Helicopter recovery:a gap-staged booster.

Discussion in 'Low Power Rocketry (LPR)' started by chejay, Apr 7, 2019.

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  1. Apr 7, 2019 #1

    chejay

    chejay

    chejay

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    Has anyone seen plans or a design for a gap-staged rocket where the booster stage uses a helicopter recovery and the sustainer continues on it's journey?
    I'm building one that uses an internal, spring-loaded mechanism to deploy the helicopter blades, but have not seen anything like it in the literature. Any ideas for some possible, alternative approaches out there?
    chejay
     
  2. Apr 7, 2019 #2

    neil_w

    neil_w

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    I haven't seen that myself, although sometimes it seems that *everything* has been tried somewhere before.

    In any case it sounds like a fun idea. Got any drawings or anything that shows what you have in mind?
     
  3. Apr 9, 2019 #3

    chejay

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    Well, here's how it started, an "initial concept" entry in my journal...
    Slingblade Concept Page.jpg
    The basic idea being that the booster stage ejection gases would pass through the interior of the booster, cut a "burn string" to deploy the spring-loaded helicopter blades, and then ignite the upper stage motor. Easy. A more detailed view of the spring mechanism looks like this:
    Spring Mechanism.jpg
    With the exception of the protruding spring arm (made of 0.032" music wire) to support the helicopter blades, the whole assembly would slide inside the rocket body. The spring arm pivots on an axel near the top and is held in tension by a spring connected by a Kevlar string. When readied for flight, the blades are folded down along the rocket body, under tension, and tied with a piece of elastic thread passing through the body tube.
    The spring arm itself was a piece of work, but hopefully will provide enough "flex" that it will absorb the stresses of blade deployment and not tear itself apart. I included a 3D .stl file of the spring arm itself below.
    Spring Arm.PNG
    Now armed with an idea of the size, weight, and locations of the spring mechanism and the upper stage transition, I worked up a draft of the proposed rocket in OR, Slingblade 3.0.ork file also below.
    OR First Sketch.PNG
    This is tricky also. Weight is a big issue since the maximum lift weight of a C6-0 is 4.0 oz.! (I'd like to avoid using a D booster if I can, but am designing for it anyway.) Also, increasing the fin size of the upper stage for it's stability plays havoc on the booster stage stability. Lots of trade offs. Note in these OR simulations, the weight and configurations of the spring mechanism have been all lumped together as an "internal mass component" using an override. (Same with the transition.)
    I'm just now starting on design for the blades themselves, but intend on using BT-55 stock, cutting them to a propeller-like profile, and adhering them to the spring arms. I know, not real stout materials but again: the idea here is for them to flex with the forces, not remain rigid.
    That's kinda where I'm at.
     

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  4. Apr 9, 2019 #4

    neil_w

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    Nice drawings. :) Looks like a fun project.

    I think boosting this with a C6 is doubtful at best, smart to design for a D12. Or a C11-0, if you can still find one....

    Don't forget that your gap staged booster must be vented near the top to maximize chances of sustainer ignition.
     
  5. Apr 9, 2019 #5

    chejay

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    The vents are going in just below the shoulder of the transition.
    And yes, I agree a C6 is underpowered for this project but it's still my dream tinker a lighter weight, more elegant solution in the future!
     
  6. Apr 9, 2019 #6

    BABAR

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    Should be do-able.

    https://www.rocketryforum.com/threads/hyp2bsquared-junior-almost-no-sanding-sport-helicopter.58912/

    Thread on helirocket.

    Would need to invert the hinges (aft instead of forward) so burn band is forward, just behind where sustainer would be.

    Instead of a burn string (or rubber band, which I use) if the sustainer mount also serves for rotor retention on boost, the simply sliding the sustainer off the booster at separation will allow rotors to deploy. Otherwise, if you try to use a burn band or string, you run into “what happens if rotors deploy before sustainer lights” problem.

    This should be do-able with a C6, as the booster won’t need much rotor surface area to retard the fall. So short stubby rotors should be fine. Use a VERY LONG body tube for sustainer, the longer it is the less nose weight you will need to get rocket stable.
     
  7. Apr 9, 2019 #7

    neil_w

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    This seems like an excellent suggestion. I had a vague unease about simultaneously doing a burn string and sustained ignition, but couldn’t put the pieces together.
     
  8. Apr 10, 2019 #8

    GlenP

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    What does the booster look like when it is in helicopter mode after separation and sustainer ignition? Hard to tell from those sketches.
     

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