Shear Pins or tape?

[AndyC2]

Hi,

A quick question.

For my first dual-deployment rocket, I've modified my PML 1/4-patriot (added 7" longer payload, and an ebay based loosely on others I've see on the Forums - thanks guys). I plan to fly it this weekend on a J350 for my level 2 (est 3500-4000'). For those not familiar, this is a 4" OD rocket made from PML's Quantum Tube (yes, with the extra weight it will stay well below 0.85 mach so the QT is OK).

My question is on securing the nose cone, which holds the main chute. I've never used shear pins before, but have seen others mention them in a number of threads. Am I better off sticking with tape/friction fit, or would pins be much better? I'm a bit concerned about the NC getting "shaken" off when the drogue is deployed. On the other hand, the NC is not very heavy, and might take a lot to knock it loose. Is there a general consensus on whether to use pins or tape for applications like this?

I guess a related question is, if using pins, then what kind? InfoCentral suggests square styrene rod, while I've seen others talk about using 2-56 screws. I saw one guy at a launch that had a nice system using styrene pins, where he flattened one end on a hot plate to make a "tack". InfoCentral also mentions using brass plates in the nose cone to deal with tears in the plastic. Is this much of an issue with either type?

Thanks for any tips.....
-Andy

 

[Jeremy Lundy]

Hi Andy, If your going to be at Pine Island this weekend I'll be there also doing my L2 with a J350! I think we might have met a few weeks ago. I flew the orange cluster G rocket. Anyway, I have not used shear pins either and will stick to tape for the time being. I don't want to experiment with something that new on a cert flight. However, others here know much more about it than I do.
Maybe I'll see you this weekend if your at METRA. What day are you flying?
Jer

 

[Art Upton]

I first used tape,
got lucky a few times, and then two in a row main deploys at apogee.

I've been using 2-56 screws since, with nothing other then drill a hole the same size as them, push them in. Then cover with masking tape, duck tape, or electrical tape to keep them from fallin' back out.

 

[WOOSHPREZ]

Shear pins are the way to go.
I have used both nylon screws and styrene rod. The screws are no better but everyone swears by them. Just make sure your nose cone is a decent fit, not too loose or tight before you get to the shear pin part. I'd say to use two 1/16" styrene pins for a 4" cone. I cut them about an inch long, sometimes sharpen the end so it slides into the hole I drill a little easier. Once it's in crimp the end of the protruding pin with your trusty pliers to keep it from pushing into the cone all the way. Works every time.

 

[mach66]

I agree with Art. I use them on every rocket. I don't even worry about the brass plate as plastic nose cones hold up fine. Your airframe is QT so no problem there. If using a cardboard non- glassed airframe, then I'd either put FG strips whre the hole will be or brass plates on the nose cone. If you have a snug fitting nose cone, plates won't be possible, so revert to FG strips on the inside of the airframe. If the nose cone is really snug, then CA the holes to stiffen them up.

Brent

 

[GaryT]

I'm a BIG Fan Of Shear Pins, I don't want My main popping out at apogee and have to walk across 2 counties to get My Rocket! Not that I cant use the walk Mind you:lol:. I use #2-56 Nylon Screws or sometimes I'll use 1.5mm Square Styrene Rod. I like using the Brass cut off plates as well, I epoxy the Brass Plates to the Collar Of The Nose cone, Slip the NC on and drill a 5/64th hole through the air frame and dead center of the Brass plate.

 

[Art Upton]

I'd like to share one other thing I learned the hard way.

Sometimes you need to shear pin your booster to the ebay (DD) or your nose cone to the booster on a single deploy.

I had a heavy nose coned 5.35" Nike Smoke Fiberglass rocket I flew many times.

Then I put a butt kicker Loki motor in it at LDRS 25 and at MECO the nose came out and of course it zipped even the fiberglass airframe.

 

[AndyC2]

Thanks for all the info. I think I will test out a couple of pins tomorrow night, esp since the NC is a bit loose before tape.

Art - I was planning to use a smig of tape for the booster/ebay joint (its pretty close without anything). Are you suggesting to use pins there as well? Is the concern drag separation after the boost? In my ~6 lb rocket, the J350 will be pretty punchy; though probably not as much as your Loki experience....

Jeremy, I'll be there. The plan is Saturday, as Frank who I drive up from Long Island with works on Sunday. Looks like the weather will be good, unlike last time when I had to scrub it.

-Andy

 

[leegscott]

Andy

I like 2-56 shear pins to. Just make sure you ground test!!

 

[Pantherjon]

Yep, ground test! Suggest 2g of BP for your ejection charge..Blow it up, or blow it out..With QT tubing you won't have any problems with 2-3g..


Tip: When putting in the shear pins do one at a time..Drill the hole thru the tube and nose cone, insert pin then do the other one..May also help making a 'key' mark on the cone and tube so the holes line up for the next flight..Oh this is for your L2, so you should know that already!

 

[pmlkid]

Shear pins are the way to go trust me!!

 

[GaryT]

I'll Be at the METRA launch on Sat as Well, Launching my Vorlon (1st Flight) On an AMW L666 Skid. See link below.


https://www.rocketryforum.com/showthread.php?t=45601

PS if either of you guys need a witness for your LV2 look me up.

 

[AndyC2]

Did a quick manual (hand-ual? ) test this morning. Used 1/16" round styrene rod, drilled with a #53 drill (0.0595"), 2 pins, and a some spare QT, a scrap of coupler and a bulkplate/eye-bolt. I was a bit concerned at first as the rod did not break easily in my hand. Anyway, 2 pins holds the piece of coupler quite well, and with a modest amount of force both pins sheered nicely. I'll actually try it in my payload section tonight, since I need to do a ground test anyway. Probably will add the brass plates later, as the PML cones have more room than others as they fit on 2 ribs, not the shank of the cone. Hopefully the gap is not enough for the pins to bend appreciably or foul.

These took a fair amount of force to break. Are the nylon 2-56 screws easier? They look larger diameter.... I guess I'm not very well calibrated on the forces involved.

Gary - looking forward to the Vorlon flight!

Thanks again,
-Andy

 

[talkin Monkey]

Andy,...quick question for when ya get back.

I'm doing something similar with an 8#-ish Endeavour:ahhhhh:, how well did the PML pheonlic coupler hold up to shearing the pins? Any damage or "oblongation" to the pheonlic material?

Thnx,
Scott

 

[AndyC2]

Scott,

After a couple of tests, I did not see any damage to the phenolic coupler. For my own sanity though, I'd probably put a drop of CA in the holes and redrill after it hardens to be sure.

-Andy

 

[talkin Monkey]

Thnx Andy

 

[AndyC2]

Did a couple of ejection tests tonight with two 1/16" round styrene pins. I wasn't sure how much BP to use, so I loaded 1g to start. This is for a 4" payload section, 18" long - with a piston. Apparently it was plenty. The cone and chute were nicely ejected, the pulled the payload section for a 5-10' ride across my backyard after the 15' shock cord was fully extended.

Thinking this might be to much, I set up to try 3/4 g. Unfortunately, I did not clean out the residue enough, and the #^$%@* piston got stuck halfway up the tube. Ugh. NC still came out, just a bit of a delay. Cleaned up OK, but I'll need to check the fit of the piston later. I'll probably stick with 1g, as there was no question about ejection with that...

As much as I like the PML pistons, I'm thinking about leaving the thing out for the cert flight. Its probably OK, just me being stupid and not cleaning it out well enough between attempts.

Thanks for all the tips.
-Andy

 

[Art Upton]

Art - I was planning to use a smig of tape for the booster/ebay joint (its pretty close without anything). Are you suggesting to use pins there as well? Is the concern drag separation after the boost? In my ~6 lb rocket, the J350 will be pretty punchy; though probably not as much as your Loki experience....

I've seen tape on that joint cause a no deploy once, no twice.

I would not worry about that joint on a J350 if it is already snug, and yhou have a vent hole in the booster.

A K960 with a 2 pound nose cone with electronics yes, but not a J350 on plastic cone.

BTW, green and blue tape both I've seen cause balistic failures at the booster/ebay joint.
edit: Blue on an H motor, Green on an N motor

White/yellow tape slips better and does not bunch.

The last one I saw was an N motor that I had ground video on and the charge blew but the green tape stuck the ebay into the booster and no seperation at apogee.

edit: forget the piston if you can

 

[talkin Monkey]

Andy, about that piston issue, have you come across this before?

https://www.deltavrocketry.com/piston.htm

That's how I'll be doing mine. BTW thanks for starting this thread, it's answering a lot of questions I had about shear-pinning my L1 build.

 

[quickburst]

I have used both and both have served me well.

I do prefer the 2-56 shearpins though. They seem more dependable.

 

[roadkill]

Yupp,
shear pins are the way to go !

I've used two 1/16" styrene rod pins,
two in the nosecone joint and another two
in the booster joint.

Did ground testing to find correct bp charges
and been sticking to it since without any
hinkies or wonkies...
*knocking wood*


I'm using the same design on a couple
of new projects slowly taking shape...

 

[bsexton]

Like others have said after having a couple of main parachutes "pop" at apogee I became a big believer in shear pins. I have used both the styrene rod and nylon screws with good success. I also just purchased these from Newton's Third Rocketry although I haven't tested and/or used them yet. Anyone have any experience with these nylon pins?

 

[blackjack2564]

They are very close to 6-60 nylon shear pins[screws]. For larger projects.

From small to large.... 2-56
4-40
6-60

These are the sizes one normally see in rockets. After that your getting into the realm of BIG.

2-56 is what is most common up to 4in airframes, I use 4-40 on 6 and 7.5in frames.However many use the 2-56, just more of them.

 

[melsman]

... and in a fit of shameless self promotion... :star:

Here's a link to a thread that contains a good discussion on shear pins and a video of ground testing.

Ashley

 

[AndyC2]

Just a quick update.

I flew my stretched 1/4 patriot last weekend at a METRA launch on a J350. Great flight to 3064', but when the apogee charge fired, the nose cone popped off too, deploying the main chute, and starting a long walk for me (95deg F out too, eesh). Concensus from talking to some of the more experienced guys in our club is that (2) 1/16" styrene pins are not enough. They said 4 is a better number. Live and learn I guess. 4 pins it is for NERRF.

Nice tests & video Ashley; thanks for the (shameless?) pointer.

 

[melsman]

You bet - always willing to take the opportunity to toot my own horn... :flute:

Ashley