B-36 - Why a Pusher??

[Zipper730]

Alas, so did -- and possibly, do -- many US planners.

That's probably true enough: General Power more or less saying that if there are two Americans and one Russian left, that we won...

The Soviets, if what I've read is correct, were of the belief that there was not some qualitative difference between tactical nuclear weapons and conventional weapons. This, I find more than slightly frightening

Yeah, and there's of course a qualitative difference: Nuclear bombs are way more destructive per bomb, and mass, and they leave a nice radioactive bonus that regular bombs do not.

Putin isn't making me any less nervous.

Yeah, the sad thing is he's not pulling all the strings even in Russia (high finance)

 

[Dimlee]

Regarding the Soviet (not Russian, of course, - that ended in 1920-1922) doctrine...
Ultimate political goal remained unchanged until mid-1980s and that was creation of world wide "socialist camp" and moving towards "Communist society". But military strategic planning was not static. In my opinion, since the end of WWII USSR's military doctrine was revised 5 or 6 times.

 

[XBe02Drvr]

Y

The other part of the thread on the 47, I've read the 47 had wing fatigue issues, and some were lost in flight from wing failure, when doctrine change to low altitude flying with a pop up to release bombs. The USAF was not sorry to retire the 47

What would you expect? The B-47 was the first really large swept wing multi-engine jet to go into service in large numbers and accumulate a fleet operating history. There was no fatigue history to guide designers in building a long life swept wing of that flexibility, aspect ratio, and size with engines mounted outboard on pylons. All the calculations and projections in the world can't compensate for a lack of hard data to base them on. Boeing was "exploring the dark side of the moon", and I think they achieved a miracle equivalent to solving the S-duct issue with the 727.
Now they weren't perfect; I've seen a number of pieces of wing structure wreckage from an early model B-52 crash site, and they were full of cracks with patches on top of patches. And that was early days, when they were still high altitude bombers.
Cheers,
Wes

 

[XBe02Drvr]

That seems to add up: The F-86D couldn't turn fast enough at altitude to reposition itself...

Never mind turning, the Dog Sabre couldn't breathe adequately at altitude with that radome schnozzola obstructing half its intake, and the engine couldn't reach its theoretical thrust output for lack of intake volume. The higher you flew, the worse it got, affecting speed, climb, and energy in a turn.
Cheers,
Wes

 

[Barrett]

I grew up on the ranch in NE Oregon, beneath the low-level route from Fairchild AFB (Spokane) and Mountain Home. My most vivid childhood memory is that huge behemoth motoring overhead. The sound was impressive but so was the FEEL. You could sense that massive thrashing of the atmosphere before the 36 hove into view. Man o man. The first 52 I saw was a disappointment!

 

[XBe02Drvr]

I grew up on the ranch in NE Oregon, beneath the low-level route from Fairchild AFB (Spokane) and Mountain Home. My most vivid childhood memory is that huge behemoth motoring overhead. The sound was impressive but so was the FEEL. You could sense that massive thrashing of the atmosphere before the 36 hove into view. Man o man. The first 52 I saw was a disappointment!

The practice area at my home airport was under an "Oil Burner" low level navigation route, and I would be frequently out with a student at 3500 - 4500 ft when a BUFF or a KC would come over at 6000 - 7000 ft. Sometimes even we would see a "conjugating pair", an awesome sight from just underneath, and audible over the sputter of our O-200.
Cheers,
Wes

 

[ktank]

The other part of the thread on the 47, I've read the 47 had wing fatigue issues, and some were lost in flight from wing failure, when doctrine change to low altitude flying with a pop up to release bombs. The USAF was not sorry to retire the 47

Interesting that the same thing happened to the Vickers Valiant when it was moved to low altitude roles (and it caused the premature retirement of the type).

 

[XBe02Drvr]

Interesting that the same thing happened to the Vickers Valiant when it was moved to low altitude roles (and it caused the premature retirement of the type).

Fatigue happens. You just gotta count on it and roll the dice. Whatever you design it NOT to do, you can count on somebody going out and doing it.
Cheers,
Wes

 

[Zipper730]

Never mind turning, the Dog Sabre couldn't breathe adequately at altitude with that radome schnozzola obstructing half its intake, and the engine couldn't reach its theoretical thrust output for lack of intake volume. The higher you flew, the worse it got, affecting speed, climb, and energy in a turn.

I didn't know that...

 

[XBe02Drvr]

I didn't know that...

There was a really good article on the Dog Sabre in "Wings" or "Airpower", or maybe it was "Flight International" back in the day (70s?) that described the teething problems it had. It, like all the interceptors of its generation, was pushing the frontiers of several different technologies at once.
Cheers,
Wes

 

[Vahe Demirjian]

Convair had a design for a flying boat based on the Model 37 airliner version of the B-36 bomber with Wasp Majors arranged in tractor configuration and high-mounted wing.

Reference:

Johnson, E.R. (2009). American flying boats and amphibious aircraft : an illustrated history. Jefferson, N.C.: McFarland & Co.

 

[BiffF15]

Convair had a design for a flying boat based on the Model 37 airliner version of the B-36 bomber with Wasp Majors arranged in tractor configuration and high-mounted wing.

Reference:

Johnson, E.R. (2009). American flying boats and amphibious aircraft : an illustrated history. Jefferson, N.C.: McFarland & Co.

Vahe,

PLEASE STOP!

V/R,
Biff

 

[swampyankee]

Does anyone have any data or links to technical papers on why the B-36 was built with pusher engines??

I assume that the Convair engineers (and the Northrup engineers working on the B-35) calculated that the drag reduction by not having the propeller airflow over the wing more than made-up for the losses resulting from the propeller having to work in the wake from the wing, but was the difference significant??

I notice that some other 'clean sheet of paper' very long range aircraft (Me 264, and the Nakajima G10N) were conventional tractor designs, so I assume the difference in efficiency between tractor and pusher was pretty close, but that is just a guess.

Comments??

Piper106

The B-35 for the same reason as the N9M: getting enough yaw stability on a flying wing is difficult; engines behind the center of gravity are stabilizing, unlike engines in front, which are destabilizing.

This doesn't answer the question about why the B-36 was a pusher, but there were a few contemporary US bomber projects with wing-mounted pusher props, but none got built except the B-36. I suspect there were some wind tunnel model tests that showed an advantage.

 

[Joe Broady]

In "Convair B-36" (Meyers K. Jacobsen, 1997) is a photo of a wind tunnel model with six tractor engines. The caption says, "Had it not been for wind-tunnel tests, the B-36 might have looked like this model with tractor nacelles, Davis wing, and a twin tail — a sort of oversized but streamlined B-24 Liberator. Installation of pusher-type powerplants was almost a foregone conclusion, for designers knew that pushers would decrease nacelle and wing drag, with corresponding increase in range using same fuel and weight. However, and to make tests complete in all respects, this tractor-type model was given a workout in the M.I.T. wind tunnel. The wooden 1/26th scale model had a nine foot wingspan. November 1941."

The photo is a plan view of the model, which appears to have the same leading edge sweepback as the production B-36 but an unswept trailing edge. Another illustration is a drawing (no date) with the propellers changed to pusher but the same straight trailing edge. The production B-36 trailing edge had a 3 degree sweepback, and the propellers were parallel to it and thus not exactly aligned to the direction of flight.

An interesting B-36 characteristic is the approach to power-on stall. The flight handbook says, "you will notice an unusually high deck angle during the approach. Propeller induced airflow, as shown in figure 6-1, maintains smooth air flow over the center section of the wing well beyond the angle at which a stall would normally occur. This extreme nose-high attitude combined with very low airspeed is another stall warning."

One advantage of the pusher design with the engines at the trailing edge is that engine fires — and they did occur on the B-36, especially in the early years — blow away from the wing, not into it.

You do pay a penalty in the form of extra stress as the props rotate through the wing wake. The flight handbook has graphs of the forbidden ranges of airspeed and rpm. These are different for the two blade manufacturers, Curtiss and A.O. Smith! Years ago I read in a book ("Men of the Contrail Country"?) the tale of a B-36 whose flight engineer made a blunder which damaged the oil seals on all six engines. The plane barely got on the ground before the oil supplies gave out. Possibly this was a case of operating for a prolonged time in the red zone.

In some circumstances it forced a departure from optimum power settings. "Deviations from the basic power schedule are caused by propeller vibration restrictions and turbosupercharger limitations." (AN 01-5EUG-1, "Flight Handbook USAF Series B-36H Aircraft," 1953)

 

[Koopernic]

In terms of the B36's minor sweep back I will offer a educated guess. I was watching a documentary on the National Geographic Chanel Regarding DC3 development. Charles Lindbergh was called in as a consultant to ensure TWA didn't get bad aircraft. As a result Douglass did a lot of wing tunnel testing and found that its pitching characteristics and stability od their DC3 were not good. A slight sweep was added, this ensured that as the angle of attack increased the wing tips generated a forward pitch. The sweep was not so much so as to cause span wise flow handling issues and tip stall issue. I suspect this effect was utilised on the B36 as well. There may have been Centre of Gravity and structural issues it helped as well.

 

[Peter Gunn]

Hey, if the B-36 was good enough for Jimmy Stewart and Harry Morgan, it's good enough for me.

Ditto the B-47.

 

[11bwmech]

Probably WX info could be obtained with the recon version, the RB-36. Don't know the numbers, but the AF had about as many of these as the bomber version. The B-36 was aptly named "Peacenaker" (not an official designation), as it never dropped a bomb in anger, but held the Russians at bay during the early to mid 1950s. Yes, it was a maintenance nightmare, but it could fly for a day or two without refueling, and the loss of an engine or two was not usually a big problem. I remember one made it back to base with all four inboard engines out, plus one jet. And to add to the drag, they windmilled at least one (not sure if one or two; memory is a little hazy after all this time) inboard engine for electrical power, as only engines 2 through 5 had alternators. Only problem they had was they almost ran off the end of the runway because they still had more power than they thought they did.

 

[SaparotRob]

I'm glad this thread was resurrected. Lots of cool info.

 

[Zipper730]

There was a really good article on the Dog Sabre in "Wings" or "Airpower", or maybe it was "Flight International" back in the day (70s?) that described the teething problems it had. It, like all the interceptors of its generation, was pushing the frontiers of several different technologies at once.

The statement "teething problems" seems to make me wonder if they were able to rework the intake...

 

[11bwmech]

I believe the B-36 was an effective deterrent, but I would shift the timeline to the right. When in March 1951 the FEAF floated the idea of conventional B-36 missions from CONUS over North Korea with dual purpose of helping that effort and providing realistic training, SAC replied that only around 30 were fully mission capable. The B-36's real combat capability in numbers only dated from late 51-early 52 and by same token real B-47 capability post dated the Korean War, though it didn't have the degree of teething problems as the B-36. Also, the SAC of formidable repuation for relentless training and readiness was a work in progress in pre KW period. But on the defense, it was really more like ca. 1957 when the Soviet air defense system seriously compromised the crediblity of the B-36 year round*, especially after B-36's were stripped down for higher altitude operation from around '54 (in part to counter improved Soviet capabilities and in part because the retractable gun turret system was never fully debugged). The B-36 was an effective nuclear strike a/c from around '52-'57, give or take a year on either end, not long by today's standards but long enough to be important in those times.

In the very early Cold War the number of US nukes and credible delivery systems was pretty limited, though the number of bombs was skyrocketing by early Korean War, and training and readiness of B-29 and B-50 units had reached a level where they posed a significant nuclear threat to at least parts of the USSR. By same token, the US acted circumspectly about Soviet capabilities once they detonated their nuclear test device in 1949, but in reality the operational versions failed their initial test, and the Soviets had no real deliverable nuclear weapons until around '52, and a very limited capability v CONUS for some years after that. But both sides tended to assume a worst case, so in morale terms you might be right that the B-36 was important even before 1950, but it lacked much actual operational capability until later on.

*since operations v the USSR would often cross high latitudes, 'day and night' tended to mean 'summer and winter'. The Soviets lacked enough high performance radar equipped interceptors to credibly counter B-36's in non-VFR conditions until around '57. The arrangement using radar directed searchlights and non-AI radar MiG-15's to bring down a few B-29's at night over Korea, in 100's of tries, defending only a small area, was not a credible counter to a general nuclear attack on the USSR.

Joe

I believe the B-36 was an effective deterrent, but I would shift the timeline to the right. When in March 1951 the FEAF floated the idea of conventional B-36 missions from CONUS over North Korea with dual purpose of helping that effort and providing realistic training, SAC replied that only around 30 were fully mission capable.

Wing size may have had very little to do with engine placement as the engines were not actually IN the wing but in the nacelles at the rear of the wing.

View attachment 237926

There are no extension shafts. Propellers are mounted on a "normal" propshaft/gearbox and the engines are pretty much in line with the flaps. Engine power section (cylinders) is much smaller than the whole nacelle, The turbos, intercoolers and ducting taking up quite a bit of space.

See: http://www.angelfire.com/dc/jinxx1/B36/B36J522217_10.jpg

Oh, the

Wing size may have had very little to do with engine placement as the engines were not actually IN the wing but in the nacelles at the rear of the wing.

View attachment 237926

There are no extension shafts. Propellers are mounted on a "normal" propshaft/gearbox and the engines are pretty much in line with the flaps. Engine power section (cylinders) is much smaller than the whole nacelle, The turbos, intercoolers and ducting taking up quite a bit of space.

See: http://www.angelfire.com/dc/jinxx1/B36/B36J522217_10.jpg

Wing size may have had very little to do with engine placement as the engines were not actually IN the wing but in the nacelles at the rear of the wing.

View attachment 237926

There are no extension shafts. Propellers are mounted on a "normal" propshaft/gearbox and the engines are pretty much in line with the flaps.

Oh, the engines were in the wing. They were accessible from openings at the wing root. I was 6'5" tall, and I could stand up in the thickest part. I have crawled to the inboard side of the #6 engine inside the wing. The nacelles were part of the wing rather than totally protruding from it, as some tractor types.