P-47 Combat Tactics 101, by Robert S. Johnson

[Jigster]

 

Originally posted by Widewing:
Ah, I don't want to cause any upset, but the F4F Wildcat was never fitted with a turbo-supercharger. The F4F-3 and F4F-4 were powered by the Wright R-1830 with a two-speed, two-stage mechanical supercharger.

The author of the above named magazine article made a noteworthy error in his nomenclature. Most likely, what he had been told or read was that the crew chiefs of the Wildcats rigged the superchargers so that they were always in 'high blower'. This causes the engine to be over-boosted at altitudes were 'low blower' should be used. Normally, 'neutral blower was used for takeoff, 'low blower' used till about 18,000 ft, where 'high blower would be engaged. Flying at full throttle/high blower at low altitudes for long durations will inevitably cause engine damage due to detonation, especially with the R-1830 which was not as over engineered like the P&W R-1820.

My regards,

Widewing

And besides that...there's no need to rig a turbocharger, they are always on!  

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 Moo! to fanatics, Neigh! to everyone else.
 -- Bessy
   
Dirty Turd Poop Group www.33rd.org

[Buzzbait]

S! St Santa

The aircraft was a 190A5.  All of the aircraft tested during the war by either the USAAF or the British Air Fighting Developement Unit (AFDU) were earlier model 190A's.  They included A3's, A4's and A5's.  The A8 was not tested in comparison with Allied aircraft.  Most of the aircraft tested were A4's and A5's which were captured when operating in the night Jabo fighter bomber role over southern England in 1942-1943.  Most of them only had the wing root cannon.  The exception was Faber's A3, which was a air superiority model, fully equipped with four cannon and 2 Mgs.  All of the aircraft were captured by the British and test aircraft were then supplied to the USAAF.  All the test aircraft were in perfect condition, after their pilots mistakenly landed at British Fields when their pilots became confused.

For more information on the German aircraft captured as well as many excerpts from various AFDU tests, I would reccommend reading "The Captive Luftwaffe"

As far as the particular test I listed above, I don't have a web site or URL for it.  I transcribed it a year ago from a book called "Thunderbolt", author I am unsure of.  The A5 tested, was the same one used in a test vs. the F4U, F6f and P51b the results of which has been posted on this board before.

A comment on P-47's performance generally:

The models used in AH are those manufactured after the re-design in early 1944.  During this re-design, the bubble top canopy was added, as well as pylons for bombs, strengthening of the under section of the fuselage for carrying more bombs, and the addition of more internal fuel tanks.  This redesign basically set the mold for the ground attack role which the P-47 found itself assigned to.  This new model began with the P-47D-25 series.  The redesign also added nearly 1000 lbs when the aircraft was loaded, bringing it up to approx. 14,500.  These models all came standard with the Paddle Blade prop and Water Injection.

The D models prior to this weighed in around 13,500.  These were the Razorback P-47D4 through D23.  The early serials of this group did not have the Hamilton Standard Paddle Blade Prop or Water Injection, but were upgraded beginning in December of 1943.

As far as I am concerned, the D4 through D23 were the "Hotships" as far as P-47's were concerned.  (not counting the P-47M)  They had low weight, but the advantages of the upgraded performance available with Water injection and the superior propellor.  Bob Johnson flew these aircraft predominantly.  If you look at wingloading for these models, with a wing area of 300 Sq. Ft., it translates to 45 lbs/sq ft with tanks fully loaded.  Considering the P-47's rarely flew with full tanks when in combat, due to the ranges at which they were operating, then you can see they became quite competitive in actual combat situations.

[StSanta]

Interesting info, buzz

If it's true, then the P47 isn't modelled correctly - it climbs only marginally better than A8, and has a marginal speed advance.

Zoom cilmbs between the two indicate a small advantage to the P47's advantage, but not enough to allow a spiral climb tactics described in your first post. And doing so with a G10 up yer rear is an invitation to disaster.

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Baron Claus "StSanta" Von Ribbentroppen
9./JG 54 "Grünherz"

"I don't necessarily agree with everything I think." - A. Eldritch

[Buzzbait]

S! Wid

These P-47's are probably not far off, except perhaps in their ability to turn at high speeds.  The reason is they are the heavier ground attack oriented version.

[Lephturn]

I'd love to get my hands on a paddle blade prop razorback.  

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Lephturn - Chief Trainer
A member of The Flying Pigs  http://www.flyingpigs.com
 
"A pig is a jolly companion, Boar, sow, barrow, or gilt --
A pig is a pal, who'll boost your morale, Though mountains may topple and tilt.
When they've blackballed, bamboozled, and burned you, When they've turned on you, Tory and Whig,
Though you may be thrown over by Tabby and Rover, You'll never go wrong with a pig, a pig,
You'll never go wrong with a pig!" -- Thomas Pynchon, "Gravity's Rainbow"

[Pongo]

Would the engines on the F6F and  F4U be able to be tuned the same way?

[Widewing]

 

Originally posted by Pongo:
Would the engines on the F6F and  F4U be able to be tuned the same way?

No, not exactly. The mechanical supercharger is geared to run off of the engine. There are several different gears that provide for several different ratios, not unlike a car's transmission. Therefore, boost will vary with the speed of the supercharger compressor, which changes speeds and stages as the altitude goes up. The turbo is different in that it will be producing the same boost pressure over the entire altitude range. When an overpressure condition exists,
the wastegates open and dump that excess pressure to ambient (outside). If the wastegates are adjusted, or have their pop-off springs changed with stiffer springs, the wastegates maintain a higher pressure.
Mechanical superchargers deliver a specific pressure according to what setting is selected. Some aircraft had mechanical lockouts preventing the use of high blower at low altitudes. This can be overriden by a mechanic, but not by the pilot. I have heard that doing this leans the mixture excessively raising cylinder head temps beyond normal limits and shortens engine life dramatically. Turbochargers simply keep induction air at the same density as sea level regardless of altitude, and do not lean the mixture by elevating the density of the intake charge, as flying in high blower at low altitude does.

Have I made this easier to understand, or did I make it only more muddled?

My regards,

Widewing

[Pongo]

The Corsair And F6F have a differnt system to boost HP at alt then I guess. The 47 and 38? have Mechanical Superchangers and the Navy birds have Turbosuperchagers....
Different system and not as tuneable...

[Widewing]

 

Originally posted by Pongo:
The Corsair And F6F have a differnt system to boost HP at alt then I guess. The 47 and 38? have Mechanical Superchangers and the Navy birds have Turbosuperchagers....
Different system and not as tuneable...

You have it backwards. The P-38 and P-47 utilize turbosuperchargers. All Navy fighters incorporate mechanical superchargers.

Turbos use exhaust gases, impinging on a turbine, to turn a compressor. Mechanical superchargers are gear driven from the accessory drive of the engine. Turbos generate horsepower without consuming horsepower. Mechanical superchargers consume a small amount of horsepower to make horsepower. When engine revs exceed 2,000 rpm, the turbo is at maximum efficiency and its speed is controlled by a regulator. A mechanical supercharger's speed is directly related to and will vary with engine rpm.

My regards,

Widewing

[Pongo]

Thanks.
So could the allison in the P38 benifit the same way? Or not robust enough to take it?

[Lephturn]

Just as a note, there is a penalty for using a turbo supercharger.  That penalty is ducting.  In order to drive the turbo, you have to duct exhaust gasses through a turbine in an efficient manner.  One of the reasons the P-47 is so big is to contain all of that ducting!  However, the benefit is that the P-47's turbo system gives it stable boost across the altitude range.  This means that the 47's power is more consistent, and maintains power better at high altitudes.

Pongo, I don't know if the Allison was as "over engineered" as the P&W R2800 was.  There was a lot of saftey margin in the engine the Jug used, meaning a good tuner could push it harder and still not have problems.  Although it would shorten the service life of the engine, the lifespan under normal normal boost settings was longer than required.  They could up the boost and still get plenty of life from it.    It's possible the Allison didn't have as much of a safety margin built into it.  Pushing the Allison may have caused problems, but I'm just guessing.

------------------
Lephturn - Chief Trainer
A member of The Flying Pigs  http://www.flyingpigs.com
 
"A pig is a jolly companion, Boar, sow, barrow, or gilt --
A pig is a pal, who'll boost your morale, Though mountains may topple and tilt.
When they've blackballed, bamboozled, and burned you, When they've turned on you, Tory and Whig,
Though you may be thrown over by Tabby and Rover, You'll never go wrong with a pig, a pig,
You'll never go wrong with a pig!" -- Thomas Pynchon, "Gravity's Rainbow"

[Jigster]

I've read many times where P-38 pilots in the Medd. were boosting to 72" MP. Most of the engagements with the LW were under 15k.

[Widewing]

 

Originally posted by Jigster:
I've read many times where P-38 pilots in the Medd. were boosting to 72" MP. Most of the engagements with the LW were under 15k.

This was certainly done, but it did not bode well for the engines. The Allison was one of those engines that did not tolerate detonation well. Most of the engine failures experienced by the P-38s operated by the 8th Air Force were a direct result of detonation.

Down low, this becomes less of a problem because the temperature is considerably higher. However, at -50 degrees, the V-1710 suffered from the lead in the fuel coming out of solution. Since cylinders 4 and 6 always ran a bit lean, this resulted in locally elevated temperatures and ultimately,
detonation which led to broken piston rings and melted piston crowns on these two cylinders. This problem was greatly exacerbated with the P-38J, which had vastly more efficient intercoolers than previous models. This resulted in intake charge temperatures running up to 50 degrees cooler than in the P-38H (both models using the V-1710-90 & -91 engines). This was corrected with the P-38J-25-LO and the subsequent P-38L.

Again, at low altitudes, this is much less of a problem. Nonetheless, mechanics were loath to fiddle with the wastegates of the p-38. As it was, frozen turbo regulators could result in over-boosting. Moreover, the regulators were notoriously slow to respond and it was very easy to obtain high manifold pressures for brief periods.

My regards,

Widewing

[Jimdandy]

That's very special Widewing. I'm sure he was very happy to talk to you. Thank you for posting it. We wont see these people around much longer. It's very important to get their stories.

[Jimdandy]

 

Originally posted by Jigster:
And besides that...there's no need to rig a turbocharger, they are always on!  

That is true but the waste gate controls the boost. If you kept the waste gate closed you could over boost the engine.