Pitch down when yawing

[NorthSouth]

I've often wondered why some aircraft pitch down significantly when yawed - particularly e.g. when demo'ing yaw in Ex.4. I've noticed it most on PA-38 and Katana which suggests it's something to do with T-tail? Could it be the change in airflow over the tailplane as the yaw moves the slipstream off the tailplane?

NS

[homeguard]

There may well be an airframe reaction with some types but it is usually a propellor effect.

What is usually encounted is that the aircraft will pitch up when yawing right and down when yawing left (on engines that rotate to the right - such as Lycoming and TCM)

The thrust from a propellor is not symetrical. The down going blade produces greater thrust than the upgoing blade. This effect changes with angle of attack. Yaw to the right and the angle of attack of the down going blade increases. Increase thrust and the aircraft pitches up, decrease thrust and the aircraft pitches down. Torque must also be a consideration. A gyro will react 90 degrees to the force applied. Tail dragger pilots know that well!

[18greens]

Isn't this the principle behind gyrobatics. Ie using the precesion effect of the engine gyro to induce turns and pitch changes.

Well done for spotting it. I thought the torque produced in low powered engines was too low to notice it.

[bookworm]

If I understand NorthSouth's account correctly, the aircraft pitches down whether the yaw is left or right. That means that it can't be a gyroscopic effect.

It would be interesting to know if the effect depends on sideslip angle or really on yaw rate. Does it pitch down (more than you would otherwise expect) if you hold it in a slip?

(BTW any reason why you didn't put this on Tech Log? Lots of expertise here, I'm sure, but aerodynamics seems to be a strength on Tech Log)

[hugh flung_dung]

I've always assumed this happens because of tailplane blanketing - very noticeable in a sideslip.

[wheels up]

Taildragger tyros rapidly become believers in the gyroscopic properties of propellors. The effect is most noticeable on take off and landing when the nose is raised / lowered, resulting in a marked yaw on most types. Clockwise rotation = yaw to left when nose is raised, yaw to right when nose is lowered.

On many types, yawing the aircraft can lead to partial blanketing of the horizontal stabilizer leading to a reduction of the down force resulting in a nose down pitching moment.