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## Effect of angle of attack on Longitudinal Stability

• Posts: 5

### Bill17 created the topic: Effect of angle of attack on Longitudinal Stability

Hello sir,

I was just wondering if any changes in angle of attack had any effect on longitudinal stability. A friend of mine mentioned that he had a question like that, although his memory of the question could be wrong I just wanted to confirm this.

To my knowledge it is mainly the position of the CoG, Tailplane volume, orientation of lift and drag and longitudinal dihedral that has an effect on longitudinal stability.

• John.Heddles
• Offline
• ATPL/consulting aero engineer
• Posts: 477

### John.Heddles replied the topic: Effect of angle of attack on Longitudinal Stability

A bit difficult without being able to see the original question.

However, the idea of long stab is that, for long stab to be positive (ie acceptable), a variation in angle of attack results in a change in pitching moment to oppose the pitch motion which gave rise to the variation in angle of attack.

Or, if you like, if we start from a trim speed, if the aircraft slows down a tad (ie angle of attack increases a bit) then the aircraft will show a tendency to pitch nose down to oppose the initial change. That is to say, to maintain the new speed, we would need to maintain a pull force on the stick to prevent the aircraft pitching nose down.

Conversely, if the aircraft speeds up a bit (ie angle of attack decreases) then the aircraft will show a tendency to pitch nose up to oppose the initial change. That is to say, to maintain the new speed, we would need to maintain a push force on the stick to prevent the aircraft pitching nose up.

That is to say, angle of attack is integrally tied up with long stab characteristics rather than just having some sort of effect on long stab.

Hence my interest in seeing the original question if that might be possible.

Engineering specialist in aircraft performance and weight control.