Actually after I went to bed I had a moment of "dee dee DEEEE" when I realized I hadn't set the blade count for a four bladed prop. It was set for 2 which is the default. Presumably that means the RPM count was off by a factor of 2 . . .
I'm away on a trip now, but I promise to remeasure correctly when I get home.
Sorry for the mistake.
P.S. I used a GloBee Tach
and a flashlight for testing.
P.P.S For what its worth I believe the motor is the blue one
shown on Art-Techs website which would mean:
output 110 watts
max current 13amps
and here is the manufacturers listing for the P51