Dual Deploy / Shear pin questions

[JackC]

54mm tube, 10 inches of open space in the tube, two 4/40 nylon shear pins. Start at 1 gram of fff? Calculators say less

I use two 4-40 pins on a 54 mm tube and they work fine for me. I would start your ground test at 1 gram and progressively go up from there.

 

[PayLoad]

OK, so now we know - 1.5G is far too much. Broke the nylon shock cord & elongated shear pin holes, I'm assuming 1 gram will do it with 2 shear pins

 

[JackC]

OK, so now we know - 1.5G is far too much. Broke the nylon shock cord & elongated shear pin holes, I'm assuming 1 gram will do it with 2 shear pins

I did say to start with 1 gram then go up if necessary.

 

[rocketman328]

Probably right. It’s friction vs inertia and drag forces. Maybe as friction likely goes like D^2 whereas mass goes ~ D^3.

I flew today at Midwest Power 20, my all fiberglass airframe used (3) 2-56 nylon shear pins between the main airframe and the avionics bay and (3) between the nose and main chute bay. I got clean shear of all pins with my ground tested pyro charges. Incidentally, I use Pyrodex P exclusively ! 1 gram on the nose, 1.6 grams on the main airframe.

 

[acalver]

I flew today at Midwest Power 20, my all fiberglass airframe used (3) 2-56 nylon shear pins between the main airframe and the avionics bay and (3) between the nose and main chute bay. I got clean shear of all pins with my ground tested pyro charges. Incidentally, I use Pyrodex P exclusively ! 1 gram on the nose, 1.6 grams on the main airframe.

How do you contain your Pyrodex? I've had some failures in testing smokeless in the past.

 

[Andrew Brown]

i use plastic push in rivets from McMaster https://www.mcmaster.com/90136A565/ There are two different thickness and different grip length. They are pretty strong and more importantly it uses a straight hole. with the same diameter on both sides. No wiggling once installed. Do buy the correct drill bit they fit snug, and you will need to tap them in (I use the back of a screwdriver). The snug fit makes sure they cleanly shear no bending. To remove them if you dont fly, just use a small screwdriver to pry them out.

They are pretty stout, I wouldnt use them on phenolic or quantum tube, but they work well for graphite and fiberglass.

Do ground test, they need a bit more umph than #2 shear screws Depending on the size of the rocket I use 2 or 3 of them

Mike Kramer

I do like this, particularly the idea of just being able to push the already sheared pin out without trying to back out a headless screw. Any idea how much force it takes to shear these? At 0.093", it puts the shank right between a 2-56 and 4-40 minor diameter, so I'm guessing somewhere in the 40 lbs range?

 

[kramer714]

do your own testing... but

from my 'fleet'
54mm fiberglass tube, head end deploy (2) https://www.mcmaster.com/90136A565/ pins gets 1.5 grams 4f (wrapped in a finger of a glove and then taped up
75mm fiberglass tube head end deploy (2) https://www.mcmaster.com/90136A565/ pins gets 2.0 grams 4f (wrapped in a finger of a glove and then taped up
98mm fiberglass tube head end deploy (2) https://www.mcmaster.com/90136A565/ pins gets 2.0 grams 4f (wrapped in a finger of a glove and then taped up

YMMV

Mike Kramer

P.S. Again, do your own testing!!!

P.P.S Dont get me started on the whole how many shear pins is the minimum you can use debate, I have done 1-3 shear pins.

P.P.P.S On smaller rockets (less than 15 lbs or so) I usually don't pin the drogue only the main. for larger rockets I have been known to usethe same number of shear pins for the main and drouge. With these pins I have never had the main come out from the 'drogue twang'

 

[kramer714]

Nice thing about these, just push the head in no need to open the av bay to try and unscrew the 'leftover' You get the cool maraca sound from the heads bouncing around in the av bay after a while. With a lipo , 'worm and gommit' and UY-2 connectors I dont have to open the av-bay for multiple launches.

 

[Handeman]

I'm sure I'm a dinosaur and counter to the new way of doing things, but I only use shear pins in fiberglass rockets and I never bother to tap the holes.
From my experience on cardboard BT rockets, a gentle but sufficient apogee charge and a good friction fit on the nose cone works just fine, just a loose fit on the booster/av-bay is fine.
I use three 2-56 nylon screws as shear pins on 3" and 4" nose cones and two 2-56 screw for the booster/av-bay joint on fiberglass rockets, although the pins at the booster/av-bay joint are probably not needed, but it usually makes the RSOs happy.

 

[Black Bart]

Hi all,
I'm new to DD. My first attempt was a scratch built BT 55 long Cherokee with BT 55 Apogee e bay. On board Eggtimer Quark set at 300'. All went well. This was a test for the upcoming launch at ROCSTOCK, LOC 4" Iris and a scratch built 4" Big Bertha XXL. The Big Bertha is built with LOC tubes, so the LOC 3.9 e bay fits both. I put in .015 G10 squares, to shear the pins. 2/56 t bolts and nylon 2/56 screws that i got from MICRO FASTENERS INC. IN PA. I was told there should be 3 pins or 4 to stop jamming on separation. ?????

 

[PayLoad]

So I used 1.5 grams, and blew everything up (broke shock cord!) I replaced with kevlar, tried it all with .75 grams and.....nothing. No seperation. Testing for the last time tomorrow with 1 gram in glove tips. So much assembly & disassembly, worried about how to do this in the field!

 

[waltr]

I install the Ematches at home with them outside the ebay. Then at the field add the BP charges.

I make paper tubes that fit over the Red ematch cover and taped on. Load BP into tube, fold over and tape very well. Found this works great for up to about 0.8 gram BP. Any more and complete combustion becomes unreliable.
Therefore, for large rockets I now install charge cups to the ebay bulkhead. These are 1/2" Copper pipe caps bought at the hardware store. They hold up to about 1.8gram BP but for my .22 inch (54mm) LOC DD rockets I use 0.8gm for drogue (no shear pins) and 1.2 gm for main with one 2-56 nylon shear pin.
I still install the ematches onto the altimeter board at home so I don't need to open the ebay at the filed. Just add pre-measured BP, some wadding on top then tape over the charge cups.
This has been very reliable.

 

[Black Bart]

So I used 1.5 grams, and blew everything up (broke shock cord!) I replaced with kevlar, tried it all with .75 grams and.....nothing. No seperation. Testing for the last time tomorrow with 1 gram in glove tips. So much assembly & disassembly, worried about how to do this in the field!

I used the glove tip on my BT 55 DD, when i tried it on the 4" rockets in testing did not separate. I switch to PVC 1/2" plugs, not end caps. It contains the blast and directs it.

 

[PayLoad]

1 gram drogue, perfect;

 

[PayLoad]

1 gram main, nothing. Moved to 1.5 grams & blew it up. Getting frustrated

 

[Kallahan11]

Just saw this post, and I hate to come in afterwards but I think the 4-40 shear pins give you way to small of a window between not enough and too much powder. 2-56 are significantly weaker than 4-40 nylons screws. They have only 60% the shear strength, this makes you acceptable charge window much bigger.

How long are your shock cords? they seem VERY short in the video. Longer is better, on something like that I wouldn't use less than 6 feet, more like 8-10. Also .2 gram increments on smaller rockets like that is better increment.

for reference, the only rocket I use 4-40 nylon screws on is my 5.5in fiberglass Super Payloader DX3, which has a dry weight of 37 pounds. I use three on the booster and three on the nose cone with 4 gram charges all around and 25ft of shock cord on both sides.

My 4in cardboard super payloader uses 3 2-56 nylon in the booster and payload on 1.8 gram charges.

I use two 2-56 nylon screws in my 38mm minimum diameter Mongoose, with .25g in the booster (It has a TINY amount of space with a 38/1320 case in it) and .5g in the payload bay.

 

[Banzai88]

Just saw this post, and I hate to come in afterwards but I think the 4-40 shear pins give you way to small of a window between not enough and too much powder. 2-56 are significantly weaker than 4-40 nylons screws. They have only 60% the shear strength, this makes you acceptable charge window much bigger.

How long are your shock cords? they seem VERY short in the video. Longer is better, on something like that I wouldn't use less than 6 feet, more like 8-10. Also .2 gram increments on smaller rockets like that is better increment.

for reference, the only rocket I use 4-40 nylon screws on is my 5.5in fiberglass Super Payloader DX3, which has a dry weight of 37 pounds. I use three on the booster and three on the nose cone with 4 gram charges all around and 25ft of shock cord on both sides.

My 4in cardboard super payloader uses 3 2-56 nylon in the booster and payload on 1.8 gram charges.

I use two 2-56 nylon screws in my 38mm minimum diameter Mongoose, with .25g in the booster (It has a TINY amount of space with a 38/1320 case in it) and .5g in the payload bay.

Agreed. For this size rocket, 2-56 screws are warranted, cords are way too short, and work up in .2 increments.

 

[waltr]

How long are your shock cords? they seem VERY short in the video. Longer is better, on something like that I wouldn't use less than 6 feet, more like 8-10. Also .2 gram increments on smaller rockets like that is better increment.

Agreed. For this size rocket, 2-56 screws are warranted, cords are way too short, and work up in .2 increments.

Agreed, the Main's cord is WAY too short.

 

[PayLoad]

Shock cord was 6 feet - make it 12-14? I was using two 4/40 shear pins, use two 2/56 instead? Just one?

This thread has been very informative, thanks, although I am getting discouraged. Holes in cardboard tube are getting elongated...................

 

[Banzai88]

2.26" airframe? 1x2-56 pin is sufficient. As was mentioned above, the margin on 4-40 screws between just-right and way-too-much is very small as compared to the 2-56 screws.
I call bunk on anyone saying "1 pin will jam" as I have many rockets with only 1 pin and they have NEVER, EVER jammed. Proper placement and prep is key. Use 2 if you're gonna go with the 'But, but, but.....it'll jam if I only use 1' line of thought.

I also install internal shear pin plates as necessary: Click here for shear pin plate tutorial. I usually put the single pin in line with the rail buttons. Oh, and place it in the BOTTOM rib of the nose cone. Hardening of the cardboard hole with CA works about 75% as good, but shear plates are forever, and never need fear elongation. I have several rockets with 25+ launches on them, and the pins fit as tight now as day #1.

I use kevlar for recovery harness, usually 20-25 feet top and bottom, 3/16" or 1/4" is perfect for this size rocket. It's cheap, light, and durable. The bottom harness has a 3rd loop for the drogue parachute. Drogue charge should be just enough to get 75%+ of the harness out and the drogue chute into the airstream. The drogue inflating will take care of the rest. Main charge should be enough to get 85-90%+ of the harness out and the main parachute bundle into the clean air. The main parachute inflating will take care of the rest.

Remember, the charges are for getting the rocket pieces apart and the parachutes into clean air. Anything approaching 100% extension risks jerking the parts. If jerking from full or over extension of the recovery harness happens on the ground, for sure in the air with 'equal and opposite reaction' of the 2 parts, it's gonna hit harder in flight....risking the integrity of the mounting points and needlessly stressing the recovery harness material!

ETA: I see that you're affiliated with MDRA. LOTS of highly experienced and friendly rocketeers there. You're almost there, but I would recommend networking and finding a local DD mentor to run things by.

 

[sharkbait]

2.26" airframe? 1x2-56 pin is sufficient. As was mentioned above, the margin on 4-40 screws between just-right and way-too-much is very small as compared to the 2-56 screws.
I call bunk on anyone saying "1 pin will jam" as I have many rockets with only 1 pin and they have NEVER, EVER jammed. Proper placement and prep is key. Use 2 if you're gonna go with the 'But, but, but.....it'll jam if I only use 1' line of thought.

I also install internal shear pin plates as necessary: Click here for shear pin plate tutorial. I usually put the single pin in line with the rail buttons. Oh, and place it in the BOTTOM rib of the nose cone. Hardening of the cardboard hole with CA works about 75% as good, but shear plates are forever, and never need fear elongation. I have several rockets with 25+ launches on them, and the pins fit as tight now as day #1.

I use kevlar for recovery harness, usually 20-25 feet top and bottom, 3/16" or 1/4" is perfect for this size rocket. It's cheap, light, and durable. The bottom harness has a 3rd loop for the drogue parachute. Drogue charge should be just enough to get 75%+ of the harness out and the drogue chute into the airstream. The drogue inflating will take care of the rest. Main charge should be enough to get 85-90%+ of the harness out and the main parachute bundle into the clean air. The main parachute inflating will take care of the rest.

Remember, the charges are for getting the rocket pieces apart and the parachutes into clean air. Anything approaching 100% extension risks jerking the parts. If jerking from full or over extension of the recovery harness happens on the ground, for sure in the air with 'equal and opposite reaction' of the 2 parts, it's gonna hit harder in flight....risking the integrity of the mounting points and needlessly stressing the recovery harness material!

ETA: I see that you're affiliated with MDRA. LOTS of highly experienced and friendly rocketeers there. You're almost there, but I would recommend networking and finding a local DD mentor to run things by.

1000% spot on

 

[waltr]

^ that ^
I have had over a dozen good DD flight with only ONE 2-56 pin on the nose with 2.2" LOC cardboard. Also, holes are still tight with no elongation.

 

[Worsaer]

I found this to be helpful in the past.

Originally found on RocketMaterials.org, retrieved from the Wayback Machine…

 

[b.wieting]

Re pins, I've used three 2-56 on LOC Mini- and Mega-Maggs modified by inserting an av-bay. Pins only between NC and bay, none between bay and booster. Not a lot of flights but successful a few times (so far). Always tweaked the 4F weight via a couple ground test trials to give vigorous deploy.

 

[teepot]

I use two 2-56 pins and brass or copper sheeting as my blades. And 15' to 20' on the drouge and main each. Between 3/4 and 1.5 grams depending on internal volume of the tubes. I have used shell casings {blew up a couple of av-bays} the PVC plugs and now the containers the BP comes in with the motors. Going to try the glove tip next.

 

[KenECoyote]

How do you contain your Pyrodex? I've had some failures in testing smokeless in the past.

I started off with Pyrodex years ago since BP was very scarce. You do need to use more than BP (about 15%?) and it's important to ensure it's well contained and not just loose. I used to use latex glove tips and wind it tightly, then it went into charge wells with some dog barf and taped over. Ground test several times and then up a slight bit due to altitude diff and to be sure. Ymmv

 

[Karlcullen]

I started off with Pyrodex years ago since BP was very scarce. You do need to use more than BP (about 15%?) and it's important to ensure it's well contained and not just loose. I used to use latex glove tips and wind it tightly, then it went into charge wells with some dog barf and taped over. Ground test several times and then up a slight bit due to altitude diff and to be sure. Ymmv

Okay, but what substances have you used, I'm interested in what companies I should not buy from because I'm new and I don't know what to start with, there are many different ones, besides they differ by price.

 

[KenECoyote]

Okay, but what substances have you used, I'm interested in what companies I should not buy from because I'm new and I don't know what to start with, there are many different ones, besides they differ by price.

FYI my reply was specifically about Pyrodex which is different than the usual bp (black powder) we use... it's seen as almost like "Beyond BP" (a substitute). If you're asking about Pyrodex, I can't recall what type, but it was Pyrodex brand.

Cabela's site notes that Pyrodex P "replaces FFFg black powder", so that is likely the one I used.



If you're asking about usual bp/black powder, I believe you'll want FFFFg/quadruple F, but you should be able to find out with a quick search.

In general, I stay away from Pyrodex unless I can't get any bp. Also it can be quite sad (or even dangerous) if you have both and mix them up/use one thinking it's the other (ex. Using 2g Pyrodex thinking it's your usual bp and then it's not enough to separate your rocket). ymmv

 

[rocketman328]

FYI my reply was specifically about Pyrodex which is different than the usual bp (black powder) we use... it's seen as almost like "Beyond BP" (a substitute). If you're asking about Pyrodex, I can't recall what type, but it was Pyrodex brand.

Cabela's site notes that Pyrodex P "replaces FFFg black powder", so that is likely the one I used.

View attachment 546658

If you're asking about usual bp/black powder, I believe you'll want FFFFg/quadruple F, but you should be able to find out with a quick search.

In general, I stay away from Pyrodex unless I can't get any bp. Also it can be quite sad (or even dangerous) if you have both and mix them up/use one thinking it's the other (ex. Using 2g Pyrodex thinking it's your usual bp and then it's not enough to separate your rocket). ymmv

I use Pyrodex P exclusively! It is a 1:1 substitute “By Volume “ to black powder. I don’t need to use more Pyrodex than black powder. I pack the charges the same way with either. I use a standard formula to determine the amount needed for 15psi. I use (3) 2-56 shear pins on airframes up to 5.5in. And of course Ground Test!!!

 

[KenECoyote]

I use Pyrodex P exclusively! It is a 1:1 substitute “By Volume “ to black powder. I don’t need to use more Pyrodex than black powder. I pack the charges the same way with either. I use a standard formula to determine the amount needed for 15psi. I use (3) 2-56 shear pins on airframes up to 5.5in. And of course Ground Test!!!

"By volume" is an important distinction for Pyrodex...

https://www.chuckhawks.com/difference_black_powders.htm
"By actual weight, it is not the same. 100 grains measured by volume of Goex FFg is about 101.3 grains by weight. 100 grains measured by volume of Pyrodex RS is about 72.5 grains by weight. Pyrodex is where confusion can start to set in, as the standard "F" designations of powder coarseness start to go out the window."