Richard Vogt and B-47 design origins – father of all jets?

[Ivan Culjak]

Most things in technology are evolutionary in nature, but some moments are truly turning points – like a B-47 moment – time could be divided before and after B-47. It is not overdoing to call B-47 a “ mother of all jets “ (https://www.dailykos.com/stories/2016/2/2/1474024/-The-mother-of-all-jets-Boeing-s-B-47) Stretching this phrase further, we can say that we know exactly the place and time when famous B-47 swept wing design was born. This moment is most vividly described on B-47 Wikipedia page:

Swept wings. In May 1945, the von Kármán mission of the Army Air Forces inspected the secret German aeronautics laboratory near Braunschweig. von Kármán's team included the chief of the technical staff at Boeing, George S. Schairer. He had heard about the controversial swept-wing theory of R. T. Jones at Langley, but seeing German models of swept-wing aircraft and extensive supersonic wind-tunnel data, the concept was decisively confirmed. He wired his home office: "Stop the bomber design" and changed the wing design.[6][7]

So here is the wing, but where does the fuselage come from? There is one hidden design point which could further lead to German inspiration for B-47, and this is a tandem, bicycle type of landing gear. At the beginning stage of B-47 design, Boeing preferred conventional or tricycle landing gear for B-47, but in the final stages, they went for bicycle. And guess what; most of the first generation jet bombers across the globe went for bicycle gear, too. It’s like a thin red line through designs, but today was completely abandoned!

A rationale behind using tandem gear for a bomber is thoroughly described by the Blohm Voss team for the P. 188 project as presented in Dan Sharp’s book – Luftwaffe: Secret bombers of the third Reich, page 82. This project explanation is a rare firsthand insight… Don’t want to repeat a full explanation, but tandem gear dictates (or is a consequence of) overall fuselage design (high wing design, maximum bomb space and equal load sharing between front and rear wheels..)

So, if we go for German inspiration for B-47 – swept wings are undoubtedly from LFA wind tunnel and his chief Alfred Busemann. But, general design is, most probably, from P.188 and Richard Vogt. Fuselage design and tandem gear definitely point to it – this is a main feature of B-47 and B-52 as bombers. P.188 was one of the first to use a new tail cone lattice parachute, also used on B-47 and B-52. P.188 went for podded engines from the start, ignoring the buried engine option. On some variants of P.188 engines were paired just like B-47. A cabin and pilot seating of B-47 is pretty much fighter -like as on P.188. Further on, Richard Vogt, pre-war and during war, was for sure one of the best informed on the state of the German aircraft industry, especially when it comes to the research and development. Post war, he worked for the US Air Force and ended his career with Boeing, working directly with Georg Schairer. So, if Boeing wanted to consult someone from the German side (as it surely did), Vogt was an excellent choice and very available.

But, it’s also very true that Richard Vogt was willing to do not one but quite a few extra miles.

There are many advantages of bicycle gear for bombers as shown by the BV team, but there is one big difficulty, too. When using tandem gear, both gears (front/rear) are getting off the ground and landing at the same time. It does not raise the nose wheel first as it has a tricycle - so how to produce lift, how to take off? His solution for takeoff and landing was use of variable incidence wings – also one old idea but repurposed to solve a no-nose rotating issue.

To be true, there was also an active US research of tandem gear for bombers - Martin XB-26H “Middle River Stump Jumper” dating back to 1944 or 1945. The prospect of getting a large bomb bay on a high-wing bomber was too tempting. So, when it comes to the inspiration for B-47 tandem gear and fuselage design, it could be Martin XB-26 or P.188. But, it seems that Martin XB-26 (and XB-48, neither) had any elegant solution for horizontal take off and landing which is a big thing. If so, it’s rather no for XB-26 as an inspiration for B-47. (As a kind of paradox, it seems that Martin Company applied almost full scope of P.188 design toolset on the marvelous XB-51, probably one of the best planes never built in series)

The other could not follow – to be able to take off, B-47 had longer nose wheel so it stays with nose pointing up, B-52 has permanent incidence of wings so it flies horizontally with a nose pointing down, some Soviet jets had two stage nose wheel….Wing design of W type is obviously superior from the point of efficiency and bending moment. Central fuselage made of steel provided almost infinite load and fire resistance, the load bearing box spar, also made of steel gave incredible torsion stability and served as an auxiliary fuel tank, … All these solutions were better than those conventional ones applied to B-47 and B-52 - but, it was simply too much new to digest ……

At the end , I admit to be not overly happy with my post, it was my intention to do some overclaim, just to make it more interesting, to make a story…. But actually, I would be really grateful if somebody would like to help me out in early history of B-47, and Richard Vogt early days in the USA.

Best regards..

 

[TomcatViP]

The tandem bicycle gear design involves widely spaced front and rear landing legs, often separated, in the central position, close to the CG, by the weapon bay. This leaves the aircraft with only a short tailplane moment to raise the nose at slow speed during takeoff with, as a consequence, a higher drag during cruise that reduces the radius of action. This was alleviated, mainly, with two design configurations:

1. the airfoil is placed at an higher incidence (angle b/w fuselage axis and wing chord - Ex. B-52 and the plane flies with a nose down attitude at the lower altitudes)
2. the front leg was actuated to extend at rotation speed - Ex. M-4

One of the main advantages however, often overlooked, with that tandem configuration is the ability to actuate the landing gear to rotate sidewise, away from the fuselage axis, to take into account crosswind during landing (and takeoff). With that in place, the drag during that phase of flight is considerably lowered, allowing for an increase in the landing mass. This allows such planes to operate in more demanding meteorological conditions or at a higher T.O mass.

What Boeing brought also to large airplane with swept wings, aside of many innovations, was a better mass distribution for the wing to accommodate the risks of flutter and a nose down automatism to accommodate for the pitch up moment (yes, the same thing you see today and decried by some pilots as a dangerous innovation they've never heard of! [/OT])

 

[riggerrob]

... What Boeing brought also to large airplane with swept wings, aside of many innovations, was a better mass distribution for the wing to accommodate the risks of flutter and a nose down automatism to accommodate for the pitch up moment (yes, the same thing you see today and decried by some pilots as a dangerous innovation they've never heard of! [/OT])

Yes, B-47's greatest innovation was its high aspect ratio wing. We suspect that was motivated by lessons-learned during the 1930s as Germany experimented with higher and higher aspect ratios on competition sailplanes (e.g. Horten).
Boeing diverged from conventional wisdom of medium aspect ratio structurally stiff wings.
Installing jet engines ahead of the wings' center reduced flutter tendencies.
Boeing also built a much lighter weight wing than previously possible.

 

[sienar]

Wright Field suggested the tandem gear when they added the A-bomb requirement. This was based on experience with the B-26. Not only did this make a longer bomb bay possible but it also allowed the bombs cg to be coincident with the aircrafts cg.

The 8 degrees of incidence was chosen based on some prior wind tunnel work. Takeoffs were supposedly fine but landing was difficult.

From "The Road to the 707"