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To aero engine or not to aero engine.......that is the question

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ekimneirbo

Well-Known Member
Joined
Oct 31, 2014
Messages
1,009
Location
Deep South
When building an airplane one of the first questions a builder must consider is cost and type of engine. Now let me say
right up front that choices will vary greatly with the type of airplane you wish to build. Small and smaller engines generally
are used in smaller,lighter,and slower flying airplanes. There are specialized exceptions. Then you move into the midsize
area where choices begin to expand somewhat with water cooling and turbocharging sometimes being employed. Moving on
up to engines above 350 cu inches........almost anything can be made to work if it produces plenty of power because you
generally are using an airplane designed for the heavier engines. Nothing is always true,you have to use generalities until
you get specific about what airplane you want to build and what its purpose in flight will be. Fast,slow,crosscountry,STOL,
single passenger, etc. Define what YOU want and then you can narrow down your choices. If you decide to go with a non-
traditional aero engine, there will be plenty of people to tell you why not. Its impossible to address auto conversions because
the absolutes of conversion do not apply.
I say this because each conversion has its own set of details to work out. Putting
an VW or Corvair will not carry the same benefits or detriments that a water cooled V8 will entail. So, when discussing
conversions, don't let the naysayers convince you that it can't be done. Oshkosh is full of sucess stories every year.

Back to the purpose of this thread........to aero engine or not

I'm sure that everything I say here will be construed negatively by believers in only using an aero engine, thats just the way
things are. But, the things I say here will be my considered opinions and true as far as I know.

First, let me say that from its birth at the factory, most commonly used naturally aspirated aero engines are very reliable
and expensive. There have been some notable exceptions and a few duds from the factories, but for the most part they are
pretty reliable.

Once the engines begin to work in the real world, used by ordinary imperfect human beings, many things can happen to them.

Each engine will come with a log book where every detail of its life and maintainance will be thoroughly documented. Don't
believe that myth. While its a good selling point and gives the buyer a feel good moment....it really not reliable.
What can go wrong....everything from a dishonest seller to an honest omission.

"Well it was just a minor prop strike in grass, nothing to be concerned about. If I document it, the engine will need to be torn
down for inspection and thats pretty expensive. Guess I'll just check the run out and if its ok, that'll be fine"

"Hmm noticed a little rust inside the crankshaft, but there is always some in these engines, probably nothing to worry about"

"Cylinder head temps seem a little high these days, but the engine runs fine....probably nothing to worry about."

"The oil sample showed a little metal in it but it was within specs, so I guess it doesn't need to be documented."

Lots of things go undocumented in the life of an engine. I remember one day many years ago walking along the grass at a local
airfield and coming upon a member of the local club who had his Cessna 150 engine partially disassembled. Being new to the
sport I didn't realize what was going on. I stopped to talk and he stressed the point that I should not mention to the AP/airfield owner
what he was doing. Eventually the fellow was forced out of the aero club because of his continued attempts to circumvent proper
mainataince and insurance for his airplane. He had a garage/hangar that backed up to the airfield. One day he landed his airplane
and rolled it in the hangar. Shortly thereafter the airfield owner placed a large dirt berm right next to his hangar door so the airplane
could not be taken out again. About ten years later I bought the airplane and removed the wings and brought it home. After a while
I decided it would be too expensive to repair the engine and sold the whole airplane to a dismantler.


Another time I worked on an engine that had been recently rebuilt by an AP and found that he didn't know the engine was
supposed to have oil squirters in it.....and he was teaching me.

You have to remember that the fifties, sixties, and seventies were a totally different era from today. We didn't have computers
everywhere. Information was not at our fingertips or even available. People had less disposable income and had to make do
with less than optimal conditions.A lot of todays engines were manufactured during that time and are still doing duty today.
You do not know what has transpired in the life of these engines no matter what log books say....and many engines don't
even have a log book. Did you ever wonder why someone would lose the log book for an expensive engine?

Another thing, when aero engines do go bad all of the attendant parts are always salvaged and stored for some future use.
While rebuilding several engines, I was directed to a stack of connecting rods from salvage engines to replace one in the
engine I was assembling. Although they all looked similar, I decided to employ an old racers trick and weighed the con-
necting rods. I couldn't believe how much difference I found in the weights. No wonder those engines vibrate.

My point is that its difficult to consider the myriad number of things that have happened in an engines life, or to believe that
all of these things were properly documented by the thousands of different individuals who have been involved with them.


While I'm sure I can't think of all of them, here is a list of things to start the potential buyer thinking.

1. Why is this engine for sale? Where did it come from?

I would have to wonder why this engine was pulled from a perfectly good airplane.

2. If the airplane was sound, and the engine run out (TBO)....why wasn't this engine rebuilt and reinstalled?

3. If the airplane was sound, why wasn't the engine used as a core for a replacement?

4. If the airplane wasn't sound, why was it no longer usable?

5. If the airplane was no longer usable due to setting, how long did it set and have the internal parts rusted.
(remember that no entry would be made in the logbook because no maintaince has been performed)

6. If the airplane was no longer sound due to a crash or ground incident, the owner of the aircraft might not
be around to document the incident and his heirs are just getting rid of stuff.

(I noticed today that there is an airplane and engine for sale on HBA that had an incident many years ago
which supposedly damaged a wing and was never flown again. His heir is now putting the engine up for sale.
While it may be perfectly sound, I would have to wonder about the engine and documentaion...and now there
probably isn't anyone who could give a detailed account of what happened. So, does the log book tell all...or not?

7. Has the engine you are buying had all ADs completed or will you have to buy parts to bring it up to compliance?

8. Have you researched the "type" or model of the engine to see if it was one of the problematic versions.

9.Is the engine a thick or narrow deck model and will parts always be available for narrow deck versions?

10. How many total hours does the engine have on it? How many times has it been overhauled?
Do you know if the crank was ground or polished undersize?

11. Have any modifications or parts swapping been done in its history? (compression ratio changes etc)

12. Are the magnetos still viable and serviceable and are parts available for them?

13. Is the engine you are buying know for having or susceptable to internal crankshaft rusting?
(This can result in scrapping the crankshaft)

14. Are all the cylinders on the engine made with the same internal surface and does the log book reflect that?

15. Have any of the valve train components ever been replaced? (If lifters were galled and needed replacement,
then the camshaft probably has some issues. If lifters were replaced...was the camshaft inspected or replaced too?)

16.Has the carburetor ever been rebuilt? If you have a high time engine its not unreasonable to think that the
internal parts and surfaces of the carb may need reconditioning. It may still work but you should check it out.

Note: A friend of mine completely rebuilt a Champ. On its maiden flight,the engine sputtered and quit and the airplane
was a total loss. Upon investigation it was discovered that the float had a large hole in it....and he had just had it
rebuilt by a well known airplane carb rebuilder. The insurance company took the airplane and sold it. Did the log
books reflect what had happened? I don't know............


The thing I want to point out here is that a well maintained aero engine is usually a robust and reliable engine....but it must be
maintained well in order to continue that reliability. The simple fact that a builder is trying to locate a used engine demonstrates
that they are looking for a cheaper way to get flying....and that in and of itself reflects the fact that many decisions about
the engine you buy and use will be economic in nature. While these engines built their reputations for reliability and safety
based on their original condition as delivered from the factory and many have continued after a 2000 hr TBO........you have to
realize that the engine you are buying is essentially not the same engine. Runs as good as new is not the same as being mechanically
new. My neighbor sold his well maintained 92 Chevy pickup the other day. It ran perfect with 249,000 miles. It ran "as good as new"
but I'm sure most mechanically inclined people would realize its only a matter of time before the timing chain gives up or some other
singular part reaches its limit. So "runs as good as new" really doesn't tell you much about the true condition of an engine or what may
be lurking inside the engine.

I have to give up the fact that an aero engine for the most part is easier to install and get running than any aero conversion will be.

Its all about what you enjoy doing and what makes you feel comfortable with YOUR build. While ongoing problems in a conversion
will ruin some peoples aero experience, those who successfully complete a conversion will have an added sense of pride in their
accomplishment. Hope you enjoyed reading this. If I forgot anything, please add it in. If you disagree with my opinion, well throw that
in too.:)
 
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