Jets tend to be horizontal, not least because you want really zero AoA on the wings once the nosewheel touches down, to dump any lift.
Some GA planes are also horizontal e.g. the TB9/10/200 but the TB20/21 aren’t unless one pumps up the gas shocks way high.
What is the reasoning behind this? It can’t be simply prop clearance because that is controlled (to the extent that you can control it) much more by the nose gear.
Peter wrote:
Jets tend to be horizontal…
Some do some don’t … (I know this because in the Concorde at the Le Bourget museum you have to go slightly upward when you walk through the cabin towards the cockpit).
And even if the fuselage is horizontal on the ground most airplane’s wings are still at a nonzero angle of incidence. Even with jets because they have other means to dump their lift (e.g. ground spoilers) and require a substantial angle of attack to generate sufficient lift at takeoff (low speed) without striking their tail.
Assuming tricycle gear, the CG is ahead of the main gear meaning it has to be lifted by the tail when rotating for takeoff. The wing is under the CG so a small angle of attack helps lift the nose as the plane accelerates. You need to be able to lift the nose to takeoff attitude below stall speed, I suppose some planes with limited elevator authority may need a little help from the wing.
A related, similar design issue is that some canard aircraft like the Varieze have difficulty lifting the nose with the their canard in ground attitude and can’t take off until above their minimum flying speed. Pilots will sometimes cycle the stick in pitch on the takeoff roll to bounce the nose up using the nose gear spring.
A little off topic, but I was reading that the Shorts Stirling
had such long legs because otherwise it could not get enough lift to take-off.
Prop diameter. Travel of front gear shocks. Main gear length. Attitude needed for take-off and landing.
ERJ145/CRJ900/Dash8 are nose down on the ground. I guess to minimize the size and weight of the front gear.
The Concorde definitely needed non-zero angle of incidence on the ground for take-off.
You can probably find more examples both ways.
