Does a left spin differ from a right spin for a single-engine propeller aircraft, in terms of spin characteristics & ease of recovery?

Question

Given a single-engine propeller aircraft with its nose-mounted propeller rotating on the right-hand side when viewed from the cockpit, and given the typical effects like P-factor, prop-wash and gyroscopic forces associated with the propeller -

1. Would there be any differences between left-hand and right-hand spin modes? (Differences both from the physics perspective as well as perceptional difference from the pilot's point of view. For example, the differences could be there from a theoretical perspective but minor enough that the pilots can ignore them in real life).
2. If the answer is yes for Q1, which side, in this particular case, would have a more severe spin in terms of spin rate, loss of altitude and so on?
3. If the answer is yes for Q1, which side, in this particular case, would have a harder recovery compared to the other side?

To reduce variables, let's assume there are no asymmetries in the aerodynamic configuration which may make the aircraft favor one direction over the other for spin and we are only considering the effect of propeller-rotation-direction-related effects on the spin.

Answer 1

Chipmunk, left-handed engine: Spinning to the left, recovery takes 3/4 turn, spinning to the right, recovery takes 1/4 turn. In either case, descent rate is 6000ft/min, so not affected by the airflow direction.

Answer 2

It differs but not as much as it does for jet aircraft.

This may seem counter-intuitive, but in spin, inertia and gyroscopic effects play major role.

On propeller aircraft, the most practical difference must be with inadvertent entering spin, where power (and the associated asymmetry) is significant. But after entering spin, the first thing one does is reducing power to idle. This makes aerodynamic asymmetry ('P-factor' etc.) negligible (unless the tail is deliberately offset, as is done on many single-prop aircraft), and the prop gyroscopic effect is rather small.

Jets, while looking perfectly symmetric, still have engine(s) rotating one way (with a few notable exceptions), and their gyroscopic moment is very significant, even at idle. (The rotor is much heavier and spins much faster). Most jet fighters have very asymmetric spin characteristics, to the point that one spin may be stable and difficult to recover while the opposite spin be unstable and difficult to enter.

If the gyroscopic moment tries to raise the nose in a given spin rotation, the spin will usually be unstable. For example, MiG-15/17, with its left-rotating engine, had a very unstable right spin, which tended to change to left over time.

Answer 3

A well known spin recovery technique is PARE. Power to idle, Ailerons neutral, Rudder Away from spin, Elevator nose down.

Power to idle is critical to avoid complications in spin recovery. Now, aerodynamicly, spin behavior recovery is much more similar left or right, with the right being slightly easier to recover from.

If your plane is stable, and CG is set right, it should not spin unless it is forced to. Rudder control remains effective through stall, and is your best friend to avoid, or stop, a spin before it becomes fully established or flat.

Answer 4

Gyroscopic effects, even with an idling engine make upright left spins flatter assuming a right turning propeller.

The left yaw force applied to the propeller moves 90 degrees in the direction of rotation and the prop disc is forced to tilt upwards. That force is transmitted through the engine to the airframe.

How much flatter will depend on the mass of the propeller, it’s speed of rotation and all the other things that vary from type to type.

Because the spin is flatter, the rotation is slower in that direction, due to conservation of angular momentum, not unlike a figure skater extending her arms while spinning.

It is certainly noticeable in the Pitts Special. Not only is the upright left spin flatter at idle power, adding power while spinning raises the nose.

To perform upright flat spins with a right turning propeller you need to use left rudder.

Answer 5

Two things have to happen simultaneously to cause a spin: stall and large enough yaw rate. To recover from a spin you need to stop both of those. Therefore anything that increases the intensity of either a stall or yaw rate will hinder you recovery.

Specifically talking about the propeller contribution: let’s say we have a clockwise prop, which produces left turning/yawing tendencies. Since it creates left yawing motion; left turning spins will be easier to enter and harder to recover from than the right spins. Because there will be more yawing moment that we need to overcome.

However whether the difference would be perceivable or not by the pilot would really be depended on the aircraft, power setting, idle power/torque, size of the prop, aircraft’s inertial characteristics etc.