0
$\begingroup$

enter image description here

I have heard about LEFT turning tendency affected by gyroscopic precession of propeller (which is turning clockwise or counter clockwise if seen from front side). But I just watched a video on Youtube explains the tendencies affected by the gyroscopic precession, that the airplane is pitch up (nose up or tail down), which means, there are two tendencies.

Then my question is, is that explanation true? Is the second tendency true?

$\endgroup$

1 Answer 1

1
$\begingroup$

Both are wrong. (Or rather, both are partly right, which makes them fundamentally wrong).

Precession happens when there is an 'input' rotation (moment) and not by itself. When you balance the airplane to fly straight and level, there is no gyroscopic moment.

The gyroscopic moment is perpendicular to the external rotation, so it can be directed anywhere across the spin axis.

On a typical airplane with the CCW prop (or turbine for that matter), if you yaw (or turn) LEFT, the airplane will want to pitch UP. (See the diagram on your picture). If you pitch UP, the airplane wants to turn RIGHT. If you pitch DOWN, the airplane wants to turn LEFT.1 And so on. The quicker you maneuver, the stronger the effect is. (And of course, the quicker and heavier the prop is, the stronger the moment, so it's most noticeable at full power).

In normal flying with GA airplanes, the gyroscopic moments are rather minor. The typical 'left turning tendency' is caused by aerodynamics. Gyroscopic moments manifest themselves when rotation is relatively fast, e.g. in aerobatics or spin. But they can be observed with quick impulse inputs on the pedals or yoke, if carefully executed.


1This latter is particularly noticeable on taildraggers during takeoff when the tail is lifted too quickly: the aerodynamic forces are still weak, and the power is full.

$\endgroup$
11
  • $\begingroup$ It's most noticeable on a taildragger if you raise the tail from 3 point to tail high very quickly while taking off. If it has a large prop at TO power the swing to the left is quite dramatic. $\endgroup$
    – John K
    Oct 10, 2019 at 0:21
  • 1
    $\begingroup$ An excellent demonstration of this principle is to remove the front wheel of a bicycle, hold the axle, and have someone spin it up for you. Now, try to move the axle one direction or another. You will see and feel the movement taking affect 90 degrees off from your input. $\endgroup$ Oct 10, 2019 at 0:59
  • $\begingroup$ Good answer. Would be more precise if you reword the first paragraph to state gyroscopic effect is only present if the aircraft itself is undergoing rotation. $\endgroup$
    – JZYL
    Oct 10, 2019 at 1:20
  • $\begingroup$ Doesn't the 2rd paragraph (and all further text) state exactly that? $\endgroup$
    – Zeus
    Oct 10, 2019 at 5:23
  • $\begingroup$ @JohnK, thanks, I added this example to the answer. $\endgroup$
    – Zeus
    Oct 10, 2019 at 6:41

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .