How to keep your plane from rolling off the runway?

[MedwedianPresident]

Most of us know this problem: you've built a nice plane that looks so aerodynamic and can't wait to fly it. But when you try to take off, it will turn right or left and roll off the runway, usually resulting in rapid unplanned disassembly. (We need to make a word for it. Siderolling?)

What are your solutions to this problem? I think Jettisonable takeoff gear for large planes will not always work.

In my case, it is a two-stage spaceplane. The first stage is a massive hypersonic jet-powered bomber, my rocket-powered spaceplane is riding on top.

Tried to place gears near the ends of the wings, did not work, instead it was even worse!

Edited October 31, 2015 by MedwedianPresident

[maltesh]

In the Editor, once the landing gear is where you want it, Use the Rotate Gizmo.

Press F to switch from relative rotation to absolute rotation.

Turn on the angle snap.

This will allow you to position gear that are guaranteed to point straight and true, regardless of the curvature of whatever part they're attached to.

[Chaos_Klaus]

It might be because your landing gear is not flat on the ground.

Another reason might be that there is more gear on the front wheel then on the rear wheels. That will cause your problem aswell, because the plane is balancing on the front gear, tipping left to right just a little. This will make you go sideways.

But that is all guesswork. We can give you more detailed advice if you post pictures.

[Sanic]

I believe it's because your speed is too high to be stable on the ground.

There's nothing to be done if your plane relies on the lip of the runway except keeping your speed managed.

[Snark]

It generally happens because there's some tiny misalignment in the gear, as maltesh said. It'll seem to work fine, but above a certain speed it freaks out the physics engine and the thing suddenly goes berzerk.

Follow maltesh's suggestion and you should be good to go.

[jhousen]

I usually just enable steering on the front gear...it's disabled by default

[Mastikator]

I believe it's because your speed is too high to be stable on the ground.

There's nothing to be done if your plane relies on the lip of the runway except keeping your speed managed.

I used to think so too, since I started making sure that the landing wheels were always perfectly aligned with the ground this problem has stopped. I've even managed to make airplanes that can go supersonic before liftoff. The landing wheels can take and speed, as long as they're facing correctly and there aren't any bumps.

[Gahooligan]

In my experience I have that problem when my gear isnt exactly plumb. or it may be slightly toe-in or toe-out.

Maltesh's method is the one youre looking for.

In cars, a slight bit of toe-out(thats then the front of the tires are farther apart than the backs) allows for more straight line stability at the cost of turn-in responsiveness and tire wear. Dunno if thats true in ksp.

Though, now im curious.

[Guest]

Flexible landing gear are not good. If the gear are placed at the end of a long wing on a heavy plane and the wing flexes at the joint, the plane will veer off the runway. Try using a couple of struts to reduce or eliminate any flex to ensure this is not the problem.

[GeneralVeers]

My solution: add more lift so the plane gets off the ground faster.

[MarvinKitFox]

1) put wheels on straight

2) put wheels on solid

3) less weight per wheel

4) Center of mass must be *just* forward of the rear wheels.

[Val]

Like others mentioned, having the landing gear aligned right and attached sturdily is most important, but it also needs to be positioned correctly in regards to CoM, as MarvinKitFox mentions.

Here's a snip from another post I made.

...

In KSP, the most stable landing gear configuration is to have a pair of load bearing wheels right underneath CoM and a nose wheel as far forward as possible.

When you load the craft up on the runway, if it lifts the nose wheel a little, before settling back down, then the main gear is perfectly positioned relative to CoM.

The main gear can can have a narrow or wide track, but attached directly to the main fuselage gives the best stability.

If you're worried about tail strikes put a tail wheel there that doesn't touch the ground until right before the tail strikes.

Another way to reduce risk of tail strikes is to attach wings with angle of incidence, which also has other benefits. More info in the spoiler here.

If you place the gear as I recommend you should have no trouble with unstable landing gear.

Here's a clip of craft weighing 318 t with small landing gear going up to 140 m/s.

[arise257]

Like others mentioned, having the landing gear aligned right and attached sturdily is most important, but it also needs to be positioned correctly in regards to CoM, as MarvinKitFox mentions.

Here's a snip from another post I made.

If you place the gear as I recommend you should have no trouble with unstable landing gear.

Here's a clip of craft weighing 318 t with small landing gear going up to 140 m/s.

So, I see this bit of advice get tossed around a lot, and while I agree with the physics of it, I don't agree with it on a practical level.

As Val correctly mentions, placing your 2 rear wheels directly under the center of mass often results in tail-strikes due to the engines being mounted behind that point. Placing a "training wheel" near the engines can introduce additional challenges. For one, it just looks ridiculous. Secondly, that wheel can still strike the ground and depending on your speed or terrain, damage your craft or bounce you off-course.

My approach is to keep the wheels back as far as possible toward the engine, wing-mount them for a wide stance (floppy wings get strutted first), and use surfaces toward the back of the plane to raise the center of lift and point its vector somewhat downward. While gears under the CoM are always more efficient from a torque perspective, the high and rearward lifting surfaces of my method provide the torque necessary to overcome the inefficiencies of rear-mounted gears. I also mount my wings with an angle of incidence in order to produce additional lift in front of the CoM.

Here's an example of one of my designs:

Javascript is disabled. View full album

The cowls over the engines in both designs use airflow to push the back of the plane toward the ground, raising the front of plane earlier than if they weren't there at all. The thin, leading edge of the wings which extend toward the front of these planes are mounted at an angle of incidence, as described above. All in all, this produces spectacular lift from runways or bumpy terrain with a greatly diminished risk of tail-strikes. The single-engine version shown gets off the runway at 45m/s. Those home-made canards up front don't even pitch up or down, I only have them there for roll and yaw authority.

Another thing to note is that since I'm wing-mounting, rather than fuselage-mounting, the airplane naturally sits higher in the front than in the back. This ALWAYS helps get you in the air faster, and lets you ease up on the angle of incidence required to get off the ground, which makes it easier to design an airplane that's properly balanced during flight (especially the super-sonic variety).

- - - Updated - - -

Press F to switch from relative rotation to absolute rotation.

Woah, wait... 'F' does something in the SPH editor!? Been playing for years and never known that one. I've always flipped the whole plane upside down, sunk it into the floor of the SPH, then used the lines on the floor as guides while using the Rotate Gizmo -- toe-in or toe-out gets done visually.

Edited November 3, 2015 by arise257
Clarity