Flying wing, piston engined bombers big planes: what are the benefits?

[tomo pauk]

Hello,

WW2 almost saw a deployment of the flying wing bombers. What would be the advantages vs. the 'classics'? Was the flying wing a viable thing in ww2, not only for bombers, but for other 'big' planes (transport, marine patrol etc).

Please note: no pi$$ contest re. who invented/applied the thing 1st.

 

[drgondog]

The primary reason for a flying wing (i.e. defined as no aft eppenage/control surfaces) is to reduce a.) parasite drag, and b.) trim/induced drag from elevator and rudder). The result should also elimintate the weight due to both the sections aft of the wing.

Less drag, less weight - better performance for same equivalent weight for conventional a/c with same wing area. -.

Secondary considerations are potentially smaller radar signature

 

[gjs238]

Was the flying wing a viable thing in ww2, not only for bombers, but for other 'big' planes (transport, marine patrol etc).

Was the flying wing a viable thing post-WWII?
My understanding is that it was not, until the appropriate fly-by-wire systems became available.

 

[tomo pauk]

The XB-35 was flying without the FBW, so did the Me-163.

 

[Balljoint]

My recollection of the Northrop flying wing is that it would fly but was unstable just as the early Wright Flyiers were before they added the rudder. The flying wing had a rudder but it lacked "leverage". With a computer monitoring the situation , instability can be caught early and made to work.

 

[tyrodtom]

There were plenty of flying wings world wide long before FBW, going back to the dawn of flight even. But some or most had control "irregularities" that might have kept them from general acceptance.

I wouldn't consider a Me163 a flying wing though, it has a definite fuselage, it just doen't have a sparate horizontal stabilizer.

 

[drgondog]

The YB-35 and YB-49 both suffered from same root aero/stability issue - namely the wing had to be designed with cambered airfoil that would increase nose down pitching forces as wing AoA increased toward stall. Exceeding that point had the opposite effect that conventional aircraft experienced. The Flying wing stall resulted in a nose up loss of control in which the aircraft attemps a loop and is uncontrollable. That is what happened to Glenn Edwards during stability evaluation - in which he exeeeded the "do not Exceed" AoA.

 

[drgondog]

There were plenty of flying wings world wide long before FBW, going back to the dawn of flight even. But some or most had control "irregularities" that might have kept them from general acceptance.

I wouldn't consider a Me163 a flying wing though, it has a definite fuselage, it just doen't have a sparate horizontal stabilizer.

I would agree with you. The definition really points to only one control surface platform for pitch and roll... namely the wing.

 

[msxyz]

The Horten brothers made some successful flying wings in the 30s. Unfortunately, their designs were too unorthodox to be appreciated. The Horten VII was a sound aircraft, a "technology demonstrator" it would be called today, and the same could be said about the most famous Horten IX / Gotha 229 although the end of the war came before it could be turned into a production aircraft.

Considering that the Germans also engineered several practical radar absorbing materials (in the shape of hard, preformed panels - a design used successfully on the submarines conning towers to reduce the chance of interception by radar equipped hunters) they had all the knowledge needed to design a 'stealth' bomber 30 years in advance.

EDIT: interesting site with pictures of several flying wings http://www.nurflugel.com/Nurflugel/nurflugel.html

 

[FLYBOYJ]

they had all the knowledge needed to design a 'stealth' bomber 30 years in advance.

Not True...

They were going in the right direction but were still decades away from fully understanding the relationship of aircraft shape and reduced RCS, let alone developing the right materials for full stealth capabilities. Their wings still had many "flaws" that would not have been able to be addressed during the 1940s or even 1950s. It wasn't until the 1960s when Soviet mathematician Pyotr Ufimtsev pulled it all together on paper regarding "shape," advances in composite materials several years later gave the right structure needed. Stealth was a manifestation of many technologies that were eventually rolled into one and there was not one real smoking bullet or exact starting point. As stated, the Hortens were in the right direction and "would have" made a very advanced aircraft with a very reduced RCS, but it would have not been a true stealth aircraft.

Now as far as a flying wing application - it was already mentioned about instability on the XB-35 and YB-49, but these aircraft were designed to be used as bombers. I believe a flying wing could have great benifits as a transport (manufacturing costs reduced, fuel efficency)

 

[msxyz]

The Germans were quite ahead in the development of coatings able to reduce the energy reflected by Radar and Sonars

This is the shroud developed to reduce the signature of Schnorkel masts against centimetric radars employed by the Allies

Notice the multi faceted structure; the material itself is quite close to what is employed today to shield anechoic chambers. Even if the Germans were quite behind in radar technology because they lacked the Magnetron, they did very advanced studies about the nature, propagation and physics of centimetric radio waves. Proof is than when they finally recovered some Magnetrons from downed bombers they created some very advanced radar designs in some respects even superior (as it was stated by post war evaluation of the captured German technology) to those of the Allies.

 

[drgondog]

Absorption properties are important but one order of magnitude less important than shapes. The primary breakthrough for Lockheed was linking an obscure paper written by a Soviet Wave propagation/Signal Processing expert.

 

[FLYBOYJ]

The Germans were quite ahead in the development of coatings able to reduce the energy reflected by Radar and Sonars

This is the shroud developed to reduce the signature of Schnorkel masts against centimetric radars employed by the Allies

And that was just one part of the puzzle

Notice the multi faceted structure; the material itself is quite close to what is employed today to shield anechoic chambers. Even if the Germans were quite behind in radar technology because they lacked the Magnetron, they did very advanced studies about the nature, propagation and physics of centimetric radio waves. Proof is than when they finally recovered some Magnetrons from downed bombers they created some very advanced radar designs in some respects even superior (as it was stated by post war evaluation of the captured German technology) to those of the Allies.

They still didn't have the whole recipe for the whole concept. As stated, they were on the right track but decades away from real stealth technology, at least with regards to aircraft

Absorption properties are important but one order of magnitude less important than shapes. The primary breakthrough for Lockheed was linking an obscure paper written by a Soviet Wave propagation/Signal Processing expert.

Pyotr Ufimtsev

From Wiki...


"Ufimtsev became interested in describing the reflection of lasers while working in Moscow. He gained permission to do work on it after being advised that work was useless and would curtail his advancement. Because the work was considered of no military or economic value, Ufimtsev was allowed to publish his work internationally.

A stealth engineer at Lockheed, Denys Overholser, had read the publication and realized that Ufimtsev had created the mathematical theory and tools to do finite analysis of radar reflection. This discovery inspired and had a big role in the design of the first true stealth aircraft, the Lockheed F-117. Northrop also used Ufimtsev's work to program super computers to predict the radar reflection of the B-2 bomber."

 

[aircro]

Here is some kind of 'flying wing' - Burnelli UB-14 - Wikipedia, the free encyclopedia

 

[Siegfried]

The Germans were quite ahead in the development of coatings able to reduce the energy reflected by Radar and Sonars

This is the shroud developed to reduce the signature of Schnorkel masts against centimetric radars employed by the Allies

View attachment 216194

Notice the multi faceted structure; the material itself is quite close to what is employed today to shield anechoic chambers. Even if the Germans were quite behind in radar technology because they lacked the Magnetron, they did very advanced studies about the nature, propagation and physics of centimetric radio waves. Proof is than when they finally recovered some Magnetrons from downed bombers they created some very advanced radar designs in some respects even superior (as it was stated by post war evaluation of the captured German technology) to those of the Allies.

They had two types of absorbers.
1 a jaumann absorber made up of multiple layers of semiconducting impregnated (paper could do) sheets. The conductivity went up in a exponential fashion across the sheets. Due to this structure there was never really a significant discontinuity for the radar to reflect of. It absorbed 95% at 9cm and 80% at 3cm.

2 The other material was Wesch, a sort of ferrite impregnated PVC or rubber. It worked differently and almost as well though at slightly different frequencies.

Jaumann was to be wrapped around masts like periscopes, snorkels and antenna due to its sheet like structure while the Wesch was to be moulded over the tops of the mast as seen in the photograph.

The two materials could also be combined for much greater performance and testing had already commenced.

This mast head stealth combined with passive radar detector, infrared and a supplementary active radar would have ensured the uboats submerged their mast well before detected.

The production Ho 229 was to have been made of a sandwich ply with a graphite impregnated particle board material (formholz) between the outer and inner ply. DeHaviland used Ecudorian Balsa for this on the Mosquito something the Germans clearly found unobtainable. The presecence of the graphite would have produced some absorbtion as opposed to reflection or transmission(which leads to reflection from inner metallic parts like undercarriage)

The National Geographic channel failed to note that for the larger production versions of the Ho 229 this material was to be used. The NG tt was based around a test bed Ho IX which used ordinary ply. The aircraft had to be enlarged since due to an unexpected accessories gearbox change the wing had to be thickened at the roots but this would have caused earlier shock wave formation so the solution on the planned production version was enlarged chord to keep the wing thin.

Reiner Horton moved to Argentina and in 1955 we have a record of him speaking to their aviation institution there of the benefits of wooden aircraft construction in providing "radar camaflauge" this was his term.

One of Reiners brothers died in a mine laying opperation in a He 111, presumably at night, and his rage at this it is said was the catalyst for the idea of radar camaflauge.

It should have been possible to put a jaumann absorber into the lesding edges of a Horton style flying wing without too much trouble. A 20 reduction of reflection from the absorber plus say about 4 to one from the flying wing shape and lack of prop gives a worthwhile reduction of around 60 to 80.

It would translate to about 3:1 reduction in detection range but would greatly enhance jamming and chaff.

 

[oldcrowcv63]

OK, I'll take the bullet, throw the grenade, toss the t*rd into the punchbowl. Provide the incendiary comment (cause sometimes it's just plane fun) pun intended.

Lot's of stories and official reports regarding the YB-35's technical problems. But consider. How many prototype aircraft were produced in such numbers as the YB-35? I don't know the answer, just asking. Also, how many of every single prototype were re-engined to become the YB-49? oops: I mean 2-3 ) And by far most important, how many prototypes were cast by Hollywood as mankind's last hope of survival against an alien invader? You gotta admit, there may be something more to this story than just technical difficulties.

One cannot (well maybe 'should' not instead of 'cannot') discuss the YB-35 without at least mentioning the conspiracy theory associated with the type: from wikipedia:

"The Army Air Force had originally ordered 200 production model B-35s. Since Northrop's facilities were not up to the task of producing them, the Glenn L. Martin Company agreed to undertake mass production. This proved irrelevant when the aircraft had too many development problems. Even disregarding these, so many of Martin's engineers had been drafted by 1944 that Martin pushed the first delivery date back to 1947. Seeing that it would almost certainly never be ready in time for the war, the Army Air Force canceled the production contract, though the Air Technical Services Command continued to run the program for research purposes."

and later in the text and with me purposefully ignoring the technical difficulties issues

"There are long-standing conspiracy theories about the cancellation of the Flying Wing program; specifically, an accusation from Jack Northrop that Secretary of the Air Force Stuart Symington attempted to coerce him to merge his company with the Atlas Corporation-controlled Convair. In a 1979 taped interview, Jack Northrop claimed the Flying Wing contract was cancelled because he would not agree to a merger because Convair's merger demands were "grossly unfair to Northrop." When Northrop refused, Symington supposedly arranged to cancel the B-35 and B-49 program. Symington became president of Convair after he left government service a short time later.[12]"

 

[oldcrowcv63]

Oooops!! I guess just two or three of the YB-35's were converted to jets... I was having too much fun to carefully read the rest of the story. (my imitation of Paul Harvey is not nearly as effective without his unmistakable voice.) and it looks like the YB-17 and other bombers were also ordered in even greater numbers... Roseanna Roseannadanna said it best: "Nevermind"

 

[Jabberwocky]

One of the major problems with the Northrop flying wings of the 30s and 40s was in their lateral and longitudinal stability. It took a long time (a minimum of four minutes and up to eight, depending on altitudes) for the YB-35 and YB-49 to totally damp out pitch and roll oscillations after a heading change. This meant that they had to fly straight and level for a long time to make an accurate bomb run, which would have been pure murder in contested airspace. The corresponding time for a B-29 was 45 seconds, at most.

There was also a great sensitivity of the aircraft to disturbed air. The various Northrop bombers suffered from buffeting when their bomb-bay doors were opened. The result was that the flying wings had only half the bombing accuracy of older platforms such as the B-29.

It was considered quite difficult to get the aircraft just to fly straight and level at a constant speed, not something that lends itself well to a bomber platform. Also counting against the aircraft didn't meet the goals for range or cruising speed set by the Air Force.

On the other hand, the overall benefits of a flying wing are fairly significant.

The general platform in and of itself has much lower drag than a comparable conventional bomber airframe.
The shape of the flying wing give it significant internal volume, meaning it can carry a lot of fuel, bombs or whatever
The lack of compound curves and the like mean that you can manufacture the aircraft easily and relatively cheaply

 

[Jabberwocky]

On a completely different point, I've often thought it was/is a shame that flying wings haven't been more successful in aviation.

There is just something aesthetically right about the flying wing shape and planform. In terms of grace on the ground and in the air, I can think of few aircraft that are as evocative or elegant as the flying wings of the 1930s and 1940s.

I got to chat to a (very) senior ex-Airbus engineer a couple of years ago. Before they did the A380 studies, both Airbus and Boeing were looking seriously at the flying wing concept. The designs promised up to 40% better fuel efficiency than then existing large aircraft designs (ie 747-400), but there were a couple of issues that were considered insurmountable.

First and foremost was the passenger. While a tube with wings isn't the best shape aerodynamically, it is probably the best shape for passengers. Loading/unloading passengers and seating was going to be horribly complex - imaging parking a vaugely triangular cinema inside an aircraft and you've got a close approximation of the layout.

The other problem was airport infrastructure. For an aircraft like an A380, most airports could get away with runway and taiway widening and a few other changes. For a flying wing, you'd have to radically overhaul any airport it operated to - runway, taxiways, apron, terminals, hangars, you name it.

 

[Siegfried]

Northrop did develop a sort of "autopilot" to control pitch instability on their flying wing in time to use on These giant bombers.

Early Jet aircraft from the Me 262 and Meteor onwards exhibited something known as high speed snaking. The solution is something called yaw damper; it is an electronic device using gyroscopes to intervene in the rudder. The Germans flew one in 1943 on a Hs 129 in preperation for fitment to the Me 262. Yaw dampers were essential on the first Boeing 707, KC 135 and A4 skyhawks. It was doable in the day.

The Northrop flying wings didn't need a yaw damper, they needed a pitch damper. Same technology, different axis.

It's important to realise that the Horton flying wings and Lippisches Messerschmitt Me 163 through tailless aircraft used different methods to achieve auto stability to Northrop.

All used a little sweep.

1 Me 163 used
A, wing sweep.
B, reflexed auto stable airfoil on the entire span.
C, full span leading edge slots which generate a forward pitch near stall

2 Horton used
A, wing sweep
B, extended auto stable reflexed airfoil on the inner wing.
C, the above is combined with the bat tail ( as on B2 spirit twin bat tail)
D, wing washout or geometric twist on outer wings which lacked the reflexed airfoil of 2 degrees.

3 Northrop used
A wing sweep
B wing washout of a rather high 4 degrees
C leading edge slats on the outer wing, which also generate a forward pitch near stall and help prevent premature stall. They seemed to only operate on landing.

To make the YB 49 worthwhile it would need
A, wings thinned to raise Mach limit, the original R4360 had driven thickness.
B, enlarged centre section to create a bat tail thereby add stabillity and safety and also all ow room for an enlarge the bomb bay to handle the larger nuclear weapons.
C, electronic pitch damper would still be needed.