Why do X-wing configurations missile/guide bombs use symmetric airfoils?

Question

From all the missiles/guide bombs I have come across, I've always observed that a symmetric airfoil is used for both the wing and tail.

1. Why not have a cambered airfoil for the wing and a symmetric airfoil for the tail? It would provide a better range for the missile/guide bomb.

2. If an airfoil were to be selected for X-tail missile/guide bomb configurations, what is the selection criteria? I'm trying to better understand the reason for this generally accepted design decision.

Any answers/suggestions would be appreciated.

Answer 1

Assymetrical wings on missiles/guided bombs do exist. However the goal of all missiles/guided bombs is to hit or come close to its target, which mean different things for various missiles. This drives their design:

1. Symmetrical airfoils on missiles are used in order to guarantee uniform turning capability. This enables the missile to immediately turn in either direction, therefore not losing time to first roll the entire missile before turning, therefore making the missile more maneuvrable. This is especially needed for air-to-air missiles like the R73-Wympel or the Diel IRIS-T. Cruise Missiles, on the other hand, can be less maneuverable (ground targets seldomly move), which is why they do not necessarily have symmetrical wings. For example, if you look closely at the image of the Tomahawk missile, you will notice the unsymmetrical wingshape. Such missiles use the bank-to-turn control strategy. *.

2. I do not know too much about this, but the main design goals for these again are good turn capabilities (aka, pull a lot of gs), and supersonic performance. Therefore basically the same considerations you have as for any other airfoil with the exception that the requirements are a bit more extreme.

* An interesting mix is the MBDA Meteor. It uses bank-to-turn because it has underbelly intakes. I cannot find the source, but apparently in the endgame the control mode is switched to skid-to-turn as it is more important to hit the target, then to keep the motor running

Answer 2

Most missiles fly at such high speeds and manoeuvre so violently that "up" means very little to them, it is simply a mild error to be corrected for.

Cruciform wings and tails are designed solely for manoeuvrability in whatever direction the missile needs at that moment. After a bit of that, there is no predicting which way up the missile will be by then anyway. A symmetrical solution gives optimum performance.

Typically, if both are present, an X-tail will be set at 45 deg to the X-wing, to minimise aerodynamic interference.

Answer 3

It's not guaranteed that the missile/bomb will stay upright relative to an asymmetrical wing throughout its whole flight, and if it were to wind up inverted, the range would be shorter and the package would fall short of its target. That might mean on civilians or friendly forces, and that's not good. Asymmetrical airfoils are effective, and they get the job done- it's simpler that way.