View Full Version : What determines the rate of rotation in a spin?
Picky Cheese
27th Jan 2015, 01:49
So my instructor told me that during a spin, aircraft with a low nose attitude rotate more slowly than aircraft who are in a flat spin. Why?
Tinstaafl
28th Jan 2015, 05:20
It's usually the other way round, all other factors being equal. A nose down spin puts the CG closer to the center of rotation, a flat spin moves the CG further out. Just a like a spinning ice skater, conservation of angular momentum will slow the rotation as the CG moves away from the centre of rotation.
I've read of inexperienced (at spinning) pilots failing to recover from a flattened spin after doing the correct spin recovery control inputs. The recovery causes the spin to transition to a nose down spin, increasing the spin rate as a result. Muggins thinks he did something wrong because the spin appears to get worse, and removes the correct control input when he should have waited for the recovery to finish.
djpil
28th Jan 2015, 07:06
From Rich Stowell's book, Stall/Spin Awareness:
In airplanes with clockwise turning propellers (viewed from the cockpit), adding power during the normal upright spin to the right typically increases the rate of rotation without an appreciable change in pitch attitude. Adding power during a normal upright spin to the left, on the other hand, speeds up the spin and can flatten the pitch attitude.
Applying right aileron in a normal upright spin to the left tends to level the wings and flatten the pitch attitude, and tends to reduce oscillations. Applying left aileron instead tends to steepen both the bank and the pitch attitude of the spin, and tends to increase oscillations.
The pilot can induce a flat spin by adding power and by applying aileron opposite to the direction of roll in a spin
Some airplanes will flat spin inherently, without provocation by the pilot.
Pushing the elevator forward while maintaining pro-spin rudder during an otherwise normal upright spin speeds up the rotation.
Spins so aggravated by moving the elevator control are called accelerated spins. (The accelerating effect associated with elevator movement may also be observed briefly as part of the normal spin recovery process.)
And from Bill Kershner's book The Basic Aerobatic Manual which specifically addresses the Cessna Aerobat only:
Note that for this airplane the higher the pitch attitude, the slower the rate of rotation
the reactions of a particular airplane.
Notice that for this particular airplane the rotation rates for the left spins do not increase so rapidly or attain as high a value as for the right spins.
During the recovery from a flatter mode, pilots may be disturbed by the nose dropping and the rotation rate apparently increasing. Actually, it is normally a good sign; the airplane is going back through the steep mode as it moves toward recovery.
Stalls, Spins and Safety by Sammy Mason is also a great book to read.