Through the Wall Low Power Construction

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Kirk G

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So about two years ago, I got a Mega Mosquito on sale from Estes and launched into it during the winter building break.

I had never done a "Through the Wall" Construction before, and the larger scale was an interesting challenge for me.

As I got the thing together, I discovered that by gluing the motor mount in place, I no longer had access to the fins meeting up with it inside.
And so, could not run a bead of glue along the base of the sandwiched fins to secure them in another logical place.

However, I DID glue the fins as they went through the wall of the body tube, and filleted them well, and the rocket served me well for a couple of years.


This Xmas, I got a Big Daddy that ALSO has "Through the Wall" construction, but again, does not specify gluing the root of the fin to the motor mount.
Again, I got ahead of myself, finishing the motor mount with two centering rings, but can't get to the root of the fins. I remember my mental note to try to
find a way to do this on the next "TTW" construction...but had forgotten.

Why doesn't Estes tell you to hold off on the second centering ring until after positioning the motor mount and glueing the forward ring in place? That would allow the savy kit builder to glue the root of the fins in place,
BEFORE slipping the rear centering ring back onto the motor mount and gluing it in place?

Doesn't this make more sense?

What can I do to secure the root of my fins, now that I'm trapped with the motor mount in place, and the centering rings glued and filleted in place.
Any suggestions?
 

Flyfalcons

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Probably because it simply isn't necessary on a low power kit.
 

TangoJuliet

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I agree with Flyfalcons, but if you put some epoxy on the root edge, it should make contact with the MMT anyway. It wouldn't have a fillet, but at least it would be glued at the root. I have an in-progress Big Daddy at home right now and I did just what you have done, and I'll mount my fins just as I've stated here. It's not going anywhere near supersonic.
 

Steve Shannon

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PML does a great job of specifying to leave the aft centering ring unglued. In fact they have you put tape on the CR to pull it out after the first layer of epoxy cures.
 

samb

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Well Estes is pretty consistent in this regard. Look at the instructions for other kits with fin tabs through the wall, like any of the PSII's. They all specify gluing all the centering rings in place. FWIW my 10 year old Big Daddy has held up fine built according to the instruction sequence. My suggestion: complete the build, post a picture, then fly it ! Then write yourself a big note and post it on your workbench:

DON'T PERMANENTLY SECURE THE AFT CENTERING RING UNTIL I FILLET THE FIN TAB/MOTOR MOUNT JOINT


...

This Xmas, I got a Big Daddy that ALSO has "Through the Wall" construction, but again, does not specify gluing the root of the fin to the motor mount.
...

Just to be clear, you did butter the root edge, as is clearly shown in the instructions, right ?

big daddy fins.png
 
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Nytrunner

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Echo the "It should be fine for lo-power". As long as you apply sufficient glue where you can, It'll work well. If you really want to do more, you can always make epoxy fillets :)

I didn't even know about leaving of the rear ring when I built my L1 rocket and it worked fine for its average motors. Pro Series II kits also fly fine without an internal fillet (but my new PSII's are destined for H's, so I'm building them with tab-to-mount fillets).

The great thing about Lo-power is that its really forgiving and gives plenty of room for improving skill.
 

smugglervt

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Double butter the fin root and it should be fine.
 

dhbarr

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For my Dig Baddy drag racer, I cut the finslots out the back and added a slice of 3in coupler.
 

Kirk G

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Just to be clear, you did butter the root edge, as is clearly shown in the instructions, right ?

View attachment 308051
I am "double buttering" the fins and doing as suggested even as we speak.

I had delayed the gluing of the fins until I had a half dozen or so responses, to make sure I wasn't overlooking something.

Once the fins (and fin tabs) are dry, I'll proceed to do a final filet around the aft centering ring, as it may need to flex or move a little in the fin position process.

But I love the large post-it note idea.... if I ever get around to doing another Through-the-Wall kit....
 

Kirk G

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Good news!
I got enthused yesterday, and began the double buttering of the fin roots as I attempted to slide them through the slots (much tougher that it may sound)
but I got them all in one-at-a-time and then let them set while drying for an hour or two.

After an 8 hour shift, all four were in place and filleted...and I popped on the straw/launch lug.

This morning, I up-ended the rocket and ran a fillet around the aft centering ring to allow it to seal/dry.

Except for tying on the nosecone, and priming and painting, construction appears to be complete.

Somebody suggested many months ago that the nosecone of the Big Daddy was beveled and so, an additional flat partition
bolted and glued to the base of the nosecone might make for a decent "plunger" for the escape charge gases to push against.
Any suggestions on how to accomplish this easily without too much weight?

Also, would you bother priming the white plastic nosecone before spraying with gloss black paint to finish? How essential is this priming?
(I'm thinking of primer on the body tube and fins below, but I'm open to suggestions.)
 
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K'Tesh

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I think the reason Estes does this is that (especially when you have only two CRs) there is a chance that the motor tube might be glued in place out of alignment (due to something like a cockeyed fin). When you have 3 or more CRs with two of them ahead of the fin/body tube joint, the chance of that is lessened considerably, but it can still happen. A cockeyed motor mount can have negative effects on your flight performance.
 

Nytrunner

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If it was my build, definitely rough up the nose cone and prime it before painting. And wash it too.
The molded plastics have difficulty bonding to paint, and sometimes there's leftover mod-release residue.
 

K'Tesh

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I'm with Nytrunner here... The more prep you do on getting your rocket ready for paint, the better the results will be (barring insects).
 

T-Rex

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I always use Valspar plastic primer on my nosecones. Then move on with regular primer and paint. I don't know if it helps, but certainly can't hurt IMHO.
 

Kirk G

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I always use Valspar plastic primer on my nosecones. Then move on with regular primer and paint. I don't know if it helps, but certainly can't hurt IMHO.
Yes, I am quite certain that I have white flat Valspar primer in my workshop, but I have always found that it has a funny consistency and is never "smooth" or "flat like silky". When I've tried to sand it back some, it always seems like a wasted step as so much comes off again. How many coats of primer to you use? My body tube is spiral, but the seam is so subtle that any filler compound (wood filler or otherwise) would probably produce more of a mess and uneven texture than just leaving it alone.
I know some guys insist that the primer helps to fill that spiral in or to cover over it, but I've never been that particular to get a mirror finish on any of my rockets.
 

dhbarr

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I like to stick my NCs on a dowel, chuck it up, then do high grit passes until the seams are gone. Smaller grit, etc, then wash & prime.
 

Nytrunner

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Yes, I am quite certain that I have white flat Valspar primer in my workshop, but I have always found that it has a funny consistency and is never "smooth" or "flat like silky". When I've tried to sand it back some, it always seems like a wasted step as so much comes off again. How many coats of primer to you use? My body tube is spiral, but the seam is so subtle that any filler compound (wood filler or otherwise) would probably produce more of a mess and uneven texture than just leaving it alone.
I know some guys insist that the primer helps to fill that spiral in or to cover over it, but I've never been that particular to get a mirror finish on any of my rockets.
My primer rounds go: light coat, 10 mins light coat, 10 mins, light coat, dry (whatever your can says). Then damp sand with ~220. I'll do that cycle 2-3 times, but itll look great on the pad after only one. Before putting the base or color coats, I've been giving it a light damp sanding with ~500 grit.

I really dont have the patience for getting a mirror finish either lol
 

TangoJuliet

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As far as the Nose Cone bevel, I've cut mine off and traced out the circle on a piece of 1/4" ply. I'll sand it to fit inside what's left of the shoulder, add an eye bolt, and epoxy it in place.
 

Kirk G

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Well, after searching for Valspar primer in the workshop, I seem to have used it up on the last project. As I recall, the spray nozzle was clogging too.
However, after a trip to Lowes I came back with another can and IMMEDIATELY remembered why I had celebrated the demise of that can. IT STINKS!

After just one pass, my wife was complaining of the fumes leaking out of the garage into the house, and I had developed a nasal sinus headache too.
So, I let it dry, took the can back and convinced them to refund my money (hey, it was bearly even used, and they bought that...). Next stop was at Kmart
where I got a more generic brand of white gloss primer, and brought that home. The second coat of primer is a bit brighter, and doesn't seem to smell as bad,
but still has that peculiar smell that only primer seems to have. So, I brought out the black gloss paint and masked the nosecone, and did the tip. Doesn't smell as bad.

Next step is going to be sanding the body tube and fins of primer, and then a base coat of red. I'm pretty sure all the rest of the coloring is water slide decals... plus, I
wanna try bolting/epoxy that flat plunger partition onto the bottom of the nosecone beveled base before I'm through. (I've got about two weeks to complete this before I
show it off at the next club meeting, and would like to have the paint job and decals finished.)IMG_20161230_134050571.jpg
 
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BDB

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As far as the Nose Cone bevel, I've cut mine off and traced out the circle on a piece of 1/4" ply. I'll sand it to fit inside what's left of the shoulder, add an eye bolt, and epoxy it in place.
I did the same. Here is a thread all about mods to the Big Daddy nose cone. I think the OP is talking about a mod like those shown in posts #26 and #45: https://www.rocketryforum.com/showthread.php?t=130943

Watch out with the cheap primer. I've had issues when mixing primer and paints that were from different "brands." This is Rustoleum 2x white primer with Rustoleum (not 2x) fluorescent green paint.

ImageUploadedByRocketry Forum1483274456.765987.jpg
 
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Peter Olivola

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The curse of VOC based finishing.

Well, after searching for Valspar primer in the workshop, I seem to have used it up on the last project. As I recall, the spray nozzle was clogging too.
However, after a trip to Lowes I came back with another can and IMMEDIATELY remembered why I had celebrated the demise of that can. IT STINKS!

After just one pass, my wife was complaining of the fumes leaking out of the garage into the house, and I had developed a nasal sinus headache too.
So, I let it dry, took the can back and convinced them to refund my money (hey, it was bearly even used, and they bought that...). Next stop was at Kmart
where I got a more generic brand of white gloss primer, and brought that home. The second coat of primer is a bit brighter, and doesn't seem to smell as bad,
but still has that peculiar smell that only primer seems to have. So, I brought out the black gloss paint and masked the nosecone, and did the tip. Doesn't smell as bad.
 

Kirk G

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I did the same. Here is a thread all about mods to the Big Daddy nose cone. I think the OP is talking about a mod like those shown in posts #26 and #45: https://www.rocketryforum.com/showthread.php?t=130943

Watch out with the cheap primer. I've had issues when mixing primer and paints that were from different "brands." This is Rustoleum 2x white primer with Rustoleum (not 2x) fluorescent green paint.

View attachment 308359
Besides the fact that it wasn't what you had intended or wanted.... THAT'S A GREAT EFFECT!!!!
 

BDB

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Besides the fact that it wasn't what you had intended or wanted.... THAT'S A GREAT EFFECT!!!!
I completely agree. I just need to figure out how to use it in an upcoming project.
 

Lowpuller

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Kirk,

That looks like the result of mold release and unwashed parts to me. I've been bitten by that snake many times.
 

BDB

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Kirk,

That looks like the result of mold release and unwashed parts to me. I've been bitten by that snake many times.
I promise that was just primer + paint. The two coats were laid down within the same night, so cure time may have been a factor. I'd like to figure out a way to reliably reproduce the effect with a variety of colors for an upcoming project.
 

rharshberger

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I promise that was just primer + paint. The two coats were laid down within the same night, so cure time may have been a factor. I'd like to figure out a way to reliably reproduce the effect with a variety of colors for an upcoming project.
They make paint kits that will doe the "crackle" effect. Your paint looks cool.
 

Kirk G

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I am pleased to report that not only has primer been completed and dried.... but the top coats have been applied and are now drying.
I am anticipating snapping some photos and posting an update. I have a bunch of decals to apply, and think they are all waterslide.

Plus, I have the parachute (very important) and the nosecone plunger/partition to finish yet.
(Nobody is thinking of finishing that circle balsa or plywood partition as it is inside, right? I mean, what's the point?)
 

Kirk G

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Time for a progress report:

I have finished the painting for all intents and purposes. Later tonight, I'll probably add the decals.
However, I am dragging my feet on this plunger/partition construction.

I went to Crafts 2000/Pat Cataan craft store and looked for the smallest thin piece of balsa, basswood or plywood from which to cut my circle partition.
I settled on an applicate, or stamped cut out, of a teacher's apple. It only ran me about a buck, and I could trace my entire circle within it's confines and still not crowd.
once I settled on this, I up-ended the body tube and traced the circle I needed onto the wood. Carefully working with a saber saw, I cut the circle and sanded it, and set it asside.

Here's a photo of the cut and sanded piece, complete with the UPC stickers still on it.Big Daddy plunger.jpg
Stupidly, I have been attempting to sand the edges to reduce this circle from an outside circumference down to the inside circumference of the body tube.
Just now, as I write this, I realize that I should have saved the card "frame" from which the centering circles were punched and used that as my template to trace the inside circle.
I probably would have or could have saved myself a lot of sanding. But, I didn't. This is getting really old as I am using a hand orbital sander with 220 or 150 grit to SLOWLY reduce the circle.
I don't want to go too far too fast, or else I am likely to have a gas leak on ejection charge, defeating the purpose of this whole modification.

As I write this, it also occurs to me that I could have trace the damn mounting circle before constructing the motor mount and done the same thing. But we're here now.

Anyone got any suggestions on how to speed this up, or suggestions on how to "finish" the partition once I get it sanded round so that it fits inside the body tube? Should I seal it with a wood glue slurry? Will it warp it? Should I paint it, or leave it unfinished when attached?

Suggestions? Ideas?
 
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