Model Airplane News

Mastering the Humpty Bump
same elevatoR = close late
incReasing elevatoR =
Round loop

Without increasing the elevator throughout the loop, the loop will “close late”
(lower) than the altitude at which it was started. To keep the loop round, steadily
increase the elevator throughout the pull over the top.

When you push over the top, negative P-factor generates a right-turning tendency, thus requiring a left rudder correction. Note that the propeller slipstream will work against the right-turning tendency of negative P-factor when pushing over the top of a humpty, and therefore it is wise to perform the first few pushes over the top without any rudder to watch and learn how much rudder is, or is not, needed in subsequent attempts.

These P-factor rules all go out the window if the preceding upline is not truly vertical. Therefore, if you go to make the prescribed rudder correction and it sometimes works and sometimes doesn’t, it probably has little to do with the rudder and more likely that your uplines are not consistently vertical.

rudder already applied to counter the propeller slipstream along the upline.

The amount of right rudder required to track straight over the top will be determined in practice by targeting different amounts until you find what works best.

When you initially diagnose the amount of rudder your airplane requires, leave out the rudder during the first few attempts to determine whether the P-factor deviation is slight, moderate, or large. Then, apply the corresponding rudder input.

Humptys witH Half Rolls Performing a half roll on either the upline or downline of a humpty will reverse your course, making it an excellent turnaround maneuver. When you intend to perform a half roll on the downline, reduce power and smoothly take out the P-factor rudder

left-tuRning tendency
RigHt-tuRning tendency

pull
pusH

Left
side
Right
side
Right
side
Left
side

If P-factor is a left turning tendency when you pull elevator, it stands to reason that P-factor would be a right turning tendency when you push.

In a positive pitch attitude, (pull) the right side propeller blade bites more air and tends to thrust the nose to the left (requiring a right rudder correction).

In a negative pitch attitude (push), the left side propeller blade bites more air and tends to thrust the nose to the right (requiring a left correction).