Auto engines for homebuilt aircraft

[briankk]

Some thoughts on using auto engines in aircraft:
The aircraft does not care how much horsepower or torque the engine makes, only how much thrust the propeller provides.

The propeller will not perform well if the tips are going supersonic, so RPM is going to be limited. You can attach a gear machanism to reduce the prop RPM. Remember to add the weight of the PSRU to the engine when making power/weight and weight/balance calculations.

The aircraft cares quite a lot how much the powerplant weighs, it influences the proportions of the aircraft (balance) and the structural requirements, and finally the overall weight of the whole thing. Which is why there are so few flying diesels.

There are two things auto engine manufactures can be depended on to lie about, how much their engine weighs, and how much power it makes.

The engine must be capable of running WFO for extended times, say more than 10 minutes at a time under full load.. This usually means that the CR is going to be limited to keep the engine from overheating.

I recently read on one of the F1 forums that Ferrari says that their engine has to run WFO for 24 seconds as a time at Spa. They seem to think this is a long time flat out.

So keep in mind that your conversion will be compression limited and RPM limited, and must still have a good enough P/W to be useful as intended, say 10:1...

Yes I do know that Pietenpols can fly with model A engines. I just don't care..

[seattle smitty]

Those are good, valid thoughts, Brian. Here are a few more:

I resent owning an engine (or anything) that I am legally discouraged from opening up and maintaining, repairing, or modifying as I choose. As long as the aircraft says Experimental on the side, and family and passengers are made to understand what that means, I think I should be able to feel free to work on any part of it.

I resent paying huge sums for an engine which doesn't merit huge sums, especially when the huge sums are largely related directly and indirectly to the activities of lawyers. I detest lawyers, who produce nothing, contribute little, and whose enormous influence impairs many activities that interest me. You all have seen those descriptions of how many months a year each of us is working for the government rather than for ourselves. I would like to see a similar figure arrived at for how many months we work for the lawyers, either directly or because of the influence of their wretched trade. In fact, much of what goes to the government is actually due to industrious lawyers, not politicians.

If Ferrari wanted to build an engine which would repeatedly and reliably maintain full climb power to maximum altitude, they could certainly do so. It might take them two tries to get to the engine we'd want. It's too bad Porsche only made one try, because their "B model" surely would have been a good one. But they probably tired of dealing with the ramifications of our legal system. Maybe somebody here knows the whole story. I know that such masterful engine makers as Yamaha have looked at aircraft engines, considered the legal exposure, and said, "Forget THAT!!"

If Lycoming, Continental, and other traditional aircraft engine suppliers were not constrained by the costs of meeting FAA requirements, and if the FAA could base its requirements soley on practical issues, and if both manuufacturers and FAA were not having to cower beneath the ever-looming specter of lawsuit-hell, new engines from those companies would be better than they are now and much cheaper.

Aircraft engines are built to do a job and avoid lawsuit-hell. Automotive engines are built to do a (different) job and be cheap. But auto engines are raced, so parts and techniques are available to upgrade their reliability, efficiency, and suitability for aircraft use. They still might not be ideal, but can be plenty good enough, especially since the certified aircraft engines aren't ideal, either.

Water cooling systems add weight. But air cooling fins weigh more than water jacketing, so the real final weight difference isn't as much as some think. The opposed-cylinders ("boxer") layout is the lightest weight configuration for a piston engine. But they still sound bad to me . . . .

[DavidHarsay]

Not sure about Magnum, but Victor still makes the "Black Edition"

Victor Aviation Service, Inc.

They never indicate "performance gains" on certified aircraft engines, as the certification for the engine, airframe, etc. is for a set power at a set RPM, etc.... so it's always safety, smoothness, fuel efficiency, reliability, etc.

Originally Posted by seattle smitty

...I resent owning an engine (or anything) that I am legally discouraged from opening up and maintaining, repairing, or modifying as I choose...

Couple of thoughts about this... because if it's one of your more significant reasons for not going with an aircraft engine, there are other things to consider.

1. There's a pretty good market for non-certified aircraft engines, and this also means significant cost savings. I'm referring to used stuff out there, but Lycoming even makes engines for non-certified aircraft (and also different vehicles like air-boats which very similar to aircraft engines, but not certified) Since you want to do the work yourself, non-certified parts are much less expensive, and you're free to make your own, or modify as you wish. Most of the stuff is pretty beefy.

2. Your're not legally discouraged from opening them up and modifying as you see fit any more than you are legally discouraged from modifying a Chevy small block aircraft engine conversion.

3. There are companies who specialize in hot-rodding aircraft engines, and there's an aftermarket for high performance non-certified components. Many sport avation people hot rod and race aircraft engines with significantly more power output than stock.

4. Aircraft engines are designed for low RPM use, swinging a prop which is also a large gyroscope, and the other demands of environment much different from any automobile or race car.

Most home-built aircraft use an aircraft engine, and at least half of those are not actually certified. The auto engine projects are statistically musch less reliable in an aircraft operating environment than the aircraft engine counterparts.

The only significant advantage I see with auto engines is cost for a home-built application towards the high power end of the spectrum.

Remember, you can have only two of the three desirable attributes pertaining to aircraft... cost, speed, and safety. If its safe, and cheap, it's definitively not fast. If it's fast and safe, it certainly isn't cheap. If it's cheap and fast, it sure as hell ain't safe!

Here's one place I googled:

Performance built Lycoming and Continental aircraft engines

Look at the different links for prices for certified and non-certified...

Dave

[BlackCat13]

Originally Posted by briankk

Some thoughts on using auto engines in aircraft:
The aircraft does not care how much horsepower or torque the engine makes, only how much thrust the propeller provides.

It takes power to push that air rearward.

[seattle smitty]

In my first sentence when I initiated this thread, I said I was hoping to get some "educated input." It's working!! I'm getting educated . . . well, better than I was, anyway.

Dave, I was aware that people are upgrading aircraft engines where they don't have to be certified (air-racing hop-ups, for a long-time example, and Vizard's IO-540 here), but have ASSUMED that the finished cost of such engines would still be well above the cost of an owner-upgraded automotive engine installation. Since I was attracted to the Rover-Buick engine in particular, I never investigated your alternative possibility with due dilligence. I probably should. Someone has pointed out that if you don't need the highly-in-demand 180hp Lycoming, the 150hp engines can be had relatively inexpensively. And a long time ago you could find mil-surplus Continental 220 radials that had been tank engines or some-such, but I expect that source has long-since dried up.