Working on first DD

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viciouspeanut

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Hey all,

Got my AV-Bay and payload section so about to start working on it. Question is do you prefer to have the NC pop off the payload bay to release the chute or do you like to pop the payload w/ NC attached to release the cute? I don't imagine there are any differences as far as performance or effectiveness. Also I know people prefer shear pins but I think I'm torn on X patterns of tape or 2 pins for attachment on this. (~70 oz cardboard)
 
If you leave the payload bay attached to the NC, you'll need to anchor your main to the AV bay instead of the NC bulkhead, to make sure the main gets out. Way is to blow the main out of the payload bay with the ejection charge. Doing it the other way would be like HED with a payload bay.
 
The standard way to do dual deploy is to put the main chute in the payload section. The first deployment charge separates the payload section from the booster section at apogee, optionally releasing a drogue chute, and then the second deployment charge blows off the nose cone releasing the main chute from the payload tube at a preset altitude like 500 ft.
 
Roger, thanks guys. I'll go with the nose cone being blown off. Just need one more harness and ready to go after testing.
 
If you are building a cardboard rocket, I would avoid the shear pins and use the x form tape for friction fit. Shear pins will tear up the cardboard.

Use CA or very thin slow laminating epoxy to seal and stiffen the ends of the cardboard tubes and harden the inside of the tubes where they slide together. You can sand it down after it dries, but having something that will soak in and harden the cardboard will greatly extend the life of the rocket. You'll have to redo the hardening of the ends from time to time, but that's just part of maintenance. I have one DD LOC tube rocket with 45 flights on it. It's always been friction fit which has worked great.

Good Luck
 
If you are building a cardboard rocket, I would avoid the shear pins and use the x form tape for friction fit. Shear pins will tear up the cardboard.

Use CA or very thin slow laminating epoxy to seal and stiffen the ends of the cardboard tubes and harden the inside of the tubes where they slide together. You can sand it down after it dries, but having something that will soak in and harden the cardboard will greatly extend the life of the rocket. You'll have to redo the hardening of the ends from time to time, but that's just part of maintenance. I have one DD LOC tube rocket with 45 flights on it. It's always been friction fit which has worked great.

Good Luck

I use the tape on the shock cord method too and it works well for me. I use 12 to 15 folds (or more if space is available) on the shock cord and usually have a few that don't break. Tried shear pins on a LOC cardboard rocket once and said never again after seeing the damage it caused.
 
Awesome, I’ll save the shear pins for the Formula 98 when I get ready to build it for lvl 2. Want to get a lot of DD flights first with progressively bigger motors.

One mlre question - I know the booster is just like motor deploy but the upper bay with the main has two attachment points (Av-Bay and NC). Do you guys just friction fit both sides of payload bay? I don’t see how you could permanently attached it to th Av-Bay since you need to fill the well and put match in. I promise I understand the theory behind DD - it’s just the small parts I never considered!
 
The payload tube is usually attached to the av bay coupler with some type of removable bolts or rivets. What I do is drill and countersink 6 holes then attach 6 hex nuts to the inside of the av bay coupler tube with epoxy putty. Then attach the payload tube with stainless flat head machine screws . . .

23807404118_f6e97f3000_o.jpg
 
Thumb rivets on smaller rockets, screws on bigger. There is also the method where the coupler is glued into the payload and then the AV bay is slid down the payload into place. GLR kits use that method. Ask questions if you need more info.
 
You can friction fit the payload bay to the av bay, but this can be an issue if you need to make a change after you have prepped the rocket. I speak from personal experience. And I've seen rockets that require 2 or 3 people to pull them apart because of a really tight friction fit. And remember that temperature changes can cause things to get tighter or looser. What seemed like a good fit at home in a nice warm house may be too tight or loose in the field. Use screws or rivets as Bat-mite suggested. If you use screws, bring a power driver to drive them in and out; especially if it is cold where you are launching. Trying to use a screwdriver in the cold is really tough. And bring extra screws or rivets in case you drop some.
 
You can friction fit the payload bay to the av bay, but this can be an issue if you need to make a change after you have prepped the rocket. I speak from personal experience. And I've seen rockets that require 2 or 3 people to pull them apart because of a really tight friction fit. And remember that temperature changes can cause things to get tighter or looser. What seemed like a good fit at home in a nice warm house may be too tight or loose in the field. Use screws or rivets as Bat-mite suggested. If you use screws, bring a power driver to drive them in and out; especially if it is cold where you are launching. Trying to use a screwdriver in the cold is really tough. And bring extra screws or rivets in case you drop some.

+3 on using screws/rivets, power driver, and extra screws/rivets.
 
The payload tube is usually attached to the av bay coupler with some type of removable bolts or rivets. What I do is drill and countersink 6 holes then attach 6 hex nuts to the inside of the av bay coupler tube with epoxy putty. Then attach the payload tube with stainless flat head machine screws . . .

23807404118_f6e97f3000_o.jpg

Jesus...I swear that's just a gratuitous shot showing off how gorgeous your paint jobs are! My Alfa Romeo Giulia doesn't even look that nice!! :jaw::sigh:
 
Thanks guys,

Have the av bay built and gonna mount everything on the sled this weekend. Couple questions - LOC seems to really want epoxy on all the nuts for the all thread - why? If I ensure it is tight and have nyloc nuts on the non wingnut side I don't see what problems there could be? I know epoxy on the eye bolts is a good idea.

Also could you perhaps post a link to the plastic thumb rivets you use? Or a picture of how they are attached to the av bay? I would think just drilled into the coupler and stuck through the drilled hole and held in place with some epoxy on the backside?

For reference this is a LOC EZI I plan to put up on a I161.
 
Ahh, I was thinking it was a two part rivet that had one side stay put. I get it now - they are ordered!

Lol, perfect. I think I am ready to go aside from e-matches. Think the ones from Chris' Rocketry are the ones I want to go with.

Last question- even with a washer and screw in the charge well do you seal it with grease or epoxy?
 
Last question- even with a washer and screw in the charge well do you seal it with grease or epoxy?

I use the Doghouse charge wells from Binder Design. I have never sealed them with anything. You do want to make sure that any holes in your bulkheads (to allow wires thru, etc.) are sealed so that the explosive gasses don't ruin the electronics inside.
 
Gotcha, I intend to seal the hole for the e match up. Vasoline work for that?

DD is simple enough in concept but trying to do it the first time is a little nerve racking haha
 
I use terminal blocks on the bulkhead and have a permanent wire that goes up from the altimeter, so I just put a drop of 5-min epoxy in mine. Clay or Play-Doh are less permanent options.
 
Thanks guys. All set up now except for BP. Hopefully I'll have a positive report soon for my first DD flight.
 
Hey everyone,

Almost all set - have vents holes piloted (gonna CA them and then drill out tonight), and hope to ground test tomorrow. Since it is my first DD flight and I want to make sure it is safe I am using motor eject backup drilled three seconds after simm'd ideal delay and I was going to fly drogue-less but am now thinking about using a 24" chute I have as the drogue so if for some reason I have issues it wont come in so hot.

Thoughts? Rocket unloaded weight is 77 ounces.
 
How are you going to ground test? Seal up holes and pull a vacuum with a vacuum cleaner? Pull e-match leads out thru a vent hole and attach an Estes launch controller?
 
I am planning on using estes igniters with a launch controller and wires ran through switch port.
 
Good luck.

Label or identify everything that needs to be hooked up a specific way. For instance, drogue and main wires in the av bay so you don't accidentally wire them up reversed. The first time I did DD I was pretty nervous and could easily have messed it up. You might want to explain and show the whole setup to someone before closing up the rocket. They don't even need to know what you are talking about, but it is amazing how talking stuff through finds mistakes.
 
Thank you,

I plan to have on of our seasoned guys watch my assembly and prep of my avbay and setup before launch. Hopefully this will help me catch and any whoopsies.
 
Don’t forget to plug the motor tube before testing the drogue or it won’t pressurize properly. Also, make sure you plug it well, or you’ll end up shooting a flaming dish towel across the yard.
 
Don’t forget to plug the motor tube before testing the drogue or it won’t pressurize properly. Also, make sure you plug it well, or you’ll end up shooting a flaming dish towel across the yard.

Nice lol. My wife is extremely supportive but if I had flaming bits flying around that might test her haha. I’ll stick and empty casing in it for this.
 
Well ground test of one charge is done and 1.8 grams stretched the cord even with forgetting to plug the motor mount.. lol

will test the other charge tomorrow.
 
Well ground test of one charge is done and 1.8 grams stretched the cord even with forgetting to plug the motor mount.. lol

will test the other charge tomorrow.

Are you saying your drogue charge stretched the shock cord out without a motor case in the MMT? Just and empty tube and you still got ejection and cord stretch?

If that's the case, then go back and do it again with the MMT filled. That amount of charge without anything in the tube will be way too much with a motor in. The result is a huge shock load when the two halves hit the ends of the drogue shock cord. Probably resulting in a main deploy at apogee. And that would be the least damaging result. Remember, the apogee charge only needs to open the rocket and get the drogue into the air stream. It doesn't need to push the two halves to the ends of the shock cord.
 
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