Trouble with Runway Take off

[riles]

I dont know if this is a issue with a MOD or the game; But as soon as I start to go down the runway the craft suddenly turns right and crashes. If I use SAS it just goes in multiple directions in what appears to be an attempt to make corrections but this also leads to crashing. I have FAR installed and I would suspect this might be the issue but have never had the issues in the past, design changes dont seem to have much of a effect. Thank you for the help or advice!

Edited July 5, 2015 by riles

[Xannari Ferrows]

I always put the back wheels higher up on the plane so the nose points up on the spacecraft, and you can lift off easier. I suspect the turning issue may be related to the center of deviation and aspect angle between your set of back wheels and front wheels. If anything, I'd try the nose up tactic first.

[Sharpy]

Almost certainly structural instability. If your wheels look perfectly straight in SPH, have a look at them when the plane sits on the runway. It's quite likely they are crooked a bit, attached to a part that bends/twists under the weight.

Usually a pair of well-placed struts fixes the problem. Sometimes you need to move the wheels onto a more stable part (e.g. detach them from wings and attach them to the hull.

If they are attached off-center to some parts (e.g. sides of engine nacelles) they will twist almost for sure. Attach them centrally (directly under).

Edited July 4, 2015 by Sharpy

[selfish_meme]

Make sure you don't have angle snap on when you place the two real wheels, use c to turn it off.

[riles]

Thanks everyone.... I tried a diffrent design and seem to be doing better, Does anyone know of a link that can explain the FAR building tool??

[Daveroski]

This used to be a pet hate of mine.

Start going down the runway, just pick up a little speed and then either the wheels skip from one to the other or the craft just veers off the runway for no apparent reason.

I felt certain that the plane was symmetrical. That it shouldn't be veering off the runway.

Now I can put undercarriage on any of my planes and be confident that there will not be a problem.

If the wheels are skewed even a little, or are mounted on wings or nacelles when the forces of lift take hold of the front of the craft and the rear wheels are taking all the weight, the problems begin.

Put the rear wheels just behind the COM. This will make it easier for lift to lift the front end of the craft.

Sometimes on launch the rear end may go down and it may look like it's going to tip over but usually it's safe.

Make sure that the rear wheels are on straight. Even a little pigeon toed will cause it to dance and veer. Make sure they are parallel with the ground. Not with the craft.

If they are attached to something other than the main body such as a wing or nacelle, make sure that the wing-part or nacelle is strutted to the main body. This makes the physics treat it like one lump and stops it from flexing during lift.

Keep in mind that generally the easier a craft is to take off the more difficult it can be to land as it now wants to be going up more than down.

Design it so that it uses a lot of runway for take off that way landing will be easier.

Edited July 4, 2015 by Daveroski

[riles]

The design I was using at the time had the wheels body mounted, then i tried mounting to the wings and fixing the front gear, I was having the same issues regardless for what ever reason. I was trying to use COM and COT to line the front wheel up as much as possible.

[Daveroski]

The design I was using at the time had the wheels body mounted, then i tried mounting to the wings and fixing the front gear, I was having the same issues regardless for what ever reason. I was trying to use COM and COT to line the front wheel up as much as possible.

The COM is or should be in the center. So lining up the front wheel is not needed.

Have snap on.

Put the wheel in the middle towards the front. So long as it's straight it will be fine.

The front wheel is only used for taxiing and keeping the nose off the ground.

As we don't tend to do much taxiing in KSP the main use is merely to prop up the front and stop the nose making a plough-line when you land.

If you remember the advice I gave you earlier, you should never have a problem with undercarriage again.

When mounting the two back wheels to the body, it is useful to use the new rotate feature built into KSP now.

It makes it easy to see if a wheel is not straight and easy to adjust. I use it with snap on and put my wheels on so that they are sticking out at about 45 degrees and then use the rotate feature to make them straight by rotating the rings on the pop-up.

This also makes the wheels slightly lower than the front wheel making the craft sit-up a little more. This helps with lift on take-off tremendously.

Nice tool. I wish we had it sooner. It's proved very useful.

If you are happy with the replies you have had and feel that the question has been answered. Please edit your first post. Go to advanced. and change the subject header from unanswered to answered.

Have fun.

Edited July 4, 2015 by Daveroski