USAAC/AAF being much improved in 1938-42?

[tomo pauk]

The big radials did not offer the performance at altitude over the Allison that the take-off power figures suggest. Not without using cowlings and exhaust set ups that were not used historically until later in the war.
Using a late 30s (P-36) state of the art cowling the P-36 had either a 22% increase in drag over the P-40 or a 22% loss due to drag and poorer exhaust thrust.
Take 22% away from the R-2600 A series at 12,000ft and you wind up with just a bit less power than the Allison -39 engine.
The R-2800 A series does a bit better (and is smaller in diameter) but is over 350lbs heavier than the Wright engine. Which is almost 600lbs heavier than than Allison (of course the Allison needs nearly 300lbs worth of radiator and coolant).

R-2800A, in 1-stage variation, was supposed to do 1500 HP at 14000 ft on military power. That is 40+% better than any in-service V-1710 before late 1942 - quite an advantage.

 

[davparlr]

This would require working out the turbo bugs for the R-2600. And it wouldn't carry the A-bomb when that was ready (at least not a useful distance) so you still need the B-29. Possibly too much even for American industry.

I've also pondered the missing generation of heavy bombers using R-2600 or -2800. But unless you get B-29 level performance by using 6 engines this might be one gap that doesn't need filling.

I wouldn't do this to replace the b-29, although it could accept some missions the B-29 flew. Rather I would replace the B-17/24 as fast as I could (26000 eighth AF men died (this number also include fighter losses but by far the most were bomber losses)). I think thousands of lives would have been saved had we had a faster modern bomber instead of lumbering old tech bombers.

As far as turbo design is concerned, I think the consistent operational parameters of bombers simplify design.

 

[davparlr]

The big radials did not offer the performance at altitude over the Allison that the take-off power figures suggest. Not without using cowlings and exhaust set ups that were not used historically until later in the war.
Using a late 30s (P-36) state of the art cowling the P-36 had either a 22% increase in drag over the P-40 or a 22% loss due to drag and poorer exhaust thrust.
Take 22% away from the R-2600 A series at 12,000ft and you wind up with just a bit less power than the Allison -39 engine.
The R-2800 A series does a bit better (and is smaller in diameter) but is over 350lbs heavier than the Wright engine. Which is almost 600lbs heavier than than Allison (of course the Allison needs nearly 300lbs worth of radiator and coolant).

22% seems high. According to Ray Wagner, a P-36C, with 1050 hp at 10,000 ft, had a top speed of 311 mph at 10,000 ft. The XP-40, with 1000 hp at 10,000 ft, had a top speed of 342 mph at 12, 200 ft. or a loss of about 10% loss. This is probably as close as we can get to a one to one comparison.

 

[davparlr]

deleted

 

[Shortround6]

and that advantage comes with around a 33% increase in engine weight (counting radiator and coolant) and the increase in drag.

When would such a plane have to ordered (and design work completed?) in order to be in action in numbers in 1942?

Since AIrplanes were often designed as package (or had multiple requirements) you might need another 15-20sq ft of wing area to support the extra weight (keeping landing speed the same) you are going to need bigger landing gear, and so on. Yes the R-2800A powered machine may well show an advantage over the V-1710 powered plane but not anywhere near what the comparison of shaft HP would seem to indicate.

BTW the P-36 did not make very good use of exhaust thrust. The nice looking bumps on the bottom of the cowling are actually fairings and not the exhaust pipes themselves.

And lets remember that the XFU-1 first flew in 1940 making a single stage, two speed R-2800 powered fighter rather 2nd rate to Navy,
Problems with the turbos weren't considered serious in 1939-40 either, just teething troubles.

 

[Shortround6]

22% seems high. According to Ray Wagner, a P-36C, with 1050 hp at 10,000 ft, had a top speed of 311 mph at 10,000 ft. The XP-40, with 1000 hp at 10,000 ft, had a top speed of 342 mph at 12, 200 ft. or a loss of about 10% loss. This is probably as close as we can get to a one to one comparison.

you are comparing a loss of speed with the change in drag. They are not quite the same thing.
Drag goes up with the square of the speed, but drag isn't really powered required either, that goes up with the cube of the speed.

 

[pinsog]

Clean up the landing gear on the P36 and P40. The Zero was very clean and very fast on not much HP, so lets help ourselves by cleaning up the airframe so we get the best out of the available engines

 

[Shortround6]

I wouldn't do this to replace the b-29, although it could accept some missions the B-29 flew. Rather I would replace the B-17/24 as fast as I could (26000 eighth AF men died (this number also include fighter losses but by far the most were bomber losses)). I think thousands of lives would have been saved had we had a faster modern bomber instead of lumbering old tech bombers.

As far as turbo design is concerned, I think the consistent operational parameters of bombers simplify design.

The "old tech" bombers had turbos that allowed for a pretty good amount of power at 25,000ft, more than the R-2600 could supply without a turbo. The few attempts at putting a turbo on the R-2600 didn't work out well. The engine seemed to have cooling problems.
Both the B-17 and the B-24 could actually fly at pretty decent speeds, the problem was that at high power settings (high speed) the fuel burn was too high for long range.
Using R-2600 engines is not going to solve this problem, in fact it may make it worse. Couple this with the need for s rather slow speed cruise due to the large formations. formation speed being based on the worst performing plane being on the outside of the formation as it makes a turn.
A B-17F under test was able to make 237mph at 25,200ft on 750hp per engine at 48,900lbs. At about 41,500lbs it could hit 258mph using 750hp per engine. Max continous was 1000hp per engine but this really sucked down the fuel.

The R-2600 also seems to have fallen into a hole as far as turbo chargers go. The B series (of which 12 different models flew before-during the war) was intended for engines of 800-1400hp while the C series was intended for 1800hp to 2200hp. At least at first. The B-29 and B-32 used two B series turbos per engine. Improved, late war versions of both types easily handled higher HP limits than those just listed, however the Turbos used in P-38Js were not available in 1940-41 when design work on the R-2600 powered bomber would have to be done. Please remember that the XB-29 was ordered in Aug of 1940 and a mock up was being inspected in May of 1941.

You might wind up with a lot fewer bombers.

 

[swampyankee]

Clean up the landing gear on the P36 and P40. The Zero was very clean and very fast on not much HP, so lets help ourselves by cleaning up the airframe so we get the best out of the available engines

"Cleaning up the landing gear" on the P-40 would likely require a new wing.

 

[pinsog]

"Cleaning up the landing gear" on the P-40 would likely require a new wing.

You may very well be correct, but if a bomb/drop tank mount cost 10 mph (several tests on wwiiaircraft performance show about 10 mph for a drop tank mount) how much speed did that P36/P40 landing gear cost? 20 mph? More?

 

[tomo pauk]

FWIW, people in Finland managed to convert undercarriages of two Fokker XXIs into retractable U/Cs.
link

 

[XBe02Drvr]

how much speed did that P36/P40 landing gear cost? 20 mph? More?

That's the trouble with aft folding landing gear; stuffing a robust wheel/strut assembly into a wing at near its thinnest point. An improvement of sorts over fixed gear, but a much greater penalty on a plane groping towards 350 mph than on its 250+ class predecessor. If you look at the innards of the wing center section area, there just isn't room for inward folding gear, and outward folding like the ME and Spit is a non starter on a plane that's likely to operate off rough fields with pilots who are new to the low wing, all metal, folding feet monoplane business. Remember, Curtiss had a thriving export business before the Hawk 75 line came along.
SwampYank is right, a wing redesign would be in order. Can you imagine enclosing that gear well with fairings and tightly fitting streamlined doors, then trying to operate off a bumpy, muddy field in China or New Guinea?
Cheers,
Wes

 

[pinsog]

That's the trouble with aft folding landing gear; stuffing a robust wheel/strut assembly into a wing at near its thinnest point. An improvement of sorts over fixed gear, but a much greater penalty on a plane groping towards 350 mph than on its 250+ class predecessor. If you look at the innards of the wing center section area, there just isn't room for inward folding gear, and outward folding like the ME and Spit is a non starter on a plane that's likely to operate off rough fields with pilots who are new to the low wing, all metal, folding feet monoplane business. Remember, Curtiss had a thriving export business before the Hawk 75 line came along.
SwampYank is right, a wing redesign would be in order. Can you imagine enclosing that gear well with fairings and tightly fitting streamlined doors, then trying to operate off a bumpy, muddy field in China or New Guinea?
Cheers,
Wes

Great feedback. To clarify, when you said "Can you imagine enclosing that gear well with fairings and tightly fitting streamlined doors, then trying to operate off a bumpy, muddy field in China or New Guinea?" did you mean enclosing the wheels on the current setup? My goal would be to eliminate the big fairings on the front of the wing where the landing gear attatches, which I agree would need a new wing. They need to be moved out farther and retract inward.

 

[XBe02Drvr]

My goal would be to eliminate the big fairings on the front of the wing where the landing gear attatches, which I agree would need a new wing. They need to be moved out farther and retract inward.

Roger that. Concur. The trouble is that by the time the need became evident, the design was cast in stone, the tooling in place, and production was pell-mell. We all know of the multiple attempts at an enhanced P40 which came to nought because the changes were too great and the improvement too small.
Cheers,
Wes

 

[Shortround6]

Rectangular cutouts by the "wall" are the spaces for the fuel tanks. We can see the hole for the wheel. Rectangular hole outboard of the wheel is the gun bays.

P-36s had a flap/door covering most of the wheel.

It is a pretty good bet Curtiss knew exactly how much speed taking the wheel cover off cost. And it did not come back even on the P-40Q set up as a race plane.

Some bomb racks/pylons were not exactly small

And the sway brace/brackets stayed on the plane after the bomb dropped.

Trying to estimate performance penalty on the P-36/P-40 fairing is going to be hard.

 

[hobbes154]

And lets remember that the XFU-1 first flew in 1940 making a single stage, two speed R-2800 powered fighter rather 2nd rate to Navy

XF4U-1? The Flying Flapjack didn't really go anywhere . . . Not a Navy thread but ironically single stage 2 speed is what they ended up wanting with the Bearcat and Tigercat.

Anyway getting more 2 stage planes to the Marines/Army in 1942 is what we need, whether P-43, F4F, or accelerated F4U. I wonder also if Mustang airframes could have been shipped to the UK and mated with British Merlin 61 production before Packard comes on line?

Kind of related dumb supercharger question - when engines were cleared for higher boost pressures, was that exploited simply through using more throttle at low altitude? I.e. you didn't need to change supercharger gear ratios or anything like that (which seems like a major mod to do in the field)?

 

[swampyankee]

XF4U-1? The Flying Flapjack didn't really go anywhere . . . Not a Navy thread but ironically single stage 2 speed is what they ended up wanting with the Bearcat and Tigercat.

Anyway getting more 2 stage planes to the Marines/Army in 1942 is what we need, whether P-43, F4F, or accelerated F4U. I wonder also if Mustang airframes could have been shipped to the UK and mated with British Merlin 61 production before Packard comes on line?

Kind of related dumb supercharger question - when engines were cleared for higher boost pressures, was that exploited simply through using more throttle at low altitude? I.e. you didn't need to change supercharger gear ratios or anything like that (which seems like a major mod to do in the field)?

I believe that the British converted a P-51 to have a Merlin as a proof-of-concept, so they could probably do a conversion. Are you asking if it would have made sense for North American to ship the RAF engine-less P-51s for completion in the UK? I'm not sure the UK had the industrial capacity needed for that without adversely affecting another program.

 

[Shortround6]

The British had about 4 squadrons of Spitfire IXs in Aug of 1942. They had about 10 squadrons in the late fall or turn of the year. Without crippling Spitfire IX production you aren't going to get very many Merlin powered Mustangs much earlier than historically. There was a plan put forward to send engineless Mustangs to England but it was rejected.

 

[XBe02Drvr]

You know, all this "what if" attempts to stretch performance of aircraft already at or near the cutting edge beyond the capacity of their inbuilt technology is beginning to sound like medieval theologians and angels and pin heads. And to what end? A partial reduction in combat losses in the first year of the war?
I submit that getting down off our high horse and admitting that our airmen could possibly someday encounter an enemy plane that outperforms theirs, and teaching them what to do about it would have been more effective and less of a strain on the resources than chasing the last 2% of performance. Those last few percentage points usually come at the cost of other important values such as reliability, cost, ease of handling, safety, and/or survivability.
Many of our pilots died when surprised by the tactics and performance of Zeke and Oscar and couldn't wrap their heads around that situation; their bag of tricks had come up empty. Because nobody had clued them in to that possibility or taught them how to deal with it. Planes that climbed a couple hundred feet/minute quicker or flew a few knots faster weren't going to make the necessary difference.
We Americans were so self-absorbed in our isolated continent that any evidence of foreign technical prowess was ignored or disbelieved.
Cheers,
Wes

 

[tomo pauk]

I believe that the British converted a P-51 to have a Merlin as a proof-of-concept, so they could probably do a conversion. Are you asking if it would have made sense for North American to ship the RAF engine-less P-51s for completion in the UK? I'm not sure the UK had the industrial capacity needed for that without adversely affecting another program.

The British had about 4 squadrons of Spitfire IXs in Aug of 1942. They had about 10 squadrons in the late fall or turn of the year. Without crippling Spitfire IX production you aren't going to get very many Merlin powered Mustangs much earlier than historically. There was a plan put forward to send engineless Mustangs to England but it was rejected.

By mid/late 1942, Mustang can get the Merlin 50. Yes, not the 2-stage version, but better engine than the best 1-stage V-1710 the Mustang ever got.