TWEAKING THE THUNDERBOLT

[Jank]

I'm trying to find more information on the performance tweaking that maintenance crews performed on the P-47 "D" and "M". I have heard and read of accounts of top speeds of 500mph for the "M".

Does anyone have any information on the increase in perfomance that was achieved by tweaking the P-47D or M models?

Concerning the "M" model, consider the following:

"The official maximum speed is 470 mph. However, over-boosting the engine could tweek another 15 to 20 mph out of the big fighter. There is adequate evidence to indicate that some of the more resourceful crew chiefs in the 56th Fighter Group, managed to hotrod the P-47M to the point that some reliable pilots were reporting 500 mph at altitude in level flight."

P-47M

Russ Kyler flew P-47's with the 56th Fighter Group in "Zemke's Wolfpack." He ended the war with 10 kills. Below is a picture of him in 2005 at an event honoring him. The scale model behind him is his mount. In 2002 he wrote, "At 34,500 feet, 2800RPM, 75"Hg and WEP, the P-47M would do 507 MPH. I know because I was there. Some pilots were pulling 3000 RPM's & 85"Hg and it was an awsome machine. Republic ran tests at 3600 RPM's (Mainfold pressure unknown)for 250 hours with no break-down of components. That P/W R-2800-57 was one TOUGH engine."

[evangilder]

The next time I am at the museum on a work day, I will ask a gentleman that worked on P-47s as a crew chief in test and evaluation in Florida. If anyone alive would know, Joe P. would be a good resource.

[Jank]

Thanks Evanglider!

Someone on this forum (I think it was RG Lunatic) once said that it wasn't uncommon to tweak the late model "D" models (2,535hp) to near "M" power levels (2,800hp).

[Soren]

Its not impossible, but I'd be very interested in knowing how they would accomplish it in the field.

I do think 500 mph is pushing it though !

[davparlr]

Pilot reports of airspeed can be, and probably are, inaccurate without proper instrumentation. I suspect most pilots used a simple flight computer and put in simple data (probably no WWII fighter had a outside air temp gage, and if it did, it probably wasn't accurate). Also, pressure was not precisely known. All of these affect true airspeed. Another factor could be that the plane was in a slight descent. This is why flight test with an instrumented plane and trained pilot is so important.

[FLYBOYJ]

Some of this was covered in earlier threads BUT;

A couple of things to think about.....

First - airspeed indicators of that day became extremely inaccurate as the aircraft approached transonic speeds.

Second - although mechanics may have done things (advance ignition timing, remove air filters to the induction system, shorten propellers to name a few I heard of) to get more performance for their pilots, to do anything that is not specifically shown in the aircraft maintenance manuals WAS HIGHLY ILLEGAL - THEN AS IT IS TODAY!!! I think stories of "tweaking" are going to be limited at best and if accomplished at all would probably be done while consulting the airframe or engine manufacturer's tech reps who were stationed in the field....

[R988]

I have heard of stuff like filing down the rivets and waxing the airframe to eek out a few more mph, but your mechanic/crew chief would have to really like you or have owed you big time for all the effort involved in that for not a whole lot of gain.

[FLYBOYJ]

Originally Posted by R988

I have heard of stuff like filing down the rivets and waxing the airframe to eek out a few more mph, but your mechanic/crew chief would have to really like you or have owed you big time for all the effort involved in that for not a whole lot of gain.

Waxing the airframe - YES. Filing rivets I think is a myth. (At least I hope). Any removal of material on a rivet head weakens it. One would have to be insane to do such a thing...

[Twitch]

In the postwar era of the Thompson races all we need to do is look at the maximum velocities they achieved with basically the same techniques as everyone combined has described. Not the race averages but top speeds, were there!

I won't say anything about my old man waiting to be discharged and the 'wrenches' arguing if the P-51D could me made to hit 500. It had to do with removing substantial weight that the war department decided it needed and supertuning that my Dad didn't understand. Lotta people got in trouble!

[FLYBOYJ]

Originally Posted by Twitch

In the postwar era of the Thompson races all we need to do is look at the maximum velocities they achieved with basically the same techniques as everyone combined has described. Not the race averages but top speeds, were there!

It's actually a lot easier to "tweak" a civilian aircraft...

Originally Posted by Twitch

I won't say anything about my old man waiting to be discharged and the 'wrenches' arguing if the P-51D could me made to hit 500. It had to do with removing substantial weight that the war department decided it needed and supertuning that my Dad didn't understand. Lotta people got in trouble!

YEP!

[k9kiwi]

I suppose we could ask DerAdler the question....

"A Pilot walks up to you and says, we want to file the rivets on the airfame, chuck out all this kit, over rate the engine and see how fast we can go."

"Want to come along on the test flight?"

And I agree with with FlyBoy, Straight line speed is one thing, but ripping the wings off in your first combat manouver would leave you looking pretty shtupid.

[Soren]

Originally Posted by FLYBOYJ

Some of this was covered in earlier threads BUT;

A couple of things to think about.....

First - airspeed indicators of that day became extremely inaccurate as the aircraft approached transonic speeds.

Second - although mechanics may have done things (advance ignition timing, remove air filters to the induction system, shorten propellers to name a few I heard of) to get more performance for their pilots, to do anything that is not specifically shown in the aircraft maintenance manuals WAS HIGHLY ILLEGAL - THEN AS IT IS TODAY!!! I think stories of "tweaking" are going to be limited at best and if accomplished at all would probably be done while consulting the airframe or engine manufacturer's tech reps who were stationed in the field....

Agreed completely ! And this goes for every airforce.

Why would a mech ever want to try and risk the life of a pilot and the a/c for some extra hp ?? This simply was not done without proper clearence and intructions from the manufacturer itself.

[Jabberwocky]

Tweaking the aircraft for 15-20 mph more speed was entirely possible, partcularly if that airframe was a little war weary:

In 1943 the RAE took a tired old Spitfire Mk Vb from storage and tested it. They found that it could only do 357 mph (about 14mph down on normal top speed).

The then proceeded to fit the following modifications:

Multi-ejector exhausts in place of fishtail exhausts
Removed carburettor ice guard (standard practice anyway)
New rear view mirror fairing
Whip aerial instead of mast aerial
Cutting ejection chutes clean with the wing
Sealing and painting the wing
Waxing aircraft leading edges

End result was the Mk V could all of a sudden do 385.5 mph, a 28.5 mph improvement in speed and a 14.5 mph improvement over nominal maximum straight line speed. The only modifaction that couldn't be carried out by station ground crew would of been replacing the fishtail exhausts with multi-ejector types (and even then Mosquito ground crew were known to have done just that). No other engine modifications were carried out, but they added almost 30 mph to the fighters speed.

[FLYBOYJ]

I think there may have been the odd rogue mechanic and pilot that might of tried "something" to improve performance on the aircraft (look at the field modified B-25s with 75MM cannon) but even there I know some sought of consultation was done with the manufacturer before the thing was flown. Even so, given the pace of wartime operation I couldn't see how any mechanic would have the time to "experiment."

[FLYBOYJ]

Originally Posted by Jabberwocky

Tweaking the aircraft for 15-20 mph more speed was entirely possible, partcularly if that airframe was a little war weary:

In 1943 the RAE took a tired old Spitfire Mk Vb from storage and tested it. They found that it could only do 357 mph (about 14mph down on normal top speed).

The then proceeded to fit the following modifications:

Multi-ejector exhausts in place of fishtail exhausts
Removed carburettor ice guard (standard practice anyway)
New rear view mirror fairing
Whip aerial instead of mast aerial
Cutting ejection chutes clean with the wing
Sealing and painting the wing
Waxing aircraft leading edges

End result was the Mk V could all of a sudden do 385.5 mph, a 28.5 mph improvement in speed and a 14.5 mph improvement over nominal maximum straight line speed. The only modifaction that couldn't be carried out by station ground crew would of been replacing the fishtail exhausts with multi-ejector types (and even then Mosquito ground crew were known to have done just that). No other engine modifications were carried out, but they added almost 30 mph to the fighters speed.

The point here is the modifications you re speaking of were probably authorized by a higher authority, formally engineered and done as a formal modification, not by some mechanic and/ or pilot "experimenting."