Plane destabilized before takoff

[Corax89]

Hi! Well, the issue is that when I make a basic plane design (Mk2 pieces) and put it on the track, it begins to move to the right or to the left inevitably, until it becomes destabilized and crashes before takeoff. That happens even when I'm going at 25% trust. I use 2 small gear bays on the center of the wings and another one at the nose of the plane. My center of mass, lift and all this stuff is well situated (I think), so I do not understand why is this happening to my plane! Thanks 4 the help!

[capi3101]

That's generally a sign that your wheels aren't set straight up and down, perpendicular to the ground. If they're at even a slight angle in any direction, they won't operate the way they should; KSP thinks your plane is wheelbarrowing, it keels over and 'splodes.

Let's be sure that's what it is. Can you post a screenie or the craft file of the plane you're having issues with?

[Kryxal]

Do note that this lack of straightness could easily be because of something bending, like the wing attachments to the fuselage.

[MarvinKitFox]

because of something bending

This is the usual cause.

People underestimate the weight on their wheels, especially if you also apply control inputs, while rolling along the runway.

Look at a picture of the real-life Antonov 225

Those many wheels are there for a reason, not (just) to look silly!

[Moesly_Armlis]

You have now joined the wobbly take-off club. I was having a crap-tonne of problems with landing gear and resolved it be using SAS (otherwise the vessel would veer south) and reducing the overall design to a basic fuelselage, engine and landing gear. Leave the wings for last. Try and have that go down the runway without a wipeout. If the vessel is heavy use struts to secure the landing gear into an sturdy triangle undercarriage.

Another tip is put the parking brake on and spin up the tubines, get the engine up to power then let the brakes go. This should reduce the take-off distance.

[The_Rocketeer]

Look at a picture of the real-life Antonov 225

Those many wheels are there for a reason, not (just) to look silly!

Yeah, but the Antonov 225 is the largest in the world*!!!. It has a maximum gross weight of 640 tonnes!

I'm guessing (literally) your typical Mk 2 fuselage plan will be more in line with a Boeing 717 at about 45 tonnes. This baby only has 3 gear trucks, tho they do have a pair of wheels each.

Experience tells me that weight alone is very rarely the cause of this sort of problem. Not that adding more gear won't solve it, but stock alignment or aerodynamic torsion are more likely the cause.

(*Except for the Hughes H4 Hercules by height and wingspan)

[percyPrune]

Yup. My single biggest problem with plane design. I have found that a quick-and-dirty solution to gear alignment is to attach the gear to a pair of I-beams sticking out from the fuselage and hide the beams in the wing roots, then add a few discreet struts between gear and wings to cope with the 'occasional' heavy landing.

I think one of the problems is that, with SAS turned on, if there is any drift off course on the ground the SAS tries to correct using the rudder alone. Once the wings start to lift this causes roll as a response to the torque of the rudder. This makes the situation worse and everything quickly goes pear-shaped...

I have just started experimenting with steering down the runway with dabs on the nosewheel steering and not turning SAS on until rotation (I have set up separate keys for rover and ship controls) but I haven't done enough takeoffs yet to prove any advantage.

Sorry for the long-winded post but that's my interpretation of the problem. Maybe a proper aero engineer will tell me I am talking balderdash

Percy

[Streetwind]

I have a similar problem, but in the reverse situation... my takeoff is perfect, straight as an arrow. But when I land, no matter how gently, the plane wants to instantly drive in a circle. And not just a little, but hard. My setup is almost identical to the Boeing 717 above, although the plane is only 1/10th of its mass. One gear bay under the nose, and one gear bay on each wing, closer to the hull than to the tip.

This is kinda vexing since this is the first time that I managed to make a plane design that is "all green" in FAR's stability analysis for all mach numbers up to twice what my engine can achieve, including transsonic, and air densities down into the single percent range. With my limited range of low-tech parts, I was so proud! But it's so frustratingly hard to to bring it back on solid ground...

[Wanderfound]

Gear vertically aligned, and mounted to places that don't flex (i.e. not wings unless they're well braced); SAS on; steering unlocked on the front gear (only).

Do that, and you shouldn't have to touch the steering during takeoff.

[SukaiSky]

Your wheels are not directly down, causing the wheels to want to go in the wrong direction, as in all the wheels going in different directions

[percyPrune]

Try looking at the plane from the back/underneath as you take off, you can see sideways movement in the gear if it is overloaded or scrabbling with misalignment.

...you shouldn't have to touch the steering during takeoff.

Not with small planes but I'm building human-size replicas and trying not to add too many wheels, so sometimes there is a fair bit of bending and shuffling about going on!

For landing, I make sure that the wings are dead level and I don't make any last-minute changes to heading to make sure I am coming in straight, not crab-wise.

[Corax89]

Hi again, thanks to all for the help!, I've tried and the wheels are the main problem. As I said I'm using Mk2 fuselage and the problem was that I was attaching the gear at the underside of the plane, and although I corrected the angle the best I've could it was a little wrong. Instead of that I opted to do some gross corrections that have worked well, whith a structural panel under the fuselage and the gear attached under it.

Thanks again to all!, Here are some pics: