p-47, p-51, p-38......

[renrich]

In Dean, "America's Hundred Thousand," he gives, in a simple analysis of relative diving accelerations starting at about 30 degree and 90 degree dives the following; #1 P38G, tied for second, P51D, F4U1D, #3 P47D. "After a few thousand feet in a vertical dive all the AC would be approaching or would reached their respective one g limit dive speeds as listed below for the altitude of 10000 feet." The P47D, P51D and P63A are all tied at 500 mph IAS, 1g. The P38 is way down the list. Now a question? In a vacuum, all objects fall at the same rate regardless of shape or weight, correct? The reason for that is that in a vacuum there is no friction or drag caused by the air, correct? If that is true then why would a P47, which has a much larger drag coefficient than a P51 in air be able to catch and pass a P51 regardless of weight or mass?

 

[billswagger]

I really don't think your going to change my opinion, but this article adds some interesting information to the discussion, even though portions of the article contradict some of the mk IV flight test conclusions as far as stability is concerned.


Mach 1: Assaulting the Barrier | History of Flight | Air Space Magazine




"The P-51 was of special interest to the pioneers of supersonics because among fast World War II fighters, the Mustang seemed the most resistant to high-speed controllability problems. (??????really??????) Apparently its unique laminar-flow airfoil managed to keep the airflow attached despite shock wave-induced perturbations. The P-51 could dive faster, under control, than any other World War II fighter. In 1946 and '47, Chuck Yeager in a P-51D with full instrumentation and cohort Bob Hoover in a P-47 dove "straight down," wide open, "from as high as we could go," Yeager later wrote to a friend. Yeager reached Mach .81 in the Mustang and Hoover managed .805 in the bluff, radial engine Thunderbolt."

Being that Yeager wrote this, are we to suggest there is some biased here??
lol

 

[HoHun]

Hi Bill,

>"The P-51 was of special interest to the pioneers of supersonics because among fast World War II fighters, the Mustang seemed the most resistant to high-speed controllability problems. (??????really??????)

According to Eric Brown's "Testing for Combat", the P-47 in fact had a problem with "graveyard dives" (as Brown called them) before the dive recovery flaps were added.

Brown's tests demonstrated that the unmodified P-47D could go out of control (diving into the ground) at Mach 0.73 under certain conditions ...

Regards,

Henning (HoHun)

 

[billswagger]

I think i read a similar article HoHun(Henning), cause that's where i pulled the 0.861M figure the p-47 achieved while testing the new dive flaps. But i can't seem to locate the article, now.

besides, what you are referring too is an early version of the P-47D which went through roughly 30 different modifications and improvements, before they made the P-47J, N, and M which out perform the 47D, particularly in climb rate.
I might also add that earlier versions of the 51 also had problems with critical mach speeds, because although critical mach problems in aircraft were evident in dives performed by the planes in WW1, engineers were now faced with the reality of creating planes suited to fly above their critical mach speeds.

The events in the article I posted in post #42 took place in 1946 and 1947, where the P-51D and the P-47(doesn't say what version, but i'd have to assume the latest D model) were both dove from their ceilings.

 

[drgondog]

I really don't think your going to change my opinion, but this article adds some interesting information to the discussion, even though portions of the article contradict some of the mk IV flight test conclusions as far as stability is concerned.

"The P-51 was of special interest to the pioneers of supersonics because among fast World War II fighters, the Mustang seemed the most resistant to high-speed controllability problems. (??????really??????)

I assume this is your clever reposte to the quote? I suspect the inference is to contrast the dive characteristics of the Mustang to well documented 'nose tuck' transonic issues encountered in 47s, 38's and even Me 262 in the Mach Crit speed range. The Mustang did NOT 'tuck'.

Actually the reason stated below might be, but may not be, the real reason. The primary causes for 'tuck were one or both of a.) movement of the aerodynamic center aft with the shockwave, and b.) separation aft of the shockwave 'blanking out' the elevator and reducing the ability of the elevator to actually control pitch 'down' when the Moment Coefficient of the wing goes increasingly negative as the AC moves rearward.

Most non-laminar airfoils with a max thickness in the 25-30% range started flow separation where the velocity profile was max (in that 25% chord range - which also pretty much coincides with AC), whereas the NACA 45-100 max thickness was at 40% further aft of the AC. If the shock wave started aft of the AC, then it would not change the Moment Cioefficient of the airfoil in the same way as the 47 and 38. I do NOT know which explanation is the correct one.

Apparently its unique laminar-flow airfoil managed to keep the airflow attached despite shock wave-induced perturbations. The P-51 could dive faster, under control, than any other World War II fighter. In 1946 and '47, Chuck Yeager in a P-51D with full instrumentation and cohort Bob Hoover in a P-47 dove "straight down," wide open, "from as high as we could go," Yeager later wrote to a friend. Yeager reached Mach .81 in the Mustang and Hoover managed .805 in the bluff, radial engine Thunderbolt."

Bill S - The 51 Did have some issues with phugoid (porpoise) motion in the high subsonic regimes in a dive and the B/C model also exhibited yaw perturbations which if uncontrolled could lead to a tail failure. The addition of the ventral fin to the D and all previous versions of the B/C in the ETO was a reflection of changes to make the 51 safer in the .75 to .8+ M range. The metal elevator kit and stronger ammo doors were also added in kit form until standard production inclusions for the P51D-20

Being that Yeager wrote this, are we to suggest there is some biased here??
lol

Bill S. - you are being silly. I'm not laughing at either Hoover or Yeager but I will make a comment. To enter the results of the P-47D dive into the realm of documented Test results, the report should be available for YOU to enter it into evidence. Is this now the basis for your claim of ".861 M dive results for a P-47D"

The inclusion of Yeager's account about .805M IS a more reliable source than a pilot's anecdotal recount of his own IAS in a dive with no instrumentation or data reduction to substantiate 'real results'

This is where you can depart from "IMO" to the realm of "here are the documented Test Results that I am using as a source in this argument"

BTW - there are a lot of pretty serious students of fact based arguments on this forum - far more serious than I am.

"IMO" is not a fearful weapon in a fact based debate,

 

[MikeGazdik]

Wasn't sure if I should even make this post, but just need to get some opinions on this thought.

Could possibly the "feeling" from either aircraft change what a normal, non test pilot may actually do in the plane? Likely in FACT the Mustang would dive faster, but the feeling it gave to the pilot was of nervousness or impending doom, wherease maybe the Thunderbolt didn't give this sensation to a pilot and thus allowed the average pilot to take his plane deeper or faster into a dive?

This is just a thought. I know from driving different types of race cars, a feeling of speed can be wrong, you think you are going fast but really are not because you are nearly out of control. And sometimes you think you are going slow but really are not because the car is stable.

 

[billswagger]

I recognize the silliness of my last post. It is funny how we give one pilots account more merit than another. I understand that indicators say one thing, but if two pilots accounts suggest the P-47 could out dive a mustang, then they deserve some merit.
To settle all the horse pucky, here is that 0.861M info straight out of the RAE (Royal Aircraft Establishment) test reports.

Table III, column five....22 seconds into the dive.

http://img113.imageshack.us/img113/3523/sd12.jpg

To find how they calculated the TAS and mach, you probably need to go to a library and check out the RAE test reports of WW2.

 

[drgondog]

I recognize the silliness of my last post. It is funny how we give one pilots account more merit than another. I understand that indicators say one thing, but if two pilots accounts suggest the P-47 could out dive a mustang, then they deserve some merit.
To settle all the horse pucky, here is that 0.861M info straight out of the RAE (Royal Aircraft Establishment) test reports.

Table III, column five....22 seconds into the dive.

http://img113.imageshack.us/img113/3523/sd12.jpg

To find how they calculated the TAS and mach, you probably need to go to a library and check out the RAE test reports of WW2.

You did notice that CIAS was not corrected for Compressibility per the CAIS note at the bottom of the tables? Unless the engineers applied the Compressibility effects to obtain TAS, the values are all artificially high.

Mach at each of the altitudes is easy and well know in WWII.

Simply, for Mph, M= 33.42*sqrt(Temp) where temp is in Rankin.

for the table value of .861 M, the altitude is 19,000 feet and R=451 at 19000

M=1 at 19,000 feet (corrected for standard pressure, density and temp) is ~709mph.

M=1 at 10,000 feet is ~ 734.5mph

 

[billswagger]

You would know better than myself.
I thought it was inline with other tests performed by the RAE.
and while the CIAS doesn't account for compressibility, the chart makes no mention of how they came to conclusions of the TAS.
It is probably information thats burried at the buttom of another pile of paperwork stuffed in some military warehouse. I'm sure a trip to a large public library or university library, would have a book that provides those kind of details on the RAE reports.

In defense of the 'mighty' Thunderbolt, i would have to assume the calculations that lead to the figure of .85M that the 51D achieved would have to fall under the same scrutiny. In other words, they were probably calculated the same way, and perhaps both figures are inflated due to the limited instrumentation at the time of the tests. But again, that is something i'm not familiar with.

 

[drgondog]

You would know better than myself.
I thought it was inline with other tests performed by the RAE.
and while the CIAS doesn't account for compressibility, the chart makes no mention of how they came to conclusions of the TAS.
It is probably information thats burried at the buttom of another pile of paperwork stuffed in some military warehouse. I'm sure a trip to a large public library or university library, would have a book that provides those kind of details on the RAE reports.

In defense of the 'mighty' Thunderbolt, i would have to assume the calculations that lead to the figure of .85M that the 51D achieved would have to fall under the same scrutiny. In other words, they were probably calculated the same way, and perhaps both figures are inflated due to the limited instrumentation at the time of the tests. But again, that is something i'm not familiar with.

I agree. It is interesting that the Yeager 'letter recount' mentioned a fully instrumented test dive comparison with Hoover (had to be post 1945) in which the Mustang outdove the 47 but only slightly - and both were at .81 M range rather than .85-.86

Here is another interesting USAAF report comparing the P-51D-5 and P-38J-25 (boosted ailerons - same as P-38L), and P-47D-30 versus the type 52

Note that in the 10,000 dive the P-51 was reported as 200 yards ahead of the Zero at 27 seconds whereas the P-47 was reported as 100 yards ahead at 30 seconds. The P-51B/C reportedly (i'm looking for reference) was a faster accelerator in dive than the P-51D. Both slower than P-51H.

M.http://www.wwiiaircraftperformance.org/japan/zeke52-taic38.pdf

Note that the type 52 out rolled and out manuevered all three types below 250TAS... but while it gained an advantage over the 51 and 38 in one 360 degree turn, it did much better (1/2 to 3/4 turn) against the 47D-30

 

[billswagger]

This is a great report.

It also demonstrates the zoom dive capabilities of the P-47D, which to my surprise, in this report, out preformed the Mustang in that particular category.

See..the Zoom Dive and Zoom from level flight results.

It is also an interesting comparison, because the Zeke was designed to turn fight, while the US line up, was designed for speed.
That's why the roll rates of all three planes became superior to the Zeke at a higher IAS.
It was no secret that the P-47D should not engage in a turn fight with a Zeke, and most of the more maneuverable Japanese plane set.
Instead they'd dive to get away, and climb up high above the enemy only to swoop down on them at a high rate of speed....then take the bird back up with the zoooooooooooom and get positioned to do it again.

There is also a potential flaw in using an airplane as a baseline for comparison of performance to other aircraft. Specifically, there is lack of dive angles for the planes, but if taken at face value, this is a very good report.

Good find.

 

[drgondog]

This is a great report.

It also demonstrates the zoom dive capabilities of the P-47D, which to my surprise, in this report, out preformed the Mustang in that particular category.

See..the Zoom Dive and Zoom from level flight results.

It is also an interesting comparison, because the Zeke was designed to turn fight, while the US line up, was designed for speed.
That's why the roll rates of all three planes became superior to the Zeke at a higher IAS.
It was no secret that the P-47D should not engage in a turn fight with a Zeke, and most of the more maneuverable Japanese plane set.
Instead they'd dive to get away, and climb up high above the enemy only to swoop down on them at a high rate of speed....then take the bird back up with the zoooooooooooom and get positioned to do it again.

There is also a potential flaw in using an airplane as a baseline for comparison of performance to other aircraft. Specifically, there is lack of dive angles for the planes, but if taken at face value, this is a very good report.

Good find.

Bill - it goes back to procedures by different groups for different report objectives.. and, again to a point this one is 'anecdotal' also.

 

[billswagger]

i stumbled on these.
intersting history, doesn't pertain to any discussion.

http://www.zenoswarbirdvideos.com/realg2/P-47aeroRV1056.ram

http://www.zenoswarbirdvideos.com/Images/Buttons/Real56K.jpg