How do you avoid using RCS on your spaceplanes?

[SpaceLaunchSystem]

I have recently gotten into building spaceplanes. However, to be controllable, for my spaceplanes, I need to place some Vernor thrusters at the front and toggle RCS and SAS. I've seen many spaceplanes (not built by me) that are controllable without RCS thrusters. Is there a trick to spaceplane building without RCS? Or it it just experience?

Edited December 6, 2014 by SpaceLaunchSystem

[RainDreamer]

Use RCS build aid, it is a god send for building anything, but especially space planes. Aim for perfect balance forward/backward and above/below of the CoM, try to keep the torque to less than 0.01 kNm. Space planes are very easy to get unbalanced due to its asymmetrical nature. Check out some of the guides for space planes around too, I am sure you will get introduce to a few after my post.

If you are using FAR, check out the stability tool and mess around until the numbers are all green, but I am not an expert in that and is still learning too.

Ideally, you don't need to use RCS in atmosphere. Might not even need to use SAS either if it is design well enough to let the aerodynamic takes the job, but don't take my word on this, I just find SAS sometimes overcompensate in thick atmosphere.

Edited December 6, 2014 by RainDreamer

[Red Iron Crown]

Control surfaces in effective locations and reaction wheels.

[sal_vager]

Don't fit any RCS and use more reaction wheels instead

[The_Rocketeer]

If I'm planning to make orbit manoeuvres or dock my SPs I always include RCS capability. It's not strictly necessary, but man does it make life easier.

The planes fly without it to orbit or even docking intercept, then I just use RCS for the real fine-tuning.

I'm not sure exactly what you mean about having to use RCS/Vernors for stability. If that's true for the ascent, it sounds like you're making some fundamental design errors, like putting your CoM behind the CoL or having CoT out of alignment.

If you're talking about once you're in orbit, it could be CoT alignment again, or it could be that you're not balancing your RCS ports top to bottom. It really depends a lot on the situation at the time that you use those nose vernors. Are you thrusting? Main burn or RCS thrust? Have you used anything with any reaction torque? How big is your SP, and where are the boosters, etc.

Try uploading the .craft file or posting a few pictures, and you'll give us a bit more to work with.

Edited December 6, 2014 by The_Rocketeer

[GoSlash27]

Control surfaces in effective locations and reaction wheels.

In addition to this:

- Build your aircraft to have proper static balance

Center of lift should be concurrent with or just barely behind the center of mass and level with it. Your fuel tanks should be in the center of the mass so your balance doesn't shift as the fuel drains.

- Build your aircraft to have proper dynamic balance

Inclining the wingtips 10 degrees will cause a natural tendency to correct roll excursions and putting a vertical surface as far back as possible will correct yaw excursions. I like to combine both functions into one by mounting the wingtips as far back as possible and inclining them 45 degrees.

- Build your aircraft to have proper high- speed stability

Put the draggy parts (intakes) in the back so the airplane wants to point where it's going.

If you do all of this well enough, you won't even need control surfaces let alone RCS. But I do like to have a small pair of elevons for pitch and roll when flying around KSC, so one more thing:

- Your airplane should be properly balanced both before and after adding control surfaces, so balance the plane without control surfaces, then add elevons, then add another pair of elevons (or canards) forward of the CoG to restore balance.

I don't add active rudders because my stabilizer is adequate to keep my turns coordinated.

This part is very important. A lot of people use control surfaces to "crutch" balance into an unbalanced airframe, and they get instability issues at high speed. While control surfaces can be used as wings, they don't behave the same way as wings and shouldn't be treated as equivalent.

Best,

-Slashy

Edited December 6, 2014 by GoSlash27

[Van Disaster]

A spaceplane is as much a spacecraft as an aircraft, remember, so the laws of building spacecraft still apply. Your spaceplane just has to make it to the upper atmosphere without burning all your fuel, and then make a controlled fall onto the runway, so you don't have to build something that will win an aerobatic contest

[panzer1b]

i NEVER TOUCH RCS on every one of my SSTOs until im docking (i bring maybee 1 of the 40 monoprop tanks, 2 if its overly heavy). The trick is stability, place ur CoG in front of ur CoL (CoG = center of gravity, CoL = center of lift). This SHOULD make your craft relativel stable. I personally use canards, and at least 2 control surfaces in teh back, as well as reaction wheels. reaction wheels, even if they are heavy, have 1 perk: they do not use any fuel (well they use electricity but 1-2 RTGs or some panels and ur set), so i strongly reccomend those if you choose to cut down on wing based controlk surfaces and prefer to stay away from RCS. Also, RCS has 1 more mega issue i forgot to mention, it is EXTREMELY inefficient. So inefficient that outside of very minor adjustments, its gonna take a crapton of fuel just o pull off a few dV.

Anyways, the best tip i have is to make it balanced, make the aircraft fly well without any control surfaces, then add some to give you some bit of control. Overall, using RCS/vernors mid-flight is a crutch, while it works for some extremely unstable craft (heck ive used them on some capital ships that just refused to fly straight), in general you want to make a craft that can fly straight, before using RCS.