RetroRacer

Discussion in 'Scratch Built' started by Rockhaus, May 20, 2019.

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  1. May 20, 2019 #1

    Rockhaus

    Rockhaus

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    Going to start work on this boy:
    upload_2019-5-19_20-56-20.png

    6" Diameter, and I'd like to do a 29 mm cluster motor config, thus:
    upload_2019-5-19_20-57-52.png

    Estes BP motors, outer six will be F15's, center will be an F50 (for a bit more kick off the pad). My concern is the fins. With the curves, tabs for the fin pod support (no motors!), and thru-the-boat-tail-wall, they'll be complicated. I'd like to do G10, but I've not requested curved fins from a vendor before. Can somebody like Public Missiles pull that off? Here's the RockSim:

    upload_2019-5-19_21-4-42.png
     
  2. May 21, 2019 #2

    Tobor

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    Cool!
     
  3. May 21, 2019 #3

    Mugs914

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    That thing is awesome! A real classic...

    G-10 isn't that hard to cut and sand if you have access to a band saw or jig saw. It actually sands pretty easily. Of course I have to add that you should wear a respirator when cutting or sanding the stuff.

    Please keep us posted on the project.
     
  4. May 21, 2019 #4

    Rockhaus

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    Thanks, Mike! That's good to know. I do indeed have a band saw and respirator. Who sells the sheet stock?
     
  5. May 21, 2019 #5

    neil_w

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    Looks nifty. 7-motor cluster should be a lot of fun.
     
  6. May 22, 2019 #6

    Mugs914

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  7. May 23, 2019 #7

    Rockhaus

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  8. Sep 23, 2019 #8

    Rockhaus

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    Made some progress this weekend on the RetroRacer. PML came through very nicely with the curved G-10 fins.
     

    Attached Files:

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  9. Sep 23, 2019 #9

    BABAR

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    Very cool!
     
  10. Oct 9, 2019 #10

    Rockhaus

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    Well, I don't think we'll lose it...
     

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  11. Oct 9, 2019 #11

    les

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    Very nice! Looks great
     
  12. Oct 9, 2019 #12

    Mugs914

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    Beyond cool!! That really came out great!!:cool::cool::cool:
     
  13. Oct 9, 2019 #13

    Scott_650

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    Very retro and slick! How did you construct the boat tail?
     
  14. Oct 10, 2019 #14

    Rockhaus

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    The boattail is from PML, and they'll put the slots in per customer requirements. For the motor mount I clustered 7 motor tubes together, and held them together at the ends with a coupler stiffener from Apogee designed to go inside a 4" tube coupler. The ID of the stiffener just happens to be equivalent to 3 times the diameter of the 29 mm. So, really no traditional motor mount. Here's the hard part: this leaves open space between all the tubes that ran along the length of the tubes into the main body tube. You can't cut a motor mount for this, as the motor mount tube walls all touch. So, that left easy paths for the ejection gases to escape, and we'd get no pressurization to eject the chute. So, I used some of PML's expanding epoxy to "plug" the larger spaces, and some Fix-it epoxy putty to plug the smaller channels. I ran some all-thread along three of the smaller channels to use for motor retention. Here's a couple of shots of the fore end, one shot showing some of the expanding epoxy that still needed trimming (Dremel), and the other is the finished product. This looks pretty air tight. The little dry wall mounts worked well to anchor the 6-32 all-thread. The three fin tabs slid through the boattail wall, and tucked in between the adjacent motor tubes.
     

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    Last edited: Oct 10, 2019
  15. Oct 10, 2019 #15

    Rocketjunkie

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    f possible, I would use electronic deployment, particularly for clusters. If all the motors don't light, your motor delay will be too long. I have a LOC Ultimate, also with 7 29 mm mounts. I left the spaces between the motor tubes open to allow unused ejection charges to vent. There is a bulkhead in front of the motor tubes, far enough for the longest motor (CTI 6G XL). With this setup, electronic ejection is mandatory. The original Ultimate had 3 long motor tubes and a 3 hole centering ring that blocked off the other 4 motor tubes.
     
  16. Oct 10, 2019 #16

    Scott_650

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    Hopefully you can post some video of this in action - should be a very pretty sight! Thanks for the details on the PML boat tail.
     
  17. Oct 11, 2019 #17

    Rockhaus

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    We're going all Estes F15 for the first launch. I've had a pretty good luck getting those to light in a cluster, with First Fire Jr's and a dab of black powder at the end, and plenty of current. With this thing, I'd love to go APCP, but that's for another day.
     
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  18. Oct 11, 2019 #18

    Rocketjunkie

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    Check all your F15s to make sure you can see the black powder in the bottom of the nozzle. Occasionally some nozzle clay will cover the BP and the motor won't light. Scrape out the clay with a small drill bit or use another motor. Also, ematches fit into the nozzle, just stick in place and use tape to hold them in. Much lower current requirements.
     
  19. Oct 11, 2019 #19

    jqavins

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    When you eventually go composite, you could mix and match propellants for color effects. As long as diametrically opposed pairs match in three sets, or equilateral triangles match in two sets, the thrust remains symmetrical. Something like a sparky or smokey in the center and red, blue, and green pairs around it would be awesome.
     
  20. Oct 11, 2019 #20

    Nytrunner

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    Woo, that thing has an I worth of impulse in it with just the F15s!
     
  21. Oct 11, 2019 #21

    jqavins

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    That's a good point. Rockhaus, are you L1 certified? If not you'll have to leave one engine out. Even if you are, it might be worth doing a sim with the center motor tube plugged (and make a plug) just in case you find yourself on an MPR only field.
     
  22. Oct 11, 2019 #22

    mbeels

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    Isn't it at "H" level impulse with 6 F15s? 6x49.6 = 297.6 Ns. Adding in the F50 (76.8 Ns) puts it into "I" territory (374.4 Ns). Still, yeah, that's a lot of impulse!
     
  23. Oct 11, 2019 #23

    Nytrunner

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    Reading comprehension fail, I just saw F15s and thought there were 7 of them.

    Still enough impulse to require certification, and definitely enough propellant weight to be Class 2
     
  24. Oct 11, 2019 #24

    jqavins

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    I also assumed 7 F15s and thus noted that leaving one out would get it down to H. Which doesn't require certification; certification is required when any one engine has more than 160 Ns or the total impulse from staging and/or clustering is over 320 Ns.

    The total propellant mass, however, is something I forgot to consider.
     
  25. Oct 11, 2019 #25

    Nytrunner

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    Good point
     
  26. Oct 12, 2019 at 5:43 AM #26

    Rocketjunkie

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    Any more than 2 F15s is HPR due to propellant weight over 125 grams and will also need a waiver.
     
  27. Oct 12, 2019 at 2:43 PM #27

    Rockhaus

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    Yep, I'm L1 certified. Originally, I was going with an F50 in the center for a bit more kick off the pad, but that motor is APCP so I don't want to mix. Although the 7 F15's get us up into H category for impulse, my bigger concern is thrust to weight ratio. With the F15 motors peaking at 7*25N = 175N, and a 140 ounce fully loaded rocket, I'm just on the edge of the 5:1 (around 4.6). And that's will all 7 motors burning. She came out a bit heavier than planned. For the first flight, I'm good with low and slow (sort of the plan anyway), but we're going to take our time prepping ignitors and (thanks Rocketjunkie) the motors as well. The simulations show a 4 second ejection delay actually being a bit early, so I've got a bit of margin. Our club's launch gear has plenty o' current and I've successfully lit 8 BP motors in the past. Launch in T minus 8 days. What could possibly go wrong?:cool:
     
  28. Oct 12, 2019 at 3:26 PM #28

    CoachSteve

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    fantastic looking rocket - I myself am partial to the retro styling (I have a couple of my originals posted up here too, G10 curved fins and pods and all)
    This one is beautiful, seriously great job.
    Cant wait to see your launch video
     
  29. Oct 12, 2019 at 6:32 PM #29

    jqavins

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    Actually, 7 gets you just into I impulse, and 6 is near maximal H.

    Is there a composite G where three or foir get you about the same impulse with a shorter burn? I'd look myself but it's a pain on my phone.
     
  30. Oct 13, 2019 at 3:25 AM #30

    dhbarr

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    I can't think of any composite G's for which three or more are below the mass limit.
     

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