Larger plane takeoff problems

[XenonSpark]

Hi everyone,

I have a relatively large SSTO (eventually) spaceplane that I've been working on for the past few hours. The first half hour consisted of designing and building, and the rest has been me trying to figure out why it can't fly.

Well, to be more specific, why it can't stay on the runway for longer than a few seconds. As I accelerate, when I reach about 45 or 50 m/s the plane suddenly veers right very sharply and banks left.

I've been focusing on making really strong (see: struts) landing gear configurations, but is there something else I'm overlooking?

Here are a few pictures of the plane:

Edited July 5, 2013 by XenonSpark
Answered

[legoheli]

Most problems you describe are caused in my experience by only having a single vertical stabilizer.

The problem is that you're essentially using wings for vertical stabilization, and a wing pulls you in one direction. If you want to just have a single stabilizer, use part clipping and place them inside each other.

[XenonSpark]

Thanks. I added a second one and instead of the plane veering and rolling (followed by intense drifting, followed by death), this time it just veers right. I had no problems with roll whatsoever. I'll continue to play with the design (further suggestions are still welcome).

[Tex_NL]

Apologies for what I am going to say legoheli: Your suggestion is total BULL! With real life aerodynamics you would be correct to say a wing as a stabilizer would pull a plane to one side but this is KSP. Here the aerodynamics don't work like that.

Sudden drift on the runway is usually cause by improper landing gear placement. The main (rear) landing gear should be placed not far behind the CoG for easy rotation. If placed too far backward it takes a lot of effort getting the nose to lift. If then the landing gear isn't perfectly perpendicular to the runway one side can loose traction before the other causing asymmetric drag resulting in a violent turn.

Reduce the number of wheels to the bare minimum and make sure you get them dead straight: single nose gear and regular main. Only double them up it it can't bare the weight but make sure you keep them perpendicular to the ground and in-line.

[XenonSpark]

Hm, alright. That makes a lot of sense given the fact that I have 10 or so landing gears. I'll try minimizing them. I will keep the second vertical stabilizer for extra in-flight stability. I'll be back in a few minutes to let you know if the landing gear adjustments worked.

EDIT: Huzzah! After some experimenting I determined that having the gears mounted on the undersides of my rear wings was the problem. The fact that the wings are mounted at slight angles means that the gears wouldn't quite snap into a straight alignment. So I moved the gears over to the undersides of my air-breathing engine mounts and takeoff was perfectly smooth. I flew the craft for a glorious two minutes before it stalled at 9000 m. Time to add more stabilizers. Thanks for your help.

Edited July 5, 2013 by XenonSpark
Success!

[KerbMav]

.

If you have a finished design, please share the craft file and note the used mods for it.

I really like the look!