The 'no-nonsense' twin-engined fighters for 1938-1943 (1 Viewer)

[Shortround6]

Clipper was also a product of months of the work in the design bureau and in the workshops, it didn't just materialized a few weeks before the maiden flight From Wikipedia:
Boeing's bid was successful and on July 21, 1936, Pan American signed a contract for six.
That is a 13 months before the contract was awarded to the XP-38. The not-P-38 needs to be mooted around one 1500 HP engine from the start.

You need to get around the US Army prejudice against air cooled engines. One reason for the whole hyper engine program. Granted it came to nothing but air cooled engines were viewed as difficult to cool at high (turbo) altitudes. Air at 20,000ft for instance is about 73% as dense as sea level which means you need a lot more airflow over the cooling fins of the radial engine. Yes you need more airflow through the radiators of the liquid cooled engine/s. but you don't need to actual change the engines, just the radiators/ducts. They were also fooling around with the ethylene glycol coolant and different coolant temperatures (too high didn't work) and settled on the glycol/water mix and pressurized system right about 1940-41.
The Army was specifying turbo-charged airplanes, They ordered 50 of these in in 1934

and the last were delivered in Aug. 1936. It had....." it was the first fighter in service with the USAAC to have a fully retractable undercarriage, it was the first fighter with a constant speed propeller, and it was the first truly successful application of a supercharger to an operational military aircraft. " The last may be a bit debatable but the Airacuda's were supposed to have turbos, the YP-37s (ordered in Dec 1937, first delivered in June of 1939.)

The Army had the non-turbo P-36s and later the non turbo P-40s as back ups.

for some reason the R-2600 fell through the cracks. GE only made two sizes of turbo. The smaller one didn't flow enough air for the R-2600 and the bigger one, if available in the late 30s, was intended for engines that were powerful than the R-2600, like the R-3350 and R-2800 and some of the experimental engines.
Wright was improving cooling (among other things) but they kept increase the regular power out put.

GE was not Bell, promissing the moon and failing to deliver, time after time.
If the 1500 HP engine will not cool well at 20000 ft, we can have the 1600 HP engine installed and down-rate it to 1500 HP. Or by 1941 install the 1750 HP engine and either down-rate it to 1600 HP, or go (oh, heresy) with R-2800. Cooling fan was also trialed in 1941 by NACA.
Still a 390- and later 400-mph aircraft.

Where was the 1750hp engine? what model number?

The 1700hp engine had design work start in Nov 1938, first test engine ran in Nov 1939 and the 5th production engine showed up in June 1941.
At what point do you decide that the 1700hp version was actually going to work and decide when to adopt it for your planned fighter?

a little back ground or side development/cautionary story.
In 1938 he Army was not happy with progress that Continental was making with ??-1430 engine and contacted Wright for a liquid cooled engine.
Wright responded with 4 different rough designs with notes on advantages and disadvantages. At this time the Army was still pushing for engines buried in the wings.
Wrights conclusion was that there was too much trouble with such installations. Like you can't use a mono spar wing construction. and spar spacing on multi spar wings was difficult.
In Jan 1939 an installation drawing (external size of the engine for airframe makers) was released for the Flat X 24 cylinder version.
By April of 1939 Wright had given up on the initial proposals 1500-1800hp Flat X and was pushing the 1800hp version of the 42 cylinder 6 row radial engine with liquid cooling (but adaptable for air cooling). In June of 1939 an new installation drawing for the 1800hp engine was released to the airframe makers for the small diameter 42 cylinder engine.
By this time the airframe makers were no longer interested in an 1800hp engine but were interested in a 2500hp engine. Bore was increase as was stroke and the engine would up as the R-2160 Tornado. A new installation drawing was released. And by Aug 1939 a supplement to original report was released with the R-2160 sales pitch, like modular engines of 14 and 28 cylinders (or as many as 56) and left and right prop rotation, coaxial-contrarotating propellers, and two speed propeller drives. Wight was also including superchargers of single speed plus turbo, two speed single stage, and two stage.
In June of 1939 a contract for a 14 cylinder test rig was obtained.
By the time the program ground to a halt in the spring of 1943 (no prototype aircraft would be using the engine, the prototypes had either been canceled outright or had been changed to other engines), it took until Spring of 1944 for Wright and the government to negotiate the cancelation/conclusion of the various contracts and disposition assets of the program
Wright had spent about $6,170,000 of it's own money.
At one time at least 4 aircraft were slated to use the engine, including the Lockheed P-58 and the Republic P-69.
At the time everything stopped they had 1,631 hours between six 42 cylinder engines, 1200 hours on two 14 cylinder engines and 130 hours on a 6 cylinder test rig.

A fighter with two V12s will also have two cooling systems to add drag, and the central pod/fuselage to add drag.
R-2800 was much earlier to have 2-stage supercharger, preceding such an R-2600 by 15-18 months? That's eternity in the lead up for the ww2. An extra of 100-250 HP is also worth mentioning.

The two V-12s have a smaller frontal area than the R-2600 although the radiators/oil coolers will pretty much cancel that out.

You pretty much have to pick out the engine/s at certain point in time and go with it. You might be able to change V-12s, a lot harder to go from twin to single or back.

 

[tomo pauk]

You need to get around the US Army prejudice against air cooled engines. One reason for the whole hyper engine program. Granted it came to nothing but air cooled engines were viewed as difficult to cool at high (turbo) altitudes.

USAAC can take a look at Bristol Type 138 - it's radial engine was working perfectly at 50000 ft in September of 1936.
(yes, Bristol can also stop and think...)
USAAC was probably of the opinion that air cooled engines on the B-17 will be cooling reliably at high altitudes (wikipedia):
Scheduled to fly [the Y1B-17A] in 1937, it encountered problems with the turbochargers, and its first flight was delayed until 29 April 1938.[37]​

Where was the 1750hp engine? what model number?

My bad, 1700 HP is the right figure.

You pretty much have to pick out the engine/s at certain point in time and go with it. You might be able to change V-12s, a lot harder to go from twin to single or back.

I'd pick the engine for a not-P-38 in 1937.

 

[Shortround6]

cheduled to fly [the Y1B-17A] in 1937, it encountered problems with the turbochargers, and its first flight was delayed until 29 April 1938

Well, not being able to fly at all is certainly different than not cooling at high altitudes.

Getting the engines used in the early B-17s sorted out is a bit difficult.
The R-1820s used in the Y1B-17A were the model -51 or G5 version. According to Joe Baugher " The turbosupercharged engines delivered 800 hp at 25,000 feet, whereas the R-1820-39s of the Y1B-17 could only deliver 775 hp at 14,000 feet."

The R-1820-39s used a single stage two speed supercharger and were good for 930hp/2200rpm take-off at sea level. They were good for 800/805 hp/2100rom max continuous at sea level.

Now things get a bit confusing, the B-17Bs are sometimes credited with R-1820-51 engines of 1200hp take-off. But that doesn't seem right, where did the extra 200hp come from?
The B-17Cs were supposed to have R-1820-65s that were rated at 1200hp/2500rpm for take-off and 1000hp/2300rpm Max Cont. To suit them for turbo use they used a slightly lower supercharger gear on the engine supercharger. These were R-1820G200 series engines. It appears that the B-17 skipped over the R-1820G100 series engines.
Point of some of this is that there were major changes in the Cyclone 9 engines as far as cooling goes (and most everything else.)

Please note that the chart is only for the changes in the fins for the cylinder head. Changes to the fins on the cylinder barrel show a similar but not identical progression through the years. The 1939 year is for the G200 series engines. The G200 had an 8% increase in cooling fin area on the head over the G100 series however the cylinder barrel fin area was increased by 60% from the G100 to the G200 for a 24% increase in total cooling area per cylinder.
I don't have the information on the R-2600 cooling areas.
It was these changes (in many countries engines) in cooling that allowed air cooled engines to equal liquid cooled ones at altitude. It also these increases in fin area that allowed better cooling with same or similar airflow for lower drag but I don't have figures. However, it often required changes to manufacturing techniques and tooling to achieve the fin depth and spacing needed.

For a picture of the change in Bristol Perseus cylinders

Book was published in 1940. Early Hercules cylinders would be identical or close to the ones on the right. These are just the cylinders.

Radial engines took a lot more work to raise the power than liquid cooled engines.

Getting back to the Wright engines and changes. The R-1820 H engines (1300hp and up) had another huge increase in fin area. As did the R-2600 BB sereis engines compared to the R-2600BA engines (the 1700hp ones) and once again, the only things the R-2600A (1600hp) and R-2600B engines shared was the bore and stroke. Now they were very similar in size so with a different engine mount you could drop the new engine onto the same airframe but you needed to retool the factory to make the new engine.