Help with Dreamchaser

[ZentroCatson]

So, I am recently working on this thing, a Dreamchaser-style crew ferry. Here it is, in the VAB:

http://imgur.com/a/Ih3yr#0

Looks good, right? (I know, it looks like crap.) It's an accurate replica of the Dreamchaser, it is even a lifting body . The spaceplane part of it flies really well, but with the booster attached, it isn't flyable at all. It flips out of control if you want to do a gravity turn. So, I want to hear your ideas about how to make it aerodynamically stable. Here are some pics of it in flight:

http://imgur.com/a/2F2fR#0

If I can fix those aerodynamic problems, I will make a stock-only version as a kind of giveaway for your help. A big thank you, if you consider helping me anyway !

Edited May 20, 2015 by ZentroCatson
fixed the problem

[SmallFatFetus]

Its because your center of lift is in front of your center of mass. If you look at an rocket plane, they're all either in fairings or they have bigger wings at the base.

[ZentroCatson]

Its because your center of lift is in front of your center of mass. If you look at an rocket plane, they're all either in fairings or they have bigger wings at the base.

I have tried out moving the center of mass even farther behind, it didn't really work. I used elevons, the game did tell me that the center of lift is behind the center of mass. Maybe I should try bigger wings or MOAR boosters. Btw, thanks for the quick answer!

[Prepper-Jack]

Try throwing a bunch of tail fins on the bottom?

[JTpopcorn]

You want the center of drag in the back. Also try to make a very shallow gravity turn and keep close to the prograde until out of atmosphere.

Put fins on the rocket as low as possible.

[Snark]

I have tried out moving the center of mass even farther behind, it didn't really work.

Should be the opposite-- you want your center of mass as far forward as possible, so that it's in front of the center of lift and the center of drag. (Bearing in mind that center of drag isn't visible in VAB.)

As JTpopcorn suggested, put fins at the bottom of your rocket, as far down as possible (i.e. not on the spaceplane part-- on the booster part). For even more stability, use something like the Delta Deluxe Winglet, which can actively steer to assist SAS, rather than just passive fins.

[Slam_Jones]

Unless I'm mistaken, it looks like you have no fins of any sort near the bottom of the booster. You may want to consider putting some there.

Generally, you want your center of lift pretty far back, and the way your ship is set-up currently, it's pretty far forward. This means it wants to flip 180 degrees, so that the CoL is further near the back.

I recommend putting fins in 4 or 8- symmetry on the very bottom of your booster. If you put too many, it will be a lot harder to do your gravity turn, but that's a much smaller problem than flipping around. Try a few different set-ups til you get it just how you like it.

Hope this helps!

[icedown]

I'd try the deluxe delta winglet. It's big enough to help keep the craft straight but the control surface isn't very big so the rocket won't be very twitchy.

[Foxster]

I was making a space plane recently and nothing I tried got it to orbit. I tried all the above ideas and more and the lift sections of the space plane on top always made it flip out.

Ended up putting the plane behind a big fairing and all was good, even though it was a lot of extra mass and drag.

[Cebi]

Been there, done that. Mk2 lift properties (even without wings) on the top of rocket will produce huge force that will flip you every time. Simple solution is to put plane inside fairing and add more fuel to compensate for added weight.

[Randazzo]

Launching with such a substantial lifting body on top of your rocket is going to require a LOT of tail fins. Have you considered a more "traditional" shuttle approach? It has it's own set of difficulties though, such as getting all the angles and thrust levels right (particularly since you can't throttle engines individually).

As the SRB's get near the end of their fuel, their TWR goes up and induces a gravity turn. Of course, this was in the 0.90 aero model. It might be disastrous in 1.0+.

A much simpler solution would just be to put fairings around it, if they'll fit. Still add some fins near the bottom.

Edited May 20, 2015 by Randazzo

[Dodgey]

You could always try my idea, I've found it to be pretty stable.

[magnemoe]

Been there, done that. Mk2 lift properties (even without wings) on the top of rocket will produce huge force that will flip you every time. Simple solution is to put plane inside fairing and add more fuel to compensate for added weight.

How about wings on the interstage who offset the wings and lifting body on the dreamchaser.

Else use an fairing like the real one does.

[ZentroCatson]

I'm actually having elevons at the back of the spacecraft. I don't really want to put it inside a fairing, but if nothing else works, I will consider putting it inside a fairing.

[ZentroCatson]

Guys, it finally works!!!

Imgur Link

I put some delta wings, elevons and strakes onto it, and it flies like a dream! Thanks for all your replies guys, now I will make a stock Dreamchaser and upload it to KerbalX.

[SlabGizor117]

In case the CoL-CoM thing is confusing you as far as the physics of it, think about an arrow. All the feathers are in the back, which puts the center of lift in the back. The farther back the CoL is, the more stable the aircraft or rocket, or arrow, will be. The farther forward, it will be less stable, but more maneuverable. Like shooting an arrow with the feathers on the front, any deviation of the arrow's orientation from it's direction of motion, the feathers on the front will catch the air like a sail and flip it around. I don't know how the real Dreamchaser does it without an absurd amount of wings on it, but at least in KSP you're gonna have to do it that way.

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Also, congrats on getting it to work!