× Welcome to the CPL Aerodynamics question and answer forum. Please feel free to post your questions but more importantly also suggest answers for your forum colleagues. Bob himself or one of the other tutors will get to your question as soon as we can.

## Spinning and stability

• weirdguy99
• Topic Author

### weirdguy99 created the topic: Spinning and stability

Hey guys,

Here's a question that I can't get my head around.

An aircraft has a tendency to stay in a spin. This shows:
A. A lack of directional stability
B. Too much directional stability compared to lateral stability
C. A tail fin which is too small
D. That ventral strakes and/or a dorsal fin extension is required
E. That the aircraft needs anhedral or less dihedral

Apparently the correct answer is B.

I thought that too much directional stability relative to lateral stability would make the aircraft more susceptible to spiral dives, rather than spinning. I went with A since B, D, and E are sort of the same thing.

Thanks.

Please Log in or Create an account to join the conversation.

• Posts: 1169
• Thank you received: 5

### Richard replied the topic: Spinning and stability

Hi,
In the spin, the aircraft rolls in the direction of the most deeply stalled wing which causes a yaw in that direction. As the aircraft yaws, it further increases the angle of attack on the more stalled wing and the cycle continues. The spin will be aggravated by a lack of lateral stability and by strong directional stability.
Option B is the answer because the lower lateral stability means the aircraft will drop a wing quite readily and the subsequent yaw (directional stability) will be quite strong thus aggravating any stalled condition on the wings as the aircraft autorotates.
Options A, C and D infer the problem is due to the aircraft having too little directional stability. Reduced directional stability would actually inhibit the spin characteristics not worsen them.
Option E is essentially saying the aircraft must be too laterally stable which would make it harder to spin, not easier.

Cheers,

Rich

Please Log in or Create an account to join the conversation.

Time to create page: 0.174 seconds