SSTO keeps curving as soon as I launch?

[WaitingCynicism]

Hi all,

 

I was using mark thrimms SSTO video for 1.3, and it's mostly stable once it's in the air, yet on the runway it curves even if I don't have engines enabled. How would I go about fixing this?

[bewing]

Veering left on the runway is a fairly common problem for SSTOs and airplanes. There are actually many things that can cause the same issue -- and each of those things can have a different solution.

However, as far as I have seen, the most common problem that causes veering is "too much drag/friction at the front of the craft, and too little at the back of the craft for it to be stable." Everyone who plays this game ends up being taught this lesson about aerodynamic stability for rockets from the school of hard knocks. But it is also true when you are on the ground. If a rover has too much friction with the ground at the front end, and not enough at the back -- then the rover will try to flip ends. An airplane on the ground is a rover. When your rover/airplane is trying to flip around backwards on the ground, it always veers left to do so, because of the way the game engine works.

So, how do you fix it? Very very simple. In the editor you open the context menu for the front wheel/wheels. You click the button to change from Auto friction to Manual friction. Depending on how bad the plane is veering, you manually set the friction to somewhere between 0.0 and 0.6. It's better to start at .6 and work your way down. If you want even more stability, you can do the same to your rear wheels and move their friction up to 1.2 or 1.4.

 

[Klapaucius]

4 hours ago, WaitingCynicism said:

Hi all,

 

I was using mark thrimms SSTO video for 1.3, and it's mostly stable once it's in the air, yet on the runway it curves even if I don't have engines enabled. How would I go about fixing this?

Without the craft file I cannot say for sure, but a few things that have helped me:

1. Doublecheck your front gear is absolutely straight.  A hair of a degree of twist will mess you up.

2.  (as @bewing mentioned above), check your friction control. I generally set the rear to full and set the front to maybe 1/4 to 1/3 (not sure at the moment what exact number that corresponds to).

3. If you are using steerable gear, make sure the steering is disabled for the rear gear.

 

I don't know if any of these things are your issue, but they are all things I check when having this problem.

Edited June 30, 2019 by Klapaucius

[Daniel Prates]

What @bewing said.

However to acheive the same result, that is, less drag on front wheels, also consider this two things that are the main suspects on airplanes that misbehave on the runway:

1. Most of the weight has to be deposited on top of your main, non-steerimg gears. The remainig, steering gear (be it a nose or tailwheel) need to have only the little remaining weight pressing on it. So try moving the main gears foward or backwards as to almost coincide with your CoM.

2. Check the CoT. Is it passing below or above the CoM? If above, the nose is being pushed downwards. Move something around to make it pass exactly through the CoM, or a little below it.

[Aegolius13]

17 minutes ago, Klapaucius said:

1. Doublecheck your front gear is absolutely straight.  A hair of a degree of twist will mess you up.

I would add to use "absolute" mode when you adjust the landing gear, and make sure to check all three axes.  Sometimes they look straight, but aren't actually when put to the test.

[Daniel Prates]

All this talk about wheel drag is correct, of course, and I am not judging, but if you have to resort to tweaking wheel drag, probably it is something else that needs redesigning - mostly, where the wheels go; if thrust forces are pushing your nose down; and where the weight is deposited upon in relation to the wheels.

I never feel the need to fiddle with wheel drag because I always mind those things. To be fair, the only thing I do is to remove break power from the nose wheel - for the same reasons: it will force your nose down.

Again, I dont judge fiddling with wheel drag. Maybe your design is as it is for a reason, and you cant really change it a lot. Many a plane in history were designed consciently with design flaws because it simply had to be as is. But if you are doing that, it is a sign that something is wrong elsewhere, and that flaw may manifest itself in other moments, not just on the runway.

[Guest]

there are so many things that you really just have to get experienced with building them. even suspension settings on some landing gear being at a default setting can cause it. 

[WaitingCynicism]

I got it figured out, just re-positioned all the landing gear.