Trolley-launched aircraft

[Matt77]

I was just having a play in the SPH and found that I can't build this.  I want to mount the tri-wing probe on the trolley, so when it reaches takeoff speed I can separate from the trolley and fly away...  I've done similar before, but I used the "SelectRoot" mod, which doesn't seem to be available any more.  I can't get it to work with the stock re-root function.

A couple of pics of the trolley and the aircraft:

It actually flies quite nicely for a thrown-together mess.  Note the front fuel tank is empty for balance, not sure how it will fly as the fuel runs out...

Just for fun, I know there are much easier ways to launch a probe core.

[moogoob]

Have you tried re-building the trolley? When I built mine, I just built it in order, like any other rocket - mini probe jet first, then built the trolley off of it.

OR! Is the issue the decoupler? Have you tried putting the decoupler on the other side, the jet probe?

[cantab]

You can't make a radial decoupler a root part.

I think what I'd do is use cubic octags on both parts, and join with a stack separator.

[bewing]

And the precise problem is that you can't get them to stick together? I think it's doable, but you may need to do it in the VAB. (BTW, I agree that the decoupler should be on the probe.)

[Matt77]

Sorry for the slow reply, I think my notifications are off.

Yes, I was unable to stick the two vehicles together, but @cantab jogged my memory by mentioning cubic octagonals so now I've got a proof of concept.  I wanted the decoupler on the trolley so as to leave as much behind as possible, but it did not work - even using "Control from here" on the fliers' probe core, focus switches to the trolley on separation.  You need the decoupler on the probe, and a cubic octagonal on the decoupler.  Make the cube Root, then you can attach the probe to the trolley.  I used the Offset tool to hide the cubic inside an octagonal.

I've been able to launch the thing, but no real flight as yet, the trolley starts to wobble a lot before the probe has enough speed to launch.

 

Edited June 1, 2016 by Matt77

[bewing]

Set the friction to zero on all the wheels to help with wobbling.

[Matt77]

32 minutes ago, bewing said:

Set the friction to zero on all the wheels to help with wobbling.

That worked, thankyou.  It felt a bit cheaty but I got a nice clean launch even from the dirt runway.  But now I know how to build it I can redesign something more practical...  or not!

[RocketSquid]

1 hour ago, Matt77 said:

That worked, thankyou.  It felt a bit cheaty but I got a nice clean launch even from the dirt runway.  But now I know how to build it I can redesign something more practical...  or not!

By "more practical" I hope you mean "with more SRBs". Rocket sleds are fun, if not totally cost effective.