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  1. #61
    Join Date
    7th August 2013
    Posts
    345
    You're good to go Fred with your rocket into the wind, just don't piss, spit, or hunt that way.

    John Haught L3
    Prefect Tripoli Pittsburgh

  2. #62
    Join Date
    23rd July 2011
    Location
    Butte, MT
    Posts
    2,112
    Quote Originally Posted by FredA View Post
    My questions to Fred in post #45 are still open. But everyone that reads this thread can come to their own conclusions. But I agree, time to move along...

    I guess I can't read but the only question I see is "why put your rocket upwind" which I didn't think was really a question.

    My response is I like to put the rocket on the front of the pad facing launch control and the spectators....period.
    If that's upwind, downwind or sideways I don't care.
    I want to see and photograph the rocket taking off.

    Your rocket should be strong enough to sit there in any wind and not excessively torque the railbuttons.
    If you need to sit out a strong gust and wait for sub-20MPH winds then it needs to survive.

    Is that a sufficient answer????
    We put our rockets on the LCO side of the rail also. That way the rocket points away from people when we put it up or take it down. And the rail doesn't obscure the rocket.
    If I felt my buttons could not hold my rocket in reasonable winds I would install larger buttons and use a larger rail and pad.

    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  3. #63
    Join Date
    13th October 2014
    Location
    SouthEastern, WA
    Posts
    5,542
    Quote Originally Posted by Steve Shannon View Post
    We put our rockets on the LCO side of the rail also. That way the rocket points away from people when we put it up or take it down. And the rail doesn't obscure the rocket.
    If I felt my buttons could not hold my rocket in reasonable winds I would install larger buttons and use a larger rail and pad.
    +1, we always position our pads so the rails lower pointing away from the crowd, that way if something weird happens before the rocket is vertical the rocket goes away from the spectators. The rockets are generally on the upwind side of the pad, no issues so far at any of our launches.
    Rich

    NAR# 99154

    L3-4x upscale Estes Cherokee-D- AT M1297W 5/28/2016 http://www.rocketryforum.com/showthr...r-rharshberger

    TriCities Rocketeers NAR section# 736 http://www.tricitiesrocketeers.org/

  4. #64
    Join Date
    25th October 2016
    Location
    Texas, United States
    Posts
    1,659
    Quote Originally Posted by FredA View Post
    If that's upwind, downwind or sideways I don't care.
    I've heard of a TARC team (it was either from my club or one of the Apogee articles - I'm fairly sure it was at one of the meetings and directed at a visiting TARC team but I'm not certain) that used a launch rail to try and mitigate the drawbacks of rod launching and was having issues, (Ok, It's almost definitely club) and when the person went to help, they found that they had the rocket oriented so that the side was facing into the wind, so when they launched, the rocket bound onto the rail. So I would say, based on my limited knowledge and hear-say, to either put the rocket up or downwind, but not sideways, especially for lighter rockets. For heavier rockets, the effect of wind is lessened. (Rocket and pad scale up but the wind speed stays constant.)

    Of course, your experiences might vary. This essentially boils down to a pile of hot electronics- the smoldering remains of an internet server- and also whatever works for you. I think it's wrong to dismiss an idea because you haven't had success with it or don't think it'll work, but also that it's silly to worry so much about what little effect rail button placement has if there are bigger issues impacting performance, say, crooked fins. Just my 53 cents (adjusted for inflation.)

  5. #65
    Join Date
    15th February 2009
    Location
    North Texas
    Posts
    539
    Quote Originally Posted by Steve Shannon View Post
    We put our rockets on the LCO side of the rail also. That way the rocket points away from people when we put it up or take it down. And the rail doesn't obscure the rocket.
    If I felt my buttons could not hold my rocket in reasonable winds I would install larger buttons and use a larger rail and pad.
    I just want to be clear as some of you seem to have misinterpreted this issue. This discussion had NOTHING to do with whether or not the buttons are strong enough to hold the rocket on the rail during launch. It is about the location of rail buttons and how they affect the launch.

    I made the mistake of bringing up wind interference and my feelings that rockets should be downwind of the rail to reduce binding. Fred took exception to that idea and argued it's too much work to accommodate. That's it, no one ever mentioned the wind blowing a rocket free of the buttons. (Fred did mention that his rockets would tear the buttons off if loaded hanging from the rail, but that's a separate issue.)

    I certainly understand the many rationales for how rockets are loaded onto rails. Certainly the ideas of the rail being lowered away from the flight line and rockets facing the LCO make complete sense. But I still stand by my reasoning that all things being equal a rocket downwind of the rail is less likely to be disturbed by the wind during launch. That was the sole point of my argument. You can agree or disagree. But somehow it has morphed into the rail buttons not being strong enough to survive the wind. That was never an issue in the discussion.


    Tony
    Last edited by manixFan; 13th February 2017 at 04:47 PM.
    why do people put so much stuff in their sigs?

  6. #66
    Join Date
    14th December 2012
    Location
    Kaysville, Utah
    Posts
    249
    Back to the original question, I'm not sure how to put the forward rail button at the CG. The CG on my rockets moves around depending on how heavy the motor is. So I like to put the forward button one body tube diameter forward of the center of pressure. Not because of physics, but because I find it to be a handy way to do a final check for stability. If the CG is forward of the forward button, stability shouldn't be a problem.

    Joe

  7. #67
    Join Date
    6th January 2016
    Location
    Austin Texas
    Posts
    104
    The forward rail button goes just above of the forward centering ring and the bottom rail button goes just aft of the aft centering ring.

    What's the scientific reason you ask?

    When I build a rocket, I get so excited about finishing and installing the motor mount, that I ALWAYS forget to think about rail button placement before hand. Hence, the rail buttons always end up just outside of all motor mount centering rings by default. I have a process!!
    NAR 101529
    Tripoli 17153
    L1 LOC Cyclotron 7/2/16
    L2 Madcow X-Celerator 1/7/17

  8. #68
    Join Date
    1st September 2010
    Location
    Tucson, AZ
    Posts
    1,041
    Quote Originally Posted by blackwing94 View Post
    The forward rail button goes just above of the forward centering ring and the bottom rail button goes just aft of the aft centering ring.

    What's the scientific reason you ask?

    When I build a rocket, I get so excited about finishing and installing the motor mount, that I ALWAYS forget to think about rail button placement before hand. Hence, the rail buttons always end up just outside of all motor mount centering rings by default. I have a process!!
    Not to one-up you, but I just discovered a DOOZY of a mistake...just finished my Rayzor 3, and because I thought it mattered, I marked as close to the CG as I could reasonably get and sunk my top button. I knew it was going to be close to the AV Bay, so I measured off the distance the bay would extend into the booster...gave myself a bit of wiggle room, and pop, there it is. Got ready for a ground test tonight after paint and everything else, and slid my AvBay in...it stopped about 1/8" shy of fully seating. Yup, you guessed it- I measured my coupler, but not with the bulkheads on...with the 1/4" rabbeted ply that MacPerformance uses, I had to remove my button.
    I thought it would at least serve as a vent hole, but the AvBay bulkhead fully occludes it.

    Oh well, nothing a little putty and paint can't fix! And lesson learned...buttons LAST (plan for them, sure, but don't drill and install!)
    NAR 96681
    L1 - May 29, 2014 LOC Norad ProMax, H120
    L2 - Feb 21, 2015 Fiberglassed Madcow Frenzy, J280

  9. #69
    Join Date
    19th January 2009
    Location
    Portland, OR
    Posts
    1,568
    DOOZY of a mistake...

    Shorten the coupler a bit....
    Fred Azinger

  10. #70
    Join Date
    1st September 2010
    Location
    Tucson, AZ
    Posts
    1,041
    Quote Originally Posted by FredA View Post
    DOOZY of a mistake...

    Shorten the coupler a bit....
    I like the cut of your jib...not sure why it didn't occur to me, but that is a simple and elegant solution (especially since it's only a hair, and I'm using sheer pins in the booster)!
    I'd like to think I'd have thought of that tomorrow while pondering it some more...but who knows.
    NAR 96681
    L1 - May 29, 2014 LOC Norad ProMax, H120
    L2 - Feb 21, 2015 Fiberglassed Madcow Frenzy, J280

  11. #71
    Join Date
    15th November 2013
    Posts
    1,017
    Your explanation leads me to a slightly different conclusion: The forward guide should be placed far enough forward to support the rocket on the rail in a safe orientation. This does not necessarily mean CG/CP90, and is likely aft of that point. Moving the forward guide any further forward than necessary merely causes it to leave the rail sooner and expose the rocket for an increased amount of time to pitching/yawing moments from the forces you cite while only one guide is in the rail.
    Bill Cook
    NAR #96751, Level 2
    Mayhem Rocketry, LLC
    That's a nice rocket you have there...if you're looking for me, I'll be under my car.

  12. #72
    Join Date
    25th October 2016
    Location
    Texas, United States
    Posts
    1,659
    Quote Originally Posted by wfcook View Post
    Your explanation leads me to a slightly different conclusion: The forward guide should be placed far enough forward to support the rocket on the rail in a safe orientation. This does not necessarily mean CG/CP90, and is likely aft of that point. Moving the forward guide any further forward than necessary merely causes it to leave the rail sooner and expose the rocket for an increased amount of time to pitching/yawing moments from the forces you cite while only one guide is in the rail.
    The rear guide should theoretically be at CP90 to minimize any turning while the rocket is connected to the rail by only one button, the front should theoretically be as far forward as necessary to prevent the rocket from being able to jostle around too much but as far back as possible to minimize the time spent supported by one button.

  13. #73
    Join Date
    18th January 2009
    Location
    SW Michigan
    Posts
    3,852
    Lawdy...we sure know how to over think things don't we?
    Dave Brunsting | NAR 85879 | TRA 12369
    L1 - 11/04/07, Three Oaks, MI | L2 - 7/25/09, Muskegon, MI
    Michiana Rocketry
    Notre Dame Rocket Team Mentor

  14. #74
    Join Date
    5th December 2013
    Location
    MD
    Posts
    6,822
    Quote Originally Posted by DAllen View Post
    Lawdy...we sure know how to over think things don't we?
    Ding ding ding ding ding ding ding!

    Like I said, i have used a wide variety of configs successfully. I don't put much thought into it, any more.

    John S. ---- NAR #96911 ---- TRA #15253 ---- MDRA #067 ---- BARC #028
    L1, 3/15/14: Aerotech Sumo, CTI H133BS
    L2, 6/21/14: Giant Leap Vertical Assault, CTI J240RL
    L3, 3/12/16: MAC Performance Radial Flyer, CTI M1101WH
    Altitude: 13,028', L3 flight; Speed: Mach ???, L3 flight

  15. #75
    Join Date
    25th October 2016
    Location
    Texas, United States
    Posts
    1,659
    Quote Originally Posted by DAllen View Post
    Lawdy...we sure know how to over think things don't we?
    What would the hobby be without overthinking?

  16. #76
    Join Date
    19th January 2009
    Location
    Stafford VA
    Posts
    6,973
    Quote Originally Posted by Incongruent View Post
    What would the hobby be without overthinking?
    The hobby would still be fun, but TRF would be down right boring!
    Handeman

    TRA #09903 L3 3/29/2015

    "If you don't use your head, you have to use your feet!" my Dad

    Tripoli Central Virginia #25 - BattlePark.org

  17. #77
    Join Date
    15th November 2013
    Posts
    1,017
    Quote Originally Posted by Incongruent View Post
    The rear guide should theoretically be at CP90 to minimize any turning while the rocket is connected to the rail by only one button, the front should theoretically be as far forward as necessary to prevent the rocket from being able to jostle around too much but as far back as possible to minimize the time spent supported by one button.
    Exactly

    Bill Cook
    NAR #96751, Level 2
    Mayhem Rocketry, LLC
    That's a nice rocket you have there...if you're looking for me, I'll be under my car.

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