Plane wobble during takeoff

[feudalord]

Is there a way to place landing gear so that i can guarantee my plane can remain stable on the runway even at high speed in excess of 200m/s? My plane tends to wobble on the runway with the stock game so i decided to download FAR, but the problem still persists. I have done everything imaginable to try to remedy this problem. I scoured the entire web for a solution, but found no working solution or at least dont work every time. I feel tat it is either due to the symmetry placement in this game being inaccurate or certain parts where i anchor my landing gears on are not perfectly symmetrical and the physics calculation is just too sensitive about even the slightest misalignment.

[RainDreamer]

Symmetry placement should give you perfect symmetry, as far as the game is concerned. The problem could be about the angle of wheels, though there could be more problems with the COM and wheels placement. Do you have a screenshot of the craft?

Also, try this mod: http://forum.kerbalspaceprogram.com/threads/99660-0-25-Adjustable-Landing-Gear-v1-0-4%28doors-fixed%29-Nov-14 (still works in 0.90 if you get updated firespitter.dll)

Saves a lot of headache in wheels placement.

[Scarecrow88]

To avoid wobble, wheels need to be absolutely vertical, and they shouldn't be attached to something that is likely to flex as speed builds up, as this could also affect the vertical alignment. Not sure why you would want that stability for speeds in excess of 200 m/s though, as most planes will take off and land at far slower speeds.

[biohazard15]

Wow, if you need 200 m\s to take off, you should think about adding more lift. Or adding a RATO boosters. Or maybe launching it in a vertical, Space Shuttle-style config.

Try not to place your gears to wings, especially wingtips - if they wobble even slightly, your plane lose the balance. Also pay attention to your fuel balance, especially if you're using several tanks placed in parallel to each other.

[feudalord]

I dont really need 200m/s for take off. My plane usually take off at a little over 120m/s. I am accelerating it to over 200m/s on the runway just to test the stability of those wheels since the faster you go, the more likely the plane will wobble and flip on the runway. Although I usually only need 50 m/s for most planes to wobble out of control.

(For test purposes, all aircraft are not pitched up and SAS is turned off.)

Stable aircraft: "Untitled" (lost the file upon loading after aircraft)

Speed over land > 260 m/s

Stable jet car: "Untitled" (Lost the file)

Speed over land > 350 m/s before veering off the runway

Unstable aircraft: "Working aircraft"

Max speed before rolling < 90 m/s

Sometimes Stable Spaceplane: "Hypersonic Experimental"

First try speed over land reached over 210 m/s before flipping in the last second.

Second try, speed over land reached over 210 m/s and it didn't flip.

Unstable Aircraft: "FAR Firehound" (Stock)

More stable aircraft: "Experimental Jet"

Speed over land reached > 260 m/s

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I have created a score of other aircrafts with different designs but deleted them because they didnt work even on the runway. I have never successfully landed a single aircraft before as they all tend to roll over when landing at high speed. Aircraft in this game is almost unfeasible, especially in career mode, you will lose all your money before you finally design an aircraft that can even takeoff. Even if you can takeoff, landing will usually destroy tat aircraft so survival rate on an aircraft for a typical kerbal is nearly zero.

[Vectura]

You main problem is your landing gear. DO NOT ANGLE THEM! And also place them further apart. Angled landing gear create rotational force for whatever reason.

Edit: I made a simple easy plane in career mode that is both stable and cheap:

Edited January 11, 2015 by Vectura

[LethalDose]

A trick i've used before is to put modular girders on the sides of the fuselage and putting the gear on the bottom of the girders. It provides a wider, more stable wheel base while keeping the wheels straight up and down (no camber).

[feudalord]

It doesn't really matter if you angle them or not, there is not a single configuration for the wheels that can work on all plane parts. If there is, I would have found it long ago. Here is an example of landing gear place on a complex geometric surface: Unstable plane Rear landing gears only seems to work on cylindrical fuselage, if you place them on a fuselage intake or anything other than a cylinder, the wheels can behave strangely.

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If you have seen the examples above, I have planes that have angled landing gear and they work perfectly, yet some planes with straight landing gears don't. The reverse also happens. I have also thought about a wider base. I have created planes that have landing gears place right under the wing tips but they still won't work. I am definitely aware that there are multiple reasons as to why the plane flips. 1. tilt of the plane. 2. How wide is the base. 3. angle of the wheels. 4. Geometric shape of the body you attach the landing gear to. 5.whether the body you anchor the landing gears to are firm. But I am still not sure if there are more reasons or perhaps it is just a physics bug which I am wasting my time on.

[basic.syntax]

One idea I haven't noticed here yet: "wire up" the landing gear, with strut connectors. When gear is placed, it has just one point of attachment. (Idea is moot, if you haven't unlocked them yet.) If rear landing gear are strutted together, or braced to a center point, they are less likely to torque in different directions.

Landing is hard. Set up for a long glide path, and watch rate of climb indicator at top of screen, aim for -5 m/s. Descending greater than -10 m/s usually makes a mess.

[Liowen]

While I am not a great plane builder there is a part in the structural (I think it is a pylon?) the I place on the wing and attach landing gear on those, it sometimes takes a few tries to find the right spot but well worth it. The SSTO I took to Laythe recently has only one minor flaw using this design, I have to raise the landing gear and pull back slightly to take off. I believe the issue is there is not enough control surfaces to offset this issue, but it comes up very easy so it is not a very big deal. I do add a strut to each wheel out of habit since my earlier versions use to roll, better safe than sorry.

I dunno why but this picture makes the one side look like it is tipped in but I know they are straight, I believe it just the angle that the picture was taken that is causing it to look like this.

Edited January 12, 2015 by Liowen

[Wanderfound]

For runway stability:

* Unlock steering and disable brakes on front gear.

* Gear perfectly straight and vertical.

* As wide a wheelbase as possible.

* Gear not mounted to parts that will flex (e.g. wings, unless they're very well braced).

And, of course, try to take off and land as slow as possible.

[feudalord]

I have found a solution to my problem. I shouldn't have placed landing gears on the fuselage, I found that placing landing gears on flat surfaces like wings make landing gears a lot more stable. Here is the best aircraft I have created to date: Jet Aircraft

I managed to successfully takeoff and land this aircraft at least 20 times in a roll now and I haven't even lost a single pilot flying this. This aircraft can takeoff at just above 50 m/s and can glide for a few minutes without engine. This aircraft handles smoothly, no matter how you turn, roll and flip this aircraft, it will never lose control. I made this aircraft based on real life commercial jet design.

Mods needed for this aircraft to work: Procedural wings, Adjustable Landing Gear, FAR.

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I have doubled the max stress value for aerodynamics failure in FAR for every category. The default max stress value is just ridiculous, its like flying in hair gel, everything gets torn apart so easily, like that will ever happen in real life.

[Mits]

Bit late i know, but i had the same problem. After externsive testing and bloodpressure rise, results:

it doesnt matter where you place the wheels, as long as they are not angled on the X (nose-tail) axis.

Depending on which surface you place them on, they might not be parallel to the axis in which case,

symmetry building makes them face slightly towards (or away from) each other, with wobbly results.

However, I want to place my wheels where i want to and not only on X parallel surfaces.

 

Cure: Draw a mental axis from the nose to the tail of the plane and use the rotate tool (summetry on)

on one of the wheels. You need to make sure that the Orange axis on the rotate sphere is parallel to your

nose-tail axis. Your wheels should now have 0 degree angle between them, meaning they are both

pointing straight - forward.

 

[ForScience6686]

After placing wheels I always use the rotate gizmo on snap with absolute orientation.  That will align with the craft axis.  Beyond that, you're going to get some wobble once you get close to take off speed.  As lift increases you remove some strain on the gear, however you've just increased the amount of sag.  So if I start encountering wobble it's time to pull back on the stick and get in the air.  I see absolutely no need to be traveling that fast down the runway.  You're going to have a bad time.  You want to get up to get the gear tucked away and reduce drag.  200 m/s runway stability just doesn't seem to have a worthwhile purpose to me, and is inducing counter productive engineering challenges.  Such as not producing lift, which is not what you want with a plane.  And at the extreme, producing down force, which I'm sure would cause more gear issues.