An "R"-powered rocket build

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Rail Dawg said:
Definitely the way to go but like you said for single-use hard to justify. Am thinking of getting a dowel that will fit into the drill chuck and cut a slit in it. See if that will do the trick.

Got a couple days here where I can do some build will find out if it works.

Chuck C.
Click to expand...

Chuck,

I think the dowel will be prone to breaking, under a side-load ( be careful ) . . . My choice would be a 3ft. long piece of 3/8" all-thread ( 1/2", if you have a 1/2" drill ).

Dave F.


pirate-talk-clipart-1.gif
 
Why side load on a friction fit? Or am I misunderstanding ? A 36" piece of allthread in a drill would not be something I'd be willing to pull the trigger on..
 
Wallace said:
Why side load on a friction fit? Or am I misunderstanding ? A 36" piece of allthread in a drill would not be something I'd be willing to pull the trigger on..
Click to expand...

When the dowel gets clamped into the drill chuck and starts spinning, their will be a side-load on it as soon as the sandpaper contacts the surface of the tube. The dowel will likely fail structurally, either from the side-load or failure of the "split end" in the dowel.

With the all-thread, a variable-speed drill would used ( I have a 1350 RPM 1/2" variable speed drill, torque, not speed ). The all -thread is not permitted to "flop around wildly", nor is it turned at high speed. A length of SCH 40 PVC pipe is used on the all-thread, as a "hand-guide" to allow control of the long shaft ( one hand on the drill, one hand on the PVC pipe ). As with any power tool, one must be careful.

Dave F.



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Gotcha. Have you ever tried running say a die grinder with a burr in or even near an I.D. ? Or chuck up a 3 foot long chunk of threaded rod in a drill and pull the trigger? Torque is not your friend at that point. I've been hurt more times than I care to remember doing things I shouldn't have. I don't care to see it happen to anyone else. Speed and feed is key.
 
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Ok making progress. Made up a little jig to mark the 8 places on the centering rings where the birch stringers will attach.

Attached the first centering ring to the coupler. This coupler assembly will be at the lowest part of the rocket. There will be another 3/4" centering ring between this coupler assembly and the 1/4" aluminum thrust plate on the bottom of the rocket.

Picked up one of those "pole sanders" at Lowe's. It swivels length-wise and will be perfect for sanding the longer tubes.

Got all the tubes cleaned up with the lacquer thinner and will sand each tube as it is needed.

Tomorrow will begin the installation of the (8) 3/4" x 1.5" birch stringers. Will then carbon-fiber those in.

This is a 24" coupler the next one up on the rocket will be a 30" one. Will slide/glue those in once they are completed.

Chuck C.IMG_4895[1].JPG IMG_4896[1].JPG IMG_4897[1].JPG
 
Is that glued on top of the coupler? Hard to tell from the pic.
 
Yes it is. The centering ring will be sandwiched along with another centering ring between the two coupler assemblies. Add in the stringers inside the coupler and it's a very stout internal structure.

Each coupler assembly has a top and bottom centering ring.

Chuck C.
 
Ok, got it now. That's gonna be a not easy to assemble system from my point of view. Assuming you've done dry runs?
 
Wallace said:
Ok, got it now. That's gonna be a not easy to assemble system from my point of view. Assuming you've done dry runs?
Click to expand...

With just a little bit of the OD taken off the coupler assembly with the belt sander they should slide right into the airframe.

And heck yes there will be enough dry runs to ensure they fit correctly. Let me know if you see something I'm missing.

Or do you see something wrong with the coupler assemblies themselves? The internal part of the assembly is actually going to be relatively easy. Just place the stringers in with epoxy, carbon-fiber them in place then insert the top centering ring. Lots of room to work with.

Chuck C.
 
phenomenal, very cool to see this project coming together.

am I correct in reading that the picture of the "surface mounted" birch ring in post 1237 is a thrust plate and that is why it is sitting the way it is?
 
I was just making an observation, thinking mainly of how all the parts would come together. Looks like your going to need extremely strict tolerance throughout. My first impression was to expect a shoulder @ that junction, not only for more glue surface but also as an assembly aide. Structurally, I see no issues, purely ease of manufacture. Theory: If I'm reading this correctly, they are all thrust plates.
 
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Theory said:
phenomenal, very cool to see this project coming together.

am I correct in reading that the picture of the "surface mounted" birch ring in post 1237 is a thrust plate and that is why it is sitting the way it is?
Click to expand...

Yes it’s a design I’m thinking is unique in the building of the bigger rockets.

Most of the big projects build the ribs and stringers and then slide the airframe over the completed structure. The airframe itself tends not to carry as much of the load. If I'm wrong on this someone please correct me.

With this rocket because G12 is so strong (especially longitudinally) I decided to incorporate both the airframe and the internal structure as one solid unit.

So what you're seeing is a combination of thrust ring and centering ring. The advantage is that the thrust rings being sandwiched by the couplers provide a LOT of strength as the thrust rings are trapped by the diameter of the coupler. Add in (8) 3/4" x 1 1/2" birch stringers that are attached to the thrust rings (and carbon-fibered to the coupler) we have a rocket able to take the 3 tons of thrust it needs to handle.

G12 is not an inexpensive way to go but the advantages are worth the cost.

This modular design like I said is unique but from the beginning was something I saw as a great way to build a solid rocket capable of multiple high-power flights.

Of course before the coupler assemblies are epoxied into place there will need to be a motor-fit test. That's just to make sure that if adjustments to the thrust/centering rings internal diameter are needed (made slightly larger) they will be easy to access.

The motor-fit test will be done mid-April.

So far it's coming along as planned. Of course there will be the normal screw-ups associated with building any rocket from an "A" powered one to the SLS. But by trying to think ahead and anticipating the problem areas they shouldn't pose too much of a setback.

Good question and it's appreciated.

Chuck C.
 
A steel bristle chimney brush with the sectional fiberglass screw together handle will scuff up the interior of that tube pretty good. Then you can clean your own chimney too.

Jim
 
Does the CF go over three sides of the stringer and then along the inside of the coupler? If so, you should round off the sharp corners of the stringers and fillet the stringer-to-coupler joint so the CF will lay flat. If the CF goes on differently, please disregard.
 
boatgeek said:
you should round off the sharp corners of the stringers and fillet the stringer-to-coupler joint so the CF will lay flatQUOTE]

agreed. from my experience CF, like other composite cloths really doesn't like sharp edges or corners. that said, I am not sure that adding CF to the top of the stringer will add much other than providing a continuous piece of reinforcement
Click to expand...
 
boatgeek said:
Does the CF go over three sides of the stringer and then along the inside of the coupler? If so, you should round off the sharp corners of the stringers and fillet the stringer-to-coupler joint so the CF will lay flat. If the CF goes on differently, please disregard.
Click to expand...

I didn't think of rounding the corners or doing fillets... that's good advice.

Let me give that some thought. Doing it the way you mentioned would definitely increase strength. But it's 13 oz twill carbon and just laying it in as flat as I can without the rounding and fillets should make it plenty strong.

Again though good advice.

Chuck C.
 
Rail Dawg said:
I didn't think of rounding the corners or doing fillets... that's good advice.

Let me give that some thought. Doing it the way you mentioned would definitely increase strength. But it's 13 oz twill carbon and just laying it in as flat as I can without the rounding and fillets should make it plenty strong.

Again though good advice.

Chuck C.
Click to expand...

Can you explain (or point to where you explained before) how you were planning on laying in the CF? I'm having a lot of trouble envisioning what you had in mind. I have some strong-ish opinions on what is easy and hard to do when laying up, but I don't want to go down the wrong track.
 
Rail Dawg said:
it's 13 oz twill carbon and just laying it in as flat as I can without the rounding and fillets should make it plenty strong.
Click to expand...

Chuck, have you saturated some of that 13oz cloth and laid it around a few of those stringers? 13oz is decently heavy and I am afraid that it wont "lay" well. if you end up with gaps / air pockets, the carbon really wont do anything but add weight.

...and not sure what happened to my last post #1250. got all sorts a messed up
 
Rail Dawg said:
Here's what it looks like with the 8 stringers installed into the coupler.

Carbon-fiber is next laid over all the stringers.

Chuck C.
Click to expand...

Chuck,

That internal shot of the "SRU" ( Structural Reinforcement Unit ), showing the Stringers, looks exactly the way I had pictured it would, from your previous descriptions.

NOW, the fruits of everyone's labors "ARR" coming together and the "Steely-Eyed Missile Men" have your back !

Dave F.



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I was wrong about the 13 oz carbon fiber and am glad I listened to you guys. It's way too thick and when I tried a dry run there's no way it's going to work on the stringers.

So I'm going to go with 6 oz fiberglass. That should lay in nicely and will minimize any gaps.

I've only done a little bit of carbon work and learned a lesson with this.

Thanks for the great inputs... I do listen.

Chuck C.
 
Cool deal. Happy you found out before you had a full piece wet out and we’re try to work it and make it fit.

6oz glass should lay much better, good choice there. Which epoxy system are you going to use for the composite work?
 
Rail Dawg said:
I was wrong about the 13 oz carbon fiber and am glad I listened to you guys. It's way too thick and when I tried a dry run there's no way it's going to work on the stringers.

So I'm going to go with 6 oz fiberglass. That should lay in nicely and will minimize any gaps.

I've only done a little bit of carbon work and learned a lesson with this.

Thanks for the great inputs... I do listen.

Chuck C.
Click to expand...
Cut off the corners of the stringers such that it looks like a trapezoid, that way the cloth will not have to make a sharp corner. You might even want to use 3oz and do two layers.
 
Chuck: Simply rotating those stringers 90 degrees will vastly increase their stiffness in the desired plane. Simple test is to attempt bending an individual stringer in either "direction".
 
I'm going out on a limb here, but I'm not sure I see the benefit of the glass on the interior. With the stringers solidly glued in, double wall (main tube and coupler), and centering rings, that thing is already bombproof without adding glass. It's going to be kind of a bastard to get the glass fully wetted out, wrapped around those stringers, and still get the voids out. Not impossible, but difficult. With voids, the glass won't add much strength.

That said, if you still want to go ahead with the glass, I'd recommend pre-wetting it, rolling it on a reasonably-sized dowel, and then unrolling it into place. You'll need some extra hands and another dowel (or possibly other tools, maybe a chip brush 90 degrees to a stick) to get the voids out. I'd also rout the plywood to a 1/2" radius and try to get a 1/2" radius fillet between it and the inside of the coupler. That will make your life much easier in getting the voids out. If you lay down the glass while the fillets are still wet/barely set, the epoxy will cross-link without having to sand more.

Disclaimers: YMMV, this isn't my project, and I've never flown more than a baby L.
 
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