Difficulties at Mach 1 [FAR]

[Dizzle]

Just a quick question. I recently built an SSTO, which, when it goes supersonic, loses the ability to pitch up. This tends to go away once it's almost hypersonic, but some altitude is lost and it would probably save some fuel if this didn't happen. Is there a way to better deal with this?

Screenshot.

Edited February 17, 2014 by Dizzle

[ferram4]

Make it less stable or add more pitch control. The problem is that the CoL is shifting backwards as you head into supersonic flight. This makes the plane more stable. When the plane becomes more stable, it takes more pitch authority to change its angle of attack. If you make it less stable you'll counteract that.

Another problem might just be that the relatively low sweep angle of your main wing is creating a lot of drag at supersonic speeds and that is enough to hurt your pitch authority. Sweeping the wings more or replacing them with delta wings might help.

[Dizzle]

Thanks for the quick reply, knowing what causes it really helps me out.

[Hodo]

The only other problem I see is your intakes are mounted high on the craft, which is creating drag on the top and behind the CoM which is pulling your nose up. I had a craft with a setup like that. When I moved the intake below the CoM it fixed it.

[Armchair Rocket Scientist]

The only other problem I see is your intakes are mounted high on the craft, which is creating drag on the top and behind the CoM which is pulling your nose up. I had a craft with a setup like that. When I moved the intake below the CoM it fixed it.

It sounds like that effect is actually helping him.

I don't use FAR, but in my experience when the CoM is too far ahead of the CoL the vehicle will want to fly a ballistic trajectory.

OP, it looks like the CoM of your fuel tank is behind your vehicle's CoM, so as you burn fuel it actually moves forwards. The CoM is also probably further forward than it looks because the VAB counts the mass of the landing gear, but they're massless in actual flight. I don't envy you the task of trying to reenter and land it with empty tanks. As Ferram said, you need more pitch control.

I also notice you have B9 installed. You may want to see if the compressed air thrusters can help you out (you'll need to be able to disable the main RCS system though).

[Guest]

Hello!

I've had the same type of problems but at low altitudes is my plane wrong or is this the physics limit?

Mach1 at 1:10

[Armchair Rocket Scientist]

Hello!

I've had the same type of problems but at low altitudes is my plane wrong or is this the physics limit?

Mach1 at 1:10

That's a completely different problem, called the Infiniglide glitch. Basically, it's caused by stock KSP aerodynamics being bad at life.