What are those picture telling us?
4-blade hamilton Standard 3155-6 outperforms 3-blade 6507A-2
above envelope.
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CSP's are not compariable at different advance ratio.
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OK, let's compare efficiency at SAME advance ratio. 4-blade Hamilton Standard 3155-6 could maintain 82% efficiency (in free stream)when advance ratio=3, that's a splendid achievement. How about 3-blade Hamilton Standard 6507A-2 at 3 advance ratio(J)?
V=J*(n*d)=3*23*4=276m/s=994km/h=0.81Mach
From the picture I posted, we can estimate 3-blade Hamilton get around 40% at 0.81 Mach.
We know fw190 dive limit is 466mph=750km/h IAS=900km/h at 3000 m altitude. Let's exam 3-blade vs 4-blade configuration at 800km/h TAS, only 666km/h IAS @3000m altitude, it's very safe for a fw190, quite smaller than Vne, isn't it?
800km/h = 0.66 Mach
For 4-blade Hamilton Standard 3155-6, no worries, efficiency around 85%, well done.
For 3-blade Hamilton Standard 6507-A2, 70-72%, not bad.
For fw190 3.3m diameter 3-blade propeller, advance ratio=2.78, let's assume it performance just like Hamilton Standard 6507-A2 at 2.78 advance ratio(0.75 Mach), we get 52% efficiency!
There are 30% efficiency difference between allied 4-blade propeller and German/soviet 3-blade, 30%, wow, that's 500-600HP engine output bleeding, serious problem if allied aircrafts drag them to 666km/h IAS=800km/h TAS@3000 m/10000ft altitude. We know even La7 could withstand 666km/h IAS, isn't it?
Don't forget German wide chord airfoil even worse than narrow old airfoil at Vmax.
Crummp, I think I've expressed my opinion clearly with my proof/data, my suggestion is to take away 500-600HP from German/soviet aircrafts above Vmax and within Vne. If you could provide the evidence that 3-blade propeller achieve 80% efficiency at 2.8 advance ratio, you'll win. Now it's your turn.