Why still no dive acceleration difference?

[Crumpp]

my proof/data

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.

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.

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!!!

Your theory is not based on facts. It would be a fundamental error to toss aside convention of n = ~.85 for it.

[Crumpp]

This is not the same airfoil....

[BlackBerry]

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.

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.

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.

IMG_0106.JPG
IMG_0107.JPG

3-blade vs 4-blade compare when developing YP47M. Do you mean these are just to get an idea of general trends?

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!!!

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?

[BlackBerry]

Originally Posted by Crumpp

Your theory is not based on facts. It would be a fundamental error to toss aside convention of n = ~.85 for it.

The test air speed is below 0.4Mach or 0.2 mach . Of course, 0.4 Mach is just a cruise speed, at medium-low speed, 3-blade CSP could get constant propeller efficiency within envelop.

4-blade propeller efficiency drops from 90% to 85% while 3-blade remaining constant 81%.....


If you test propeller with slow air speed and small propeller rpm, a 4-blade propeller could maintain constant efficiency up to 3.6 advance ratio.

It is the high Mach number decrease propeller efficiency. No air compressibility, no significant effociency drop.

Btw, in late WWII, almost 100% allied aircrafts equipped with 4-blade propeller.

[BlackBerry]

Note that ClarkY 4,6 blade test was carried in a low speed wind tunnel, only 110mph, only 550rpm. So there is no air compressibility in the test, 4-blade propeller could maintain 80% efficiency up to 3.6 advance ratio.


I have no direct proof of 4-blade NACA16 efficiency at high Mach number. I just suspect that 3-blade 3.3m propeller lose efficiency much more than a 4-blade Naca16 around 0.65-0.75 Mach----above level speed envelope, within dive limit.

[BlackBerry]

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.

Flight Tests on the North American
P-51D Airplane, AAF No. 44-15342

Summary
Clean Configuration (with bomb racks).

1. Maximum speed at critical altitudes

High Blower

War Emergency power (3000 RPM and 67") 26000' 442 MPH
Military power (3000 RPM and 61") 28000' 439 MPH
Normal Rated power (2700 RPM and 46") 29400' 420 MPH

XP-51G max level speed=495 mph, P-51D=442 mph.

If everything being equal, XP-51G need (495/442)^2= 125% engine thrust of P51D. Obviously, 2200HP Rolls Royce RM-14SM is around 125% output of 3000 RPM and 67" stanard Merlin(1760HP at altitude).

Roughly, we can say Britain Rotel 5-balde wood propeller is as effective as those 3-4 blade CSP at speed envelop. Namely, around 80% efficiency at 495mph=800km/h TAS.

It seems that allied believed in wwii that 4 or 5 blade propellers are better than 3-blade when speed is high(>700km/h?).

[Crumpp]

Do you mean these are just to get an idea of general trends?

Yes

It seems that allied believed in wwii that 4 or 5 blade propellers are better than 3-blade when speed is high(>700km/h?).

Power absorbtion is what they were going for....

3000 hp engines where the next step on the horizon.

Large amounts of effort for little gain in a 3000 hp piston engine aircraft.

Jets eclipsed any further piston engined development.

[Crumpp]

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.

I think you answered this one yourself.

[BlackBerry]

Originally Posted by Crumpp

Yes



Power absorbtion is what they were going for....

3000 hp engines where the next step on the horizon.

Large amounts of effort for little gain in a 3000 hp piston engine aircraft.

Jets eclipsed any further piston engined development.

1945 version Dora, 2200HP. 3-blade propeller.

1944 late Spitfire XIV, 2200 HP, 5-blade propeller.

1945 version Spitfire XIV,2200HP, 6-blade(2X3-blade contra rotating ) prop. To remove massive torque.

[RegRag1977]

Originally Posted by BlackBerry

XP-51G max level speed=495 mph, P-51D=442 mph.

If everything being equal, XP-51G need (495/442)^2= 125% engine thrust of P51D. Obviously, 2200HP Rolls Royce RM-14SM is around 125% output of 3000 RPM and 67" stanard Merlin(1760HP at altitude).

Roughly, we can say Britain Rotel 5-balde wood propeller is as effective as those 3-4 blade CSP at speed envelop. Namely, around 80% efficiency at 495mph=800km/h TAS.

It seems that allied believed in wwii that 4 or 5 blade propellers are better than 3-blade when speed is high(>700km/h?).

It is interesting to note that there was also attempts to switch back to 3 bladed-prop during the developpement of the famous P51.

The lightweight XP-51F, just as XP-51G, is a completely new design, NOT a modified P51D: can we just compare them to the D series?

The XP-51F apparently used a 3-bladed hollow Aeroproducts prop in 1944 for max speed of 491 mph.

Would be interesting to know more about this propeller too.