> I have a question I have not been able to get a strait answer for
> any dealer. Can anyone tell me if there is some rule of thumb or
> will directly compare 2-strokes to four stroke engines
This one generates endless debate because the engines don't produce
power in exactly the same way. I'll leave the theoretical discussion to
the engineers out there, but heres's a practical comparison:
Many people equate 60 2-strokes to 90 4-strokes because they might have
similar hp ratings, but in the real world that doesn't really check
out, and here's why: A 2-stroke will produce good power at considerably
higher rpm than a 4-stroke, So say, for example, you're looking to run
a 14X6 prop on your "60 size" sport/aerobatic plane, the OS 61 FX will
only spin it at around 8600 rpm because this large a prop doesn't allow
the engine to ever enter its power zone. An OS 91 Surpass (4-stroke),
on the other hand, will spin the same prop at 9500 rpm which will
result in excellent vertical performance. So for that type of airplane
the 91 4-stroke will give better overall performance.
Now, say instead, that you're looking for top speed in a pylon racing
or jet type airplane. The 2-stroke's ability to safely rev up to 14,000
rpm and higher will result in an level flight speed for beyond the
reach of the 4-stroke. Being limited to about 11,000 max, the 4-stroke
simply cannot safely rev as high as the 2-stroke so therefore cannot
keep up in the "speed contest".
Think about the type of flying that you like to do, and the flight
envelope your plane was designed for and the choice of engine will
become more apparent.
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