(Air|Space)planes, yaw control, what am I missing...?

[Lunknumb]

So, I tried some planes the last couple of days, and I've found it quite frustrating to get them to handle "properly". I know the aerodynamics of the game are very primitive and glitchy, but the rudder/yaw-control seems to be a special lousy case for every design I make.

Typical scenario: I go down the runway and take off and start ascending. On the way up the nose will drift slightly left or right somewhere along the way. I instinctively nudge the rudder a bit the other way to compensate, but yawing does not seem to turn the craft. It turns the nose while I'm pushing the control, but the plane will continue on the same vector. On top there seems to be an excessive rebound effect when letting it go, often slinging the nose back even past the point where I started to turn... (so yawing left may will end up with the nose further right than it was to begin with).

Now, I've flown RC airplanes for quite some time, and have a fairly strong "insticnt" of what the flight controls should do on a mid-winged craft, and what my KSP inventions are doing, is sort within reason for roll and elevation, but I have yet to create any resemblance of yaw control...

This is frustrating me, I think mostly because I have specific expectation of what a yaw control is, but every time I touch it, something else seems to come out of it...

What am I doing wrong here?

Is there any mid-winged plane design that can steer using yaw control? I know it sort of works if I dial in a significant dihedral or move the CoL way above the rudder CoM, but then it's just the roll-effect doing the steering, and the yaw is stil rebounding and bouncing all over when letting go...

[bsalis]

I think some pictures would help a lot. Link craft file too if you are keen - plenty of peeps around here like to d/l them and tinker.

Although the aerodynamics are primitive, when you get an understanding of it, you can work with it and build very nice flying planes.

I instinctively nudge the rudder a bit the other way to compensate, but yawing does not seem to turn the craft. It turns the nose while I'm pushing the control, but the plane will continue on the same vector. On top there seems to be an excessive rebound effect when letting it go, often slinging the nose back even past the point where I started to turn

Hard to say without seeing the craft. Some speculation...

* Flying too fast... stay under 100m/s in the the lower atmo

* Too much longitudinal stability perhaps. Try a smaller tail, move it closer to CoM, more rudder control surfaces. You need more control surfaces than you probably think.

* Engines in front of the CoM (the vectoring does not reverse, so will work against you control inputs!)

[cpt_nosh]

Screenshot of your plane please.

[Kasuha]

Planes usually have very small amount of vertical wing area to control yaw, most of wing area is horizontal. Once your plane gets moving in certain direction, that little of control surface may be able to turn the nose of the plane but has not enough lift to change your movement direction. And since that surface is usually behind CoM, once you release the control, the airflow rebounds it to the other side and it oscillates a little before it returns to stable position along the airflow.

Instead of turning your plane using yaw, roll the plane a little in desired direction and pitch up to use lift of main wings to change the movement direction.

Edit: notice that model planes often have both great amount of power in their propulsion (able to hang in air by it with no lift from wings) and a lot more vertical lift-generating area, often whole body of the plane is used as lifting surface, allowing the plane to fly when rolled by 90 degrees just fine. Such planes behave very differently than KSP planes as in KSP, lift is only generated by dedicated wing parts and normal parts do not generate any lift (unless you're using FAR).

Edited April 15, 2014 by Kasuha

[Claw]

As has been said, there are several reasons this could be happening. Pictures of your craft really do help us give specific advice.

That being said, most stock airplanes benefit a lot from turning on the SAS (if you haven't). It will generally get rid of that unwanted yaw, but it will make the roll/pitch a little more "snappy." Some people don't like that, but the plane flies better overall.

Also, when I see people building larger flat aircraft or aircraft with a lot of wingspan, they generally under estimate the amount of tail required. This will often cause a lot of yaw and springy behavior.

By the way, a lot of real airplanes react similarly to rudder input. You put in some rudder and let go, the nose of the plane will spring around a bit unless the plane is augmented with a rudder dampener.

As Kasuha pointed out, you shouldn't do the majority of your turning with the rudder. You'll wantr to roll into a bit of bank and pull the nose up in pitch. I haven't done a lot of RC airplanes, but I think you can get away with that a lot more with those.

I really think turning on SAS will get rid of the yaw and bouncing you describe, but it isn't going to allow you to skid your airplane sideways. You'll need more tail or SAS modules for that.

[KerikBalm]

It turns the nose while I'm pushing the control, but the plane will continue on the same vector.

Why shouldn't it? in really thin atmosphere, its like its not even there, even if you turn 90 to the left, or backwards, it keeps flying the direction it was going.

Most RCs are flown with ailerons and elevators.

If you fly full scale sailplanes, you don't use the rudder to turn, you use the rudder to coordinate your turn.

You can also use it to execute maneuvers like a forward slip.

http://en.wikipedia.org/wiki/Slip_%28aerodynamics%29#Forward-slip

A slip in general is when a plane's nose is not pointing in the direction of flight (perpendicular to the lift vector lets say)

Now, I've flown RC airplanes for quite some time, and have a fairly strong "insticnt" of what the flight controls should do on a mid-winged craft

Many RC planes have specific design parameters that allow them to be flown with just rudder and elevator.

You won't find high performance full scale sailplanes ot be controllable with just elevator and rudder.

Lastly, KSP has reaction wheels, which provide non-aerodynamic torque, which allows you to point your craft in orientations you couldn't with just aerodynamic forces alone. When that torque stops, you get the aerodynamic forces taking over and a "rebound"

Try flying your craft in the lower atmosphere with and without reaction wheels (including the pod/cockpit reaction wheels- ie, toggle the torque - if you're flying a space plane, action group the torque, because you'll want it when you're out of the lower atmosphere)

[Javster]

Planes usually have very small amount of vertical wing area to control yaw, most of wing area is horizontal. Once your plane gets moving in certain direction, that little of control surface may be able to turn the nose of the plane but has not enough lift to change your movement direction.

True, I've piloted a small aircraft before and the yaw quite viciously moves the nose, but doesn't turn much. It is enough for taxiing though.

[TechnicalK3rbal]

You say you have flown RC planes and have a good feel for flight control.

Have you ever flown something in a flight simulator at higher sppeds?

(Besides KSP) Aircraft react much differently at 200 mph than the ~20-30 of an RC plane.

[cantab]

In the VAB you can right-click the flight controls and select what inputs they'll respond to. So you can make sure, for example, that the ailerons on your dihedral wing don't go trying to control pitch and yaw.

And in general remember that yeah, stock aerodynamics are dodgy. You can make flyable aircraft and have fun with them, but it's probably the least realistic aspect of the game.

And, as mentioned, I'd try and fly it more like a real plane, using pitch and roll. In KSP I often don't touch the rudder at all.

[O-Doc]

Short answer is you need to place your rudder closer to, preferably behind, your center of thrust. You've mentioned RCs. Do you scratch build? Are you flying pushers or pullers? EDFs or props? KSP is most like an EDF pusher with a short and wide exhaust nozzle with at least 0.9 TWR. That's how the programming works.

Like Kashua said, you are going to have to introduce plenty or vertical stabilisation. Those winglets are generally not going to cut the mustard on all but the smallest craft. I like to hide vertical winglets inside the plane right behind the engine and tweak all control directions to the off position. My test is a rock solid barrel roll to tell me if I have enough vertical stabilisation.

[luizopiloto]

hmmm... did you know you have to roll the plane to turn, right?

Edited April 16, 2014 by luizopiloto