Comparison in Diving Performance

[Zipper730]

I'm curious what planes had the highest dive performance. In particular the P-47, P-51, Fw.190, the J2M, Ki-61, and Ki-84.

 

[pbehn]

In what way?

 

[Shortround6]

I'm curious what planes had the highest dive performance. In particular the P-47, P-51, Fw.190, the J2M, Ki-61, and Ki-84.

Highest diving speed?
Best acceleration in the dive?
easiest pull out at the end of the dive?
Controllability in the dive? Pitch, and roll? Yaw?

 

[Admiral Beez]

I'm curious what planes had the highest dive performance. In particular the P-47, P-51, Fw.190, the J2M, Ki-61, and Ki-84.

If it's the fastest dive speed of this lot you want, that would be the P-47.

Per Wikipedia, a loaded P-47 weighs between 12,731 lb (5,775 kg) and 16,300 lb. (7,394 kg.), depending on the version. That's a lot of mass rushing downward, propelled by at least 2,000 hp. This page quotes 725 mph in a controllable, recoverable dive.

 

[Zipper730]

Acceleration in dive

 

[Greyman]

Can't speak to the Japanese aircraft but for acceleration in a dive the Mustang (Merlin) was best, followed by the Fw 190, then the Thunderbolt.

 

[wuzak]

If it's the fastest dive speed of this lot you want, that would be the P-47.

Would it though?

Maximum dive speed is about aerodynamics, and the critical Mach speed for the P-51 was higher than the P-47.

Per Wikipedia, a loaded P-47 weighs between 12,731 lb (5,775 kg) and 16,300 lb. (7,394 kg.), depending on the version. That's a lot of mass rushing downward, propelled by at least 2,000 hp. This page quotes 725 mph in a controllable, recoverable dive.

If you are talking about acceleration, the P-47 comes up trumps. And that's where the weight comes into effect.

A P-47 in a controllable, recoverable 725mph dive is bollocks.

That's the speed of sound at around 13,000ft.

The fastest dive speed for a WW2 piston engine fighter that was confirmed (in actual, instrumented, dive tests) that I know of was 606mph (Mach 0.89) by a Spitfire XI. The tests also achieved a maximum Mach number of 0.92, albeit with exploding superchargers, loss of propeller (broke the reduction gear housing).

A Spitfire XIX fell from over 50,000ft with a maximum speed estimated to be 690mph. It was far from a controlled dive.

 

[Admiral Beez]

A P-47 in a controllable, recoverable 725mph dive is bollocks.

IDK. This page says IAS was 725 mph starting at 30,000 feet.

Republic P-47 Thunderbolt

But they do add some qualifiers that may support your assertion.

Also one would have to wonder how this airspeed was calculated since the early P-47 airspeed indicators only went up to 500 mph. To clarify this, the airspeed indicated was the equivalent of 725 mph, so the indicated airspeed would be calculated by engineering on the ground. Since this phenomena was not unique only to the P-47, later model airspeed indicators showed airspeeds up to 700 mph.

 

[Shortround6]

The 725mph figure amy have been reported at the time and since there were a number of other rather elevated 'claims' of 600mph and higher dives being reported in the popular press at the time the 725mph figure may not have seemed that far out of line.

 

[wuzak]

An IAS of 725mph @ 30,000ft is approximately 1,017mph ~ Mach 1.499
An IAS of 725mph @ 10,000ft is approximately 813mpg ~ Mach 1.106
An IAS of 725mph @ 3,000ft is approximately 850mph ~ Mach 0.996

I think if you are still doing 725mph at 10,000ft or below the chances are they will be digging you out of the ground.

To illustrate the rapidity of the increase in airspeed of the P-47 in a high speed dive, an event occurred during testing on November 13, 1942 by Lieutenant Harold Comstock and Roger Dyar of the 63rd Fighter Group who were performing a test level run at 30,000 feet at over 400 mph. After the first run, they put their P-47Cs into a dive to go to the next level for testing and during the dive, the airplane's speed increased very rapidly. Within seconds their airspeed indicated the equivalent of 725 mph. As velocity increased, they experienced extreme buffeting as they were approaching the realm of compressibility.

Compressibility you say. At over Mach 1 in a P-47.


They do say this:

At this altitude, this airspeed would put them beyond the speed of sound, but this would only be indicated airspeed since the terminal velocity of the P-47 is 600 mph

Terminal velocity is usually referring the speed at which aerodynamic drag is equivalent to force due to gravity. Obviously if you have a means of propulsion other than gravity that limit can be broken.

The Indicated Air Speed is usually less than True Air Speed at altitude, unless something is amiss with the instruments.

Fortunately, they were able to recover, unlike others who experienced the same phenomena, and began dive recovery at too low an altitude to experience what is euphemistically called "uncontrolled flight into terrain."

I can see that happening in a P-47 diving at supersonic speeds.

FWIW, critical Mach speed of the P-47 was around 0.79 - 0.80.

 

[wuzak]

I'm certain of one thing, though. I've heard pilots who claim to have reached Mach 1 in a P-47, but no propeller-driven airplane ever reached Mach 1 - not even the mighty Thunderbolt. It's just not possible, because, at that speed, the propeller no longer delivers thrust, becoming instead a drag which prevents further acceleration.

Upon entering a vertical dive in a P-47, rapid acceleration was inevitable and, at high altitude it was exaggerated. At about 550 MPH indicated, buffeting became evident and it rapidly became severe. The control stick jerked violently in all directions and it was necessary to hold on firmly, with both hands, to manage it. Quite suddenly, the buffeting stopped and the stick became rigid - as though set in concrete. At that point, you jammed both feet hard against the rudder pedals and pulled back on the stick with all your strength - still with both hands. And you stayed that way, simply waiting for the airplane to respond.

I'm not an engineer so cannot speak with technical competence, but I know of only one other propeller-driven airplane capable of such unrestrained dives - the P-38. And the Lightning had a tendency to "tuck under" early in the dive which made for a greater loss of altitude during the pull-out. It too, experienced buffeting.

http://www.510fs.org/wwii/war-stories/item/221-p-47-compressibility-dive

The P-47 - and P-38 - accelerated rapidly to their dive limit speeds, which could cause problems.

The Spitfire, and others, could dive to higher speeds (Mach numbers), but would not build the speed as quickly.

 

[pbehn]

An IAS of 725mph @ 30,000ft is approximately 1,017mph ~ Mach 1.499
An IAS of 725mph @ 10,000ft is approximately 813mpg ~ Mach 1.106
An IAS of 725mph @ 3,000ft is approximately 850mph ~ Mach 0.996

I think if you are still doing 725mph at 10,000ft or below the chances are they will be digging you out of the ground.



Compressibility you say. At over Mach 1 in a P-47.


They do say this:



Terminal velocity is usually referring the speed at which aerodynamic drag is equivalent to force due to gravity. Obviously if you have a means of propulsion other than gravity that limit can be broken.

The Indicated Air Speed is usually less than True Air Speed at altitude, unless something is amiss with the instruments.




I can see that happening in a P-47 diving at supersonic speeds.

FWIW, critical Mach speed of the P-47 was around 0.79 - 0.80.

We went through all of this with the 800+MPH Spitfire wing.

 

[wuzak]

We went through all of this with the 800+MPH Spitfire wing.

Yes, but the Spitfire is a fragile aircraft that wrinkles its skin if you look at it wrong.

The P-47 is a big, tough, American built man's plane that can take the punishment of repeatedly diving beyond the realms of possibility!

 

[Shortround6]

There were newsreel reports of a P-40 doing 661mph in a dive (totally impossible) but if people thought that a P-40 could do 661 then 725 for the Thunderbolt doesn't seem unreasonable. Of course in both cases on board airspeed indicators may have been wildly inaccurate at higher normal speeds.



Republic can't rival Curtiss hold the speed record with their old P-40 design

 

[pbehn]

Yes, but the Spitfire is a fragile aircraft that wrinkles its skin if you look at it wrong.

The P-47 is a big, tough, American built man's plane that can take the punishment of repeatedly diving beyond the realms of possibility!

Early problems were solved by removing RAF roundels and replacing them with anything else.

 

[tomo pauk]

This might help:
Dive limits

 

[fastmongrel]

Early problems were solved by removing RAF roundels and replacing them with anything else.

A new paint job can do wonders for a plane, I wonder why the RAF didnt use this magic paint.

 

[Shortround6]

A new paint job can do wonders for a plane, I wonder why the RAF didnt use this magic paint.

the Germans had cornered the market and patents on it and were using in the paint for crosses and swastikas.

 

[pbehn]

Zipper, the grand slam bomb, weighing 10 tons dropped from 18,000 ft didn't break the sound barrier and it could hardly be more aerodynamic. A P-47 had 2000 BHP but no means to produce thrust, at speeds close to Mach1 the propeller comes off and the wings come off, even what is remaining wouldn't break the sound barrier. Pic from wiki

 

[wuzak]

The Tallboy and Grand Slam were, of course, designed to be dropped at greater altitudes than 18,000ft and may , had that been the case, have been able to break the sound barrier.