Quote:
Originally Posted by ConnClark
Ummmm.... humidity hurts FE and robs power from the engine.
This is the only reference I can find at the moment.
"Fog and humidity affect the performance of aircraft. During takeoff, two things are done to compensate for their effect on takeoff performance. First, since humid air is less dense than dry air, the allowable takeoff gross weight is generally reduced for operations in areas that are consistently humid. Second, because power output is decreased by humidity, pilots must compensate for the power loss."
SPECIFIC HUMIDITY
Not only for that reason but it also decrease the specific heat ratio of the combustion gases. |
Increased humidity (and air temperature) increases the density altitude seen by aircraft operating under those conditions. An increased density altitude means the aircraft is operating as if it were at a higher altitude than it actually it. In other words, an aircraft taking off from a runway at 1000 ft elevation when the density altitude is 1800 feet will perform as though it were at 1800 ft elevation. Pilots have temperature/humidity tables they can use to calculate density altitude, which they add or subtract from their actual elevation. As altitude increases, the stall speed increases (but not the indicated airspeed), which increases takeoff and landing distances. Also the power output of normally aspirated piston engines is reduced, further, increasing the takeoff distance. This is why they reduce the gross weight as mentioned mentioned above. But, provided their air-fuel mixture is leaned properly, a normally aspirated piston engine will burn less fuel while operating under higher density or actual altitudes