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Recommended Drogue chute size?


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  1. #1
    Join Date
    17th April 2011
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    Kelowana, BC
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    Recommended Drogue chute size?

    I've taken a Madcow HoJo, lengthened it to 43" and made it dual deploy. Unfortunately it's grown in weight as well lol! The specked weight from MC is 28oz, mine's coming in at 47oz! I was going to swap the 30" main for a 36", but I've got no idea what size to use for the drogue as this is my first DD. Maybe even the 36" is a little small for the main chute. Recommendations? BTW, I've notice all my builds are way heavier than the manufactures target weight. Is that the norm, or do I just build porky rockets?
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  2. #2
    Join Date
    20th February 2009
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    Cayuga, Indiana
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    Quote Originally Posted by SRBell View Post
    I've taken a Madcow HoJo, lengthened it to 43" and made it dual deploy. Unfortunately it's grown in weight as well lol! The specked weight from MC is 28oz, mine's coming in at 47oz! I was going to swap the 30" main for a 36", but I've got no idea what size to use for the drogue as this is my first DD. Maybe even the 36" is a little small for the main chute. Recommendations? BTW, I've notice all my builds are way heavier than the manufactures target weight. Is that the norm, or do I just build porky rockets?
    You might be a little small on the main. My calculator shows 40" for a 3 pound rocket. As far as a drogue, it could be anything small, 12" to 18" would be fine. In simulations I try to keep my drogue descent at around 80 fps.

  3. #3
    Join Date
    15th January 2009
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    Virginia, USA
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    Those look nice!

    Trying for 50 feet per second descending from apogee and going for about 20 feet per second (or less) at landing are the numbers I seem to be hearing.

    There are a lot of descent rate calculators out there.

    http://www.aeroconsystems.com/tips/descent_rate.htm says an 12" chute would get you about 63 feet per second from apogee.

    It also claims a 36" chute would get a landing speed of about 21 ft/sec.
    Will Marchant, KC6ROL
    NAR 13356, Tripoli 10125 L3, AMA 800142, FBIS

  4. #4
    Join Date
    11th December 2010
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    Between the topsoil and the sun. A surface dweller.
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    Quote Originally Posted by SRBell View Post
    I've taken a Madcow HoJo, lengthened it to 43" and made it dual deploy. Unfortunately it's grown in weight as well lol! The specked weight from MC is 28oz, mine's coming in at 47oz! I was going to swap the 30" main for a 36", but I've got no idea what size to use for the drogue as this is my first DD. Maybe even the 36" is a little small for the main chute. Recommendations? BTW, I've notice all my builds are way heavier than the manufactures target weight. Is that the norm, or do I just build porky rockets?
    Beautiful rockets!!!

    Well, you could put as large of drouge as you could fit or stand for drifting from apogee, then add a second main chute of a smaller size to accomplish landing softly.
    If that was my rocket i would like a 36-40 main. or even a 24" drouge(like Aerotech Sells), with a 30" main...

    obviously not a good idea on windy days....

    "Dad, I am going to put a big motor in this skinny rocket... its going to disapear like a ghost!!!.....

  5. #5
    Join Date
    29th November 2009
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    Fort Collins, CO
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    588
    I don't know the elevation you launch at, but my spreadsheet (set for 2500' elevation) for a 20 fps descent rate you would need a 36" flat circular parachute. For 15 fps you would want a 48" parachute.

    As for a drogue a 50 fps descent rate could be attained by a 15" circular parachute. At that point I'd almost just use a longer streamer.

    Edward

  6. #6
    Join Date
    18th January 2009
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    Stafford VA
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    I never really looked at descent rate for drogue size. I want the upper section of the rocket with the drogue to fall slightly slower then the fin can. I want the fin can below when the main deploys so there is no chance of fouling the main by having the fin can fall through it.

    I've been using smaller and smaller drogues as I work toward the proper profile while it's falling. My 8.5 lb rocket is now at a 18" drogue, although only about 4 lbs are actually dragging on the drogue.
    Handeman

    TRA #09903 L2

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

    Tripoli Central Virginia #25 - BattlePark.org

  7. #7
    Join Date
    17th April 2011
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    Kelowana, BC
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    128
    Well, I found a 14" for my Mini Nuke I think would work fine for the drogue and I'll order up a 48" for the main. Doesn't seem like there's anything available between 36 and 48. After all that painting, I would want to see it smack the ground too hard. My son's Minie Magg is about the same weight and with a 36" chute it fall like a rock lol!

  8. #8
    Join Date
    18th December 2010
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    Maryland, 20794
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    328
    SRBell,

    Handemanís advice on this topic has been consistent and spot-on. The purpose of drogue chutes is separation of the fincan and payload sections. I use an 8-inch drogue on a 14-pound LOC 5.5 Phoenix. Descent rate from apogee is marginally less than drogue-less.

    Feckless Counsel

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