Spaceplane veering off on runway

[Kantall]

So I've started a new game after a long absence to test out the latest update, and when trying to make a spaceplane for the survey missions I'm having very little luck. I think I'm doing it mostly right from what I remember such as COM and COT aligned, COL just higher and behind the COM etc. and as best I can see I've put the wheels straight. The problem I'm having though is when I'm trying to go along the runway, the plane is veering off to one side and blowing up. This is happening about 5-10 seconds in, and dropping my acceleration doesn't seem to do much to help it. Any insight or help as to why this is happening would be really appreciated.

 

[Martian Emigrant]

Hi.

 

Welcome to the forum.

I am at a lost as well.

Never figured it out. Sometime I will change something and wacko-Jacko. Can't control no more.

Othertime it's as if it has been behaving it's whole life and nothing bad can happen.

 

I am working on a space plane right now and keeping it on the runway is a nightmare.

 

ME

 

[Val]

You need to have the main landing gear right behind CoM for stability, similarly to having CoL right behind CoM.

Assuming you're using tricycle gear with nosewheel.

[Tex_NL]

 

[StahnAileron]

I find the default settings on the landing gear to be too soft for the planes I designs. I usually crank the settings to max to stiffen them. My planes tend to be less wobbly and more likely to stay straight during take-off/landing after I do that.

A test I sometimes do is immediately brake the plane and turn on SAS. Then I try to roll the plane. If it deflects more than I'm comfortable, I stiffen the (main) wheels (at least).

(Side note: I miss the ALG mod during my 1.0.5 days...)

[Starhawk]

This question about playing the game has been moved from KSP Discussion.

In my experience this is most often caused by the wheels not being perfectly straight.  Depending on where they are attached, they may be angled slightly in any one of the three dimensions.

If you click the rotate gizmo and select the landing gear, and then press 'F' this places the gizmo in absolute mode.  Rotating the part will force it into angle increments from a dead straight attachment.  Rotating it out and back in each of the three degrees of freedom while in absolute mode should leave the gear perfectly straight.

If they are attached to a flexible part, they can also move out of true when the plane begins moving or even when physics loads.  Attachment to the main fuselage rather than a flexible part will mitigate or eliminate this.

Also note the excellent advice above from @Val.

Happy landings!  (or takeoffs, even)

[adsii1970]

Not only does this happen when the wheels are not perfectly aligned, it can also happen if one side of your craft weighs more than the other. I have noticed that sometimes I will place an asymmetrical piece on one side of the aircraft and it does have an impact on how the craft handles...

[bewing]

It also happens because the wheels that are ahead of your CoM have too much friction, and the wheels behind the CoM don't have enough. If you just reduce the friction on the nose wheel to .4 or below, it will probably help a lot.

[sal_vager]

Not too long ago we had another report of this, turned out the engines on one side were blocked.

[diomedea]

We've had asymmetric aerodynamic forces, wheels, reversed control surfaces, choking engines starved of air. Most often, seen planes veer suddenly to the left for no apparent reason; however there's always some hidden cause.

Unless your plane has some asymmetry (like not centered wheels, or wheels with some camber), finding the cause may require some effort.

I'd start with having aero forces displayed (F12), and keeping all of engines and wheels action menus displayed at the same time while taking off (keep Alt down while right-clicking each part). If all goes well, you may capture a shot (F1) of the moment anything weird starts to show and some asymmetry should show with the parts data (then, of course, please show that shot here). If nothing, have an exorcist ban the kraken.

[Aegolius13]

You could also try going one set heavier on the landing gear, especially the rear set.  I was having similar problems with a plane recently, and going from medium to large landing gear on the rear seemed to fix it.

But do double check the wheel alignment first, that seems to be the most common issue.

[ForScience6686]

22 hours ago, StahnAileron said:

I find the default settings on the landing gear to be too soft for the planes I designs. I usually crank the settings to max to stiffen them. My planes tend to be less wobbly and more likely to stay straight during take-off/landing after I do that.

A test I sometimes do is immediately brake the plane and turn on SAS. Then I try to roll the plane. If it deflects more than I'm comfortable, I stiffen the (main) wheels (at least).

(Side note: I miss the ALG mod during my 1.0.5 days...)

I find this to a bad idea.   how bouncy are you on landing?  I prefer to reduce spring and increase damper.   this allows more cushion for the landing and reduced recoil as well as sway.

[StahnAileron]

6 hours ago, ForScience6686 said:

I find this to a bad idea.   how bouncy are you on landing?  I prefer to reduce spring and increase damper.   this allows more cushion for the landing and reduced recoil as well as sway.

Landing isn't usually my problem; it's take-off. I will admit, however, I don't land anywhere near as often as taking-off. When testing designs, I usually skip landing and just revert.

In any event, it's just me being lazy and maxing both settings rather than tuning it properly. It's worked for me well enough so far. Probably not good practice, I'll admit, but I'll be forced to change practice if/when I make a design that requires it. (Or ALG gets updated...)

[foamyesque]

The most common physics reasons for the "spaceplane veering" problem that people run into is either asymmetric lateral wheel loading or a nose-heavy wheel loading due to aerodynamics:

The one I usually see is this:

The center of lift of the plane is behind the rear gear.

This tends to lift the rear wheels up before it does the nose gear, producing wheel loading and drag on the nose gear and reducing it at the rear. This nose drag can very easily overwhelm a plane's yaw stability, just the same as mounting a giant fin on the front would, causing a violent yaw. This can be mitigated to some extent by a strong pitch-up command, which will act to pull the nose up instead, but it's better to redesign the gear.

 

Another I have encountered is this:

The plane rolls while taxi-ing, placing an asymmetrical load left-to-right on the wheels.

If the plane is rolling right, the left wheels will have less load and the right wheels will have more, while corresponding drag changes. This will make the plane slideslip right of prograde. The correctional forces will usually then cause a roll left, which tends to result in an increasing oscillation and then a crash. This is usually caused by planes that have enough lift to nearly, but not-quite, take off, and which are too stable to rotate up and away.

 

Bad wheel loading can be caused by other things, such as floppy craft, tilted wheels, offset or angled thrust, etc, but in general it's down to gear and wing placement. It can usually be solved by sliding things around with the offset tool.

 

Edited November 19, 2016 by foamyesque