Stability of Tail Spin

[smau1]

Hi,

Does anyone know what design parameters
determines the stability of tail spin?

How can you design an aircraft that does
not want to tail spin?

Thanks

smau1

[Capt. Electron]

You'd have to design it to be stall proof. No stall, no spin.

Jimmy

[Tony Oliver]

Answer 1 : No, I don't know

Answer 2 : Fly tailless models

I had to get that in before the jokers got there!

Seriously, what do you mean by 'tailspin' ?

A spin is usually the result of flying too slowly when drag overcomes lift. However the cause of stalling is a matter of angle of attack, not speed. If the angle of attack is too steep, and causes the airflow to separate, the wing stalls. Usually on one wing before the other, causing a yaw in the direction of the stalled wing, a roll into that wing, a violent pitch down and loss of control so long as the aircraft remains stalled.

The speed thing is the confusing bit as most stalls are at low speed. However a high speed model will stall at highspeed if full up is pulled - watch poorly designed pylon racers, the 'departure' happens at a speed considerably higher than the speed on the glide in to land, often coinciding with a shout something like '****, I've lost it' or 'radio failure' or 'interference'.

Tony

[Capt. Electron]

A spin is a stall with rotation added. If a plane is stalled with wings level and no yaw occuring it will usually just drop the nose and recover straight ahead. If the plane is banked or yawing one direction or the other when the stall occurs it will start to rotate as it stalls. Generally it will rotate around the inner wing tip keeping the inside wing stalled with no lift, but the outside wing will still be flying in circles around the inside wing. Even though the nose is down the inside wing doesn't have enough forward airspeed because of the rotation and it's hard to break the stall. Not good.

Best recovery is throttle closed, pitch down, ailerons neutral and all the rudder you have against the turn to stop the rotation. Just hang onto it, most planes will come out within a half to one turn, some may take several turns.

Jimmy

[Capt. Electron]

tonyo,

The reason why it stalls at a higher speed than when landing is due to the wing loading. A 60 deg bank turn requires 2g's to maintain level flight. Wing loading is doubled at a 60deg bank. At higher bank angles the loading could go to ten, twenty or more g's. R/C flyers frequently pull more g's than any human pilot could survive. When your wing loading exceeds the lift the wing can produce it stalls. Up, down, left, right the direction doesn't matter.

Jimmy

[Tony Oliver]

I totally agree - the point I was trying to get over is that stalling is the result of separation. Not the speed, but the excessive angle of attack.
I use the pylon racer as an example because the glide speed on landing , although higher than many models, is considerably lower than the speed at which stalls occur when pulling round the pylons and still managing to stall (product of thin wings and low effective range of angle of attack?). I've seen the highest speed stalls at the British Nationals when pulling-up after completing the course but prior to the engine stopping. Very spectacular. Seeing a model apparently trying to swap ends - damaged the model but not as much as rolling in from a turn does.

Tony