I was reading a description of the Boeing X-45 that described it as having "lambda wings." What is a lambda wing and why is it called that?
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2 Answers
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Indeed, it is due to resemblance with Greek letter 'lambda', though not the capital one ($ \Lambda $), but the small one: $ \lambda $.
I am attaching a pic of X-45 with me drawing a lambda over it. Typically, the wing has two taper ratios. The inboard wing tapers heavily, corresponding to legs of small lambda, and the outboard wing tapers slightly or do not taper at all.
Other examples include B-2 bomber:
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$\begingroup$ This answer seems to be correct. Related link that could be included in answer : fas.org/man/dod-101/sys/ac/docs/fatereport/sld034.htm . Google "lambda wing" for more. However it's not impossible that at one time in the past, the term would have been applied to the wing of the English Electric Lightning, etc. $\endgroup$ Jul 9, 2019 at 17:58
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$\begingroup$ I must be missing something. You stated, "a pic of X-45 with me drawing a lambda over it". Unless it's a GIF that's supposed to actively show you drawing a lambda and whatever mechanism that's supposed to show GIFs is disabled in my browser, I'm not seeing anything drawn over the X-45A. $\endgroup$– FreeManJul 9, 2019 at 18:15
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$\begingroup$ @FreeMan - notice the odd black mark on one side? $\endgroup$ Jul 9, 2019 at 18:42
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$\begingroup$ Wow. No, I completely missed that. Hangs head in shame $\endgroup$– FreeManJul 9, 2019 at 19:15
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It's because the shape of the wing resembles the uppercase Greek letter lambda with the leading and trailing edges having the same sweep angle.
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1$\begingroup$ What makes it different from simply “swept wings” though? $\endgroup$ Mar 30, 2019 at 13:27
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$\begingroup$ Here's a presentation from Lockheed Martin: fas.org/man/dod-101/sys/ac/docs/fatereport/sld035.htm $\endgroup$ Mar 30, 2019 at 13:50
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$\begingroup$ I see—the confusing point is that there are actually two very different X-45 concepts. The X-45A has swept wing and fuselage with pronounced chines, while the X-45B/C is a flying wing. According to the presentation, the term applies to the later. $\endgroup$ Mar 30, 2019 at 13:55
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$\begingroup$ I had read through that presentation before I posted the question, but it isn’t at all clear what distinguishes a “lambda” planform from any other swept wing. $\endgroup$– TomMcWMar 31, 2019 at 21:21
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$\begingroup$ I’m no aeronautical designer, just a dude who knows why that particular wing shape is called ‘lambda’. An educated guess is that a ‘swept wing’ is a more generic term for wings of a configuration with a swept leading and trailing edges unlike a Piper Cub, for example, which has straight leading and trailing edge. There may be several distinct ‘swept wing’ configurations with curved leading and/or trailing edges, but the ‘lambda’ configuration is unique, with straight leading and trailing edges. Again, I’m no expert, and would like to know if there is any deeper explanation. $\endgroup$ Apr 1, 2019 at 9:31