First Dual Deployment Launch....help?

[johnhardy1]

I've put it off for too long so at this weekend's launch I will attempt my first DD launch. I'm using a 2.6" av-bay by Binder.
A Perfectflite MAWD is the altimeter. Rocket, w/bay is 70" tall.
It's set up using 1/2" pvc endcaps for the ejection charges. I see from pictures to drill a hole at the base of them for the e-matches.
There's still a few things I'm not so sure of ...

1) How should these holes for the e-matches somehow be covered once the e-match is in place? What should I use ? Tape ? Glue ? Clay?

2) I'll be using 4-F powder...how much should I use ? Just re-fill the lil red AT container ? Once in, should I just fill the rest up with wadding and cover up with a piece of tape ?

3) What size tubular nylon is the minimum size that should be used for this size rocket ? All I have at the moment is 9/16 but I was thinking I could maybe save a lil weight by using some 1/4" stuff. Is this OK ? And what lengths do you suggest for each event ? I was thinking about 30+ ft for destabilization at apogee and about the same for the main.

Thanks for helping the new guy. Of course a lot of these questions can be answered at the launch but I would like to be as prepared as possible come this Saturday.
Thanks again,

John

 

[Loki]

Originally posted by johnhardy1
I've put it off for too long so at this weekend's launch I will attempt my first DD launch. I'm using a 2.6" av-bay by Binder.
A Perfectflite MAWD is the altimeter. Rocket, w/bay is 70" tall.
It's set up using 1/2" pvc endcaps for the ejection charges. I see from pictures to drill a hole at the base of them for the e-matches.
There's still a few things I'm not so sure of ...

1) How should these holes for the e-matches somehow be covered once the e-match is in place? What should I use ? Tape ? Glue ? Clay?

2) I'll be using 4-F powder...how much should I use ? Just re-fill the lil red AT container ? Once in, should I just fill the rest up with wadding and cover up with a piece of tape ?

3) What size tubular nylon is the minimum size that should be used for this size rocket ? All I have at the moment is 9/16 but I was thinking I could maybe save a lil weight by using some 1/4" stuff. Is this OK ? And what lengths do you suggest for each event ? I was thinking about 30+ ft for destabilization at apogee and about the same for the main.

Thanks for helping the new guy. Of course a lot of these questions can be answered at the launch but I would like to be as prepared as possible come this Saturday.
Thanks again,

John

1) Tape or clay is fine. They don't have to be filled, but it does help keep BP residue out of the electronics bay.

2) How much BP to use depends on the volume of airframe you are trying to pressurize. For 2.6" airframe, 3/4g might be a good starting point.

3) 1/4" nylon is fine. How long is up to you. Some people advocate using as much as will fit. I tend to use about 15 feet for small rockets.

 

[Rocketmaniac]

Originally posted by johnhardy1
1) How should these holes for the e-matches somehow be covered once the e-match is in place? What should I use ? Tape ? Glue ? Clay?

2) I'll be using 4-F powder...how much should I use ? Just re-fill the lil red AT container ? Once in, should I just fill the rest up with wadding and cover up with a piece of tape ?

John

John, to answer question one. Install the ematch in your ejection charge holder. Put in the BP. Next I put in a some recovery wadding and pack it in a little. Finally cover with masking tape.

#2 Go to the EMRR website https://rocketreviews.com and go the "tools and calcs" section. Then go the Black Powder Calculator. Fill in the dimensions of your electronics bay. This will give you a ballpark amount to use.

 

[johnhardy1]

Hey thanks for the replies already. One other question, if I may be bold, is what gauge wire should I use inside this bay ? The alt is now screwed onto the tray, basically all is done except battery install and wiring.

Can I use some of the wire from an ematch or do I need a smaller gauge ?

Thanks again,

John

 

[Rocketmaniac]

Originally posted by johnhardy1
Hey thanks for the replies already. One other question, if I may be bold, is what gauge wire should I use inside this bay ? The alt is now screwed onto the tray, basically all is done except battery install and wiring.

Can I use some of the wire from an ematch or do I need a smaller gauge ?

Thanks again,

John

I have used extra ematch wire and the next larger size. It has worked for me, but some of the electrical engineers might jump in here and give reasons this is not good to do.......

 

[lalligood]

Don't be afraid to test your setup either. You can test everything on the ground first. Then you could do a launch by deploying the main at apogee--not to mention use motor ejection as a backup--and then deploy a (useless) drogue at 300/400/500/800/whatever feet. By doing it backwards you are guaranteeing that everything works safely with a reduced risk of your electronics and rocket. With a successful test or two, switch everything around & go for it!

HTH,

 

[KermieD]

I wired terminal blocks to the end of the alt bay. Wires went from the alt to the terminal blocks outside the bay, then the ematches went into the terminal blocks. This allowed me to completely seal the alt bay from ejection charges.

 

Originally posted by johnhardy1
I've put it off for too long so at this weekend's launch I will attempt my first DD launch. I'm using a 2.6" av-bay by Binder.
A Perfectflite MAWD is the altimeter. Rocket, w/bay is 70" tall.
It's set up using 1/2" pvc endcaps for the ejection charges. I see from pictures to drill a hole at the base of them for the e-matches.
There's still a few things I'm not so sure of ...

1) How should these holes for the e-matches somehow be covered once the e-match is in place? What should I use ? Tape ? Glue ? Clay?

2) I'll be using 4-F powder...how much should I use ? Just re-fill the lil red AT container ? Once in, should I just fill the rest up with wadding and cover up with a piece of tape ?

3) What size tubular nylon is the minimum size that should be used for this size rocket ? All I have at the moment is 9/16 but I was thinking I could maybe save a lil weight by using some 1/4" stuff. Is this OK ? And what lengths do you suggest for each event ? I was thinking about 30+ ft for destabilization at apogee and about the same for the main.

Thanks for helping the new guy. Of course a lot of these questions can be answered at the launch but I would like to be as prepared as possible come this Saturday.
Thanks again,

John

I fly almost the same setup on my 3" THOR. I use 1/2" PVC caps for a charge holder as well. I build my ejection charges in plastic wrap. A corner of a baggie works good for this. Cut off the corner, pour in your BP, insert match, and tape it up so you have a nice ball of BP around the match head. This keeps the BP in contact with the match head, prevents misfires. 3/4 to 1 gram would be a good starting point for charges.

I would plug the holes your matches pass through with wax or clay to prevent BP residue from fouling your electronics.

I'm building a DD 2.6" rocket right now. I'm planning on using 1/2" strap nylon for harnesses, but there's nothing wrong with the 9/16" stuff you already have. I'd use 15-20 ft per harness.

 

[johnhardy1]

Thanks for all the help. Wow, this place is great !
I think you really answered my questions for the most part but a couple of things have spurned more thought...

Well I saw some 20 gauge wire from the Shack, it looked about right so I bought it.
Lalligood,
I'll probably take you up on your suggestion. Being an original design I'm going to put it up with the ebay as alt only for the first launch anyway to see if my calcs were right then on to dd.
KermieD,
Yes, Im using the euro-type terminal blocks from the Shack on each bulkhead.
asmqajm,
I believe I'll use the baggie trick...sounds to me like it will pretty much completely prevent any misfires.

Maybe the last question I have concerning all this is ....since I'm using the "ejection charges on both ends of ebay" method, what is the cleanest yet secure way to attach the upper(main) section to the forward end of the e-bay ? Compression fit using masking tape not good enough eh ? I ask this just because I've heard it mentioned but it seems wrong to me to have to use screws or otherwise put a hole into the e-bay(plastic rivets) What gives ??

That may be the bit of any grey area for me but no promises.
At any rate...thanks for all the help.

-John

 

[KermieD]

It depends. Are you separating the aft section first? Do you have much for nose weight? If the answer to both of these is yes, I would definitely go with shear pins. If the drogue is in the front end of the rocket, a friction fit would be just fine.

 

[Adam Selene]

Originally posted by lalligood
Don't be afraid to test your setup either. You can test everything on the ground first. Then you could do a launch by deploying the main at apogee--not to mention use motor ejection as a backup--and then deploy a (useless) drogue at 300/400/500/800/whatever feet. By doing it backwards you are guaranteeing that everything works safely with a reduced risk of your electronics and rocket. With a successful test or two, switch everything around & go for it!

HTH,

What a great idea! i never would have thouht of that but i'm definitely going to do that when i'm ready to try dd.

 

Originally posted by johnhardy1
Maybe the last question I have concerning all this is ....since I'm using the "ejection charges on both ends of ebay" method, what is the cleanest yet secure way to attach the upper(main) section to the forward end of the e-bay ? Compression fit using masking tape not good enough eh ? I ask this just because I've heard it mentioned but it seems wrong to me to have to use screws or otherwise put a hole into the e-bay(plastic rivets) What gives ??

That may be the bit of any grey area for me but no promises.
At any rate...thanks for all the help.

-John

Use screws or plastic rivets to retain the payload section to the altbay. The altbays I build usually end up with 10 or more holes in them by the time they are done. (screw holes, vent holes, switch hole) The altbay dosen't mind it a bit. While we're on the subject of holes in the altbay, you did put vent holes in your bay, right?

You could friction fit, but you'll run the risk of ejecting the alt bay from the payload section instead of ejecting the chute out the payload section - depending on how tight the nosecone is. That would be bad.

 

[johnhardy1]

Originally posted by asmqajm
Use screws or plastic rivets to retain the payload section to the altbay. The altbays I build usually end up with 10 or more holes in them by the time they are done. (screw holes, vent holes, switch hole) The altbay dosen't mind it a bit. While we're on the subject of holes in the altbay, you did put vent holes in your bay, right?

You could friction fit, but you'll run the risk of ejecting the alt bay from the payload section instead of ejecting the chute out the payload section - depending on how tight the nosecone is. That would be bad.

Yes, Youre right I do have a 1/4" hole in the bay...however its on the outside....I guess that makes sense in that the additional holes would end up being forward of any ejection gasses anyway.

So what is the cleanest way to attach the bay to the forward section ? Actually I dont have any spare plastic rivets. Is there a good low profile screw I could find locally you think ? Should I use some sort of blindnut in the bay too ? Also, just use CA to reinforce things ?

KermieD,
Yeah I was just planning to do it the regular way I guess and use the upper paylod for main deployment. And yes, I believe I'll have to add just a few bb's to the NC . I imagine I should just find some small nylon screws to use? Seems to me I'll need some sort of blindnut to accept the screws into the bay though right ?

Thanks again,
John

 

[KermieD]

You can do that, or take thin sheets of metal and glue them to the inside of the BT and the outside of the coupler in the same spot. Of course, you may have to sand into the surfaces to make the metal fit and not jut out. Then, when you drill your (very small) hole, make sure it goes through those. That will ensure a pretty clean break and keep the parts intact. If you're like me and you're on a budget, you're never going to be able to launch the bird enough to make the slight widening of the hole in the BT from the screw/pin breaking an issue anyway. I've never seen a blindnut small enough for the nylon screws you'll be using for shear pins (doesn't mean they don't exist though).

 

[llickteig1]

So what is the cleanest way to attach the bay to the forward section ? Actually I dont have any spare plastic rivets. Is there a good low profile screw I could find locally you think ? Should I use some sort of blindnut in the bay too ? Also, just use CA to reinforce things ?

#1, you definitely want to use some positive connection. Friction fitting is begging for trouble here because you have pressureization which might cause the pieces to come apart plus the jerking during ejection. Best to be safe.

I've done the connection both with and without nuts to screw into. I prefer using nuts and I actually use the screw-in brass insert type. On the applications where I use nuts, I use small pan-head screws or stove bolts. On the non-nut applications, I found a low-profile machine screw with a rounded washer that works well.

For the application using nuts:
First I make an alignment mark on the two airframe sections and e-bay so that everything lines up when I take it apart and re-assemble it. If the rocket is already painted, Sharpie ink works well and will wipe off with alcohol. Make sure to off-set the screw locations from the vent hole and the launch lug/rail guides; for 3" and smaller I use 2 screws, 3 for 4" and up. Then I drill pilot holes with a really small drill bit through the airframe and into the e-bay. I epoxy a small piece of plywood (about 1"X1/2") at each screw location inside the e-bay. You can sand these small pieces to round-off the edges so they fit flatter against the wall of the e-bay.

After these dry, I make a bigger pilot hole for the screw-in brass inserts and screw them in so they are just below the surface of the e-bay coupler tube. Sand off any burrs created to return to s nice clean soupler surface. Drill holes the size of your screws in the airframe sections at the pilot hole locations.

Now re-assemble the aiiframe pieces using your alignment marks and everything should line-up just fine. Run your screws in and you're done.

If feel much more confident using nuts instead of just screwing directly into the e-bay phenolic. I have done it without nuts, and do put the small backing plywood pieces at the screw locations. I have 1 e-bay like this that has probably 30 flights on it, but over time the holes do get bigger. I went back and put the screw-in inserts in and expect 100 more flights from that e-bay.

You can use plain old nuts inside your e-bay at the hole locations, you just will need slightly longer screws. You can also use standard t-nuts, but if they stick-up above the surface of the e-bay you will have to grind them off, which is an unnecessary added aggrivation, IMHO.

I hope this is clear and helps you out.

--Lance.

 

[rocketgroupmike]

The "baggie" method works to keep the BP around the ematch head only until the charge begins to ignite... I think you should pack the baggie into the charge cylinder with wadding to keep the charge together as long as possible. Of course, this reduces the need for the baggie in the first place, but the more confined the BP is, the more efficient the charge will be.

 

[Adam Selene]

Originally posted by johnhardy1
1) How should these holes for the e-matches somehow be covered once the e-match is in place? What should I use ? Tape ? Glue ? Clay?
John

i was just looking at perfectflite's web site and they show (with a pic of a switch they sell) using 2 brass machine screws through the bulkhead. connect the wires from the alt. to the inside and the wires to the ematch on the other side. no holes thru the bulkhead so no ejection gases or powder residue inside the ebay! looks like a great idea to me.

 

[Adam Selene]

Originally posted by KermieD
I've never seen a blindnut small enough for the nylon screws you'll be using for shear pins (doesn't mean they don't exist though).

so what size nylon screws do people use for shear pins anyway?

 

[llickteig1]

Use Nylon Pan Head Phillips Machine Screw, 2-56 Thread, 1/4" Length (McMaster-Carr #91766A077). Adjust the number of pins for airframe size vs. qty of black powder ejection charges.

Always static test when using shear pins to be sure you get everything apart with the amount of ejection charges you are using.

BTW, I only use the baggie method. I keep an old butter tub in my range box to put all my little motor grain baggies in and recycle them as ejection charges. I use electrical tape to wrap the e-match and powder in the baggie. These ejection charges NEVER fail.

HTH, --Lance.

 

[AlexM]

Where is the best place to get these?

 

[jraice]

I designed a way to make the connection extremly strong with 4 screws, my rocket was 4" kraft tubing. I glued 4 curved pieces of wood into the e-bay and attached T-nuts to them, I then drilled 4 holes in the body tube and that way I can put the machine screw through the hole, into the e-bay, and into the T-nut. If the rocket is kraft I would also use some epoxy on the inside of the tube, smooth it on and sand for the fit, you can also add rubbing alchohol to the epoxy to make it more liquid like. Works great!!!

 

[gregzo]

Originally posted by AlexM
Where is the best place to get these?

I have never ordered from these guys before - but I got this website from another thread on TRF:
https://www.microfasteners.com/

Also - MissileWorks sells them:
https://www.missileworks.com/Mercha...n=CTGY&Store_Code=MWC&Category_Code=cat103030

And as someone else mentioned - you can get darn near everything from McMasterCarr....