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Recent news that the "reusable lifting-body spaceplane" Dream Chaser has arrived at Kennedy Space Center and may launch in August launched led me to read Wikipedia's Lifting body which begins:

A lifting body is a fixed-wing aircraft or spacecraft configuration in which the body itself produces lift. In contrast to a flying wing, which is a wing with minimal or no conventional fuselage, a lifting body can be thought of as a fuselage with little or no conventional wing. Whereas a flying wing seeks to maximize cruise efficiency at subsonic speeds by eliminating non-lifting surfaces, lifting bodies generally minimize the drag and structure of a wing for subsonic, supersonic and hypersonic flight, or spacecraft re-entry. All of these flight regimes pose challenges for proper flight safety.

Trying to distill that, I'm seeing a minimization of surfaces that don't provide lift in both. To me, one is "almost all wing" and the other "almost no wing" where the definition of "wing" in this context is left to the readers imagination.

Suppose a large number of 3D models of craft capable of flight and with relatively low drag at low speed but having a wide variety of supersonic drags were presented to a group of aerospace engineers "skilled in the art".

Would they be able to classify them as either "flying wing-llike", "lifting body-like" and "winged airplane-like" based on visual appearances with significant agreement? If so, is it possible to explain objectively how to tell the difference?

Or is it more of a Duck test or I know it when I see it?

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    $\begingroup$ I think it's pretty easy: A washing machine is a lifting body, a washing machine with wing is an airplane, a washing machine with a rotor is a helicopter, a washing machine with at least four rotors is a drone/UAV, a washing machine shaped like a wing is a flying wing 🤗 $\endgroup$
    – sophit
    Commented May 22 at 5:50
  • $\begingroup$ @sophit Hmm... how does one treating "shaped is like a wing" as boolean? By what criteria does an observer arrive at a True/False value? Personally, I think that it is the opposite of "pretty easy", but if you can post a convincing answer that is well-received, I might be able to see the ease more clearly. $\endgroup$
    – uhoh
    Commented May 22 at 8:08
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    $\begingroup$ @sophit can you post it as an answer, and see if it "flies"? $\endgroup$
    – uhoh
    Commented May 22 at 8:30
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    $\begingroup$ I think you should not check too strictly the definitions. It is mostly an engineering way to think (and to optimize a design). Wings have problem at the blade (at supersonic speed), large bodies not (air will create a cushion), but without wings you lose most controls (leverage, farther from center of mass) so you need engines or reaction trusts. And in any case every design is affected by many trade-off, so forget definition, it is mostly about pedigree of original design/revolution/evolution), and people use it to seems smarter. $\endgroup$ Commented May 22 at 10:02
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    $\begingroup$ "how does one treating "shaped is like a wing" as boolean? By what criteria does an observer arrive at a True/False value?" Step 1: Let go of trying to do this. $\endgroup$ Commented May 22 at 14:57

3 Answers 3

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Actually, they are both flying wings, or, they are both lifting bodies

A "wing" is simply something with a higher coefficient of lift.

Coming back from orbit, at around 17,500 mph, the V$^2$ part of the lift equation takes care of producing lift even though area, angle of attack, density, and coefficient of lift may be smaller.

Even the Space Shuttle, considered "winged", had a landing speed of over 200 mph.

A "lifting body" trades coefficient of lift for strength. High aspect ratio wings remain most efficient at producing lift, but are not as strong.

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  • $\begingroup$ I'm trying to see how this fits "... just by looking at it?" (the question's title) The body of the question reiterates "Would they be able to classify them... based on visual appearances with significant agreement?" Right now this nicely answers a question I didn't ask. $\endgroup$
    – uhoh
    Commented May 22 at 12:10
  • $\begingroup$ @uhoh in reality application determines design, so that may provide a more clear cut understanding. "Just by looking at it", they both produce lift. Interestingly, a low aspect, stumpy design is much better at handling re-entry, the most dangerous part of the flight. Once subsonic, the wing wins efficiency hands down, but orbiters need only a longer runway and good tires. $\endgroup$ Commented May 22 at 13:10
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    $\begingroup$ If the answer to the question is "No, not really, because..." then that would be helpful to add. $\endgroup$
    – uhoh
    Commented May 22 at 13:33
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I think that the historical perspective is the best way to tell those two classes of aircraft apart.


Flying wing

Between the world wars, both the Horten brothers of Germany and Jack Northrop of the USA experimented with the idea of striping out all the "useless" part of a conventional airplane in order to get the "purest" form of flying machine. Their idea was that tailplanes, fuselages, nacelles,... everything but the wing adds weight, drag and complexity and should therefore be eliminated and its function gathered in the wing itself. Their idea was actually not wrong and both the Ho 229 and the YB-49 proved to have exceptional flying characteristics for the time. This is an example:

enter image description here No fuselage, no tailplane, no nacelles but it flies! (Gif source)


Lifting body

"Aerospace-related lifting body research arose from the idea of spacecraft re-entering the Earth's atmosphere and landing much like a regular airplane. Following atmospheric re-entry, the capsule spacecraft from the Mercury, Gemini, and Apollo series had very little control over where they landed. A steerable spacecraft with wings could significantly extend its landing envelope. However, the vehicle's wings would have to be designed to withstand the dynamic and thermal stresses of both re-entry and hypersonic flight. One proposal eliminated wings altogether: design the fuselage body to produce lift by itself." (from Wikipedia). This is an example:

enter image description here A lifting body doesn't fly, falls with style. This Northrop HL-10 needed a B-52 to go in the sky (source Wikipedia)

And this is how they landed sometimes (no worries, the pilot survived and returned to fly!):


That being said and not pretending to be general or definitive, we can say that:

  • If the main purpose of the aircraft is to fly, possibly more efficiently than a conventional subsonic airplane, then we have a flying wing.
  • If the main purpose of the aircraft is simply "falling with style", possibly from supersonic speeds, then we have a lifting body.

Therefore, a flying wing can be recognised by the fact that:

  • it can take off, fly and land on its own feet;
  • it doesn't fly supersonic;
  • the fuselage is "laterally stretched" in the shape of a wing in order to be used not only to transport the payload but to generate the needed lift as well, with the goal of being more efficient than a conventional airplane;
  • it lacks proper nacelles and vertical and horizontal stabilisers;
  • it's powered by conventional aeronautical engines.

A lifting body can be recognized by the fact that:

  • it cannot move from the landing field unless another machine brings it in flight;
  • the fuselage doesn't resemble a wing i.e. it doesn't create much more lift than drag;
  • it falls with AoA bigger than some 10/15° (stall angle of a conventional wing);
  • if something resembling a fin/airfoil is present, then it's normally mounted almost vertically and mainly to provide stability;
  • it might have some form of heat shielding;
  • in the mission profile there might be a phase where it actually flies powered by a not conventional aeronautical engine, like a rocket.

Now I let you decide what this thing is (picture from Wikipedia) 🙃

enter image description here

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  • $\begingroup$ OTOH the photos in the linked wikipedia article show something more like an aircraft then a spacecraft, $\endgroup$ Commented May 22 at 12:49
  • $\begingroup$ "... a wing is present then it's normally mounted almost vertically, ..." errr, what?? $\endgroup$
    – MikeB
    Commented May 22 at 15:04
  • $\begingroup$ @sophit Read again: "A lifting body can be recognized by the fact that: it cannot move from the landing field unless another machine brings it in flight; the fuselage doesn't resemble a wing i.e. it doesn't create much more lift than drag; it falls with AoA bigger than some 10/15° (stall angle of a conventional wing); if something resembling a wing is present, then it's normally mounted almost vertically and mainly to provide stability;" Are you saying that a vertical stabiliser "looks like a wing"? $\endgroup$
    – MikeB
    Commented May 23 at 10:17
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    $\begingroup$ I don't like "lifting surface". Because everyone understands that lift opposes gravity, so no vertically mounted fin would ever be mistaken for a lifting surface. I'd go back to "something that looks like a wing", or fin, or airfoil, or protuberance, or... $\endgroup$ Commented May 23 at 15:19
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    $\begingroup$ @MichaelHall, well at 22.5° of AoA a square has a $C_l$ of 0.15 (and an outrageous $C_d$ of 2)... So, a washing machine does indeed meet the definition 😄 $\endgroup$
    – sophit
    Commented May 23 at 18:48
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Since the question is specifically about visual identification it probably helps to get some pictures up on the screen.

Flying Wings

Horten H.VII
Artist impression of the Horten H.VII (author FOX 52, via Wikimedia Commons, CC-BY-SA-4.0)

Horten flying wings Horten Brothers flying wings (author Greg Goebel, via Flickr, CC BY-SA 2.0)

Flying wings YB-35, YB-49, B-2 (author Nacht Eule, via Wikimedia Commons, CC-BY-SA-4.0)

Wikipedia defines a flying wing as:

a tailless fixed-wing aircraft that has no definite fuselage, with its crew, payload, fuel, and equipment housed inside the main wing structure.

A Universe Today article adds some additional visual specifics:

From the top, a flying wing looks like a chevron (inverted V), with the wings constituting its outer edges and the front middle serving as the cockpit or pilot’s seat.

Although not necessarily authoritative, it's an interesting point "the wings constituting its outer edges" as that is definitely a visual indicator, and seems to imply that top-down is a primary angle for visual identification. For example the B-2 flying wing when viewed from the side seems to have something of a discernible fuselage, however this does not change the shape of the "outer edges" as seen in a top-down view.

B-2
B-2 Spirit

Lifting Bodies

As defined by Wikipedia:

In contrast to a flying wing, which is a wing with minimal or no conventional fuselage, a lifting body can be thought of as a fuselage with little or no conventional wing.

Visually speaking, lifting bodies seem to be distinguishable from most angles by the absence of a wing:

X-24A, M2-F3, HL-10 X-24A, M2-F3, HL-10 (NASA)

M2-F1 F3 diagram
(NASA)

However the top-down view may not always be sufficient, for example the X-20 Dyna-Soar has a similar top down chevron shape as the B-2:

X-20 Dyna-Soar
From "Frontiers of Space" by Philip Bono & Kenneth Gatland, 1969 (via Flickr, CC BY-NC 2.0)

The distinguishing feature in this case seeming to be the "winglets" which act as a tail:

X-20
X-20 Dyna-Soar (NASA)

But the X-20 Dyna-Soar spaceplane is also not really a lifting body and is more of a blended wing design. The the distinction between lifting bodies and blended wing aircraft is a separate discussion outside the scope of this question. Some examples of blended wings are more obvious such as the NASA X-48 prototype:

X-48
X-48 (photo by Alan Radecki, via Wikimedia Commons, CC BY 2.5)

or the X-47B:

X-47B X-47B (U.S. Navy)

Although not a lifting body, the X-47B seems similar in shape to the B-2 flying wing, and it is also tailless. However circling back to the Universe Today definition it is not quite as angular of a chevron shape as the B-2.

Spaceplanes such as the Space Shuttle and the X-37B are often described as lifting bodies:

Space Shuttle
(NASA)

X-37B
X-37B (NASA)

Although while they have lifting body characteristics, the wing size would seem to make them more of a blended wing design than the lifting body spaceplanes such as the Dream Chaser or the X-33 concept design:

Dream Chaser
Dream Chaser (NASA)

x-33
X-33 (NASA)

Again lifting body vs. blended wing is a separate discussion which does not seem to affect the visual distinction between flying wings and lifting bodies.

Of course aeronautical engineers would be evaluating these type of images based on their knowledge of the functional differences between flying wings and lifting bodies, the type of details mentioned in this answer. How engineers would translate those technical definitions into visual identifiers which can be described in terms of shapes and relative component sizes, would probably be the definitive answer to your question.

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    $\begingroup$ I declare you the winner! (@sophit, i wonder why Steve didn't include any washing machine photos?) $\endgroup$ Commented May 23 at 20:57
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    $\begingroup$ MichaelHall - copyright free photos of flying washing machines are hard to come by. $\endgroup$ Commented May 23 at 21:45
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    $\begingroup$ @MichaelHall: sorry, I didn't know you folks needed a picture, next time I'll do even better and add a onlyfans link as well 😄 $\endgroup$
    – sophit
    Commented May 24 at 3:57

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