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How do missiles steer in the air? What techniques do they use?

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    $\begingroup$ Exactly (by definition) the same way as an aircraft, identical to most airplanes as well. $\endgroup$ – user3528438 Sep 7 at 23:16
  • $\begingroup$ Unclear as to whether the op is asking about how the control surfaces work, or how the missiles decide which way to maneuver. it seems (to me at least) that the answer to the former is obvious, so op is probably asking about the latter. $\endgroup$ – Charles Bretana Sep 10 at 14:13
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Take a look at the following image. What do you see?

Missile Steering Diagram

The Fins, Wings, and Canards, as seen in the diagram, work in a similar fashion to rudders/elevators/ailerons to develop drag to yaw/pitch/roll respectively.

Fins: Most missiles use tail fins which give extreme maneuverability and high angles of attack. Often they are fitted with wings to give extra lift and improved range. Maverick, Harpoon, AIM-9X Sidewinder are good examples of tail fin controlled missiles.

Grid Fins

Seen above: Grid fins

Wings: Generally, wings play the same role as for an aeroplane by providing lift, and are the oldest type of control surface. Moreover, wings cannot work independently and in most cases are used as vortex generators to improve the efficiency of the fins. In addition, they are mostly used in subsonic cruise missiles like Tomahawk and Sparrow AIM-7. The problem is that the wings must be long enough to produce necessary lift.

Missile Wings

Canards: They work more effectively with great maneuverability on low angle of attack, and work the same way as fins. However, located near to the nose of a missile, canards can cause a missile to stall at high angles of attack, which limits them to short range. Almost all smart bombs and laser-guided missiles use canards.

Furthermore, the split canard is a modern development (found in missiles like Python-4 and AA-11) which uses two canards, one of which is fixed, and the second is located just behind the first set and is movable. The role of the fixed canard is to develop high power vortices for the movable canards, for better performance at high angle of attack.

Source

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    $\begingroup$ Under "Wings," I don't think you mean the Sparrow, which is a supersonic surface or air to air missile with the common triangular "rocket style" fins. Besides the Tomahawk, the US has used a series of winged, subsonic missiles or guided bombs including the AGM-86, AGM-129, and AGM-154. Other countries have or had similar missiles. $\endgroup$ – fluffysheap Sep 9 at 10:51
  • $\begingroup$ Then there is also the old "BOMARC MISSILE", but it was definitely not an Air to Air missile. Definitely had wings though. $\endgroup$ – Forward Ed Sep 9 at 14:05
  • $\begingroup$ minor correction... AIM 7 sparrow is supersonic. $\endgroup$ – Charles Bretana Sep 10 at 13:57
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Not sure how much detail you’re looking for, but most current missiles control their pitch, yaw and attitude via control surfaces that are actuated by electromechanical actuators. Some also use thrust vectoring of their rocket motor exhaust gases. The control system is typically driven by input from inertial measurement units (accelerometers, rate sensors and gyros), seekers and sensors such as radar and laser, and GPS.

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    $\begingroup$ Can you show me a picture or diagram please? $\endgroup$ – Luke Justin Sep 7 at 23:45
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    $\begingroup$ @Luke Justin, I just Googled "missile steering fins" and got a huge return. There is no shortage of information out there, please look around and post questions only when you are genuinely stumped about something. $\endgroup$ – Michael Hall Sep 8 at 0:01
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A unique variation on the control surfaces is the Starstreak missile:

Each dart consists of a rotating fore-body with two canard fins attached to a non-rotating rear assembly which has four fins. The rear assembly of each dart also houses the electronics that guide the missile, including a rearwards facing sensor.

The sub-munitions steer by briefly decelerating the rotating fore-body with a clutch. The front wings then steer the missile in the appropriate direction.

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Not really an answer, but I think it's relevant:

You look at an airplane, you see big honking wings and tails. You look at a missile and you see stubby little things. What you don't realize is that they're the same thing. Airplanes don't need big honking wings to cruise, they need them to fly at low speed for takeoff and landing.

A missile, however, will be launched from an aircraft already moving along rapidly, it never needs to be able to fly at low speed and thus the fact that the wings are utterly inadequate for low speed flight doesn't matter. Most missiles have minimum launch velocities that are far above normal runway speeds.

Yes, some missiles are capable of taking off from the ground, this is done by boosting them into the sky on a separate rocket booster that then falls away and allows them to fly normally.

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Missiles steer either by commands from internal computers, (for Air-to-Surface missiles with GPS or Inertial navigation systems), by commands from a ground radar station over a datalink (SAMs such as SA-2, SA-3, use this technique) or, (for missiles designed against moving Air-to-Surface or Air-to-Air targets), by using Proportional Navigation. Proportional Navigation basically just locks a gyroscopically stabilized seeker head onto the target (by centering a sensor on radar, infrared or video energy, (AGM-65 Maverick), coming from the target), and then turning the missile in the same direction as the Line of Sight (LOS) rate of that seeker head (as measured by the gyroscope), until the LOS is zero'd out. If the LOS rate is zero, you are on a collision course.

The proportional in the name comes from the fact that the turn rate commanded by the electronics is not always the same as the measured LOS rate. Missiles that know the rate of closure with the target adjust that proportionality constant. The higher the closure, the harder they try to turn. Missiles that do not know the closure, use a fixed (constant) proportionality ratio. The AIM-9 Sidewinder, for example, commands the missile to turn at 4x the measured LOS rate. This design, in fact, is responsible for the missile's name. When launched it is still relatively slow, and must pull a lot of lead on a turning target to zero out the LOS rate and intercept. As the missile accelerates, it needs less lead, and turns back into the the target, then, after the motor burns out and it begins to decelerate, it needs more lead again. The end result is a snaking flight path, like a rattlesnake. Radar missiles, that are aware of the closure, eliminate this inefficiency by tailoring the proportionality constant so that the commanded turn rate is lower at low closure rates.

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