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Thread: V2 for my L3

  1. #361
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    Why would people grief you for tapping your shear pin holes?

    I bet I know.....cause I do it too.
    Purists get a little pinchy when you drill and tap the hole in one fell swoop.
    The proper way is to have a clearance hole on the outer body-tube layer and threads just in the coupler.
    This keeps the shear pin from being in "thread-tension" which can cause premature failure due to the stress.

    Drilling and tapping both works for me....can't be bothered with the extra step.
    But all you need to do is drill the tap hole though both parts when aligned and then separate them and re-drill the body and tap the coupler.

    Did I get it right, Eric?

    Fred Azinger

  2. #362
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    I used to thread the body tube but not the nosecone shoulder. The reason I don't thread the shoulder is because I want to just push the broken remainder of a stub inward instead of having to screw it in or out. Because the head stays with the body tube portion, that part is easy to unscrew.


    Steve Shannon

    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  3. #363
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    I used to thread the body tube but not the nosecone shoulder. The reason I don't thread the shoulder is because I want to just push the broken remainder of a stub inward instead of having to screw it in or out. Because the head stays with the body tube portion, that part is easy to unscrew.
    Different Not seen that. Makes sense.

    I drill them out starting with a small drill up the middle, then switch to a left-handed drill of diameter just under the minor diameter of the thread. At some point the drill bites and the remains of the screw just unscrews.
    TRA 13430, Level 3

    "Everybody's simulation model is guilty until proven innocent" (Thomas H. Lawrence 1994)

  4. #364
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    Quote Originally Posted by FredA View Post
    Why would people grief you for tapping your shear pin holes?

    I bet I know.....cause I do it too.
    Purists get a little pinchy when you drill and tap the hole in one fell swoop.
    The proper way is to have a clearance hole on the outer body-tube layer and threads just in the coupler.
    This keeps the shear pin from being in "thread-tension" which can cause premature failure due to the stress.

    Drilling and tapping both works for me....can't be bothered with the extra step.
    But all you need to do is drill the tap hole though both parts when aligned and then separate them and re-drill the body and tap the coupler.

    Did I get it right, Eric?
    I think the general reason I've been "picked on" for drilling/tapping shear pin holes is because it takes more time and effort than just drilling a clearance hole for the major diameter of the nylon screw. That said, for the many reasons mentioned, I prefer having a proper thread/fit of the screw to the hole, rather than the slop of drilling a hole the size of the major diameter and all the wiggle room to the minor diameter.

    That, and there's a lot of playful banter in our parts. Many folks don't pass up a good opportunity to lightly jab others. I can sometimes be a bit OCD, which is in direct conflict with some others that I fly with regularly. Different methods of madness for sure; not that one is right or wrong!

    Honestly never gave thought to threading the surface underneath (coupler, cone, etc) and drilling a clearance hole in the airframe. Not a bad idea at all!
    Eric Cayemberg
    TRA 7783 L3
    TAP

  5. #365
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    Excellent discourse!

    I'm not sure how I feel about the clearance hole, if I went that way I'd probably do slight interference hole so the threads "bite" and keep the pins from working loose.
    Or I'll just keep drilling and tapping lol. I've just used an exacto tip in the sheared nub and never saw it as a hassle.

    @Over the top: Are we still talking 4-40 or 2-56 screws? Cuz that's an incredibly tiny left handed drill to fit the minor diameter!

  6. #366
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    Typically I thread both sides. This NC being plastic I drilled clearance on the NC, and threaded the tube.

    A left-handed drill bit is a genius way to remove them too.
    So much of my rocket building time has been diverted toward my "other hobby": Race Timing

  7. #367
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    Quote Originally Posted by ECayemberg View Post
    I think the general reason I've been "picked on" for drilling/tapping shear pin holes is because it takes more time and effort than just drilling a clearance hole for the major diameter of the nylon screw. That said, for the many reasons mentioned, I prefer having a proper thread/fit of the screw to the hole, rather than the slop of drilling a hole the size of the major diameter and all the wiggle room to the minor diameter.

    That, and there's a lot of playful banter in our parts. Many folks don't pass up a good opportunity to lightly jab others. I can sometimes be a bit OCD, which is in direct conflict with some others that I fly with regularly. Different methods of madness for sure; not that one is right or wrong!

    Honestly never gave thought to threading the surface underneath (coupler, cone, etc) and drilling a clearance hole in the airframe. Not a bad idea at all!
    Just for clarification, I used to thread the outer surface and make the inner surface an interference fit so it took a little pressure to insert the screw/shear pin. A few years ago I started just making both layers interference fit so I just push the shear pin into place. After the flight I push the inner one through (some of my nosecones rattle now) and either unscrew or lift out the outer one with the screw head.


    Steve Shannon
    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  8. #368
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    Only on in an L3 thread would there be a discussion of a gnat's ass (i.e., the approximate thread depth of a 2-56 nylon screw). 😋

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  9. #369
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    Quote Originally Posted by Cl(VII) View Post
    ..I know the rocket had a big time spin...can't quantify because no video, but enough that I was cringing (probably 2-3 rps). Also, spin doesn't quite describe it. It wasn't a perfect down the Z-axis spin...more of a tight spinning wobble of the type that give the corkscrew smoke trail....
    I have video of your flight. I'll PM you a link to my dropbox. It's not my best work - really just barely had time to grab my camera and then I lost my balance while filming. But I stabilized it in After Effects enough for you to see the flight profile for quite a ways up.

    Coning is what I call the type of rotation you were seeing.


    Tony
    why do people put so much stuff in their sigs?

  10. #370
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    Quote Originally Posted by manixFan View Post
    I have video of your flight. I'll PM you a link to my dropbox. It's not my best work - really just barely had time to grab my camera and then I lost my balance while filming. But I stabilized it in After Effects enough for you to see the flight profile for quite a ways up.

    Coning is what I call the type of rotation you were seeing.


    Tony
    I got it. Thanks very much. Was the video real time or half speed?
    So much of my rocket building time has been diverted toward my "other hobby": Race Timing

  11. #371
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    The video is 50% speed. It was shot at 1080i (interlaced). I use a somewhat complex technique in After Effects to deinterlace the video and slow it down at the same time. Each field becomes a frame so there is no interpolation like with normal slow motion. It is essentially 60 frames per second played back at 30fps. I cropped it (not scaled) to 720P to reduce file size without losing any information other than sky.

    If you want a real-time version let me know.


    Tony
    why do people put so much stuff in their sigs?

  12. #372
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    Quote Originally Posted by manixFan View Post
    The video is 50% speed. It was shot at 1080i (interlaced). I use a somewhat complex technique in After Effects to deinterlace the video and slow it down at the same time. Each field becomes a frame so there is no interpolation like with normal slow motion. It is essentially 60 frames per second played back at 30fps. I cropped it (not scaled) to 720P to reduce file size without losing any information other than sky.

    If you want a real-time version let me know.


    Tony
    That was great. Just wanted to make sure I was calibrated correctly.

    Coning is a much better description of the problem than spin.
    Last edited by Cl(VII); 14th September 2017 at 03:09 AM.
    So much of my rocket building time has been diverted toward my "other hobby": Race Timing

  13. #373
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    I replayed the video and noticed a couple of small jumps. I've fixed those and also output a normal speed video with audio. Links via PM.


    Tony
    why do people put so much stuff in their sigs?

  14. #374
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    Any way for the rest of us Joe's to see it? Kurt

  15. #375
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    Thanks very much to Tony for the excellent video. It is way easier to work from video than memory.



    Excluding the coning, I am really happy with the look of the flight. It just looked and sounded "like a rocket" if that makes any sense. The flame to rocket ratio is even about right for a V2.
    Last edited by Cl(VII); 14th September 2017 at 03:07 PM.
    So much of my rocket building time has been diverted toward my "other hobby": Race Timing

  16. #376
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    Quote Originally Posted by Cl(VII) View Post
    Thanks very much to Tony for the excellent video. It is way easier to work from video than memory.

    The rocket really starts it's dance about 4-5 sec into burn as the motor is tailing off. The altimeters say it stopped accelerating around 5.5 seconds, and was decelerating by 6 sec.
    So much of my rocket building time has been diverted toward my "other hobby": Race Timing

  17. #377
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    That's really interesting. Do you think it's exaggerated mass imbalance of the motor coupled with the stubby nature of the V2 (and associated nose heaviness)?

    I think the concept of the long moonburner is cool, but I Really don't like the asymmetric thrust and mass distribution.
    (*begins thinking of only using moonburners in symmetric cluster formation.....*)

  18. #378
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    Quote Originally Posted by Nytrunner View Post
    That's really interesting. Do you think it's exaggerated mass imbalance of the motor coupled with the stubby nature of the V2 (and associated nose heaviness)?

    I think the concept of the long moonburner is cool, but I Really don't like the asymmetric thrust and mass distribution.
    (*begins thinking of only using moonburners in symmetric cluster formation.....*)
    In the end I don't know. There is a lot of asymmetry in this rocket. 1) Asymmetric drag from camera shroud, 2) Asymmetric mass distribution from motor geometry, 3) Asymmetric thrust (?), if only slightly, from offset core. Issues 2 and 3 are small effects, so my money is on issue 1. In the end all of these will be taken out of play on the next flight, so I'll never know which is determining...unless it still cones, then I know it was none of them.

    A compounding issue may be that the fins are scale. They are not increased in area as some V2 kits are, so they are relatively small compared to the amount of weight they are supposed to be steering.

    I have everything in the garage cleaned up from Airfest, and the damaged swivels cut off the recovery train, so the retrofit can begin. Mercifully none of the parachutes were damaged in whatever occurred on deployment.
    So much of my rocket building time has been diverted toward my "other hobby": Race Timing

  19. #379
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    Quote Originally Posted by Cl(VII) View Post
    Thanks very much to Tony for the excellent video. It is way easier to work from video than memory.

    (video snipped)

    Excluding the coning, I am really happy with the look of the flight. It just looked and sounded "like a rocket" if that makes any sense. The flame to rocket ratio is even about right for a V2.
    Chris,

    I agree with your sentiments - it was a great flight and I really liked that motor. As you can see in the video I lost my balance as I followed the flight upwards and the camera jerks around quite a bit. But the smoke trail clearly visible in spite of that.

    I've had a lot of discussions with folks about causes coning and there is no simple answer but it clearly can produce a significant amount of additional stress on the rocket.

    Great to hear that damage was minimal and easily fixed.


    Tony
    why do people put so much stuff in their sigs?

  20. #380
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    Use a Bates grain motor. It really didn't seem to get whipping around until late (or what seems later) into the flight.
    If you see the same behavior with a Bates grain then O.K. it's an inherent "rocket thing". If you get a better flight with the Bates, put the camera back on
    and see what happens. I've seen some large camera shrouds flown before, some forward and some aft without any issues. Yeah, the V2 is an exception
    but wow, if that's part of the problem that's an eye opener to me.

    Another thing, that camera shroud seems to be pretty small. For that to add to your problems, you must've hit some sort of a sweet spot for that to happen.
    Good luck with the next shot. Kurt

  21. #381
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    I have 6in. & 4in.scale V-2's. Both use nose cone main deploy with electronics in NC shoulder to keep weight forward.

    The 6in. nose cone weighs 9lbs with all gear. Rocket 19.5 lbs.
    I have 6 flights ranging from 4grain K's to 5grain M's.....all high thrust motors [V-max/white thunder/blue thunder] & all bates grains.

    Under thrust both fly straight & true, as coast begins,so does a bit of coning. I just have accepted it as V-2 wiggle. I also notice, probably due to short/stubby design and weight associated with it, they always begin gravity turn shortly after coast begins.
    I just fly on calm days as I also have 3 of those flights expelling main at apogee. [3 worst flights for coning]. 2 of those showed excessive speeds at apogee due to the long arcing flight. I stripped 2 drogues & main came out.[3of 6 flights, main at apogee.] Charges during all flights fired when supposed to, no issue there.

    I think it's due to so much NC weight exacerbating the issue. There is plenty of shock cord [30ft] to scrub off speed, but due nature of trajectory, it doesn't slow down like a "normal" flight.
    I have upped shear pins to 5 #4-40 from 4 2-256 hoping this will solve issue. First 2 flights all went as planned, but they were on smaller motors with less thrust.

    I have seen my/your issue with several scale V-2's and so far the solution that seems to work, is more NC weight, and adding more pins.

    So don't feel to bad as you're not alone with this issue.
    Jim Hendricksen
    L-3 Tripoli 9693
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  22. #382
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    I have the same 4" that Jim flies with HED deploy. Only have 4 flights on it but every flight, coning is prevalent and she turns with gravity as coast begins too. Never had main deploy at apogee but because she turns so much, it has always been a bit of a walk for recovery.


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  23. #383
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    Good to hear the voices of experience on the coning and arc. I anticipated the arc over, but the coning did suprise me.

    The work started last night. I laminated a wrap of 5oz fiberglass to the NC shoulder. This made it too snug, which is what I wanted. I will sand it to a good fit, and redrill the 4 shear pin holes, and probably add 4 more.

    So much of my rocket building time has been diverted toward my "other hobby": Race Timing

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