Recently I was wondering how hard would it be to design a RC aircraft propeller. I have some basic idea about aerodynamics, but I'm an electrical engineer and computer scientist by trade. What I found so far was this really nice paper here: https://repositorio.unican.es/xmlui/bitstream/handle/10902/16634/418495.pdf?sequence=1
What I'm still struggling to get is a couple of things:
- How does a designated RC aircraft propeller size and pitch, such as 5045 relate to geometric pitch? 50 expresses the length in tenths of an inch, so it's 5 inch diameter and 45 is probably how long the spiral drawn by the tip of the blade screwed into a solid medium would be. Is that correct?
- If the above is correct, how do I convert from the spiral length to the actual angle of attack of the airfoil?
From what I noticed, the angle of the airfoil also flattens towards the tip of the propeller. If I get it right, it's to keep the length of the spiral per revolution uniform regardless of the point of measurement along the propeller blade? Is it always done precisely to keep that length uniform, or is it much more complicated than that and the actual shape assumes some "slippage" (air is not a solid block of wax after all) etc?
I found this article here: How would flow angle change along the length of a propeller airfoil? But in order to calculate the angle of attack, the airspeed and the rotational speed must be known. With that being said, it almost turns into a chicken egg problem (but I'm most likely missing something). In my lacking understanding of the problem, the air speed will depend on the propeller shape, but I need to know the pitch and RPM to calculate the shape in the first place! What's the starting point of those calculations? Do they just assume some fixed RPM and airspeed to design the propeller for?