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When engines get more powerful there are only a few ways for a propeller to convert the increased horsepower into more thrust; get bigger in diameter, wider blades or more blades.
Getting bigger in diameter is usually a problem since diameter is limited by the landing gear length.
The Spitfire had to have been a propeller problem since HP more than doubled from the Mk.I to the Mk.22/24, but the landing gears legs stayed short.
Another issue is that the propeller has to be big enough to absorb the engine power at high altitude where the air is thin (low density). A fighter that flies at high altitude has to have 'more propeller' than the same HP fighter that is limited to a lower altitude. Again the Spitfire is an example of a fighter where the 'working' altitude the propeller had to be designed for also increased significantly over its production life.
On the other hand, you want to stay with just a few blades if you could because (think of the propeller's blade path) more blades are more likely to get in the wake turbulence (or even sonic disturbance) of the proceding blade which reduces the ability to convert horsepower into thrust.
That is all I think I know.
Piper106
With the exception of a couple of test aircraft, no F4U prior to the F4U-4 used a four bladed prop. The higher horsepower of the -4 dictated the change of props.
The P-47 went with a smaller diameter, four-bladed prop for ground clearance consideration, versus the larger diameter three-bladed props used on the F6F and F4U.
The XF6F-6 was abandoned in favor of the F8F.
This thread has already been discussed on the forum. However, I am unable to find it as I am unable to find anything on the search function.
Propellers are similar in aerofoil section to a low-drag wing and thus do not operate very well when at other than their optimum angle of attack. Therefore a method is needed to alter the blades' pitch angle as engine speed and aircraft velocity are changed.
A further consideration is the number and the shape of the blades used. Increasing the aspect ratio of the blades reduces drag but the amount of thrust produced depends on blade area, so using high-aspect blades can result in an excessive propeller diameter. Using a smaller number of blades reduces interference effects between the blades, but to have sufficient blade area to transmit the available power within a set diameter means a compromise is needed. Increasing the number of blades also decreases the amount of work each blade is required to perform which limits the local Mach number. This establishes a significant performance limit on propellers.
A propeller's performance suffers as the blade speed nears the transonic. As the relative air speed at any section of a propeller is a vector sum of the aircraft speed and the tangential speed due to rotation consequently a propeller blade tip will reach transonic speed well before the aircraft does. When the airflow over the tip of the blade reaches its critical speed, drag and torque resistance increase rapidly and shock waves form creating a sharp increase in noise. As a result aircraft with conventional propellers do not usually fly faster than Mach 0.6. There have been propeller aircraft which have attained speeds up to the Mach 0.8 range, but the low propeller efficiency at this speed makes such applications rare.
There have been efforts to develop propellers for aircraft at high subsonic speeds. The 'fix' is similar to that of transonic wing design. The maximum relative velocity is kept as low as possible by careful control of pitch to allow the blades to have large helix angles; thin blade sections are used and the blades are swept back in a scimitar shape. In addition a large number of blades are used to reduce the work per blade and to maintain circulation strength contra-rotation is used. Such propellers are more efficient than turbo-fans and their cruising speed, in the range of Mach 0.7–0.85, is suitable for airliners, but the noise generated is tremendous.
Well you evidently know what your talking about. Do you know why the Hellcat, Corsair and P47 would all have such different props when they are all large, heavy fighters, all 3 have the same basic engine and all 3 started out with 2000 hp? I can't see why all 3 wouldn't have the same prop.