Propeller tip would be stalled?
Having read FAA's PHAK chapter 6, I have a question about propeller which has the same angle of incidence from the hub to the tip.
Below is from the page 6-5 of PHAK A propeller blade designed with the same angle of incidence throughout its entire length would be inefficient because as airspeed increases in flight, the portion near the hub would have a negative angle of attack while the blade tip would be stalled. |
The prop's (for any position along the blade) AoA is vector sum of the blades rotational velocity, and the aircraft's forward speed. The blade section has a much lower speed near the hub compared to the tip due to the smaller diameter for the same RPM. Hard to show with a text a diagram so bear with me...
HUB vs TIP: Vertical lines represent rotational speed downwards, horizontal represents forwards speed. Slash is prop section. Imagine a line between the full stops to picture the resultant airflow vector. hub at a greater AoA .\ | | | |__. tip at a lesser AoA .\ | | | | | | | | |__. If the tip is at some reasonable +ve AoA, then the hub is at an excessive AoA If the hub is at some reasonable +ve AoA, then the tip could even be at a -ve AoA |
Propeller tip would be stalled?
The PHAK extract says the hub has a lower AoA than the tip. Tinstaafl's explanation says the hub has a higher AoA than the tip.
I think I need to draw myself a diagram and see if I can make sense of it... |
Your original question was for a blade without twist. In the real world, blades are twisted, to try to keep a more or less equal AoA. Go out & look at a propellor and you'll see.
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