ekimneirbo
Well-Known Member
Just my opinion
Why aren't there more auto engines used in airplanes?
The basic idea to many new builders is that you purchase a used engine, mount it in an airplane and bolt a prop to it.
While this can be done, and has been done.....it really requires more thought and caution than the simplified idea
presents for consideration.
1. Well meaning builders will immediately provide a multitude of reasons why NOT to use an auto engine.
I think this is the main reason many potential builders abandon their dream. They look at the costs involved in using
an engine designed just for airplane use and decide they can't afford it, and have been sumarily cautioned against the
pitfalls of using an automotive engine.
2. Many builders have little knowledge or experience with engines and are hesitant to try to learn.They may not
have the aptitude forassembling mechanical assemblies. What they want is a proven conversion that can be
purchased for rock bottom prices. When they find that purchasing a proven conversion will rival the cost of a
certified engine, they again decide not to build.
3. There is continual misrepresentation/misinterpretation of data concerning auto engines and aero engines. One
continual comparison is that the auto engines can never compare to the reliability record built by certified engines.
While that is a somewhat true statement in airplanes, auto engines are more reliable .What you have to accept is that you are comparing the records set by professional
manufacturing companies, overseen by government regulators,and maintained by professional mechanics. They
are then installed in professionally designed, tested, and manufactured airplanes. Further, both the engines and the
airplanes are then required to be inspected and maintained to professional standards. Would you expect ALL
homebuilt airplanes to be built equally as well? I mean its a given that with every homebuilt being a prototype in its
own right, there will be some problems.
4. If an auto engineis used, you need to employ a reduction drive so you can make use of all the power available
higher rpms. Then the potential builder realizes again that costs will be high for a proven redrive,and/or the
combined weight of both the engine and redrive now makes the unit too heavy for the desired airplane.
5. Builders are continually warned that converting an engine will require the continual need to work on the
conversion and be a never-ending source of disappointing problems and poor performance.
These are what I feel are the main reasons many builders get dissuaded from using auto engines. I think the thing
potential builders should realize is that converting can be problematic, but it can also be a source of immeasurable
satisfaction. Thereare many conversions out there working well and flying well.....inexpensively. You should also
realize that automotive engine reliability is second to none. With reasonable thought and installation, you can expect
that the engine will be the least of your problems as far as reliability goes. Where the issues often develop is in
improper design or execution of the peripheral systems that support the engine. These are the things that would make
any engine stop......like the fuel supply system or the cooling system. But when one of these peripheral systems fails,
its always the engine that ultimately gets blamed in the eyes of the naysayers.
One thing I think would benefit the adaption of auto engines is if builders would get away from the idea that they
must use reduction drives with auto engines. The Corvair engine conversions have proven very successful with the
use of a 5th bearing. Its simply an adapter that bolts tothe engine and provides an extra support bearing to relieve
the crankshaft from bending loads exerted by the propeller.I think this same technology applied to an auto engine
being run at 2700/4200 rpms would be beneficial and reasonably inexpensive. This not to saythat larger homebuilt
airplanes cannot benefit from using reduction drives and higher rpms, but on smaller and slower airplanes, I think
reduction drives are unnecessary. Its a case by case decision though. The thing I recommend to builders is to
research what is out there and don't be dissuaded by wellmeaning but biased "experts" who tell you that its easier
to just install a formerly certified engine. If there were no problems with obtaining and using a certified engine there
never would have been any reason to look for alternative engines.
(Note there are some smaller engines which do use redrives successfully, but it really is a case by case decision)
Why aren't there more auto engines used in airplanes?
The basic idea to many new builders is that you purchase a used engine, mount it in an airplane and bolt a prop to it.
While this can be done, and has been done.....it really requires more thought and caution than the simplified idea
presents for consideration.
1. Well meaning builders will immediately provide a multitude of reasons why NOT to use an auto engine.
I think this is the main reason many potential builders abandon their dream. They look at the costs involved in using
an engine designed just for airplane use and decide they can't afford it, and have been sumarily cautioned against the
pitfalls of using an automotive engine.
2. Many builders have little knowledge or experience with engines and are hesitant to try to learn.They may not
have the aptitude forassembling mechanical assemblies. What they want is a proven conversion that can be
purchased for rock bottom prices. When they find that purchasing a proven conversion will rival the cost of a
certified engine, they again decide not to build.
3. There is continual misrepresentation/misinterpretation of data concerning auto engines and aero engines. One
continual comparison is that the auto engines can never compare to the reliability record built by certified engines.
While that is a somewhat true statement in airplanes, auto engines are more reliable .What you have to accept is that you are comparing the records set by professional
manufacturing companies, overseen by government regulators,and maintained by professional mechanics. They
are then installed in professionally designed, tested, and manufactured airplanes. Further, both the engines and the
airplanes are then required to be inspected and maintained to professional standards. Would you expect ALL
homebuilt airplanes to be built equally as well? I mean its a given that with every homebuilt being a prototype in its
own right, there will be some problems.
4. If an auto engineis used, you need to employ a reduction drive so you can make use of all the power available
higher rpms. Then the potential builder realizes again that costs will be high for a proven redrive,and/or the
combined weight of both the engine and redrive now makes the unit too heavy for the desired airplane.
5. Builders are continually warned that converting an engine will require the continual need to work on the
conversion and be a never-ending source of disappointing problems and poor performance.
These are what I feel are the main reasons many builders get dissuaded from using auto engines. I think the thing
potential builders should realize is that converting can be problematic, but it can also be a source of immeasurable
satisfaction. Thereare many conversions out there working well and flying well.....inexpensively. You should also
realize that automotive engine reliability is second to none. With reasonable thought and installation, you can expect
that the engine will be the least of your problems as far as reliability goes. Where the issues often develop is in
improper design or execution of the peripheral systems that support the engine. These are the things that would make
any engine stop......like the fuel supply system or the cooling system. But when one of these peripheral systems fails,
its always the engine that ultimately gets blamed in the eyes of the naysayers.
One thing I think would benefit the adaption of auto engines is if builders would get away from the idea that they
must use reduction drives with auto engines. The Corvair engine conversions have proven very successful with the
use of a 5th bearing. Its simply an adapter that bolts tothe engine and provides an extra support bearing to relieve
the crankshaft from bending loads exerted by the propeller.I think this same technology applied to an auto engine
being run at 2700/4200 rpms would be beneficial and reasonably inexpensive. This not to saythat larger homebuilt
airplanes cannot benefit from using reduction drives and higher rpms, but on smaller and slower airplanes, I think
reduction drives are unnecessary. Its a case by case decision though. The thing I recommend to builders is to
research what is out there and don't be dissuaded by wellmeaning but biased "experts" who tell you that its easier
to just install a formerly certified engine. If there were no problems with obtaining and using a certified engine there
never would have been any reason to look for alternative engines.
(Note there are some smaller engines which do use redrives successfully, but it really is a case by case decision)
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