Has the construction team of the Northrop Grumann B-2 Spirit made use of the features of the German Horten Ho 229?

Question

1) 2)

In the first picture, we can see the German-made Horten Ho 229. See also this video.

The second picture shows the American-made Northrop Grumman B-2 Spirit. See also this video

Clearly, both air wings show a remarkable similarity. The German plane looks much smoother though than the quite linear and edgy American one (is there a reason for this? Hasn't a smoothly formed plane less resistance?).

The Horten brothers, who supervised the construction and came up with the design, had no computers at their disposal like plane designers have these days. Every time some adjustments had to be made to make it fly better. In this BBC article one can read the plane was its time far ahead.

The designers and constructors of the NG B-2 Spirit did have computers and more advanced technology at their disposal to construct a working flying wing which clearly shows much resemblance with the wing developed decades before (maybe in a more "instinctive" way?).

My question is simple (I couldn't find this on the internet}:
Did the people who made the NG B-2 Spirit make use of the information of the Horten Brothers. Did they use the blueprints of the HH Ho 229?

Extra question: Why does the Northrop Grumann have such an "edgy", straight form, while the Horten has a smooth, curved form? Isn't curvature and smoothness better for the aerodynamics?

Answer 1

If the objective is very similar, good engineers will independently arrive at a very similar solution.

Yes, the Northrop engineers knew of the Go-229 / Ho-IX. But Jack Northrop has also played with flying wings before – witness the YB-35 and YB-49. Unfortunately, those designs "did not fly" with the conservative bureaucracy of the Air Force. While the Ho-IX was a very advanced concept, there was no "secret" in its design, so how a low RCS airplane should look like was quite obvious to the Northrop engineers.

That the B-2 looks more "edgy" is caused by more insights into stealth technology. While the Horten IX tried to minimize frontal area, used wings of wooden construction (which are transparent to radar energy) and Reimar Horten had planned to use radar absorbing charcoal, the B-2 uses edge alignment in order to reflect radar energy at specific angles, besides using radar absorbent material. When Northrop was designing the plane, it had a rhombic inner section with rectangular wings, much like what is now shown of the new B-21 design, but the small chord at the wing root created a structural weakness when the Air Force added a low level flying requirement. That only was overcome after Boeing got involved. Boeing engineers changed the planform to the current shape by adding more chord at the inner wing which resulted in the typical "W"-shaped trailing edge of the B-2.

B-2 design evolution and its Lokheed competitor (picture source)

After the B-2 production run had ended and after Grumman had merged with Northrop, a full-scale RCS model of the Horten jet was fabricated by Grumman engineers with modern techniques to simulate the aircraft as it would appear to electromagnetic energy. It was tested at a RCS test facility, using similar frequencies as those used in WW II. While the design did show a markedly lower RCS than comparable airplanes of the time, this can be fully attributed to its shape and the use of wood.

Horten IX replica on a sting at the RCS test range (picture source)

Reimar Horten was a bit dogmatic about his designs and insisted that they only use a wing and not even a vertical tail, even though this would had benefited its flight stability. As it turns out, a straight vertical tail produces in combination with a wing or the horizontal tail a nearly perfect corner reflector. While this dogmatism helped to reduce the airplane's RCS, it resulted in marginal lateral stability.

Answer 2

Reimar Horten applied to join the "paperclip" expat technologists in the US, and also in the UK, but was refused both. This despite working for the Brits for a time in Germany, in the immediate aftermath of war, and being interviewed by many in the industry. This must in part be down to an unsympathetic summary of his knowledge by a British official interviewer. On the other hand his chief rival and architect of the Me 163 Komet tailless fighter, Alexander Lippisch, had also been working on flying wings and was taken to the US.

One reason for this difference in perception of the two rivals was that Lippisch had fifteen years of solid financial backing and academic research programmes behind him, leading to a large pile of materials attesting to his standing. By comparison the Hortens had always struggled and much of their accumulated expertise was never given the resources to be written down and remained in Reimar's head or notes, at best published informally in gliding magazines. His rather high-handed "I don't need experts, I am the expert" attitude may have had some truth to it, but it lacked a visible evidential base and consequently was not believed.

As mentioned in another answer, Northrop's B2 was derived from the B-35/49 programme (The B-49 was just the B-35 with jets and mini-fins). That in turn derived from his work over the previous decade, when the Hortens were all but unknown to wider industry. He would have been far more aware of Lippisch, but even there they plowed fairly distinct aerodynamic furrows.

To return to Reimar Horten. In part due to the recent release of classified reports, the claim has arisen that he was able to design what is known as proverse yaw into his flying wings. Together with sweepback, this created a plane that was directionally stable. None of his WWII or earlier designs (that I can recall offhand) needed fins. Those of Lippisch and Northrop suffered from adverse yaw - a tendency to shy off course when banked into a turn - hence their constant need for fins. If this claim is true (and I have not seen the evidence), that would mark him out as the first designer since pioneer J W Dunne to fully conquer the stability of the finless aeroplane.

The B2 exchanges such aerodynamic subtleties for computer algorithms.