Single deploy, shear pins...testing and alternatives

[MarsLander]

If you have a heavily weighted nose cone and large draggy fins you might consider shear pins on a single deploy but I would consider the need to be a rare occurrence.

^^^ From another thread.

Working on my L2 build: Link--> L2 4X upscale EAC Viper Motor deploy, JLCR.

Not particularly draggy fins. Nose cone weighs 650 grams. Total rocket about 4500 grams with NC.

NC fit is "loose." No tape on shoulder, it slides out on its own. One layer, it slides out on its own. Two layers, I can't get it into the tube.

Seems like I need to pin it.

1. How do you test BP charge with motor deploy?
2. Any other alternatives to pinning? (I'd actually like to pin it if I can answer #1.

Thanks for the thoughts.

 

[tg08]

How do you test BP charge with motor deploy?

Get either these ejection canisters from Apogee or make your own, run it through the MMT until it reaches about the end of the MMT, and detonate it using an Estes or any other brand launch controller. (hint: don't forget the recovery wadding, or you'll end up with a toasted parachute) Thankfully, I've never done this, but I came close a few times.

 

[Handeman]

When you put tape on the shoulder, make an X so the single piece's slide into tube and the thicker area where they are crossed will also slide in without catching the edge of the tube. One X may be enough, but you can usually fit up to 4 around the shoulder. Add another piece of tape across each X, one at a time until you get a snug fit, not too tight. If you can pick up the rocket by the nose cone that usually is sufficient to stop drag separation, even if a shake will make it come apart.

You might want to try it without any tape. Most motor eject rockets will work just fine without any drag separation, even with loose nose cones. Don't over think it.

 

[jmasterj]

You're over-thinking, I've been there. I don't know how you're applying your tape, but running lengths parallel to the cone gives the most room for adjustment.

 

[MarsLander]

All great excellent ideas. Thanks for taking the time to respond!

Thanks for the charge canister link!

Tried 4 Xs in increments of 1X. 3Xs still loose but better, 4Xs tore the tape at intersection. 3Xs and another 1/2 X is PERFECT!

 

[David Schwantz]

When you ground test deployment charges, make sure to plug mmt with a spent motor.

 

[MarsLander]

So, after reflection, reviewing the following video, I'm going to pin and test this rocket (my preference anyway). I'd like to run this rocket up to K motors, so it makes sense...

@tg08 those are great idea
@David Schwantz I had the same conclusion!

Thanks for all the help folks!

https://youtube.com/clip/UgkxbuusmJlGs4zwTfKX6k9xncKfqIQHdYpB?si=neBABQvhxLofDPlT

 

[86mustang408w]

So, after reflection, reviewing the following video, I'm going to pin and test this rocket (my preference anyway). I'd like to run this rocket up to K motors, so it makes sense...

@tg08 those are great idea
@David Schwantz I had the same conclusion!

Thanks for all the help folks!

https://youtube.com/clip/UgkxbuusmJlGs4zwTfKX6k9xncKfqIQHdYpB?si=neBABQvhxLofDPlT

Probably the best choice to use them, I'll be doing the same myself. Have fun.

 

[Handeman]

Totally disagree. On a single deploy where the nose cone comes off to deploy the chute, you don't even need friction fit in most cases. A totally loose NC will work in almost all cases. It's a very rare rocket that has enough drag from the fins vs. the frontal drag of the nose cone or enough inertia difference between the nose cone and the rest of the rocket to require any significate friction on the nose cone. Pinning single deploy is just way over kill. Just a TRF rabbit hole to my thinking.

Put enough tape on it you can pick the rocket up by the nose cone without it coming completely out of the BT. 1/2 to 3/4 out is OK. Don't over think it.

 

[Art Upton]

Totally disagree. On a single deploy where the nose cone comes off to deploy the chute, you don't even need friction fit in most cases. A totally loose NC will work in almost all cases. It's a very rare rocket that has enough drag from the fins vs. the frontal drag of the nose cone or enough inertia difference between the nose cone and the rest of the rocket to require any significate friction on the nose cone. Pinning single deploy is just way over kill. Just a TRF rabbit hole to my thinking.

Put enough tape on it you can pick the rocket up by the nose cone without it coming completely out of the BT. 1/2 to 3/4 out is OK. Don't over think it.

I have taped mine so it fits what you describe. I don't need full wraps ; if 1/2 wrap works it's fine, if 1-1/2 wrap works it is fine. I don't need even number of wraps in my past experience.

 

[Art Upton]

So, after reflection, reviewing the following video, I'm going to pin and test this rocket (my preference anyway). I'd like to run this rocket up to K motors, so it makes sense...

@tg08 those are great idea
@David Schwantz I had the same conclusion!

Thanks for all the help folks!

https://youtube.com/clip/UgkxbuusmJlGs4zwTfKX6k9xncKfqIQHdYpB?si=neBABQvhxLofDPlT

Nice video, I have been reading Trip's articles in the NAR paper magazines starting in 1973-74 era plus his in Model Rocket Magazine in the 67-69 era.

It was one of the great enjoyments of my Rocketry life to be Trip's L3CC/Tap at NSL [2010 ?]when he got his L3 as the FIRST NAR president to get L3. All NAR Presidents after him also got their L3s.

 

[Art Upton]

I have taped mine so it fits what you describe. I don't need full wraps ; if 1/2 wrap works it's fine, if 1-1/2 wrap works it is fine. I don't need even number of wraps in my past experience.

Dual Deploy is when you need pins as the lower section will stretch out the nylon/Kevlar cord and when it reaches the end will knock the nose off your main in the upper chute cannon and pop the main at the top...

There is one exception, if you have a whole bunch of weight in the nose and you have a large "punchy" motor with quick cut off it can come off...

 

[MarsLander]

On a single deploy where the nose cone comes off to deploy the chute, you don't even need friction fit in most cases.

There is one exception, if you have a whole bunch of weight in the nose and you have a large "punchy" motor with quick cut off it can come off...

Thanks Jeff and Art, I appreciate the input. I think I may be an edge case (maybe not?), and willing to pin anyway for safety.

The nose cone (WM FWFG, MAC NC Bay and electronics) are about 1.7lbs in 9lb rocket.

Fins are draggy (55% of total drag during acceleration) and have a large Aspect Ratio ~1.342 (fin root 7.5", span 8.2"). Compared to most L2 rockets on a K (Large motor?), this rocket is short 55" (lower mass) and big "dumbo ear" fins.

I want to run I-K motors. Given the aspect ratio, I'm going to have to use 3/16" G10 instead of 1/8" to run ANY K motor (or larger J) and avoid flutter. https://www.rocketryforum.com/threads/l2-build-flutter-analysis-design-help.183596

What is the downside of pinning for safety other than time and cost of testing?

 

[Art Upton]

Thanks Jeff and Art, I appreciate the input. I think I may be an edge case (maybe not?), and willing to pin anyway for safety.

The nose cone (WM FWFG, MAC NC Bay and electronics) are about 1.7lbs in 9lb rocket.

Fins are draggy (55% of total drag during acceleration) and have a large Aspect Ratio ~1.342 (fin root 7.5", span 8.2"). Compared to most L2 rockets on a K (Large motor?), this rocket is short 55" (lower mass) and big "dumbo ear" fins.

I want to run I-K motors. Given the aspect ratio, I'm going to have to use 3/16" G10 instead of 1/8" to run ANY K motor (or larger J) and avoid flutter. https://www.rocketryforum.com/threads/l2-build-flutter-analysis-design-help.183596

What is the downside of pinning for safety other than time and cost of testing?

Sizing the pins to motor ejection charges ; I used 2/56 plastic screws on many rockets but you need to do your own testing if you want to pin to keep safe if the motor can't pop it off.

SO you need to take the motor , empty the charge in it and use your own charge and test it to break the pins. Keep in mind that at 5K or 10K high BP does not have the same power.

I Know one person found that out once at Airfest at 15K testing charges at ground level. Always add More ...

 

[MarsLander]

I'm now to the point I'm ready to fly. In reading many threads on ejection charges, seems the configuration of the packing and design of the ejection charge will have a different effect. i.e. tightly packed vs. surgical tube vs. match on top vs. match on bottom etc.

I'd like to test with the actual motor, using the charge well in the motor. However, that requires a grain liner, o-rings, ejection charge spacer, delay insulator and spacer and o-rings.

I have the RAS floating forward closure.

Short of buying a standard forwarc closure, any good suggestions on how to assemble an empty motor so the floating forward closure will stay in place for testing?

 

[jmasterj]

Do you have your motor? I'd guess the liner and nozzle would be good enough. Run the ematch leads down through the touch hole (seal with hot glue) and out the nozzle.

Or just use the closure down in the bottom of the tube with something else sealing off the motor mount.

And next time save yourself the trouble and use electronics; you're doing almost as much work but without the reliability upside.

 

[tsmith1315]

Anything to hold the closure in place- liner, length of paper towel tube, or tightly packed with dog barf, etc.

 

[MarsLander]

Anything to hold the closure in place- liner, length of paper towel tube, or tightly packed with dog barf, etc.

Finally got around to testing. e-match in the charge well, dog barf tightly packed in the reload. Worked great! Looks like 2.2-2.5g will work great! Thanks for the help...

https://www.rocketryforum.com/threads/l2-design-and-build-4x-upscale-eac-viper.183182/post-2566018