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With the exception of cruise missiles, most missiles don't have any obvious lifting device.

If you watch a missile being fired, prior to its rocket firing it does exactly what you'd expect: momentarily plummet toward the earth. And yet the moment it ignites, it stops falling completely, but without any pitch that you'd expect to counteract gravity; even big missiles like the Phoenix or HARM seem to have gravity-defying characteristics.

Missiles that fire on the rail seems to experience no drop at all.

AIM-9M launch from an FA-18F AIM-9M launch from an FA-18F source

There's a good slow-motion video of the firing of an AMRAAM here.

Now this isn't magic, so I presume either a) the little fins make adjustments so that the rocket is, despite appearances, pointing a little downwards or b) the fins are smart enough to configure themselves to provide the lift needed to keep the missile in the air. But it might be neither.

The question is - generally, how do conventional missiles fly?

Rodrigo de Azevedo
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Party Ark
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    don't have any obvious lifting device - from the picture you post they look obvious to me - just because they're small does not mean they're not wings. Here's a toy radio control model "missle" made of foam: https://www.youtube.com/watch?v=v_wRls4aG78. It's controlled like a regular airplane with tiny wings – slebetman Apr 03 '19 at 01:43
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    Bear in mind, if it's solid fuel propulsion, you really don't want it igniting while it's under your wing. You want it to fall away a few metres before flames shoot out of it. – RedSonja Apr 03 '19 at 10:25
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    "With such engine even barn doors would fly." - I was told that years ago about some soviet fighter jet with oversized engine, which seemed to be built like manned missile. Brute force can work miracles! – PTwr Apr 03 '19 at 12:49
  • $PTwr: Would that have been the Je-166 by any chance? They took the biggest engine and added the smallest wings they could get away with. – Peter Kämpf Apr 04 '19 at 22:27

4 Answers4

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Air-to-Air guided missiles are little airplanes. If there are only fins at the tail, it's a ballistic rocket, basically a fin stabilized artillery shell accelerated by a rocket motor instead of an explosion in a pipe.

On missile like AMRAAM, Sidewinder, or Sparrow, the vanes are wings and the missile is a rocket powered aircraft that can climb, descend and turn as required. The vanes/wings don't have to be very big because the thing is going superdupersonic. The X plan form means the wings can support and control the missile equally well in any axial position.

The front vanes are movable and do the controlling. It's effectively a rocket powered robot canard aircraft on a suicide mission, really.

Since the missile accelerates to >Mach pretty quickly and operates supersonically, the wings/vanes use a supersonic airfoil profile, either biconvex (like the F-104's airfoil) or a diamond profile. The vanes on the AIM-9M look like biconvex airfoils.

The missile descends when it is first launched because it's going too slowly for its teeny tiny supersonic wings to do enough lifting, and has to accelerate first.

enter image description here

Now, for a change of pace, slow something like an AMRAAM or Sidewinder down to subsonic speed, make the fins bigger and provide control surfaces on the rear ones, power it with a turbojet instead of a rocket except for boosting it into the air, and you have the CL-89 surveillance drone, basically a reconnaissance cruise missile that flies hither and yon at low level taking pictures.

enter image description here

John K
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    Also for "going superdupersonic." – reirab Apr 02 '19 at 17:46
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    Re, "...it's a ballistic rocket...", Ballistic means unpowered. A ballistic missile gets a big kick from its booster at the start of its journey, and then for most of the way, it's just a dumb, thrown object. Guided missiles (including cruise missiles) are powered the whole way, and use vectored thrust and/or moveable airfoils for steering and lift. – Solomon Slow Apr 03 '19 at 13:13
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    No ballistic just means it's travelling an arc that is determined by velocity and gravitational pull, falling as it moves in other words. A rocket with fixed tail fins is a ballistic projectile, the motor running or not, once it leaves the rail. – John K Apr 03 '19 at 13:47
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    @JohnK, so essentially what you are saying is that the faster you go the smaller wings you need to generate enough lift? – ZeroOne Apr 03 '19 at 13:55
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    @ZeroOne yes that's pretty much the case for most airplanes. Go fast enough and you can get enough lift from just the body alone although it's still nice to have wings/vanes to maneuver. You don't necessarily have to go that fast if you have a large enough area; seaplanes get enough lift from their floats to be able to cancel out most of the floats' weight and there is only a small useful load reduction if at all. – John K Apr 03 '19 at 14:18
  • This answer does a good job of answering the "They don't seem to have wings" part of the question, but doesn't discuss the impact thrust has on the question. Strap a powerful enough engine to anything and you can make it "fly" – Jon Story Apr 03 '19 at 15:18
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    @SolomonSlow Think ICBM. That's intercontinental ballistic missile. No, you don't shoot an intercontinental missile from a big gun. Although now I'm curious if that was ever done. Probably not. – Nobody Apr 03 '19 at 15:22
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    @Nobody, An ICBM takes approximately 45 minutes to reach its target. Its flight is powered during maybe the first three minutes of that time. Except for small course adjustments using RCS thrusters while above the atmosphere, it basically is a dumb, thrown object for almost the entire flight. – Solomon Slow Apr 03 '19 at 15:28
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    The missiles in this answer are all guided, not ballistic. If their course was only effected by gravity they would be unable to strike targets at higher altitudes. An air to air missile that can be evaded by a hot air balloon is useless. [ Also, submarine launched ballistic missiles are expelled via compressed gas because of the obvious drawbacks of igniting a rocket motor inside the launch vehicle, making them effectively shot from a big gun as well as yielding ballistic->powered->ballistic flight paths.) – Matthew Gauthier Apr 03 '19 at 15:37
  • @Matthew Gauthier: That's simply not true. Missiles, whether guided or not, don't NEED lift. (Though some may use it.) The fins are for directional control. Strip the fins off, set the missile on the ground pointing upwards, and light the fuse, andI guarantee it will go up. – jamesqf Apr 03 '19 at 16:59
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    @jamesqf Any guided missile has to make lift somehow, to fly in any other trajectory than a ballistic arc, or straight up. It may get lift off the body alone if it's operating at a positive angle of attack but it won't be able to maneuver much or fly efficiently without the little wings that are the fins. – John K Apr 03 '19 at 17:10
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    "rocket powered robot canard". I know it doesn't mean that but I still picture a suicide duck. – DJClayworth Apr 03 '19 at 18:18
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    @JohnK, think vectored thrust. – Solomon Slow Apr 03 '19 at 21:21
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    @SolomonSlow All vectored thrust can do is provide a yaw/pitch moment independently of a control surface. If you want your missile to fly horizontally in level flight it still has to generate lift somehow, using wings, the body of the missile itself, or a combination thereof. – John K Apr 04 '19 at 00:23
  • @John K: No, the missile does not have to make lift, in the sense we think of lift as something keeping an airplane airborne. It uses fins to provide directional control, but a missile could use vectored thrust, reaction control jets, gyroscopes, &c for the same purpose. Indeed many large missiles don't have fins, so they have to use other types of control. – jamesqf Apr 04 '19 at 05:04
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    @jamesqf Show me a missile with no fins, or tail fins only, that relies on vectored thrust or movable tail fins only, that can make sharp turns at high speed, because that's what we are talking about here. Perhaps the term "guided missile" is too broad because that includes ballistic missiles that can alter their ballistic trajectory to some degree. What we are talking about here are missiles that can turn sharply while in level flight. – John K Apr 04 '19 at 13:08
  • @John K: Leaving out the "sharp turns at high speed" because that isn't one of their design criteria (and it's not what we're talking about, either), how about the Atlas, Delta, Saturn, SpaceX's Falcon... down to the "rockets" I made as a kid by wrapping aluminum foil around a match, with a pinhole for the exhaust. The fins are used for directional control, like the rudder/elevator of an airplane, not to produce lift. – jamesqf Apr 04 '19 at 17:18
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    @jamesqf well the discussion here is about missiles fired from jets that fly horizontally and maneuver to hit a target. "Guided missile" is probably not a good term to use because that includes ballistic missiles that fly ballistic trajectories but can alter their trajectories to some degree and can therefore be considered "guided". AMRAAM doesn't go in a ballistic trajectory. It flies, horizontally. It turns, quite sharply, considering. In its case the fins, and the missile's body to some degree, are creating lift and it's effectively a rocket powered aircraft. That is the point. – John K Apr 04 '19 at 17:39
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    This is one of the best answers I have ever read on Stack exchange. Not just in terms of content.but the writing style as well! Even a 5 year old can understand it! – Hanky Panky Apr 04 '19 at 17:52
  • @John K: Not the point, because missiles in general (of course there's a spectrum with cruise missiles at one end) don't need lift, and often aren't using it. The ones with fins are using aerodynamic forces to control their direction. – jamesqf Apr 05 '19 at 04:36
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The missile's wings are very large for it's mass, and produce a great deal more lift than the wings of the aircraft firing the missile.

One thing to note from the OP's linked video is that the F-35 and the chase plane are traveling at the same speed, so the F-35 appears stationary. However, that aircraft is likely traveling in excess of 0.8 Mach. Therefore, upon release, the missile is also traveling at 0.8 Mach. The large wings provide plenty of lift. Some missiles may thrust vector as well.

dotancohen
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In the video you posted, the missile appears to continue falling even after the motor ignites -- you can see the missile start to overtake the aircraft even as it continues to drop:

enter image description here enter image description here enter image description here enter image description here

By the last frame, it appears to have taken a slight nose-up attitude to maintain altitude:

enter image description here

Johnny
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    That dropping down is desired and enforced by a negative angle of attack on the missile fins. Look here what can go wrong. – Peter Kämpf Apr 04 '19 at 22:31
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    @PeterKämpf - Hmm yes, I can see why shooting yourself with your own missile would be undesirable. – Johnny Apr 04 '19 at 22:53
  • Either this answer only applies to the initial phase of the flight (so it's not really an answer to "how do missiles fly?") or it suggests that missiles continue to free-fall as they fly, which is simply wrong. – Dmitry Grigoryev Apr 05 '19 at 08:31
  • @DmitryGrigoryev - I was mostly addressing this point in the question: And yet the moment it ignites, it stops falling completely, but without any pitch that you'd expect to counteract gravity, which is clearly not the case in the video he linked to. – Johnny Apr 05 '19 at 16:27
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Depending on the range and mission of your missile, body lift alone may be enough to keep it aloft.

@dotancohen pointed out that a typical missile's wings are large for its mass, but look at the ASRAAM - it has only small tail fins which are there purely for attitude control, rather like an AIM-9X (which already has much smaller wings than the 9M) but with even fewer lifting surfaces. It's extremely slender to reduce drag, probably with the intent that it should retain as much of its energy (and thus speed) as possible. With enough speed, you'll only need a little AoA for the missile fuselage itself to create sufficient lift. This seems to be a typical strategy for short-range missiles, but the ASRAAM takes it to the extreme.

Missile meant for longer-ranged engagement may employ a lofting profile during the boost phase, opting to use the rocket motor to gain altitude as well, in which case the thrust will directly offset some of the weight of the missile.

aerobot
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