Advice needed, Minimum Diameter, Conformal Rail guides or Fly away rail guides?

Discussion in 'High Power Rocketry (HPR)' started by Rob702Martinez, May 17, 2019.

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  1. May 17, 2019 #1

    Rob702Martinez

    Rob702Martinez

    Rob702Martinez

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    So lets skip the discussion about MD rockets with external rail guides not being "true" Minimum Diameter and all that.

    I have a Wildman Mach 2 I am building, 54mm MD kit.

    It will have 4 , 4-40 LumaDyne inserts in the middle of the airframe with titanium screws to hold a Aeropack MD retainer. For ease of install and assembly etc. So there will already be some very small surface disruption.
    Right now a tower is not an option unless someone has one for sale that is in the budget.

    The only other options are Fly Away Rail Guides or ACME Conformal Rail Guides.

    My Questions/Concerns are;

    Fly Away Rail Guides-
    Do they usually break when the fins hit them?
    Who makes the best kind?
    Is there any question of an unstable flight or unsafe liftoff if a malfunction occurs?
    Are they reliable?
    Any other advice or experience or observations?

    Conformal Rail Guides-
    I have a set of the aluminum ACME ones.
    Can these be properly bonded to the Airframe? With JB Weld, Aeropoxy, rocketpoxy?
    Any experience with these being broken off?
    Is there any question of an unstable flight or unsafe liftoff if malfunction or breakage occurs?
    Are they reliable?
    Any other advice or experience or observations?

    I would plan to have these pinned/pressed into the airframe with 2-56 steel pins on all 4 corners, with the pins being flush on the inside of the airframe and outside of the rail guide, then bonded.

    Thanks
     
  2. May 17, 2019 #2

    mikec

    mikec

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    I have never had a problem with Acme guides breaking off. Clean and rough the mating surface and the BT to be bonded to, then glue on with JB Weld. I don't see the point of your pin idea.

    I'm not a big fan of the fly away guides, I have seen them break more often than not.
     
  3. May 17, 2019 #3

    timbucktoo

    timbucktoo

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    I have a 54mm MD Mongoose. I got 2 flights out of the fly away rail guides. On 2nd flight, the fins struck the guides and that caused the rocket to leave the rail at about 15 degrees off of vertical.
    Since then I have been using the rail guides that Wildman sells. They are only attached with thin CA. On the last flight however, the rail was a bit sooty and used a little too much force while placing rocket on rail and one broke off. Easy fix in the field.
     
  4. May 17, 2019 #4

    Rob702Martinez

    Rob702Martinez

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    My thought about the pins would be additional physical/mechanical transfer of energy to between the guide and airframe and also to help avoid shearing off if it is getting resistance/binding from the rail on the way up.
     
  5. May 17, 2019 #5

    heada

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    Not MD but I used the ACME guides on a 15# 7.5" rocket and used the JBWeld process but also drilled a small hole in the center of the guide and used a 4-40 screw. It was only as deep as the fiberglass tube wall but it seemed to enhance the bond since previously it pulled off and hasn't since the modification. Since it was between the "wings" of the guide and flush with the bottom of the "wings", it didn't add any additional protrusion.
     
  6. May 17, 2019 #6

    mikec

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    In my experience when people break them off it's because they get a side load on them getting the rocket on the rail, especially if the rocket is heavy. Unlikely to happen with a rocket the size of a 54mm MD.
     
  7. May 17, 2019 #7

    manixFan

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    I have used all three, FARGs, conformal rail guides, and a tower. All my MD now fly out of a tower. The FARGs are too problematic in actual use, based on my personal experience and from what I’ve witnessed. The conformal guides work well on smaller rockets, like 54mm. Like Mikec says, they seem to have trouble with larger, heavier rockets during loading - the first guide is very unforgiving of any side loading. Obviously buttons have far more latitude. I have actually mounted them on thicker walled minimum diameter rockets using screws ground to fit precisely. The hold is plenty strong enough for smaller, lighter MD birds.

    If you do use FARGs and plan on more than one flight at a launch, bring a backup. At BALLS a few years ago I had a 38mm and 54mm FARG I was going to use for several flights on each. The 38mm broke in transit and the 54mm broke on the first flight. Fortunately there were several vendors that had replacements, and I did get both of them replaced under warranty. But if they hadn’t been there it would’ve been beg and borrow to keep flying.

    FWIW.

    Tony
     
  8. May 17, 2019 #8

    Flyfalcons

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    I'm putting conformal rail guides on my Mach 2. Not looking to break records; just have a go-fast machine.
     
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  9. May 18, 2019 #9

    mperegrinefalcon

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    Neither, use a launch tower. You can make one out of some old bike wheels and some metal rod for pretty cheap.
     
  10. May 18, 2019 #10

    Rob702Martinez

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    Got a link to a build or tower builds?
     
  11. May 18, 2019 #11

    Binder Design

    Binder Design

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    I use the conformal guides but then I attach a steel "knock-off" plate to the top of the rail. It knocks the guides off the airframe at the top of the rail and after the flight you go retrieve them from inside the rail. I think I'm the only person doing this, but it allows you to still fly true minimum diameter from a rail without using one of those fly away contraptions.
     
  12. May 18, 2019 #12

    Locksmith

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    Neat idea, the force of knocking it off doesn't effect anything?
    I personally use fly away rail guides the ones from addictive aerospace are a better design imo. That being said I have only flown it twice so...
    The aluminum conformable rail I no longer use I had a rocket jump forward about 2 feet and then get stuck in the launch rail. maybe there was a problem with the rail but it slid down just fine so I no longer use them.
     
  13. May 18, 2019 #13

    manixFan

    manixFan

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    See also this thread:

    https://www.rocketryforum.com/threads/shearing-rail-buttons-on-purpose.148256/


    Tony
     
  14. May 18, 2019 #14

    Rocketjunkie

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    CHAD 54mm tower

    You will need
    5 gallon bucket
    bag of Quickcrete or a lot of plaster
    3 or 4 (same number as fins) lengths of conduit a couple feet longer than the rocket. Can be purchased at Lowe's or Home Depot. Get 1-2" diameter.
    Length of airframe or the rocket.
    Tape, etc. Maybe a mixing container.

    The day before the launch -
    Wrap enough paper around the airframe to build up the diameter about 1/16"
    Evenly space the conduit sections around the airframe and tape or retain so they don't move.
    Mix enough Quickcrete per instructions to fill the 5 gallon bucket a couple inches from the top.
    Insert conduit assembly and support straight until concrete cures.

    Next day
    Remove airframe and check to make sure rocket is free in tower.
    Cheap enough to dumpster on the way home from the launch - just make another when needed.
    I've seen these used from BT-5 to 6" O motors (rails were 4 x 4s, bucket was 55 gal drum).
     
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  15. May 19, 2019 #15

    Binder Design

    Binder Design

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    Not a problem so far. My flights are usually high thrust to weight. I started doing this after the guides were already tearing loose during launch and getting lost. I have a photo around here somewhere of one of my launches with the loose rail guides falling away at the top of the rail. They are literally inside the flame plume just past the top of the rail.
     

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