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For example, Tomahawk Cruise Missile, or Harpoon anti-ship missile. They fly straight and level for the most part of their flight regime. I think if they had a fuselage optimised for level flight then they could have a greater range. Something of a lifting-fuselage.

I know that even their cylindrical body generates lift at some angle of attack but it comes at the expense of drag, so a more optimised shape could result in a greater L/D ratio and hence a longer range.

I think that space and volume constraints may be an issue, like a circular cross section probably has the largest volume to store whatever.

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    $\begingroup$ These missiles are nowhere near comparable. The AMRAAM flies at Mach 4 while the Tomahawk is subsonic. The former is unlikely to benefit from lots of extra drag in exchange for some additional lift in horizontal flight, while it might make sense for the latter. Consider narrowing your question down. $\endgroup$
    – TooTea
    Commented Oct 31, 2022 at 11:51
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    $\begingroup$ I suppose that some missiles spin around their axis to augment their stability, just like a bullet. A cylindrical shape makes in that case sense. $\endgroup$
    – sophit
    Commented Oct 31, 2022 at 13:08
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    $\begingroup$ ease of construction, and thus cost considerations no doubt come into play. The ALCM is triangular mostly because it was designed for packing on a rotary launcher, and a triangular shape allows for more missiles to be packed on that so the shape made sense there, not for aerodynamic reasons. $\endgroup$
    – jwenting
    Commented Oct 31, 2022 at 14:13
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    $\begingroup$ Once you reach the point of having "enough lift", there's no benefit to "more lift". Instead, the design focus becomes "less drag". $\endgroup$
    – Mark
    Commented Oct 31, 2022 at 21:37
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    $\begingroup$ I don't know how much of a contributing factor this is, but some (maybe most or all) big munitions need to be periodically rotated while stored to prevent the composition of their propellants and explosives settling into layers. Easier to build racks that allow this if they're cylindrical. $\endgroup$
    – Grimm The Opiner
    Commented Nov 2, 2022 at 7:59

5 Answers 5

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Rockets with solid fuel must be round, or they would weigh more. Remember that the rear part is filled with fuel which gradually burns away, so the whole fuel container has to withstand the pressure which in the end propels the missile. Only a cylindrical body will do this efficiently. Depending on the routing of cables and the position of actuators, the aeroshell (the outer skin that defines the body of the missile) can be different from the casing of the rocket motor, however, structural efficiency favors to have a cylindrical body.

The throat of the rocket nozzle allows to position the actuators of the rear surfaces within the cylindrical contour and sometimes you will see a cable conduit running along the outside of an otherwise cylindrical fuselage.

For the turbojet-propelled missiles: their body shape is determined by their storage. Submarine-launched cruise missiles have the same diameter as a torpedo, for very practical reasons: They are meant to be launched from torpedo tubes.

Air-launched cruise missiles which are stored on rotary launchers have a rounded trapezoidal cross section, so more of them can be stored in a constrained space.

Regarding the myth of the efficiency-enhancing lift-producing fuselage: This has been laid to rest for more than half a century by now. What counts is the lift-to-drag ratio and producing lift is trivial when the minimal speed during your mission is somewhere around Mach 0.5.

At high dynamic pressure everything will produce ample lift. Now the goal has to be to do so with minimal drag. Using proper wings makes lift production very efficient, and the cross section of the fuselage will not have much influence here. As a slender body the fuselage produces lift mostly where its width increases, regardless of cross section shape.

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    $\begingroup$ @Peter Kämpf the aeroshell and the cylinder containing the rocket fuel are normally not the same. If it were, you would see an racetrack containing conduits for ignition and actuators, like you see on big rockets (like the Falcon 9). I would therefore put this down as an "argument" rather then an reason... With your permission I would extend my answer with this "argument" $\endgroup$
    – U_flow
    Commented Oct 31, 2022 at 20:15
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    $\begingroup$ @johnDanger: There are submarines with dedicated vertical missile launch systems, but there are also submarines where the torpedo tubes are the only way to launch something out of the boat. $\endgroup$
    – Jörg W Mittag
    Commented Oct 31, 2022 at 22:05
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    $\begingroup$ @U_flow: Good point! No need to ask for permission, though. $\endgroup$
    – Peter Kämpf
    Commented Nov 1, 2022 at 7:10
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    $\begingroup$ @TonyStark At high dynamic pressure everything will produce ample lift. Now the goal has to be to do so with minimal drag. Using proper wings makes lift production very efficient, and the cross section of the fuselage will not have much influence here. As a slender body the fuselage produces lift mostly where its width increases, regardless of cross section shape. $\endgroup$
    – Peter Kämpf
    Commented Nov 1, 2022 at 7:49
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    $\begingroup$ @PeterKämpf I did not want to look like a copy cat :D. $\endgroup$
    – U_flow
    Commented Nov 1, 2022 at 10:12
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There are several reasons why most missiles have a round shape. I try to list (some of them) in roughly ascending order of importance:

  • Round shapes with wings are easy to calculate: Well known rough calculation methods exist which tell you which performance you can expect from a tubular shape at which you attach some wings. For example Missile Datcom is extensively used to calculate some performance numbers.

  • For the rocket engine, normally solid fuel is used. As the canister containing this fuel has to withstand the pressure of the rocket fuel while burning, a circular cross-section is optimal. However the aeroshell and the cylinder containing the rocket fuel are normally not the same. If it were, you would see an racetrack containing conduits for ignition and actuators, like you see on big rockets (like the Falcon 9).

  • Wings are efficient: Instead of going through the hazzle of designing, testing and manufacturing a complicated lifting body for which you probably still need wings, a tubular body is well tested and worked in the past. Wings are very well understood, and a lot of expertise exists to design these.

  • Wings can be deployed: You can unfold a wing, but you cannot unfold a lifting body. This is also important for my last argument.

  • A round shape is easy to manufacture: A tube with a pointy nose and some fins is easy and cheap to manufacture. As missiles are produced in fairly high numbers, ease of manufacture is therefore an important consideration.

  • A circular body is easy to be containerized into some launch/deployment canister. Missiles and similar weapons are often delivered in some canister out of which it is then deployed. The missile has to fit in this container. A circular cross-section is the most efficient way to put such a missile into this canister, as it has the least surface for the most amount of space (which also optimized aerodynamics). This containerization is also important for folding out wings and fins. Taken from https://en.wikipedia.org/wiki/Tomahawk_(missile)#/media/File:USN_Tactical_Tomahawk_launch.jpg

However all of these are only arguments for a circular crosssection. With the proliferation of modern CFD methods for example, it becomes much easier to design more complex shapes. More modern missile designs may feature quadratic or triangular shapes, e.g. the AGM-86 ALCM (Air Launched Cruise Missile) as pointed out by WPNSGuy.

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    $\begingroup$ For missiles which have to fitted in the rotary launcher of the B-52s, a more or less trapezoidal cross section is better, like for the AGM-86 ALCM $\endgroup$
    – sophit
    Commented Oct 31, 2022 at 17:26
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And some missiles are NOT cylindrical. Here, 6x AGM-86 ALCM (Air Launched Cruise Missile) on a B-52 left wing pylon.

enter image description here

photo courtesy of NARA - https://nara.getarchive.net/media/technicians-check-the-left-wing-pylon-of-a-92nd-bomb-wing-b-52g-stratofortress-6d1f18

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  • $\begingroup$ The Taurus KEPD 350 (another air-launched cruise missile) has a similar body shape. $\endgroup$
    – Mookuh
    Commented Nov 1, 2022 at 6:30
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    $\begingroup$ What are we looking at here? Three missiles attached to a support? Two? Or is the whole thing one missile? $\endgroup$
    – WaterMolecule
    Commented Nov 1, 2022 at 22:01
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    $\begingroup$ @WaterMolucule - That's actually 6x missiles. 3 front and 3 behind. Mounted on a B-52 wing pylon. $\endgroup$
    – WPNSGuy
    Commented Nov 1, 2022 at 22:15
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    $\begingroup$ Note that these missiles were designed for fitting 8 on a rotary launcher in the bomb bay. That's the main reason for the body shape, another shape wouldn't fit that number in the bomb bay so this one maximises the number of missiles that can be carried internally. This was especially important for the B-1 as it was initially designed for internal weapons only. $\endgroup$
    – jwenting
    Commented Nov 2, 2022 at 4:22
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Another factor: Missiles need a nice, smooth skin for aerodynamic reasons. You use less skin to contain a round missile than you use to contain a non-round missile. Thus the round missile flies a bit further than the otherwise-identical non-round missile.

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Missiles are essentially rockets, and rockets don't have lifting surfaces for the simple reason that they don't need to generate lift, because the thrust that their engine(s) produce is more than able to overcome both gravity and aerodynamic drag.

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    $\begingroup$ Both types of missiles mentioned by the OP (Tomahawk and Harpoon) have lift-generating wings. It's simply not true that rockets categorically don't have lifting surfaces, or that they cannot benefit from lift. $\endgroup$
    – Nuclear Hoagie
    Commented Nov 2, 2022 at 15:41
  • $\begingroup$ Some rockets/missiles are expected to follow a ballistic trajectory, so don't need wings. The remainder are intended to 'fly', but that is not directly connected to the propulsion type. The Space Shuttle was a rocket, and is a classic example of a rocket-with-wings. $\endgroup$
    – MikeB
    Commented Nov 3, 2022 at 13:50

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