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mooffle

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Got this idea while building lego spaceships with my son one day. I figure it's time for Benny to live out his dream of flying in a real spaceship.
Power will be a C5-3, recovery is 2x 12 inch chutes, one for the booster and one for the capsure/fairing.
The paint scheme and overall shape is loosely based on the original space theme from Lego.
Hopefully he keeps his excitement until launch day!
 

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mooffle

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I left the side pods open and *could* cluster with a couple 13 mms, however I'm not fond of putting the thrust so far from the centerline. Does anyone make a delay only sort of engine for effect or would I have to pack that myself? I've never done reloadables only single use BP.
 

jqavins

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I've brought up the tracking only engine idea before, and there are some issues.
  • No one makes a certified engine like that.
  • If you make your own it has to fly under research rules, which means a Tripoli event and L2 HPR certification. Or...
  • You could fly it on your own park or yard launches, but then you're violating the safety code and losing the insurance benefits, and just generally being a naughty boy.
  • There's also the troubling possibility of a very long delay grain that's still burning when the rocket is down.
You could use 1/4A3T-3 engines, which have only 0.6 Ns impulse, 2.4 N and 5.0 N average and peak thrust, and 0.3 s burn time. As long as the central engine swamps it you shouldn't have a problem. I think. I hope.
 

mooffle

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Eh, it's not really worth it then. The Legos are heavy enough that a C has to be used, maybe some 1/4 A's after a few flights so I see how it operates.
 

mooffle

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If I had rocksim I would try, I can't get OR to handle anything this complex.
I did run a swing test with the nose on a slightly shorter rocket with similar fin area before it was built and that was promising.
I need to get some more C's to swing test it in full.
 

GlenP

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If only there was some way to alter the thrust line of the lower thrust engines in the side pods so that they point toward the cg, to compensate for the off axis thrust line, there must be some idea, but I just CANT think of one.
 

jqavins

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Off center centering rings. Let one ring, probably the forward one would be easier, be normal then offset the hole on the lower one to cant to motor. That's how motor canting is almost always done, isn't it?
 

lakeroadster

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If only there was some way to alter the thrust line of the lower thrust engines in the side pods so that they point toward the cg, to compensate for the off axis thrust line, there must be some idea, but I just CANT think of one.
Off center centering rings. Let one ring, probably the forward one would be easier, be normal then offset the hole on the lower one to cant to motor. That's how motor canting is almost always done, isn't it?
Something like this...

EOTM Sheet 7 of 7 Rev 02.jpg
 

mooffle

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The pods on this are bt-5 so to cant them now I'd have to cut them and sand the fins down. Good suggestions though, and I've never done any canted builds, scratch or kit. Maybe for my next purchase.
 

jqavins

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OK, another way would be to put a small block between the pod and the BT at the aft end.
1597071229986.png
 

mooffle

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Even though the rocket portion of this build is done i was looking at the Lego pod, should I be concerned with the underside being 'holey' and causing the rocket to divert? And then there also holes in the front that I'm similarly worried about. Any ideas on filling them? I tried wood glue but that's a lot to fillet, balsa inserts become too weak for me at this scale.
 

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neil_w

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Neither will be a big problem, but both will certainly increase drag.

For the front, I would just try to use some clear tape to cover the holes. From the pics it seems like that could work.

For the underside, it's a little iffier. I would try laminating a piece of cardstock under there, but you really need to make sure that the leading edges are well sealed so it won't peel back in flight. Clear tape could work again.

Nice thing about tape and cardstock is that it's not permanent, you can experiment and see if it looks like it's gonna work without committing anything.
 

GlenP

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You could use some peel and stick label paper. Maybe even print some designs on it to add to the decoration of the model around the front edge to lock down the canopy and wrap around the bottom to cover the lego dot receptables. You could try like a simple lightweight spackle but I don't think that would stick to the plastic and it would just peel off.
 
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Funkworks

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I’m no LEGO expert but I’m pretty sure they are some master builders out there who could make a smooth surface cockpit using only LEGO bricks. Many new parts have been released in the last decades.

If I didn’t have so many projects already going on, it’s a challenge I’d enjoy.
 

mooffle

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I’m no LEGO expert but I’m pretty sure they are some master builders out there who could make a smooth surface cockpit using only LEGO bricks. Many new parts have been released in the last decades.
I was playing with some different designs, most of the Lego windshields hinge from the back or don't have the studs like the one pictured for enough grabiness of the parts. Of two hinge designs I swing tested one flew open and the other shattered.
I didn't try to make it smooth though, I suspect it would lose structural integrity trying to smooth the bottom but it's worth a shot.
 

jqavins

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As a kid, did you ever get your plasticine modeling clay stuck in your Lego pieces? That stuff is a real bugger to get out. So if you don't mind the weight and want a nice smooth surface that won't peel away, you could fill the whole bottom with clay then smooth it out with a hotel key, credit card, or such.

Lego pieces are made of ABS, and one can make a chemical weld with acetone. Soaking card stock with acetone before applying it might work, but of course I've never tried it. If it sounds like a possibility you might like, try it first on a sacrificial brick.
 

Funkworks

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I was playing with some different designs, most of the Lego windshields hinge from the back or don't have the studs like the one pictured for enough grabiness of the parts. Of two hinge designs I swing tested one flew open and the other shattered.
I didn't try to make it smooth though, I suspect it would lose structural integrity trying to smooth the bottom but it's worth a shot.
Kra... Gl..e?
(Probably not)
 

mooffle

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After much R&D and design prototyping (read: playing with lego) trying to make a cockpit studless at this scale and still retain structural integrity is close to impossible. That is the only windshield I have that will stretch all the way from the front to the back and not require any other pieces to retain it, along with being the same height as a BT-50. Not to mention having as few of those stud holes in the front as possible.

Clear plastic tape seems to be the way to go and will almost certainly be the end covering.

Kra... Gl..e?
(Probably not)
I'm trying to retain as much playability with the design so after real airtime my son can strap the capsule to some lego boosters.

C5-3's get here this week, hopefully not long after I'll have some flight results.
 

BABAR

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C5-3's get here this week, hopefully not long after I'll have some flight results.
Launched my first rocket on a C5-3 this past weekend. GREAT motor!
 

GlenP

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Launched my first rocket on a C5-3 this past weekend. GREAT motor!
If you are a BAR, BABAR, then are you sure that was your first C5-3?

Or do you mean your first of the recently reissued C5-3s? :)
 

BABAR

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If you are a BAR, BABAR, then are you sure that was your first C5-3?

Or do you mean your first of the recently reissued C5-3s? :)
To the best of my knowledge. Of course, my memory now isn't as good as it never was;)
 

mooffle

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C5-3's came in today (thanks, jonrocket.com :D) and I just did a swing test. The spaceship! seems over stable but not as much as I would have expected, I did swing it twice both ventral and dorsal sides out with the same results. My worries about the underside catching air doesn't seem super relevant.

Side note: the C5 plugs are blue and say B8/C5. I didn't even know there was a B8 and I can't find much info on it. Is this an old plug mold or another new engine?
 

jqavins

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Did you test it sideways, i.e. either ventral or dorsal side up?
 

jqavins

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I'm not sure, but yes, I think so. Also, by testing dorsal away and ventral away, either way you've got the pitch axis horizontal and the yaw axis vertical. What I'm suggesting reverses those, and that seems like a good idea. I'm not so sure even that is necessary - after all, unstable is unstable in any direction. But it is more different from what you've done that the two tests you've done are from each other.
 
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