Building an Alt. Bay

Hi again guys,
Not to take attention away from my thread on the flight of T&L (I'm still coming down from last Saturday's high) but I gotta get back to building. Because of a trip I took for a science fair thing, I didn't get the parts ordered for that alt. bay yet, but I plan to order them tomorrow. I was just wandering if there was anything that any of you learned from building your own alt. bays? Any problems? Tricks of the trade?
So far, the design goes like this...
One 11" long 4" diameter coupler with a 9.5" sleeve inside to hold back the two 1/2" thick bulkheads on either side. Two 1/4" all thread rods running throught the length of it and one u-bolt at each end for TN attachment. An ejection charge holder at each end and a piece of ply inside with 1/4" LLS glued on to slide down the all thread rods. Altimeter is attached to this. The whole bay is removable in and out of a 36" length of PML quantum tube. In the quantum tube, just past where the coupler slides up to is a saftey switch with long leads to go through the bulkhead at that end. The swith is also confined in a small compartment to keep it from getting too much BP residue on it. The bay will be held in place in the tube by 6 plastic rivets and 4 socket head bolts. I think that is just about everything.
So, does anything I've said here sound wrong or does anyone know of a better way to do this?

Dave

. . . sounds like you've covered the bases. Just make certain that the altimeter is sealed inside the bay, so that the pressure resulting from the primary ejection charge won't cause the altimeter to fire the secondary charge simultaneously.

My only concern would be the placement of the switch. I don't know how you can run the switch wires thru without allowing ejection charge to leak through. It seems like it is normally better to have the switch in the altimeter bay.

If there are wired going thru a bulkead and there is a concern about residue leakage, you can seal the hole around the wires. Hot glue, epoxy, maybe Liquid Nails, probably any flexible glue will work. Also, size the thru-hole so the wires are snug.

First of all, I have ordered the parts from PML and they should be here by, I'd say, about next Thursday.
Secondly, I have changed the location of the switch to be on a 1.75" long piece of Quantum tube that is glued to the coupler and will butt-up against the bottom edge of the fore recovery airframe. This way, the wires run directly through the airframe to the altimeter, not through any bulkheads and it is not exposed to any ejection residue.
Third, the foreward facing bulkhead is epoxied in place and therefore sealed. The rear bulkhead is going to have a small nitch cut into the edge that an O-ring will slip into and then it will be compressed between the bulkhead and coupler sleeve by the force of the wingnuts on the all thread rods. This should create a seal at that end. If not, I may use a little of that stiky-tac stuff from office supply stores to fill in any gaps in the joint.

Dave

BTW- I also ordered a 38mm Aeropac retainer for Dad's eclipse and we finally started priming it. We also ordered 4 nomex chute protectors from Magnum for the eclipse and for this alt bay which will be going in my dad's patriot. Finally, we ordered some more e-matches and I am thinking about starting to build a cluster bird. An extended Big Daddy with a central 24mm motor mount and six 18mm motor mounts. Would be an awesome flight on a G55 and six D21s or C6s!

Hey Mav, where are the pics of your Alt bay? I've shown you mine now show me yours. Seriously, I built the alt bay the way I thought was best and it shall be tested, hopefully, in a few months. I am very interested in seeing your bay dude...

Oooops, just saw that you just ordered the parts. Oooops, well I shall expect pictures...

BTW, have you seen that PML now has a new CPR for 7.51" and 6" tubes? It looks really cool, but, gulp, expensive. It uses two internal motor tubes instead of the one like you and I designed.

Yeah, I know, I'll get pics as soon as I begin construction. And, I did see that new CPR-max thing. It looks cool but very expensive. Personally, I think PML should design and start selling alt. bays that are very inexpensive like the new ones from LOC and Binder Design. They all follow the basic design of a coupler, bulkheads and a couple of all thread rods. I just know that a lot of people really like PML part quality (me included) but they want to build an inexpensive, removable alt. bay for their rockets. Just because most of the CPR components can only be used in one rocket, where as with a removable alt bay you pop it in and out of payload sections between rockets or even swap the whole bay and payload section and NC between different fin cans. Just my opinion though!

Dave

BTW- I am priming eclipse right now (took a break while it dries to type this) and it looks like Dad's lvl 2 flight may be on June 8 (tenatively).

I forgot to ask!
Do you think that 6 plastic rivets and 4 allen-head screws are enough to hold the bay into the payload section, or do I need more?

Dave

In my experience, the 4 screws should be enough. I have a bay that's held to the drogue tube with 3 screws and the main with 4. These go into T-nuts that attached to wooden spars inside the bay. I forget the size screws I used though.

Ok, well I am using four small screws about the same size as the screws that come with PML's PMR unit. If you don't know what that is then, well, they're pretty small basically. Its four of them plus six rivets. I know a guy used nothing but three rivets in his and it works fine but I prefer over engineering things a bit.

BTW- I got my aeropack retainer and it is already installed, from box to motor mount in 5 minutes flat! I also got my four nomex chute protectors from magnum and installed two in the eclipse. I am waiting on the parts from PML before I can do anything else.

Dave

I forgot something again!

I know this deals more with that thread on the "Level two kit" but I don't know if anyone really checks that one any more so I'll just run this by you guys here.

The paint scheme for Eclipse looks like this-

Mirage purple/green over whole thing(spraypaint).
Metallic orange lettering on side saying "Eclipse"(airbrush).
Metallic gold and silver flames on NC and upper airframe(airbrush).
Clear gloss overtop(spraypaint).

So, what do you think?

Dave

Wahoo!
My parts from PML are in! Unfortunately I start final exams tomorrow. Darn! I'll have to wait till Fri. afternoon to start construction...too busy studying now. Oh well, I'll let you guys know how construction goes and I'll take some pics when I'm done.

Dave

Wahoo!
Alt. bay is almost done. I should have it finished by next Wed. or so. This thing ways a ton though. I think I'll need an I284 just to get it off the ground.
About to start painting eclipse. I have the mirage paint but the humidity is high here in the northeast so I'll think I'll wait until tomorrow.
This Sat. is the next launch up at club NEPRA and I am definitely planning on flying T&L again. This time on an I300 to an H123. It should reach about 4200'. The only way I am going to be able to fly is because a generous soul (club pres. Drake) is letting me purchase an I300 he has. Motors are really hard to come by right now! Even better than flying T&L though, there could be as many as three two-stage flights this Sat. My T&L, a PML Quantum Leap kit, and a Mini BBX and Terrier booster. Wow, crazy!

Dave

Alt. bay is pretty much finished. I'll have pics in a little while, remember, no digital camera (have to get film developed) . Just a few cosmetic things left to do- Fill gaps between switch and airframe with putty and drill altimeter vent hole. Speeking of an alt. vent hole....
Do you think it would be wise to drill a 3/16" hole on the side of the bay opposite the altimeter and then drill a couple of 1/4" holes in the altimeter mounting board so air goes through the airframe, then through the board, to the opposite side where the altimeter is attached?
-OR-
Drill a 1/8 or 5/32 hole in the side of the bay that faces the altimeter so air just travels through the airframe and right to the altimeter?
????

Dave