# B-17 and B-24: plausible upgrades?



## tomo pauk (Mar 20, 2013)

The 4-engined work horses that bore the brunt of daylight bomber effort vs. Axis countries, conceived under belief that high altitude cruise and numerous defensive MGs would enable them to destroy enemy targets with impunity, even if the enemy is technically tactically adept. The realities of war proved that reasoning to be mostly wrong, it took friendly fighters to make heavy bombers viable again vs. LW, while the B-29 took the fight to Japan proper.

So what plausible upgrades could USA undertake, in order to make the B-17 and B-24 better suited for the tasks, even if planes taking those tasks might be contested by enemy actions? There was one real-life upgrade to the B-17, namely the version with V-1710s, so that might get the ball rolling.


----------



## fastmongrel (Mar 20, 2013)

I think the main problem was a low cruising speed so anything to get that up is good maybe even start stripping the guns off. I know thats controversial but surely a shortened time over the continent is better than a leisurely 180 which I believe was the usual speed. What was the cruise speed of the V1710 version and did it have turbos.


----------



## tomo pauk (Mar 20, 2013)

Yes, the XB-38 was using turbos. The B series of turbos was used on P-38, B-17 and B-24. The performance, from Wikipedia:

Maximum speed: 327 mph (284 knots, 526 km/h)
Cruise speed: 226 mph (197 knots, 364 km/h)
Range: 3,300 mi (2,870 nmi, 5,310 km)
Service ceiling: 29,600 ft (9,020 m)


----------



## gjs238 (Mar 20, 2013)

With the benefit of hindsight, embrace the Schnellbomber concept and abandon the fortress concept.


----------



## Shortround6 (Mar 20, 2013)

Then you need entirely new airplanes, not an upgrade. Ditching the turrets might only gain you 20-30mph. Not enough to give immunity from interception. Formation flying requires lower speeds and streaming un armed or lightly armed bombers across Europe at around 260mph in daylight is setting up a shooting gallery even worse than what was done. 

http://www.zenoswarbirdvideos.com/Images/B-17/17FOIC.pdf

Please note that any fuel above 2800 gallons required bombbay tanks.


----------



## cimmex (Mar 20, 2013)

Why upgrade old models when new designs (B-29, B-32) are almost ready.
cimmex


----------



## tomo pauk (Mar 20, 2013)

The key word is 'almost'. Allies needed heavy bombers in overwhelming numbers in 1942-45, not in 1945-46. The better bombers, the better.


----------



## T Bolt (Mar 20, 2013)

tomo pauk said:


> The key word is 'almost'. Allies needed heavy bombers in overwhelming numbers in 1942-45, not in 1945-46. The better bombers, the better.


Bombers needed in 'overwhelming numbers' is an impotent phrase. Some of the major upgrades of those bombers that were in the works were not followed through with because it would have slowed down production so minor upgrades were settled for that did not disrupt the production lines.


----------



## drgondog (Mar 20, 2013)

If the cruise speed for B-17G could be increased for same bombload to say 190mph IAS at 25000 feet - it would be a huge benefit. The figures on the XB-38 are unclear regarding whether 226 is TAS with a load.. 226mph is only 20mph TAS over 150IAS at 25000 feet.

I would strip both waist guns, the two lateral 50's next to Bombadier/Navigator, and the radio operator hatch 50... reduce crew to 8 to help get there. That would be ~ minimum 1300-1400 pounds (keep half the ammo for another 400+ pounds)

Boosting the speed to that level (240mph TAS) drastically reduces the Essing cycle for the escorts, conserving fuel for them. Moving along at 190 at that altitude reduces the number of passes an Fw 190 and 109 can make if they start with head on pass.. If coming in trail they are exposed to more firing solution time from the B-17s because the closing speed is less. Makes it tougher for Me 110's and Ju 88's to maintain contact from favorable position of their choice. Tougher (and shorter time) tracking solutions for flak batteries, more flexible mission planning due to less air time over Europe, probably a lot less fuel and oil consumed per mission. After bomb load gone, the B-17 would really be moving right along making for tougher intercepts.

Is it a major advantage vis a vis losses in August/October 1943? I don't think so. 1944 - definitely. 
Disadvantages - only so much capacity for Allison, different logistics set up, Additionally the Allison/glycol cooling system is more vulnerable which probably increases loss % as a function of battle damage.

If I had the latitude I would make the following defensive changes. Reduce defensive gun stations to four.

Eliminate the G chin turret and replace with B-29 type 2 Gun turret for lower drag. Replace the top (manned) turret with a four gun B-29 top turret. Replace Ball turret with two gun B-29 lower turret and install the B-29 tail turret so that all gun stations are controlled by same fire control system.

Gunner stations (five - Bombadier, new blisters (3) with Primary at radio hatch but both waist positions can be manned later, and Tail). The Central fire control area is dominated by the one replacing radio hatch. The Engineer moves there. The radio operator can man either of the waist systems or back up engineer. The 'Radio hatch blister is same size as the YB-40 turret there. He can control upper turret with option to control lower for beam attacks or tail in case the tail gunner taken out. The tail gunner has primary control of tail turret and lower turret. The bombardier has chin and top and lower for company front attacks. 

There is a complete lack of coverage for a cone below the new B-17 due to lack of visibility at any gun station. For all practival purposes that is meaningless. For head on attacks the bombardier has 8 .50's slaved to his sight. For trail attacks the tail gunner has lower and tail with 4x.50's slaved.

This system was installed in first prototypes so was available in 1942 but certainly in late 1943. The 'lull period' would have been a good time to retrofit at Service Centers.

This concept with computing gunsights and lower drag, fewer crews, ability to mix and match your best gunners at controls and put most firepower in one hand should be of benefit.


----------



## razor1uk (Mar 20, 2013)

In the samilar way to how Stalin said and ordered Shturmoviks like bread for the soviet army, so constant 'B' production could be thought of for the USAAF until the end of the war was insight.

Thats why the infuriating slow production build up and of Willow Springs (Mile-Long?) plant caused congressional inqueries public/media outrage, possibly with some threats of jail-time or off-to-the-front to some employees along its way to building staff skills/knowledge and production momentum.


----------



## tomo pauk (Mar 20, 2013)

The demand for V-1701s was less in 1944, than in 1943. The P-40 P-39 were nearing cancellation, the P-51 already switched to Packard Merlin. Because of that, Allison delivered just a tad less engines in 1944 than in 1943, contrary to other engine manufacturers, despite the production lines beginning to reap the benefits of mass production.
Thanks for pointing out the often overlooked threats for the B-17s, Bill. The Flak and heavy fighters would not like the faster B-17, that's for sure. 



T Bolt said:


> Bombers needed in 'overwhelming numbers' is an impotent phrase. Some of the major upgrades of those bombers that were in the works were not followed through with because it would have slowed down production so minor upgrades were settled for that did not disrupt the production lines.



Sorry that you feel that is an impotent phrase. 
The bombers were flown by airmen. That little thing might one have in mind when deciding whether is 50 or 100 bombers more produced is worth 200 or 300 airmen killed, missing or POW. 
The B-17 (with V-1710s) cruising at 220-230 mph will be above German-held Europe maybe 4 hours, while the other, cruising at 180 mph, will be there 1 hour more. That's 25% more time the Germans have the opportunity to kill the slower bomber.


----------



## T Bolt (Mar 20, 2013)

tomo pauk said:


> Sorry that you feel that is an impotent phrase.
> The bombers were flown by airmen. That little thing might one have in mind when deciding whether is 50 or 100 bombers more produced is worth 200 or 300 airmen killed, missing or POW.


I didn't say I agreed with that line of thinking, I just believe it was a large factor in which upgrades to incorporate into bomber production. My father's B-24 was shot down by anti-aircraft fire and he spent some time as a guest of the Third Reich, so my feeling is that any upgrades that could have been made to the heavies to increase there survivability should have been made regardless of a possible drop in the number of bomber coming off the assembly lines.


----------



## tyrodtom (Mar 20, 2013)

I've seen the B-29 turret control system talked about, but how effective was it in real use. 
It's hard to say if it was really given much of a test over Japan, and later over Korea, it evidently wasn't much help against the Migs.


----------



## dobbie (Mar 20, 2013)

Instead of going to water cooled Allisons, why not move to a larger radial engine instead? Some of the old Privateers-a modified B-24, were upgraded from the P&W 1830 to the Wright R2600 and used for water bombing for quite a while. Dont know if the B-17 could be modded to accept them, but seems logical. I would rather see an R2800 but Im not sure thats feasible.


----------



## drgondog (Mar 20, 2013)

Tyrod - the fire control system for the B-29 with the centralized capability apparently was 'more effective' but I don't offhand know how to quantify the increase. 

Two factors were different - one the armor plating and top speed of most of the Japanese fighters were less than German counterparts. The second was all power turrets which was a more stable gun platform not only for firing but also for being slaved to hand held post mounted gunsight - making turret slew and gun elevation changes slaved to the computing gunsight. The latter was really important - eliminating the required hand/foot co-ordination of the manned turret.

The intangible factor - the high speed of the B-29 made a pursuit curve approach much more difficult - making only head on and trail attacks feasible, reducing most shooting to low deflection shots from the bomber.

The problem in Korea was the same as B-17/Me 262 issues in ETO. The MiG 15 and Me 262 were too fast for the slewing speed of the turret to track when the deflection angle opened up due to a high speed pass.

If the 'imaginary' retrofit had been feasible I believe it would have been far more effective to have up to 8 forward firing 50's blasting at a fighter making a head on pass - all under control of one person with computing gunsight. Having said that, the computing gunsight could never account for a high speed break as the wing span ring would have no meaning whatsoever for keeping a firing solution on a deflection shot on a high speed head on pass as the fighter breaks off.

On the other hand, that firepower would be equivalent to a P-47 from each B-17 in range, shooting low deflection for a couple of seconds.

From the stern, only four but shooting at 1/4 the closing speed - a much longer relative time with concentrated fire from tail and ball or from 'ball', tail and top (when rudder interrupter isn't engaged).


----------



## tomo pauk (Mar 20, 2013)

The B-24 was supossed to cruise faster than B-17. Data from Wikipedia:

Maximum speed: 290 mph (250 kn, 470 km/h)
Cruise speed: 215 mph (187 kn, 346 km/h)
Stall speed: 95 mph (83 kn, 153 km/h)
Range: 2,100 mi (1,800 nmi, 3,400 km)
Ferry range: 3,700 mi (3,200 nmi, 6,000 km)
Service ceiling: 28,000 ft (8,500 m)

The max continuous power was 1100 HP per engine, ie. same as in turbo V-1710, and 100 hp more than B-17's Cyclones.


----------



## cimmex (Mar 20, 2013)

I don’t think changing the motors of an aircraft is an easy task. I’m sure there are fixed contacts between aircraft manufacturers and the motor supplier. You cannot simply cancel such a contract without losing a lot of money. Don’t forget even during war this is a financial business. But these things are often forgotten in those hypothetical scenarios.
Cimmex


----------



## dobbie (Mar 20, 2013)

Its certainly not easy, but can and had been done. Probably the most famous swap was the P 51 changing from Allisons to Packard-Merlins. The Curtiss C46 was originally supposed to have the R2600 but was changed to the P&W R2800. P-40F models swapped the Allison and used the Packard Merlin with a single stage supercharger. The original B 17 used P&W Hornets before the Wright Cyclones. Im sure theres more examples......


----------



## Shortround6 (Mar 20, 2013)

dobbie said:


> Instead of going to water cooled Allisons, why not move to a larger radial engine instead? Some of the old Privateers-a modified B-24, were upgraded from the P&W 1830 to the Wright R2600 and used for water bombing for quite a while. Dont know if the B-17 could be modded to accept them, but seems logical. I would rather see an R2800 but Im not sure thats feasible.



The B-17 and B-24 both grew in weight quite a bit from early models until late but there is an upper limit somewhere before you have to beef up a considerable amount of structure ( redesign the aircraft). 

46,250 pounds gross for a British Liberator II? First delivery June 2, 1941

B-24D; 32,605 pounds empty, 55,000 pounds gross, Maximum takeoff weight 64,000 pounds.
B-24J; 38,000 pounds empty, 56,000 pounds combat, 71,200 pounds maximum overload.
PB4Y-2 Privateer: 39,400 pounds empty, 64,000 pounds gross

The water bombers saw the elimination of several tons of guns, turrets, ammo and armor, self sealing tanks may have been removed and replaced with normal fuel cells/tanks. The Mission profile was also quite different. Water bombers don't usually fly 400-800 miles one way from their base to make drops? Even in the Rocky Mountains operational heights are thousands of feet lower than flying over Europe. 

For some reason the R-2600 was never fitted with turbos ( at least not more than a handful). This means a non-turbo R-2600, while quite useful for getting a loaded plane off the runway ( and pulling up to avoid a ridge after dropping a load of water) overs very little power advantage over a turbo R-1830 at 20,000ft and above. It _WILL_ burn more fuel. The engines and props alone will go 1 1/2-2 tons more than the R-1830s.


----------



## Shortround6 (Mar 20, 2013)

Swapping engines could be done, a lot of these planes were contracted for in batches. Company "A" might be told they were getting on order for 2000 planes all on one day but the actual contract might state that the first batch of 400 had to finished by a certain date. later Batches could be modified. Republic got contracts for the P-47B and P-47C on the same day. 

*BUT* engine swaps cannot be done with a just a few weeks notice and you have to be sure that the engine swap is going to do what you think it will. Again swapping a bigger non-turbo engine for a smaller turbo engine may not give the performace you want were you want it.


----------



## GregP (Mar 20, 2013)

I think the Allison engine, R-2000's, or R-2600's would have been good. A slight reductin in armament along the lines Drgondog suggested would not hurt in a large formnation, but might prove fatal for a straggler. Then again, stragglers were pretty much a target anyway.

Some armor plating along the nose to protect the flight crew froma head on pass might also help. Of course, if you take away weight and then add it back on, would there be enough gasoline left for the mission given the new engines? It would take some figuring.

I'm thinking a strecthed version of the B-26 Maraduer with four R-2800's might have been a good possibility. Longer would give more bomb bay space and the 4 engines would certainly not be more complex than the B-17's and B-24's already were. I've wondered why nobody ever pursured even a prototype of it for a long time. It would look something like the Japanese Nakajima G8N-1 Renzan, which was not produced serially. They only made 4 after the 3 prototypes.

The Renzan was also fast at 358 mph, with a supposed 242 mph cruise speed. Not saying the 4-engine B-26 would have been the same, but would have been a faster airplane than were either the B-17 or B-24, and with the R-8000's, would almost certainly have hauled more payload. The Douglas A-26 could haul a normal load of 4,000 pounds internally plus another 2,000 pounds externally with only two R-2800's.


----------



## FLYBOYJ (Mar 20, 2013)

tomo pauk said:


> So what plausible upgrades could USA undertake, in order to make the B-17 and B-24 better suited for the tasks, even if planes taking those tasks might be contested by enemy actions? There was one real-life upgrade to the B-17, namely the version with V-1710s, so that might get the ball rolling.



You mentioned the V-1710 upgrade for the B-17. Outside of that and the actual evolution both aircraft went through, I really don't think there was much more that could be done to them that would have been real cost or performance effective.

Regarding the B-24 - it's original proposal sketch below...







Because of the time contraints of bidding on the contract that awarded the B-24, the actually production aircraft looked much different. I think, however, Consolidated had this in mind the whole time...


----------



## gjs238 (Mar 20, 2013)

GregP said:


> I'm thinking a strecthed version of the B-26 Maraduer with four R-2800's might have been a good possibility. Longer would give more bomb bay space and ehe 4 engine would certainly not be more complex than the B-17's and B-24's already were. I've wondered why nobody ever pursured even a prototype of it for a long time. It would look something like the Japanese Nakajima G8N-1 Renzan, which was not produced serially. They only made 4 after the 3 prototypes.



Martin XB-33 Super Marauder - Wikipedia, the free encyclopedia

Seems they considered "Supering" things before the Super Hornet


----------



## GregP (Mar 20, 2013)

Thanks gjs328,

I had seen that many years ago and forgotten. Unfortunately they didn't pursue it. The point is they COULD have had them available well before the B-29 and they could have been in the fray in Europe. Alas, they weren't in real life, but it's nice to know they were considered. I suppose there was some reason why it wasn't pursued, and the reason probably included the B-17 and B-24.

Given the specs though, it seems like one or the other should have been replaced with the new design that was faster, had enough range, and hauled a lot more weight. Of course, I'm speaking from hindsight, not from within WWII production realities and I am no doubt unaware of the pressures and resource constraints they were facing at the time, though it would seem as if the Martin project would not take up Boeing or Consolidated resources ... other than GFE (government furnished equipment), of course, such as Aluminum, engines, propellers, etc. .


----------



## davebender (Mar 20, 2013)

1935. R2600 engine prototype first run.

29 Dec 1939. B-24 prototype first flight.

B-24 could have been designed for R2600 engine from the beginning. There should have been no production delay.


----------



## tomo pauk (Mar 20, 2013)

So far this is the best information I have about the turbo R-2600. 






The second engine might be the C series R-2600, that one was in production from 1944 on.
Installing them, in turbo guise, could be too much for historic B-24. A whole new airframe would indeed be needed for that, as proposed with XB-33.


----------



## GregP (Mar 20, 2013)

Not sure about the turbo, but the B-25 used the R-2600 and was in sercvice soon enough to fly the Doolittle Raid on Tokyo. It was introduced to service in 1941, so the "Super B-26" COULD have been fielded not much later, with trubos coming later.

Sure, it's a "what if," and I don't like theose much .... but the point is the timeline for European deployment could have been met easily if authorization to proceed had been forthcoming. In the real world it wasn't, of course.


----------



## syscom3 (Mar 20, 2013)

Would take some work, but I would rather see the bomb bays redesigned so that the center structural member is moved outbound to the sides (same as the B29 and Lanc). That way both bombers could carry the large bombs (4000 pounders) internally instead of the drag inducing external hard points.


----------



## GregP (Mar 20, 2013)

Good point Syscom. I was thinking more of a newer or faster airframe than of the improvements that could be made for operational ease of use on existing airframes. But they are important, too.


----------



## Shortround6 (Mar 20, 2013)

tomo pauk said:


> So far this is the best information I have about the turbo R-2600.



Only one A-20 was completed as such out of an order for 63 planes, it was decided to complete the rest as A-20A's without the turbo. Most of these were actually completed as P-70s. 3 were completed as F-3A recon planes. Both the A-20D and O-53 died on the drawing boards, no example ever flew. Not sure about the YF-3 but one source only gives two serial numbers. Flown as YF-3s or converted to/from something else? 

Leaving out the turbos probably means a lower than desired cruise height with a trade off from flak. faster speed means less time in flak range at turbo altitudes but lower operational height means more time in Flak range. How close it comes to equaling out I don't know. 

The 1200hp engines burned about 50-55 gallons each at around 180mph True. B-17 Cyclones at 2050rpm and 30in MAP. At 210-212mph true the engines were burning 71 gallons each at 2100rpm and 31.5in MAP. 

AN R-2600 from a B-25 making 810hp at 15,000ft. (minimum cruising) uses 80 US gallons an hour at 2000rpm and 27in MAP. 

An R-1820 in a B-17 can make 1000hp (max continous, NOT Military) at 30,000ft. It can make 1200hp at 27,000ft using Military power.
An R-2600 WITHOUT turbo makes 900hp at 25,000ft at Military power. 1100hp Military at 20,000ft. 

This _may_ be why little or no effort was made to re-engine the B-17 and B-24. The R-2600 offered _less_ power at the operational heights wanted over Europe. It weighed about 500lbs more per bare engine and burned more fuel.


----------



## tomo pauk (Mar 20, 2013)

Thanks for the effort to type out the numbers 
You can note that I don't try to push forward the turbo-less R-2600 for the USAF bomber's use in the ETO. My pet engine being the turbo V-1710 for that task. The take off power would also go up, with those installed.

Another ideas: R-2000 in the B-24? Maybe having the engines with water injection, so the take off power can be greater?

Question for people well versed in HP Halifax: was there a difference in speed with differently equipped models, but with same engines?


----------



## model299 (Mar 20, 2013)

I've seen before that the B-24 crews would razz the B-17 crews about arriving back at the base sooner.
The '17 guys would counter that they flew higher and thus were harder to "reach" than the '24s.



The problem with the XB-38 was the additional weight and complexity the installation brought with it.

In fact, the prototype was lost to an engine fire. Sound familiar?






You certainly can't argue about the looks though. They did a great job on those cowls.


----------



## GregP (Mar 20, 2013)

I understand they "cobbled together" the exhaust manifolds, there being no other application for them, and so they tended to leak after a few hours. If production manifolds had been designed and used, it would not have been a problem ... as it wasn't in the P-38 after the usual teething troubles. We have many P-38 exhaust components today and they work just fine when they get installed in a flying P-38.


----------



## bob44 (Mar 20, 2013)

Would a faster B17 or B24 have helped with bomber losses?


----------



## MikeGazdik (Mar 20, 2013)

tomo pauk said:


> So what plausible upgrades could USA undertake, in order to make the B-17 and B-24 better suited for the tasks, even if planes taking those tasks might be contested by enemy actions? There was one real-life upgrade to the B-17, namely the version with V-1710s, so that might get the ball rolling.



More Mustangs, sooner.


----------



## GregP (Mar 21, 2013)

A B-17 cruising at 230 mph would have been better than 180 mph. The closing speed would have been less, so the gunnery from both sidres would have been better, and the losses to B-17 bubbers would have been higher ... as might have been the B-17 losses. Without emprical data, we will never really know.


----------



## Aozora (Mar 21, 2013)

There was an attempt made to modify the B-17 - it was called the "Reed Project" Plane Talking - HyperScale's Aircraft Scale Model Discussion Forum: More Reed Project B-17 photos

Essentially this was a B-17E modified by an 8th AF engineering officer, Major Robert J. Reed. For a start he noted that all operational B-17s were flying with their cg aft of the rearward limit of 32% MAC at the operational weights then in use (early 1943); of course this had bad effects on the stall characteristics, slower cruise speeds, worse fuel economy etc.

Major modifications:
Incorporating Consolidated turrets into nose and tail positions - because the turrets had their own armor plate, which turned with the turret, fixed armor was no longer needed in the nose and rear gunner's compartments: turrets were also equipped with more effective sights and could cover a greater area more effectively than the hand-held weapons. 

Change the bombardier's position to a streamlined blister under the nose, closer to the aircraft's cg.

Relocate the radio operator and radios to the nose compartment, rectifying the cg problems and allowing more effective co-operation with the navigator, plus the operator manned the turret leaving the bombardier free to concentrate on one task.

Modifications to the ventral ball turret: remove ammunition boxes from within the turret to the yoke carrying the turret, which also allowed a much increased ammunition capacity of 1,400 rpg. The internal components of the turret were rearranged to provide more room and better accessibility to oxygen outlets, etc which meant that the gunner could now wear his parachute.

Replace the Sperry upper turret with a Martin 250CE unit which was 120 lbs lighter, with more efficient sights, better armor plating and visibility for the gunner, plus it took up less room behind the cockpit and the seated gunner was more comfortable. It was also possible to dispense with the waist guns.

Add a powered twin-machine gun installation in what had been the radio operator's compartment.

Replace the folding bomb bay doors with units that slid forward and aft, meaning that there was far less drag than with the standard doors open.

Overall it was calculated that there would be a decrease in gross loaded weight of 1,000 lbs, while the mean cg would be at 27% MAC, decreasing the stress on the airframe, improving flight characteristics and increasing cruising speed by 10 mph.

From _Air Power_ January 1984 Vol 14, No. 1


























The main problem I can see is that with the hinged bomb bay doors bombs could be jettisoned through them, if need be, whereas with the fore and aft sliding units that might not have been possible.


----------



## johnbr (Mar 21, 2013)

I so a photo with a B-17 with 3 50s cil in the tail.


----------



## VBF-13 (Mar 21, 2013)

bob44 said:


> Would a faster B17 or B24 have helped with bomber losses?


I'm thinking the same thing. Negligible, if anything. These aircraft were in just too tough.


----------



## Readie (Mar 21, 2013)

Boeing XB-38 Flying Fortress - Wikipedia, the free encyclopedia

This was another avenue explored. I read this and wondered if 4 Griffons would have been another option.

Cheers
John


----------



## tomo pauk (Mar 21, 2013)

I guess Griffons would've made performers of any plane. The quirk was that it would take two stage versions, and even the UK was not exactly awash with those.


----------



## Shortround6 (Mar 21, 2013)

England wasn't exactly awash with even single stage Griffons in the quantities that B-17s could suck them up.


----------



## tomo pauk (Mar 21, 2013)

Indeed. One might contemplate 2 stage Packard Merlins on heavies, yet the turbo V-1710s seem like only engine that would provide both extra HP and numbers produced, for 1943-45.


----------



## GregP (Mar 21, 2013)

While the trubo V-1710 B-17 was a viable option, it would have required two supply chains ... one for the radial engines and one for the V-12's. That is probably what doomed the XB-38. It WAS a better mousetrap in my opinion, but was it worth the expense of mechanic training and the spares / tools supply chain? My guess is "no," but I have no magic spyglass into the decision-making process.


----------



## Shortround6 (Mar 21, 2013)

There may _not_ have been enough difference between them in _everyday_ operations to make much difference.

http://www.zenoswarbirdvideos.com/Images/P-38/38SEFC.gif

http://www.zenoswarbirdvideos.com/Images/B-17/17SEFC.pdf

At MAX cruise (lean condition) the Allison is good for 795hp at 63 gallons an hour. The Cyclone is good for 750hp at 62.5 gallons and hour. 

At MAX continuous (rich) the Allison is good for 1100hp at 113 gallons and hour and the Cyclone is good for 1000hp at 103 gallons an hour. 

Is the reduction in drag good enough to increase the cruise speeds? The increase in power is marginal at best and power per gallon of fuel burned seems to be of no _practical_ difference.


----------



## wuzak (Mar 21, 2013)

Shortround6 said:


> There may _not_ have been enough difference between them in _everyday_ operations to make much difference.
> 
> http://www.zenoswarbirdvideos.com/Images/P-38/38SEFC.gif
> 
> ...



I would say that much of the aerodynamic drag advantage was lost because the V-1710 nacelle fitted onto the standard firewall. That is, the nacelle was actually larger than needed for the V-1710.

The problem with the XB-38 project is that it used radiators mounted in the wing leading edge between the inner and outer nacelles. This required modifications, and would have caused delays in production to implement. If the V-1710 was designed with the coolers all within the nacelle, and designed as a bolt up replacement the concept could have been explored further.

Also, regarding power numbers, one would think that even in 1942 it could be recognised that the the V-1710 had more potential for performance improvements.


----------



## GregP (Mar 21, 2013)

That can't be the case.

The standard B-17G had top speed of 287 mph (up to 300 mph depending on who you believe) and a cruise speed of 180 mph.

The XB-38 had a top speed of 327 mph and cruise speed of 226 mph.

Speaks volumes to me of reduced drag with near equivalent power. The Allison engined version would have been better for penetration speed and carried an equivalent payload. The range was 3,300 miles which was better than the 2,000 miles for a standard B-17G.


----------



## wuzak (Mar 21, 2013)

The XB-38 was based on the B-17E which was being used as a pattern aircraft for the B-17F, neither of which had the chin turret. It is those to which the XB-38 should be compared, not the B-17G, which suffered an increase in drag due to the chin turret.


----------



## wuzak (Mar 21, 2013)

I like Bill's idea of fitting low drag remote turrets in place of the manned turrets/flexible gun positions of the historic B-17. I would ask if the system was reliable enough for an earlier introduction?

Perhpas something based around the P-61's turret? Or was that the same family as the B-29's turrets?


----------



## Shortround6 (Mar 21, 2013)

Cruise speeds without altitudes or power settings are near useless for comparison. 

http://www.zenoswarbirdvideos.com/Images/B-17/17FOIC.pdf

Please note that the B-17F could fly at 149mph Indicated at 15,000ft ( 193mph true?) while burning 52.5 gallons and hour per engine. 

OR 151mph Ind. at 20,000ft burning 71 gallons an engine per hour. Isn't that about 211mph true? 

OR at max continuous (not really practical) 172mph Ind. at 25,000ft ( 258mph true) while sucking up 104 gallons an hour per engine. 

The 300mph for a B-17G may be the speed when using WEP which for some "G"s gave them 1380hp at 25,000ft according to some sources. 

The engines used in the XB-38 were supposed to be good for 1425hp at 25,000ft. They were the -89 model as used in the G H P-38s. 

We should also compare apples to apples. One source (Joe Baugher"s website) gives the following performance for a B-17E and since the XB-38 was the 9th B-17E airframe (no chin turret and perhaps some other drag producing additions of the "G") it seems a fairer comparison. 

"Maximum speed 318 mph at 25,000 feet. cruising speed 195-223 mph."

The XB-38 also crashed on the 9th test flight with about 12 hours of flying which may not have allowed for a full exploration of performance. Numbers given may have been estimates or may have been able to be tweaked (improved) with more time. I don't know either way. 

I am not seeing a huge improvement here though.

True airspeeds are a rough calculation using about 2% per 1,000ft as in 20,000ft Indicated airspeed would be multiplied by 1.4, those of you who are pilots are welcome to correct the figures.


----------



## GregP (Mar 21, 2013)

The XB-38 with the Allisons was at least 25 mph faster than any other B-17. The cruise speed was at least 40+ mph faster, whatever the circumstance.

Ergo, it would have been a better penetrator by speed alone. Equivlent armament and bomb load. Better aircraft unless proven more vulnerable by combat, and it wasn't since they didn't produce it.

A lot of better aircraft also weren't produced, not just the XB-38. Personaly, I like the Beechcraft XA-38 Grizzly, but they only built two. Wildly capable but not proceeded with. Too bad.


----------



## Shortround6 (Mar 21, 2013)

Where do you get the 25 mph and 40 mph from?

25 mph faster than a 318 mph "F" is. 343 mph.

Cruising 40+mph faster than any other B-17 means a cruise of 250-263mph, not counting max continuous.


----------



## GregP (Mar 22, 2013)

B-17's cruised at 180 mph. The XB-38 cruised at 226 mph. That's about 46 mph in my book, if not yours. No B-17 was much faster than about 300 mph in actual combat trim.

Facts speak well, and the Allison engined version was faster and carried the same or greater load, depending on whom you believe. I beleve it was. It was better but not produced ... like the He 277.

You are free to disagree ... in good humor, hopefully.


----------



## wuzak (Mar 22, 2013)

Looking at the numbers on Wiki the R-2000 gained about 150hp over the R-1830, and around 300lbs. Is changing the B-24 from R-1830s to R-2000s going to be worth it?


----------



## tomo pauk (Mar 22, 2013)

From what I can gather, non-turbo R-2000 offered about 10% more power at max continuous setting vs. non-turbo V-1830.

The (Allison's?) proposal, B-24 with V-1710s. Too little cooling capacity for my taste, but worth a look:







Wuzak, do you know anything about speeds of Halifaxes with different turrets, and/or any other aerodynamic improvements?


----------



## wuzak (Mar 22, 2013)

tomo pauk said:


> Wuzak, do you know anything about speeds of Halifaxes with different turrets, and/or any other aerodynamic improvements?



I don't know much about Halifaxes. 

So, no is the answer.

But there are some data sheets over at ww2aircraftperformance.com


----------



## yulzari (Mar 22, 2013)

There is another aspect to bear in mind. 

RAF Halifax crews found that, once later models had improved speed and lighter weight with the removal of the front turret etc, Bomber Command said, excellent, so they can carry a greater bomb load at the original speed and height. The RAF calculated in terms of tons of bombs not in numbers of aeroplanes.

Would the USAAF not go down the same road if the improvements let them? They were already embarrassed by the 'teeny weeny' bomb loads compared to RAF night bombers over the same target.

There is a story (almost certainly apocryphal) that, when the first Flying Fortresses were being delivered to the RAF, a company representative was extolling their virtues at a FAA mess on an RAF station. He boasted that they could carry 4,000lb of bombs to Berlin or 8,000lb to the Netherlands on their 4x1,000 bhp engines. The FAA crews gently pointed out that their 4 1,000 bhp engines, on 4 Swordfishes, already flew 8,000lb to the Netherlands so it didn't seem that much of a step forward.


----------



## Readie (Mar 22, 2013)

How about lifting power?
The whole object is too get as many bombs dropped on the enemy so, while speed is good, you need to maximise the ability to get bombs in the air.
Four Merlins could lift a larger bomb load than the B17's, and yes I know the Lancaster was not as heavily armed so there was more bomb weight capacity.
Does anyone know if Boeing experimented with Merlins on B17's? I cannot find any evidence to suggest they did....
Cheers
John


----------



## tomo pauk (Mar 22, 2013)

The turbo V-1710s were offering 1325 HP for take off from mid 1942 on, and 1425 from mid 1943 on. That would be some 10 and 20% more than historic B-17s and B-24s have had on tap.

No Merlin Fortresses were ever tested, I'm afraid.


----------



## Shortround6 (Mar 22, 2013)

The B-17 _started_ at 26,520 pounds empty, 37,000 pounds gross, 45,650 pounds (Y1B-17A)

Went to: 29,021 pounds empty, 39,320 pounds gross, 49,650 pounds maximum. (B-17C)

Jumped to: 32,350 pounds empty, 40,260 pounds gross, 53,000 pounds maximum (B-17E)

And finished at: 32,720 pounds empty, 55,000 pounds normal loaded, 72,000 pounds maximum. (B-17G) 

A few structural modifications and beefed up landing gear along the way. Bomb Bay fit between wing spars so it was limited in length. 

On lot of these big bombers (especially ones that _grew_ in weight) you cannot stick what ever you want, where ever you want. 

From the B-17 Manual:

A) B-17F airplanes, with modified landing gear
and added chord-wise wing tip tanks, can be flown up to
and including a gross weight of 64,500 pounds, with
the following restrictions:

(B) At 64,500 pounds,the extra wing tip tanks
must be full to obtain the effect of a relieving load on
the wings in flight. Care must be exercised in taxying
avoiding rough ground. Take-offs, above a gross
weight of 56,000 pounds may be made only on smooth
fields or prepared runways. All pivot turns on one
wheel, while taxying, will be avoided.
(C) All B-17 type airplanes, equipped with extra wing tip
chord-wise tanks, must be operated in accordance
with (B) preceding, whenever the wing tip
tanks are more than half full. Maximum permissible
indicated air speed of B-17F airplanes, with extra
wing tip tanks full, must be limited to 230 mph, when
loaded to 64,500 pounds. Maximum maneuver permissible
at 64,500 pounds; positive, 2.056; negative,
1.22; landing gear, 2.1.

A B-17 running light (40-45,000lbs) could hit 226mph at sea level (true and indicated speeds the same?) using max continuous power. A B-17 at 53,000lb could probably pull a 2.5 G maneuver and in the low 40s it could pull 3 "G"s. 

Even if you increase the power you are starting to run in "placard" limits that restrict the actual performance increase.


----------



## Readie (Mar 22, 2013)

Shortround6 said:


> The B-17 _started_ at 26,520 pounds empty, 37,000 pounds gross, 45,650 pounds (Y1B-17A)
> 
> Went to: 29,021 pounds empty, 39,320 pounds gross, 49,650 pounds maximum. (B-17C)
> 
> ...



Thanks SR6.
So, are we saying that the B17 had reached the end of its development with the G series?
Cheers
John


----------



## Readie (Mar 22, 2013)

Boeing YB-40 Flying Fortress - Wikipedia, the free encyclopedia

This is a fascinating version too. I see that speed was a problem so, this may have been a candidate for more powerful in line engine. Maybe retractable guns too to save drag.

Cheers
John


----------



## Shortround6 (Mar 22, 2013)

I don't know if it had reached it's limit but you are getting into an area where any major improvements are going to need some major modifications to accommodate them and and that throws the easy estimate of the size of the improvement out. 

The XB-38 was a modified "E" and ONE .30 cal gun in the nose (if it was ever installed for the tests?), in fact from looking at photos it may have had no tail guns installed (at least when pictures were taken) no waist guns and a remote control belly turret. 


Trying to estimate the improvement on the "G" is a bit difficult as the "G" had a lot more drag than the "F" (or figures are given for much higher weight?) 

At least one version of the B-17 was rated for a 20,800lb bomb load but both the bomb load and the flight "profile" were rather useless. 8 1600lb armor peircing bombs inside and a pair of 4000lb demolition bombs out side. Drag was horrendous, fuel limited, and flight maneuvers severely restricted. 

Say you take your "72,000lb" B-17 and up the installed engine weight by 1200lbs and up the landing gear and structural weight by several hundred pounds (say 300?) do you now have a 73,500lb plane with the same restrictions (and payload=fuel+bombs) as the 72,000lb "G"? of course your empty weight is 1500lbs greater so less than max load flights may suffer a bit. 

Weights for the XP-38 were supposed to be 34,748 pounds empty, 56,00 pounds gross, 64,000 pounds maximum.

Note the 2400lb increase in empty weight over the parent "E". at 64,000lbs gross that is 2400lbs less fuel or bombs. It better get more range for the same fuel.


----------



## Readie (Mar 22, 2013)

Shortround6 said:


> I don't know if it had reached it's limit but you are getting into an area where any major improvements are going to need some major modifications to accommodate them and and that throws the easy estimate of the size of the improvement out.
> 
> The XB-38 was a modified "E" and ONE .30 cal gun in the nose (if it was ever installed for the tests?), in fact from looking at photos it may have had no tail guns installed (at least when pictures were taken) no waist guns and a remote control belly turret.
> 
> ...



I guess every design reaches the stage where an 'improvement' does not necessarily give the sought exponential increase in performance / usability.
Thank you for your facts and figures, I hadn't considered many of them when I thought that the simple application of more power would 'do the trick'
Cheers
John


----------



## GregP (Mar 22, 2013)

Good post Shortround. It's starting to look like U-2! Then U-2 had severe limitations in flight but did the job very well.

The B-17 was a workhorse until the war ended, despite any limitations. I don't really think the Allison, Merlin, or anything else would have made the B-17 all that much faster or better. It was a good design as designed and to make it a significant notch better would have taken another design. Most aircraft perform about as they do regardless of modifications made.

One example that was noticeably better was the difference between the F9F Panther and the F9F Cougar. The difference was the swept wing. The fuselage and tail were essestially the same. It made a speed difference of 75 mph. The modifications we've been talking about are engines, drag elimination, and some weight savings. They just won't make all that much of a difference. The cruise speed delta of about 40 mph for the Allison engine variant is nice, but hardly significant when the attackers come in at 400 mph. Now if you could put on an engine that would cruise at 1,200 HP, that would make a real difference. 

A 300 mph B-17 would have been wonderful ... but the engines would have burned fuel fast enough to preclude bombing Berlin from England. That's why "what-ifs" are not my favorite subject. Almost everyone forgets the real-life consequences of what may LOOK like easy changes. The specific fuel consumption of high output radials is fairly well known and upping the power from 750 - 850 hp at cruise to 1,200 hp materially affects the range. Real performance changes can be had from reducing weight, drag, or both. Adding power without reducing drag or weight will help but will also reduce the range. It's OK if the range is already more than enough but, if the range is critical at all, adding power won't help much since you can't get there and back again.


----------



## Readie (Mar 22, 2013)

GregP said:


> .. Adding power without reducing drag or weight will help but will also reduce the range. It's OK if the range is already more than enough but, if the range is critical at all, adding power won't help much since you can't get there and back again.



Which is the objective after all said and done.


----------



## tomo pauk (Mar 22, 2013)

About fuel consumption, kindly posted by SR6:



> At MAX cruise (lean condition) the Allison is good for *795hp* at 63 gallons an hour. The Cyclone is good for *750hp* at 62.5 gallons and hour.
> 
> At MAX continuous (rich) the Allison is good for *1100hp* at 113 gallons and hour and the Cyclone is good for *1000hp* at 103 gallons an hour.



At max cruise (lean), the V-1710 produces 6% more power, while using 1% more fuel per hour. So the distance covered in an hour should be better for V-1710 engined plane, since such plane should cruise faster. That is even if we don't account for improved streamlining of the former.

At max cruise (rich), the Cyclone uses some 10% less fuel to make 10% less power. It is also a less streamlined affair than V-1710. So yes, the V-1710 onboard will consume more, but the plane with it can make more miles in a same time than a Cyclone-engined one.


----------



## Shortround6 (Mar 22, 2013)

True, Tomo, but the size of the bombbay and the size/type/number of bombs is pretty much fixed without redoing the wing-center fuselage. 

I don't agree with Greg, the Allison power does add a bit of speed but I doubt the cruise goes up by 40mph *IF* both planes have the same nose/guns/weight and use _about_ the same power. a 10% increase in power is good for about a 5% increase in speed if the drag stays the same. A 40mph increase in cruise is over 20%. The Allisons are more streamlined but they didn't reduce the size/cross section of the nacelles and unlike the P-36 to P-40 conversion the engines, even four of them, are a smaller percentage of the total drag. 

And unless you increase the gross weight of the airplane, if you want to carry the same bomb load to Berlin you *have* to do it with 2400lbs less fuel (400 gallons).


----------



## tomo pauk (Mar 22, 2013)

deleted - messed up my math


----------



## GregP (Mar 22, 2013)

Actually Shortround, I was using the numbers supplied by history, not doing any calculations. The reported specifications for the XB-38 say it cruised at 226 mph ... I didn't claim that. They also say the top speed was 327 mph. Again, not my claim, just a number from a reference.

You are bringing up things about drag and guns. etc. that the reports on the XB-38 don't cover. Since you are doing a "what if," claim anything you want and nobody can prove or disprove it. I really don't think all the things you can think up are covered in the reports of the day, so we are both left wondering what really might be true. 

Personally, I don't even know if the cowlings were mated up to the stock B-17 firewalls or if maybe they made newer, smaller firewalls since they were chaning the engines anyway. If I were in charge, I would have if only to see what effect the lesser drag had. I wasn't in charge but firewalls aren't all that tough to make. I calculate a 10% increase in power to be worth about a 3.1% increase in speed if drag is the same, so obviously I think the drag of the XB-38 was lower than the drag for a radial powered unit. One reason may well be smaller cowlings mated to a smaller firewall ... I can't really say unless I, or WE, get access to some of the design data on the aircraft. Personally, I haven't seen that to date. Then again, I also haven't looked for it.

Since they only built one and it crashed, we are both left speculating a bit. If you happen to have information about the fiitment of the XB-38, or the final configuration, maybe you could share that. I don't have any such data at this time from which to form a basis for a sound opinion, just the reported historical performance numbers. The historical reports say 327 mph max, 226 mph cruise and I have no reason to doubt the claimed numbers. They are also relatively meaningless in importance since they didn't produce and deploy the XB-38.

I DO think there was room for improvement in the B-17 airframe. Whether or not the Allison or Merlin would be the basis for improvement I can't say, but the British tried going between powerplant types on several designs and none seemed to make a huge difference unless the installed power was also very different. Likely as not, the B-17 would have followed suit with that regard even if V-12's were used in production.


----------



## wuzak (Mar 22, 2013)

GregP said:


> Actually Shortround, I was using the numbers supplied by history, not doing any calculations. The reported specifications for the XB-38 say it cruised at 226 mph ... I didn't claim that. They also say the top speed was 327 mph. Again, not my claim, just a number from a reference.



You are comparing the XB-38, which was based on a B-17E, with the later B-17G. The performance comparison you should be making is between the XB-38 and the B-17E/F. It is well known that the nose turret on the B-17G cost it performance, particularly in maximum speed.




GregP said:


> Personally, I don't even know if the cowlings were mated up to the stock B-17 firewalls or if maybe they made newer, smaller firewalls since they were chaning the engines anyway. If I were in charge, I would have if only to see what effect the lesser drag had. I wasn't in charge but firewalls aren't all that tough to make. I calculate a 10% increase in power to be worth about a 3.1% increase in speed if drag is the same, so obviously I think the drag of the XB-38 was lower than the drag for a radial powered unit. One reason may well be smaller cowlings mated to a smaller firewall ... I can't really say unless I, or WE, get access to some of the design data on the aircraft. Personally, I haven't seen that to date. Then again, I also haven't looked for it.



The V-1710s were definitely hooked up to the standard B-17 firewalls. There is a picture of the V-1710 on the XB-38 in _Vees for Victory_, the engine without cowling. It has a lot of spare space around it.

The V-1710s used the same turbo in the standard location as for B-17s. Not sure about the intercoolers, but since the chin on the nacelles didn't include coolant radiators I would surmise that there were intercoolers in there.


----------



## yulzari (Mar 22, 2013)

As has been mentioned, the key limit to the B17 is the size of the bomb bay. Pimp it up how you may it can only carry just so much inside.

Along time ago on another forum it was suggested that early (pre tail turret) B17s with high altitude optimised Bristol Hercules engines and the Type 442 Wellington B Mark VI pressurised cabin could make a viable huge PR machine capable of vast photo coverage at heights above interception. Someone else reckoned it would take the Luftwaffe about 3 weeks to strip something (an Me 109T with a DB605 was suggested) down that could reach it with a single 20mm cannon.


----------



## GregP (Mar 22, 2013)

As for comparing variants, the B-17E, F and G and all the rest cruised at about 180 mph. The E might have been a bit faster if it was flying alone, but bomber streams of B-17's cruised at about 180 mph as a matter of record.

I've seen that picture of the XB-38 as I happen to own that book. I can't tell if the firewalls are stock or not, and when the fitment is finished, there isn't much room left at all for anything else to be stuffed into the cowling. The book SAYS they were stock, but where did Dan get that data? The radiators are buried in the wing leading edge according to the book, and there are some good pics supporting that. Whatever the case, the reported cruise speed was 46 mph faster than the reported cruise of wartime B-17's. Had the XB-38 been produced and deployed, it might well have also cruised at 180 mph just to fly with it's radial engine brothers, I can't say since it didn't happen. It is interesting that Dan Whitney has the information to write a few paragraphs about the XB-38 but supplpied no performance data in his book. I had to get the reported performance from other references.

I'm not making wild claims and I'm not trying to change the reported numbers ... they are what they are. If you want to compare the XB-38 to anything, have at it in good health. The reported numbers are from a total population of only one, so it was certainly the fastest XB-38 ever produced, being the only one.


----------



## wuzak (Mar 22, 2013)

Greg, here is the data drom Joe Baugher:



> Specification of Boeing B-17E Fortress:
> 
> Four Wright R-1820-65 Cyclone radials rated at 1200 hp for takeoff and 1000 hp at 25,000 feet.
> 
> ...



Boeing B-17E Fortress




> Specification of B-17F:
> 
> Four Wright R-1820-97 Cyclone radials rated at 1200 hp for takeoff and 1000 hp at 25,000 feet.
> For brief intervals, a war emergency power of 1380 hp could be delivered.
> ...



Boeing B-17F Fortress




> Specification of Boeing XB-38:
> 
> Four Allison V-1710-89 liquid-cooled V-12 engines, rated at 1425 hp at 25,000 feet.
> 
> ...



Vega XB-38


So, the XB-38 was 9mph faster at 25,000ft than the B-17E, 2mph faster than the B-17F (when it was using WER).

On the face of it the XB-38 was 26mph faster than the B-17F's cruise speed, but the cruise speed of the E is between 195mph and 223mph - that is between 3mph and 31mph slower than the XB-38. The range would, probably, be the difference between cruise settings - maximum cruise, best economy cruise.


I do think that the cruise speeds employed by B-17s in combat were the result of formation flying and the need to maximize range.


----------



## wuzak (Mar 22, 2013)

Double post.

I would like to correct something I said earlier. 

The XB-38 had the oil coolers in the chin position in the nacelles. It used the intercoolers in the standard position, though the ducts were opened up slightly to give greater cooling capacity. The turbo wasn't exactly the same as used in production B-17s at that time, but it was a B-series, so it fit into the standard position.


----------



## wuzak (Mar 22, 2013)

The V-1710-89 was rated at 1425hp Military power @ 54inHg MAP and 1600hp @ 60inHg MAP WER. Using WER could give a few more mph over the recorded results.

A quick estimate gives 340mph.


----------



## wuzak (Mar 22, 2013)

Was just looking at a test report on the B-17F http://www.wwiiaircraftperformance.org/B-17/B-17F_41-24340_FS-M-19-1470-A.pdf and found, interestingly, that the inboard and outboard engines had different critical altitudes by 1500ft! 27,800ft for inborad engines, 29,300ft for outboard engines.


----------



## GregP (Mar 22, 2013)

I don't really have any quarrel with any of your post above, Wayne. I have the speed for the standard E as a bit slower, but a few mph either way isn't going to make or break it. And I also think you are right, the 180 mph was a formation cruise speed ... and that's where they cruised on most missions regardless of whatever speeds they were capable of.

In any case, they didn't proceed with the V-12 B-17, so it's pretty much a moot point. I like the XB-38's looks but, in the end, only the radial variants saw service. I prefer the two-row Pratt 1830 to the single-row Wright 1820, but that's personal preference only. The specific fuel consumption is better for the Pratt by about 20%.


----------



## wuzak (Mar 22, 2013)

http://www.wwiiaircraftperformance.org/B-17/B-17G_Standard_Aircraft_Characteristics.pdf

This characteristics data sheet for the B-17G shows a "high speed" mission profile. Cruising speed is listed as 214kt @ 10,000ft (246mph @ 10,000ft) and combat radius 595 miles with a military load of 10,000lbs. Ammunition is listed as 5970 rounds of 0.50". I assume the weight of the ammo is included in the military load?

The speed curves show that with maximum power the G could do 282kt = 325mph.


----------



## wuzak (Mar 22, 2013)

This chart, from http://www.wwiiaircraftperformance.org/B-17/B-17G_Standard_Aircraft_Characteristics.pdf, seems to be showing a 10,000lb load could be carried on a 600nm (690 mile) radius mission at an average speed of 214kt (246mph).







If it could do that, why didn't it?


----------



## wuzak (Mar 22, 2013)

GregP said:


> In any case, they didn't proceed with the V-12 B-17, so it's pretty much a moot point. I like the XB-38's looks but, in the end, only the radial variants saw service. I prefer the two-row Pratt 1830 to the single-row Wright 1820, but that's personal preference only. The specific fuel consumption is better for the Pratt by about 20%.



The XB-38 fell, like so many projects of the time, to the alter of production. The V-1710 was suggested as an alternative to the R-1820 in case there was a supply shortage of the latter. There wasn't. The XB-38 was intended to explore possibilities for performance improvements, but the prototype was delayed by higher priority works for Vega (ie production, and setting up their B-17 line). 

Basically the XB-38 would have needed to show a much larger performance increase over the B-17 for it considered for production.


----------



## Shortround6 (Mar 22, 2013)

wuzak said:


> Greg, here is the data drom Joe Baugher:..................
> 
> So, the XB-38 was 9mph faster at 25,000ft than the B-17E, 2mph faster than the B-17F (when it was using WER).
> 
> ...




Thank you for the work of typing out all that information. 

The report you posted the link to is also very interesting as it shows that an "F" could do 309mph running light (42,452lbs) and 299mph at 49,463lbs at 25,000ft at Military power. it also shows a possible cruise of 219mph at 650hp per engine with a specific fuel consumption of .485 lb/hp/hr. unless there is a misprint ( and there is at least one on that chart). 

Operational cruising speeds were often different than book or tested cruise speeds.


----------



## GregP (Mar 22, 2013)

The 0.485 lb/hp-hr would be for the Pratt engined version of the B-17. I think the Wright 1820 was right at 0.6 lb/hp-hr.

I can't find a single reference that says any G model B-17 could get to 325 mph. It is usually listed as 287 - 295 mph with maybe 302 at WER, which was never used in real life unless they were trying to get the bird to a landing spot on 1 or 2 engines after the others were shot out. We happen to have a B-17 that we are returning to flight status. I wish I had a proposed flight date, but that depends on money. All aircraft fly on money, despite the occasional references to oil and gasoline / jet fuel.

I don't believe the chart above. If it were true, we'd surely have reports of 10,000 pound bomb loads being used in the war from B-17's on a regular basis. I daresay they might have flown a few, but not many. Once we had airfields in France, if the chart were true, we'd be regularly hauling 10,000 pound bomb loads to Germany ... and we didn't, even at the end of the war, when we surely were within range.

But, I'll keep an open mind and look at the flight manual for our B-17 tomorrow ... if Steve Hinton is there and lets me see it ... we'll see.


----------



## wuzak (Mar 22, 2013)

GregP said:


> The 0.485 lb/hp-hr would be for the Pratt engined version of the B-17. I think the Wright 1820 was right at 0.6 lb/hp-hr.



219mph TAS @ 25,000ft, 48,583lb weight, engine rating - 650hp @ 1900rpm, 27.5inHg MAP, 0.485lb/hp.hr
299mph TAS @ 25,000ft, 49,643lb weight, engine rating - 1190hp @ 2500rpm, 45.5inHg MAP, 0.670lb/hp/hr

One is lean and one is rich thus giving the discrepancy between the specific fuel consumptions.

Which P&W engined B-17?

SR, was the discrepancy you found the difference between MAP settings for two conditions when the engines were at 1200hp @ 15,000ft?


----------



## wuzak (Mar 22, 2013)

GregP said:


> I don't believe the chart above. If it were true, we'd surely have reports of 10,000 pound bomb loads being used in the war from B-17's on a regular basis. I daresay they might have flown a few, but not many. Once we had airfields in France, if the chart were true, we'd be regularly hauling 10,000 pound bomb loads to Germany ... and we didn't, even at the end of the war, when we surely were within range.



I wonder if the 10,000lb "bomb load" is actually 10,000lb military load, including nearly 6000 rounds of ammo?


----------



## GregP (Mar 23, 2013)

You got me there Wayne. I was thinking of the DC-3 / C-47 since I worked on it last weekend and typed it into a B-17 thread. Duhhhhh ....

Production B-17's were Wright 1820's while the DC-3 / C-47 was produced with both engines before settling on the Pratts. I have seen a post about a turboprop B-17 powered by four Darts, but it was a fire bomber conversion. Engage brain before posting ...

By the way, our DC-3 is nearing flight status again. It is unlikely to be mistaken for a B-17.


----------



## wuzak (Mar 23, 2013)

I proposed a twin engined B-17 previously, using V-3420s. I don't think the R-2800 has enough grunt to be used in the B-17 as a twin, and is probably too heavy and uses too much fuel in a 4 engined version, so what about a triple engined B-17 with R-2800s?

The bombadier would have a window below and behind the fuselage engine for sighting his bombs.

Forward defence would be taken car of by the front upper turret, perhaps a secons one to the rear helping with rear defence too. Perhaps a couple of synchrnised 0.50s firing through the prop to make the pilot feel better!


----------



## cimmex (Mar 23, 2013)

wuzak said:


> , so what about a triple engined B-17 with R-2800s?
> 
> The bombadier would have a window below and behind the fuselage engine for sighting his bombs.
> 
> Forward defence would be taken car of by the front upper turret, perhaps a secons one to the rear helping with rear defence too. Perhaps a couple of synchrnised 0.50s firing through the prop to make the pilot feel better!



I’m aware that the „what if”-guys have strange ideas but this statement is ridiculous. It is simply not possible to install a motor cannon in a R-2800 or another two row radial.
cimmex


----------



## Neil Stirling (Mar 23, 2013)

Greg,

_I don't believe the chart above. If it were true, we'd surely have reports of 10,000 pound bomb loads being used in the war from B-17's on a regular basis. I daresay they might have flown a few, but not many. Once we had airfields in France, if the chart were true, we'd be regularly hauling 10,000 pound bomb loads to Germany ... and we didn't, even at the end of the war, when we surely were within range._


Altitude, and weight. The flight manuals for the B-17 and B-24 show a marked increase in consumption above about 20,000ft. Consumption testing here B-24 Performance Air miles per gallon fell from IIRC about 1.1 ampg to about .65. Also tactics I believe the practise was to fly about over the UK and get into formation before setting out.

Neil.


----------



## wuzak (Mar 23, 2013)

cimmex said:


> I’m aware that the „what if”-guys have strange ideas but this statement is ridiculous. It is simply not possible to install a motor cannon in a R-2800 or another two row radial.
> cimmex



Who said anything about a motor cannon? I said synchronised machine guns. Mounted on the cowl.


----------



## cimmex (Mar 23, 2013)

sorry, I missed that.
cimmex


----------



## Shortround6 (Mar 23, 2013)

wuzak said:


> SR, was the discrepancy you found the difference between MAP settings for two conditions when the engines were at 1200hp @ 15,000ft?



No, it was just above the 1190hp setting at 25,000ft. The two 425hp settings, one at 1900rpm and 18.78in and the next one at _2800_rpm and 20.2in. 

2800rpm would definitely be over revving . 1800rpm might make sense and is a simple typo.


----------



## tomo pauk (Mar 23, 2013)

Looking at the wing area of B-24 ( 1,048 ft², span 110 ft 0 in ), the Avro Manchester actually have had more (1,131 ft², span 90 ft 1 in ). Developing it into Lancaster also involved increase of wing area span, now being 1,297 sq ft and 102 ft 0 in. The wing was also greater in later B-26 vs early models. Maybe a wing root plug would not be too much for the B-24? Say, 3-5 feet at each side, so the wing grows in span and area, thus lowering the wing loading?


----------



## drgondog (Mar 23, 2013)

With 10 extra feet of wing at root, there is probably at least 5% extra profile drag - not good for cruise speed and definitely not for range - but better take off performance and heavier load capacity


----------



## tomo pauk (Mar 23, 2013)

Bill,
What was the usual altitude of bombed-up B-17s and B-24s, cruising toward targets in ETO?


----------



## GregP (Mar 24, 2013)

Didn't get anywhere near the office today to look at the B-17 pilot's manual. Spent the whole day riveting and making stiffeners for the fillets on the tail of our Bell YP-59A. Sorry ... space-cased the load chart. Will try to correct that next weekend.


----------



## drgondog (Mar 24, 2013)

tomo pauk said:


> Bill,
> What was the usual altitude of bombed-up B-17s and B-24s, cruising toward targets in ETO?



24-26,000 for B-17, 20-22,000 for B-24s.


----------



## bob44 (Mar 24, 2013)

> What was the usual altitude of bombed-up B-17s and B-24s, cruising toward targets in ETO?



Here is some interesting reading on the B17 and B24.
Typical altitude for B-17 missions? | ArmyAirForces
8th AF - B-17 vs B-24 | ArmyAirForces


----------



## tomo pauk (Mar 25, 2013)

Thanks for the feedback, Bill and Bob.

The altitude of 20-22000 ft makes the B-24 just within of the envelope for the most numerous Flak, the 56 caliber 8,8cm. Even the ones with well worn barrels could reach it? Parsifal, maybe you could chime in, about the realistic envelopes of the Flak?
The R-1830 was able to make same power from SL up to 25000 ft (no ram), so the wing area seems likely to be main culprit for the Lib not cruising higher? Data from Wikipedia, for B-24J and B-17G: 

Wing area: 1,048 ft² 
Max. takeoff weight: 65,000 lb

Wing area: 1,420 sq ft
Max. takeoff weight: 65,500 lb

The B-17 did have about 35% lighter wing loading, according to that. So the B-24 with a wing of 10% greater wing area might cruise maybe 2000 ft higher; the engine have enough power for that. The air at, say, 23000 ft is thinner than at 21000 ft, ie. less drag, so the speed and range would remain the same? The wing 'plugs' can allow for increased fuel tankage, if the range needs to be further increased (to seal the Atlantic gap?).
The increased cruising altitude can make the job harder for interceptors, too.

From here, web 'version' of Ray Wagner's book "American Combat Planes of the 20th Century":



> The Eighth Air Force in Britain favored the B-17 because it was easier to fly, had a higher ceiling, and seemed more resistant to enemy gunfire (see Table 5, page 243 for comparisons). Both heavy bombers had added much weight, but the smaller area of the B-24’s narrow wing handicapped it at high altitudes.


----------



## tomo pauk (Mar 30, 2013)

Mike Williams has updated his site with new data about B-17, B-24 and B-26


----------



## wuzak (Mar 30, 2013)

GregP said:


> I don't believe the chart above. If it were true, we'd surely have reports of 10,000 pound bomb loads being used in the war from B-17's on a regular basis. I daresay they might have flown a few, but not many. Once we had airfields in France, if the chart were true, we'd be regularly hauling 10,000 pound bomb loads to Germany ... and we didn't, even at the end of the war, when we surely were within range.





wuzak said:


> I wonder if the 10,000lb "bomb load" is actually 10,000lb military load, including nearly 6000 rounds of ammo?




B-17G Range vs Bomb Load

This shows 13,000lb internal load @ 1100 mile range, and just over 4000lb at 2500 mile range. It also states that the bomb load includes 2000lb for crew, 1080lb for oil and 1368lb for ammunition. That totals at 4448lb, so the 13,000lb bomb load really is 8552lbs, and the 2500mile range can only be for ferrying.

10,500lb (real bomb load 6000lb) gives a range of 1500 miles,


----------



## GregP (Mar 31, 2013)

Same objection applies. We didn't ... why not?

I know it COULD carry 10,000 pounds, but not at the range in your post. I am given to understand that at 10,000 pounds the entire range was less than 600 miles, so the radius would be less than 300 miles minus whatever it took for reserves, explaining why we didn't bomb with 10,000 pounds very often. This comes from B-17 verterans who were crew members in WWII. We have 2 - 3 in our volunteer group. All said they never flew or heard of anyone else flying with 10,000 pounds in the bomb bay. But they DID hit the target with what they had.

Alas, I still didn't manage to find the B-17 manuals today again. But I DID get the covers and hatches back on the Bell YP-59A and it will be on display at our airshow in all it's glory. We are all in airshow mode at this time (May 4 5). We are almost done with the windscreen and finished the sliding canopy more than a year and half ago. Closing in on it .... and can't wait for it to start and taxi and fly under its own power. Hopefuly sometime SOON. I KNOW its close when Steve Hinton is reading and studying the pilot manual for the aircraft. It won't make this year's show as a runner, but will in 2014 ... even if it just taxies. Hopefully, 2014 will be its debut as an airshow performer.

If not, then something extraordinary would have to happen to postpone it. It's that close to being done. The port aileron is being reskinned now and the starboard one is next ... then the instrument panel had to be made and populated. The rest is just about all done.

If it doesn't happen, the culprit will most likely be leaky fuel cells ... but we all hope not. We'd have to de-rivet the wing skins to change them ...


----------



## wuzak (Mar 31, 2013)

GregP said:


> Same objection applies. We didn't ... why not?
> 
> I know it COULD carry 10,000 pounds, but not at the range in your post. I am given to understand that at 10,000 pounds the entire range was less than 600 miles, so the radius would be less than 300 miles minus whatever it took for reserves, explaining why we didn't bomb with 10,000 pounds very often. This comes from B-17 verterans who were crew members in WWII. We have 2 - 3 in our volunteer group. All said they never flew or heard of anyone else flying with 10,000 pounds in the bomb bay. But they DID hit the target with what they had.



You seem to have glossed over the fact that the chart shows that 4448lbs of "bomb load" was actually men, oil and ammo.


----------



## wuzak (Mar 31, 2013)

It is also my understanding that the B-17 could not be configured to carry 10,000lb of _bombs_ internally. The closest is, maybe, 6 x 1600lb bombs.


----------



## Shortround6 (Mar 31, 2013)

It was actually _rated_ for eight 1600lbs internally 

B-17F, -G, Fortress Mk. II Pilot's Flight Operating Instructions.pdf‎

Available in the manuals section of this website. 

See pages 53 55. 

Also see page 98. Basic (NOT _empty)_weight for B-17F was 41,300lbs:

Including:

Crew nine
nine .50 cal guns
3500 rounds of .50 cal ammo.
144 gallons of oil
1500lbs of wing tankage. (not fuel) 

See condition II.

65,000lb gross.

6,000lb inside
4,000lb external
2280 gallons of fuel.


----------



## drgondog (Mar 31, 2013)

Offhand I don't recall seeing any 8th AF mission with more than 6,000 pound bomb load (2x2000 + 2x1000) for early missions on sub pens 1942-early 1943. After that, probably 95% w/5000 for intermediate, and mostly 4000 pounds for Berlin and beyond.

I do know some experiments were made with bombs on wing bomb racks but the drag penalty was too high to be useful - hence the Aphrodite program.


----------



## wuzak (Mar 31, 2013)

Shortround6 said:


> It was actually _rated_ for eight 1600lbs internally
> 
> B-17F, -G, Fortress Mk. II Pilot's Flight Operating Instructions.pdf‎
> 
> ...



Interestingly page 55 shows only 6 stations can take a 1000lb bomb, racks 1 4 able to take the 1600lb bomb, but not the 1000lb bomb. I wonder if that is because the 1600lb bomb is SAP and is narrower than the 1000lb bomb?


----------



## Jugman (Mar 31, 2013)

Individual stations did not have load ratings. The maximum load raiting for outboard racks was ~2000lb and ~5000lb for the inboard racks. This link list a good number of homogeneous bomb loads. Note that the chat lists stations 7/28, 10/31, 18/39 for the 1600lb AP bomb. But the hoisting diagram shows the more common 8/29, 11/32, 16/37. My take is the chart lists a load that maximizes space for smaller bombs on the outboard racks. The maximum heterogeneous internal bomb load may be as high as 13,200lbs or six 600lb and six 1600lb AP bombs.


----------

