Why still no dive acceleration difference?

[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.

[Crumpp]

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

6 blades!!!

No, that is TWO 3-bladed propellers turning in opposite directions from each other.

[BlackBerry]

Originally Posted by RegRag1977

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.

* * * *
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XP-51F 43-43332, 43-43333, 43-43334
(Different references give different speeds obtained by the lightweights. I am going to use speeds from the book "Mustang Designer - Edgar Schmued and the P-51". The speeds from this source are 20-30 mph more than given in other sources). Max speed was boosted to 491 mph at 21,500 feet with a ceiling of 42,100 feet. The XP-51F used the RR Merlin V-1650-3 and a 3-bladed hollow Aeroproducts prop. Armament was four .50 cal guns. In all, NAA stripped about 1600 pounds off the combat weight! The second XP-51F was tested in the U.S while the third was given an RAF serial of FR409 and shipped to Brittan for testing.

XP-51G 43-43335, 43-43336

The XP-51G used a 5-bladed Rotol prop. This was installed because of a deal with the Brittish so NAA could get some of the new RR RM.14.SM engines. The new engine was down-rated from the intial of 2,200 to 1,190 horsepower. The 5-bladed prop was installed prior to the 5th test flight. The XP-51G clocked in at 492 mph at 20,700 feet, the fastest yet. The new Rotol prop was not very stable but the climb performance was very good: 3.85 minutes to 20,000 feet. The second XP-51G was shipped to Brittan with an RAF serial of FR410 for evaluation. THe XP-51G was essentially the XP-51F with the new engine and prop.

Some resource pointed out that xp-51f is 20-30mph slower than xp-51g. Only 466mph=750km/h TAS.
btw,750km/h TAS is not a very high dive speed.


Engineering inspections were held in February 1944. The first XP-51F was flown by Bob Chilton on February 14, 1944. The second and third XP-51F flew on May 20 and 22 of that year. Equipped empty weight was about 2000 pounds less than that of the P-51D, and combat weight was 1600 pounds less. The engine was the Packard Merlin V-1650-7 engine of 1695 hp, same as the powerplant of the P-51D. Considering that the equipped empty weight was about a ton less than that of the P-51D, the performance improvement was not as spectacular as might have been anticipated-- maximum speed was 466 mph at 29,000 feet.


The second XP-51G was shipped to the United Kingdom in February 1945. This plane was also named Mustang V, and bore the RAF serial number FR410. It is widely reported to have achieved a speed of 495 mph during tests at the A&AEE at Boscombe Down in February 1945, although NAA claimed only 472 mph for the other G at the same altitude. However, by this time RAF priorities had changed, and no further flight testing took place. The fate of FR410 after the end of test flying is uncertain.