Take-off thrust question
Thread Starter
Joined: Aug 2001
Posts: 865
Likes: 15
From: Greater Aldergrove
Take-off thrust question
Folks,
With an aircraft like the 777, the engines are mounted very low down, I think the ground clearance is only 18 inches or something like that. On rotation, does the proximity of the engines to the tarmac give the aircraft any benefit? Does the aircraft get any additional 'thrust' due to reaction with the ground?
Just curious.
With an aircraft like the 777, the engines are mounted very low down, I think the ground clearance is only 18 inches or something like that. On rotation, does the proximity of the engines to the tarmac give the aircraft any benefit? Does the aircraft get any additional 'thrust' due to reaction with the ground?
Just curious.
)
Joined: Feb 2002
Posts: 554
Likes: 0
From: The Sandpit
I think you may have misunderstood the nature of thrust. The only way the ground would give any assistance to an a/c taking off would be if the generated thrust were to 'reflect' back and provide extra upward moving air to assist the a/c. This would only happen at an angle of approaching 90 degs with the ground.
What can happen is a ground effect where downward moving air (created by the motion of the a/c) 'bounces' off the ground and impinges on the a/c fuselage, wings and tailplane to create extra LIFT. This, whilst a factor during take off is more apparent when landing and can cause an a/c to 'float' along the runway. It is the reason that most commercial a/c autopilots land 'firmly'. I seem to reacall a prototype Trident (first full autoland a/c) crashed due to this phenominum and the Rad Alt and pitch logic was altered to compensate.
What can happen is a ground effect where downward moving air (created by the motion of the a/c) 'bounces' off the ground and impinges on the a/c fuselage, wings and tailplane to create extra LIFT. This, whilst a factor during take off is more apparent when landing and can cause an a/c to 'float' along the runway. It is the reason that most commercial a/c autopilots land 'firmly'. I seem to reacall a prototype Trident (first full autoland a/c) crashed due to this phenominum and the Rad Alt and pitch logic was altered to compensate.
