This week I talked about pitch stability. Pitch stability is such a big subject that I had to break it up into two “Ask the RCadvisor” segments. This was part one.
This was episode #148 of The Crash Cast in the segment we call “Ask the RCadvisor”.
Differences from Full-Size Airplanes
The needs for stability are different on model airplanes than on full-size airplanes. In the podcast I try and explain some of these differences.
Static and Dynamic
Airplanes can exhibit two types of stability: static and dynamic. Model airplanes often get away without having any dynamic stability. Listen to learn why.
Short and Long Period Dynamic Stability
Long period dynamic stability, also known as the phugoid, is what most RC pilots would call “pitch stability” on model airplanes.
CG, NP and AC
Some terms that I define include the CG (center of gravity), the NP (neutral point), and the AC (aerodynamic center). They are all closely related and all play key roles in determining pitch stability.
Pitch Stability
So how does pitch stability really work in an airplane? Well, there’s a real simple explanation of how the CG, the wing and the tail work together to balance an airplane. Unfortunately, if I try and describe it in words or through a podcast all I’ll manage to do is confuse you. When I get around to it, I’ll have to record a short video. Once in a while I give presentations at RC clubs, and this is a popular demonstration that I like to give. Pitch stability is a bit of a mystery to most people. To finally hear how it really works is a revelation–you can hear a pin drop every time I explain it!
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Thanks. I’m afraid that this segment might be a bit too technical for some. I tried to make it very clear what the important points were.
Cruise flight. Hmm. I wonder what aerodynamic principle(s) explain how a negative flap setting improves performance. How the designers figured out that -6 was better than any other setting.
Full-size airplanes have been able to fly with pretty good sensors on board for a long time. If you fly early in the morning in still air conditions, logging the airspeed versus sink rate is not too hard. Then it is just a matter of measuring the effects of different flap positions.