Why does the B2 bomber's trailing edge sawtooth shape negatively effect its stealth characteristics?

Question

I read an article about how the new B21 would have (in theory) a W shaped trailing edge, which was the initial shape intended for the B2 before the gust alleviation system was added to the requirements causing it to have the sawtooth trailing edge.

From what I see from the planform of the B2, there aren't any more unique angles on the sawtooth compared to the W shaped trailing edge even though it has more 'sides'.

I was wondering if this is true in that the W shaped trailing edge has better stealth characteristics than the sawtooth edge and if so, is it significant?

The article mentions Bill Sweetman's Inside the Stealth Bomber book as its source.

score 3 · Answer 1 · answered Jun 02 '22 at 12:19

I think it has to do with the radar frequencies of interest that one is trying to defeat. According to the article you referenced, adversaries are starting to deploy lower frequency (UHF) surveillance/tracking radars than existed when the B1 and B2 were designed. The size of the "W's" on the trailing edge impact the stealthiness as a function of the radar's operating frequency.

Note that a lot of the details behind these designs is highly classified, held at the SAP/SAR level, and so only show up in very generic terms in publications.

score 3 · Answer 2 · answered Jun 02 '22 at 14:28

3

The more "sides" a body has, the higher its radar reflection. Note that the MBB Lampyridae prototype had vastly lower (calculated, I must say) radar returns than both the Have Blue prototype and the F-117 that followed from it. When looking at the return of radar energy at grazing angles, it is the number of surfaces and edges that counts, not their size. The addition of the wing chord extension by Boeing to Northrop's original design made the B-2 possible, but increased its radar returns slightly over those of the original design.

answered Jun 02 '22 at 14:28

Peter Kämpf

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Ah okay I see now, I thought it was the number of uniquely angled sides that mattered rather than the number of total sides. I would've thought that the waves would simply reflect along the same angles as the other parallel edges or is it more complex than that? – Yourhelpismuchapprecciated Jun 02 '22 at 23:29
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@Yourhelpismuchapprecciated Radar waves bounce off like light only when they hit a surface more pr less perpendicularly. At grazing angles they behave much more like waves of lower wavelengths which travel along the length of the material and produce diffuse emissions at edges and discontinuities. – Peter Kämpf Jun 03 '22 at 08:39
thank you so much for your reply! That is really interesting, is there any good books or textbooks I can read to grasp this concept better? – Yourhelpismuchapprecciated Jun 10 '22 at 15:03
@Yourhelpismuchapprecciated I learned that stuff from the people who designed the Lampy stealth research aircraft. At that time there were no books. I'm sure there are some now, I would go for basic physics first. – Peter Kämpf Jun 10 '22 at 16:47
@Yourhelpismuchapprecciated Try this webpage which gives a pretty solid introduction into the topic. And here is part two. – Peter Kämpf Jun 11 '22 at 19:59
Thank you so much for your help! – Yourhelpismuchapprecciated Jun 22 '22 at 22:41

Why does the B2 bomber's trailing edge sawtooth shape negatively effect its stealth characteristics?

2 Answers2