Radial engine 2-stage superchargers (R-2800, etc)

[gjs238]

Can anyone shed some light on the development use of multi-stage/multi-speed superchargers in the radial engines of WWII?

When did radial engine 2-stage superchargers become available?
I understand later versions of the F4U Corsair had 2-stage superchargers.

Allison seems to have taken a lot of heat for lack of development of 2-stage superchargers, but what about the makers of radial engines?

How did radial engine supercharger development compare to that of inline engines?

 

[hrandy]

I believe the first two stage mechanical supercharger was on the P&W R-1830-19 in 1938. Later -76 and -86 variants of the two stage R-1830s were used on Grumman F4Fs. There were some significant problems with engine surging that were not well understood at the time but were probably connected to poor diffuser design.

All the wartime P&W R-2800 powered F4Us as well as Grumman F6Fs had 2 stage mechanical superchargers.

While Rolls-Royce, Bristol, Napier, Daimler-Benz, Junkers, BMW and others were receiving generous financial support in the 1930s from their respective governments, Allison and all the other American engine manufacturers got no money from the U.S. government. Additionally the USAAF wanted all their high altitude aircraft powered by single speed mechanical superchagers assited by turbo chargers. This worked well with bombers with podded engines, but was a disaster with small single engine fighters. By the time the USAAF realized the error of its ways it was too late for Allison to make up lost ground to Rolls-Royce or Daimler-Benz.

The Allison 1710 in my opinion was a better basic design than the Rolls-Royce Merlin. It suffered greatly in comparison to the simply brilliant two stage two speed after cooled Merlins. The small engineering department at Allison simply coudn't develop the 1710 as quickly as the large well funded engineering department at Rolls-Royce.

Nothing on the radial engine side compares to the sophistcation of the two stage two speed after cooled Merlins. For long range bombers the turbocharged radials were the best. Of course turbojets were about to eclipse all piston engines as the war ended.

 

[gjs238]

All the wartime P&W R-2800 powered F4Us as well as Grumman F6Fs had 2 stage mechanical superchargers.

I thought only the F4U-4 "4-Hog" had 2-stage supercharging, using the -18W engine (?)

 

[hrandy]

Every reference I have seen states that the F4U-1 and the F4U-2 were powered by either the R-2800-8 or 8W. My favourite R-2800 book, Graham White's "R-2800 Pratt and Whitney's Dependable Masterpiece" shows the -8 and -8W as two stage intercooled engines. The second stage supercharger had a fixed drive ratio of 7.93 to 1, while the first stage supercharger had neutral, 6.46 and 7.8 to 1 ratios available.

Graham White's book has a few pages of information on the Corsair. On Page 463 he states that the only production Corsair with a single stage engine was the F4U-6 (AU-1), which was produced as a ground attack aircraft well after the end of WWII.

I've often wondered if the two stage R-2800s were worth the cost, complication and weight. It seems to me that the BMW 801 was close in output to the two stage B series R-2800s in a much more compact, lighter and probably cheaper package.

Another comparison that makes me wonder about the value of the two stage intercooled R-2800s is the big difference in speed between the P-61B (two stage mechanical supercharged C series R-2800-73s) at 366 mph at 20,00 ft. and the P-61C ( C-series R-2800-57s with CH-5 turbo-supercharger) at 430 at 30,000 ft. These are both two stage engines engines but the P-61C is a lot faster despite the very unaerodymanic looking turbo-supercharger housing under the engine nacelles.

 

[jerryw]

I came across the PATENT for the -32W "sidewinder" type superchargers recently. Makes interesting reading.
The number of the doco is US 2,667,298 and it is titled, "Arrangement of Opposed Superchargers".(Five very nice drawings) It can be downloaded free from the uspto.gov website.
Written by the designers, it gives a lot of insight into the thinking at the time.

 

[gjs238]

I came across the PATENT for the -32W "sidewinder" type superchargers recently. Makes interesting reading.
The number of the doco is US 2,667,298 and it is titled, "Arrangement of Opposed Superchargers".(Five very nice drawings) It can be downloaded free from the uspto.gov website.
Written by the designers, it gives a lot of insight into the thinking at the time.

Nice drawing!
It would be great to see a photo of this and any other supercharger arrangements.

 

[renrich]

All F4Us including the XF4U had two speed, two stage superchargers on the R2800s. See Dean's "America' Hundred Thousand" for a description of how they worked.

 

[renrich]

All F4Us including the XF4U had two speed, two stage superchargers on the R2800s. See Dean's "America' Hundred Thousand" for a description of how they worked.

 

[krieghund]

For the Allison check out the V1710-119 in the P-51J they finally got there but too late to make an impact

 

[krieghund]

For the Allison check out the V1710-119 in the P-51J they finally got there but too late to make an impact

 

[Shortround6]

All F4Us including the XF4U had two speed, two stage superchargers on the R2800s. See Dean's "America' Hundred Thousand" for a description of how they worked.

All WW II Production F4U's had two stage superchargers.

The F4U-5 and the F4U-6 were post war aircraft. In fact the F4U-6 wasn't delivered until the end of 1951. The F4U-5 had the "sidewinder" set up and the F4U-6 (or AU-1)was a dedicated ground attack plane and had the single stage supercharger with 2 speeds.

There is some doubt/confusion in various sources about the engine in the XF4U. It may or may not have had a two stage engine. It may have been re-engined at some point leading to the confusion.

 

[renrich]

I never heard the AU1 being called the F4U6 but it had a single stage single speed supercharger. The F4U7, the last production model had the same engine as the later model F4U4s, the R2800-43W.

 

[Sgt. Pappy]

I know that the R-2800-8W fitted to F4U-1A/-1D Corsairs allowed 5 minute water injection at some 60" Hg/2700 RPM and 54" Hg/2700 RPM for max 5 minute use without the water-methanol injection.

Some tell me that the F4U-1 (fitted with an R-2800-8 not an -8W) could not achieve a War Emergency Power setting; i.e. a setting above 54" Hg/2700 RPM.

Is this true? Did the F4U-1 have no WEP at all?

 

[Shortround6]

Is this true? Did the F4U-1 have no WEP at all?

For a bad answer, it depends.

Some Corsairs with -8 engines were retrofitted in the field with water injection (ADI) kits. They had the same WEP as the -8W engines but according to one source the engine designation was not changed to add a "W" when the conversion was made. This makes it rather hard to figure out which planes had it and which didn't.

It also makes it rather hard to tell from a pilots action report if he had a modified engine/aircraft or not. I mean if a pilot says he used WEP on such and such a date in his F4U-1, the reader has no way of knowing if the plane had been retro fitted or not.

I would also note that the P&W R-2800 at 54" was running at 12 lbs of boost or about 1.8 atmospheres which is pretty high for an air-cooled engine WITHOUT some sort of help.

 

[Sgt. Pappy]

Ah got it.

Yes, I've read of those modified -8's before. I suppose no old birdcage F4U-1 was ever factory fitted with the kit though.

Side note: Why would air-cooled engines be less inclined to produce higher boost pressures than liquid-cooled? Or at least that's what your note suggests.

 

[Shortround6]

Side note: Why would air-cooled engines be less inclined to produce higher boost pressures than liquid-cooled? Or at least that's what your note suggests.

Two reasons that I can think of.

1. The cooling issue. This is in reference to WEP settings. The air cooled engine had no real reserve of cooling "power". It's normal take-off or military setting usually ran the temperature up against the limits pretty quick. And once the cylinder head and parts (valves) got too hot the engine was more likely to suffer from detonation.
With liquid cooled engines you had to raise the temperature of the circulating coolant before this happened and not just the metal in the cooling fins. It gave an extra few minutes before bad things started to happen.
ADI did several things but most of them relate to keeping the engine cool in one way or another.

2. Strength of the engine itself. In a v-12 engine. at least the ones used in WW II the cylinders were in one piece blocks fastened to the crankcase. The heads, if they were separate from the cylinder block were also one piece. The air-cooled engines used separate cylinders which meant that the whole assembly wasn't quite as strong as the V-12. You also had either 7 or 9 cylinders acting on a single crankpin vs the 2 cylinders acting a single crankpin in the V-12.

Please note that this is not automatic. The V-12s that you hear about using the higher pressures are pretty much the Merlin, Allison and Griffon. All three tended to be heavy engines for their displacement which may mean they had a bit of extra "beef" to begin with. The Hispanos and Hispano derived engines were very light engines for their displacement and tended not to like over boosting very much. THe German engines were sort of in between.

 

[Timppa]

Side note: Why would air-cooled engines be less inclined to produce higher boost pressures than liquid-cooled? Or at least that's what your note suggests.

looking at the late war U.S. fighters the boost levels between the engines were quite comparable. For example, with 150 grade fuel the
P-38 was cleared to 65"
P-47 was cleared to 62 to 67"
P-51 was cleared to 72".

Post war P-51H could run at 90", but on the other hand R-2800 "C" engine was tested with 150" and 3800 hp. So it seems that the differences were because of the design of the individual engines rather than any fundamental difference of characteristics between water -cooled V's and air-cooled radials.

 

[Tony Kambic]

I just finished helping rebuild the two R-2800-43 that are in Martin B-26 Marauder 'Flak Bait' for museum display. They are equipped with 2-speed single stage superchargers.

Tony

 

[MIflyer]

The F4F was the first operational fighter with two stage supercharging. The R-2800 used in the F4U, F6F, and P-61A/B used that same approach.
Attached are the control diagrams for the two stage superchargers in the R-1830 and R-2800.
Pilots flying these engines had an unusual degree of control over their supercharging. P-38, P-39, P-40, P-51 and Spitfire IX pilots had virtually no control, except for the few Mustangs modified to give the pilot direct control over activating the 2nd speed manually.

 

[tomo pauk]

...
Pilots flying these engines had an unusual degree of control over their supercharging. P-38, P-39, P-40, P-51 and Spitfire IX pilots had virtually no control, except for the few Mustangs modified to give the pilot direct control over activating the 2nd speed manually.

Pilots if the ww2 aircraft have had too much to do anyway in order to extract the desired propulsive power from their engines - RPM, boost, prop pitch, mixture. Double of that for the P-38 and it requires a 'ten hand ape' to control the engines. And all while expecting from pilots to do their missions and come back in one piece. Thus people coming out with automatic boost control units, automatic gear change, up to the single lever operation as it was the case with BMW engines. P&W went with variable speed S/C for the R-2800-30W.
BTW - it will be impossible to change the S/C gear in P-39s, 38s, most of the P-40s and some P-51s.