Re-entering atmosphere's is really hard... (and another thing)

[Andrezado]

Well, every time I re-enter any atmosphere and want to face retrograde (so my heatshield faces the re-entry flames, and I know there are no damage yet, but I want pretty re-entries ) my spacecraft starts to spin around like crazy, it doesn't matter if I put ASAS, RCS, winglets, NOTHING works. Help, please? And also, there's another thing; how the hell do I even make VTOL's? I have no clue how to make them, every try I do, it doesn't works.

[gmpd2000]

Maybe the craft is aerodynamicly unbalanced? so the most aerodynamic spot points prograde?

Also, For VTOL's, make the center of mass and center of thrust crosses each other while the CoT points Down

and use Danmed Robotics for making the engine rotate.

[Andrezado]

So what can I do to balance the craft? And thanks for the tip on VTOL's!

[stupid_chris]

So what can I do to balance the craft? And thanks for the tip on VTOL's!

Make it as symetrical as you can. Maybe a picture of the said craft would help identify the issue pretty quickly ^^

[masTerTorch]

So what can I do to balance the craft? And thanks for the tip on VTOL's!

If it is a spaceplane, make sure that you shift your fuel in the front of the plane. So that your center of mass is before your center of lift. You have to adjust this before reentry.

[Blackbird]

So what can I do to balance the craft?

if it's a biger craft with winglets or other lift, the center of mass is normaly ahead of the center of lift at reentry, so if you point your craft retrograde it should look like this:

way of movement ---> [< center of lift -- center of mass <] --> way of movement

symetry can be a problem, too. Your craft starts to spin if there is more drag on one side as on the other.

hope that helps somehow.

-BB.

[Klajan]

I don´t know why this happens, but I have this often. To me it seems KSP likes to pull your COM Prograde in any atmosphere. At least thats what happens to everything I deorbit. My engines go first then my heatshield.

[Scrogdog]

Yeah, space planes are a whole 'nother matter, but I have no issues using the stock one-man or three-man capsules. I suppose it goes without saying, but just in case , there is no need to 'junk up' your capsule. The only thing it should have is a chute in my opinion, everything else goes on the service module you create. Typically I would seek to re-enter with only the capsule and chute, all else is discarded with the service module.

In that scenario, the capsule has no particular tendency to seek a particular orientation that I can see. In fact, the craft stays by itself in retrograde as the re-entry effects occur.

[Blackbird]

So I have made some testing and found a solution of the problem. here are some pictures to explain everything I have found out so far:

if it's a biger craft with winglets or other lift, the center of mass is normaly ahead of the center of lift at reentry, so if you point your craft retrograde it should look like this:

way of movement ---> [< center of lift -- center of mass <] --> way of movement

symetry can be a problem, too. Your craft starts to spin if there is more drag on one side as on the other.

hope that helps somehow.

-BB.

tested this and it seems to work that way. however, if you don't have any winglets on your craft there is another rule that works pretty well for me.

You take your craft and draw a line trough half of the craft (in lenght). The one half in wich the Center of gravity lies is also the half that points towards your way of movement while reentering:

I used hyperedit to put it into the atmosphere so i dont loose fuel and the COM shifts. Pointed it upwards to see wich way it turns:

The COM turns towards your prograde, wich makes some sense (thinking about physics) :

I don't know how your craft looks like, but i asume that the problem is your center of mass being to close to the rear (to your engines) rather than the other side, since your tanks are drained/empty and your engine is probably to heavy to keep the center of mass inside the other half of your craft.

Edited May 22, 2013 by Blackbird