Shear Insanity: a build thread

[neil_w]

It has been seven months since completing my last build, which is a travesty. I've spent much of that time in the rocketry doldrums, at a loss what to do next or how get my mojo back. I'm as surprised as anyone that this is the rocket that has brought me back:

Those who follow my half-baked thread might remember this one. I've slightly updated/improved the design. I do not yet have a clue about the paint scheme, except to say that it's not going to be anything incredibly fancy or complex.

I'm not in the habit of building oddrocs, but somehow this one seemed like fun. Really it's not that hard of a build, just requires planning, and some special centering rings, which were my excuse for not doing it until my forum buddy @Sandy H. was gracious enough to offer to cut them for me on his laser. And so away we go.

 

[cwbullet]

that could be a neat 3d printed rocket

 

[neil_w]

that could be a neat 3d printed rocket

Maybe, but my build shall include exactly zero 3D-printed parts.

 

[cwbullet]

Maybe, but my build shall include exactly zero 3D-printed parts.

What did you design it with?

 

[neil_w]

What did you design it with?

TinkerCad, but that was just to visualize the design.

 

[cwbullet]

If you post the STL files, I will be glad to print one. I will send you a copy if you wish.

 

[neil_w]

If you post the STL files, I will be glad to print one. I will send you a copy if you wish.

Check your PMs.

 

[lakeroadster]

It's just a 4FNC....... shearly, I jest.

Looking forward to following this one @neil_w.

It reminds me of a sci-fi movie I saw where some folks walked through a chamber, and there were horizontal lasers.... they were unknowingly sliced into pieces.

Ham steaks anybody?

 

[cwbullet]

Thanks.

 

[neil_w]

It's just a 4FNC....... shearly, I jest.

LOL, I meant to write in my first post up top that this was as close as I'll ever get to building a 4FNC... too late now.

 

[neil_w]

PARTS IS PARTS



The main BT segments are BT60, 4" long; the top segment that connects to the nose cone is 3". A BT50h core tube extends through the entire rocket, and also serves as a 24mm motor mount. The short piece of BT50H in front is the stuffer for the top segment (the rocket will split between the first and second segments.) This rocket will enable me to consume the last of the BT60 conical balsa nose cones I purchased at BMS. I had bought one extra in case of mishap with either the Skywrite Deluxe or the Plasma Dart.

The two BT50 couplers will be used at opposite ends of the rocket.

As per my current routine, the BT60 segments were all completely covered in CWF and sanded down. This time, I gave the glassine a quick sanding with 400 grit beforehand, and I think it did improve the adherence of the CWF.

Not shown (yet) are the centering rings and other miscellany.

 

[BigMacDaddy]

Wonder if you staggered the segments around a helix (rather than just horizontally) if the rocket would spin as it went up...???

You could just 3D print couplers to connect the segments instead of printing the whole rocket...

 

[neil_w]

Wonder if you staggered the segments around a helix (rather than just horizontally) if the rocket would spin as it went up...???

It might, but I expect not that much.

In any case, that would be a completely different rocket from this one.

 

[GlenP]

It's just a 4FNC....... shearly, I jest.

“I am serious, and stop calling me Shearly”

 

[lakeroadster]

The neat thing about this design is it's radically different, yet won't take weeks and weeks of effort to build. Kudo's on that @neil_w

Question: Do you have some "better than just slopping it on" technique for applying CWF to the body tubes?

​

 

[neil_w]

Do you have some "better than just slopping it on" technique for applying CWF to the body tubes?

Nothing super special, and to be honest I'm still not 1000% sure that this is the best thing to do... but it has been working for me so far.

The main thing is to put on as thin a layer as possible, to minimize sanding afterwards. Here was my process for this one, for what it's worth:
1) Support the tube with a coupler if possible. It will soften a bit as the process goes. This was easy for me this time with the short pieces of tubing.
2) Slop a bit of thinned (but not too thin) CWF onto a tongue depressor, and then apply it as thinly as possible on to the tube. Do not try to cover the whole tube in one shot.
3) Use finger (the most versatile tool in the shop) to spread it out more evenly and thinly.
4) Repeat steps 2 and 3 until entire tube is covered.
5) Keep running the finger over the tube to keep removing excess, until is dries to the point where that your finger stops doing anything. This takes less than a minute for me.
6) Let dry. Takes a bit longer than usual.
7) *Gently* use 220 grit to remove excess.
8) Sand fully with 400 grit

On my first piece, I oversanded with the 220 in one spot and scuffed the tube. Fixed that with a Q-tip application of thin CA, followed by 400 and 800 grit sanding.

IMHO this is all still less work than applying CWF just to the spirals themselves, and then sanding carefully to avoid scuffing the bare tubes. Bonus is that the CWF also fills other imperfections in the tubes.

Caution: in my experience, after doing this, the tube diameter increases ever so slightly due to the layer of CWF. Slight adjustment of fin wraps and such may be necessary, centering rings may need to be sanded out a bit, etc.

 

[lakeroadster]

Nothing super special, and to be honest I'm still not 1000% sure that this is the best thing to do... but it has been working for me so far.

The main thing is to put on as thin a layer as possible, to minimize sanding afterwards. Here was my process for this one, for what it's worth:
1) Support the tube with a coupler if possible. It will soften a bit as the process goes. This was easy for me this time with the short pieces of tubing.
2) Slop a bit of thinned (but not too thin) CWF onto a tongue depressor, and then apply it as thinly as possible on to the tube. Do not try to cover the whole tube in one shot.
3) Use finger (the most versatile tool in the shop) to spread it out more evenly and thinly.
4) Repeat steps 2 and 3 until entire tube is covered.
5) Keep running the finger over the tube to keep removing excess, until is dries to the point where that your finger stops doing anything. This takes less than a minute for me.
6) Let dry. Takes a bit longer than usual.
7) *Gently* use 220 grit to remove excess.
8) Sand fully with 400 grit

On my first piece, I oversanded with the 220 in one spot and scuffed the tube. Fixed that with a Q-tip application of thin CA, followed by 400 and 800 grit sanding.

IMHO this is all still less work than applying CWF just to the spirals themselves, and then sanding carefully to avoid scuffing the bare tubes. Bonus is that the CWF also fills other imperfections in the tubes.

Caution: in my experience, after doing this, the tube diameter increases ever so slightly due to the layer of CWF. Slight adjustment of fin wraps and such may be necessary, centering rings may need to be sanded out a bit, etc.

Thanks for the detailed how to.

Did you attempt an Open Rocket simulation? Just wondered if you had some trick for that.

 

[neil_w]

Did you attempt an Open Rocket simulation? Just wondered if you had some trick for that.

Another thing I forgot to include in my first post. Geez, I'm out of practice.

Here's the model:


My working assumption is that all the slicey stuff does not significantly affect CP, just drag. And therefore I model it as a normal rocket. Obviously, I expect drag to be much higher than OR predicts, and will be using shorter delays than predicted by OR, and expecting significantly lower apogees. This is another rocket that won't be winning setting any altitude records.

 

[lakeroadster]

Another thing I forgot to include in my first post. Geez, I'm out of practice.

Here's the model:
View attachment 496496

My working assumption is that all the slicey stuff does not significantly affect CP, just drag. And therefore I model it as a normal rocket. Obviously, I expect drag to be much higher than OR predicts, and will be using shorter delays than predicted by OR, and expecting significantly lower apogees. This is another rocket that won't be winning setting any altitude records.

Cool. More questions...

What's the inner tube below the nose cone? Is that the newer version of OR... looks a bit different?

 

[neil_w]

Cool. More questions...

What's the inner tube below the nose cone? Is that the newer version of OR... looks a bit different?

It's a coupler inside a tube, so the line looks heavier.

 

[boatgeek]

I was inspired by the original post in the half-baked builds thread (and @jqavins office supplies rocket) to start saving toilet paper tubes for just this kind of design. I haven't gotten past that point yet, but someday when I finish Venn... I'll look forward to see how this one flies.

 

[BABAR]

Another thing I forgot to include in my first post. Geez, I'm out of practice.

Here's the model:
View attachment 496496

My working assumption is that all the slicey stuff does not significantly affect CP, just drag. And therefore I model it as a normal rocket. Obviously, I expect drag to be much higher than OR predicts, and will be using shorter delays than predicted by OR, and expecting significantly lower apogees. This is another rocket that won't be winning setting any altitude records.

I hope to be wrong, but I I don’t buy it,

those forward offsets are gonna pull CP forward. Assuming you can put a big enough motor in it, can probably overcome with nose weight as long as you can get the speed off the rail with the added weight,

this is almost a natural for Break Away (e.g. Estes Wacky Wiggler) recovery!

 

[neil_w]

I don not agree. Plus Rick Randol is/was developing a version of this for Newway and he said it flies fine. We’ll see.

in the meantime, onward.

 

[GlenP]

The offsets are only affecting CP in that one plane, and probably just a small amount. One way to visualize this effect is how would the airflow look, if you had smoke trails around the rocket. Each forward facing step will have a little air pocket just in front of the step. Each aft facing step will have a little air pocket behind it. The effective rocket shape would include those air pockets. Alternatively, you could estimate CP via cardboard cutout method by including little triangular fins that kind of fill in the air pockets at each step. So, yes by adding little fins, just in the one plane, you are slightly shifting the CP forward, but these small virtual vanes probably won’t eat up the entire margin you have designed in when totally disregarding them.

 

[neil_w]

Consider the Rocketarium Rebel rockets as much more extreme examples of this.

Prefer not to get into too much debate about stability at this point in the build.

 

[Bruiser]

Build it and it will fly

BTW, good to see you doing another build

-Bob

 

[neil_w]

鼻錐

Let's do some actual building already.

This design pretty much requires either a balsa or 3D-printed nose cone, with balsa being the obvious choice for maximum build enjoyment. So I used the spare conical nose I had on hand.

Each body tube segment is 4". I made the segment that connects to the nose 3", so the next "cut" is 1" up on the nose. I used a paper shroud template to create a good mark on the cone in the correct location, and then taped the rest of the cone to protect it during the cutting phase.

Then I went at it with a hobby saw to make the initial cuts, followed by a hacksaw to finish (my Atlas hobby saw doesn't have a deep enough blade to go half-way through a BT60).

I don't know why I find sawing through balsa nose cones so satisfying. I shall have to take it up with my therapist.

Anyway: I certainly didn't expect to see the dowel hole that far up into the nose. So I decided to take advantage by loading up the hole in the tip with some nose weight (I know I'll need some) using lead shot that I bought a long time ago and epoxy:

I ended up getting about 1/2 oz in there, which might be all I need if I'm lucky. I will make the final determination after the build is complete, and add additional weight to the base of the nose if needed.

Then I applied CA to the two pieces

And followed up with CWF.

I glued the two pieces together with TBII, offset by 8mm (same as the other joints in the rocket). I originally made half-hearted attempts to add some pins to the joint to add strength, but it didn't work, so I just glued normally and will hope for the best. I suspect a TBII joint on large surface area joint with end grain on each side will be quite strong.

Finally I took about 1/4" off the shoulder, which will be necessary to avoid hitting the internal tube (to come later). Another chance to saw balsa, yay!


Thus completes the nose cone.

 

[lakeroadster]

I'm diggin' that old school red Craftsman vise.... any idea what vintage it is?

 

[neil_w]

I'm diggin' that old school red Craftsman vise.... any idea what vintage it is?

Not in the slightest; it was left in my house (attached to the bench, which is far less vintage) when I bought it. Is there any way to tell?

 

[mbeels]

Very nice! I've liked this one since you first posted the concept for it, and I'm glad to see that it is getting built.