Round vs Square Props

Jaybird180

Jaybird180

Final Approach
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Jaybird180
I reading about some changes Mooney made in the M20-J in switching from square tips to rounded tips. What's the overall effect?
 
Harder to put your eye out on a round one
 
I believe it's a tradeoff between efficiency (round tip, less drag) and power delivery (shorter radius, allowing a higher propeller speed before the tip goes supersonic.)
 
Sac Arrow said:
I believe it's a tradeoff between efficiency (round tip, less drag) and power delivery (shorter radius, allowing a higher propeller speed before the tip goes supersonic.)
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This article supports Sac's comment: http://www.airspacemag.com/ist/?next=/need-to-know/are-more-propeller-blades-better-108981404/


Capt. Geoffrey Thorpe said:
Cost and or marketing.
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Acrodustertoo said:
someone's wife thought the round tip looked "nicer".
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I suspect the real reason is one of the two above though.
 
Here's a square-tip prop (Republic XF-84H) ...

P1030935.JPG


From Wikipedia:

The XF-84H was quite possibly the loudest aircraft ever built [...], earning the nickname "Thunderscreech" as well as the "Mighty Ear Banger". On the ground "run ups", the prototypes could reportedly be heard 25 miles (40 km) away. Unlike standard propellers that turn at subsonic speeds, the outer 24–30 inches (61–76 cm) of the blades on the XF-84H's propeller traveled faster than the speed of sound even at idle thrust, producing a continuous visible sonic boom that radiated laterally from the propellers for hundreds of yards. The shock wave was actually powerful enough to knock a man down; an unfortunate crew chief who was inside a nearby C-47 was severely incapacitated during a 30-minute ground run. Coupled with the already considerable noise from the subsonic aspect of the propeller and the dual turbines, the aircraft was notorious for inducing severe nausea and headaches among ground crews. In one report, a Republic engineer suffered a seizure after close range exposure to the shock waves emanating from a powered-up XF-84H.
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What were they testing, indiscriminate enemy incapacitation?
 
Jaybird180 said:
What were they testing, indiscriminate enemy incapacitation?
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They were trying for a supersonic propellor driven plane to try to gain efficiency IIRC, I can't recall if they busted Mach with it or not.
 
this is like the whole dyson fan argument as to why he went turbine with his designs
 
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