No pitch-down control with wings placed close to COM

[Fetch!]

First off, I'm new to all forms of horizontal building in KSP. Roughly 400 hours and I've made only a handful of SSTOs following tutorials, nothing more. I only recently learned that control surfaces react inversely to control inputs when placed in front or behind a plane's centre of mass. In KSP1, simply inverting the deployment of the control surface fixed this.

Now, with procedural wings, I'm trying out all sorts of plane designs with the procedural wings and am loving it. However, on multiple designs I have encountered a bug where the pitch controls of a wing stop working when the wings are mounted close to the COM along the longitudinal axis of the vessel, see here: https://medal.tv/games/requested/clips/X9wyjTgVAeZVP/d1337T2OylTx?invite=cr-MSx2V3UsMTQwODI4ODE0LA. 

In the clip, the horizontal stabilizers on the back of the plane behave as expected when trying to pitch up, but the wing elevators don't. Instead, they twitch, causing drag. Pitch down does work. Inverting the controls  in the parts manager makes that pitch down stops working instead.

In these screenshots you can see where my COM/COL are compared to the wings: https://imgur.com/a/iM5AAo5. 

Placing the wings slightly backwards fixes the problem, but prevents take-off from too much pitch-down moment.

Please correct me if this is a common bug carried over from KSP1, but I believe this is a bug that needs looking into.

Edited February 26, 2023 by Fetch!

[sgt_flyer]

the control twitches because it's too near the com to know if it needs to go up or down.

you should go into the advanced section of the wing controls to disable pitch & yaw on your wing control surfaces. (keep only roll on those) - on your tail, the horizontal elevators only need pitch, while the vertical rudder only needs yaw

Now, the fact that wings have little effect on pitch is normal (it's basically physics).

Also, you should not keep the center of lift lined up with the COM - real life planes center of lift is behind their center of mass. (but not too far, as it will decrease the pitch control surfaces effects)

Basically :

the center of lift too far behind the COM : the plane will react sloowly to pitch control.

Center of lift very slighthly behind the COM o centered on the COM  : the plane will react strongly to the control surfaces effect (acrobatic plane)

Center of lift in front of the COM : the plane will want to flip to get the COM in front of the Center of lift (and promptly crash ^^)

Hence the saying : a nose heavy plane flys poorly - a tail heavy plane flies only once

 

think of control surfaces as levers acting on the plane, with the rotation point being the center of mass. pressing or lifting the tail will require not much force to affect the pitch of the plane, while pressing or lifting something near the center of mass will need much more force to affect the plane the same way.

https://en.wikipedia.org/wiki/Flight_control_surfaces

on a conventional plane with wings near COM (not delta Wings) :

wing tips control surfaces are for roll control.

Horizontal tail control surfaces are for controlling pitch

Vertical tail stabilizer is for controlling yaw.

 

On planes with delta wings or similar (military jets / space shuttle / Concorde),

wing control surfaces can manage both roll & lift,

the vertical tail stabilizer controls yaw.

l

Edited March 2, 2023 by sgt_flyer

[PyroSA]

Just an addendum to that. You can create a V-tail to have a mix of yaw, roll and lift on the tail.

[JoeSchmuckatelli]

On 3/2/2023 at 4:12 AM, sgt_flyer said:

Hence the saying : a nose heavy plane flys poorly - a tail heavy plane flies only once

Grin!