Build Thread - Long Burn 129

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Ever since Aerotech came out with the H13ST over a year ago I've wanted to scratch build a model that could take advantage of it. I played with a design for over a year to get to a point where I was ready to build it. I tend to design models that can meet multiple objectives so that I can fly it multiple times to try to meet different design criteria. My goals for this one were:
  1. Ability to fly on long burn engines safely in low to moderate winds (< 7MPH). Specifically, the H13ST and also the G12ST and the Apogee F10 (in lower winds, <3 MPH).
  2. Ability to fly on F & G motors on smaller fields.
  3. Ability to fly on high thrust motors when the winds are so friendly, up to an H195NT.
  4. Ability to fly at or above Mach 1 on high thrust motors (stretch goal).
  5. Large enough airframe to allow TTW fins to handle the high thrust motor options (over 40 G's on an H250G).
  6. Include a nose cone E-bay with a deployment altimeter for apogee deployment and a GPS tracker, since this sucker will go WAY out of sight on either the H13ST or the H195NT.
  7. Be able to come down on a parachute small enough that I can use a JLCR to keep it from drifting for miles. No room for a drogue.
The design is a series of compromises to meet these goals, some of which will fall just short (I'll note those as I proceed on the build). Finding the balance was a highly iterative process.

Below is the side view from Rocksim.

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What's the stability with the H 13 loaded ? Those fins look like they may be on the smaller side.
You would think so in looking at it, but it comes out fine. I intend to take an output to the RSO when I fly it, they'll have the same question. I found the shape of the fin to be very critical to meeting the design objectives. Having a zero length tip chord is key on this design.

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Out of curiosity, why is that the case?
Don't know. I only lasted one semester in Aero/Astro engineering in college (50 years ago), too much calculus and my fellow students were too nerdy even for me. I could figure it out if I went into the weeds but that would make my brain hurt. I prefer to trust Rocksim and continue building.
 
Here are the (original) assembled parts. I say original because I had to make an adjustment or two as the build progressed. I'll get to that as I go. The build is actually complete except for ground testing (maybe this week). I am documenting it after the fact because it makes me think through the issues I encountered and document them so I can remember what not to do in the future.

Below it the pic of the parts. I'll post the E-bay separately since that was already built and was a mod of the Badass design.

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AFAICT Apogee Aspire components are the lightest you can find in this size, and you might be able to get away with just a streamer.
 
Here's the nose cone E-bay. Badass (now Mach 1) nose cone deployment/tracker sled. The base design calls for a Quantum and an Eggfinder Mini. I wanted to use a Featherweight GPS instead and I've asked Ian for this combo in a sled but he's too busy spinning up the new Mach 1 to make it happen, so I modified (butchered) the sled to accommodate the FW. It's not elegant looking but it will work. I do not have an external switch for powering up the electronics (damn E-bay is really tight as it is) but the solution was acceptable, which I'll explain when I get to mounting it in the nose cone.

LB1 Badass Sled Mod for FW GPS.jpgLB1 Badass Sled - Quantum.jpgLB1 Badass Bay - FW GPS.jpg
 
AFAICT Apogee Aspire components are the lightest you can find in this size, and you might be able to get away with just a streamer.
Nope. This will be way too heavy for a streamer with the E-bay and motor combo. Even if I could size a streamer to bring it down slowly I do not think it would fit in the 38mm airframe. This baby is tight!

Bird is 484 g. The streamer calculator (https://www.rocketreviews.com/index.php) has a 4" streamer being 160" (13+' long)...
 
My first step was to cut out the plywood fins. I want to cut all three at the same time so I taped three sheets of plywood together and then taped the fin set template root edge printed out of Rocksim to one edge of the plywood sheets. I used a protractor on my clear 45 degree triangle to measure and note the angle cuts on the template for setting up the cut on my miter saw.

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The next pic shows the miter saw setup before the first cut.

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Here are the cut fins before cutting the fins tabs.

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Next I cut out the fin tabs with a razor saw. The next tool I have to buy is a band saw... The finished product...

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I mod'ed a LOC Magnum Park Flyer for this very same quest - to fly on the H13. I added an altimeter (single deploy) and a FW tracker. Your parts look similar to my build.

If you haven't already, thoroughly simulate different wind, rail length, and rail angle scenarios. To get adequate rail exit velocity, stability, and low weathercocking, I had to use two lengths of 1500mm MakerBeam 10mm x10mm rail and microbuttons. (The MakerBeam rail nests nicely into a standard 1010 rail which allows a practical and secure launch guide.) Still, from my analysis, I didn't feel comfortable launching in any wind much more than 5 mph.

After a year of waiting, I finally got the right conditions - sunny skies and near zero wind. The rocket came out of the 3 meters of rail a little weak, but the H13 kicked in for good and the rocket climbed for 15 seconds of burn - quite the crowd-pleaser. Max altitude was 5900 ft per the GPS.
 
I mod'ed a LOC Magnum Park Flyer for this very same quest - to fly on the H13. I added an altimeter (single deploy) and a FW tracker. Your parts look similar to my build.

If you haven't already, thoroughly simulate different wind, rail length, and rail angle scenarios. To get adequate rail exit velocity, stability, and low weathercocking, I had to use two lengths of 1500mm MakerBeam 10mm x10mm rail and microbuttons. (The MakerBeam rail nests nicely into a standard 1010 rail which allows a practical and secure launch guide.) Still, from my analysis, I didn't feel comfortable launching in any wind much more than 5 mph.

After a year of waiting, I finally got the right conditions - sunny skies and near zero wind. The rocket came out of the 3 meters of rail a little weak, but the H13 kicked in for good and the rocket climbed for 15 seconds of burn - quite the crowd-pleaser. Max altitude was 5900 ft per the GPS.
My launch pad can go to 14' of 1010 rail or I can add my rails to my club's setup. Winds tend to need to be less than 7 MPH, ideally less than 3 MPH. Launch rod angle is about 1 degree per 2 MPH of surface winds if over 3 MPH; if lower it doesn't matter. I've run the sim 100 times.

Thanks for sharing. Now I just need to ground test and get a decent day. I bought the H13ST a year ago as incentive to get my butt going and build it...
 
Next step was to cut the centering rings. Again, I cut out three squares of 1/8" plywood and tacked them together on the corners with CA. This stack is tacked to a piece of cheap plywood so that the bottom ring doesn't splinter on the back side of the cut. I drew the inner and outer cuts on the top piece with a compass and centered the stack in the drill press and clamped the stack down. The inner cut is done first with a hole saw slightly smaller than the hole size required. After the first cut, the second cut is made with a hole saw bit slightly larger than the size required. The pilot bit is of no use on the second cut, hence clamping the stack before the first cut ensures the stack stays centered for the second cut.

The only disadvantage of using the stack is that after the first layer of the stack gets cut (on either the 1st or 2nd cut), the freed piece sticks in the hole saw and the friction between it and the next piece causes some burning. At that point I stop and remove that piece from the hole saw and then continue. I could do one ring at a time, but that requires swapping the bit out for every cut. It's really six of one and a half dozen of the other.

After the rings are cut out, I finish sizing each ring's inner and out diameter with a Dremel. Below are pics of the process and the final fitting.

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My father and I had similar thought to you. How could we the maximize the performance of this motor? So we scratch built a 29mm Minimum Diameter rocket with an altimeter to eject parachute at apogee. I believe we were able to reach almost 8k feet. We also put a spin tap on one fin that was made out of painters tape to give it a little spin to keep it going straight as possible.
 
Next step was to cut the fin slots on the airframe. I have started using Badass (now Mach 1) build guides for all of my builds 38mm and up. They hold the fins great and have drill hole guides in three sizes. The first step was to use the guide to mark the three slot locations. Then I used the fins them selves to mark the width of the lines to cut and drew straight lines with an aluminum 90 degree angle bracket. To make the cuts, I tape an aluminum ruler along the lines to be cut and use it as a straight edge. After cutting the first slot I put the Aeropack retainer on the MMT with the centering rings slipped on and verified the slot matched the MMT design.

I use the Z xActo blades for cuts like this. The LOC tubes are thick and the Z blades are way sharper than the standard blades; they make easy work of it. Pics below with the final fitting of the fins in the airframe.

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I'd love to see some usable drawings so some of us could build one for ourselves. It looks FUN!
Here’s a sketch of the rocket. We flew it first on the G8 couple of years ago but that wasn’t enough thrust. When that H13 came out, it was just right for the rocket! This rocket is pretty long. If you wanna go higher/faster you could probably cut down on some of the body tube length.
 

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Here’s a sketch of the rocket. We flew it first on the G8 couple of years ago but that wasn’t enough thrust. When that H13 came out, it was just right for the rocket! This rocket is pretty long. If you wanna go higher/faster you could probably cut down on some of the body tube length.
I agree the G8 is too low of thrust. That engine is really intended for boost gliders. The G12ST sims out OK in my build with low wind speeds. How many calibers is the mod above? I think you ought to be able to cut the body tube down quite a bit. Mine is coming out to 28" long (just enough room for the parachute).

I'll post my Rocksim file after I finish this build thread.
 
The next phase of the build was to build out the nose cone E-Bay. This turned out to be quite a challenge. In using the Badass (Mach 1) nose cone sled, it was originally designed for fiberglass nose cones and couplers, so using a plastic nose cone required some re-engineering.


The first step was to cut out the bulkhead to fit into the coupler that the nose cone would attach to. Below is the pre-drilled coupler, marked for cutting out and drilling the necessary holes the altimeter terminals, charge wells and eye bolt and dry fit to the coupler.

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The next challenge was fitting the coupler into the nose cone. The LOC small nose cones are pretty thick (for strength) so the coupler did not fit into the nose cone shoulder after the end was cut off.

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In a previous build I had inserted the Badass sleeve directly into the nose cone without a coupler (reinforced it with a light coat of epoxy), but that wasn't ideal because the taper of the nose cone did not allow enough of the sleeve to go into the nose cone far enough. It might have worked EXCEPT the sled was also too wide at the junction to go into the nose cone as well. Luckily, with the nose cone plastic being so thick, the solution was to Dremel down the inside of the nose cone shoulder to make the coupler fit. I didn't take a pic of the coupler in the nose cone after the Dremeling but it fits.

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Next step was to build out the bulkhead. This was probably the biggest challenge of this build. I used two charge cannisters instead of one because with the H13ST being a plugged motor, I really wanted some redundancy built into the recovery design (even though it has only one altimeter, it avoids a dud e-match being an on the primary). The first issue, which isn't pictured, is that the holes for the charge terminals were to close to other components. Consequently, I had to cut out a second bulkhead. Lesson learned, in tight spaces you really need to think through your spacing and tolerances.

The first pics shows the charge wells installed. I'm using 3/8" copper piping here instead of PVC because I want to use centrifuge tubes to hold the BP and the ones I could find fit the copper and not the PVC. I had just put the caps in place at this point, I'll solder on the copper tubes later. The caps are attached with 6-32 screws and lock nuts. I tapped the caps as well, so these charge wells aren't ever moving.

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The next thing I noticed was that when I put the charge wells in the eyebolt wasn't long enough to attach the quick link. That was solved by adding extending the eyebolt with a coupler (just another trip to the hardware store).

Below are pics of the completed bulkhead. The terminals are 2-56 screws. The knurled nuts are upside down because the terminal screws should have been another 1/4" long, but I have 100 of the length I used, so upside down they go.

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Time to install the Badass Sleeve and bulkhead into the coupler. The sleeve is easy, I used some laminating to install it.

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The bulkhead provided some concerns. It is not a stepped bulkhead, so it must sit in the coupler at the end of the coupler yet take all of the force of the BP ejection charges, any jerk at the end of the shock cord ejection and the parachute opening. I used three methods to anchor the bulkhead. The first was I recessed it slightly into the coupler. I then epoxied the inside edge to the coupler. The second method was to create an epoxy dam on the outside face of the bulkhead. This makes the bulkhead, the topside components, the coupler and the epoxy one single unit. Finally, I counter sunk three 2-56 wood screws through the coupler into the bulkhead. It's not going anywhere. The finished product below. I can safely say this is the last 38mm E-bay I am going to build. It was tough!

For those wondering, the tolerances on the terminals are close, but there is 1-2mm between them. It will require careful prep of the e-matches, but it's doable (even with arthritis).

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