Was the B-17E really better than the B-17D?

[Conslaw]

Before Pearl Harbor, Boeing had already switched from producing the "sharkfin" B-17D and was delivering the extended fin B-17E. The "E" evolved into the "F" with the ball turret and then the "G" with the chin turret. Each of these variants, the E through the F made the B-17 a better "fortress" but not so great at the "flying" part. The later models, even with occasional power upgrades became heavier, and slower, with lower effective ceilings and sometimes lower effective combat radius. Supposedly the E model was inspired by feedback from early models tested by the British. With this thread I'd like to explore how thorough that British testing really was, and entertain arguments that a faster, higher flying (and longer-ranged) B-17 would have actually been more effective in many theaters, especially in the Pacific, where Japanese interceptors were slower and had less high-altitude capability.

 

[davebender]

That would require more powerful engines such those which powered British Lancaster bomber.

 

[nuuumannn]

The first variant of the B-17 used by the British was the B-17C, which the Brits named the Fortress I. Whilst testing the type at Boscombe, initial reports were very favourable and the British were very impressed with its ease of handling, crew comfort and altitude performance. Trials concerned the usual performance envelope and handling, with ground handling and compatibility with British weaponry and equipment being carried out. It appears that in intial trials the British didn't test gunnery. One of the criticisms the Americans had of British operational use of the Fort was that aircraft were being sent on individual sorties over enemy territory, which negated the type's defensive armament, but practice by the 8th Air Force with B-17Es and their heavier armament (B-17Es also had the Sperry ball turret) and the use of box formations found that these measures were also inadequate and without escort fighters were severely mauled.

In brief, British findings from combat experience was issues with the Norden bombsight, numerous mechanical failures and a tendency for equipment, notably guns, to freeze at altitude. Defensive armament was inadequate and there was no defence of the tail.

 

[vikingBerserker]

Interesting, I had no idea the British used the Norden bombsight.

 

[nuuumannn]

The British report on the Fortress II and IIa (the B-17E was the Fortress IIa and the B-17F was the Fortress II - go figure) stated that the Norden auto-flight system was trialled for seven flying hours and demonstrated its ability to control turns at all speeds and hold heading even when two engines on one side were fully throttled. These models were used as maritime patrol aircraft only with Coastal Command by the British.

 

[Jabberwocky]

That would require more powerful engines such those which powered British Lancaster bomber.

That's a really odd statement Dave.

Fitting Merlin 20 family engines to a B-17 would probably have a negative affect on the B-17's speed at altitude and cut the cruising altitude and ceiling. A turbocharged R-1820 makes progressively more power than a Merlin 20 family engine above 16,000 ft. I'm not sure about range, as I dont have specific consumption for the R-1820 and Merlin 20 family handy at the moment.

The main thing fitting more powerful Merlins would do would be to improve load carrying, low level speed and rate of climb up to about 15,000 ft.

The B-17's turbocharged R-1820s made their full power of 1200-1245 hp up to about 25-27,000 ft, depending on the exact engine and turbo fitted.
The Merlin 20 family made full power at 12,500 to 16,000 ft, depending on sub-type. The Lancaster's best speeds were somewhere between 14,000 ft and 16,000 ft. Ceiling was only about 23,000 ft when loaded, even lower with heavy bomb/fuel loads.

At typical B-17 altitudes (20-25,000 ft), the Merlin 20 family engines would have been wheezing compared to the R-1820. At 25,000 ft, the Merlin 20 has about 700 hp per engine at max continous cruise. An R-1820 at the same conditions makes about 900 hp per engine (or almost 30% more power).

 

[GregP]

That's funny considering the B-17 fitted with Allisons (that would be the XB-38 fitted with turbosupercharged Allisons) was faster than the standard B-17 at equicalent heights. With Merlins, including the later 2-stage, 2-speed units, the max speed should have been up in the 340 mph range. Since we ALL know that Mosquitoes cruised around at 90%+ full speed, why couldn't Merlin-engined B-17s do the same? ... IF they had been built?

 

[Jenisch]

View: https://www.youtube.com/watch?v=OhpJv1eTsLs

 

[varsity07840]

That's funny considering the B-17 fitted with Allisons (that would be the XB-38 fitted with turbosupercharged Allisons) was faster than the standard B-17 at equicalent heights. With Merlins, including the later 2-stage, 2-speed units, the max speed should have been up in the 340 mph range. Since we ALL know that Mosquitoes cruised around at 90%+ full speed, why couldn't Merlin-engined B-17s do the same? ... IF they had been built?

The XB-38 may have been slightly faster than the B-17E, but given the problems with the turbo Allison on the P-38 in Europe, it's use as a high altitude bomber engine in that environment would have been a mistake. I don't know how you project a 340 mph max speed using a two stage two speed but regardless, the term max speed is almost meaningless since it's not with a bomb load, and certainly no enough to avoid German fighters. Also, I would think that an increase in power would to some degree be offset by the added weight
of the Merlin(more than an Allison) and it's associated systems, especially cooling which in itself would have made the aircraft more vulnerable to flak and gunfire.

Duane

 

[yulzari]

IIRC the RAF intention was to use the altitude capability of the Fortress I as it's defence and bomb from (then) very high altitude. They found that the crew and minor equipment could not cope with the cold and low pressure. Whilst the Fortress I could reach a high altitude it was not built to actually operate usefully that high. This reinforced the research into pressurised high altitude aeroplanes. eg Westland Welkin and Wellington V.

Despite the use of the Fortress name, the RAF had no intention of risking them at lower levels and relying on the gun armament as they were already convinced that would be a disaster without fighter escort. They saw the defence of the Fortress I as being it's altitude not it's guns so hoped to be able to bomb accurately (or at least more accurately) in daylight than their night bombers.

Had the RAF wanted to continue down this road with the Fortress they would have looked to have them with a pressurized crewspace and possibly ditch the guns etc. in a search for more height.

Maybe one can have visions of Fortress Is with Wellington V cockpits, high altitude Hercules engines and escorted by Westland Welkins? Maybe not.

 

[fubar57]

Cool video Jenisch though I do like the Monty Python video shown at the end(top right).

Geo

 

[Jabberwocky]

That's funny considering the B-17 fitted with Allisons (that would be the XB-38 fitted with turbosupercharged Allisons) was faster than the standard B-17 at equicalent heights. With Merlins, including the later 2-stage, 2-speed units, the max speed should have been up in the 340 mph range. Since we ALL know that Mosquitoes cruised around at 90%+ full speed, why couldn't Merlin-engined B-17s do the same? ... IF they had been built?

So, we're turbosupercharging Merlins now? Wonderful. The RAF will be delighted. Now it can have Mosquitos that make sea level power all the way up to 27,000 ft. Or are we just limiting turbos to heavy bomber use?

Rolls-Royce will be a little miffed though. Are we limited to GE 'B' bomber type turbosuperchargers, or can we get the 'C' fighter types as well?

The Lancaster never had 2 stage, two speed Merlins. The Lincoln did, but that was a proper rework, a la Spitfire into Spiteful.

 

[Shortround6]

Apparently there were quite a few changes form the "D" to the "E". At least in brief accounts, it might take pilots manuals of each to really bring out the details.

Possible changes.

Bomb load goes from eight 600lb bombs to eight 1000lb bombs internal or twelve 500lb bombs?
Provision for more fuel tanks?
Increase in gross weights? enough to cover the increased guns/structure or more?

And why the big increase in tail area? just to counter the change in fuselage shape or was there a problem in lateral stability to begin with?

 

[meatloaf109]

Short answer, Yes.
The "E" was better. That's why they did it.

 

[Conslaw]

Meatloaf, you say the B-17E was better. But that wasn't the only direction they could have gone. The lower turret on the B-17E, though compact, was hard to use and of questionable effectiveness. As a general rule, the B-17 did need tail protection, and the new tail gunner position was effective.