WI: Bell makes the P-39 around a big radial

...instead of the V12 engine. Big radial being the R-2600 and/or R-2800. Extra points if you can have it accepted by the USN/USMC.

(the thread can be expanded to foreign countries, ie. mid-ship radial engine driving a prop via extension shaft, resulting aircraft used as a fighter, fighter bomber, carrier-capable A/C etc.)
 
It wouldn't work. Radials are air cooled engines and wouldn't get enough airflow around the cylinders to keep it cool. It would seize up in minutes.
 
It wouldn't work. Radials are air cooled engines and wouldn't get enough airflow around the cylinders to keep it cool. It would seize up in minutes.

There was several A/C that featured the 'burried' radial engine (Piaggio P.119, Northrop XP-56, Kyushu J7W).

Plus no more 37mm cannon, which the P-39 was built around...

The extension shaft + reduction gear enables the prop gun, exactly as it was the case with P-39. Please see here (pdf), pg. 16, the P.119 featuring a prop cannon plus 4 HMGs under in front of the pilot.
 
It would look like a pregnant P-39. How well it would work? Cooling is the problem for buried radial engines without an additional cooling fan. I just don't see any advantage to trying to make this work.
 
It would look like a pregnant P-39. How well it would work? Cooling is the problem for buried radial engines without an additional cooling fan. I just don't see any advantage to trying to make this work.

The layout of the P-39 provides a cooling fan in front of the engine ;)
The advantage might be a much increased power available, especially once the R-2800 is installed, while keeping the drag penalty bearable.
 
Hee!
Hee!
Why am I picturing an Airacobra with radial cylinders protruding from its Center fuselage ..... surrounded by a NACA ring?

Returning to reality .... proper cooling on the grounds d would require scooping fan (more sophisticated than FW-190) and a completely-enclosed engine. Install inlets and exits wherever convenient. My bias would be to install air ducts in wing root fairings so that the centre fuselage becomes almost "square" (like AD-1 Skyraider) because that vastly reduces interference drag.

And yes, it would look "pregnant" considering that those radials are 52 or 55 inches in diameter.

The bigger issue is weight. Start by considering that the original Allison V-1710 engine weighed about 1400 pounds (29 inches wide generating up to 1700 horsepower for take-off), while the radials weigh 2,000 and 2,300 pounds respectively. The extra weight would require a larger wing to keep landing speeds short enough for existing runways.

Wright R-2699 Cyclone 14(Twin Cyclone) engine produced 1700 horsepower for take-off, but weighed 2,000 pounds and was 55" diameter = not much advantage over the original Allison engine.

OTOH Pratt's R2800 engine produced substantially more power: 2100 horsepower (2400 pounds, 53" diameter). It had (almost the same as the other radial) but substantially more horsepower than the original Allison. The disadvantage is that R2800 weighs a thousand pounds more than the Allison and drinks a lot more gasoline .... meaning a much larger airframe. ..... larger than Kingcobra (1800 horsepower 8800 pound gross weight).

Consider the difference in weight between Grumman's Wildcat (1200 horsepower and 8800 pound gross weight) and Hellcat (2200 horsepower and 15,400 pound gross weight).

And this uber-Cobra would still need 20mm or 37mm cannon(s) to intercept any Axis plane built after 1940. It would still be possible to install a 37mm cannon. Just chose the cannon with the best ballistics for tank-puncturing or bomber-busting, then install it in the nose the same as the original Aircobra.
As long as you installed a drive-train similar to M-18 Hellcat (tank destroyer AFV) you could keep the drive shaft on the cockpit floor and still leave plenty of room for guns in the nose.
 
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I have no doubt the aircraft is possible, but it would seem to look more Piaggio than Bell, and with provision for a much larger propeller, perhaps a cranked wing, or extending main gear. I would be dubious of a tri-gear. The Piaggio made no impression because the design was not timely, and performance estimates weren't outstanding enough to require attention.
 
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The bigger issue is weight. Start by considering that the original Allison V-1710 engine weighed about 1400 pounds (29 inches wide generating up to 1700 horsepower for take-off), while the radials weigh 2,000 and 2,300 pounds respectively. The extra weight would require a larger wing to keep landing speeds short enough for existing runways.

Wright R-2600 Cyclone 14(Twin Cyclone) engine produced 1700 horsepower for take-off, but weighed 2,000 pounds and was 55" diameter = not much advantage over the original Allison engine.

OTOH Pratt's R2800 engine produced substantially more power: 2100 horsepower (2400 pounds, 53" diameter). It had (almost the same as the other radial) but substantially more horsepower than the original Allison. The disadvantage is that R2800 weighs a thousand pounds more than the Allison and drinks a lot more gasoline .... meaning a much larger airframe. ..... larger than Kingcobra (1800 horsepower 8800 pound gross weight).

Let's look at engines of mid-1941.
The original V-1710-35, on the P-39s of the era, was good for 1150 HP for take off and 1150 HP at 11200-12000 ft (different tables disagree); 1375 lbs dry + weight of liquid cooling system (was ~325 lbs on the P-39) = 1700 lbs
The R-2600-9, used on early B-25s, was making 1700 HP for take off, 1450 HP at 11800 ft; 1980 lbs.
R-2800-5, used on early B-26s, was making 1850 HP for take off, 1500 HP at 15000 ft. All figures are 5 minute ratings (military power at altitude); 2270 lbs.

Weight difference does not seem excessive - around 200 to 600 lbs. Power figures are far better for the radials, especially for the R-2800. V-1710 will gain more power at lower altitudes once war sets in, in a more or less official manner, however the R-2800 will get an upgrade in winter of 1941/42. Having no wing armament means more fuel can be installed there instead.

Consider the difference in weight between Grumman's Wildcat (1200 horsepower and 8800 pound gross weight) and Hellcat (2200 horsepower and 15,400 pound gross weight).

Early Bearcat - 9670 lbs clean, max fuel & ammo, 2100 HP mil power.

And this uber-Cobra would still need 20mm or 37mm cannon(s) to intercept any Axis plane built after 1940. It would still be possible to install a 37mm cannon. Just chose the cannon with the best ballistics for tank-puncturing or bomber-busting, then install it in the nose the same as the original Aircobra.
As long as you installed a drive-train similar to M-18 Hellcat (tank destroyer AFV) you could keep the drive shaft on the cockpit floor and still leave plenty of room for guns in the nose.

I'd went for armament nominaly similar to the Piaggio P.119 - one 20mm cannon whrough the prop, 4 .50s inthe nose.
 
I have no doubt the aircraft is possible, but it would seem to look more Piaggio than Bell, and with provision for a much larger propeller, perhaps a cranked wing, or extending main gear. I would be dubious of a tri-gear. The Piaggio made no impression because the design was not timely, and performance estimates weren't outstanding enough to require attention.

The 'elevated' prop should improve ground clearance, akin to the upright V12s - thus 'classic' wing and U/C should do it? The pilot seats almost in the front, it will have far better wiev forward, making the A/C well suited for carrier landing. This, coupled with radial engine, should make it appealing for the USN, and there is no novelty (for them) in form of the tricycle U/C to be afraid off.
 
The 'elevated' prop should improve ground clearance, akin to the upright V12s - thus 'classic' wing and U/C should do it? The pilot seats almost in the front, it will have far better wiev forward, making the A/C well suited for carrier landing.

Raising the thrust line by elevating the prop will get rid of forward visibility. The R-2800 seems to favor a prop of 12'7"-13' for single engine fighters. You never get anything for free.
 
Raising the thrust line by elevating the prop will get rid of forward visibility. The R-2800 seems to favor a prop of 12'7"-13' for single engine fighters. You never get anything for free.
The P-47 was using 12 ft 2 in prop in 1942-43, later went to 13 ft along with increase in chord. But indeed, the prop for the engine with 'base' power of 1850-2000 HP is going to be bigger than for the engine of 1150-1500 HP. The P-61 (a two-engined fighter, of course) also used 12 ft 2 in prop. On the other hand, the P-39 went from 10 ft 4 in to 11 ft 7 in in some late models; P-63 experienced the similar grow in prop size, plus they were of wide chord ('paddle blade').
Re. forward visibility - it will be one thing to have a full, wide cowling of the radial engine in front of the pilot, vs. just the prop spinner instead. Along with the pilot seating above the leading edge vs. further back in the 'classics', due to the powerplant placement.
 
The R-2800 seems to favor a prop of 12'7"-13' for single engine fighters.
They could always adapt the contra-rotating (pusher) propeller from the R-2800 powered XP-56 into a tractor configuration. That would preserve a smaller propeller arc and allow continued use of the tricycle landing gear. Of course, that would also make it a difficult sell for the Navy but the P-39 did not sit so high off the ground that a tail hook couldn't still be installed a little behind the trailing edge of the wing.
 
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