Planes keep veering off runway

[ProjectXMark1]

Once my planes hit around 100m/s they have a tendency to turn off the runway for no real reason. I have a wide wheel base, which supposedly helps, but it doesn't seem to be doing its job.

[gompasta]

Gear in KSP are not really reliable. If they are at an angle in any way, they have this tendancy to veer. Make sure they are not backwards, or at an angle.

[shoveycat]

Gear in KSP are not really reliable. If they are at an angle in any way, they have this tendancy to veer. Make sure they are not backwards, or at an angle.

If that doesnt work, strut them to the rest of the plane, and add a bit more SAS

[katateochi]

yeah SAS is more important in planes than you'd think. Also struts, be very careful to have symmetrically placed struts. If you have a strut on one side of the plane but not the other it can cause you to veer off. And also make sure you have enough struts, if there is any compression at joints during take off that can cause problems.

[Hodo]

Are your wheels straight?

Are they straight up and down? (In other words no camber)

If there is any camber in the wheel placement it will cause the craft to pull one way or the other in KSP.

[ccik]

Try to mount your nosegear lower than the main gears. So that when you are sitting on the runway, the nose points slightly upwards. Or mount the wings with the leading edge slightly higher than the trailling edge. With this configuration you ensure that your nosewheel lifts of first.

If your planes are perfectly straight, or perfectly level, it could be that your main gears lift off first. Now you only need a small momentum, one main gear lifts off, the other one stays on the ground, and you go off the runway.

If you already do this, than disregard my post and get more struts.

[Starglider]

Try to ensure a lifting balance between your front and back wheels. If the front or back generates excess lift, that reduces the sideways friction between the wheels and the ground; thus you see you start veering when you get up to speed. Also, at 100 m/s you should be able to lift off by pitching up (actually, if its a spaceplane then 50 m/s is preferable); if not, your rear wheels may not be close enough to your CoM, or you simply need more lift somewhere on your plane.

Pics would help.

[TDplay]

I find the problem is even worse with Mk3 spaceplanes. I do find that it helps to use a bigger tail - don't go with stock tails, they're way too small (unless you're making a very tiny plane) make one yourself with wing segments, structural wings, delta wings and elevons. Mk2 fuselage helps because it has a lift area.

[AeroGav]

Rotate the gear once in each axis with angle snap mode on and absolute rotation mode toggled instead of local (press F while in rotation mode).  This will remove any stray angles.

Also a tip from @bewing  ,  or shall I say automotive engineers,  right click on the nose gear and use Friction Control Override to give the nose wheels low friction.    Override the main legs to have high grip and friction.  

That way you understeer like an Audi (not a TT) instead of oversteering like a Porsche 911 

[Wanderfound]

Alternately: if your gear are perfectly vertical but you're still veering, it may be body flex. Mount your gear to the fuselage, not laterally-attached parts. Translate them outwards if you want a wider wheelbase.

[renhanxue]

I'm sure the guy who posted this back in 2013 appreciates this advice!

Edited February 11, 2017 by renhanxue

[lukavago]

The guy who just did a google search to find solutions to the same problem does very much appreciate these answers.  I now have more things to try. Where am I putting the struts though? On the wheels or everything else?

[bewing]

13 minutes ago, lukavago said:

The guy who just did a google search to find solutions to the same problem does very much appreciate these answers.  I now have more things to try. Where am I putting the struts though? On the wheels or everything else?

Glad it helped. In current versions of KSP, wheels are automatically strutted ("autostrut"). If you have the wheels attached to wings or nacelles, it's the wings and nacelles that you want to strut. You may also want to use autostruts there, because autostruts have no drag or mass. However, as AeroGav said -- my main piece of advice is that most veering is caused by having too much drag ahead of the CoM, and not enough behind the CoM. And that includes drag with the ground. Aerodynamic drag at takeoff speeds is really pretty low. To fix the "drag with the ground" problem: lower the friction on your front wheels, and increase it on your rear wheels.

 

Edited February 15, 2017 by bewing

[fourfa]

Good info here so far.  For me, I always turn off 'auto friction control,' set front gear to 2.0, set rear gear to 4.0, and find it works very well.  Lowering front friction control below the stock 1.0 - for me it makes the nosewheel steering very vague and too understeer-y. My 2.0/4.0 probably ends up making the brakes overly powerful, but it's a balance that works well for me.

On really large 200t+ planes I might even go up to 3.0/5.0 as well as maxing out spring and damper.

[Hodari]

1 hour ago, bewing said:

Glad it helped. In current versions of KSP, wheels are automatically strutted ("autostrut"). If you have the wheels attached to wings or nacelles, it's the wings and nacelles that you want to strut. You may also want to use autostruts there, because autostruts have no drag or mass. However, as AeroGav said -- my main piece of advice is that most veering is caused by having too much drag ahead of the CoM, and not enough behind the CoM. And that includes drag with the ground. Aerodynamic drag at takeoff speeds is really pretty low. To fix the "drag with the ground" problem: lower the friction on your front wheels, and increase it on your rear wheels.

 

Or go for the true Kerbal solution:  autostrut EVERYTHING.  Then add a few extra regular struts for good measure.

Spoiler

And then more boosters too.

 

[fourfa]

just don't dock that autostrutted spaceplane to your big space station you spent months assembling.  Ask me how I know

[Blaarkies]

1 hour ago, fourfa said:

just don't dock that autostrutted spaceplane to your big space station you spent months assembling.  Ask me how I know

OK, how do I know?

[fourfa]

Autostrut works pretty well with small, stiff structures like planes. With long wobblefests like your typical space station, it's kraken food

[foamyesque]

This issue is almost always caused by aerodynamic loading pressing down on your nose gear as you get up to speed. @bewing's suggestion about re-tuning the friction controls can work, but it's a very hacky solution.

A cleaner way is to take a close look at how your wings are laid out and where they're generating lift. Typically, you want you main gear very close to your center of mass (either slightly forward or slightly behind, depending on if you're building a tail-dragger or a trike). You generally want your wings center of lift to also be near your center of mass, so that your plan can be controlled instead of turning into a lawn dart. It's also generally best to put a hair of inclination on them to get lift even when you're nose-level, which helps with take-offs too. The upshot of this is that, if you're building a trike and tailed design, you want inclined wings with a center of lift in further in front of the center of mass than the main gear is behind it. The tail will then bring the overall CoL back behind the CoM, but on take off this layout will lift the nose gear up first (particularly if there's a commanded pitch up), allowing for quite high runway speeds to be achieved.

I've had planes able to stay in control as they jump off the end of the runway at Mach 1

[bewing]

A plane on the ground is a rover. Rovers have different stability needs than a plane in the air. To make a rover stable at speed, you need to take the wheel friction into account -- so I completely disagree about "hacky". It's not always about aerodynamics -- I think @foamyesque's method simply ignores an entire branch of physics. One of my spaceplanes will drive stably on the Mun. One of his won't.

Edited February 16, 2017 by bewing

[foamyesque]

2 hours ago, bewing said:

A plane on the ground is a rover. Rovers have different stability needs than a plane in the air. To make a rover stable at speed, you need to take the wheel friction into account -- so I completely disagree about "hacky". It's not always about aerodynamics -- I think @foamyesque's method simply ignores an entire branch of physics. One of my spaceplanes will drive stably on the Mun. One of his won't.

It isn't always about aerodynamics, but if you're losing stability as you go fast in air on a thing with wings on, it probably is. I'd prefer to understand and address root causes instead of blindly putting bandaids on the problem.

Edited February 17, 2017 by foamyesque

[Th232]

Easily one of the biggest bugs in this lovely game. Still... 

[kevnuke]

@gompasta mentioned making sure the landing gears are not backwards.I'm playing the Enhanced Edition on PS4 and by default when you attach landing gear to the fuselage the lights are shining towards the front of the plane. Is that right or should I turn them around?

Edited October 4, 2019 by kevnuke

[bewing]

1 hour ago, kevnuke said:

@gompasta mentioned making sure the landing gears are not backwards.I'm playing the Enhanced Edition on PS4 and by default when you attach gear to the fuselage the lights on the shining towards the front of the plane. Is that right or should I turn them around?

The landing lights are supposed to point forward to light the terrain that you are approaching. However, I have never had a single problem with turning them around when I felt like it.

[TheKSPBeginner]

It kinda happens