The advent of Stealth aircraft

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phylo_roadking
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Post by phylo_roadking » 11 Jul 2007 17:26

The YB-49 was the first of the Northrop protypes that received US govt. financial backing, Jack Northrop had built the rest in-house with his own money, and are not quite as well known as the YB-49. But its immediate predecessor was the same size of aircraft - the same one? - fitted with props and engines. It experienced problems however with gearboxes and driveshafts to the rear prop positions, a problem that Northrop hadn't engineered out before jet engines were made available to him. The Prop version of the full-size wing had much smaller upright control surfaces than the jet version - it wasn't a "true" flying wing in the modern B2 Spirit sense. "Not particularly stable" would be in interesting comparison with the lumbering B-36 which eventually won the big orders LOL yes the YB-49 had to be "flown" but was a lot more nimble. Look for example at the nice banking turns it makes on the limited surviving film of the prototype - later incorporated in the George Pal version "The War Of The Worlds"!!!

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TexasRanger
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Post by TexasRanger » 11 Jul 2007 23:44

"The aircraft's instability in pitch and yaw made it impossible to bomb accurately. A stability augmentation system eliminated some of the yaw problems, but none of the pitch problems. The result was that bomb runs by experienced bombardiers took four times as long as in the B-29, and average miss distances of 3,000 feet were twice those of other bombers."

"I flew the airplane eleven times, evaluating the aircraft as a bombing platform both with and without the autopilot. The bombing
results were very poor…. I never said it was acceptable, and none of us who flew bombers and knew bombing ever said it was an acceptable bombing platform. (R. E. Schleeh, personal communication, July 20, 1983; R. E. Schleeh, personal communication, to E. T. Wooldridge, National Air and Space Museum, November 24, 1982.)"

http://www.dau.mil/pubs/arq/2001arq/Baker.pdf

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Visionist
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Post by Visionist » 11 Jul 2007 23:51

phylo_roadking wrote:The YB-49 was the first of the Northrop protypes that received US govt. financial backing, Jack Northrop had built the rest in-house with his own money, and are not quite as well known as the YB-49. But its immediate predecessor was the same size of aircraft - the same one? - fitted with props and engines. It experienced problems however with gearboxes and driveshafts to the rear prop positions, a problem that Northrop hadn't engineered out before jet engines were made available to him. The Prop version of the full-size wing had much smaller upright control surfaces than the jet version - it wasn't a "true" flying wing in the modern B2 Spirit sense. "Not particularly stable" would be in interesting comparison with the lumbering B-36 which eventually won the big orders LOL yes the YB-49 had to be "flown" but was a lot more nimble. Look for example at the nice banking turns it makes on the limited surviving film of the prototype - later incorporated in the George Pal version "The War Of The Worlds"!!!


The modern B2 lacks any vertical control surfaces.

Does this generate instability? How does the aircraft succeeed as a level bomber?

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TexasRanger
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Post by TexasRanger » 12 Jul 2007 03:25

The short answer is that there are apparently a lot of computers which help fly the airplane.

Edit to add: Also, because the B2 launches 'smart' munitions, keeping the plane steady and level and intersecting a particular point in space at a particular point in time is not as important.

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Post by HistorianSr » 12 Jul 2007 04:25

In a book published by a Northrop insider, the jet powered flying wing was contracted to serve as a reconnaissance platform. The stability problems were a myth. The government pressured Northrop to merge with Convair, but when he refused, the contract was pulled and the flying wings were cut up. (Jack Northrop and the Flying Wing, Ted Coleman.)

Yes, in the George Pal War of the Worlds, the Flying Wing appeared as a versatile and agile aircraft, not at all like the ten-engined, mixed propulsion monstrosity that Convair put into the air (a maintenance nightmare).

Do not compare British or American radars to the radars of today when mentioning the Go-229.




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Post by JonS » 12 Jul 2007 05:32

HistorianSr wrote:Do not compare British or American radars to the radars of today when mentioning the Go-229.

I don't think anyone has done that, but your post raises an interesting conundrum - why is it ok to compare the Go229 with the B2, but not 1940s radar with 1950s radar?

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Re: The advent of Stealth aircraft

Post by maltesefalcon » 12 Jul 2007 11:54

Visionist wrote:
Today, we often hear of the "Legendary Mosquito", about it's massive speed, superior handling, elite flightcrews, highly accurate bombings etc.

But I have heard nobody state it was hard to detect. Was this possible advantage not known when it was designed?


The Mosquito mainly survived because it was both faster and flew higher than contemporary aircraft, including many fighters of the day.

Its had a reduced radar signature which also helped. By the time the enemy radar picked it up on the screen, the interceptor in most cases couldn't catch up before it was out of range.

One other point-stealth aircraft today navigate by passive means ie GPS. WW2 aircraft would need active radar transmissions for accurate target location. This would immediately betray their presence to the enemy.
They would also need to travel in small, dispersed formations to prevent midair collisions.

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Re: The advent of Stealth aircraft

Post by Visionist » 12 Jul 2007 12:13

maltesefalcon wrote:One other point-stealth aircraft today navigate by passive means ie GPS. WW2 aircraft would need active radar transmissions for accurate target location. This would immediately betray their presence to the enemy.
They would also need to travel in small, dispersed formations to prevent midair collisions.


What about an inertial navigation system utilising gyroscopes and analogue computers?

Or is this beyond the technological limits of the time? I would have thought the Type-XXI would have had such a system if it existed...

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Re: The advent of Stealth aircraft

Post by TexasRanger » 12 Jul 2007 12:40

Visionist wrote:
maltesefalcon wrote:One other point-stealth aircraft today navigate by passive means ie GPS. WW2 aircraft would need active radar transmissions for accurate target location. This would immediately betray their presence to the enemy.
They would also need to travel in small, dispersed formations to prevent midair collisions.


What about an inertial navigation system utilising gyroscopes and analogue computers?

Or is this beyond the technological limits of the time? I would have thought the Type-XXI would have had such a system if it existed...


From what I have read, inertial guidance systems were developed mostly for rockets at that time (Goddard). I'm not sure when they passed to aircraft. The V-2 had gyros...

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Post by TexasRanger » 12 Jul 2007 14:06

HistorianSr wrote:In a book published by a Northrop insider, the jet powered flying wing was contracted to serve as a reconnaissance platform. The stability problems were a myth. The government pressured Northrop to merge with Convair, but when he refused, the contract was pulled and the flying wings were cut up. (Jack Northrop and the Flying Wing, Ted Coleman.)


The jet powered flying wing (and its prop predecessor) was originally designed as a bomber. If it was a great bomber, why would it be contracted as a reconnaissance platform?

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Post by phylo_roadking » 12 Jul 2007 15:16

It was designed as a bomber, but Jack Northrop was constantly at loggerheads with the Air Force over their specifications - which were written to favour one planform and design solution. And let's face it - probably favoured one company LOL Hence the proceeding with design and evelopment work on his own private funding for so long. When the recce-bomber specification appeared, it allowed Jack government development money - hence D&D proceeding even after the Convair flying ocean liner won the bomber contract. When this specification was withdrawn...the Air Force cut up the Flying wings as being their property. The pics of the YB-49's sitting in an open lot sliced up like cold meat on a plate are some of the saddest I've ever seen, given those short minutes of glorious flying footage

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Post by TexasRanger » 12 Jul 2007 15:54

Well ... most sources agree that the YB-49 was not capable of delivering the atomic weapons of the time, as the spec for its bomb bays had been written in 1940 (as well as the instability/stall recovery issues -- there were crashes). I don't know if that's a 'favor one platform' sort of thing, but it certainly was a very big disadvantage post-war.

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Post by phylo_roadking » 12 Jul 2007 16:54

Technically that would have been irrelevant, as Northrop's flying wing technology was capable of being scaled up - don't forget they were also being pushed - in BIGGER form - as airliners, with a huge amount of useable free space in the wing for passengers. Whereas good ol' "six turning four burning" proved how underpowered the Convair "winner" was! :-) Right at the end of then-current prop technology for the size of aircraft. Size of bomb bays wasn't really a show stopped compared to that LOL

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Re: The advent of Stealth aircraft

Post by maltesefalcon » 13 Jul 2007 00:31

Visionist wrote:
maltesefalcon wrote:One other point-stealth aircraft today navigate by passive means ie GPS. WW2 aircraft would need active radar transmissions for accurate target location. This would immediately betray their presence to the enemy.
They would also need to travel in small, dispersed formations to prevent midair collisions.


What about an inertial navigation system utilising gyroscopes and analogue computers?

Or is this beyond the technological limits of the time? I would have thought the Type-XXI would have had such a system if it existed...


Even in the 1960's inertial guidance was not accurate enough for pinpoint precision with convential dumb bombs. It could locate a 500 kiloton nuclear bomb over the centre of a city, but not over a specific building. The V2 had the same problem.

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Post by maltesefalcon » 13 Jul 2007 00:43

Visionist wrote:
Tim Smith wrote:I suspect that metal airscrews (propellors) are great at reflecting radar energy as well. So I doubt if any prop plane can be as stealthy as a jet.


One problem facing jet aircraft is that a radar can "see" the entire, relatively large fanblade area, which is why stealth designs bury the engines deep within the fuselage and feature very fine mesh intakes, the openings smaller than a radar wavelength.

A wooden construction may have been useful for maintenance, since aircraft like the B2 Spirit spend 90% of their time grounded, undergoing cosmetic skin smoothing.

With a wooden plane, you can just sand it smooth, but you have to repaint the whole thing...



Was it possible (at least for the US, maybe not Germany) for the manufacture of ferrous paint, containing millions of microscopic iron balls, which absorb the Radar signals (used on the SR71 I believe), to have occured during the war?


The German long range radars had a longer wavelength. I don't think they would be able to pick up a rotating propeller. The airborne Leichtenstein sets had a shorter wavelength and probably could, but only at fairly short ranges. Germany only had a few airborne radar equipped aircraft that could actually catch up to a Mosquito. The Ju-88 HaHa comes to mind. (Nitrous oxide equipped)

Modern radars are more powerful and have wavelengths small enough to pick up a jet turbine. However engines are also shrouded this way to minimize their heat signature for SAM missles.

One thing that occured to me is that the Mossie had a much smaller surface area than a Lancaster, hence it would inherently have a reduced radar profile.

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