P-47 with a healthy dose of hindsight?

[Shortround6]

Hooker was part genius.

I don't have the information on the Merlin but for the Allison it goes something like this:

Assuming you can get 10,000lbM/hr of air through the engine it will give you (after taking out 147hp for friction,etc) 1285hp for an engine with 9.60 supercharger gear and 1425 hp for an engine with 6.44 gears. of course the 6.44 gear engine can only deliver the 10,000lbM/hr at sea level. Now stick on the auxiliary stage. depending on gear ratio used in auxiliary stage the the aux stage needs from 220hp to 370hp to deleiver 10,000lbM/hr. (drive ratios from 6.85 to 8.8 ) so if you use the 6.44 gear on the engine and pick a middle gear for the aux supercharger ( it really used a variable drive) you need to subtract about 275hp from the 1425hp to give you 1150hp at whatever altitude the aux supercharger will give 10,000lbM/hr of air with the gear ratio used.

If you want say 1400hp from the engine at the prop at 20,000ft you need to strengthen the engine to stand up to the power developed in the cylinders ( and the cooling system to go with it) to drive the superchargers and the prop. Pull the Aux supercharger off and you may have a 1700hp engine at sea level

The Corsair and Hellcat ( and Wildcat) did use two stage superchargers, just not quite as well developed as the "sidewinder"

 

[tomo pauk]

A question: where was the throttle and carburetor of the two-stage R-2800 located? Before aux stage, or between the stages?

 

[drgondog]

Put those R2800 engines in F4U airframes with a supercharger / turbocharger suitable for the bomber escort mission. Or else fix P-38 for the bomber escort mission and use F4U for the multitude of missions taking place below 20,000 feet.

No obvious place to put the Turbo/ducting/intercooler up front and still keep fwd fuel tank volume. If you try to stick it aft of cockpit the ducting has to run under the cockpit and has questionable effect on drag increase. Only the F4u-1 series had enough fuel to match the late model P-47D's - still too short range independent of fuselage fule storage impact a Turbo probably would have introduced. Having said this...

http://commons.wikimedia.org/wiki/File:XF4U-3_NAN6_46.jpg

P-38 could have been a long range escort for most of Germany if the increased leading edge fuel cells had been designed earlier and the other pre J-25 issues resolved by end of 1942.

 

[Shortround6]

A question: where was the throttle and carburetor of the two-stage R-2800 located? Before aux stage, or between the stages?

Between the stages, on the F4U there were doors in the intake ducts that would route the air from the wing leading edges right to the carburetor by bypassing the Aux stage completely when it was in neutral. On the F6F the air always went through through the Aux stage regardless of wither the impeller was powered or not.

 

[gjs238]

P&W's achievements are pretty amazing. Their (non-turbo) 2-stage development seems way ahead of their US peers.

 

[tomo pauk]

Going by the AHT, the 1st serial produced fighter with two-stage engine (the F4F-3 with a version of the P&W R-1830), was delivered in August 1940. Unfortunately, the 2-stage R-1830 was immediately equaled or surpassed in power by single stage European engines.
The 1st six two-stage R-2800s, B series, were delivered through second half of 1942, production was in double digits monthly from March 1942 on, and above 100 pcs monthly from July 1942.
The P&W 2-stagers were providing plenty of power (not so much the R-1830, but still) early enough. Main shortcomings was that they were radials (= more drag than decently installed V-12), low capability to recover as much of ram as possible (= shortcoming for higher altitudes; comparable with BMW-801 with internal intakes) and late or no introduction of individual exhaust stacks (= lower exhaust thrust = less speed). The later two shortcomings were due to way the engines were installed; P&W was testing the individual exhaust stacks and fan cooling as early as winter of 1941/42 in the XP-42.

 

[Shortround6]

As a bigger change - opt for a two-spar wing, retract the main wheels in front of the front spar, so there is ample space in the wings for consumables, predominantly fuel?

P-47 wing was often described as "5" spar but the definition of "spar" seems fairly elastic, much like the debates about the Spitfire single spar wing

Going from front to back and using my numbering system (others may vary).
The #1 spar ran from the wing root to just short of the tip (last rib) in front of the wheel well and gun bay. It was the forward attachment point for the wing to fuselage.
The #2 spar ran from the outside of the wheel well to the inside of the gun bay. it did NOT attach to the fuselage and was not reintroduced on the outboard side of the gun bay.
The #3 spar ran from the wing root to just short of the tip (last rib) in back of the wheel well and gun bay. It was the rear attachment point for the wing to fuselage.
The #4 spar ran from the wing root to the 5th rib past the flap/aileron joint. It did NOT attach to the fuselage and was the mounting point for the slotted flap.
The #5 spar ran from flap/aileron joint to the last rib/end of aileron and overlapped the #4 spar by 4-5 ribs but was behind it at that point. It was the attachment point for the ailerons.

Now you can call "spars" #2,4 and 5 what you want but #4 and 5 take up little or no room inside the wing and many single or two spar wings had "mounting plates", "false spars", "local reinforcing" etc to mount flaps and ailerons to.

Spar #2 is the only one that takes up much room in the wing but it's primary purpose is to provide local support/strengthening for the landing gear attachment point. Take it out and you need to add weight to the exiting spars/ribs/skinning to handle the load.

Wheel well and gun bay take up the room between spars #1 and #3. The P-47 wheel/tire was 34in X 9in if I am reading the diagrams correctly. Moving the #1 spar back far enough to clear the wheel/tire (without a wing root bulge like a P-51) is going to be a major change and/or result in a major kink in the spar as it moves forward to clear the gun bay. Or cut holes in spar to clear gun receivers (not just barrels) or move guns back into wing, but then they hit the rear spar, unless you move that back to the flap joint line?

The standard P-47 wing might have been able to hold around 50 gals in each wing just in the leading edge and tank/s behind undercarriage leg.

For it's size the P-47 wing is not all that thick and you may have some trouble moving things around without adding bulges and bumps like a late Bf 109 wing.

 

[tomo pauk]

I was thinkering about the 2-spar wing to be designed from the get-go, not as a part of a redesign. The 'kink' for tires should be mandatory, leaves a far more space instead of going with two closely-mounted spars.
BTW, it would be great if someone can toss some info about flight tests of that XP-47 (-F?)prototype outfitted with laminar-flow wing.

The standard P-47 wing might have been able to hold around 50 gals in each wing just in the leading edge and tank/s behind undercarriage leg.

Agreed.

 

[Shortround6]

Thing is that the P-47 wing was close to a two spar to begin with. While the front main spar (#1) web thickness tapered from 0.25 in at the wing root to .032 in at the out board end the landing gear spar was .091 in thick and the spars #4 and 5 varied from .072 to .032in thick.

A P-47 wing went about 1450lbs, taking out spars and reinforcement may actually run the weight up if ribs and skinning have to be increase to compensate for the spars being taken out. Moving the front spar from 12-15in back of the leading edge to 24-30in from the leading edge may require a bit of reinforcement to the leading edge. It also shifts the guns and ammo rearward in the wing unless you cut a few large holes in the front spar (which means it actually needs to be heavier there).

 

[GregP]

The people at Allison offered the USAAF an integral 2-stage supercharger at least twice and were told, "No thanks" at least twice. The government got exactly what it specified .... a low-to-medium altitude engine. The turbocharger was also specified. There is nothing wrong with the Allison other than the intake issue and not anticipating different fuel in Europe that the government didn't cause. Nobody knew in 1929 (when the V-1710 was designed) that Europe would be a high-altitude war. When they found out, there SHOULD have been a crash program to make a 2-stage engine and there wasn't. Who's fault is that?

I do not think the P-47's turbo could have been relocated forward when the P-47 was first designed, but things could have been done to make it better. One might have been move the turbo back another 2 feet and the cockpit forward another 1 foot. Another possibility would be to move the R-2800 back about 3 feet, sort of like the Polikarpov I-16 Rata's engine location. The the turbo could move forward some. and the airframe gets smaller, which equates to lighter.

Bubble canopies had NOT been invented yet, so that is pie in the sky. Likewise, ALL military fighter control surfaces to that point and been fabric covered. The Ford Trimotor and Junkers Ju-52 (and earlier civil planes) may have had metal control surfaces, but were not fast enough to excite flutter to any degree. What would cause anyone to cover them with metal without considerable testing of same? Particularly flutter testing. It had not been done and there was NO indication that it SHOULD be done until combat at high speeds indicated maybe quicker roll and pitch were needed. I doubt the fabric rudder ever inconvenienced anyone with lack of effectiveness. The rudder was probably covered with metal the first time just because the rest of the surfaces were.

To me it would make much more sense to ask P&W to make a 2-stage supercharger for the R-2800 instead of a single stage with turbocharger. Then the engine could have been moved back maybe a foot and the cockpit maybe the same or forward slightly in an overall smaller and lighter airframe ... but not a LOT smaller and lighter ... but some. Other than that, there isn't that much wrong. The Germans and British never anticipated long escort missions or they would have had long-range fighters. They never DID.

So maybe we get some slack for the P-47, which solved a LOT of problems when it got to Europe. Not entirely, but it certainly flew missions the Spitfire and Hurricanes could not fly. All in all, a pretty decent high-altitude fighter. In fact, probably the best of WWII above 30,000 feet.

I might have gone with different armament had I been there and in charge ... and maybe NOT. Depends on what could be found that was demonstrably better than the Browning .50 and also available to the USA in quantity at the time. Maybe the Browning .50 was the best we had to offer at the time.

There was no possibility to come up with a Bearcat-like thing since the specification for the P-47 called for both the turbocharger AND the range.

 

[pbehn]

Bubble canopies hadnt but the Malcolm hood had

 

[Shortround6]

True 'bubbles' no but something better than than the 'razor back'?

Off course with a large chunk of armor and heavy framing rearward vision is a bit restricted even with a transparent rear section of canopy.

 

[tomo pauk]

...

Bubble canopies had NOT been invented yet, so that is pie in the sky.

Not bubble canopies, but Republic can take a peek in the X(P)-38 for some hints.

Likewise, ALL military fighter control surfaces to that point and been fabric covered. The Ford Trimotor and Junkers Ju-52 (and earlier civil planes) may have had metal control surfaces, but were not fast enough to excite flutter to any degree. What would cause anyone to cover them with metal without considerable testing of same? Particularly flutter testing. It had not been done and there was NO indication that it SHOULD be done until combat at high speeds indicated maybe quicker roll and pitch were needed. I doubt the fabric rudder ever inconvenienced anyone with lack of effectiveness. The rudder was probably covered with metal the first time just because the rest of the surfaces were.

With what were the control surfaces of the Spitfire, Bf-109, P-38 and P-40 covered with?

To me it would make much more sense to ask P&W to make a 2-stage supercharger for the R-2800 instead of a single stage with turbocharger.

It would be really cool - the two stage R-2800. Produce those in thousands?

...

So maybe we get some slack for the P-47, which solved a LOT of problems when it got to Europe. Not entirely, but it certainly flew missions the Spitfire and Hurricanes could not fly. All in all, a pretty decent high-altitude fighter. In fact, probably the best of WWII above 30,000 feet.

I might have gone with different armament had I been there and in charge ... and maybe NOT. Depends on what could be found that was demonstrably better than the Browning .50 and also available to the USA in quantity at the time. Maybe the Browning .50 was the best we had to offer at the time.

There was no possibility to come up with a Bearcat-like thing since the specification for the P-47 called for both the turbocharger AND the range.

Agreed with this.

 

[Shortround6]

With what were the control surfaces of the Spitfire, Bf-109, P-38 and P-40 covered with?.

Ailerons
Spitfire started with Fabric.
P-38 used metal
P-39 used fabric
P-40 used fabric
F2A used fabric
F4F used fabric
F4U used plywood wight fabric covering, off course the F4U also used fabric on the rear part of the outer wings.
F6F used fabric

A number of the American planes used a combination in which the leading of the aileron ( around 25%) was metal with the rest fabric. The use of fabric covered ailerons was certainly a common design practice at the time the P-47 was designed.

 

[gjs238]

Can someone explain why one would want to make these parts from wood and fabric?
Sounds very WWI to a layman.

 

[Shortround6]

A lot of it had to do with weight. Fabric can be a lot lighter than even thin sheet metal and you need a certain minimum thickness of sheet metal for strength. For coverings, either fabric or metal you are talking about ounces per sq yd.

as far as WW I goes, aircraft built in the late 20s and early/mid 30s were often described as "all metal" when in fact they were almost completely fabric covered. The structure ( frames, longerons, spars, ribs, struts etc) being all metal instead of wood.