Why does this plane become uncontrollable?

[THX1138]

This plane flies okay with two RAPIERS and two turbo jets but not with four turbo jets. What's going wrong?

Video:

When I re-enter with the RAPIER version it does the same thing and spins around and around. I need that to not happen because it destroys the cargo I have banging around inside.

Edited May 19, 2015 by THX1138

[icedown]

My guess would be a lack of a vertical stabilizer. Without that, there is no way to control yaw on that craft. While flying wings are a nice idea, they are very difficult to fly in reality due to this.

[Murph]

I'd start by adding a tail and rudder, or pair of them. The loss of control in the video looks like it starts with uncontrolled yaw, that's what the tail and rudder control. The video shows more or less expected behaviour for rudderless planes.

[THX1138]

Okay, thanks a lot.

Since I already have a crap plane out there that I'm hoping to land, is there any advice for how to stop a spin when it happens? Are there different kinds of spin?

[icedown]

There's not really a good way to bring that craft back in safely. The only thing you could try is shutting down the an engine on the outside of the spin to try to stop the spin, but the chances of actually pulling that off and getting it back actually under control are pretty slim.

[Murph]

One other thing, more for the ascent, than the descent, is that I'd check for differential thrust (getting more thrust from one side than the other). I'm not yet clear on the details, but I've seen a pair of turbojets do that in 1.0.2, e.g. producing 140kN on one side, 120kN on the other, at the same time, resulting in a constant yaw battle while it's happening. I think it's a bug that is triggered by the order the parts are added, possibly for quite specific cases.

[Kryxal]

You seem to be going pretty fast there ... 300+ m/s at low levels?

[Murph]

You seem to be going pretty fast there ... 300+ m/s at low levels?

It's fast (almost mach 1.0), sure, but that's not the real problem. Mach 1 at sea level is just fine under the new aerodynamics, although not really a valid ascent profile if orbit is the intended destination (you don't want to be going for speed until you're above about 7,500–10,000m, possibly even 15,000m, depending on the design).

[MaverickSawyer]

Okay, thanks a lot.

Since I already have a crap plane out there that I'm hoping to land, is there any advice for how to stop a spin when it happens? Are there different kinds of spin?

Airbrakes, tied to fully deploy when you hit the ABORT group. Put them as far back as you can, and they'll shuttlecock you to a nose-first attitude every time.

Also, I've noticed that a lot of times, locking your SAS can in fact cause a LOSS of control. It's too twitchy nowadays for high-speed aircraft. Set your ship up with the CoM and CoL like this:

With the CoM and CoL located closely, like in the pic, you'll only need a little elevator trim, and you'll have a rock steady plane that is highly responsive to control inputs and can be easily hand flown, no SAS required.

Oh, and get the RCS Build Aid mod. It'll help you build a ship where the CoM doesn't shift as fuel burns off.

[mattinoz]

If the problem is lack of yaw control could you come in to the atmosphere with the wings vertical to the ground?

May not be a fun ride for the pilots but well better than the alternative.

[Jaeleth]

In real world flying spins are recovered from like this:

neutral stick, full oposite rudder. Engines idle.

some aircraft are extremely difficult to recover.

in this case you have no rudder... I guess this one should fall into the " extremely difficult to recover category" : P

try NOT to spin, that is, reenter with high angle of attack to loose speed in high atmosphere but return to a prograde, unpowered, only flight as soon as possible, when stable at low speed and lower altitude, turn engines on and get back to base

[Murph]

Oh, and get the RCS Build Aid mod. It'll help you build a ship where the CoM doesn't shift as fuel burns off.

I also recommend RCS Build Aid, but I do not consider it important to prevent CoM moving with fuel usage. It doesn't matter if it moves a little, only that you understand how it moves, and that it doesn't leave you with an unstable plane. It is wrong, in my opinion, to artificially restrict your designs by making it a requirement that CoM does not move. Just be aware of the issue and know how the plane will behave, move fuel from aft tanks to forward tanks in orbit, before re-entry.

[icedown]

Yaw is rotation about the vertical axis of an aircraft. Just because you turn the vertical axis horizontal has nothing to do with the inherent instability around the axis. It would just appear to cartwheel instead of spin.