FAR and Rocket Tail fins

[G'th]

So basically, what should I be looking at as far as putting fins/wings on my rockets while using FAR? I get the basic idea of where to place them, but how exactly should everything line up? My rockets aren't going out of control as long as I don't over-pitch, but it takes a lot of effort to get a good gravity turn while also not pitching over too much, and as far as I can tell its the wings that need tweaking.

[Tortoise]

I never actually put fins on my rockets, but I do use an SAS module on each stage.

But I'd say just put the fins on the bottom 4-symmetry

[FenrirWolf]

The basic principle is that you want more drag at the back of a rocket and less up front. As long as the fins are near the back they ought to be doing their job, so the problem could have to do with the front of your ships. Do they have fairings and nosecones where appropriate?

[Hodo]

You don't "have" to put fins on your rockets in FAR.

This is my UR-1 "StiK" solid booster rocket for Realistic Solar System with the Earth system (space is at 180km not 69.1) and full Realism Overhaul.

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Note it has NO fins on it, and it worked just fine even takes a small 5 ton payload into orbit.

[Jimbimbibble]

You can check your CoM and CoL in the VAB. If the CoM is behind the CoL the rocket might be unstable. 4 winglets ought to do it unless you have an especially wonky payload.

[Master Tao]

As the others have said, it sounds like fins are not the problem. It sounds like you could afford to make your pitchover earlier. As you've noticed, with FAR, rockets lose control if they are pointed too far away from the prograde marker. The solution to that is making a gentle (< 10 degrees) pitchover at low speeds (< 100 m/s). Then you adjust the throttle down or up to keep the rocket from going above or below the prograde marker. Gravity will turn the rocket the rest of the way over as long as you keep the TWR low enough.

My ascent goes like this:

• Adjust throttle so the launch TWR is about 1.2
  
• Launch with SAS on
  
• Fly straight up until between 50-75 m/s
  
• Pitch over of 2-5 degrees east and turn off SAS
  
• Adjust throttle to let the rocket turn these pitches:
  
  • 5-10 degrees by 5 km
    
  • 15-20 degrees by 10 km
    
  • 25-30 degrees by 15 km
    
  • 45-50 degrees by 20 km
    
  • 55-60 degrees by 30 km
    
  • 75-80 degrees by 40 km
    

  [*]Hold 5-10 degrees above the horizon until apoapsis is high enough

Here's a demonstration where the first stage has no attitude control, so the pitchover is entirely on the capsule torque. I barely had to touch A, S, or D the whole way up, but it had a tendency to pitch south, so I was holding W through most of the first stage.

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[Geschosskopf]

So basically' date=' what should I be looking at as far as putting fins/wings on my rockets while using FAR? I get the basic idea of where to place them, but how exactly should everything line up? My rockets aren't going out of control as long as I don't over-pitch, but it takes a lot of effort to get a good gravity turn while also not pitching over too much, and as far as I can tell its the wings that need tweaking.[/quote']

FAR's demands vary with each update. A version or 2 back (still for KSP 23.5), you had to mount short-lived boosters way up near the top of your rocket because the effects of their body lift on the CoL and CoM overpowered any number of tailfeathers you put on the central stack. And at the same time, main stack tailfeathers had to be aligned orthogonally and their control surfaces limited to only pitch or only yaw.

The current version of FAR, OTOH, doesn't care as much about the positioning of early boosters so you can do asparagus with it no problem. Also, it seems to work best with main stack tailfeathers oriented at 45^ and free to work on all axes.

My SOP for lifters with FAR is to have a subassembly called Tailfeather. This consists of a stock Delta Wing with a stock large control surface on the trailing edge, and 3x RCS blocks on the wingtip. Depending on the mood FAR is in at the time, I mount 4 of these either orthogonally or diagonally. If diagonally, I use 4x symmetry and move the RCS blocks to the orthogonal points of the main stack. If orthogonally, I use 2x symmetry, leave the RCS blocks on the wingtips, and set each pair of control surfaces to either pitch or yaw.

[Geschosskopf]

To append to my last: If your main stack drops a stage on the way up, where the atmosphere is still relatively meaningful, it's best to put some small tailfeathers on the next stage up. Small, so you don't need any more on the bottom stage, but big enough to keep the rocket heaing in the desired direction. So if my bottom stage has delta wings with big control surfaces, the upper stage has merely AV-R8 winglets.