3 inch "Frequent Flyer"

Discussion in 'Plans' started by Bill Hanson, Nov 30, 2018.

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  1. Nov 30, 2018 #1

    Bill Hanson

    Bill Hanson

    Bill Hanson

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    Hi All,

    As I’m working through my L3 planning, I’m also scratch-building a 3” DD rocket with a 38mm motor tube that will be a “frequent flyer” for everything from G-J. I’m trying to make it light enough to fly under a Class 1 waiver with a G or small H, but robust enough to handle high transonic/supersonic with a J. I’ve attached my OpenRocket file with my current thinking FYI.

    Nothing too cosmic about the design, but making it both light and robust enough for supersonic flight is the main challenge.

    I haven't completely decided, but I’m pretty sure I’m going to go with canvas phenolic (MAC Performance) for my airframe and fins. That will make it light enough to fly as a class 1 and strong enough for supersonic. I’ve heard great things about their kits, and that if you custom order stuff they will make it just like one of their kits. I’ll probably order it right after Christmas (once I decide on the final design).

    If you look at the .ork file, you will notice that it gets less than 1 cal. stability margin with heavier I and J motors, so I’m adding provisions for removable weight in the nose. Depending on how much I need, that may be as simple as adding a quick link with some large flat washers (I’ve found a size where 2 washers = 25 grams, so easy to adjust) to the nosecone eyebolt -- okay up to about 150 grams. If not, I’ll probably “roll my own” version of a removable nose weight system – thinking a threaded rod with swappable weight cylinders made from epoxy and lead. Or, I may just go really modular with two different nose cones of different weights. Hmm.

    Frequent Flyer.jpg

    Please feel free to kibitz on the design -- prime directive is to make the thing work the way I want it to. Any and all suggestions are welcome! I'm pretty close to happy with it, but not entirely.

    <brace for incoming>
    Bill
     

    Attached Files:

    Hazmat54 likes this.
  2. Nov 30, 2018 #2

    Mike Helm

    Mike Helm

    Mike Helm

    360LTR

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    Have you considered moving your Av Bay forward like on a Punisher or Avalanche?
     
  3. Nov 30, 2018 #3

    Bill Hanson

    Bill Hanson

    Bill Hanson

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    Hi Mike,
    Thanks for the suggestion! That hadn't occurred to me, but a quick look over at Wildman and MadCow looks promising. Since MAC Performance offers the Wildman nosecone with av bay, that's a real plus. Will have to find an .ork file (none on the Wildman site or in Rocket Reviews) so I can play with it, but that looks like a good possibility.
    Bill
     
  4. Nov 30, 2018 #4

    woferry

    woferry

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    Here are .orks for two similar 3" HED rockets (the original Rocketry Warehouse/Madcow Osprey 75 [I think the newer kit is different] and the Madcow Avalanche). I have a 3rd 3" HED kit I plan to build, it was a custom spec'ed tube-fin rocket from MAC Performance, I opted for HED on this one since the tube fins push the Cp pretty far back, so it's overstable anyway, no need to make it longer and even moreso, and I've had no trouble fitting my main in the nosecone for the other 2 HED rockets.
     

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  5. Dec 1, 2018 #5

    blackjack2564

    blackjack2564

    blackjack2564

    Crazy Jim's Gone Banana's

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    well.... if you really want an everyday sport flier, without any fuss. I would make the fin can 34 in. & payload 17in. Because standard tubing is 34 in long. Payload would be 1/2 tube. Sim it...you no longer need any weight for any motor flown.
    Easy to prep...easy to fly.:cool:
    nothing against HED rockets.. I have several, but my most flown 'everyday' rocket is a standard DD design with above dimensions.
     
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  6. Dec 2, 2018 #6

    AdAstraPerAspera

    AdAstraPerAspera

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    The standard length depends on the source, PML is 36", LOC I believe is 34", and a lot of FWFG is 60". MAC to tubing is something else fairly long, 54" if I remember correctly.
     
  7. Dec 14, 2018 at 4:44 AM #7

    Bill Hanson

    Bill Hanson

    Bill Hanson

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    Thanks Jim,
    (sorry for the hiatus -- was in Puerto Vallarta and <horrors> left my computer at home. ;-) )
    Thanks for the suggestions -- after I looked up the HED designs and played with what's available via simulation, I find that the heavier nosecones increase rocket weight over a conventional DD. Since one of my design goals is to keep the thing under 1500 grams with either a G or smaller H motors (like an H123), going to HED looks like it's moving in the wrong direction for that.
    So I'm sticking with standard DD, and trying to finesse the fuselage length plus fin size to get lower than 1500 gm. So far, the best I've gotten is 1513 -- so close.
    Maybe if I stuff a helium balloon in the thing?
    I basically solved the stability issue by going to 4 smaller fins (more surface area -- duh), so that's no longer a factor. I really don't want to drop to a smaller fuselage diameter, so will keep playing with it.
    Bill
     

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