First run at 10000 MSL, Baro 30.07, OAT of -2C, 2500 RPM about 125* ROP

 

WOT, 184 KIAS, 214 KTAS, 21.2" MAP, 10.9 gph

 

Reducing MAP about 1",

 

170 KIAS, 196 KTAS, 20.1" MAP, 8.9 gph

 

A loss of 18 Knots (21 MPH) true airspeed.

 

Then, at 12000 MSL, Baro 30.07, +1C OAT, 2500 RPM

 

WOT, 175 KIAS, 213 KTAS, 20.1" MAP, 9.8 gph

For the second run at 10k, was the rpm held to 2500 rpm as before?

 

If so, then why does the fuel flow increase from 8.9 gph to 9.8 gph with a temperature increase of 3 C for the first run at 12k?

 

With constant MAP and RPM, a 3 C increase in OAT should amount to roughly 1% decrease in mass air flow. It seems as though the fuel flow should decrease by the same amount to maintain the same enrichment. Shaft power should decrease by slightly less than this due to the reduction in throttling losses at WOT.

 

Am I missing something here?

 

As for a 3% increase in power resulting in a 9% increase in TAS at a given altitude, a change from 61% to 64% is a 5% change, not 3%. Even so, 5% added power resulting in a 9% increase in speed defies basic fluid dynamics. At normal aircaft Reynolds numbers, speed will change roughly with the cube root of power until you enter the transonic region. In other words an 8 fold increase in power will result in about twice as much speed.

 

I think it is the data that is fibbing.

 

Rob