Guys
We have to look at the purpose of the run up to come to a usable solution.
Two reasons come to my mind:
1. we test for function of all crucial parts. Magnetos and Carburetor heat .
2. we test for take off performance.
For the first test we don't need a full throttle run up. We have to notice a
drop during the magneto test to verify that both are working and can be
switched off.
And the carburetor heat is tested also by noticing the drop in rpm.
The magneto drop should not be excessive, a drop of more than 100 rpm would
indicate a non firing or barely firing spark plug. That's why you do the run-up.
Not to satisfy some numbers.
Since the Ercoupe brakes are suited for slowing the plane down, but not so much
for holding the plane at full throttle in a static position, it is common sense
to do this kind of run up at a lower rpm. I am using 1600 rpm and I am seeing
magneto rpm drops between 25 and 75 rpm. Anything more and I have to look
deeper into the issue. Think about it, you don't do a full throttle run up in a
tail dragger either.
As for the performance test, I do briefly a full power test where and when
applicable before take off to be sure to reach the recommended static rpm. That
rpm value differs between the allowable engine propeller combinations.
For the latter reason, I am also inclined to say that the experienced drop in
rpm when doing the magneto test also depends prop pitch.
So in result, there is no strict rpm to do the run up with. Nor is there a rpm
number of magneto drop that you should or should not see.
Rather than requiring a certain rpm number, I would recommend using always the
same number when doing the run up. Learn what the drop usually is and be alert
when it is different from the usual.
Hartmut
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