve timing in a low RPM engine, especially one that only operates over a very narrow RPM span. However, modern ignition is a HUGE advancement, as you aren't stuck with fixed timing. Likewise with modern EFI. Let the computer monitor EGT, CHT, coolant temp, and power setting and determine the mixture that will create the most power the most efficiently.

As to making this stuff work on an airplane, it's easy. They're had stand alone, batteryless EFI on snowmobiles and motocross bikes for years. You can't tell me a system that can survive that environment can't survive in an aircraft. And to those of you worry-warts, you still have two of them (upper and lower, just like mags) so if one craps out the thing still runs.

None of this is rocket science, it's just held back by the economics of the cost of certification, and then the liability that the companies who'd introduce this bear.

 

[Patrick]

If you look at it that way. Compare a Rotax 912 to a comparable aviation engine (O-200) and it is much more modern (Water cooled, much lower displacement for similar horsepower, etc). They've been working on putting fuel injection on them, but from what I've heard, all it does is increase the fuel burn. At least the 912 can run on Mogas with ethanol in it. I'd just like to see them build something that is in the 160-200 hp range, ala O-320/360. Could be sold with an STC for tons of airplanes.

It is more modern than an 0-320/360, but it's still a far cry from being a modern engine.

If I felt that I'd have any realistic chance of returning the investment and making some money, I would take on this challenge. To me, there's nothing inherently wrong with the basic layout of these ancient motors, and the internals, while not modern, are proven. They really do need liquid cooled jugs, however. A bit of work to get the heads to flow better wouldn't hurt. A tuned induction and exhaust system (absolutely zero reliability concerns to those who would ask) and as previously stated, the biggest gains would come from modern management of the engine and we could be seeing massive improvements in power and efficiency and no concerns at all of the prospect of moving away from leaded avgas.

You want Nikasil'd bores? ECI offers it as a product they've trademarked Cerminil.

Everyone wants to talk about how simple and reliable these things are (ever seen the inside of a mag? LOTS of moving parts) and how great that is, and there is some merit to that, but let's be honest, how many modern, well maintained cars do you see on the side of the road because the engine ECU died? I'm willing to bet that the percentage of cars that that pull over due to engine related issues, as a percentage of say fleet miles driven, is lower than that of piston aircraft who have had to make unplanned landings due to magneto or mechanical fuel injection problems.

Problem is, we're never going to get modern Otto cycle engines in aviation. We'll have modern diesels LONG before that ever happens, and thankfully, the diesels that have been put into light aircraft are state of the art.