deep stall
Thread Starter
Joined: Sep 2003
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From: south
deep stall
First time on this site so good day to you all....
I have some feedback that gives conflicting answers. Have looked through all of my notes and cannot find any info on this particular subject. Crap notes i guess!
My question is this.. What is most prone to deep stall?
a. T-tail
b. Swept Wing
c. n/a
d. n/a
cheers
I have some feedback that gives conflicting answers. Have looked through all of my notes and cannot find any info on this particular subject. Crap notes i guess!
My question is this.. What is most prone to deep stall?
a. T-tail
b. Swept Wing
c. n/a
d. n/a
cheers
Joined: Nov 2002
Posts: 110
Likes: 0
From: UK
Joined: Aug 2001
Posts: 775
Likes: 0
From: Dorset
The term "Deep Stall" refers to the situation where an aircraft pitches nose up as it stalls. The loss of lift then causes it to descend. This combination of nose- up pitching and downward flight increases the angle of attack, taking the wings deeper into the stall. This deepening of the stall is the reason why it is called deep stall.
For the sequence to commence it is necessary for the aircraft to pitch up as it stalls. Straight wing aircraft tend to pitch nose down in a stall. This decreases angle of attack, thereby taking them out of the stall rather than deeper into it.
With swept back wings the airflow tends to migrate outboard towards the wing tips. This produces a very thick low energy boundary layer over the tips. This low energy air separates very easilly as angle of attack increases. So swept back wings tend to stall first at the tips. The tips are further aft than the roots, so tip stall represents a loss of lift at the rear area of the wings. this moves the C of P forward, which causes the aircraft to pitch nose up. This nose-up pitching motion is the first step in the process of deep stall. So swept back wings are inherently more prone to deep stall.
The position of the tailplane then influences how hard or easy it will be to recovery. A T-tail is likely to be in the turbulent air flowing from the stalled wings, so it will be of little use in pitching the nose down to get out of the stall. A low tail will therefore probably be more useful. But it is the stalling of the tips of the swept back wings that started the deep stall.
The reason the CAA ask this question is because many books give the impression that the deep stall is caused by the T-tail.
For the sequence to commence it is necessary for the aircraft to pitch up as it stalls. Straight wing aircraft tend to pitch nose down in a stall. This decreases angle of attack, thereby taking them out of the stall rather than deeper into it.
With swept back wings the airflow tends to migrate outboard towards the wing tips. This produces a very thick low energy boundary layer over the tips. This low energy air separates very easilly as angle of attack increases. So swept back wings tend to stall first at the tips. The tips are further aft than the roots, so tip stall represents a loss of lift at the rear area of the wings. this moves the C of P forward, which causes the aircraft to pitch nose up. This nose-up pitching motion is the first step in the process of deep stall. So swept back wings are inherently more prone to deep stall.
The position of the tailplane then influences how hard or easy it will be to recovery. A T-tail is likely to be in the turbulent air flowing from the stalled wings, so it will be of little use in pitching the nose down to get out of the stall. A low tail will therefore probably be more useful. But it is the stalling of the tips of the swept back wings that started the deep stall.
The reason the CAA ask this question is because many books give the impression that the deep stall is caused by the T-tail.
Last edited by Keith.Williams.; 1st October 2003 at 05:21.
