3 ms·

This is a nice set of lectures. I looked through the notes on aerodynamics and they are better than most sources, however I do have an issue with two items ther

by zzless 6y ago

This is a nice set of lectures. I looked through the notes on aerodynamics and they are better than most sources, however I do have an issue with two items there. When talking about the minimal drag every book (for pilots that is) mentions that it occurs where the induced drag and the parasitic drag are the same (they even have a graph to reinforce that) while some simple calculus shows that it is rather the point where the two grow/decrease at the same rate and I have seen no reason to believe these are the same point (most aerodynamics books just state that such a point exists). The discussion of the left turning tendency, while technically thorough and correct fails to mention the relative contributions of the various sources. Again, any introductory aerodynamics test has a 'back of an envelope' calculation that shows that for the majority of GA aircraft 95 percent or more (in terms of force) of left turning tendency is due to the spiralling slipstream. Precession and torque are only significant for very large radial engines (and helicopters, of course) and the asymmetry of lift is responsible for barely 1-2 percent (this is why during landing the plane still tends to turn left even though the asymmetry of lift would suggest otherwise). They formulas for lift calculation were a nice touch. I wish they would also mention the Coanda effect. Edit: of course most of this is totally unnecessary for a pilot to know. Even though it helps to understand the spiralling slipstream if one is flying a high-tail plane.

zackbloom 6y ago
Precession and torque are uniquely important to understand in tailwheel aircraft where you are pitching the plane up and down while the wheels remain on the ground. The thing that always bothers me about the explanations personally is how rarely it is explained that precession is a function of the change in angle, torque the change in power, slipstream absolute torque, and p-factor absolute angle.
- gbacon 6y ago
  I like the way this 2-minute video illustrates the increase in P factor during a climb. https://www.youtube.com/watch?v=VJOYERf6380 https://www.youtube.com/watch?v=VJOYERf6380
- zzless 6y ago
  While theoretically true, the numbers do not lie. The angular momentum of the prop alone and the applicable geometric (dis)advantage are just not enough to significantly affect a typical taildragger. Not to mention that while (both) mains are on the ground, torque has almost no effect at all (aside from the microscopic compression of the tires :)). Once you start flying something like the T-6 things change, of course, because of the large radial engine. The effect of the P-factor (pitch asymmetry) is so miniscule that aside from making pretty pictures and explanations with a prop mock up and its shadow it can be disregarded entirely. Again, things are different in helicopters (this is why a typical helicopter tends to roll appreciably on takeoff).

by zzless 6y ago

zackbloom 6y ago

Precession and torque are uniquely important to understand in tailwheel aircraft where you are pitching the plane up and down while the wheels remain on the ground. The thing that always bothers me about the explanations personally is how rarely it is explained that precession is a function of the change in angle, torque the change in power, slipstream absolute torque, and p-factor absolute angle.

gbacon 6y ago
I like the way this 2-minute video illustrates the increase in P factor during a climb. https://www.youtube.com/watch?v=VJOYERf6380 https://www.youtube.com/watch?v=VJOYERf6380
zzless 6y ago
While theoretically true, the numbers do not lie. The angular momentum of the prop alone and the applicable geometric (dis)advantage are just not enough to significantly affect a typical taildragger. Not to mention that while (both) mains are on the ground, torque has almost no effect at all (aside from the microscopic compression of the tires :)). Once you start flying something like the T-6 things change, of course, because of the large radial engine. The effect of the P-factor (pitch asymmetry) is so miniscule that aside from making pretty pictures and explanations with a prop mock up and its shadow it can be disregarded entirely. Again, things are different in helicopters (this is why a typical helicopter tends to roll appreciably on takeoff).