Level 2 Build Thread and Sim Questions

Discussion in 'High Power Rocketry (HPR)' started by Sevian, Apr 30, 2015.

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  1. Apr 30, 2015 #1

    Sevian

    Sevian

    Sevian

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    Hello there! I figured my first build thread should be for my Level 2, which I'm going to do with the Level 2 rocket from Madcow.

    All parts have been sanded and will be dry fitting shortly, just a quick question about OR sim I ran with it. I'm planning to cert with a J285, but the eventual "big" flight will be with a K2045.

    I ran the simulation at first with a 17 second delay, said the the velocity was too high at 70ft/s. Optimal was 13, so I edited it for a delay of 13 and it came out correct. Does that seem right? Here is the screen cap of the sim:

    [​IMG]


    Any comments or concerns will always be appreciated, more build pictures coming soon!
     
  2. Apr 30, 2015 #2

    DAllen

    DAllen

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    What is the thingy on the tip of the nose cone? Weight? Probably not needed since your stability is at 3.93 or so.

    On a K flight to a mile I am not sure I would rely on motor deploy at all. Maybe as a backup but if I did that I wouldn't reduce the delay. Just figure on the electronics doing the heavy lifting.
     
  3. Apr 30, 2015 #3

    Nick@JET

    Nick@JET

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    Like D said , use motor for backup.

    17 seconds to apogee sounds pretty long to me, seams like it would be on its way back down ballistic by then and risk high speed pop. Although I haven't flown a J yet, so this just an opinion. I'll try my cert on a J400 with 8-9 sec delay based on a friend past experience with similar weight rocket as mine.
     
  4. May 1, 2015 #4

    Sevian

    Sevian

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    Thanks for the input! I've never had electronics do both the drogue and main ejection before, so that'll be a new experience for me.

    I also did think that 17 seconds was very long for it to coast to apogee, although the momentum from the very fast acceleration may just carry it for that long. Thanks guys!
     
  5. May 1, 2015 #5

    Bat-mite

    Bat-mite

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    thrustcurve.org shows a 13 sec delay for that bird as well.
     
  6. May 1, 2015 #6

    Coop

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    The 54 DAT is calibrated to the half-second, so that option is open for you as well, if needed. While I understand why you're seeing what the rocket will do, here, it's probably best to wait until it's built before you really worry about delay settings... They may well change, depending upon finished weight, etc.


    Later!

    --Coop
     
  7. May 1, 2015 #7

    DAllen

    DAllen

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    That's another thing to consider that Coop just mentioned...finished weight. Unless you've built a bunch of birds the finished weight will rarely match what it actually weighs in real life. Typically, finished will be significantly heavier. That said, build it, weigh it and find the actual CG and input the weight and CG using the over-rides.

    To expand on what I've said previously, leaving the motor ejection charge in is optional if you have electronics. In fact, if you have 2 altimeters IMHO with a flight like this leaving the motor ejection charge out is preferable. A one mile flight that goes a little too much off of vertical can have a more significant variation in time to apogee over a flight that only goes 1k. Try it on your sim with varying the rod angle all the way up to 20 degrees and see what happens.
     
  8. May 1, 2015 #8

    webtech

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    One thing I would look at, is a test flight before putting a snappy VMAX motor in it.
    VMAX is great for trusts out of the gate! but they are snappy!

    like the boys said above, you need a final weight before getting a good delay setting.
    I haven't been worrying about delay seconds lately, I have been using electronics. and it is super awesome. when they work :)

    if it's your first time with using electronics, I would suggest building a nice/cheap rocket that you can put a H or I in, so it gets up in the air. Use motor deployment as a back up.
    this way you can play around with something new, get the learning curve out of the way without the stress of a cert fly. And use real black powder, the 4F stuff.
     
  9. May 2, 2015 #9

    Handeman

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    All good advice above. If you are flying a v-max to 1 mile, I wouldn't bother with motor ejection, even as a back up. Use your altimeter(s).

    I understand being timid about the use of altimeters, but if you ground test your charges and then use a vacuum source to ground test the altimeter functions and do several test with this, you'll be more then familiar with the operation of the altimeter.

    I would say you should use the altimeter for DD on the cert flight with the J motor and then using it with the K will be much more comfortable.
     
  10. May 3, 2015 #10

    Sevian

    Sevian

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    Thanks for the replies everybody!

    I am definitely waiting to weigh the rocket once finished, as it will have a few extra parts not in the kit and I am using a different MMT than the kit (pictured below). I have built and prepped the Torrent, and that is going to launch next month for use with electronics. The 2045 launch isn't until at least two "test" launches to make sure the rocket is stable and I have the electronics fully worked out beforehand. But the 2045 is the ultimate goal at least for me for this year to do.

    Since that motor is my goal, the stock tube just was too short for it. So I got a bit longer once that'll fit it nice. Currently have the retainer with JB weld curing:

    [​IMG]

    This rocket will have a total of 6 CR's, 4 G10 FG and 2 plywood rings.

    The two plywood rings will have small grooves in them, and it is for the fins to "snap" into, similar to how the aerotech has those plastic snaps. I've used this method before, and it seems to work great and allows for more surface area for a bit more glue, which is great.

    [​IMG]

    and how it fits:

    [​IMG]
     
  11. May 3, 2015 #11

    DizWolf

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    The entire length of the Motor doesn't need to be in a motor mount. It's really just more weight with little benefit. It's quite typical to run motors longer than the mmt.
     
  12. May 3, 2015 #12

    Sevian

    Sevian

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    It was about 6-7 inches longer, I've always been afraid that there would be an issue with the shock cord, the longer tube was only about $20 and the G12 is only a tid bit heavier than the short G10 tube amazingly enough.
     
  13. May 3, 2015 #13

    DAllen

    DAllen

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    Why so many CR's?
     
  14. May 3, 2015 #14

    timbucktoo

    timbucktoo

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    I only see 2.
     
  15. May 3, 2015 #15

    DAllen

    DAllen

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    timbuktoo:

     
  16. May 3, 2015 #16

    timbucktoo

    timbucktoo

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    oops. I missed that. Good question !
     
  17. May 3, 2015 #17

    Sevian

    Sevian

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    The two plywood CR's are mainly there just to do the fin lock like pictured above. Since the VMax has such a powerful liftoff thrust, I wanted to overbuild a little and have 2 more G10 CR's just to help hold everything together...just in case.
     
  18. May 7, 2015 #18

    webtech

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    With good internal fillets and/or foam, you shouldn't have to worry about fins locked in to plywood.. - my opinion

    I would use one in the back of the fin, one in the front of the fin, and one in the very front of the motor tube. again my opinion.

    me I would cut the motor tube down, so you would have more room for recovery laundry.
    and I would use a lot of shock cord on each side, like 30ft on each. - again my opinion, I have been bit in the past with short cords.

    that is my two cents
     

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