Question regarding lifting bodies in FAR and spaceplane design

[ElR0acho]

How accurately is body lift calculated in FAR? For a while I have been using a design(Below) where I rotate Mk2 fuselage until they blend together to form an almost perfect shaped lifting body. Is the shape being calculated to give me wing type lift or is it just giving me generic body lift based on the amount of fuselages I have?

As you can see, the body is blended together to make an almost perfect lifting body. Is this accurately calculated or am I just making my plane blunt and more susceptible to drag?

p.s. This craft in question doesn't want to stay nose first. When re-entering the atmosphere, at around mach 6, the nose either pitches up or down violently and goes engine first and it's impossible to get it going nose first after that. No matter where I move the CoL too, it always flips over engine first. Is it the gull wings or is it the body? I included the FAR analysis if someone more familiar with aircraft/spaceplane design could give me some advice.

[Heagar]

I used FAR with deadly reentry only once to test a plane for an contest several times under different conditions, discovering it was mutch easyer to make an pinpoint landing.

From that experance i assume, that FAR changes the atmospheric layer and - to an certain extend - the impact of control surfaces at an given altitude. But it changes not the general behavior of KSP.

Thus said - and with the pictures you provided - i come to the following conclusions:

• A lifting body will not be computed (exept an given constant value provided by the spaceplane plus parts (build in winglets)) by KSP.
  
• A liftforce is provided at an 90 degree angle to an wing surface.
  
  • Your wings at an 45 degree angle will provide lift to up and to (inner section)/up and away (outer section) from your spaceplane.
    
  • The same is valid for your control surfaces. Because of that it would make nearly no sense to tell them to act only as pitch/roll/yaw control. Especially for roll/yaw, because they acting - when used - as yaw/roll control at the same time, witch lessens their value for a desired movement.
    

  [*]The drag isn't displayed in the editor, but important. It has nearly the same impact as an engine placed out of the CoW (in flight direction). Because of that your plane with its gullwings on top will most likely tend to pitch up, witch means:

  • With activated SAS your control surfaces will try to counteract - as usual in KSP at the outermost range of their movement. When reaching the desired AoA (Angel of attack) they "overshoot" it and the process is repeated for the other direction.
    

In total all above means:

At reentry your plane tends to pitch up, forcing the SAS to conteract in it's ways. Your plane will perpendicular widen it's pitch down and up movement. And since you are at high altitude with low aerodynamic value in FAR the controls arent enough to stabilise your craft and it flips over (after stalling, i presume).

Possible counter measures (You have to test out, witch will have the most effect/best result with your design):

• As you certainly know, in KSP the SAS forces a craft in space to rotate without using RCS.
  
  • The SAS force of your craft is currently at 30.0 (The two cockpits) it seems. You can increase it with mounting several FS2G ASAS within the fuselage, witch would dampening the pitch movement.
    
  • Fly the reentry - without SAS - by hand. Preferably with an gamecontroller or flightstick/rudder in witch way you can use slight deviations to control the pitch movement.
    

  [*] Trim your plane with "Alt" and "W,A,S,D" keys. To zero them afterwards, "Alt" and "X" key.

  [*]Alter the angle (lesser than now) of your wings to an extend, where the currently installed SAS force is enough to handle it.

  [*]Mount your gullwings lower on your craft, that the drag is in the CoW.

  [*]Elongate the fuselage of your craft. The longer it is, the more effect have your control surfaces.

Edited October 10, 2014 by Heagar