P-40 Twin

[Ivan1GFP]

They could be mounted much like the P-61C, which had the same engine and turbo supercharger (x2): in the upper nacelle with inlets and ancillaries in the wing.

I commented because I saw indications of neither in the drawings. If ducting and turbines take up the space behind the engines, the articulation and attachments for the main gear would get really interesting.

I was running into similar problems doing the layout for a twin P-40.
Engine is heavy and when you double them up front and add armament and ammunition all up in the nose, there is nothing to offset the weight to maintain CoG. Of course it could end up being a bit poorly balanced like a P-39. My drawings which attempted to address these issues were looking a lot less like a P-40 than I liked.
I build for flight sims, so fuel and armaments as disposable loads must be accounted for in the flight model.

 

[GrauGeist]

Here's the layout and plumbing in the P-61's engine nacelle and wing...

 

[Ivan1GFP]

For the plastic for this model, a nose from a P-80 might work.

For the twin P-40, one of the requirements was that the profile look as much as possible like a regular P-40. Thus the nacelles had to line up with the fuselage. It would be a long tail profile with a straight wing center section, stub nose like a Beaufighter and armament in the belly under the pilot and have a tail like the Constellation. Fuel would be in the wing center section and behind pilot. P-63 type supercharger would live in each nacelle along with oil coolers, coolant radiators, inter coolers and such. Wing center section would have no dihedral and outboard of nacelle would be same platform as regular P-40 but without gear fairing or armament. Nacelle also houses main gear.

 

[GrauGeist]

But the P-63's supercharger was integral to the Allison V-1710.

The P-47's supercharger and turbo system was unique to the R-2800-59 (and R-2800-73 for the P-61C)

 

[Ivan1GFP]

A V-1710 is a reasonably appropriate engine for a twin P-40 which is what I was describing. Turbos would have been interesting but then the short exhausts would be wrong and they are a visual feature I wanted to retain.

For a twin P-47, designer needs to have some excuse for the extra deep aft fuselage and contour now that the turbo and ducts are no longer mounted there.

 

[tomo pauk]

For a twin P-47, designer needs to have some excuse for the extra deep aft fuselage and contour now that the turbo and ducts are no longer mounted there.

Fuselage was pretty deep already from the nose (this is also why the gun nose from the B-25 might be a good fit).
Excuse: "those big honkin' R-2800s are drunkards, so we took advantage of the extra deep fuselage to install additional fuel tanks"

 

[tomo pauk]

Tubro is would be in the nacelles similar to the B-29 but only one turbo per engine.
The pivot for the landing gear would be in the structure of the wing but would extend through the nacelle with a 4 section gear well cover. 1 part covering the lower wheel hinged to the wing root like the original. A second section covering the upper wheel would be a shorter version of the original attached to the gear leg.
The 3rd and 4th sections would be a hinged clamshell covering the gear leg opening in the nacelle

Any thought about the rear part of the nacelle of the Ki-83, with it's turbo at the aft end of the nacelle?

 

[Ivan1GFP]

Fuselage was pretty deep already from the nose (this is also why the gun nose from the B-25 might be a good fit).
Excuse: "those big honkin' R-2800s are drunkards, so we took advantage of the extra deep fuselage to install additional fuel tanks"

Well, what happens when there is no longer an engine in the forward section of the fuselage as in this case? What is reason for a deep fuselage then? THAT was the question.

 

[tomo pauk]

Well, what happens when there is no longer an engine in the forward section of the fuselage as in this case? What is reason for a deep fuselage then? THAT was the question.

Extra fuel tankage, since 305-370 gals is no longer sufficient.

 

[T Bolt]

Well, what happens when there is no longer an engine in the forward section of the fuselage as in this case? What is reason for a deep fuselage then? THAT was the question.

Also more room for guns and ammunition

 

[GrauGeist]

Also more room for guns and ammunition

Like the belly cannon in the P-61, perhaps?

 

[Ivan1GFP]

Extra fuel tankage, since 305-370 gals is no longer sufficient.

I am certain that a fairly trim fuselage could hold sufficient fuel without the engine and turbo ducts taking up space. Think F7F Tigercat with similar engines and heavy armament close to CoG.

 

[Ivan1GFP]

Like the belly cannon in the P-61, perhaps?

Same idea as what I had in mind for the twin P-40. Help balance the extra few thousand pounds in the nose from the extra engine and propeller and other accessories.

 

[GrauGeist]

If we look at traditional twins, the engines and wings were situated close to the CoG on the airframe - once you start loading the nose down with ordnance, you better have something to the rear of the fuselage to balance that weight.
The Me210 had major issues because it's fuselage was too short.

 

[GrauGeist]

I am certain that a fairly trim fuselage could hold sufficient fuel without the engine and turbo ducts taking up space. Think F7F Tigercat with similar engines and heavy armament close to CoG.

The F7F had three fuel tanks:
one ahead if the cockpit and two directly behind.
This preserved relative CoG as the fuel was consumed.

 

[Ivan1GFP]

If we are designing a single seat twin engine fighter from scratch either with the V-1710 or R-2800 engines, we would probably lay out the internals quite differently than we would with the idea that we are trying to keep the appearance looking somewhat like a P-40 or P-47. The question is really how much of a change in appearance are we willing to accept and still call the result a "Twin P-40" or "Twin P-47". Just tacking on an extra engine to an existing airframe doesn't work because adding a couple tons of extra weight in the nose of an already "balanced" aeroplane generally doesn't do good things.

The actual mock-up for the Twin P-40 had lots of problems from a practical standpoint. There was no room for extra fuel in any reasonable location. The wing area did not grow for an aircraft likely to weigh about a ton and a half more than a standard P-40. The horizontal and vertical stabilizers did not grow which would be interesting for stability considering how much more airframe was now ahead of the wing. P-40s were already having directional control problems with the higher powered engines to the point that extensions were added to the fin in some models.
With a twin setup, getting both propellers to rotate outboard would help as long as you didn't lose an engine at low speed.
Another issue from an appearance versus practical standpoint is the location of the engines. It is a given that the view from above will not resemble the original nor will the view from the nose. If done properly, the view from the side CAN look like the original P-40, but causes some problems. A high cowl line is needed for appearance but is lousy for visibility to the sides.

With the Twin P-47, as we already agreed, without an engine and ducting in the fuselage, fuel doesn't need a fat fuselage. Guns and ammunition are heavy, but don't tend to take up a lot of volume either. Now a piece of equipment that might be an excuse for a bigger fuselage is a radar installation in the nose with a nice battery of guns in the belly.

 

[SaparotRob]

I'm thinking with all that plumbing, two thinner (no pilot) fuselages with the pilot in a gondola mounted cockpit. A P-38 version of the Thunderbolt. A P-47 version of the Lightning?
I prefer T Bolt's original plan. Who says it has to work?

 

[tomo pauk]

I prefer T Bolt's original plan. Who says it has to work?

Bingo.

 

[Ivan1GFP]

I'm thinking with all that plumbing, two thinner (no pilot) fuselages with the pilot in a gondola mounted cockpit. A P-38 version of the Thunderbolt. A P-47 version of the Lightening?
I prefer T Bolt's original plan. Who says it has to work?

T Bolt's design looks nicer. The original mock-up of a Twin P-40 looks nice.
If you are building just in plastic, neither one is a problem. If you are building for a simulator, all of a sudden silly little things like locations and weights of components become an issue as to sizes of wings and tails and such.
Having a design that was looking less and less like a P-40 is why I didn't finish mine.

 

[GrauGeist]

Ok, so back to Glen's original question:
I'd suggest looking at a P-61C's nacelles and wing ducting.
That should be the closest I can think of to the the P-47's cowling and engine.