AeroTech Open Thread

Discussion in 'Propulsion' started by ATGM, May 16, 2015.

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  1. Jan 9, 2020 #3,271

    tbonerocketeer

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    I believe igniter placement in motor affects delay times as well.
     
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  2. Jan 9, 2020 #3,272

    John Kemker

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    Hey, guys, I've got a radical idea!

    Why not use electronic deployment and skip all the delay drilling inaccuracies?

    Oh, wait. Silly me. There I go making sense, again. I'll stop. Promise.

    Seriously, though: If 1/2 second tolerance is required, you're much better off going for the electronic method, rather than the motor ejection. The inherent lack of accuracy in measuring delay adjustments leads to the poor precision you're complaining about. There's more than one way to skin a cat, after all. You can have a precision milling machine setup to make your delay grain adjustments and still not get where you want because of variations in manufacture/motor configuration/igniter installation. So, keep that in mind and use a different method.
     
  3. Jan 9, 2020 #3,273

    Nytrunner

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    The closer the igniter to delay element, the earlier it lights?
     
  4. Jan 9, 2020 #3,274

    bill_s

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    ^^-- the longer it chuffs, the shorter the delay.

    -----

    The claim is that the 3 second gaps between drill tool settings doesn't matter because the motor itself is +/- 1.5 second (with shorter delays). 1.5 + 1.5 = 3. You should be able to get it within 2 sec. in reality.
     
  5. Jan 9, 2020 #3,275

    rcktnut

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    Rockets have to be built to be able to withstand delays + or - a few seconds from optimal delay.
     
  6. Jan 9, 2020 #3,276

    Steve Shannon

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    As does the altitude at which the delay grain burns. An AT delay grain at one mile altitude consistently burns 8% slower than one burned at sea level.
     
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  7. Jan 10, 2020 #3,277

    bill_s

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    I read that, for model rockets, deployment should be at 50 fps or less. That's within about 1.5 seconds from apogee. There might be an impression that since this is on the Aerotech thread etc. we're all talking heavy duty high power type rockets. I am not. Mostly I'm talking about getting 29 mm G reloads in 7 second delay and taking a couple seconds off.

    The improvement I get from using a drill bit wouldn't necessarily be worth $20, but it's worth NOT spending it.
     
  8. Jan 10, 2020 #3,278

    rharshberger

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    plus or minus 1.5 seconds from apogee is recommended for ALL rockets LPR to HPR, depending on materials is how much damage can occur from being earlier or later whether its the airframes or recovery components.
     
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  9. Jan 10, 2020 #3,279

    afadeev

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    At least reasons:
    1). Extra weight (battery, electronics, etc)
    2). Extra complexity
    3). Extra cost


    1/2 second ejecting timing is simply NOT required.

    Let me qualify the above statement - I can't think of any situation, nor look back on any of my personal experiences, where 1/2 second ejection timing precision is necessary. It may be desirable, and it's sure nice to time the ejection to apogee, but it's not necessary.

    In a perfect world, we would want to separate the airframe and eject some kind of laundry at apogee.
    But there are plenty of ways to work around the lack of ejection precisely at apogee, and still have good time.
     
  10. Jan 10, 2020 #3,280

    ChicagoDave

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    I always fly the JL Altimeter 3 - it reports apogee to ejection times. <2 seconds is my target. If it's >2 seconds something went wrong either with my SIM or with drilling the delay. Getting a more accurate delay than that I found isn't feasible due to the variations in building the motor, the burn time of they delay grain and the errors in drilling the delay. (Not to mention variations in the flight time of the rocket, etc.) If I recall, the delays are +/- 20% to start with.

    For example, I built two G64 reloads at the same time and drilled the delays with the same drill the same way (taking 2 seconds off of the 10 second delay grain). I flew them both in the same rocket within 30 minutes of each other. The 1st flight "apogee to ejection" was .9 seconds!! Perfect.
    The second flight, "apogee to ejection" was 2.9 seconds :( Way off!! But I built both motors at the same time, drilled the delays the exact same way with the same drill and flew both motors in the same rocket within 30 minutes. What did I do wrong on the 2nd reload? Who knows. I certainly can't figure out anything I did differently. :confused:
     
  11. Jan 10, 2020 #3,281

    BEC

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    You probably didn't do anything wrong. Delay elements vary. That's kind of an extreme example. Of course the apogee-to-eject time is also dependent on the flight path. Did the second flight weathercock more than the first or otherwise arc over more?
     
  12. Jan 11, 2020 #3,282

    UhClem

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    Igniter placement can do it. If it isn't up close to the delay element it could result in a delay of its ignition. Remember that all of those combustion products are trying to get out the nozzle so they give the delay grain a miss.
     
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  13. Jan 11, 2020 #3,283

    Steve Shannon

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    Also, surface contamination of the delay, such as getting grease on the surface, can really throw off consistency. One thing I’ve noticed is that the more experienced and careful people become, the more consistent their delays burn. I haven’t had an “Aerotech bonus delay*” now for over a decade.
    Also, Alan Whitmore and I did some testing. The actual delay grain material from Aerotech burns at a very consistent rate as long as nothing external changes, but very slight changes in motor performance cause huge changes in the delay times. Delay grains burn loosely five times faster while the motor is pressurized than when only the delay is burning in ambient pressure. A motor that burns one fifth of a second longer removes a whole second more from the delay. So, I believe that failure to consistently and immediately ignite the motor is probably the greatest detriment to consistent delays. Igniter placement can affect that greatly.

    *I used to blame these on Aerotech. I’ve had to eat those feelings.
     
    Last edited: Jan 11, 2020
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  14. Jan 12, 2020 #3,284

    ChicagoDave

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    If I recall, the G64 has a "C-Slot" grain. (I'm out of G64's at the moment so I can't check) If those slots aren't well aligned there is a chance the igniter could hit the bottom of the top grain and stop there. That might explain the two different behaviors from the two motors.

    I've had a "healthy" paranoia of getting contamination on the delay grain. I may take it just a bit far by using nytril gloves when building the motor so I can keep the grease on the gloves not my skin & remove the gloves when handling the delay grain.

    I believe that something outside of the motor build process was causing the different results. I'm reasonably convinced that it's not the delay grain burning significantly longer but instead something in the environment or in my process that is causing the difference. How I insert the starter could explain it, especially with the C-Slot grains.

    I'm going to try marking the igniter where it is verified at the top of the grains, then double checking when I install the starter on the pad. That way I can either verify or eliminate that as a cause. It shouldn't be too hard to mark the point with a sharpie and then check on the pad.
     
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  15. Jan 12, 2020 #3,285

    John Kemker

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    The G64s that I remember were one monolithic grain with a C-slot. There would be no misalignment in assembly.
     
  16. Jan 12, 2020 #3,286

    cerving

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    A 20% difference can be a huge amount in a longer motor delay... nearly three seconds on a 14 second AT DMS motor. For any delay over 7 seconds, you need to be thinking about using electronic deployment.
     
  17. Jan 12, 2020 #3,287

    rcktnut

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    They are made in 2 grains now to avoid hazmat shipping. You have to tape them together to align the slot.
     
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  18. Jan 12, 2020 #3,288

    grouch

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    Let's all be the same and do things the way John does.
     
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  19. Jan 12, 2020 #3,289

    John Kemker

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    Context, Jarrett, context. The discussion was about 1/2 second delay adjustments. I was pointing out that if you need that level of precision, you're better off using electronics. Others have rebutted my point quite effectively. Day late and a dollar short.
     
  20. Jan 13, 2020 #3,290

    grouch

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    I'm always late and short on plenty of things, nothing new there.

    For fun, who the hell would need 1/2 second precision anyway?
     
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  21. Jan 13, 2020 #3,291

    John Kemker

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    No Earthly idea, myself! I was just trying to bring a bit of levity to the discussion. As you can tell, I don't always succeed in my goals.
     
  22. Jan 13, 2020 #3,292

    FlyBy01

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    I know Aerotech is running behind in production again and was curious if Aerotech has considered pre-orders? I do not know if this is cost prohibitive or if there needs to be a certain number of orders before production can begin? Does anyone know if clubs do club orders from Aerotech; (i.e. One club member becomes licensed and places an order once a certain dollar amount is reached)?
     
  23. Jan 13, 2020 #3,293

    timbucktoo

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    We got a guy like that. He does pre orders whenever AT gets ready to make a price hike.
     
  24. Jan 13, 2020 #3,294

    ATGM

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    Not sure where you are ordering from but we currently have a 2-4 week lead time.
     
  25. Jan 13, 2020 #3,295

    rharshberger

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    Charlie, where are we at on 38mm end burn closures? Waiting on that for a warranty replacement from you guys as well ascthe rest of the hardware.
     
  26. Jan 14, 2020 #3,296

    Quixote

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    A couple days ago, I posed the question regarding the status of Explosives Regulatory Division of Natural Resources Canada authorization for the Quest/Aerotech Q-Jets for purchase and use in Canada. It has been three years that our American compatriots have had access to these model motors. About a year ago, Gary did comment to me on Facebook that some work was being done, and upon consulting the current ERD Authorized list, which regrettably is almost a year out of date, there is no mention of any authorized Quest motors. It would be interesting to know which if any of the newer Aerotech/Quest products have been submitted for testing. Such as the F67 Enerjet (Econojet) and any or all available Q-Jets. There are many of us chomping at the bit to get access to these products.

    Thanks to Bernard Cawley for encouraging me to attempt to contact Charlie directly, regarding news of any further activity post Gary's post to Facebook.

    Thanks

    Garth Illerbrun
    NAR 26894 L2
    CAR S04 L3
     
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  27. Jan 15, 2020 #3,297

    AeroTech

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    Garth, thanks for the comments. Charlie is no longer working for RCS/AeroTech. We will make contact with one of our Canadian representatives who helps with the authorizations and see where we stand with the newer motors.

     
  28. Jan 15, 2020 #3,298

    AeroTech

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    I will ask Karl where we stand on this and report back. Thanks for your patience.

     
  29. Jan 15, 2020 #3,299

    samb

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    Well that's some news, at least to me. Thanks for starting this thread Charlie and good luck with whatever's next.
     
  30. Jan 15, 2020 #3,300

    crossfire

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    What is Charlie doing now?
     

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