My first MPR launches

Discussion in 'Mid Power Rocketry (MPR)' started by ABlock, Jun 24, 2019.

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  1. Jun 24, 2019 #1

    ABlock

    ABlock

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    In anticipation of a trip to the Alvord Desert, I decided to build a couple of mid-power rockets: an Aerotech Strong Arm and Public Missiles Bull Pup. I won't go into build details except to say that the epoxy clay Apogee sells made the fillets easy and that I preferred the plastic airframe of the PM kit and was not a fan of the Aerotech snap-lock fin system. I primed but did not have time to further finish either kit before the trip.

    I replaced the stock chutes with a 24" Fruity Chute connected with a quick link so I could easily move it between rockets. Also, as noted in another thread, I bought a Public Missiles payload nose cone, on which I mounted a Featherweight Tracker. I only planned to use it on the Bull Pup since the stock Strong Arm nose cone is 2" longer.

    Launch 1
    Timestamp: 6/21/19, 11:55 am
    Conditions: Fair, wind 0-3 kts SE
    Rocket: Strong Arm
    Motor: Aerotech 29mm Loadable Motor - G77R-7

    I built the LMS, which I found annoying due to the epoxy requirement, then went to set up the launch system. I used a jaw clamp with 1010 extrusion. I fabricated blast deflector from sheet metal and attached it and a rocket stop to the rail using the flat nuts designed to fit the extrusion channels.

    Supplied igniter was installed in the motor and then rubber-banded to the nozzle as per the documentation. After connecting the ignition leads I used blue tape to ensure the weight of the ignition wire didn't pull on the alligator clips. Power supply was a deep cycle 12V battery showing 12.7V.

    Got back the required distance, cleared the range, and had a couple of bystanders do the countdown. At zero I pressed the launch button and nothing happened. After one or two seconds I could see a wisp of smoke. At about 5s after pressing the button the rocket left the rail with a whoosh of red flame. At around 100' the ejection charge fired and the parachute came out. The rocket landed safely almost directly at the launch site, but as expected had a 3" zipper in the body tube.

    Clearly the igniter started the delay charge but failed to ignite the motor itself for a couple of seconds. Any ideas why?

    Launch 2
    Timestamp: 6/22/19, 12:27 pm
    Conditions: Fair, wind 3-5 kts NW
    Rocket: Bull Pup
    Motor: Aerotech 29mm RMS G53FJ-5

    For this launch I switched to the Bull Pup and a reloadable motor. I like the RMS assembly way better. I did find that the sleeve that holds the propellant grains was a tight fit in the RMS29/40-120 casing and required a little grease to seat. I decided not to mount the Featherweight Tracker in the nose cone for this launch, reasoning that the lack of wind and flat ground would make it easy to retrieve the rocket after landing.

    Using the same prep and launch sequence as Launch 1, this launch went off flawlessly, taking off with a whoosh of black smoke. I was relieved to see a good chute near the apex. The rocket landed on the hard playa about 400 yds away from the launch pad. An exuberant bystander rode out to get it on a Onewheel, and then proceeded to drag the nose cone through the dirt as she raced back to return it. It was hard to get mad because she was super excited.

    Launch 3
    Timestamp: 6/22/19, 8:19 pm
    Conditions: Fair, wind 3-5 kts S
    Rocket: Bull Pup
    Motor: Aerotech 29mm RMS G64W-7

    For this evening launch I chose a White Lightning motor. This one fit more easily into the motor case. I mounted the Tracker and confirmed that the app on my phone had connectivity with the ground station and that the ground station was communicating with the onboard unit.

    This one screamed off the rail, disappearing into the sky before the chute became visible at around 900'. It came down about 400 yds north of the launch pad, but it wasn't until I jogged half way back to the launch point that I noticed the nose cone was missing.

    A bystander pointed to a white object out on the playa near where the main body had landed, so I turned around and began walking back. A guy on a dirt bike beat me to it, returning the nose cone for inspection. The swaged wire loop that connected to the shock cord had opened, leaving the fitting on the wire. The ballistic impact had torn the avionics sled out of the tube, driving it towards the tip of the nose cone. Luckily the tracker electronics appeared totally unharmed, though I don't see how I will be able to salvage the nose cone without Dremeling out the CR and starting over. If I do this I will use a different retention device than an 18-ga. steel cable with swaged fitting.

    Conclusion
    All in all I think these launches represented a good learning experience and prep for a future L1 cert flight. A few thoughts:

    Launcher
    The jawclamp and 1010 rail worked beautifully. I did notice that the rail got a little less slick on subsequent flights, presumably from a combination of propellant residue and fine playa dust. I'll clean and put some dry lube on it before the next use.

    Ejection
    I'm not super excited overall about the idea of delay charges. Altimeter deployment makes more sense to me. Is there any reason that I can't use the ejection charge black powder from an Aerotech reload kit, but fire it using an altimeter and ejection canister cap or similar? That would also give me a path to Dual Deployment.

    Power supply
    The 12V deep cycle battery I borrowed was super heavy. I just ordered a LiPo-powered jump starter that has battery clamps and should work fine. It weighs like 4 oz. and will fit in the range box.

    Motors
    Only RMS for me from now on. I don't know why the LMS didn't fire correctly, but in any case the ease of RMS assembly is compelling.

    Nose cone
    I plan to rebuild the avbay nose cone. I'll cut out the existing tube and CR and add a new fiberglass CR. This time I'll notch the CR and epoxy in a loop of kevlar webbing just like I did for the motor mounts in the kits.


    Thanks for reading! Any feedback or advice is very much appreciated.
     
    Last edited: Jun 24, 2019
  2. Jun 26, 2019 #2

    ascastil

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    I wish they made that tracking system for Androids
     
  3. Jun 26, 2019 #3

    Theory

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    glad to hear that you are taking your first MPR launches in stride. ...and you really went for it with some good sized G motors too! The G64 is one of my favorite loads for the 120 hobby case.

    yes, you can absolutely use the BP that comes with a reload for your altimeter base deployment charge. if/when you do remember to put a little grease forward of the delay element when you build your motor.

    I am with you on the LMS. I have a G77 in my range box that I got from Aerotech to replace a defective G74. I feel the same as you do that "gluing" a motor together just doesn't seem right. I am sure I will fly it one day, cursing the idea the entire time.

    keep on keepin on my friend!
     
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  4. Jun 26, 2019 #4

    Nytrunner

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    You won't like HPR DMS motors or the ones that require grain bonding then :cool:

    I'm interested in what kind of epoxy the OP used, and how soon before launching he glued it.
     
  5. Jun 26, 2019 #5

    Theory

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    i have no issue with grain bonding, however, gluing closures IMHO is a different story. so yea, no HP DMS in my future, but I'm not concerned about that
     
  6. Jun 26, 2019 #6

    ABlock

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    This is the epoxy I used. Launch was probably 20m after assembling the motor, which might very well have been too soon — though it's not clear to me how having slightly tacky adhesive on the motor casing threads would have prevented good motor ignition...?
     
  7. Jun 26, 2019 #7

    ABlock

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    Thanks for the support!

    So one thing I'm wondering...if I am planning to use electronic ejection, why insert the delay element at all? To keep the main propellant from pressurizing the body tube? Is there not an inert way of plugging an RMS forward closure?
     
  8. Jun 26, 2019 #8

    Theory

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    yes, the delay is used to seal the forward closure. the 29-40/120 does not have the option for a plugged closure, so the delay must be used or a catastrophic event will occur that will destroy both the closure and the rocket.
     
  9. Jun 26, 2019 #9

    ABlock

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    Got it, thanks.
     
  10. Jun 26, 2019 #10

    kuririn

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    I think that was the problem. Instructions say to set the case assembly aside in a vertical position after gluing to let the epoxy fully cure.
    So 24 hours instead of 20 minutes. Otherwise the pressure will blow the forward end out.
     
  11. Jun 27, 2019 #11

    dr wogz

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    It also acts as tracking smoke..

    I'm also not a big fan of epoxy putty. It doesn't really adhere well; can flake off.
     
  12. Jun 27, 2019 #12

    ABlock

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    Well the instructions say, "The motor may be fired as soon as the bulkhead epoxy has solidified." I guess I should have read "solidified" as "fully cured".
     
    Last edited: Jun 27, 2019
  13. Jul 6, 2019 #13

    blackjack2564

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    I read the link to epoxy you provided, it says full cure in 24 hrs.Always read glue instructions and go by that.

    All single use hobby line motors are glued, no problem with glue, as long as it reaches full cure.
    Every LMS failure I have seen was due to not letting cure time go full 24 hrs. I used to build them few days ahead of time just to be sure.
     
  14. Jul 6, 2019 #14

    ABlock

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    Yeah, that was clearly the problem. Thanks.
     

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