Two-stage model rockets: Why are special ignition procedures necessary?

Discussion in 'Physics' started by Stanly, Jan 1, 2018.

  1. Stanly

    Thread Starter Member

    Mar 29, 2014
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    Hi everyone,

    First, I want to thank all of you who stepped in to answer my questions regarding clustered-engine rockets.

    Well, I have simply abandoned the entire project — it started to become just too complicated especially for an rocketeer like myself.

    For a more reasonable challenge, I have decided to concentrate instead on flying a two-stage rocket. On the Apogee Components website, I have been reading about the Solar Eclipse rocket. Here is a link to the page:

    https://www.apogeerockets.com/Rocke...lipse?zenid=1rm22qi1721pb4b9glaa4rf2e0#motors

    I myself don’t have tremendous construction skills. However, my wife is quite good with arts and crafts, and she is willing to help me out with my rocket projects. Between the two of us, I think that we will be able to assemble this rocket.

    But I have these questions. Right at the bottom of the page to which I gave the link, Apogee says that they offer a couple of choices for mid- and high-power size rockets. One of their recommendations is sold out, but here is their link for the other choice:

    https://www.apogeerockets.com/Launch_Accessories/Launch_Controllers/Go_Box_Launch_Controller

    As I understand it, however, with a two-stage rocket the engine on the booster stage ignites the engine on the sustainer stage. So why would a special launch controller be necessary?

    That was my first question. And here is my second question.

    Let’s say that I do need this special launch controller? I certainly do not want to go lugging around an automobile battery to the launch site so as to power this Pratt Hobbies Go Box Launch Controller. I need a convenient-to-carry 12 V power source for it. What I need is a container that holds eight 1.5 V batteries so as to provide the necessary total of 12 V. Does such a thing exist?

    Thank you.

    Stanley
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    What makes you think you need a special launch controller to ignite the boost engine?

    The "recommended" controller for mid- and high-power models is probably either for the greater likelihood of clustered engines or because it has longer wires to provide a greater set back from the launch pad when igniting the larger engines.

    There are all kinds of holders for battery cells. Another option is to use a lightweight automotive jump starter.
     
  3. Stanly

    Thread Starter Member

    Mar 29, 2014
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    Hi WBahn,

    OK. So I don't need a special controller to launch a two-staged model rocket. It is just recommended for the reasons that you stated. That's good to know.

    Just in case i wanted to pursue acquiring one, however, it just so happens that my wife and I are going to Lowe's today. While I am there, I will see what they may happen to have in terms of holders for battery cells. I will look for something that can hold eight 1.5 V batteries to provide 12 V.

    Thank you.

    Stanley
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    You might find a small 12V sealed lead acid battery more cost-effective in the long term.
     
  5. Stanly

    Thread Starter Member

    Mar 29, 2014
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    Hi Alec_t,

    Thank you for the suggestion. I will think about that, and see what's available.

    What you said sounds too industrial for me. I might be more comfortable with something that holds AA or D batteries. But I will definitely inquire at the store once we get there.

    Stanley
     
  6. Ylli

    Member

    Nov 13, 2015
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    Great controller for mid/high power or your Estes clusters. But using AA, C or D cells is not a good idea, they have too much internal resistance. Would be OK for the single solar igniter you would be using for that two stager, but not strong enough for some of the mid power igniters or clusters. Here's a 12 V SLA that even comes with its own charger: https://www.amazon.com/UPG-UB1250-B...514843593&sr=1-4&keywords=12+volt+sla+battery .

    Yes, with a two stage you only need to ignite the lower stage. The second stage is lit by the blowthough of the first stage into the nozzle of the second. Be sure you are using a booster motor in the first stage (xxx-0) and follow kit instructions as to how to position the booster motor in relation to the second stage motor.

    Then be sure when you launch you have someone who is tasked with watching the booster so it doesn't get lost :)
     
  7. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    I'm not a rocketeer myself -- never launched one -- but I've been following these threads with great interest.

    The main problem seems to be getting lots of power to the igniters quickly -- and preferably with small batteries.

    Small batteries can house a great deal of energy, they are just unable to move it out quickly (they tend to have higher internal resistance than larger capacity batteries). Yes, I can start a fire with an 'AA'.

    Why cannot the batteries be used to (relatively) slowly charge a large cap (or supercap), and then dump that energy into the igniter instantaneously?

    Knowing the current and time requirements for reliable ignition would make such a system trivially easy to design. And I bet you'll get at least one -- if not many more -- launches from a stack of 'AA's.
     
  8. BR-549

    AAC Fanatic!

    Sep 22, 2013
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    Would it help to physically restrain the vehicle a few milliseconds.....to insure full ignition from all engines before liftoff?
     
  9. WBahn

    Moderator

    Mar 31, 2012
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    You would have to be very careful in doing that because of the risk of producing damaging forces on the rocket. But, if that is taken into account, it might be possible (and possibly is done for high power amateur rocketry, I don't know). But the complexity and cost would probably be too much for small scale rockets plus these engines have very limited burn times and even a fraction of a second could cost you significant altitude.
     
  10. Stanly

    Thread Starter Member

    Mar 29, 2014
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    Hi everyone,

    Thank you for your useful comments.

    And Ylli, thanks in particular to the link that you sent. Maybe I will purchase that from Amazon. Actually, when I was at Lowe's earlier, I inquired and I found the very thing that you linked to, but it was only 6 V.

    So, let me be clear. Let's say that I am firing a two-stage rocket, and all I need to do is ignite the lower stage. To do that, do I really need to use 12 V, or is the 6 V launcher sold by Estes sufficient?

    If I need 12 V, then I will purchase the item to which Ylli linked. And then I will also purchase this launcher from Apogee Components:

    https://www.apogeerockets.com/Launch_Accessories/Launch_Controllers/Go_Box_Launch_Controller

    So, is the Estes launcher sufficient? If not, then I will buy the 12 V charger from Amazon and the Go Box Launch Controller from Apogee.

    Everyone is being wonderfully helpful. I really appreciate it.

    Stanley
     
  11. WBahn

    Moderator

    Mar 31, 2012
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    I think you are over thinking this to a pretty extreme degree. Keep in mind that model rocketry has been a safe and reliable activity for kids in the 10 year old range for decades. They tend to approach it like they approach everything they do -- without a lot of thought and just charge ahead and do it. If something doesn't work, then they futz around with it until they find something that does (or they decide that something else sounds like more fun and switch paths altogether). We adults have a tendency to suffer from analysis paralysis and we miss out on a lot of pure fun as a result. Go buy the rocket kit you want to. Build it. Then go someplace safe and launch it. If it doesn't launch and you can't get it to go, then come back the next day or the next week with a better launch system. The best way to ensure that your launch system will work is to burn up some igniters at home testing your system, whether it be one you buy or one you build. As long as you are using an igniter that is recommended for the engine you are using, that should be sufficient. If, for some reason, you are going to be using some other combination, then go ahead and burn up an engine or two during your testing. Hell, you will likely find that the building and testing of your launch controller turns out to be as much fun, if not more, than a few of your launch days are going to be.
     
  12. Ylli

    Member

    Nov 13, 2015
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    The little Estes controller is fine for a single estes solar igniter. Use fresh alkaline batteries for greatest reliability.
     
  13. Stanly

    Thread Starter Member

    Mar 29, 2014
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    OK, WBahn and Ylli. Maybe I am overthinking it.
     
  14. Janis59

    Active Member

    Aug 21, 2017
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    Watch first on international boarders!!
    For space scale the planet is so small that Your trajectory easily may be cached by military radars on neighbour countries and classified as `evil peril` making the "start dastardly imperialist war onto so friendly and so peace loving people`s republic" that "only veracious and decent answer must be to laid the nuclear peace-making-missile" back straight to Your head.
    I had at least twice coming very near to this, once in Soviet occupation epoch when at Baltic coast it was cached by Swedish (70 km off the boarder), and another time already at epoch of free state, when russians was trying to make a problem (distance 270 km).
    In such distances may not stand any radar station, even inland’s, otherhow You may get in trouble or other wording deep into sh**).
    My advice - get the permit beforehand and then the radars will be warned to not overreact.
    Just try to not cause by a mistake the Last World War, pleeease.

    RE:""Keep in mind that model rocketry has been a safe and reliable activity for kids""
    That refer only to 100 meter high rocketry and outside the city. As soon them are to go 100 km or at least some 50, then the play-rules are slightly other.
    Few years ago in my city at NY salute time one family laid their small daughter to watch that illumination, mum one side, daddy other side and daughter in middle hand by hand. One moment she just fall down dead. Later police find that some unburnt 50 gram heavy part of salute was falling down at unexpected trajectory from height of few hundred meters, so none is responsible for this death.
     
    Last edited by a moderator: Jan 2, 2018
  15. Janis59

    Active Member

    Aug 21, 2017
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    RE:""I need a convenient-to-carry 12 V power source for it.""
    Why not to use a accu from Your car?? 12V, 100A and some length of thick (probably audio?) wire.
    Controller is needed if one need a proper time-shift between a stages ignition, probably. If it happens by itself, then use just a thick switcher.
     
  16. BR-549

    AAC Fanatic!

    Sep 22, 2013
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    Is there a limit to the height of an amateur rocket, here in the states? I would assume some restrictions around airports.

    What about a balloon? Can anyone launch a 30 ft dia helium balloon?

    Anyone know of such things?
     
  17. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    72 miles?

     
  18. WBahn

    Moderator

    Mar 31, 2012
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    In the U.S., the rules are governed by Title 14 of the CFRs, specifically Part 101, Subpart C. Within that, as long as the rocket falls within the category of "model rocket" (a.k.a. Class 1), then there are only a few general restrictions. Essentially, it must be suborbital, not cross the boundaries of another country unless an agreement is in place, and must not create a hazard to any person, property, or aircraft. As long as those guidelines are met and as long as you are not operating within otherwise restricted airspace, you do not need any authorization or need to provide any notification of any kind for your launches and you may fly at any time or in any weather.

    For all forms of amateur rocketry (of which model rocketry is a subset) there is a general altitude restriction of 150 km (about 92 miles). I believe the current record is in the 120 km range. Since the current model rocketry record for G class engines is under 3 km (though a conforming H class rocket might double that), this restriction is effectively non-existent for model rockets.

    A "model rocket" is essentially one whose total weight is less than 1500 g (about 3.3 lb), has no more than 125 g (about 4.4 oz) of slow-burning propellant, and is made of lightweight, non-metallic structural components, primarily wood, paper, and/or breakable plastic.

    Once you move into Class 2 (High Power) and Class 3 (Advanced High Power) you have other restrictions you have to adhere to, principally authorization and notification requirements as well as additional general airspace restrictions.

    That's covered under Subpart D. Take a look.

    Google.
     
  19. Ylli

    Member

    Nov 13, 2015
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    NFPA code 1122 (model rocketry) adds an average thrust limitation of 80 N and total impulse <320 N-s for a 'model rocket'.
     
  20. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Your idea of 8 AA batteries will be fine.
    Their poorly written news letter from 2007 says so...

    198BFAE2-D3AE-45D4-836A-34D09B88DEA2.png
     
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