Why do my space planes always unstable?

[Narrov]

It doesnt seem to matter how I build my space planes they are always unstable. Most of the time they never get off the ground. I've tried everything I can think of.

I'm pretty much a noob to all this so go easy on me. I've put my latest attempt in the link below. Please help.

Narrov

Link

http://db.tt/ieefmv6n

[SoldierHair]

Going to test it now , but my game will take a few good minutes to load (too many mods).

At this point i will asume your center of mass is far from your center of lift.They should be in the same spot , the lift can be a little forward though.

[SoldierHair]

It says it is not compatible with my version.

[Rickenbacker]

I tried your plane, and I think it simply doesn't have enough lift. By using the rockets from the start, I got it off the ground, and flying OK. But you probably want to fly on the jet for a while, and this plane simply won't stay up with the jet alone.

Also, make sure your main landing gear is straight! It's currently tilted, which makes the plane very squirrelly on the ground. Straighten it (By using shift and the WASD keys to rotate it until it's straight up and down) and you'll have a much easier ground run. But I think this plane needs less weight or more wings!

Oh, and the center of lift should NEVER be in front of the center of mass. Nose heavy planes are a little annyoing to fly, tail heavy planes are impossible to fly.

Edited June 9, 2013 by Rickenbacker

[Klajan]

There are some things, that can make your (Space)plane unstable. I will do a short list:

1: Center of mass is not aligned with center fo Lift.

2: Sloppy placed center of mass (Actualy, your center of mass is shifting heavily while you drain fuel) Simple fix: TAC Fuel Balancer

3: Not enough control surfaces

4: To many conrol surfaces

5: Gearbay is placed to far in the rear, so your Plane can not push its tail down to get some angle of attack. Fix: try to place your rear gearbay a bit closer to your center, also try to place teh front gearbay elevated, so your Plane is already angle a bit.

6: A lot of thing I have not mentioned, ranging from Engines Placed in front of the COM, to not enough Lift or TWR.

[Motokid600]

How do you guys deal with a huge shift in weight? How do you plan for it? I have this great SSTO. It can climb up too 100k with ease and dock with my station. The problem is getting back. I'm using B9 and I have 3 mono tanks up front just after the command pod. So when I go to drain the tanks ( fueling the station with mono ). My center of mass shifts to the rear behind my SoL. All is fine until after reentry. The plane wants to pitch up. So if I give it too much input or it travels to far from prograde... It does backflips and I go into a yawrates. So.. how can I counter this? What can I change to make reentry stable, but at the same time preserve its awesome ascent stability?

[Klajan]

That is the most dificult task you ahve to deal with while building an SSTO Spaceplane. You usualy have two options for this. Either you accout for this while you build your plane or you balance the fuel during flight. The best way of doing the latter is the TAC fuel balancer Plugin

I usualy try to balance it in the SPH, but I USe the fuel balancer, since it will help a lot, especaly if you try to build "realistic" Spaceplanes, with the fuel in tanks spread along your plane.

[Nibb31]

Planes are unstable because aerodynamics don't work yet. There really is no point in bothering with spaceplanes until KSP has a semi-realistic flight model.

[Motokid600]

That is the most dificult task you ahve to deal with while building an SSTO Spaceplane. You usualy have two options for this. Either you accout for this while you build your plane or you balance the fuel during flight. The best way of doing the latter is the TAC fuel balancer Plugin

I usualy try to balance it in the SPH, but I USe the fuel balancer, since it will help a lot, especaly if you try to build "realistic" Spaceplanes, with the fuel in tanks spread along your plane.

That plugin would be nice, but the plane only has one tank.

[Klajan]

This is actualy nice to balance then. You should try to balance every tank around your center fo mass. So for example you place one rcs tank infront and one behind the fueltank, which is the center of mass. this way your COM does not shift if you use fuel.

I have build this little plane.

Note the little black box. This is where the COM is located. Both full and empty. I also have this Fueltank as the rootpart of the craft, this makes it easier to balance the Plane. But it will be unbalanced if there is only some fuel consumed, so I have to use the fuel balancer Plugin.

[feudalord]

I found the problem to be caused by the pitch of the plane during take off. If your plane is tilted slightly up or down, the aerodynamics in this game will cause your plane to wobble during take off. I am not sure why, but putting your plane perfectly horizontal during take off will make your plane stable on the runway. However, if you prematurely start pitching up the nose of your plane before it has reached sufficient take off speed, it will also wobble.

If your plane do not take off on the runway even at high speed, it could be due to the position of your rear landing gear being placed further behind than your elevon, which means even if you pitch up your elevon, the downward force will not provide a moment to pitch up the nose of your plane about the pivot which is your rear landing gear. I didnt know this until I came cross a tutorial by Scott Manley.

[vexx32]

This thread is quite old, and it's very unlikely to still be relevant. Please check the date of the last post before posting -- if the thread is more than a few months old, it's better to let it rest quietly unless there's a pressing need to resurrect it.

Closing this for now...