4" Upscale Screaming Green Meenie

Discussion in 'High Power Rocketry (HPR)' started by 75Grandville, Oct 4, 2019.

Help Support The Rocketry Forum by donating:

  1. Oct 4, 2019 #1

    75Grandville

    75Grandville

    75Grandville

    Well-Known Member

    Joined:
    Feb 20, 2014
    Messages:
    710
    Likes Received:
    12
    OK, this has been in the back of my mind for over 5 years. Rediscovering my Screaming Green Meenie gave me the impetus to pick this project back up. And it's improved for having waited 5+ years. The original version had a 29mm MMT. The current version has a 54mm MMT :D My plan is to eventually fly it on a Aerotech J-315R. If you've got a 54-852 casing that you are looking to sell, PM me. I've got a 1706 motor and a RAS, but that's a little too big for this rocket.

    So, this will be as much of a build thread as I usually manage. I sometimes remember to take pictures, but more often I get too excited and just push ahead. Hoping to have this ready for the UROC launch on 12 October, provided that the fire danger is low enough.

    Here are the .ork, .pdf, and .rkt versions
     

    Attached Files:

    Last edited: Oct 4, 2019
  2. Oct 4, 2019 #2

    75Grandville

    75Grandville

    75Grandville

    Well-Known Member

    Joined:
    Feb 20, 2014
    Messages:
    710
    Likes Received:
    12
    The first step was to order the parts. The nose cone and centering rings came from Rocketarium. The 4" body tube came from Apogee. The 3" body tube in the nose and the 54mm MMT tube came from stuff that I have laying around, as did the plywood for the fins.

    After my "wanted" post for the tube fins, I realized that I could just order qty 3 x 2" switch bands in 4" fiberglass tube from Wildman. Along with more RocketPoxy because my existing supply is too old and almost empty.

    Step 1 was to put the nose cone in the body tube, then drop a centering ring down on top, and draw a circle with a white paint pen. Remove the nose cone, cut carefully along the white line, and I now have a 3" diameter hole in the nose cone.

    I fitted a length of 3" cardboard tubing into the nose cone, trimmed to length, then glued a centering ring to the end of the 3" tube.
     
  3. Oct 4, 2019 #3

    75Grandville

    75Grandville

    75Grandville

    Well-Known Member

    Joined:
    Feb 20, 2014
    Messages:
    710
    Likes Received:
    12
    The next step was to dig out (and it truly was digging out) my plywood from where I store it. I printed the fin template out several times. Confusion with scaling to fit, page orientation etc. But, I finally had my template.

    Took the plywood outside, then used a circular saw and a T-square to rip it to length. Yes there are easier ways, but one table saw is in storage and the other is just buried. And my 4' clamping straight edge is in hiding for reasons unknown. So I went low tech. It worked.

    Took the piece of plywood, and used the dining room table to lay out the fins. I've heard that other people use their tables for eating. Weird.

    Fired up the scroll saw, and rough cut the fins. I have no idea how people actually make precision cuts with one of those. I am getting better, but my cuts are all still wiggly. Then clamped all three fins together and sanded the heck out of them until the profile was correct. Then rounded the leading edge, and tapered the trailing edge. They have the fin tab, but not yet the notch for the tube fins.
     
  4. Oct 4, 2019 #4

    75Grandville

    75Grandville

    75Grandville

    Well-Known Member

    Joined:
    Feb 20, 2014
    Messages:
    710
    Likes Received:
    12
    And then tonight I actually had a couple free hours, and the inclination to work on this.

    Used the belt sander to get all three tube fins to the same length. I had hoped not to need to do that, but there was probably a 1/8" variation in the heights. Also took the opportunity to sand the epoxy off the fins from my LOC Tri-Star (the only surviving bits).

    Used the fins as a guide to mark the body tube for the slots. A sharp razor knife and an angled piece of aluminum made the cuts go pretty quickly.

    The rings provided a template to mark for the notches. Cut the notches, dry-fit the tube fins, re-cut the notches, then dry-fit with the body tube IMG_0077.JPG IMG_0078.JPG IMG_0079.JPG IMG_0083.JPG
     
    Last edited: Oct 4, 2019
    aerostadt and ep29030 like this.
  5. Oct 4, 2019 #5

    75Grandville

    75Grandville

    75Grandville

    Well-Known Member

    Joined:
    Feb 20, 2014
    Messages:
    710
    Likes Received:
    12
    Next, marked the motor tube for the position of the centering rings. Then cut the glassine overwrap to give the epoxy something to stick to.

    Mixed up a small batch of RocketPoxy, then epoxied the centering rings to the motor tube. Then epoxied the tube fins to the plywood fins. IMG_0084.JPG

    And that is where I stopped for the night.
     
    dhbarr and ep29030 like this.
  6. Oct 7, 2019 #6

    75Grandville

    75Grandville

    75Grandville

    Well-Known Member

    Joined:
    Feb 20, 2014
    Messages:
    710
    Likes Received:
    12
    Made time to work on this over the weekend. U-bolt added to the top of the motor mount, and the fins are on! Not pictured yet - I got the fillets done as well. Two sets inside the tube fins as well as the big ones on the fins themselves. A final batch-o-stuff on order from Rocketarium (planning to put the avionics in the nose, up at the very top).

    Of course, fire restrictions have not yet been lifted, which means that the launch this weekend is at risk. Bummer if we can't fly, but not as big a bummer as starting a wildfire.
    IMG_0085.JPG IMG_0088.JPG
     
  7. Oct 9, 2019 #7

    75Grandville

    75Grandville

    75Grandville

    Well-Known Member

    Joined:
    Feb 20, 2014
    Messages:
    710
    Likes Received:
    12
    Mistakes were made...

    Using John Coker's suggested method, I added two 1/4" aluminum rods across the nose cone to help hold the weight in. Yes, 1/4" is overkill - it's all I could find at the local big-box store. I used 16 oz of loose hardware (screws, nuts, bolts) purchased from Harborfreight for just this purpose. And yes, I would prefer lead shot or something similar, but I already have this in hand. I dumped the hardware in, then poured in the two-part expanding foam.

    I tried the set-and-forget method, where you pour the foam and then ignore the part for 24-48 hours. My discovery after the fact was that the foam had risen up the tube intended to hold the chute and AV bay.

    Insert your choice of expletive here.

    I tried cutting the foam away from the tube with a long knife, but when I twisted and pulled, all of the foam slug above the aluminum rods came out attached to the tube!

    Additional expletives as required.

    So, I cut the blob foam and hardware free, trimmed as much as possible, tossed it back into the nose cone, and added more foam. I also added a third aluminum rod just above the original material, to hold the entire thing in place.

    We'll see how that seems to be holding up tonight. I think I just cost myself a couple inches of tube - I need to trim to the new length.

    Otherwise, fillets are mostly done (some filing/sanding still required. Got word from Rocketarium that the rest of my parts shipped today. So it's down to waiting. Again.
     
  8. Oct 10, 2019 #8

    RainierWolfcastle

    RainierWolfcastle

    RainierWolfcastle

    Well-Known Member

    Joined:
    May 24, 2017
    Messages:
    77
    Likes Received:
    15
    When using nose weight like that I prefer to use epoxy to hold it in, you need mass up the front anyway so just count it as part of it. If you need to attach something else you can bury a bit of threaded rod or my favourite is a coupler nut with a button head screw and washer in it, use longer threaded rod to hold it in place and then you end up with a female thread and can use it for an eye bolt or threaded attachment point. Using this method I managed to get a 2.5” parachute tube, AV bay with two altimeters and a lot of nose weight in a 5.5” loc nose cone with room to spare.

    Or after the epoxy over the weight then fit your centre tube and foam around to lock that in. Either way roughing the inside of the nose as much as possible helps keep things in.

    Extra tip: use some tape or blutack over the aluminium dowels so that epoxy doesn’t weep out. It’s easy to clean off the nose, not easy to get off the garage floor.
     
  9. Oct 10, 2019 #9

    75Grandville

    75Grandville

    75Grandville

    Well-Known Member

    Joined:
    Feb 20, 2014
    Messages:
    710
    Likes Received:
    12
    This is the "before" shot, with the foam just added. Next time I will definitely use epoxy. Definitely.
    IMG_0090.JPG

    And this is take two. Tonight I dig out my angle grinder and trim the aluminum rod. Yes, I share my rocket table with my kids, who think of it as their slime table.
    IMG_0093.JPG

    I wound up losing about 1.5" from the tube for the AV bay and parachute
    IMG_0096.JPG

    The foam rose too high, so I wound up using a 1" spade bit on a cordless drill to grind up the excess for removal.

    IMG_0098.JPG

    Launch definitely cancelled. Seriously considering road trip to fly with Tripoli Las Vegas.

    Found the shock cord I plan to use. Mail snail, please hurry with my package!
     
  10. Oct 13, 2019 #10

    75Grandville

    75Grandville

    75Grandville

    Well-Known Member

    Joined:
    Feb 20, 2014
    Messages:
    710
    Likes Received:
    12
    Coming down the home stretch. At least I hope so!

    I added some tee nuts to the final centering ring, to hold the motor retainer clips in place.
    IMG_0099.JPG

    Then I whipped up some more epoxy, and placed the final centering ring.
    IMG_0101.JPG

    At which point, box of happiness arrived from Rocketarium, several days ahead of schedule!

    I still had some leftover epoxy, so I added the rail guides.

    IMG_0102.JPG

    Then I started in on the AV bay. First gluing two bulkheads together to make one lid. Then drilling out to run the U-bolt through. IMG_0103.JPG

    I was also sanding down the aluminum rod that was protruding from the nose cone. Here's a tip. If you are using a belt or disc sander to smooth down the aluminum, it also makes it very hot. Hot enough to melt the nose cone. So I took a little more care with the rest of it, and filled the melted hole with epoxy mixed with glass microspheres. New rocketry scale arrived at the same time. Nose cone plus weight is 667 g.

    IMG_0104.JPG

    Back to the AV bay. The way it will work is that the actual AV bay will sit toward the nose of the rocket.

    IMG_0107.JPG

    Once it has been slid into the tube into the nose cone, a second coupler with another centering ring slides the AV bay forward.

    IMG_0106.JPG

    IMG_0105.JPG

    The epoxy is drying on the coupler centering ring. Once that is all dry (tomorrow), I will use some sort of tee nut (not as wide as the ones I originally purchased, but at least those will work for motor retention) to fasten the 3" body tube and centering ring into the nose cone, then something similar to add the coupler and bolt it on to the first centering ring.

    The AV bay is staying unfinished for now - maiden flight will feature motor deploy. However, I have enough space to get two small (RRC2+ and/or Stratologger CF) altimeters in the bay, plus batteries. Not sure if I'm going to use charge wells, or just use vials/latex glove fingertips for the primary charge. And I should be able to use cable cutters for dual deployment.

    Oh, and since I've had the epoxy etc out, I also worked on my TriStar clone. The fins and shock cord were all that survived from the original rocket. It was a perfect flight - all three H219T's lit. Up part was super. Then it didn't separate. Sigh. That's why I use DMS for my riskier flights. I'd hate to be out the cost of a rocket, plus three (or more depending on the flight) motor casings.

    IMG_0100.JPG

    IMG_0108.JPG
     
    JDcluster likes this.
  11. Oct 13, 2019 #11

    JDcluster

    JDcluster

    JDcluster

    Well-Known Member

    Joined:
    Feb 23, 2009
    Messages:
    5,245
    Likes Received:
    70
    Gender:
    Male

Share This Page