Shear pinning FG nose cone?

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Nick@JET

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First time for shear pins, quick question. First DD project, 3 shear pins in my Vindicator (2x56).
Am I over killing this?
I have 3 brass studs that will back up the shear pin. The FG looks like it will hold up sufficiently well to shear the pin, but I decided to take brass , thread my nose cone, then will cut of and sand flush, then drill the .085 hole all the way through the brass piece.
See pic, I'm open to suggestions thanks for the help.
Nick AdamsImageUploadedByRocketry Forum1429638628.911854.jpgImageUploadedByRocketry Forum1429638640.840047.jpg
 
On my Vindicator Jr. I just thread the shear pins into the fiberglass. Have flown it three time so far with no issues.
 
Am I over killing this?
Yes, FG will shear the pins fine on its own. I generally tap the holes on the NC side for the shear pin threads and enlarge the holes on the airframe side, so the pins are retained.
 
Cool thank you guys, hopefully can ground test tomorro
, I'll definitely insert on the cardboard, Magnum I'm planning
 
Anything beyond fiberglass to shear nylon pins on a fiberglass rocket = overkill.

Threading 2/56 shear pin / screw holes = overkill.

2" rocket - 2 pins
3" rocket - 3 pins
4" rocket - 3 pins
6" or greater rocket - 4 pins

Don't forget pressure relief holes in every airframe section.

--Lance.
 
I don't have relief holes yet, thanks.
I'll start the ground test with 2 pins in booster and payload and 0.75 grams in upper and 1.25 in booster
(2.1" x 10" payload and 20" booster)

As I drilled the holes in my brass inserts, as I was breaking through , the spun into the nose cone, Argg so now no inserts :).

Oh well I'm wired and ready to ground test
 
Ground tested tonight
Drogue didn't come come out at 1.25 grams (2 pins), but I think I caused this, didn't pack it tight enough and still had the plastic shroud around the e match.

Main came out with .75 gram (2 pins)

It did scorch the crap out of
My Kevlar, need a nonexistent cover for the cord. Seamed like it burned more than popped. That's why I ground tested though.
Thanks for the help and suggestions
 
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This was my first ground test so pretty disappointed I dorked up my shock cord and brand new custom parachute. I think since it didn't pop, the flame didn't have anywhere to disperse. Since I didn't have a motor in it... I'm sure that was the problem.ImageUploadedByRocketry Forum1429705842.756487.jpgImageUploadedByRocketry Forum1429705857.792930.jpg

Friction fit sounds good for the booster.

I didn't attach the main cord to the top of the AV since I was just testing shear pins.
 
Simple rule of ground testing:

Always test with EVERYTHING loaded as in "ready to fly" configuration.

Don't need a loaded motor, but al least an empty case.
Another point...not often mentioned:
When flying a full length motor [6xl or 1380 case] vs a smaller [say 3grain or 360 case] you can cut back amount of BP needed on apogee side.
You have reduced the interior volume substantially & reduce the "cannon-ball" effect by doing so.

Any time I fly a long motor in a small diameter rocket I cut back. My Vindicator Jr. uses 1.25 Bp on small size & .8 Bp on long motors, reduces the chance of shaking out the main, at the top.

Having shock cord hooked up during GTest will show how far the parts separate. Allowing for add/reduce charge, so you don't reach the end of cord and parts snap back.
 
Were you using a chute protector? If not, I suggest ground test with rags and they should still be protected from flame. Even if you stuff your motor case in the rocket, make sure you stuff the case with some rags and make sure they are snug. Still a good idea to secure nose cone as that will aid in deploying your shock cord. Just my 2 cents!
 
Thank you. I'll test again today or tomorro , the right way
1gr booster .75 payload
 
I use dog barf and a nomex chute protector. I hold the shock cord to the side and put a few hand fulls into the tube to take the direct hit from the BP and keep the cord to the side. the chute in the nomex sits on top of that.
 
OK, you really got my curiosity up on this one, why stuff a motor case with rags?

By the way, just curious, not ragging' on ya.....LOL:grin:

So gas doesn't leak out through the motor. I don't see why you couldn't just use a closure but I guess you can't do that if your using CTI.
 
So gas doesn't leak out through the motor. I don't see why you couldn't just use a closure but I guess you can't do that if your using CTI.


Why Conner...thankyou, never thought of that!
Makes perfect sense, I got enough At stuff laying around, I always use those.
But with CTI....you would need a solution. I do fly a lot of CTI, just never used them for G-test.
 
I just tape the forward end of the casing (CTI) or the charge well/closure (AT) for ground testing - works fine for my tests...

Like Jim said in Rules for Ground Testing, "READY TO FLY", minus a live reload of course, is the way to ground test. Pack the chutes, shock cords, install all shear pins and rivets, etc, etc, etc. If it's ready for flight minus the motor, you're ready to ground test.

One other thing I noticed in your photos above is that it looked like you have the rocket lying on the ground. I think most folks prop it up on something at about a 30-35 degree angle to the ground to get a sense of the extension of the shock cord. Some even ground test vertically, though I don't think that's recommended for a number of reasons, not the least of which is getting popped in the head with a nosecone that snaps back from straight above :)

I like to see the parts separate from the 30-35 degree angle to about 1/3 the length of the cord attaching them...
 
Cool thank you guys, hopefully can ground test tomorro
, I'll definitely insert on the cardboard, Magnum I'm planning

I've never found it necessary to insert even with cardboard (thick wall). I use 3 2-56 nylon screws in my cardboard DD birds. After I drill the holes I harden them with 2 or 3 soaks of thin CA. After 13 flights and 4-5 ground tests the cardboard on my Prion exhibits no deformation at all. One thing I do think is important, though, is that if you have a plastic nosecone with ridges on the shoulder (e.g. Madcow & LOC 4" cones), make sure you drill the shear pin holes into one of those ridges. This way, there is no gap between the airframe and NC at the shear pin, and you get a cleaner shear.

David
 
I am new to shear pins as well and have limited ground-testing under my belt. However based on my limited experience I simulate "ready-to-fly" configurations with my Kevlar harnesses, hardware, and nomex blankets, but I will pack something of equivalent volume for the chutes. The rational, it's a ground test and the result is not subject to change based on using a chute or something of equivalent packing volume. You are testing to see if you have correctly calculated enough BP to create the pressure required to shear your pins and separate your rocket. If once you get the desired result and you still feel there is value in testing with your chute, then go for it. At least in this case you will be mitigating your chute to heat exposure.
 
Coop's Unsolicited Advice:

I save old nozzles to serve as plugs for the MMT. For 24, 29mm, it's easy: handful (or almost a handful) of dog barf in the case, throw the nozzle in to secure that, then secure the dummy motor prior to ground testing.

38 is even easier: I had the foresight to run wires up through the nozzle hole. I can use this to activate the charge rather than running a wire into the av-bay. small 38 case, screw in nozzle, secure. Done.

54mm: while I have a 54mm nozzle, I typically use the 38 rig with a 38/54 adapter.

75mm: aft closure already blocks the case. Dowel length to spent nozzle.

98: no gots... can see me using a variation of the 75mm theme, though... or a 75 setup with a 75/98 adapter.

And I calculate shear pins by how much they're trying to hold together, not the diameter of the rocket, but hey... sometimes it's slow at work, and if I'm playing with numbers on scratch paper, people tend to leave me alone. Heh.

(N.b.: for first time with new motor size, when the nozzle isn't yet available... a plywood blank will do just fine)

Later!

--Coop
 
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Tested today with a motor installed , altimeter armed 1.1g stogie (friction fit) and .85 Nose - Main ( - 2 shear pins)
- both drogue and main were armed.
Maybe I should have done them individually?
I have a couple questions:
1. When I pulled the vaccum, they both went off and it happened pretty fast but sounded like both went at pretty close to the same time. Is this normal when simulating by a vaccum?

2. Should I have only have done the Main with the vacuum and launch controller with the drogue?

3. It had one long beep when I armed it ...then very long pause - then repeated a 3 beep (Drogue and Main)

Not sure how to post a video from my phone - I don't have that option, so here are some pics
ImageUploadedByRocketry Forum1430491980.749485.jpg
ImageUploadedByRocketry Forum1430491992.941344.jpg
ImageUploadedByRocketry Forum1430492003.461201.jpg
ImageUploadedByRocketry Forum1430492015.431573.jpg

Afterwards the RRC3 beeped out
2. - 1. - 9. ( appears to be 219') which just shows that altimeter works.

I kinda think I can fly it, but was a little concerned that both charges went off - maybe the vacuum test not to accurate on the timing of the deployment triggers?
 
The problem is that the altimeter thought you reached apogee at an altitude lower than your setting for main deployment and dutifully did its job. You really can't control a test with a vacuum cleaner very well or repeatably.

There is no need to involve your electronics in a recovery system ground test. Simply fire them with a battery and long wires fed through your vent hole(s).

If you feel the need to test your electronics, do that separately in a chamber you can reliably pull, hold, and release vacuum; not in the airframe. With a vacuum pump or plunger induced vacuum.

--Lance.
 
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I've done it once with a vacuum and it should fire drogue once vacuum reaches its max suction. Once the drogue fired, I held vacuum for a few more seconds and then shut it off and the main fired as it was suppose to but as others have said and how I now ground test is with a battery only. So much easier!
 
Thanks guys, I figured individually would be the way to go by battery.
 
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