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First dual deploy - issues.

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TheTank

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I finished my first dual deploy rocket and test fired charges today. Drogue charge was perfect. Energetically ejected with no issues. Main chute failed to shear the pins (3) and eject the cone twice even after increasing the powder well over recommended on the calculator. In the video, it appears i am venting at the cone as well as through the bulkhead (removable) And into the av bay base on the puffs i see out of the static port.

any suggestions? My initial thought is to snug up the fit of the cone and only use one of the three pins as it appears to vent far worse at the cone. All feedback is appreciated!
 

Jmhepworth

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Can you provide more information? Size and material of rocket, space being pressurized, amt of BP, size of pressure relief holes, etc.
 

TheTank

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Can you provide more information? Size and material of rocket, space being pressurized, amt of BP, size of pressure relief holes, etc.
sure. Kit is a LOC Deployer. 3” tube - cardboard. Plastic cone with 3 2-56 shear pins. Av bay connected to payload tube by 3 reusable rivets. Top payload section is only about 7”. BP calculator called for .40 gram. Tried .5 on The first attempt. 2nd attempt was .70/.75 grams. And no better. 3 static ports in the av bay per missleworks recommendations but it can only vent there if it pushes past the bulkhead.

Drogue section (9”) called for .5 grams. I used .7 or so and the result was great. Video attached.
 

David Schwantz

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Did you by mistakkke use steel 2-56 screws iiinstead of plastic?
 

spigalau

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Are you using 4F black powder ?

We also have 3" rocket, and use 1.1g on Primary charge for main ejection charge. Our payload tube is 19" long and we use 3 x 2-56 nylon screws to hold nosecone in place. Initially we had 2 pins, but on first successful flight, we had a flat spin separation, so upped it to 3. No issues since.
The backup charge for main is 1.3g
 

Jmhepworth

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The only time I tried to use sheer pins on a cardboard rocket I blew the tube apart. So I won’t be any help to you at all. I do recall seeing posts about reinforcing the body tube with a brass sheet, which helps to sheer the pin.
 

Handeman

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Looking at your videos, you seem to have too much for the apogee charge. All you need is enough to get the drogue into the air flow. The charge you used shot the upper section so hard it jerked the lower section pretty hard when it hit the end of the shock cord. Over sized charges like that is the primary reason you need shear pins on the nose cone, excessively long shock cords, and other compensation for that large charge and the shock it creates.

The force to shear those three pins is going to be much more than just pushing off the nose cone like the calculators assume. I would highly recommend using a lower apogee charge and a friction fit for a plastic nose cones and cardboard tubing. If you insist on shear pins and the large apogee charge then you need to add brass shims to the cardboard tubing, and maybe the plastic nose cone and a much larger main charge.
 

TheTank

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I believe I solved the issue. I worked on the nose cone and the forward av-bay bulkhead to make sure they had a more complete seal. I removed 2 of the 3 shear pins and used the same charge as attempt #2. Got a good seperation and sheared the pin without issue.

I too was concerned about shear pins in cardboard but everything I read talked about nose cones deploying at apogee from the shock of the drogue deployment. I had even started a thread here to get some opinions. To create a shearing surface and protect the tube, i soaked the holes and surrounding tube with thin CA and allowed it to dry slowly. The result was rock hard and seems to have sheared the pin without issue and no deformation of the hole.

Updated video of the result. Dont mind my poor aim that missed the blankets. No paint damage though.

 

o1d_dude

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<snip>

Dont mind my poor aim that missed the blankets. No paint damage though.
I can pretty much guarantee your rocket will “miss the blanket” every time you launch it but from a much higher altitude.

That’s the nature of this hobby. ;)
 

TheTank

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I can pretty much guarantee your rocket will “miss the blanket” every time you launch it but from a much higher altitude.

That’s the nature of this hobby. ;)
True! But hopefully it will be under canopy! I was thinking that if I packed that shoot properly, it might have opened before impact!
 

o1d_dude

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True! But hopefully it will be under canopy! I was thinking that if I packed that shoot properly, it might have opened before impact!
We remain optimistic...because in rocketry, nothing is guaranteed. LOL!
 

Antares JS

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I use .5g for the drogue and 1g for the main in my Deployer, with no shear pins. I have never used shear pins in my life and have gotten consistent results just making sure my fit was snug.

And yes, make sure your av-bay is sealed. That lightweight av-bay from LOC does not really seal the end that opens well. I set mine up to open from the bottom, and after multiple instances of the drogue charge gasses leaking into the av-bay and setting off the main with a pressure spike, I started sealing the end with plumber's putty for flight.
 

rocketman328

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How tightly are you packing your ejection charges, perhaps the Powder is too loose which may cause some of it not to burn causing insufficient pressure.
 

Handeman

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I too was concerned about shear pins in cardboard but everything I read talked about nose cones deploying at apogee from the shock of the drogue deployment. I had even started a thread here to get some opinions.
That shock is cause by too large of apogee charge. Too much "Blow it out or blow it up" thinking. That and using shear pins for the apogee joint when not needed which leads to oversized charges to shear the pins. The correct sized charge will eliminate that excessive shock and then you don't have to compensate for it with long shock cords, heavy duty links, shear pins, and other things on the payload end.

The rocket is a complete system and anything you do in one part of it affects the whole system.
 

crossfire

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I use .5g for the drogue and 1g for the main in my Deployer, with no shear pins. I have never used shear pins in my life and have gotten consistent results just making sure my fit was snug.

And yes, make sure your av-bay is sealed. That lightweight av-bay from LOC does not really seal the end that opens well. I set mine up to open from the bottom, and after multiple instances of the drogue charge gasses leaking into the av-bay and setting off the main with a pressure spike, I started sealing the end with plumber's putty for flight.
You will someday
 

TheTank

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I use .5g for the drogue and 1g for the main in my Deployer, with no shear pins. I have never used shear pins in my life and have gotten consistent results just making sure my fit was snug.

And yes, make sure your av-bay is sealed. That lightweight av-bay from LOC does not really seal the end that opens well. I set mine up to open from the bottom, and after multiple instances of the drogue charge gasses leaking into the av-bay and setting off the main with a pressure spike, I started sealing the end with plumber's putty for flight.
Thanks! Sealing it and the cone made all the difference. My cone was really loose so i wrapped the shoulder and pinned it to be sure. Wrap wasnt enough to seal it though. A second wrap and one pin and it popped real well along with sealing the av bay as there was blow by there as well.
 

TheTank

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That shock is cause by too large of apogee charge. Too much "Blow it out or blow it up" thinking. That and using shear pins for the apogee joint when not needed which leads to oversized charges to shear the pins. The correct sized charge will eliminate that excessive shock and then you don't have to compensate for it with long shock cords, heavy duty links, shear pins, and other things on the payload end.

The rocket is a complete system and anything you do in one part of it affects the whole system.
great feedback. I appreciate it!
 

TheTank

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How tightly are you packing your ejection charges, perhaps the Powder is too loose which may cause some of it not to burn causing insufficient pressure.
I pack them down with dog barf as tightly as I can and the tape over the top and around the charge well.
 
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