Spaceplane: slightly broken?

[biggles1]

So I'm working on making a spaceplane for a personal challenge between a friend and I, and I have it working well. It's pretty stable in flight, gets up to great speeds and such.

I only have 1 problem. On launch, it tends to veer sharply to the right when going over ~60-70 m/s for no apparent reason, and often crashes as a result.

Can anyone help? Mechjeb can't control it either.

Version 1: https://www.dropbox.com/s/x3elnv6p5dzew9i/Atlantis.craft

Version 2 with more tail fins and droptanks: https://www.dropbox.com/s/lt63mhotqhxske4/Atlantis%20mk%203.craft

If anyone can tell me what i'm doing wrong or even upload a working .craft I'd greatly appreciate it. I don't usually make spaceplanes

[Shrike42]

Assuming you mean that you haven't lifted off yet, veering on the runway usually means that your wheels are probably not exactly straight/symmetrical.

[Naf5000]

Due to extremely poor internet, I can't download the craft file. However, I have had similar issues, and I can offer a couple of suggestions. First, move the center of lift further back. One of the buttons in the bottom left of the SPH/VAB lets you see it, in case you were unaware. Second, make sure there are some control surfaces on the front. A pair of winglets can be the difference between an acrobatic plane and a pile of rubble.

[biggles1]

I can lift off (sometimes) only after veering massively to the right off the edge of the runway and pulling up quickly. Sometimes the plane flips and crashes, other times it just about lifts off.

I have readjusted the wheels a couple of times to make them symmetrical and I can't seem to see anything off centre.

[derkaderka]

Experienced SSTO spaceplane builder here. The issue is often caused by the plane getting lifted, just not enough, and in asymetrical places. This causes uneven-ness in load to the landing gear, causing a cornering effect. As this continues, the lift surfaces naturally curve the spaceplane into a roll and kersplat.

A quick fix to this is to have the front gear slightly higher than the rear gear. This makes the entire spacecraft point down a few degrees. Since KSP uses angle of attack to simulate lift, this creates downforce and lots of contact and stability with the ground. Also in my experience angled landing gear (like an upside down V) can do this, so maybe keep them upright.

As to what NAF says, front canards aren't always necessary and IMO lead to more flip-outs then they're worth. A streamlined design with all control surfaces at the back likes to weather-vane into the direction of travel. They do provide alot of lift during take-off tho, so its a trade-off. If you're having trouble lifting off, try moving the control surfaces as far back from the gear as possible, and moving the gear to right behind the COM.

[Rdivine]

I've always had this irritating problem too.

1. At liftoff, the plane sways wildly even before takeoff. I tried everything i could.

2. Using will cause the same problem. However, using the less-powerful engine does not cause any problem. I tried putting struts and stuff.

I've also readjusted the wheels a couple of times and it did not work. The engine problem, maybe?

[biggles1]

The problem isn't lifting off, it's not veering into the ground before I can lift off

I'll try the higher Gear fix now and see if it works.

I'm doing better than my friend though, he's on a Mk 12 design and hasn't made it to orbit yet, and I made it with a mark 3 design

[biggles1]

Ok neither winglets at the nose (delayed the super hard turn by a few seconds) nor a lowered nose gear worked.

[derkaderka]

Not on KSP-ready machine. Can you attach a JPG of your craft on runway? Also a pic of your COM and COL in the VAB BBQ. Also try struts. Struts to landing gear. Struts to everywhere.

[biggles1]

What's the COM and COL?

[derkaderka]

Oh. Center of Mass and Center of Lift. They are the buttons near symmetry and snap. You use the symmetry button right?

[biggles1]

Here's a link to the album of screenshots I took.

http://s1112.photobucket.com/user/biggles1994/library/KSP_atlantis_problems

This is the slightly updated mk 6 with the droptanks further off the ground.

Edited May 30, 2013 by biggles1

[biggles1]

Oh. Center of Mass and Center of Lift. They are the buttons near symmetry and snap. You use the symmetry button right?

Yeah of course. I'll take a pic of the COM and COL and add it to the photobucket album in a moment.

[biggles1]

Photos including COM and COL have been added.

http://s1112.photobucket.com/user/biggles1994/library/KSP_atlantis_problems

[derkaderka]

Ah yes. I feex.

First off, for hyper-sonic planes it is a good idea to have the center of lift slightly behind your center of mass. You might already know that and when you drop those tanks I suppose the COM moves forwards.

Secondly the crashing on the runway might be because the gear are wobbley. Thanks to ksp physics, parts that are attached to parts that are attached to parts are wobbley. Look at how many things are attached to other things, you should visibly see some wobble. Try adding struts from the gear to the main belly parts or at least to something it's not already attached to. If that fails, redesign so that the gear are less wobbley.

Edit: yeah I can definetly see how much the plane saggs in the middle. That ain't good while you're on the ground. add spacetape

[derkaderka]

Also don't fear. Spaceplanes and ESPECIALLY SSTO's are infuriating but extremely rewarding once you get it down.

[sauliukas]

When I was building the space planes with drop tanks, I had similar problems. The steering is caused by landing gear wobling. Moving drop tanks on top and attaching to centre column gives more stability. In that way you won't need the extension for landing gear, so you will be able to attach landing gear straight to fuel tanks. You can secure the fuel tanks with struts to centre too, for more stability.

[biggles1]

Struts worked! It's now about as stable as can be

Struts clearly are the Kerbals best equipment. Thanks!