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Originally Posted by Crumpp
Is not correct.
Let's looks at the report. The first thing that stands out as a glaring anomaly in the chart you posted is the fact a 4 bladed propellers appears to be more efficient than a 3 bladed propeller.
This violates a basic principle, sort of like all those people who want to claim their higher wing loaded aircraft can outturn a lower wing loaded airplane. Sounds nice but is not going to happen.
That principle is the fewer blades, the higher the efficiency.
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Will a 4-blade propeller outperforms 3-blade one?
It depends on many factors such as diameter, airfoil, revolution, chord width, blade thickness, TAS, an so on. You know propeller is very complicated.
But for Hamilton standard 6507A-2(~4meters, Naca16 airfoil), 4-blade configuration is better than 3-blade, this is a fact you should accept.
In fact, in late WWII, Rotel, the name is a contraction of "ROlls-Royce" and "BrisTOL", had introduced the first five-bladed propeller to see widespread use
http://en.wikipedia.org/wiki/Rotol
21lbs boost Griffon 65 engine of spitfireXIV is around 2200HP, with a five-blade , wood propeller.
The fastest Mustang----XP51G, with a 2200HP engine, with rotel five blade wood propeller.
The XP-51G was a development aircraft that combined the light weight airframe developed for the XP-51F with an experimental Rolls Royce RM-14SM engine, capable of producing 2,000hp at 20,000 feet. The new aircraft achieved a top speed of 495 mph, and a climb rate of 5,000 feet per minute, well over 1,000 feet per minute faster than the P-51D. However, the new Rolls Royce engine was too complex and did not always produce its best power.
1945 early, the 13lbs boost TempestMKV, 2700HP sabreiib engine, with rotel five blade wood propeller.
After WWII, people developed 6 and even 8 blade propeller.
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The NACA is not claiming a 4 bladed propeller is more efficient. In fact, they quite notably point out several times in the report that none of the data is corrected for wind tunnel installation.
In English, it is not good for specific comparison and they plainly state that in the conclusions. They just hung the propellers and went with it to get an idea of the general trends.
The NACA conclusion are the ONLY thing that can drawn from this report.
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IMG_0106.JPG
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3-blade vs 4-blade compare when developing YP47M. Do you mean these are just to get an idea of general trends?
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You calculated for an advance ratio of 2.78. The 4 bladed propeller produces NO THRUST for most of the power loading conditions at J = 2.78.
When the polar line ends, the blade is stalled!!!
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1350 rpm=23rps, 4 meter Hamilton standard 6507A-2, when advance ratio is 2.78, the TAS=2.78*23*4=256m/s=920km/h=571mph.
When P47 dive to such speed, no propeller thrust? How does il2 FM calculate propeller in this situation? Still 85% efficiency?