Spaceplanes

[Kerbalsaurus]

I'm having an issue with this. I've been trying to design a spaceplane in a style similar to the ESA's Hermes concept, or the more modern Dream Chaser concept by NASA. But here's the thing: it keeps flipping over! I've tried airbrakes on the side, fins, RCS, and a billion SAS units and it still wants to flip. How can I combat the force.

[darthgently]

13 minutes ago, Kerbalsaurus said:

I'm having an issue with this. I've been trying to design a spaceplane in a style similar to the ESA's Hermes concept, or the more modern Dream Chaser concept by NASA. But here's the thing: it keeps flipping over! I've tried airbrakes on the side, fins, RCS, and a billion SAS units and it still wants to flip. How can I combat the force.

It probably needs more mass up front than in back and/or more drag in back than front.  The Dream Chaser -ish shape should give you the lift and drag you want so maybe you need to move all remaining fuel to forward tanks or something.  Knowing KSP, the mass of the engine at the aft end is what is likely throwing off your center of mass.  You want it to weathercock like a badminton birdie

[Martian Emigrant]

Hi @Kerbalsaurus

I assume you are talking about a spaceplane on top of a rocket stack and not one taking off horizontally.

The wings are developing lift (At the very top) as the stack accelerate. Said lift is overpowering the control fins of the rocket.

You need to enclose your spaceplanes in fairings

or install huge control surfaces on the bottom of the rocket

or (depends on the spaceplane itself) climb verticaly and slowly until you are out the lower (And mid) atmosphere.

 

ME

Edited April 11, 2023 by Martian Emigrant

[Gargamel]

Moved to Gameplay Questions 

[jimmymcgoochie]

If it flips during ascent: BIG fins on the bottom of the rocket and lock the spaceplane’s control surfaces if possible.

If it flips while flying as a plane: check that the CoM is always in front of the CoL no matter how much fuel is in the tanks.

In both cases you want the drag towards the back of the vessel and mass towards the front, like a shuttlecock or a dart, as this will make it much more stable.

[Kerbalsaurus]

So, should I maybe add Airbrakes at the bottom of the rocket? That's should increase surface area, and thus drag.

[18Watt]

2 hours ago, Kerbalsaurus said:

So, should I maybe add Airbrakes at the bottom of the rocket?

No, don't use airbrakes.  That might work, but it's not the ideal way to correct your problem.

What you want are big fins at the bottom of the rocket.  Or just more fins will accomplish the same thing.

Drag is not the issue- to be more precise it is the location of the COL (Center of Lift).  You want the COL behind the COM (or under the COM for vertical rockets).  You are not really adding drag, but rather changing the location of the COL by adding fins.  Yes, fins will also add some drag, but not much.

Airbrakes will add a lot of drag, but will not make as much of a difference to your rocket's COL location- so I would not use airbrakes to correct that particular problem.

[jimmymcgoochie]

11 hours ago, Kerbalsaurus said:

So, should I maybe add Airbrakes at the bottom of the rocket? That's should increase surface area, and thus drag.

It might work, but it’ll add a lot of drag and cost you a lot of delta-V. Fins with control surfaces are the better choice. You could also try adding some small vernier engines e.g. Twitch or Making History’s Cub, or Thuds for a larger rocket, which would give you more control and a bit more thrust at the cost of reduced fuel efficiency (just turn them off in the upper atmosphere), but would still be a good idea to add fins too.