Problem placing control surfaces on swept wings

[C04L]

I sometimes get this problem and I can't for the life figure out why. please help.

 

when placing control surfaces on swept wings the way they work when I press W/S is switched.

as an eg:

The Inner control surfaces are ok, S makes the plane pitch up etc. but the outer ones are opposite. I haven't flipped them or anything all i've done is rotated them a few degrees to line up with the wing.

in the sph ive tried fully rotating them (3-6-9 oclock) but that does not change the opposite way they work.

 

Why does this happen to only swept wings?

[Snark]

(Moved from a thread in Science & Spaceflight, since this is really more of a gameplay question.)

[Foxster]

Yup, been doing it a while now and I think it's a bug. Doesn't seem to do it with other than the swept wings. 

I either don't use those wing or put the control surfaces elsewhere. 

[FullMetalMachinist]

I'm fairly certain that this happens because control surfaces use the CoM to figure out which way to deflect to get what you want. You're having a problem on the swept wings because out at the ends it looks like they are in a different enough position relative to CoM to get confused. 

There are two ways to fix it. Either right click the control surfaces in the SPH and set the control deflection slider amount to a negative number.

Or, what I recommend is to turn off pitch and yaw for those surfaces, and have them take care of roll only. The reason is that they are very close to the CoM, which is what the plane rotates around. That means that they don't have a very long lever arm to put much torque toward rotating for pitch. They're placed really well for roll, because they're way out on the wingtips, giving them a long lever arm from the CoM. 

Generally speaking, for most planes you want each control surface to be only responsible for one of the three attitude motions. Elevators at the tail for pitch, vertical rudder at the tail for yaw, and ailerons on the wings for roll. 

[Starhawk]

16 hours ago, FullMetalMachinist said:

I'm fairly certain that this happens because control surfaces use the CoM to figure out which way to deflect to get what you want. You're having a problem on the swept wings because out at the ends it looks like they are in a different enough position relative to CoM to get confused. 

There are two ways to fix it. Either right click the control surfaces in the SPH and set the control deflection slider amount to a negative number.

Or, what I recommend is to turn off pitch and yaw for those surfaces, and have them take care of roll only. The reason is that they are very close to the CoM, which is what the plane rotates around. That means that they don't have a very long lever arm to put much torque toward rotating for pitch. They're placed really well for roll, because they're way out on the wingtips, giving them a long lever arm from the CoM. 

Generally speaking, for most planes you want each control surface to be only responsible for one of the three attitude motions. Elevators at the tail for pitch, vertical rudder at the tail for yaw, and ailerons on the wings for roll. 

^^ This.

Your wing is attached in front of the CoM, but your control surface is placed behind the CoM.

I absolutely agree that pitch and yaw should be disabled for those mid-ship control surfaces, leaving only roll affected by them.  You probably only need one set to control roll.

It's very good practice to assign each function (pitch, roll, yaw if necessary) to its own set (or sets) of control surfaces.

Happy landings!

Edited June 15, 2016 by Starhawk

[ajburges]

Best thing to do with ailerons is to disable pitch and yaw. They offer little authority in those axis.

The exception is when you combine ailerons and elevators to make a elevon (common in Delta wing designs). Even then, KSP flight control often struggles to make good use of any surface granted authority over more than one axis. Better to split into two surfaces with singular axis authority.

Due to the low pitch authority, ailerons do make excellent flaps. Most of their force is applied to lift CoM instead of being applied as torque. This lowers stall speed.