I don't know how many times I've read this, or heard this. Not an apples to apples comparison. The actual RPM's are similar. My car cruises at 2300 rpm, just like the plane. It's the percentages that, while accurate, are intentionally misleading.

"Car" engines are virtually always measured and advertised for PEAK or MAXIMUM horsepower that it can produce. Horsepower being a measurement of torque, and multiplied by RPM, in it's simplest form (there are many world standards for this, but the basic theory remains). Twisting force, measured over time.

If you were to spin the Car engine faster than it's maximum horsepower, it will actually make LESS POWER. For the typical RATED horsepower engine, like an airplane piston engine. If you were to spin one faster than the RPM with which it is RATED for it's horsepower, it will generally make more power (until the dinosaur engine blows up, or it reaches its PEAK power, if it's still running at all).

Any industrial, mostly steady state engine will have a similar rating.

If I had two identical sized engines, say an unmodified Lycoming 360 and a Chrysler 360, they would make very similar power at 2700 rpm. But, the water cooled 8 cylinder Chrysler will be much, much heavier, and WAY cheaper (mostly do to mass production and no FAA certification), than the limited production, air cooled, 4 cylinder Lycoming. That 2700 rpm is 100% for the Lyc, and maybe 40% for the Chrysler. Same power, same size cubic inch displacement engine, vastly different %'s.

I wouldn't even want to guess how much money you'd have to spend to make that same Lycoming stay together at the RPM and Horsepower level that can relatively easily be produced by the Chrysler.



Destroyed?????? Come on. That TIO-540 could be derated overnight in any number of ways to continue operation in a "worse-case" scenario.

The compression ratio could be lowered, relatively cheaply with a piston change. The turbocharger manifold pressure could be reduced. The ignition system could be modified.

Jet engines typically take off at some "flex" or reduced setting. Adopt a similar strategy for pistons. That would be a short term answer if lead was lost tomorrow, and mostly a paperwork exercise. Yes, there may be some short airports that won't be available.

The reality, however, is that compression and manifold pressure could probably stay the same, and virtually everything fixed with ignition and fuel delivery, at the same or even slightly increased power at less fuel burn... JUST LIKE CARS, MOTORCYCLES, AND THE REST OF THE WORLD !!!!

The piston aviation business drags its feet to advance engines at its own peril, in my opinion. You can fill in all the reasons why, but the fact will remain.

 

If you are making the point that these two types of engine are different in several ways, I tend to agree. But they are mighty similar as well, specifically, typical dyno curves for these two engines are similar even if the airplane engine stops revving at 2700 RPM while the car engine keeps going. But this does not shoot any holes in the percent-of-design-RPM-operating-range analogy. Yes, they have different approved RPM operating ranges and each is designed with its own range. However, many authorities on the subject seem to think the percent-of-RPM-operating-range analogy is valid. You suggest that airplane engines are not as strongly built as car engines, probably so. They are optimized for light weight with a fairly low limit on upper RPM range. If you rev them beyond their approved operating range they self-destruct. But they are strong enough for their approved operating range, and they are used at a high percentage of it as well. To say the designs are somewhat different is correct, but this does not serve to nullify the present analogy.

Nothing I said above is comprised of my own opinion. Your statements about certification and poor economies of scale adding much to the cost of making of airplane engines or even tweaking them against knock, is quite true. But to broadly say the airplane engine industry drags its feet on purpose is faulty. They would love to mass produce airplane engines like Ski Doos and Toros and put a couple of airplanes in every yard. Airplane engines are held to higher standards than car engines and even tweaking them with piston of cylinder head swaps costs far more in terms of certification and manufacturing than for the same in a surface vehicle. Same technology, different cost. If you are saying it is intentional on their part to stay behind the other manufacturing camps, well I doubt it. They go where the FAA allows and the money is the best. If there is price rigging going on here, I would say to blame it on the FAA.

 

Durban company flies high on biofuel: Durban company has unveiled a light aircraft engine which can operate on biofuel or liquid petroleum gas.

[See also previous article here]

(5/17, Sapa, Times Live) "Our technology benchmarks South Africa against the finest aviation engineering in the world,” said Andre Schoeman, chairman of ADEPT Airmotive, the company that developed the engine. The liquid-cooled engine, with advanced electronic engine management, was launched at Virginia Airport in Durban.It was fitted to a South African designed SA Ravin 500 light aircraft.The department of science and technology invested R10.5 million to fund ADEPT Airmotive to a pre-production stage.“Through investment in local research and development, it is fair to say that ADEPT is providing the catalyst for a genuinely world class general aviation manufacturing industry,” said Schoeman.He said the engine produced 320 horsepower, and boasted the lowest lead, nitrous oxide and carbon dioxide emissions and noise levels. United Kingdom based AgustaWestland Helicopters also provided financial support to ADEPT's certification process through the European Aviation and Safety Agency (EASA).

 

They think it's valid because they are absolutely correct. Aircraft engines operate at up to 100% of rated power.

If I used the above example of a Lycoming / Chrysler 360 cubic inch engine; if they RATED the Chrysler's horsepower at 2700 rpm just like the same cubic inch Lyc, now we have a more "apples to apples" comparison.

It's a paper exercise to hopefully more clearly make my point. But in reality, Chrysler DID make (not sure about now) "Chrysler Industrial" engines based specifically on their auto versions, that were flat rated JUST LIKE AIRCRAFT ENGINES. Same hunk of cast iron as an engine in a car, with typically a few simple modifications like stellite valves, hardened valve seats, more robost torsional dampening, etc.

With both of the above referenced engines at "100% power" at 2700 rpm, I'm not so sure which engine would last longest. My money would be on the liquid cooled engine with modern fuel and ignition. There's no magic in a Lycoming. It's crude, simple, very old technology. Noisy, high on vibration, couldn't pass an auto emission test no matter what, very expensive, and light enough to be used in airplanes.

 

Several people have expressed various shades of doubt on this thread that the FAA, Continental, Lycoming, and various parties are honest and forthwith. In this case the concern is that certain airplane engines, usually higher compression 6 cylinder models will not operate reliably on unleaded gasoline and therefore cannot be approved for it. This could be a conspiracy attempt on their part. There also may be aliens living among us, which is the beauty of any conspiracy theory in that you really don't know. The suspicion usually is along the lines that these agencies want to retard the development of new airplane technology, keep prices fixed, keep automotive suppliers out of the business, disallow Mogas from airplane use, and of course always go unchallenged. So if it boils down to a matter of trust as far as what these so called aircraft authorities say, then I guess I trust them. Maybe they are erring on the side of caution and maybe you can drop a couple of $900 AutoZone rebuilds into your Beechcraft Baron, burn Mogas all the time, spend the other $49,000 on a backyard pool and all will be well between you and the airplane. But it's really not for me to say. I certainly cannot contradict established experts without some pretty strong evidence to back it up. As of now, the latter are saying that we need a substitute for leaded Avgas for certain airplane engines.

 

My old watercooled japanese sedan cruises at about 3000 rpm, it has 190K miles, and well on track to make it to 250K. At an average 50 mph, that's about 3800 hours without a mechanical hiccup.

Aircooled VW's usually last about 100K (if you take care of them). Assuming an average 50 mph and 3000 rpm (also pretty typical), that's 2000 hours. Sounds familiar?

The only two advantages to aircooled engines are weight and mechanical simplicity, which translates to more reliability with respect to fewer things which can go wrong.

The big disadvantage AC engines have is tolerances...for max wear longevity you want parts machined to very tight tolerances, just enough to allow for the needed oil film but no more. Loose tolerances allow parts to flop and bang
around (especially at high RPM or load) drastically increasing wear.

Since different materials and sizes of parts expand at different rates, there is only one temperature where any two parts will have the ideal fit with respect to each other.

With a WC engine, you design the parts to be at the ideal tolerance at normal operating temp (NOT). When you start the car, it is not at NOT so there is potential for flopping around. That's why you should go easy until the car warms up. After 5 minutes or less, the WC engine is at it's NOT with ideal parts tolerances and there it stays. The colling system maintains NOT under a wide variety of laod and OAT conditions by adjusting coolant and air flow and/or The only way to screw that up up is by seriously overheating the engine.

But the AC engine does not get to stabilize at a consistent temp, normal load and OAT variations mean that there is wide potential range of "normal" operating temps. If you design the tolerances to be ideal at some median OAT and load, they would be too loose or tight under other conditions. Since loose is better than too tight, an AC engine under typical conditions is operating with loose tolerances which means more wear than a comparable WC engine.

Aircraft engines have an advantage in that they spend more time at a predictable rpm than a auto engine, but they still have to allow for T/O power on a hot day (or flight training ops).

Modern design, manufacturing, and QA techniques (and synthetic oils) have almost eliminated random mechanical failures so the simplicity of AC engines no longer counts for much. A WC engine is probably more reliable for abuse operations like flight training.

There is still weight savings but I think as WC airplane engines become the norm we will find that higher TBO's and fuel efficiency offset the benefits of lighter AC engines.

 

Rick, all that is true, but the single largest problem facing aircraft engine manufacturing is the poor economics of making a new model. You are going to make a new aircraft engine at an enormous cost of development and then sell maybe 5,000 or 10,000 of them total. By contrast, the engine in my Nissan Frontier is the VQ40 model, and the VQ series in some stripe or other is used in an enormous number of brands, sizes, models, and even multiple countries. Nissan will sell literally millions of these engines before moving on to the next design. So its not really a matter of design or even willingness to design something better, it is a matter of economics.

 

Obviously, lead needs to be removed from the gasoline that we use. It should have been done a long time ago, and it will get done. And all the excuses will look pretty lame as to why it didn't happen sooner.

Besides cost of aircraft engines based on scale of production, the government certification is probably the single biggest cost. Both become economic.

Experimental aircraft that use non-certified engines that can burn unleaded gas do so at a much cheaper price, because they typically use cheap mass produced engines that are already designed for unlead gas, and because the government hasn't increased the cost through certification.

Hopefully the LSA class will remain closer to the experimental class than the "certified" one.

By the way, these "certified" Lyc's and Continentals have no problem "blowing a jug" or otherwise failing quite spectacularly. I'll take a Toyota design (they did certify a V-8 engine in a Navajo and a Malibu, if I recall correctly).

 

I know, but I think there may be potential for conversion of stock LC auto engines to aviation applications...I think both Diamond diesels are based on automotive plants.

 

Mercedes Benz.