11. How do the differences in temperature, pressure, density and other conditions affect the aircraft perfoman

Answer 1

For best performance you want cool dry air.

The four "H"s of aviation are Hot, Heavy, High and Humid. This describes your worst performance for takeoff. For example taking off from Denver on a 105 degree summer day after a quick rain shower a max takeoff weight. That's why the high altitude airports all have such long runways.

There is actually a term "density altitude" that is used to tell pilots the effective altitude of a field. If the barometer is low, that means less dense air and therefore a higher density altitude. Same correction for temperature, but higher is bad.

Humidity seems backwards, but humid air is actually less dense than dry air.

Answer 2

The higher temperature the less dense is the air, so you need more power to keep above the stalling speed of the aircraft. In cold weather you would need less power to stay airborne. I have film of a Russian transport using every inch of a Australian runway and staggering into the air because the ground temperature is over 40'c. If the temp had been about 20-22'c that aircraft whould have been off the ground long before being halfway down the runway. I believe the film is on the Utube somewhere. It gave the air traffic control boys some heartache and had the rescue crews on their toes expecting a crash.

Answer 3

Another example to illustrate Huron's point: Less dense air is dangerous for low-level flying and aerobatics, for example. If you want to do a vertical loop, even if you start the loop at the same velocity and pull the same amount, with less dense air, the circle you make will be bigger, and at the end of the loop you'll lose more altitude. If you're not careful, you'll pancake into the ground as you didn't leave yourself enough air to pull up.

Answer 4

Huron has it exactly right, just to add some more insight. All aircraft performance is based on "Standard Day". Which is 59deg F, Sea Level pressure.

Answer 5

Except for Heavy, all other 3 Hs are elements that reduce the air density. But this is related to be able to fly. When it comes to speed, then air density becomes your enemy. I asked a specialist why we don't build planes with larger wings to fly easier. He told me this would be a problem at high speed.