lakeroadster
When in doubt... build hell-for-stout!
I'm not well versed on them, but I know collectors are on the hunt for them.... I'll do some digging and get back to you.
Shear Insanity: a build thread
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lakeroadster
When in doubt... build hell-for-stout!
I think the vice dates back to the 1970's, and was made in Japan. Here's a pdf, if you ever need parts, I'm betting they are still available.
Cool. Maybe dates back to the first owner of this house (built in 1968)...
This is a really cool design Neil! Looking forward to more build and flight posts!
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I have the exact same vise. At least 35 years old....
GlenP
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No debate here, just physics and engineering judgement. I was just pointing out that in this situation seems that both views presented are correct. The CP will move, but likely not enough to really be a stability concern.
You can always swing test to verify nose-forward flight stability adding nose weight as needed since those minor Cp effects are not represented in the sim, and then update the sim to predict speed off the rod with any actual nose weights added for a variety of motors.
I just cut the fins today, a bit larger than in the previously posted sim, so margin is now around 1.5 (before un-modeled effects). I should be able to maintain an OR-predicted 1.5 with additional nose weight at the end of the build, and should be fine.
As we've both so often told so many, a PVA joint is stronger than the balsa (and cardboard) pieces joined. What I'm concerned about is edge chipping and denting. I hope the CA soak has strengthened and hardened the edges adequately.
NOSE BLOCK
I promise we'll get to some more exciting stuff soon. In the meantime here is too much information about a nose block.
I needed a BT50 nose block or equivalent for where the body splits below the first segment. Lacking a balsa block, I figured I should just make one out of a coupler. I needed a bulkhead, so I decided to whip up some basswood ply. I figured four plies of 1/16" would make a nice stout 1/4" bulkhead, suitable for mounting a screw-eye.
I started with four oversized pieces, glued them together, and sanded to fit.
Nice. One small problem though...
So I glued four more layers to it, although I didn't try to make them round or anything, just enough so I could screw the eyelet all the way in.
And then I glued it into the end of a 2" piece of coupler.
That was fun.
I promise we'll get to some more exciting stuff soon. In the meantime here is too much information about a nose block.
I needed a BT50 nose block or equivalent for where the body splits below the first segment. Lacking a balsa block, I figured I should just make one out of a coupler. I needed a bulkhead, so I decided to whip up some basswood ply. I figured four plies of 1/16" would make a nice stout 1/4" bulkhead, suitable for mounting a screw-eye.
I started with four oversized pieces, glued them together, and sanded to fit.
Nice. One small problem though...
So I glued four more layers to it, although I didn't try to make them round or anything, just enough so I could screw the eyelet all the way in.
And then I glued it into the end of a 2" piece of coupler.
That was fun.
I'm still curious about some of the internal details, especially around the body split. I'm interested to see how it comes together, or errrr, goes apart.
I have learned to put some asterisks on that fact. I've had at least two occasions where a wood glue joint snapped cleanly apart (example: when I fumbled my IRIS-T during constructions and one of the fins came off cleanly). I have not yet determined what the factors are that contribute to a weaker joint, but in all cases where I've had the problem it's been basswood, and the joint has been parallel to the wood grain.
A balsa end-grain joint, though, I expect to have full strength.
Probably not, but chips are easily fixed (if desired) when they happen, and this isn't likely to be a frequent flier in any case.
Not to derail too much, but I have a Craftsman 391-5181. We built the house in 1978 so I bought it probably later in 78 or early 1979.
It's had the living snot beat out of it... the main screw is even bent! When in doubt, beat it with a hammer, right?Oh man, yours is one better than mine.
CENTERING RINGS
The custom lite-ply centering rings that @Sandy H. laser-cut for me have arrived, and they are beautiful. In the batch on the right, you can see alignment ticks at top and bottom. On the left, I extended them with pencil lines. There's gonna be a whole lot of precise ring alignment coming in this build.
They are cut with the OD a bit large and the ID a bit small, so after sanding off the char I can sand them to perfect fit.
The custom lite-ply centering rings that @Sandy H. laser-cut for me have arrived, and they are beautiful. In the batch on the right, you can see alignment ticks at top and bottom. On the left, I extended them with pencil lines. There's gonna be a whole lot of precise ring alignment coming in this build.
They are cut with the OD a bit large and the ID a bit small, so after sanding off the char I can sand them to perfect fit.
That is one reason why they don't make vises out of Murano glass.It's had the living snot beat out of it... the main screw is even bent! When in doubt, beat it with a hammer, right?
STUFFER TUBE/MOTOR MOUNT
A BT50H provides the core of the rocket. I don't know why I do this to myself, I hate stuffing parachutes into BT50. Anyway, most of the action happens at the motor mount end, and that is where we'll start.
The cant angle of each BT60 segment is set at 4.4°, so I started at cutting an equivalent angle at the MM end of the tube, so it will match up with bottom BT60 segment.
And now I finally had to decide on how to assemble the motor mount. My goal was not just to build this motor mount, but to come up with a good, solid, repeatable process. After getting as much input as I could, I decided on a modified approach that was... well, not exactly the right choice. It worked, but I probably wouldn't do it this way again, or recommend it to anyone.
My general approach would be to cut the tube above the MM use a coupler as the thrust ring. I filed a notch in my coupler to provide room for the Kevlar to squeeze between the coupler and body tube:
So far so good. The next step is where I... "innovated". I poked a hole in the center of the coupler (where the pencil mark is in the above picture) and threaded the Kevlar through. Then I tied a nice beefy knot in it (to keep it from pulling through the hole and gave the whole interior mess a nice coating of epoxy:
Then I went a couple of steps without pictures as my epoxy was starting to set and I had some on my gloves and I just needed to get it done. But here's what I did:
1) The *far* end of the coupler in the above picture was glued into the motor mount, pushed up against the top of the hook.
2) The *near* end of the coupler, along with the Kevlar in the coupler notch, was pushed into the remainder (long piece) of the stuffer tube.
The whole thing was laid into a piece of angle to keep it straight while it cured.
My thought process was that by doing the Kevlar this way, the loose end of the Kevlar would emerge into the body above the coupler, which would give a couple inches of buffer from the ejection charge. That's fine, but what I failed to consider was that pushing the coupler in that direction meant that the Kevlar wanted to push back. I realized this once I started pushing it in, and then needed to try to pull on the Kevlar to keep is straight as the whole thing was going in. I think I was only partially successful, but since the whole thing will be hidden it's OK.
So I didn't come up with my clean and repeatable motor mount process, but I learned some things. Will do better next time. I like the coupler approach, but the Kevlar installation needs improvement.
Finally, I put a 5055 ring around the motor hook to secure it, and electrical tape to hold the top.
Final note: the motor hook was aligned (approximately) with the "short" side of the tube. That is where the thick side of the centering ring will go, so I have lots of wood to work with there to cut a slot for the hook.
A BT50H provides the core of the rocket. I don't know why I do this to myself, I hate stuffing parachutes into BT50. Anyway, most of the action happens at the motor mount end, and that is where we'll start.
The cant angle of each BT60 segment is set at 4.4°, so I started at cutting an equivalent angle at the MM end of the tube, so it will match up with bottom BT60 segment.
And now I finally had to decide on how to assemble the motor mount. My goal was not just to build this motor mount, but to come up with a good, solid, repeatable process. After getting as much input as I could, I decided on a modified approach that was... well, not exactly the right choice. It worked, but I probably wouldn't do it this way again, or recommend it to anyone.
My general approach would be to cut the tube above the MM use a coupler as the thrust ring. I filed a notch in my coupler to provide room for the Kevlar to squeeze between the coupler and body tube:
So far so good. The next step is where I... "innovated". I poked a hole in the center of the coupler (where the pencil mark is in the above picture) and threaded the Kevlar through. Then I tied a nice beefy knot in it (to keep it from pulling through the hole and gave the whole interior mess a nice coating of epoxy:
Then I went a couple of steps without pictures as my epoxy was starting to set and I had some on my gloves and I just needed to get it done. But here's what I did:
1) The *far* end of the coupler in the above picture was glued into the motor mount, pushed up against the top of the hook.
2) The *near* end of the coupler, along with the Kevlar in the coupler notch, was pushed into the remainder (long piece) of the stuffer tube.
The whole thing was laid into a piece of angle to keep it straight while it cured.
My thought process was that by doing the Kevlar this way, the loose end of the Kevlar would emerge into the body above the coupler, which would give a couple inches of buffer from the ejection charge. That's fine, but what I failed to consider was that pushing the coupler in that direction meant that the Kevlar wanted to push back. I realized this once I started pushing it in, and then needed to try to pull on the Kevlar to keep is straight as the whole thing was going in. I think I was only partially successful, but since the whole thing will be hidden it's OK.
So I didn't come up with my clean and repeatable motor mount process, but I learned some things. Will do better next time. I like the coupler approach, but the Kevlar installation needs improvement.
Finally, I put a 5055 ring around the motor hook to secure it, and electrical tape to hold the top.
Final note: the motor hook was aligned (approximately) with the "short" side of the tube. That is where the thick side of the centering ring will go, so I have lots of wood to work with there to cut a slot for the hook.
Yeah, even BT55 is soo much better.
That is quite specific and precise. Getting a good perpendicular cut is one thing, how did you do 4.4°?
I meant to ask, what's the weight as modeled? Would a streamer do?
4.4° (well, 4.39871° or so) is a 1:13 slope. So it shouldn't be hard to set up a jig.
My problem here is that I wanted a significant size difference between the core and the outer tubes, to facilitate reasonable centering rings. A BT55 inner tube would have required a BT70 outer tube, which would have bloated the whole thing a bit more than I wanted to (also I didn't have a suitable nose cone). So 50/60 it is.
Miter cut wrap, generated by my own script.
4.2 oz dry. I dunno, would it? I'm not sure I'd enjoy stuffing a streamer any more than the parachute.
Ah! Very nice, I recognize that, is that similar to what you used to generate PDII shrouds? Useful and flexible tool.
It's derived from the same code. In general, I find myself customizing/rewriting the script for each application, because every application seems to have a unique twist.
lakeroadster
When in doubt... build hell-for-stout!
As a kid we used streamers a lot. IMO: Streamers are a good recipe for busted fins, but opinions vary.
I'd rather do what I can to keep ground hit around 14 fps or less for a scratch built rocket that I'm trying to minimize damage to..
Streamers are easier to pack, up to a point, I think, because they can be rolled along one exis and end up with the package length only the same as the original width. I'd see what OR has to say about the grass impact speeds with some different streamer dimensions and see if you're satisfied.
Some quick fiddling in OR suggests that it would need to be very large indeed to match the performance of a 15" parachute. E.g., a 6x60 inch streamer would yield 32 mph ground impact. Not interested.
FIN CAN
Now the fun can begin. First comes the bottom segment of the rocket, aka the fin can, and then we'll work our way upward.
Most of the segments will be assembled and slid onto the core tube, but the motor mount prevents me from doing that with the fin can. And so, the rear slotted centering ring goes on first, parallel to the mitered tube end (almost flush):
For the BT segment, the four fin positions are marked, two straight and two at 4.4° cant (I used a custom marking wrap for that.) Using my small snap-off blade I scraped off the CWF and a bit of the glassine where the fins go (a surprisingly satisfying process) and crudely re-marked the edges with pencil. This showed me that I left a bit too much CWF on the tubes, will need to sand it down more in the future.
I installed the top centering ring, checking and re-checking over and over to make sure I had it in the correct orientation. Note the alignment mark is centered in a straight fin root. The ring is glued absolutely flush to the tube end.
Then is is slid almost into position. Note the marks on the ring and the tube are aligned. We want this tube to be as close to correct position as possible before gluing.
Then glue was applied to the ring, and the tube is pushed into place. No glue yet on the top side. The bottom ring is almost but not perfectly flush with the tube end, due to very slight error in the angle at which the bottom ring mounted. It's more than good enough.
A small fillet of TBII is applied at the top ring, more than enough to keep it secure.
At this point it occurred to me to check whether the canted fins will end up properly straight on the rocket. So I made another line on the core tube and sighted down from the end. And the answer is...
...maybe? It doesn't look perfect to me, but I'll have to study more closely when it comes time to install the fins. Possibly, during all the CWF-scraping and remarking, the fin position drifted slightly. Easily fixable when the time comes.
Now the fun can begin. First comes the bottom segment of the rocket, aka the fin can, and then we'll work our way upward.
Most of the segments will be assembled and slid onto the core tube, but the motor mount prevents me from doing that with the fin can. And so, the rear slotted centering ring goes on first, parallel to the mitered tube end (almost flush):
For the BT segment, the four fin positions are marked, two straight and two at 4.4° cant (I used a custom marking wrap for that.) Using my small snap-off blade I scraped off the CWF and a bit of the glassine where the fins go (a surprisingly satisfying process) and crudely re-marked the edges with pencil. This showed me that I left a bit too much CWF on the tubes, will need to sand it down more in the future.
I installed the top centering ring, checking and re-checking over and over to make sure I had it in the correct orientation. Note the alignment mark is centered in a straight fin root. The ring is glued absolutely flush to the tube end.
Then is is slid almost into position. Note the marks on the ring and the tube are aligned. We want this tube to be as close to correct position as possible before gluing.
Then glue was applied to the ring, and the tube is pushed into place. No glue yet on the top side. The bottom ring is almost but not perfectly flush with the tube end, due to very slight error in the angle at which the bottom ring mounted. It's more than good enough.
A small fillet of TBII is applied at the top ring, more than enough to keep it secure.
At this point it occurred to me to check whether the canted fins will end up properly straight on the rocket. So I made another line on the core tube and sighted down from the end. And the answer is...
...maybe? It doesn't look perfect to me, but I'll have to study more closely when it comes time to install the fins. Possibly, during all the CWF-scraping and remarking, the fin position drifted slightly. Easily fixable when the time comes.
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I ran with Neil’s design. Here’s my square version. The square tube made some things easier than a round tube, for example, attaching the launch lug. The square tube also made the alignment easier. The centering “squares” are glued in each end of the tubes 180 degrees apart. To accommodate the angled stuffer tube, I just doubled up the centering squares at the very bottom and very top and kept the long side of the stuffer tube even with the flat of the centering square. BT-50 stuffer tube with standard 18mm engine mount with Kevlar shock cord attached to mount. Nose cone is 3D printed in 3 parts. Small top point of nose has a hole on the bottom that slides over a pin printed on top of the large part. Bottom of nose has a shoulder that slides into the BT-50. I added no nose weight. I’m old school, I just went out and test flew it to see what happens. Used either a 14” or 17” chute with no issues. It’s kind of like the FlisKits Acme Spitfire, doesn’t look like it should fly right, but it does. Flew nice and straight. 
Hi Rick!
LOL, I am putting off the launch lug until later, gives me a headache thinking about it. I also am jealous that you get a flat surface on which to glue the canted fins. Big old pain the butt for me.
I imagine our basic construction approach is identical (really only one way to do it). I diverged in the nose section a bit.
I am very happy to hear that. Actually I've been working off the knowledge that you had mentioned this previously, which gave me more confidence to go forward. Now I just have to get those darned canted fins on straight....
