This is a picture of the supposed SR-72 Aurora. What kind of advantages would this have over the SR-71, in terms of its triangle design? Paper airplanes have the same shape, and fly really well.

Views of "Aurora" aircraft with A340 for scale

SR-71 top planform view

The SR-71 design that I am comparing it to.

  • $\begingroup$ Please no negativity. A triangle design is something pretty new the only time an aircraft was built triangle was by Germany during ww2 and I don't believe it actually was in service. With this new design of triangular if it exists or not hat aerodynamic advantages come with a triangle design like the sr-72.For those of you who don't believe NASA actually said they are building an sr-72 spy jst like the one I provided in the picture (flightglobal.com/news/articles/…) $\endgroup$
    – Ethan
    Commented Sep 11, 2015 at 21:47
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    $\begingroup$ Paper airplanes have the same shape, but do not fly well They fly very well. What makes you think this? $\endgroup$
    – Simon
    Commented Sep 11, 2015 at 22:06
  • $\begingroup$ @Simon the ones I build don't fly well. I did make a recent one that had the top of the wing bent down and it had lots of lift (the only successful one I have made) so you are right the fly pretty will. I will edit the question. $\endgroup$
    – Ethan
    Commented Sep 11, 2015 at 22:09
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    $\begingroup$ The only reason they don't fly for long is because the only thrust they have is the initial throw. Since they generate drag, as does anything creating lift, but have no thrust, they slow down and can no longer produce enough lift to keep them flying. Because they have very thin wings and fuselage, they fly very effectively. $\endgroup$
    – Simon
    Commented Sep 11, 2015 at 22:14
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    $\begingroup$ triangle design is something pretty new - nope, that's just a delta wing - the most pure form you can get, really. Avro Vulcan, Handley Page HP.115, Convair F-102 & F-106, Boeing X-32... there are triangular planforms everywhere. $\endgroup$
    – egid
    Commented Sep 12, 2015 at 0:05

1 Answer 1


The 'triangle' wing design that you refer to is pretty common. It is called the delta wing design and is used in a number of high speed aircraft, for example, the North American XB70 Valkyrie.

XB 70

In fact, the SR 71 wing planform is also a delta, if one removes the engines. One of the reasons is that the wings of the aircrafts are kept inside the Mach cone formed by the aircraft. The Mach angle is given by,

$\mu = sin^{-1} \frac{1}{M}$,

where M is the Mach number.

As the aircraft speed increases, the Mach angle decreases, which means that the aspect ratio should become smaller and smaller. At hypersonic speeds, the delta wing (or a modified one) is the best option as the wing needs to be pretty short for aerodynamics and structural reasons while able to carry the required fuel and generate lift.

The main advantage of the SR-71 Blackbird is its speed, which was about Mach 3.3. It is logical that its replacement should have better speed characteristics. SR 71 used a ramjet during its high speed dash, while its (rumored) successor is expected to use a scramjet engine.

Engine types
"Turbo ram scramjet comparative diagram" by GreyTrafalgar - Own work. Licensed under CC BY-SA 3.0 via Commons.

The first one(a) is a turbojet engine, the second one(b) is ramjet, and the third one(c), a scramjet. The ramjet and scramjet engines are similar, though the combustion happens at supersonic speeds in the scramjet engine.

NASA has a hypersonic aircraft for experimental purposes called the X43,which uses a scramjet engine, though the aircraft size is pretty small compared to the A340.

X 43
Source: hapb-www.larc.nasa.gov

The closest actual aircraft have come to the shape of the 'Aurora' are the experimental aircraft like the X-37, which has short wings.

X 37
"Boeing X-37B inside payload fairing before launch" by US Air Force - http://www.af.mil/News/Photos.aspx?igphoto=2000374856 (direct link). Licensed under Public Domain via Commons.

There are a number of aircraft with triangular wings, most notably almost all European combat aircraft have delta wings.

And by the way, the Lockheed Martin SR 72 Aurora concept looks like this.

SR 72
"Lockheed Martin SR-72 concept" by Source (WP:NFCC#4). Licensed under Fair use of copyrighted material in the context of Lockheed Martin SR-72" href="//en.wikipedia.org/wiki/File:Lockheed_Martin_SR-72_concept.png">Fair use via Wikipedia.

  • 1
    $\begingroup$ Could you clarify the reference to the image of the turbine/ramjet/scramjet, for example by referencing a,b & c in the text? I guess people who don't know anything about ram/scramjets will not know what's what. $\endgroup$
    – ROIMaison
    Commented Sep 14, 2015 at 13:26
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    $\begingroup$ @ROIMaison. I've added the references. However, please do note that this is just a comparative diagram, nothing more. $\endgroup$
    – aeroalias
    Commented Sep 14, 2015 at 16:31
  • $\begingroup$ Strictly speaking, the SR-71 actually used turbojets with compressor bleed and a very effective afterburner. The afterburner acted much like a ramjet, and was almost the only source of thrust at maximum speed. See also aviation.stackexchange.com/questions/14710/what-is-a-ramjet. $\endgroup$ Commented Sep 14, 2015 at 19:10
  • $\begingroup$ @NathanTuggy You're right. Basically the afterburner acts like a ramjet combustor. I didn't go into much details because the question was about wing planform rather than engine. $\endgroup$
    – aeroalias
    Commented Sep 14, 2015 at 22:37

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