Bob Johnson's observation of Luftwaffe fighters

[Widewing]

Originally posted by HoHun
Hi Widewing,

>Once engaged, most pilots pushed everything forward and never even glanced at temp gauges until the fight was over.

Even with pushing everything forward, 72" Hg gives you no more than 300 extra HP (you only claimed 200 HP) over 64" Hg.

Starting from 2600 HP, that's around 10% of power gain, which yields around 3% of extra speed.

To get to 470 mph TAS, Johson's P-47 would have had to go at 456 mph TAS at standard power settings. And that below its optimum altitude, so the total top speed must have been even higher.

Where's your evidence for a 460+ mph top speed standard P-47D?

Regards,

Henning (HoHun)

We have an old saying here in America, "says you".

Your calculations tell you that the USAAF's actual test data is incorrect. Pardon me if I giggle.....

Fact: The XP-47J reached 507 mph @ 34,300 feet on 2,800 hp. The same aircraft tested by the USAAF reached only 484 mph, but they admitted that the engine suffered a misfire and loss of turbo efficiency due to an exhaust leak in the collector.

Fact: The USAAF rated the P-47M at 475 mph @ 32,600 feet on 2,800 hp.

Fact: The USAAF rated the P-47N at 467 mph @ 32,400 feet,
450 mph @ 26,000 feet, on 2,800 hp.

Clearly, there's a problem with your calculations if they disagree with empirical test data. Theory is like a smokescreen, it blinds you, yet it lacks any substance.

Someone's full of baloney, and I doubt that it was the USAAF's Experimental Engineering Division. Thanks, but I'll cast my lot with the professionals who actually tested the aircraft, than with some unknown character who has previously shown he has an axe to grind with anything of American origin.

I was wondering, do you actually fly Aces High, or just post on their BBS?

My regards,

Widewing

[HoHun]

Hi Widewing,

>Please, stop being obtuse.....

Please stop being impolite. If you mistake thoroughness for obtuseness, that's your fault only. You were posting speed figures with no altitude given - quite obviously, that's useless for a detailed discussion.

This is your claim:

>>Then, how do you account for the P-47M-1-RE and P-47N-1-RE recording CORRECTED speeds of 475 and 467 mph respectively on 2,800 hp?

I'm quite ready to give you the benefit of doubt, but if you go and use capital letters, then I assume you have something to back up your claim.

>If you need actual data, see Dean's "America's Hundred thousand", pages 282 and 283.

Do you mean this is your source? If it is, does it contain speed and power curves like the F4U-4 comparison?

That would be a useful basis for a thorough discussion of these aircraft. Your single figure quotes are not.

Regards,

Henning (HoHun)

[bozon]

very interesting thread.

thank you widewing.

Bozon

[HoHun]

Hi Widewing,

>Someone's full of baloney, and I doubt that it was the USAAF's Experimental Engineering Division.

Try to concentrate on the question:

>>Where's your evidence for a 460+ mph top speed standard P-47D?

The laws of physics are pretty consistent, and the P-47D tested for the F4U-4 comparison is never going to get anywhere 475 mph for certain.

Either you prove the data for the tested P-47D is in error, or you prove my calculations are in error. Both could easily be possible, but I'm not going to believe it without positive proof.

And if you look at the P-47M and P-47N issue, you'll see that I've done nothing but asking questions. I've not made a single statement regarding their performance.

I'm mildy surprised that this was enough to make you lose your composition and resort to ad hominem statements. I'm not going to comment on your emotions - but please, keep them for yourself.

Regards,

Henning (HoHun)

[moot]

Polished, P47s may or may not have been, but Henning certainly is.

[Widewing]

Originally posted by HoHun
Hi Widewing,

>Please, stop being obtuse.....

Please stop being impolite. If you mistake thoroughness for obtuseness, that's your fault only. You were posting speed figures with no altitude given - quite obviously, that's useless for a detailed discussion.


I'm not being impolite whatsoever; but don't stand in the road because it's right around the bend.


This is your claim:

>>Then, how do you account for the P-47M-1-RE and P-47N-1-RE recording CORRECTED speeds of 475 and 467 mph respectively on 2,800 hp?

I'm quite ready to give you the benefit of doubt, but if you go and use capital letters, then I assume you have something to back up your claim.

First of all, it's not "my claim", these are established facts.


>If you need actual data, see Dean's "America's Hundred thousand", pages 282 and 283.

Do you mean this is your source? If it is, does it contain speed and power curves like the F4U-4 comparison?

That would be a useful basis for a thorough discussion of these aircraft. Your single figure quotes are not.


What did you think I meant? Yes, Dean provides speed, power and climb curves for many versions of the P-47D, as well as the P-47M and N. The F4U-4 is included. Dean's work is thorough (over 600 pages) and well respected. Invest in a copy.

My regards,

Widewing

[Widewing]

Originally posted by HoHun
Hi Widewing,

>Someone's full of baloney, and I doubt that it was the USAAF's Experimental Engineering Division.

Try to concentrate on the question:

>>Where's your evidence for a 460+ mph top speed standard P-47D?

The laws of physics are pretty consistent, and the P-47D tested for the F4U-4 comparison is never going to get anywhere 475 mph for certain.

Either you prove the data for the tested P-47D is in error, or you prove my calculations are in error. Both could easily be possible, but I'm not going to believe it without positive proof.

And if you look at the P-47M and P-47N issue, you'll see that I've done nothing but asking questions. I've not made a single statement regarding their performance.

I'm mildy surprised that this was enough to make you lose your composition and resort to ad hominem statements. I'm not going to comment on your emotions - but please, keep them for yourself.

Regards,

Henning (HoHun)

Where did I state that a "standard" P-47D was a 460 mph fighter? Answer: Nowhere.

I reported what Johnson said, and what Pappy Gould said with regards to Pratt & Whitney tech reps, who showed Gould how to modify the standard wastegates to provide for higher boost pressure. In my interview (which I assume you didn't bother to read), Johnson stated the following:

---------------------------------------------------------------------------------
CCJ: I remember reading where you thought that your P-47 was the fastest fighter in the ETO.

RSJ: I still believe that it was.

CCJ: Really?

RSJ: Sure. My second Jug, a D-5 was the best P-47 that ever flew, and I flew them all, including the P-47M which the 56th got near the end of the war.

CCJ: What made this one Thunderbolt so fast?

RSJ: Several things. My crew sanded every joint smooth, and waxed it to a high gloss. Factory technical reps showed my crew chief, Pappy Gould, how to adjust the wastegates to keep the boost pressure higher than normal. My D-5, which I named Lucky, had water injection. I never used the water injection in combat. I didn't need it. From time to time I'd switch it on, push the throttle up to 72" of manifold pressure and the head rest would smack me from behind. I would let her run for a few minutes just for the fun of it.

CCJ: 72 inches!? Did you ever take note of your airspeed during one of those runs?

RSJ: Of course.

CCJ: And....... how fast did it go?

RSJ: I've seen just over 300 at altitude.

CCJ: 300 indicated?

RSJ: Yes.

CCJ: What was your altitude?

RSJ: I guess it was right around 32,000 feet.

CCJ: Geez, that’s well over 450 mph!

RSJ: Oh, I figure closer to 470.
----------------------------------------------------------------------------------

Now, if Gould and the P&W rep's handiwork produced the expected 2,700 hp, and based upon the P-47D-5-RE having less drag and weight than the P-47M-1-RE, why should it surprise anyone that its performance should generally mimic that shown on the P-47M speed and climb charts?

Note that Johnson used water injection for the 72 in/Hg power setting.

Finally; we read the comments you post, and reflect upon your posts in the Bf 109 thread and realize that you have a personal agenda. Yet, you tell us you only want to be "thorough". Clearly, you are the one suffering from the permanent "wedgie".

So far I have watched you quote out of context and twist facts, either because you failed to fully read posts, or because you wish to obfuscate the discussion. If you wish to be "thorough", you can begin by actually reading the posts and addressing the points therein, rather than create new ones out of thin air.

By the way, you didn't answer my only question... An easy one too.

Do you fly Aces High?

I'm fairly certain that your answer would be no. That's too bad, because an expert of your caliber could certainly point out any errors in the flight model physics of the P-47 or Bf 109. No doubt, Hitech Creations would hang on your every word.

My regards,

Widewing

[leitwolf]

Were modifications to engine and plane limited to the ETO or is reasonable to believe the Navy also had souped up F4Us and F6Fs ?
How'd they perform?

[Widewing]

Originally posted by leitwolf
Were modifications to engine and plane limited to the ETO or is reasonable to believe the Navy also had souped up F4Us and F6Fs ?
How'd they perform?

It is entirely possible that some mechanics did. However, the opportunity and means was extremely limited. Why? Because modifications on the P-47 were not to the engine itself, but to a system. Unlike mechanically supercharged engines like those on the F6F and F4U, the P-47 employed a turbo-supercharger powered by exhaust gas. There were two parts of this system that could be easily modified to alter performance. These were the wastegates and the turbo regulator. Wastegates were generally modified by shimming or stretching the spring (stretching required a heating stress relieving process or the spring will simply collapse back to its original free length, but actually provide less force at working height). New springs could be easily fabricated using a simple screw lathe and mandrel (if one has the required spring wire on hand). Turbo regulators could rigged to allow for greater turbo RPM, or could be internally modified by changes to the spring, poppet or even orifice diameter (not just at the valve seat). At speeds above 18,250 RPM, a warning light would illuminate in the cockpit. This could be overridden by the machanic, or the switch could be adjusted for a higher velocity (not easy to do). The G.E. C-21 turbo could withstand rotational speeds about 50% higher than normal operation, but bearing wear was greatly magnified if higher speeds were sustained. Major turbo failures could severely damage the aircraft, and posed a significant fire risk (leaking oil on a hot manifold or hot exhaust gas leaks). So, I'm sure pilots were cautioned about the potential and inevitable engine and turbo damage resulting from maintaining high boost pressures for extended periods. These modifcations were done to provide the pilots with the absolute maximum power for emergency situations, not for general use, and that is an important point that needs to be emphasized.

There were some things an F6F or F4U mechanic could tweek to add a bit more power. Things like prop indexing and magneto timing changes were feasible. However, these changes could have serious negative effects, especially retarding the ignition too far. Also, unlike the USAAF, the Navy did not blend its fuel at airfields. It was supplied already blended by the manufacturer. Once onboard tankers, and even once aboard and in the carrier's fuel bunkers, there was little anyone could do with the fuel beyond running basic quality and contamination testing. Any local fuel depot within the 8th AF could custom blend fuels to achieve higher anti-knock properties. This is evidenced by Doolittle's order specifying custom blends for the P-38s. He ordered the fuel service depot supplying Kingscliffe to increase the minimum octane rating to 110, and even specified the additives (Doolittle was part of the team at Shell that developed 100 octane aviation fuel in the 1930s). I actually have a copy of that order.

The best way for mechanics to improve the performance of the F6F and F4U was simply maintaining the highest possible state of engine tune, waxing the aircraft and sanding/filling joints in the skin. Removable panels must fit as precisely as possible. For example, badly fitting wing fillets on the P-38 could cause a loss of speed as much as 12 mph and generate vortices that would buffet the elevator (ref. Bodie). So fit and finish were important to obtaining the maximum possible speed.

My regards,

Widewing

[HoHun]

Hi Widewing,

>Where did I state that a "standard" P-47D was a 460 mph fighter? Answer: Nowhere.

As I pointed out above, to get a standard P-47D up to 470 mph by a power increase from 2600 HP to 2900 HP, you need to start with a standard P-47D that makes 460 mph at optimum altitude.

Here is the data:

Critical altitude at 64" Hg: 27700 ft.
Critical altitude 72" Hg: 26500 ft.
Power at 26500 ft, 64" Hg: 2600 HP
Power at 26500 ft, 72" Hg: 2900 HP
Speed of a standard P-47D @ 2600 HP @ 26500 ft: 438 mph
Speed of a standard P-47D @ 2600 HP @ 27700 ft: 441 mph

Here's the result of my calculation:

Speed of a standard P-47D @ 2600 HP @ 26500 ft: 454 mph

If you don't like the result, you either have an issue with the data of the F4U-4 comparison report, or you have an issue with my math. You shouldn't have an issue with my personality, though, as it has no impact on the results at all :-)

I assume you can verify the data. If you need more details on the reference P-47 (or the full report), just drop me a line and I'll help.

If you can't do the math yourself, there are a lot of people on this forum who could help you. Just ask a friendly question on the board, and you can let the community check my simple calculation.

For example, you could ask Badboy, who's a real expert - hey, you could even ask Hitech himself. If you're on friendly terms with Francis Dean, send him the data and ask for his estimate - I'm confident he would come up with a result very similar to my own.

Just to make sure you don't misunderstand the implications a second time: If there was no standard P-47D doing 460 mph, there was no way that going from 2600 HP to 2900 HP would produce a 470 mph P-47D.

I hope you recognize now that my question regarding the 460 mph standard P-47D was well in context.

If you don't have data on such a P-47D, any data would help our analysis, for example by illustrating the possible variations between different Jugs.

I appreciate that you think me worthy of being flamed, but I'm a bit disappointed that you do so before we've really dug into the data ;-)

>By the way, you didn't answer my only question... An easy one too.

I purposefully left it unanswered because I fail to see what me flying Aces High or not has to do with the top speed of the P-47.

However, I never made it a secret that I don't fly Aces High. I'm tempted to say "yet", though, as I follow its development with great interest and consider it the most promising online fight simulator currently available to the public.

>That's too bad, because an expert of your caliber could certainly point out any errors in the flight model physics of the P-47 or Bf 109. No doubt, Hitech Creations would hang on your every word.

In the discussions on this forum, Hitech has occasionally commented on my posts. If you'd care to look up these comments, you'd find that Hitech has usually given me very thoughtful answers that prove that he really knows his stuff.

I don't think Hitech have written such nice answers if he'd have thought me to be a lunatic Luftwaffe fanatic :-)

Regards,

Henning (HoHun)

[Widewing]

Originally posted by HoHun
Hi Widewing,

>Where did I state that a "standard" P-47D was a 460 mph fighter? Answer: Nowhere.

As I pointed out above, to get a standard P-47D up to 470 mph by a power increase from 2600 HP to 2900 HP, you need to start with a standard P-47D that makes 460 mph at optimum altitude.

Here is the data:

Critical altitude at 64" Hg: 27700 ft.
Critical altitude 72" Hg: 26500 ft.
Power at 26500 ft, 64" Hg: 2600 HP
Power at 26500 ft, 72" Hg: 2900 HP
Speed of a standard P-47D @ 2600 HP @ 26500 ft: 438 mph
Speed of a standard P-47D @ 2600 HP @ 27700 ft: 441 mph

Here's the result of my calculation:

Speed of a standard P-47D @ 2600 HP @ 26500 ft: 454 mph


Let's stick to Johnson's Jug.

P-47D-5-RE, R-2800-21

Power at 25,000 ft, 52" Hg: 2,000 hp
Power at 27,000 ft, 64" Hg: 2,300 hp

Those are the baseline numbers for Johnson's Thunderbolt as delivered per P&W data sheet for the -21 engine (ref. Bodie collection).

Gould was told by P&W that 72" Hg would generate 2,700 hp.

Baseline speed for the P-47D-5-RE was 433 mph @ 27,000 ft. on 2,300 hp.

Base your calculations on these numbers.

Either way, the fact that the P-47M attained 475 mph on 2,800 hp at 32,600 ft is a major stumbling block opposing your assertion that a P-47D-5-RE would require 2,900 to reach 470 mph when it has less drag and weighs 800 lbs less.

In the meantime, why don't you download the software, it's free. Then set up an account, the first two weeks are also free. This way, if we become annoyed with each other, there's some minimal recourse for revenge! LOLOLOLOL

No, that wouldn't be fair, I've been doing this a while. But, I would be willing to show you the "ropes" so to speak, to help shorten the learning curve (which is remarkably steep).

My regards,

Widewing

[HoHun]

Hi Widewing,

>P-47D-5-RE, R-2800-21

>Power at 25,000 ft, 52" Hg: 2,000 hp
>Power at 27,000 ft, 64" Hg: 2,300 hp

>Gould was told by P&W that 72" Hg would generate 2,700 hp.

>Baseline speed for the P-47D-5-RE was 433 mph @ 27,000 ft. on 2,300 hp.

OK, one additional assumption is that critical altitude for 74" Hg drops by 1200 ft compared to 64" Hg just as suggested by the F4U-4 comparison documents.

In this case, the calculated speed at 25800 ft/2700 HP would be 450 mph.

This is based on a 5 mph drop in speed at 2300 HP that I calculated for the increased density at the lower altitude.

If the drop is only 3 mph as indicated by the F4U-4 comparison, the final speed at 2700 HP would be 454 mph.

Despite its lower 64" Hg top speed, "Bodie's" P-47D is more efficient aerodynamically as it has 300  HP less available and yet reaches a top speed that's only slightly lower though it has a lower critical altitude, too. If you virtually put the "F4U report" engine into the "Bodie" P-47D airframe, you arrive at a calculated 462 mph airspeed at 2900 HP/26000 ft, which is a considerable improvement over both individual reports. If we suppose both are accurate, that might actually be realistic!

>Either way, the fact that the P-47M attained 475 mph on 2,800 hp at 32,600 ft is a major stumbling block opposing your assertion that a P-47D-5-RE would require 2,900 to reach 470 mph when it has less drag and weighs 800 lbs less.

In fact, it would be a quite interesting comparison and a good "sanity check" - if I had any data for a P-47M and N.

>But, I would be willing to show you the "ropes" so to speak, to help shorten the learning curve (which is remarkably steep).

Now that's a nice offer :-) I'm patiently waiting for Aces High 2 in the hope that the learning curve will get even steeper ;-)

Regards,

Henning (HoHun)

[Nilsen]

Great post widewing, thx