Unexpected Turning

[Ege Kocatepe]

My planes always abruptly turn during take off, even though the center of mass, thrust, and aerodynamics are all in the center. Why is it turning and what can I do to fix it?

[Vanamonde]

There are several possible reasons for this common problem. If the plane is large, it might be flexing under its own weight, which can cause the wheels to mis-align. If it has a single forward wheel, it might be that the rear is rising first and turning it into a unicycle. Pics of the your craft can help diagnose the problem. 

[Ege Kocatepe]

2 minutes ago, Vanamonde said:

There are several possible reasons for this common problem. If the plane is large, it might be flexing under its own weight, which can cause the wheels to mis-align. If it has a single forward wheel, it might be that the rear is rising first and turning it into a unicycle. Pics of the your craft can help diagnose the problem. 

Thank you. I found it's weight, as lowering gravity makes it fly normally. Im going to make it lighter if possible.

[bewing]

Another possibility is drag/friction on the front wheel. After you turn gravity back up, you can turn on "Manual friction" on the front wheel, and then turn down the friction to .5 or lower.

[pincushionman]

38 minutes ago, Ege Kocatepe said:

Thank you. I found it's weight, as lowering gravity makes it fly normally. Im going to make it lighter if possible.

Try making it stiffer. Struts, autostruts, KJR mod.

Pics would still help, there may still be something apparent to us that is not obvious to you.

Also: rockets are easy; planes are hard.

[Fierce Wolf]

11 hours ago, pincushionman said:

Also: rockets are easy; planes are hard.

KSP, where launching rockets is easier than making a plane

[Curveball Anders]

7 hours ago, Fierce Wolf said:

KSP, where launching rockets is easier than making a plane

Because it's Kerbal Space Program.

Where atmosphere is something you want to spend as little time as possible in

 

[DeadJohn]

I assume it's turning on the runway, not in flight, and you are using the common landing gear arrangement of 1 gear in front and 2 in back. For very small planes in early career, the fixed gear angles outward and can be finicky. The rest of what I'm writing is applicable to the 4 sizes of retractable gear.

• Only allow steering on front gear. Turn it off for rear gear. (only small and medium gear can be steered)
• Experiment with SAS on and off. Sometimes it can stabilize a wobbly design, other times it will overcompensate.
• Make sure the rear gear is perfectly vertical and aimed forwards. Attaching gear to a curved fuselage or wing can sometimes put it at an angle. Use the rotation tool ("3" in VAB/SPH) if needed.
• Don't place rear wheels too far out on the wings. The width between the rear pair should be less than their distance to the front gear.
• Are you using large enough gear for the plane's mass? Add up the total number of wheels (actual wheels, not gear), multiply by 10, and that should be close to the tonnage of your plane. There's a lot of leeway here, but you don't want 3 small gear on a 100 ton plane.
• The rear gear should be just a little bit behind the center of mass to facilitate nosing up slightly during takeoff. They carry most of the weight, letting you use the medium front gear (2 wheels) even on very large planes.
• Putting canards/elevons near the nose helps many craft liftoff sooner, before they can wobble to death on the runway.