Peter wrote:
In a QNH of say 1030 the peak-EGT fuel flow will be 6% bigger than it would be at say 970.
I don’t get that. For the same MAP/RPM the peak EGT FF should be the same regardless of QNH if everything else remain constant (particularly temperature). The difference is that your true altitude will differ depending on QNH at the same pressure altitude.
At a QNH of 1030 the air will be denser than at 970. About 1800 ft worth. More air weight means more fuel required to get same Peak mixture. More fuel means more power at same MAP/RPM. For normally aspirated engines the formula LOP is Fuel Flow x 15 = HP.
dirkdj wrote:
At a QNH of 1030 the air will be denser than at 970.
It will not if you fly at the same pressure altitude.
I would say that Density Altitude (Pressure Alt corrected for nonstandard temps) is what counts.
