To deploy at coupler (eBay) or nose cone

[shawn_rocket]

Doing my first dual deploy rocket. 4" LOC Mystic Buzz and have a question about whether to deploy at the ebay (shear pins to fin can and shear pins to payload), or shear pins on the fin can and deploy at the nose cone. I attached a picture for a better view of what I am thinking. If I deploy at the nose cone, can I use some M4 bolts through the payload to eBay to deploy at the nose cone? I wouldn't need to epoxy it to the payload bay, correct? I've done some searching and haven't been able to determine anything definitive.

 

[sharkbait]

Doing my first dual deploy rocket. 4" LOC Mystic Buzz and have a question about whether to deploy at the ebay (shear pins to fin can and shear pins to payload), or shear pins on the fin can and deploy at the nose cone. I attached a picture for a better view of what I am thinking. If I deploy at the nose cone, can I use some M4 bolts through the payload to eBay to deploy at the nose cone? I wouldn't need to epoxy it to the payload bay, correct? I've done some searching and haven't been able to determine anything definitive.
View attachment 507670

blow the fin can off to deploy your drogue and blow the nose off to deploy your main.

 

[David Schwantz]

Yes, you may use steel screws. I like to back them on the inside with blind nuts and ply mount.

 

[crossfire]

Doing my first dual deploy rocket. 4" LOC Mystic Buzz and have a question about whether to deploy at the ebay (shear pins to fin can and shear pins to payload), or shear pins on the fin can and deploy at the nose cone. I attached a picture for a better view of what I am thinking. If I deploy at the nose cone, can I use some M4 bolts through the payload to eBay to deploy at the nose cone? I wouldn't need to epoxy it to the payload bay, correct? I've done some searching and haven't been able to determine anything definitive.
View attachment 507670

No don't glue couple into main chute tube. If you keep avbay separate its makes it easier to work on avbay. You could use removable plastic rivets to secure avbay coupler to main chute tube.

 

[sharkbait]

No don't glue couple into main chute tube. If you keep avbay separate its makes it easier to work on avbay. You could use removable plastic rivets to secure avbay coupler to main chute tube.

shear pins can be tough on Loc airframes even when hardened with CA, if you use a razor knife and remove a layer on the inside of the tube then epoxy in a small piece of brass sheet the same size then drill your shear pin hole you will maintain the integrity of your shear pin hole and your airframe

 

[mtnmanak]

For cardboard tubes, you can use plastic rivets to hold the Ebay onto the payload bay tube or you can use blind nuts as David suggests above or you can epoxy some PEM nuts into the coupler and place screws through the airframe into those. Photo below of a LOC Ebay with PEM nuts in it.



For cardboard rockets at this diameter that have streamlined fins, I usually don't put shear pins in the booster. I have not had a drag separation on those rockets yet, but, if I was going to put shear pins in the booster, they would definitely be 2-56.

For the nosecone of a rocket this size, 2-56 is more than enough. 4-40 would be way overkill. I don't usually use 4-40 pins until I hit 6" diameter fiberglass rockets and above.

For shear pins in cardboard tubes, I use this method describe by @Banzai88 - works great to ensure your tubes don't get chewed up: https://www.rocketryforum.com/threads/shear-pin-shear-plates-in-your-cardboard-tubes.136706/

 

[OverTheTop]

I normally use single-ended dual deploy, with everything coming out of the front of the rocket. There still needs to be avionics in front of the motor to push the main chute out, but you should make that removable as others have said. I guess it has the advantage of only needing one set of shear-pins.

A lot of people do regular dual deploy but it is personally not how I do it. Have a think about both methods and go with what you think is better for you. You can always change your mind, or even try both .

 

[shawn_rocket]

Some great ideas here! I want this rocket to be a workhorse for me and it seems that carefully placed brass shims seems the way to go for shear pins and cardboard tubes. I plan to do a lot of L1 practice with this and an Apogee Zephyr DD with an L2 attempt early next year with an Apogee Katana (or maybe the Mystic Buzz with a K550!). I appreciate all the responses! I've learned so much on TRF, I couldn't even begin to thank everyone!

 

[OverTheTop]

Remember too that if you go for the 4-40 screws and you want them to be toned-down for a flight in the future then a 2mm drill up the middle reduces the area to about that of the 2-56. I have been known to do this drilling in the past. Usually easier to do once the shear pins are fitted to the rocket.

 

[shawn_rocket]

Remember too that if you go for the 4-40 screws and you want them to be toned-down for a flight in the future then a 2mm drill up the middle reduces the area to about that of the 2-56. I have been known to do this drilling in the past. Usually easier to do once the shear pins are fitted to the rocket.

I have both and looks like I'm going with the 2-56. Probably 3 per deployment (fin can and payload). Need to do some testing and research before I finalize, but if I run out, I'll certainly utilize those 4-40's as you've described! Waste none, want none as my grandmother used to say!

 

[mtnmanak]

I have both and looks like I'm going with the 2-56. Probably 3 per deployment (fin can and payload). Need to do some testing and research before I finalize, but if I run out, I'll certainly utilize those 4-40's as you've described! Waste none, want none as my grandmother used to say!

Don't worry, if you stick with this and start building larger fiberglass rockets, you'll go through those 4-40s like skittles.

I remember buying a pack of 100 2-56 pins and a pack of 100 4-40 pins from McMaster-Carr and thinking "these will last me a lifetime!". Between ground testing rockets and larger multi-day launches when I may get 15-20 rockets in the air, I sometimes now have single months where I burn through 100 shear pins. Buy them in bulk.

I also recommend getting them longer. I can't stand the 1/4" pins. Makes it so difficult to get the sheared off portion out of a tube wall or nosecone. I use 3/8" 2-56 pins for small rockets and then 1/2" 2-56 and 4-40 for everything else. It saves your sanity and doesn't make a difference in price. The only thing I use 1/4" pins for now is to plug the hole when I am painting the rocket.

 

[Buckeye]

Go with drawing #2. If you can fit your arm in the 4" tube to manipulate the forward bulkhead, etc, then gluing the av-bay in the payload is an option. Else, keep it removeable with plastic rivets or machine screws

I have a Katana built pretty much stock. I foamed a tube into the nose cone to hold a tracker, so it is a little heavy. Three (3) #2-56 nylon pins are plenty to hold on the nose cone, and 1.5g black powder is the charge to blow it off.

Shear pins in the booster tube are not needed.

 

[shawn_rocket]

Go with drawing #2. If you can fit your arm in the 4" tube to manipulate the forward bulkhead, etc, then gluing the av-bay in the payload is an option. Else, keep it removeable with plastic rivets or machine screws

I have a Katana built pretty much stock. I foamed a tube into the nose cone to hold a tracker, so it is a little heavy. Three (3) #2-56 nylon pins are plenty to hold on the nose cone, and 1.5g black powder is the charge to blow it off.

Shear pins in the booster tube are not needed.

So as long as the fit is good (shake test) at the booster, then no need for shear pins there? You don't worry about separation? I like the brass sheet idea, but I'd like to get this in the air next weekend. These dual fins can be a bit draggy on deceleration. I'm only sending it up to 1200ft (H268 or I200) or so, so I can watch everything before sending it higher.

 

[AdAstraPerAspera]

You can do dual deploy without shear pins. I've got a 4 inch diameter PML kit that I've modified to dual deploy and done this with successfully for years. You just need a good snug fit on the nose cone. This is not recommended for heavier rockets (fiberglass) or anything with a weighted nose cone, but with an empty plastic cone you can make it work just fine. Just check the fit before every flight, and adjust with tape as needed.

 

[Buckeye]

So as long as the fit is good (shake test) at the booster, then no need for shear pins there? You don't worry about separation? I like the brass sheet idea, but I'd like to get this in the air next weekend. These dual fins can be a bit draggy on deceleration. I'm only sending it up to 1200ft (H268 or I200) or so, so I can watch everything before sending it higher.

Yep, no worries about separation on the Katana or my Madcow Frenzy. Both are 4" cardboard/plastic with a fair bit of fin area. I put just a tiny vent hole in the booster.