Drop rocket from wing?

[dafidge9898]

How would one go about doing a Pegasus style launch? You know, dropping the rocket from the wing of an airplane, igniting the engines, etc. When I would try to mount the rocket under a wing, I would always run into some complications, whether it be explosions during separation or the part just not wanting to stick on properly. Do I make the rocket in a subassembly or merge two craft files? I'm essentially clueless on how to make this work, yet it seems so simple. 

[Spricigo]

How fast and high you are when decoupling? Horizontal flight or climbing? Are you using any mod?  

Also a few screenshots would really help people to visually what your problem is. 

 

 

[Streetwind]

There two parts specifically designed to allow you to attach things to wings that are meant to be decoupled later-on. They are called "small hardpoint" and "structural pylon". Perhaps you'll have more success with these than with traditional decouplers.

Of course, if your rocket is simply too large and heavy, it'll need struts to stay still during flight. Struts automatically vanish when you decouple, so they shouldn't get in the way of that.

[Palaceviking]

I would also recommend the hydraulic decouplers to limit the amount of unplanned disassembly.

[Geschosskopf]

6 hours ago, dafidge9898 said:

How would one go about doing a Pegasus style launch? 

Well, to start with, I've never gotten the whole "merge" thing to work right so I use regular subassemblies instead.  The whole process would go like this:

1.  Build the Pegasus by Itself
Design and build this in the SPH as if it's the only thing you're going to build.  This will eventually become a subassembly.

2.  Attach a Hardpoint to the Pegasus
Put this on top of the CoL of the Pegasus so the aerodynamic loads of the Pegasus don't try to twist it off.  The hardpoint will separate between itself and the Pegasus leaving no residue on the Pegasus.  It blocks crossfeed so the Pegasus will have full tanks when dropped, and it has an ejection force to toss the Pegasus clear.

3.  Create the Pegasus Subassembly
Attach any other part (such as a small box girder) to the top of the hardpoint opposite the Pegasus.  This extra part is just to facilitate making the subassembly so it doesn't matter what it is.  Now use the re-root tool to make this extra part the root of the Pegasus.  Open the subassembly creation page in the editor.  Now grab the hardpoint and pull it and the whole Pegasus below it off the extra part.  Drag this assembly over to the subassembly creation box and save it.  The Pegasus subassembly is now complete.

4.  Build the Carrier Plane
Start a new ship and build the carrier plane (or open a pre-existing plane).  

5.  Attach Pegasus to Carrier Plane
Open the subassembly tab, select the Pegasus subassembly, and attach it under the wing of the carrier plane.  The subassembly will be able to attach to the carrier plane only by the top end of the hardpoint (thanks to the re-rooting done above).  Attach the subassembly under the wing.  This will add the hardpoint's decoupler and the Pegasus' engine to the staging menu of the carrier.  Move these as needed so they don't conflict with the engines of the carrier plane.  I would recommend putting the hardpoint and the Pegasus engine together in the same stage, separate from and above the stage with the carrier engines.

6.  Save the Combined Carrier/Pegasus
Don't do any merging.  Just save the whole thing as you normally would.

7.  Conducting the Mission
Launch the combined thing.  When you get to the speed and altitude you want, hit SPACE to stage the Pegasus and fire its engine.  The Pegasus should detach cleanly and go flying off.  Quickly use [ or ] to switch to the Pegasus so you can control it.

[bewing]

2 hours ago, Geschosskopf said:

 

7.  Conducting the Mission
Launch the combined thing.  When you get to the speed and altitude you want, hit SPACE to stage the Pegasus and fire its engine.  The Pegasus should detach cleanly and go flying off.  Quickly use [ or ] to switch to the Pegasus so you can control it.

7b. And accept the fact that your carrier plane is going to get autodeleted as soon as the Pegasus is out of range. So make sure it's robotic.

[Geschosskopf]

3 minutes ago, bewing said:

7b. And accept the fact that your carrier plane is going to get autodeleted as soon as the Pegasus is out of range. So make sure it's robotic.

Yeah, important safety tip.....

Hmm, if you have the Stage Recovery mod, would that work on the carrier plane once you switch to the Pegasus?

[bewing]

2 minutes ago, Geschosskopf said:

Yeah, important safety tip.....

Hmm, if you have the Stage Recovery mod, would that work on the carrier plane once you switch to the Pegasus?

Yes, there are several mods that allow for the recovery of the carrier ship -- but not stock.

[magnemoe]

Also note that the Pegasus is fairly light compared to the carrier plane. if its an 1/4 of total mass or more you will have problems and is probably better of with an stratolauncher design

[Foxster]

I'd say though that it's only worth doing for the fun of designing it and making it work. It will likely be a bit of a pig to fly, the separation is fraught and keeping the dropped craft on-track for orbit is tricky. In KSP there is no advantage in doing this. You'll make a better craft with a small rocket on top of a jet-powered lifter launched vertically. 

Here's a Mun-return capable craft I was messing with the other day. Got it to work in the end but it wasn't worth the bother really. 

[foamyesque]

I like sticking a Mk2 rocketplane inside a Mk3 cargobay. Fun times.