How to extend the range of the B-29 and other Allied heavy bombers.

There are always drop tanks, that would reduce the bomb load but would give extra range.
An axillary fuel tank in a Bomb bay like the B-36 had it's also possible.
The simplest solution would actually be cutting down on the aircraft's weight, plastics were starting to become a thing.
 
Dynasoar,

What? I thought the only reason - and the only way - the B-29 could meet its specs was with those R-3360s. I wasn't aware there was anything else in the same league that could've been substituted! That being the case, why didn't the Army go with the option you described?

thorr, Quickest way to answer this is to compare the HP output of the R-3350 and the wide range of R-2800 dash numbers of W (water injected) variants. I chose engines successfully employed in the P-47 and P-61, both listing power as claimed for the B-29. There are even more powerful R-2800 models listed. Check Wiki for a quick survey.

My engine data includes specific fuel consumption (F sub e), which shows better cruise fuel economy for the (single) turbocharged P&W, than the dual turboed C/Ws in the '29. Reliability under overloaded takeoff operations was a major problems for the '29s- seldom for the water injected R-2800s. The need for full open cowl flaps on the early part of the climb to try to cool the C/Ws along with their well documented mixture distribution problems at higher power settings (some cylinders overheating lean while others were fouling out rich) cost both range and aircraft.

As for why this engine substitution approach was not undertaken during the war, I can't even speculate- was only in grammar school at the time and no one in ATIC was listening to me until seven or eight years later.

Dynasoar



 
There are always drop tanks, that would reduce the bomb load but would give extra range.
An axillary fuel tank in a Bomb bay like the B-36 had it's also possible.
The simplest solution would actually be cutting down on the aircraft's weight, plastics were starting to become a thing.
The Silverplate B-29s carried auxiliary fuel tanks in the bomb bay. “Bock’s Car” had the fuel pump on the 640 gallon bomb bay tank fail on the Nagasaki mission. Was the bomb bay tank only on the Silverplates or was it standard?
 
The Allison V3420 had tons of problems of its own and and although it began development about the same time as the R-3350 (1937) never reached the reliability standards of the R-3350. The P&W 4360 was several years behind the other two it was used in the follow on to the B-29, the B-50.

https://oldmachinepress.com/2017/04/20/allison-v-3420-24-cylinder-aircraft-engine/

Here is a link to a quite extensive article describing Allisons' experiences in developing the V-3420. To quickly summarize the V-3420 was a sound and reliable design that suffered mainly from poor company management and redirected priorities. It was a missed opportunity.

Of course once the Army Airforce settled on the Wright R-3350 then every effort and resource had to be made to correct the numerous flaws in its design. It took years to get the R-3350 working reliably. And eventually they went to a better engine for the B-50 anyway. As @Dynasoar points out why didn't the Army Airforce select a better radial engine for the B-29 in the first place?

The Allison V-3420 would have been a great engine for the B-29 if the design and development team at Allison had received even a fraction of the money and support misdirected on the R-3350. The V-3420 worked quite well on the B-19 and also on the XB-39 even without the turbosuperchargers installed due to another V-3420 delay one can attribute to the lack of love for inline bomber engines in the USAAF.

Another advantage if the V-3420 had been chosen for the B-29 program is the radiator housing design could have utilized the Meredith effect is a similar way as was done with the P-51. An important benefit for an airplane that spends many hours flying at a high cruise speed.
 
The Silverplate B-29s carried auxiliary fuel tanks in the bomb bay. “Bock’s Car” had the fuel pump on the 640 gallon bomb bay tank fail on the Nagasaki mission. Was the bomb bay tank only on the Silverplates or was it standard?

I think the auxiliary fuel tanks carried in the bomb bay was a standard range increasing method. At the cost of reduced bomb load of course. I think it stands to reason that it would have been in all standard B-29s either right from the beginning of production or close to it. But I'm not certain when exactly they where introduced. But certainly not just for the Silverplate planes. They were for example used on the Operation Boomerang planes. Also those bomb bay tanks were jettisonable.
 
Easy for me in hindsight, but the entire quest for a "Hemisphere Bomber" in 1939-41 and a SAC (non-jet) "Peacekeeper" later in the game, did not take advantage of available technology. This being said in the absence of midair refueling or towed fuel gliders.

If the problem is providing an aircraft capable of flying fast, high and far to drop heavy objects on people who would like to do the same thing to us, pick a starting point for the exercise by imagining leadership at Wright Field was more technically attuned and less West Point ring knocker. The first item would be to redirect the liquid cooled Hyper engine program toward larger displacement cylinders and lower specific output, with the emphasis on HP per pound rather than HP per cubic inch. This is somewhat like the then contemporary German approach. Specified engine configuration would be a flat twelve of perhaps 2500 cubic inches and something over 2000 HP for less than 2000 pounds without supercharger package, which would be external. No accessories extending beyond engine frontal area, supercharger shaft coupling at the rear and the ability to stack two for an H-24 and three to make up a square frontal aspect for a 36 cylinder bomber engine producing up to 6000+ HP * in essentially the same volume as a large radial. One basic engine which could be optimized for individual applications with only minor compromises. Several potential sources for candidate designs. Still need air cooled radials for non-critical applications.

More later- Dynasoar

* Would expect the bomber engine to be configured for best cruise fuel consumption- higher compression, like projected Studebaker XH-9350 at 0.35Lb/Hp Hour. Would require milder cam and ADI on takeoff.
 
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@Dynasoar Though not an exact fit your description reminds me of this monster. If there had been something that prevented the development of jet engines then this might have been the resulting path.

https://en.wikipedia.org/wiki/Lycoming_XR-7755

800px-XR-7755-3_Reciprocating_Aircraft_Engine.jpg
 
The hypothetical core engine building block I roughed out earlier would share some features with the XR-7755. The key would have been flexibility of external supercharging at the rear, reduction gear (single or combining) at the front and camshafts for the intended application at the sides. Bore and stroke about 6-1/2", yielding an O-2590, H-5180 or E-7770. A slightly enlarged B-29/32 aircraft might be built around a pair of H variants in the inner nacelles and Os outboard, providing a relaxed net output of 12K HP for takeoff and cruise HP specific of less than 0.35 pounds of fuel per HP per hour leaned on 100/115 octane. This latter demonstrated (as low as 0.29 without compounding) during cylinder testing of Studebaker H-24 in 1945. In the elongated (Tupolev or Republic F-12 style) nacelle behind the engine I'd expect only an external turbo driving a two stage blower, with intercooler, coolant and oil heat exchangers in a Meredith configuration, possibly including an exhaust input to help aspirate the system. Fuel supplied via low pressure constant flow injectors into manifold adjacent intake valves; ADI where convenient. Nothing suggested that hasn't been done before. Engine described could also be easily compounded with velocity turbine/reduction gear/clutch connected to the (unused in this example) rear external supercharger drive.

B-29ish airplane, possibly with span increased by 20 feet or so containing fuel to be used last. All tanks nitrogen inerted. Possibly fewer defensive gun turrets due to ship's speed and altitude potential Longer bomb bays since who knows what might have to be put in them.

Dynasoar
 
Couple of more thoughts on the modular bomber engine: The WADC air procurement group only got serious on looking for an appropriate engine in March 1940 with the issuance of Request For Data R40-D (approximately five years too late) The looked for engine would be in the 4000 to 5500 HP range. No suitable proposals, so the program was delayed more than a year, till late 1941.

Demonstrated fuel specifics (1944-45) without turbo compounding or real understanding of combustion chamber turbulence and quench area to increase detonation margin in cruise, were excellent. Just six years too late.

Dynasoar
 
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thorr97

Banned
Dynasoar,

Gotta love those Hyper engines the Army had companies developing. If they'd come through as planned then several of those R40-D designs would've been world beaters for the Air Corps.

Ah, if only...
 
Dynasoar,

Gotta love those Hyper engines the Army had companies developing. If they'd come through as planned then several of those R40-D designs would've been world beaters for the Air Corps.

Ah, if only...

Problem with the Hyper engines is they might have given good power per cubic inch but by 1940 conventional engines were equallinging the power in a lighter engine. Power per pound is what counts.
 
https://oldmachinepress.com/2017/04/20/allison-v-3420-24-cylinder-aircraft-engine/

Here is a link to a quite extensive article describing Allisons' experiences in developing the V-3420. To quickly summarize the V-3420 was a sound and reliable design that suffered mainly from poor company management and redirected priorities. It was a missed opportunity.

Of course once the Army Airforce settled on the Wright R-3350 then every effort and resource had to be made to correct the numerous flaws in its design. It took years to get the R-3350 working reliably. And eventually they went to a better engine for the B-50 anyway. As @Dynasoar points out why didn't the Army Airforce select a better radial engine for the B-29 in the first place?

The Allison V-3420 would have been a great engine for the B-29 if the design and development team at Allison had received even a fraction of the money and support misdirected on the R-3350. The V-3420 worked quite well on the B-19 and also on the XB-39 even without the turbosuperchargers installed due to another V-3420 delay one can attribute to the lack of love for inline bomber engines in the USAAF.

Another advantage if the V-3420 had been chosen for the B-29 program is the radiator housing design could have utilized the Meredith effect is a similar way as was done with the P-51. An important benefit for an airplane that spends many hours flying at a high cruise speed.

The following is my response on one of the other B-29 related thread. I am including it here in case someone is not following the other thread

That is a very interesting article. I appreciate you pointing it out. It does appear the problem with the V-3420 was not technical but bureaucratic The fact that there were only about 30 engines delivered by the beginning of '44 meant that it was far behind the R-3350, which was already being installed (and debugged) in production aircraft.

I think the B-39 could have been a follow on to the B-29, fitting between it and the R4360 powered B-50. I think the V-3420 also suffered from the bias of the Army Air Corps/Forces for radial engines in large aircraft. It may be because there were two manufacturers working on efficient radial designs during that era and the competition drove both of them to improve their designs

I will say the 3 separate B-29 related threads is getting confusing
 
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