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  1. #1
    Join Date
    10th February 2013
    Location
    Fremont, CA
    Posts
    348

    Delay vs opening shock

    Having a backup motor eject is a nice security feature I use whenever practiable.

    Open Rocket indicates that my dual deploy Super DX3 on a J575FJ will be at 63 mph when the installed 10-sec ejection charge blows. Optimum delay, according to OR, is 12.6 sec.

    If I cannot pick up a 14-sec delay tomorrow at the launch site, I am tempted to go for it and the risk the effects of premature ejection. Or is there a chance of serious damage at 63 mph going straight up? If so, I can always pour out the BP charge, put in some grease, and just hope the Adept 22 does it's job.

    NAR TRA BAR L2

  2. #2
    Join Date
    14th March 2009
    Location
    Ohio
    Posts
    3,240
    Just rely on the electronics. 63 is too fast to deploy the laundry.

    Zeus-cat
    NAR# 92125 L1
    Total Impulse for 2017: 1,493.8 N/s Flights: 56
    2017: 1/2A:0, A:6, B:11, C:2, D:12, E:4, F:1, G: I have NEVER launched a G motor, H:1, I:1

  3. #3
    Join Date
    17th December 2013
    Location
    Slagle, La
    Posts
    1,317
    The Adept22 will do it's job if you have have it hooked up right. I have used one several times, it even saved my level 1 flight when another altimeter clonked out on me.
    Pour out the BP and let the Adept22 handle it.
    Nothing is foolproof to a sufficiently talented fool.
    TRA #16513
    Level 1: Danger Close ---AT H123W to 1240'--- 29 OCT 2016
    Level 2: Binder Design Tyrannosaur ---AT J315R to 2148'--- 30 SEP 2017

  4. #4
    Join Date
    13th February 2016
    Location
    Gilroy, CA
    Posts
    579
    Quote Originally Posted by Mr G View Post
    Having a backup motor eject is a nice security feature I use whenever practiable.

    Open Rocket indicates that my dual deploy Super DX3 on a J575FJ will be at 63 mph when the installed 10-sec ejection charge blows. Optimum delay, according to OR, is 12.6 sec.

    If I cannot pick up a 14-sec delay tomorrow at the launch site, I am tempted to go for it and the risk the effects of premature ejection. Or is there a chance of serious damage at 63 mph going straight up? If so, I can always pour out the BP charge, put in some grease, and just hope the Adept 22 does it's job.
    How vulnerable is your SDX3 to zippering? A small drogue at 88 ft/sec (60 mph) shouldn't be too bad... unless you have a thin shock cord and cardboard tube that might easily zipper.
    It's been my experience that the darn motor delays are usually shorter than specified... something to consider... how fast would your rocket be traveling if the delay was only 8 seconds?

    I've had 10 second delays that fired the ejection at just 7 seconds a few times on my LOC Athena 3, cardboard rocket with 15 feet of ~3/16" Kevlar shock cord for the drogue. It's happened about 4 times now. It has a small drogue, 9" or 12", thus the early deployment didn't create too much force and there's been no sign of zippering.

    The plot below shows a typical early ejection at 100+ ft/sec
    Click image for larger version. 

Name:	20171022 LOC Athena3 H250G-M TCC October Skies Helm CA.jpg 
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  5. #5
    Join Date
    18th March 2009
    Location
    Wisconsin
    Posts
    3,611
    I would ditch the motor delay and just use the electronics. As others have mentioned, there can be a quite a bit of variation in delay time.


    Sent from my iPhone using Rocketry Forum
    Mark Koelsch
    Tripoli 6155 L3
    Owner of http://www.rocketryfiles.com/
    Editor of http://www.thrustcurve.org/
    Member of the Tripoli Motor Test Committee, and keeper of the motor file

  6. #6
    Join Date
    24th April 2010
    Location
    Wisconsin
    Posts
    1,655
    Quote Originally Posted by Mr G View Post
    Having a backup motor eject is a nice security feature I use whenever practiable.

    Open Rocket indicates that my dual deploy Super DX3 on a J575FJ will be at 63 mph when the installed 10-sec ejection charge blows. Optimum delay, according to OR, is 12.6 sec...
    I personally would NOT call it "back-up" when the motor delay fires before apogee. Ejection more than 2 seconds early is a potential disaster.
    -Scott Sager
    NAR 91621 L2
    TRA 15982 L2
    Woosh #558
    KC9WQK

  7. #7
    Join Date
    19th January 2009
    Location
    Stafford VA
    Posts
    7,048
    Quote Originally Posted by Mr G View Post
    Having a backup motor eject is a nice security feature I use whenever practiable.

    Open Rocket indicates that my dual deploy Super DX3 on a J575FJ will be at 63 mph when the installed 10-sec ejection charge blows. Optimum delay, according to OR, is 12.6 sec.

    If I cannot pick up a 14-sec delay tomorrow at the launch site, I am tempted to go for it and the risk the effects of premature ejection. Or is there a chance of serious damage at 63 mph going straight up? If so, I can always pour out the BP charge, put in some grease, and just hope the Adept 22 does it's job.
    Just dump the powder and use the altimeter. Where and why would you add grease? It's just my experience, but with over a 100 DD flights and never a motor backup charge, I only remember one very early flight where it might have helped.

    Personally, I thing motor eject is way too unreliable on timing and would prefer altimeter every time.
    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

  8. #8
    Join Date
    30th January 2016
    Location
    US > OK > NE
    Posts
    3,480
    I believe some people grease the touch hole end when they dump powder to make sure that potential burn surface is inhibited.

    I'd jam dog barf in the charge well and electrical tape it, but that's just my personal opinion.

    30m/s no es bueno.

  9. #9
    Join Date
    19th January 2009
    Location
    Stafford VA
    Posts
    7,048
    Quote Originally Posted by dhbarr View Post
    I believe some people grease the touch hole end when they dump powder to make sure that potential burn surface is inhibited.

    I'd jam dog barf in the charge well and electrical tape it, but that's just my personal opinion.

    30m/s no es bueno.
    Yes, I don't even do that. I don't grease or put anything in the well, I just don't add the powder. Maybe I'm not PC, but I've never had a problem with that.

    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

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