Interesting. Do we have any thermodynamics trained individuals out there who might comment on this. When I went through my engineering thermo courses it seems to me that the overall power (efficiency) of ANY heat engine (gas, diesel, turbine, etc.) was always higher as the temperature spread between engine operating temp and outside air temp increased. In plane language higher efficiency as it got colder out there.
As far as the airplane example was concerned, the reduction in payload was caused by a reduction in density altitude at takeoff. That could have effected the airplane two ways. Either the runway was too short and the reduced engine efficiency did not allow a the heavy plane to accelerate to takeoff speed before you ran out of pavement, or the takeoff speed needed to be higher due to less dense air caused by the heat and airport altitude, and you were still in danger of running out of pavement. Each aircraft has performance diagrams that tell the pilots (or commercial airlines dispatcher) how the aircraft is going to perform with a given load, temperature, and density altitude.
