SpaceX's Falcon 9 - a question about wings.

[JRF2k]

Greetings and salutations!

So here it is, the Falcon 9! Epic!

I've watched several of SpaceX's launches and after playing KSP for a while, I got to thinking why don't they add stability wings? Is it is a determent to the rocket overall? Is the aerodynamic shape all that's needed for stability? Does it just not need them due to its size?

I usually put 4 wings on the lifter stages of my rockets in KSP.

Wasn't sure how to prefix this, so I chose physics, because it all comes down to physics.

Thanks for answering my question fellas!

[Nibb31]

Rockets don't usually need wings. Stabilisation and guidance is done by thrust vectoring: the engine nozzles are on gimball joints with mechanical actuators. By directing the nozzles in the proper direction, you can control roll and attitude.

Edited December 17, 2013 by Nibb31

[JRF2k]

Rockets don't usually need wings. Stabilisation and guidance is done by gimballing the engines: the nozzles are on ball joints with mechanical actuators. By directing the nozzles in the proper direction, you can control roll and attitude.

Thanks for answering.

When would wings be needed? If non-gimbaling engines are used?

Going back to KSP, since you do have engine gimbaling then I guess my wings really aren't needed.

[Nibb31]

Old rockets like the V2 didn't have gimballed engines, so they needed fins. There is a bit of a controversy about why the Saturn V had fins AND gimballed engines. Some are of the opinion that Van Braun wanted them because they looked cool, but they quite probably allowed to take some stress out of the thrust vector system or to provide some level of redundancy. They also probably allowed to maintain stabilization during staging when the engines were throttled down.

In KSP you're right, on a properly designed rocket with gimballed engines, fins shouldn't be needed.

[K^2]

Most rockets in KSP don't need any stability fins. There are two exceptions. Sometimes, you don't have enough vectored thrust to provide good control in mid-ascent. I've had this happen, and adding fins improved performance. This might be a case with some real rockets as well.

Second is purely a KSP problem. The way thrust vectoring works is that it assumes engine is placed behind center of mass. If for some reason center of mass ends up bellow center of thrust, your ship's controls will be reversed. Except ASAS doesn't know that, so if you keep it on, it will throw the rocket into a spin. If this is the case, you can disable gimballs on engines and try to make it on fins and RCS alone. This shouldn't happen to a real rocket, unless programmers screwed up.