Chuck Dunlap wrote:

Second, I noticed that on take-off at the low elevation fields, which was most of them
on this trip, the RPM would be at 5200 which is normal, then it would drop off after 3
or 4 seconds into the takeoff roll to maybe 4700.

Presumably this means that your prop is (partially) stalled at airspeeds less than
whatever you're at 3-4 seconds into your takeoff roll; I'd WAG about 20 KTAS.  I guess
you have a cruise prop?

The other alternative is that the engine is momentarily producing less horsepower during
your takeoff roll (being starved of fuel or air?).

Why either mechanism would only happen at "low elevation fields" is curious.

Russell Kent

 
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