When you do your research online to find out more about the resulting gyroscopic forces created by the spinning propeller, you quickly find yourself clicking through a huge amount of pages to find a simple and effective explanation. These forces are discussed in detail when we brief lessons for Climbing, Descending, Stalling, Spin Prevention and off course, the Circuit.
In this post we’re not going to delve in to the overly technical theory of Gyroscopic Precession, but it is important to know the definition of it and how it relates to our single engine aircraft.
Gyro Basics: The propeller acts a a big spinning gyro. The axis it rotates around can be tilted by the pilot by pitching the nose up or down for a climb or descend. The faster the propeller is spinning, the more it wants to remain fixed in it’s position. This is referred to as rigidity in space. An example would be that of a bicycle’s wheels. As the bicycle wheels increases in speed, they become more and more stable in their plane of rotation. When you ride your bicycle and you experience a sudden imbalance, it’s easier to fall from a slow ride than from a fast one…
Gyroscopic Precession: This is where it becomes very interesting. The spinning gyro is always trying to prevent tilting of it’s axis, but in the event the axis is in fact tilted, there is a resulting experience called Gyroscopic Precession. It is defined as follows: the force applied (which moves a propeller out of its plane of rotation) is felt 90° from that location, in the direction of rotation.
Downward tilt, Descending
Have a look at the image below. If the nose of the model is to be tilted downwards for a descend, a forward force is ‘automatically’ applied onto point A, away from the pilot. The same forward force onto point A is carried to point B by the clockwise rotating disk. It remains a forward force, so point B is also pushed away from the pilot. With this ‘push’ from the back of the prop at point B, the aircraft will experience yaw to the left.
Upward tilt, Climbing
If the nose of the model is to be tilted upwards for a climb, a forward force is ‘automatically’ applied onto point C, away from the pilot. The same forward force onto point C is carried to point D by the clockwise rotating disk. It remains a forward force, so point D is also pushed away from the pilot. With this ‘push’ from the back of the prop at point D, the aircraft will experience yaw to the right.
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Before we see it in action, a quick explanation of the model being used. It is balanced by the Battery at the back and the DC motor in the front. The disc is spinning clockwise as viewed from by pilot in the cabin. A weight is added onto the top of the vertical fin and can be manipulated to tilt the longitudinal axis upwards or downwards. See the image below and note the shifting of the weight at the back.
Here it is in action!
Thank you for your time!
Written and model build by Al Vorster,
SFC Flight Instructor.
