Thin wall HPR candidate - Smash Build

[Off Grid Gecko]

Alright, I said I would try to start this thread up tonight, so here I am.
Little background. Since I heard of people launching the Estes Mean Machine on G motors (some win, some lose, seems to be the failure point on the stock model) I've wanted to try this. I actually wanted to try something similar a long time ago with a 2.6" thin-wall kraft tube, but that's another story.

I've bashed up my Mean Machine kit and launched the first piece, the "Mini Meanie," on a D motor last weekend. Winds were too high for me to attempt the E12.

Anyway, there's plenty of 41.6mm tubing in this kit (which is why I bought it). I purchased a nosecone 3-pack with what looks like a 9" ogive included. Still figuring out the other parts, they look like they are payload adaptors or something. The design will be similar to "Mini Meanie" in outward appearance, but the guts are quite different. Here's a sketchup:



I'm hoping that this design will endure G motors easily, and possibly some H's as well. I didn't stuff that 29mm tube in there to look at it, but testing will need to be done on some smaller motors before I attempt anything too crazy. In theory, this should be go for an I, just need to figure out a way to track it at that altitude first.

Not in the picture is the payload assembly, which is kind of optional, but I'll be running DD on the bigger motors. Actually, that's what this bird is being built for, a solid introduction and experience fountain for rocketry electronics and DD. At least, a simple setup DD bird. Perhaps a reflective streamer for the drogue and a 12" - 15" chute for the main, depending on how heavy the motor is.

As the second derivation from the kitbash, this was going to be named "Mean Monster," but after finding a Monster energy sticker to use as a decal, I think I'm simply going to call her: "Monster" Designation GP007

Pictures incoming of the build process. This message will self destruct in thirty seconds.

 

[Off Grid Gecko]

Some of you will be familiar with this pic. After testing a few non-composite fin ideas, these were constructed for Monster. The base material is 1/4" Lauon. Some people like it, some don't. The stuff I have is three layers of thin birch veneer with two layers of the Polynesian wood sandwiched between them. Actual thickness is 0.203 inches after adding the top-layer. The top-layer is a single piece of Kraft paper, held down with TBIII, and folded/bent over the leading edge of the fin. The fins have been beveled with 10 degree tapers for airfoiling. They are finished with a touch of CA on the trailing edge to stiffen it against harder landings (Not necessarily rocks, but clay and hard soil). Several designs were tested, this one won out.


How to launch a High Power Rocket using a Kraft paper tube? Most of us depend on our air-frame not only to streamline the rocket but also as the primary structural material. This double-duty use has become common practice even in very large rockets like the Delta rockets (5 meter stir-welded aluminum can).
In this design, I wanted to take advantage of the fact that many rockets (especially MPR and LPR) have motor mounts that are much stiffer and stronger than the airframe. Extending the MMT to 14" adds a little weight, but also sets an anchor point far forward along the tube, meaning that the fuselage from that point down is essentially a large, welded, double-wall tube, with the interior wall being thick phenolic.
From that point forward, couplers inserted into the tube strengthen the wall there, which only needs to handle the weight and pressure of the mass ahead of it,,...well, unless it gets sideways.
BT-60 is pretty stiff for a Kraft tube already, and probably the reason Mean Machines can take some serious torture on F and G motors. By shortening and stiffening the tube in this way, I'm hoping the improved airframe will be no question on a G80, and able to handle much higher thrust loads. This is the secret to the internals. Everything is extra stiff and strengthened from the inside. The 29mm motor mount becomes a bone in the body of the Monster.

 

[Off Grid Gecko]

Okay, so, I decided to go with a centrally mounted eye-hook for this model. To do that, I purchased a coupler bulkhead from Apogee and then drilled it out. I started with 1/8" pilot holes, and then drilled them to 3/8". Four of them. Because reasons:



The bulkhead was completed with a thin slathering of JBWeld and secured in the center of the coupler that attaches to the top centering ring of the MMT and left overnight.

Then installed on the rocket along with the MMT and two forward centering rings and lower launch lug. I used Zap Z-poxy for the rest of the gluing for ease of insertion and lack of shrinkage that would de difficult with wood glue. I actually had to sand the CRs quite a bit to make them fit the MMT, but I've had it for a long time, so it may have swollen a bit.
I had some leftover epoxy so I put the second coupler in as well, and the whole assembly is awaiting fins, rear centering ring, and upper tube section.

 

[Nytrunner]

Tracker is right. Looking at nearly 3000 ft on the G80 if you keep it light, and it has a very small visual signature. Maybe one fin finished with trim monokote would add some flash to help keep eyes on it.

What's your deployment scheme? Even a G80-7 may not have sufficient delay time to reach the end of coast which could lead to premature deployment at speed.
Eggtimer quark is a self-solder kit that should fit well in a BT-60 with a thin LiPo for power. Mounting it securely in the airframe is an exercise left to the reader.

 

[Daddyisabar]

PO Boy philonic. Soak that Kraft tube in thin CA till it is smokin' like Jim Carey in the mask! Watch out for those vapes! Many think they are toxic.

Then get real bad and go for the DOPE! Be a little dopey like the workers were in the WWI aircraft factories. Ain't gonna hurt ya, better than working in the radium watch dial factory!

 

[Off Grid Gecko]

PO Boy philonic. Soak that Kraft tube in thin CA till it is smokin' like Jim Carey in the mask! Watch out for those vapes! Many think they are toxic.

Then get real bad and go for the DOPE! Be a little dopey like the workers were in the WWI aircraft factories. Ain't gonna hurt ya, better than working in the radium watch dial factory!

I like your style. She's going naked, no CA cept on the end points
Not totally naked though, that would be lude. I'll dress her in a skimpy lingerie of paint and primer.

As for the fumes, the epoxy is pretty good stuff. CA is nice for those lonely nights. What I really need is some ether

 

[Off Grid Gecko]

Tracker is right. Looking at nearly 3000 ft on the G80 if you keep it light, and it has a very small visual signature. Maybe one fin finished with trim monokote would add some flash to help keep eyes on it.

What's your deployment scheme? Even a G80-7 may not have sufficient delay time to reach the end of coast which could lead to premature deployment at speed.
Eggtimer quark is a self-solder kit that should fit well in a BT-60 with a thin LiPo for power. Mounting it securely in the airframe is an exercise left to the reader.

Planning to launch it first on an E or a high-thrust D(Aerotech D-21 maybe). Electronics bay will be added and I'll likely set up a dual deploy. First stage just a streamer of some type. I was going to do separation only (with a tether) but something showy would be better. Smoke bomb? Nah, maybe just some reflective ribbon.
Then pop a chute around 300-500 feet.
You hit the nail on the head. Big worry here isn't the thrust curve, it's being able to follow the little thing into the heavens. Launched the other one on a D and it got really really small quite quickly. Perfect cheap platform to test a micro-RF transmitter though...maybe. I'm more interested in the thrust than the impulse. I want to know what she can take. E's and F's are the main targets...for now.

 

[Off Grid Gecko]

Attaching fins tonight with 30-minute epoxy. If only I had some 5-minute epoxy on hand for this job. I consider this "tacking" for TTW stuff, as the inards will be substantially covered in a gel layer by the time I'm done. Not on purpose, it's just a tiny space to work inside without making a mess. I might try a drip from the leading edge area since the cutout is large enough for me to goop some in there, but we'll see about that. Dripping epoxy makes me nervous.

I took the pic earlier. I have one left to go and will be setting it up momentarily. So far the new jig is working flawlessly. At least, that's how it appears. I don't have a laser micrometer handy, lol.

Next will come some fillets (probably tomorrow night or this weekend) and figuring out how to fill the unsightly hole that will be left by the leading edge bevel. One of these days I will stop tormenting myself and cut the tab further back from that area. It'll be easier on bigger fins.

 

[Off Grid Gecko]

Will attach pics later, but I've finished with the epoxy job on the fins. Came out pretty decent, and the epoxy filled most of the gap around the leading edge, enough that a little wood putty should finish the job nicely. 1010 rail buttons installed on the tube, upper 6" section permanently attached with couplers running from the upper centering ring of the motor assembly all the way to 1.5" shy of the top of the tube (enough room for the nose cone or future E-bay to slide in there comfortably).
Now I'm thinking about the DD bay itself. I'm going to order some bulkheads and build from there. Considering an RRC2+ or RRC2L, both are around $50 and I'm still a little behind on my money so I might need to save for a couple weeks before I can purchase that. I have the tubing and a small bit of coupler leftover from the Mean Machine kit, so sizing everything up to prep for finishing and paint of the fuselage.
My main concern is the length. I'm thinking that I need about 4-1/2 inches of empty tube at the top for chute/charge/cord/NC Shoulder. The altimeter will need about 3" of space, plus another 2" for the battery. I'll have a coupler bulkhead for the bottom which will mate up to the existing internal coupler system for the rocket, so the bay will extend past the bay BT section 1.5"

When I sketch this all up, I see an 8" BT section with < 1.5" of coupler sticking out of the bottom, and the rear bulkhead sealing it from that direction. This theoretically leaves enough space for everything, even if I run the main chute on top (which I plan to do). I have more space below in the main BT if needed as a backup.
Is there anywhere I should add some more room to play it safe? Any "ah crap" moments in my future for a space taker that I didn't consider? My original inclination was to make a 10" tube section, adding an inch to both the inside of the E-bay and the hollow recovery system area, just in case. This will make the overall length somewhere around 44" tall for the rocket. I plan also on sketching this up on the simulator a little later tonight.

 

[Off Grid Gecko]

Ah crap... If I'm ever going to have hope of launching this on an H or an I, then I need to make room for the tracking system gear. 18" electronics bay it is! My radio guy hasn't gotten back to me on our secret micro Tx yet and I don't know which GPS unit I'll be looking at yet. Answered my own question. No need to cut down the other tube. She's starting to resemble a Black Brandt.

 

[Off Grid Gecko]

Here's the fin attachment. Trying to figure out how I'm going to prep the Kraft-papered fins for paint so that I don't get little fuzzies the second I try to start sanding down. Using wood filler to smooth everything out, thought the epoxy went on pretty slick. I still have some little divots at the rear of the fin root, but they are consistent across all the fins, so I'm good with it.
I decided on 13" for the payload/electronics bay. 5" for chute/wadding/etc and the rest for electronics, giving me some extra space for recovery beacon tests.
I've been studying for my HAM license for the last couple days, so rocket progress has been slow. Hoping to finish up the rough smoothing and get a primer spray on here pretty soon.

 

[Off Grid Gecko]

Finally got around to another picture. I want to include some specs here going forward as well, sort of for the record with regard to paint weight.
Since I'm still engineering the guts, the total weight will change quite a bit, but had I thought of my solution to that sooner, I would have gotten a weight before sealing.
I sealed the whole body with spray laquer. Then sanded down smooth and shot my first coat of sealing primer.

Total primer weight, including the excess on the dangling masking tape parts was ~5g. It went from 203 to 208 on my kitchen scale for total. I've added some more tape to secure the tube breaks better. I'm only going to do a light sanding, but if there is a significant drop I'll let you guys know. Just what's needed to remove some wayward spiral remnants and etc. I will likely redo the area around the fins with what is left in my spot putty tube. The leading edges still have a bit of a dimple from the hole.

 

[Off Grid Gecko]

Thought it was time for an update. I put down the first layer of color yesterday before leaving for the club launch. Total weight bumped to 244g, that's including several more applications of primer. So yeah, paint weighs quite a bit, but I was trying to fill every tiny little spot I could find and at the same time trying to avoid those "hair raising" moments while spraying a new coat. Got it pretty well hashed out now.


And leave it to me to start painting before everything is finished. I have the parts now to start on my electronics bay, so I started with the sled and getting all of the guts glued into this piece. Four more couplers to keep with the double-wall philosophy. There are also a couple of centering rings in there... for what?

So here's the internals on the tube: From right to left. 3-3" couplers, two cardboard centering rings (as as small as I could find) and another coupler. The rings will act as a stop for the sled. The piece on the left will be permanently attached to the sled. It will slide in from the nose end and stop at the couplers, with the bolt hole near the motor end of the tube. There is about 4" of space behind the nose for a chute and pyrotechnics. The aft closure bolts on at the bottom with the regular laundry behind that in the rest of the body tube.

Basically, the sled mounting "squeezes" the guts of the E-bay to hold itself in place, it also acts as another thrust transfer mechanism to keep most of the heavy lifting off the skin of the rocket. The bits were glued so that the bottom bulkhead rides just above the top coupler in the rocket tube.

The sled was cut just a touch wide to fit through my centering ring, so I'll need to trim it down a bit, but it should be pretty easy. I had forgotten how exactly I was going to make this work so I cut it wrong. It's also designed to ride offset from center so there is room for .. say.. a 9v battery, etc. I will poke holes and cut slots when the time comes, for now, would like to just get it all together. Looking at less than 300g at the moment, but we'll see when all the painting is finished.

 

[Off Grid Gecko]

Painted up, waiting on the smell to clear before adding some clear coat. Been wondering lately what kind of clears people use to get a nice hard finish on their rockets. There are a couple of spots where the masking didn't work out so well, minor blemishes, but overall I would like to keep this paint job looking decent. I have a can of Rusto acrylic 2x that I was planning on using up for this job. Just curious what people use (from a rattle can) for the most durable finishing coats.
All up with the sled mounted and parachute attached, she's weighing in at 312g, which is a touch heavier than I wanted. After clearcoat she might go up to into the 320s. Still a good bird to test dual deployment and some other recovery goodies once I get the money, but I'll have to launch on something bigger than an E12 unless it's a super calm day. I tested at 6' of launch guidance in open rocket at 350g (415 with motor) and came up with 13.4m/s. Little slower than I would like off an 8' rail. It's also a late deploy on a 12-6, so either way I'm buying some motors.
Anyway, making this post for the pics so I guess I should post them.


Extreme close up of the fin can:

 

[o1d_dude]

“Dripping epoxy” is only kinky the first time.

After that, it’s that thing you do...when you cannot easily reach the place the epoxy needs to go.

It’s just another tool in your rocket building toolbox.