Originally Posted By: fdcg27
Originally Posted By: dwendt44
IIRC, Volkswagen modified a auto engine to work in a light aircraft.
Did very well, quieter, better fuel economy, etc....
This was same years ago.
Lycoming and Continental engines are basically old designs, with up-dates.
Fornier powered gliders (a bit of an oxymoron, but this is a class of aircraft) used VW flat fours. Mira Slovak flew one of these across the Atlantic.
Porsche did build and certify a flat six. The only application I recall for this Porsche Flug Motor was the Mooney PFM. The engine has long been gone from the scene.
The thing about auto versus aircraft engines is that aircraft piston engines are typically direct drive. The prop is bolted directly to a flange on the crankshaft. Since the prop tips must not reach the speed of sound, which causes a huge loss in efficiency as well as a horrible increase in noise, aircraft engines make their rated power at around 2200 revs. They typically make around 30 bhp/liter and are a few times more costly than auto engines of similar output. Auto engines turn quite a bit faster, so some sort of reduction drive is required.
Also, aircraft engines have dual magneto ignition and can run on left, right or both with the engine's ignition being entirely independent of the aircraft electrical system. Fuel injection is common, but it's a simple and dead reliable mechanical system. Many aircraft still fly with carburetors. Turbocharging is also widely used, but not typically to boost output at sea level. There are some engines that always operate at greater then ambient pressure, but they are usually not long-lived in service. Forced induction is most commonly used to maintain output with altitude in aircraft applications.
All of the above applies to powerplants for type-certified aircraft. For a builder intending to license something in the experimental category, any engine can be used although most of the higher-end kit planes use real (and expensive) aircraft engines.
Then there's the gear box, don't forget that fabulous point for catastrophic failure! You gott have that in there yo hey the rpm down. That adds a whole mother element and maintenance issues. Seriously the only saving grace in those old continental designs were the hugely sloppy tolerances on everything. Built like an AK 47 and the 4 bangers vibrate and shake like a mixmaster.
I recall a 1994 article from avweb telling of a trip through the process by which the turned in core engines were re manufactured back to zero time ( new) by the definition. They take em apart piece by piece tossing the hardware but piling like engine components in bins. Somebody takes all those parts from the bins inspects, x rays as necessary cleans and checks tolerances with a michrometer as needed. Then that same collection of everything that came in with countless hours many decades oldp,accidents, prop strikes and who knows what goes right back into making a new recertified engine. It does get new jugs and pistons, rings ect. All for the princely sum of $15000 at the time. [censored] I could do a better job on my workbench and at least would know how nasty worn and old my parts were.
The one that cinched it for me was the AD to stuff a dowel down on top of a piston to sort of lock it up and wiggle the prop to feel for slop. This was for newly replaced 0200 4 cyl Continentals that power Cessna 150s. If under 25 hours don't bother and all others disregard. If you had one and it wiggled sloppy you had main bearings for an 0300 6 cyl. And had to pull the jugs and switch bearings immediately as a few planes had caged engines at inopportune times. And you want to pay $15 G for that sorta job, not this old boy.
I owned a plane too long to believe everybody puts everything in log books. There's more info in what's not there than what is in most instances and sticking props in the dirt is common. That almost always stops em dead and often requires a tear down. So just remember that engine you're bettin your life on somewhat has connecting rods and a crank shaft that came out of...........a pile .
I will say some of the newer Rotax stuff is pretty nice in spite of there being that little issue of having to send them back to the factory and have the case split every 300 hours. For $1800 ish I'm told. Even then they cost nearly as much as a certified sort with parts nearly the same lofty figures. At least those with more than 85 hp. With all that in mind it's pretty easy to see why light aviation is continuing its death spiral.