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neil_w

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Is the loop around the end of the motor tube opposite of where the motor is? I did something similar once and the force of deployment just crushed the tube. If you can, put the loop down at the other end (where the motor hook is) so it is around the motor, that gives it much more strength and the loop won't crush anything.
Wow, that's interesting. I always tie behind the frontmost centering ring, regardless of where the motor is... *but* my Kevlar only extends to the end of the body tube, and the rest is elastic. So there isn't such a harsh shock on the anchor point. I'm guessing when you've had that happen it's been with a fully non-stretchy shock cord, like all Kevlar or something?
 

mbeels

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I'm guessing when you've had that happen it's been with a fully non-stretchy shock cord, like all Kevlar or something?
Yeah, it was all Kevlar, and a somewhat higher speed than optimal deployment. But now the damage is in a really hard place to repair, and I can't replace it easily either. Now I run my Kevlar down through all centering rings, and loop around the motor. It makes it easy to replace as well.
 

BABAR

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Is the loop around the end of the motor tube opposite of where the motor is? I did something similar once and the force of deployment just crushed the tube. If you can, put the loop down at the other end (where the motor hook is) so it is around the motor, that gives it much more strength and the loop won't crush anything.
Good thought. I might see if I can find a very long Thin tube to run between the motor mount and the outer side wall from the rear centering ring to the forward center ring to do exactly what you’re talking about,but also use the @hcmbanjo technique for possible replaceable/inspectable shock cord. I hate Estes trifolds, not so much a breakable issue as much as I like the forward inside tube section to be as smooth as the proverbial baby’s hiney, so everything slides out easily.
 

mbeels

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I hate Estes trifolds, not so much a breakable issue as much as I like the forward inside tube section to be as smooth as the proverbial baby’s hiney, so everything slides out easily.
Yeah, that's a good idea, especially for the smaller body tube sizes. I've found that some of the perfect tubes are the ones that Aerotech initiators are shipped in, several inches long, and something like 3/16" diameter. Or, I just noticed that Balsa Machining Service has 12" long 3/16" launch lugs.
 

BABAR

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Here is @hcmbanjo ‘s article for anyone interested. I have some paper straws that might do the trick. It’s not really weight bearing, just a guide tube that gives you access across the length of the motor mount. The loop goes around the motor tube WITH the motor installed, probably can’t get much stronger than that.

 

BABAR

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I am at the same time wondering how hard it would be to put a baffle in that huge coupler.
 

mbeels

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Here is @hcmbanjo ‘s article for anyone interested. I have some paper straws that might do the trick. It’s not really weight bearing, just a guide tube that gives you access across the length of the motor mount. The loop goes around the motor tube WITH the motor installed, probably can’t get much stronger than that.

Yeah, I think that is a great method (Figure 3.), it is strong, light, super easy, and replaceable. I've done it without the straw and just taped the Kevlar to a length of music wire and pushed it through like a sewing needle. But the tube makes it super easy.
 

afadeev

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Well, here is the stuff John Pursley recommended to coat the skins before cutting and attaching them.
Got it from Jerry's Artarama, about $16 including tax and shipping. Took about 4 days.
I had used regular clear coat spray paint, whichever one I have on hand (Krylon, DupliColor, etc). All worked great. DupliColor dries the fastest.
Just spray 2-3 super light coats, to avoid puddling and runs. Let each one dry, as per instructions, then apply the next one.

The first time I had applied the vinyl's, I neglected this step, and had smudged some of the black paint on my Mercury wraps. Not a big deal, but definitely avoidable.

I am at the same time wondering how hard it would be to put a baffle in that huge coupler.
I am, personally, not a fan of baffles.
The better ones trap the plastic motor ejection cap and don't let it fall out.
The crappier ones singe the chute, and prevent you from accessing the FWD end of the motor mount if you need to push out the stuck engine with a dowel (especially common when friction fitting motors).

For my Interceptor E, I'm seriously considering installing 1010 rail buttons.
Either in addition to (aerodynamics are not much of a concern on this model), or instead of launch lugs.

a
 

prfesser

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Good thought. I might see if I can find a very long Thin tube to run between the motor mount and the outer side wall from the rear centering ring to the forward center ring to do exactly what you’re talking about,but also use the @hcmbanjo technique for possible replaceable/inspectable shock cord. I hate Estes trifolds, not so much a breakable issue as much as I like the forward inside tube section to be as smooth as the proverbial baby’s hiney, so everything slides out easily.
Suggestion: a coffee stirrer, the tubular ones are about 1/8" diameter. If one isn't long enough (better coffee shops have long ones), get three. Splice two together: cut a piece from the third, slit down the side, slide the other two inside this coupler. A bit of epoxy to be sure they won't come apart, and be careful not to get it on the tube ends.

Some tubular stirrers have a stiffener-strip down the inside that divides the tube in half. The ones without that strip are probably easier to deal with.
 

dhbarr

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Suggestion: a coffee stirrer, the tubular ones are about 1/8" diameter. If one isn't long enough (better coffee shops have long ones), get three. Splice two together: cut a piece from the third, slit down the side, slide the other two inside this coupler. A bit of epoxy to be sure they won't come apart, and be careful not to get it on the tube ends.

Some tubular stirrers have a stiffener-strip down the inside that divides the tube in half. The ones without that strip are probably easier to deal with.
http://www.merlinmissiles.com/the_sword_2.html was the first place I saw this technique, as well as adapting thinwall Estes tubes to thickwall LOC nosecones via coupler.
 

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afadeev

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Here is @hcmbanjo ‘s article for anyone interested. I have some paper straws that might do the trick. It’s not really weight bearing, just a guide tube that gives you access across the length of the motor mount. The loop goes around the motor tube WITH the motor installed, probably can’t get much stronger than that.
I remember reading about this a few years ago, it's a nice method. It is also applicable for feeding 2nd stage ignitor wires for electronically started staging.
However, how many of us have actually experienced a shock cord / harness failure, and had to go in and replace it?
On low power rockets?
Me - never.

Not counting the first few times I had followed Estes advice and relied on rubber cords. Those do break.
Once I had switched to Kevlar cords, I am yet to have one fail.

I had singed one harness on a HP rocket (due to motor CATA via FWD closure failure), and redid it out of over-abundance of caution.

a
 

BABAR

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I remember reading about this a few years ago, it's a nice method. It is also applicable for feeding 2nd stage ignitor wires for electronically started staging.
However, how many of us have actually experienced a shock cord / harness failure, and had to go in and replace it?
On low power rockets?
Me - never.

Not counting the first few times I had followed Estes advice and relied on rubber cords. Those do break.
Once I had switched to Kevlar cords, I am yet to have one fail.

I had singed one harness on a HP rocket (due to motor CATA via FWD closure failure), and redid it out of over-abundance of caution.

a
I uses Kevlar thread for a while, and did have some burn breaks. I think it was too thin.

Also one of the down sides of motor mount shock cord attachment. The tail end of the shock cord is constantly exposed in the same area to the ejection blast. I've seen films of engine ejection Charges going off on test stands and it seems like there's a touch of flame that last for maybe a second or two after ejection fired that may fry the cord a bit.
 

BABAR

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I had used regular clear coat spray paint, whichever one I have on hand (Krylon, DupliColor, etc). All worked great. DupliColor dries the fastest.
Just spray 2-3 super light coats, to avoid puddling and runs. Let each one dry, as per instructions, then apply the next one.

The first time I had applied the vinyl's, I neglected this step, and had smudged some of the black paint on my Mercury wraps. Not a big deal, but definitely avoidable.



I am, personally, not a fan of baffles.
The better ones trap the plastic motor ejection cap and don't let it fall out.
The crappier ones singe the chute, and prevent you from accessing the FWD end of the motor mount if you need to push out the stuck engine with a dowel (especially common when friction fitting motors).

For my Interceptor E, I'm seriously considering installing 1010 rail buttons.
Either in addition to (aerodynamics are not much of a concern on this model), or instead of launch lugs.

a
I am definitely going buttons. Not sure if i need something other than the cardboard body tube to attach them.

Debating trying to predict to their location before the build and glue internally tiny piece of wood or something to hold them in place. The cardboard itself looks pretty tough and there shouldn't be that much stress on them on the pad.
 

afadeev

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I am definitely going buttons. Not sure if i need something other than the cardboard body tube to attach them.

Debating trying to predict to their location before the build and glue internally tiny piece of wood or something to hold them in place. The cardboard itself looks pretty tough and there shouldn't be that much stress on them on the pad.
Same here. That's why I brought it up.
I'm putting mine at the aft edge of the airframe, and the CP.

For the former, you can just glue a block of wood to the CR, and that will become the anchor for your button.
For the latter, I use buttons that attach to a flange inside the paper airframe, similar to this: https://www.apogeerockets.com/Building_Supplies/Rail_Buttons/1in_1010_Rail_Button_Standard?cpath=&
 

BABAR

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Same here. That's why I brought it up.
I'm putting mine at the aft edge of the airframe, and the CP.

For the former, you can just glue a block of wood to the CR, and that will become the anchor for your button.
For the latter, I use buttons that attach to a flange inside the paper airframe, similar to this: https://www.apogeerockets.com/Building_Supplies/Rail_Buttons/1in_1010_Rail_Button_Standard?cpath=&
Hmmm. I am thinking I will probably end up going with @neil_w E-20 recommendation for a motor. So I am not going with higher thrust motors. I am wondering if I screw the rear button into the rear ring, or out some wood in front of that area. That would be easier. I think that the forward button anywhere into the coupler would probably be okay.

I had idea. If I planned in advance where the buttons would go,

drill the holes a bit smaller than the screws.

Finish the rocket.

Put blue masking tape over the areas of the holes and re-drill them.

Put a drop of polyurethane foam glue into each hole, maybe use a toothpick to force a bit inside.

Wipe of as much from the outside as I can.

Allow to dry.

Take the tape off.

Re-drill the small hole.

I though this might create a wad of foam glue inside the body tube to hold the screw.

I need to try this with a scrap tube.....
 

kuririn

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You can use a weld nut if there's nothing behind the airframe for the screw to grab.
 

BABAR

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@neil_w is it worth it to put rounded airfoils on the balsa?
 

neil_w

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Define "worth it".

I always round my edges, but never actual airfoils. Do the instructions comment one way or the other? If so, I'd follow the recommendations.
 

BABAR

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I was thinking heat shrink tubing could be used to run a path from the rear centering ring through the forward ring for access to shock cord. Would go 2-1 shrink with the minimum post shrink diameter enough to pass the kevlar.

A member from my local club, Mid South Rocketry, told me you can attach a small plastic ball as an antizipper device to the shock cord
 

mbeels

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I was thinking heat shrink tubing could be used to run a path from the rear centering ring through the forward ring for access to shock cord. Would go 2-1 shrink with the minimum post shrink diameter enough to pass the kevlar.
If I were doing it, I'd want something not flexible, and not shrinkable. I bet if you rolled up a section of paper and glued it into a simple tube, you'd have something strong, straight, and heat resistant (enough).
 

kuririn

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Chris M. uses the plastic tubing that Q tips are made of nowadays.
 

BABAR

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Chris M. uses the plastic tubing that Q tips are made of nowadays.
That would be great if i could find a foot long qtip!
 

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Does Plastruct offer tubing that would suffice (that might be readily available in a local hobby shop (assuming it is a decently stocked one))?
 

stantonjtroy

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They do; (1/8"dia Plastruct # pls90605). You can also look at push-rod guide tubes for R/C planes. If you can deal with a tad more weight, K&S has small dia aluminum tube as well. All is typically available at most dedicated hobby shops.
 

BABAR

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20200925_191933.jpg


Motor mount.
Seems like it made more sense just to make a measurement, push the motor block in exactly that measurement and then use the same mark on the tube to Mark the outside for the whole so that's what I did. I did put the knife in the hole and checked from the end to make sure that it was just aft of the motor mount.
 

BABAR

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Pre-inking

The skins are "chameleon " in this case a black background with blue marks on it. There are some areas that I think are going to be possibly exposed underneath the Skins. I figured I would free black those areas with a black Sharpie marker. This also includes a small portion of the motor mount which is going to stick out the back. The instructions also say to glue in the decorative motor nozzle, which in the paint Scheme and ends up being painted black. I figure I'm going to paint that separately and then install it after it's already painted.
 

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BABAR

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Was looking for some kind of tube that would allow me to put in a replaceable shock cord. For some reason I kept the yellow doohickey that was on the windshield wipers. Anyway, drilled matching holes in the centering rings, glued it to the rear ring.

Little trick to match it all up. If I had 15 minute epoxy instead of 5 would have given me more time, I put in 5 minute , placed the tube assembly in, THEN put the forward ring in which pushed it back a bit.
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BABAR

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The final yellow tube cut segment was 14 inches long, came out to about 3 grams, not including epoxy
 

BABAR

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I started gluing the fin pieces together. I guess it is cheaper for Estes to make each fin out of multiple pieces that have to be glued together before your put the fins and wings on the rocket. I had glue a few pieces together before I though, “it’ll be a lot easier if I round the appropriate edges BEFORE I glue them together.” The instructions say round the forward edges and taper the backs, I decided the heck with the taper, I am just rounding all the exposed edges. Obviously the tabs and the pylon attachments are left alone, there are some root edges that are not inserted into tabs, those get sanded flat.
 

BABAR

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@neil_w , did the wrap stick well to the body untreated body tube? I don’t think the spirals would show through, but wondered if I needed to gloss surface for the wrap to stick? I know I will need to prime the balsa. JohnPursley recommenced latex trim paint. Might try some on some balsa scraps.....
 
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