Violent Agreement: Two Stage 38mm to 33,290 feet

Discussion in 'High Power Rocketry (HPR)' started by Adrian A, Sep 6, 2019.

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  1. Sep 6, 2019 #1

    Adrian A

    Adrian A

    Adrian A

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    Here’s a picture of the completed rocket, on the head-end-ignition-leper’s-colony prep table at LDRS. Note the pointy end is pointed away from the flight line, in accordance with instructions from very nice LDRS volunteers. It’s a 38mm minimum-diameter rocket, most of which I built about 8 years ago, and which has been having semi-successful flights ever since. This weekend’s flight was also semi-successful, though it was a little more successful than most of its flights.

    IMG_5036.JPG
    The booster’s motor is sticking out of the back because the booster was originally designed to be stage #2 of a 3-stage 38mm diameter rocket, and the motor case serves as the inter-stage coupler. At LDRS, the booster flew an Aerotech J570, chosen for combination of kick-butt initial thrust to get the stack heading straight up, and relatively high total impulse. The sustainer flew on a Cesaroni Mellow Yellow J150, which I picked for its long burn time to keep under Mach 2 to preserve the airframe, high-ish total impulse and easy ignition. You can’t see in these photos, but the sustainer motor also sticks out the back to be the inter-stage coupler.

    The sustainer and the booster both have carbon tubes that I laid up myself around a 1.5” thick-wall aluminum mandrel. Both use mostly uni-directional carbon fiber with the fibers oriented along the flight direction. The sustainer is a thin and light layup but the booster is quite thick, to make it stiffer for use as a middle stage airframe. The sustainer’s fins have a leading edge angled back enough so that a Mach 3 flight would keep the fins within the shock cone. The booster’s fins are relatively large so that the whole stack has a lot of stability margin. I made them and the sustainer fins with thin carbon fiber plate and then did a tip-to-tip layup, so they're pretty stiff and strong despite being about 0.060" thick.

    Sustainer fins, one of which was painted with silver BBQ grill paint, which actually works quite well:
    IMG_4728.JPG

    Booster fins*:

    DM med.jpg

    *The black DM sticker stands for Darrell Mobley, who was the owner and force behind the Rocketry Planet, a former alternative to TRF where I used to post all of my rocket build threads and post-flight data 8-10 years ago. Sadly, Darrell took his own life around the time I built this booster stage, so I had a bunch of these stickers made at that time to memorialize him and his contributions to the hobby.

    The sustainer's nosecone used to be a nice basalt fiber and fiberglass cone that I laid up a number of years ago with a very slender L/D ratio, but that cone imploded at Mach 2.2 at the July NCR launch this year, so for this flight I used a stubbier VK fiberglass cone on a relatively heavy fiberglass tube.

    The sustainer uses a chute cannon style recovery system, shown here bolted onto the front of a different airframe:

    VA w chute holder.jpg

    A 24mm tube holds the main chute inside the front of the rocket, and the Kevlar shock cord is taped down around the outside of the cannon. At apogee, the nosecone is ejected away from the rocket using a charge at the tip of the cannon, for a drogueless descent which exposes the cannon. At the main chute altitude, the chute is fired from the cannon with a piston. The chute cannon concept has a few advantages:

    • Dual deployments from one av-bay break
    • The av-bay stays next to the motor throughout the flight, making sustainer ignition easier
    • Efficient use of nosecone volume
    • No tube zippers

    The downside on a 38mm rocket is that the shock cord can't be very beefy and still fit, and the cannon likes to break off the end of the rocket after landing. The cannon is also difficult to install with the way I did it in this version, though I have a redesign in mind that should make it stronger and easier to use.

    The booster has an ejectable av-bay recovery system. There is a long coupler tube that holds the electronics and the chute. The ejectable av-bay is positioned just behind the sustainer motor. At burnout, the electronics fire the stage separation charge, and at apogee, electronics fire a charge at the other end that ejects the av-bay and chute from the booster. The front end the tube that holds the chute is cut into two L-shaped pieces that fit together when they are inside the booster so that it can support the sustainer motor during the boost, but also easily release the chute when it is ejected from the booster airframe tube. I'll add a picture later if people are interested but I don't have one handy at the moment.

    Both stages have a Featheweight Raven4 altimeter and a Featherweight GPS tracker, side by side, in an av-bay only 2" long. The av-bay uses a Featherweight 38mm av-bay kit for mounting the Raven, which includes a magnetic switch and enables the threaded rods to fire the deployment charges. I'll add some pictures later if people are interested. The sustainer adds a separate screw switch for the sustainer airstart igniter, so that I can arm all the electronics for deployments and make sure they're ready before arming the airstart. The booster's thick carbon fiber tubes prevented GPS reception until the av-bay was ejected.

    The chutes for both stages are ones that I design and sew myself that are nearly hemispherical, but made out of one sheet of thin ripstop to minimize the hems and the packing volume they take up. A 14" diameter chute, piston, and protector all fit in about 6" of 24mm chute cannon tube.

    The booster motor is held in place with a forward retention device made from a Home Depot 1.5" expandable pipe tester that I have screwed onto the end of the forward closure. When I install the ejectable av-bay in the booster, I shove it up against the back of the sustainer motor using the booster motor, and then just twist the booster motor to expand the rubber motor retention to lock it into place. That leaves the whole inside of the 2-stage rocket, from the sustainer motor on down, all stacked together so that none of the innards can move during the boost.

    Here it is in my tower in the way-away 80s pads. In the background is a nice M-powered min-diameter rocket in another tower, which was also flying a Raven altimeter and Featherweight GPS tracker.



    IMG_5037.JPG

    Ray Lapanse (Chris Lapanse's dad) took some awesome shots of the boost, which I hope to reproduce here if/when he posts them.

    Here is some flight data from the sustainer's Raven:
    upload_2019-9-6_11-2-7.png

    Zoomed in on the two boosts:

    upload_2019-9-6_11-3-59.png

    The boost off the pad peaked at about 36 Gs. The velocity after the first stage was 1119 feet/second (Mach 1.0) and it coasted down to 609 feet/second when the sustainer motor pressurized, and then at sustainer burnout it was moving at 1991 feet/second (Mach 1.7).

    The sustainer ignition was set for 6000 feet, with a timeout. The purple line shows when the altimeter was firing it. It took about 1.7 seconds for the motor to pressurize after the igniter fired. The head-end ignition was pretty simple, just an igniter stripped and potted into the front end of the Cesaroni 38mm forward closure with a lot of 5-minute epoxy. The igniter head nestled into the center hole of the pressed BP that CTI uses for ignition.

    At apogee, the altimeter fired the charge, but then nothing happened. When I saw from the GPS data that the rocket was coming in hot, I thought maybe I just sized the charge too small, but from this data there isn't a hint of any pop in the acclerometer data. I have had undersized charges before, but you can always see them in the accel data. This one was a dud. The rocket was going 620 feet/second when the main charge fired, which blew off the nosecone and then the chute ripped off the chute cannon when it inflated. Here's how it landed:
    IMG_5040[1].JPG

    The back end of the sustainer took a Kansas soil sample and packed dirt in and around the Raven altimeter (but it still worked after I soaked the mud off). The front end of the sustainer landed without a scratch since the blown-open chute slowed it down enough. In between the Featherweight GPS tracker was ripped out of the av-bay and had its antenna torn in half, but it was still transmitting while laying in the dirt when I walked up to it. Here's data recorded by the GPS:
    upload_2019-9-6_11-27-53.png

    The GPS withholds its data above 500 meters/second, but otherwise it was in lock for all of both coast periods. The vertical and horizontal velocity can be used to compute the flight angle from vertical: (oops, ran out of photos so I'll continue with anther post)
     

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  2. Sep 6, 2019 #2

    markg

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    I'm interested in seeing these. Could be useful for me 38mm min diameter two-stage project.

    cheers - mark
     
  3. Sep 6, 2019 #3

    Adrian A

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    Here is the flight angle data from the sustainer's GPS:

    upload_2019-9-6_13-1-48.png

    The flight did take off at a substantial angle from the beginning. The squirrely looking angle values, above, are during the sustainer boost. The flight angle was around 16 degrees when the sustainer fired.
     

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  4. Sep 6, 2019 #4

    markg

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    Are you going to add a flight angle check to the logic options for the Raven? Can you the Raven settings for the Sustainer? I don't have a Raven but am thinking of picking up a couple for some two stage flights.

    thanks - mark
     
  5. Sep 6, 2019 #5

    Adrian A

    Adrian A

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    The Raven4 can't compute the flight angle directly, and it doesn't have a connection to the GPS which does have that information. At the moment, the best it can do is to have an altitude trigger with a timeout, so that if the flight goes really far off it will inhibit the ignition.
     
  6. Sep 6, 2019 #6

    BDB

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    Very cool flight. Thanks for the report.
     
  7. Sep 6, 2019 #7

    rocketace

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    Great flight and awesome detailed report. I flew my Featherweight Tracker on 5 flights at LDRS and walked/drove straight to each one!
     
  8. Sep 6, 2019 #8

    Nytrunner

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    Man, don't they have any tables that are less....staticy? for HEI prep?
     
  9. Sep 7, 2019 #9

    timbucktoo

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    Great flight Adrian. Sorry about the recovery.
     
  10. Sep 7, 2019 #10

    mbeels

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    That's a good point, I get static shocks just looking at that table.
     
  11. Sep 7, 2019 #11

    A-N-D-R-E-W

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    Thanks for the after action report, and sorry to hear it came in a little hot. On a side note, I used a Featherweight GPS to track down my rockets at LDRS and it worked like a charm. Really enjoying the product.

    What day did this fly? Because I don't recall seeing this one!
     
  12. Sep 7, 2019 #12

    crossfire

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    Adrian. I would like to see more on the build.
     
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  13. Sep 7, 2019 #13

    manixFan

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    Adrian,

    Great write up, thanks for all that info. I think I understand how your motor retention works but if you could post a photo of how you have it stacked up I would really appreciate it. I assume the motor needs to have a threaded forward closure with a threaded rod inserted in it in order for it to work? I looked around on Home Depot's website but I don't think I found exactly what you are using. Also good info on the chute canon, helped me understand it better.


    Tony
     
  14. Sep 8, 2019 #14

    Adrian A

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    Last edited: Sep 8, 2019
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  15. Sep 8, 2019 #15

    heada

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    I miss Darrell. He was a great builder, both of rockets and websites.
     
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  16. Sep 8, 2019 #16

    Adrian A

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    Liftoff was Sunday, at 3:13:31.5 PM. (GPS logging is cool)

    I found a couple more photos from 2011 when I did most of the work. Taking off the peel ply zfter tip-to-tip layup: IMG_0101.jpg

    After some sanding and trimming:
    IMG_0105.jpg
     
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  17. Sep 9, 2019 #17

    plugger

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    What a blast from the past! Your 3 stage Violent Agreement write up on Rocketry Planet was a thread I looked at many many times. I reckon I've still got a copy somewhere that I printed to PDF, and possibly a hard copy to boot!

    Sorry to hear about the down part of the flight but credit to you Adrian. 30k'+ on a two stage 38mm is quite a serious flight!

    Any and all information you are comfortable with sharing regarding this rocket would be greatly appreciated.
     
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  18. Sep 9, 2019 #18

    Cameron Anderson

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    Personally, i'd like to see the booster electable av bay
     
  19. Sep 9, 2019 #19

    manixFan

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    Ahh, thank you for that link and explanation. I had found those but could not figure out how it could work with that large piece. I definitely will give that method a try.

    Tony.

    ps: I'm now the proud owner of a couple of test plugs. I don't see why they would not work for even larger rockets as long as the body tube is strong enough to capture the plug. I would love to use it on my 98mm rocket so I could adjust it to match the motor case. Will have to do some testing.
     
    Last edited: Sep 10, 2019
  20. Sep 10, 2019 #20

    Adrian A

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    Thanks. It would be awesome if you could find that pdf and upload it here. There's a lot that I've forgotten about rocket building since then!

    Today I took another look at the chute and found that I still have the dud charge that prevented a successful apogee deployment, since the wires were tangled in the harness:


    IMG_5070.jpg
    IMG_5071.JPG
    I make these charges by potting BP into a cardboard tube with 5-minute epoxy at both ends. It looks like this one leaked pressure through the hole where the wires were pulled over. Normally these tubes blow completely apart. I made the charge a few hours before the flight and the epoxy was still soft, so I'm guessing that I pulled on the wires too hard, making the hole, and then maybe the broken seal combined with the high altitude (34400 ft ASL) prevented complete ignition of the BP.

    Here are the electronics that went into the booster's av-bay. A Raven4 altimeter, a Featherweight GPS tracker, two batteries, and a Featherweight 38mm av-bay that has an active bulkhead with a magnetic switch, battery charger, and electrically-active rods, all smooshed together in a 2" long av-bay that fits into a 38mm coupler.

    IMG_5078.JPG
    IMG_5079.JPG

    Later I'll show the fiberglass pieces that this fits into to make the booster's ejectable av-bay.

    I think I'll start a new thread on the re-build of the chute cannon.
     
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  21. Sep 11, 2019 #21

    plugger

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    Found it! See attached. I've also got the FIPa files from your 2010 Balls Violent Agreement flight, two videos (Violent Agreement LDRS at 30.mp4 and Violent Agreement.mp4), and quite a number of images that I directly downloaded to have higher resolution. If you want any of that just let me know.
     

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  22. Sep 11, 2019 #22

    Adrian A

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    Wow, thanks so much for finding that and sharing it.
     
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  23. Sep 11, 2019 #23

    watheyak

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    FYI, I still have the plug for this rocket's nosecone if you want it back.

    It's made a few molds by a few different folks in those 8-10 years. Still in great shape.
     
  24. Sep 11, 2019 #24

    Adrian A

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    More good news, thanks Scott. I was wondering where that went. I would like to use it to replace the one I busted this summer. I'll PM you my address.
     
  25. Sep 11, 2019 #25

    Adrian A

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    I have used a 2" one for a 54mm rocket by over-expanding the central rubber part. It worked, but it seemed a little iffy about how much it would hold like that. One other tip is that for the 1.5" one, I found I needed to trim down the rubber a little bit in order to make it easier to get in and out.
     
  26. Sep 11, 2019 #26

    Adrian A

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    Your wish is my command:

    IMG_5085[1].JPG

    With the way it's split like this, it can still carry the load of the sustainer motor through the middle of the booster airframe down to the forward retention of the booster motor.

    The electronics go into the bottom end of the photo above.

    IMG_5084[1].JPG

    The little blue-taped 2-pin connector is to pass through the separation charge to the front end of the assembly.

    More on the end that holds the electronics:

    IMG_5086[1].JPG
     
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  27. Sep 12, 2019 #27

    Cameron Anderson

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    An elegant, lightweight solution. I need to think about using something like this.

    You've got me wanting to do a Wildman Mach 2 two-stage now. I've been thinking about it all day. L935 to an L265 seems like it would punch a pretty good hole in the sky.

    Any plans for a 54mm Featherwright av bay?
     
  28. Sep 12, 2019 #28

    Adrian A

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    No, but the Power Perch fits nicely on a 54mm sled.
     
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