Nose Cone A/V Bay

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iter

HPR Glider Driver
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I'm experimenting with a cable cutter setup so both charges connect to the same end (nose cone). The nose cone is a standard LOC 3" item. Challenge with polyethylene nose cones is that nothing sticks to them. My idea is to fill the bottom of the NC with epoxy. Epoxy sticks to A/V bay and creates a physical "stopper" that prevents A/V bay from falling out. I epoxy a strap to the A/V bay similar to how some Wildman kits attach straps to MMTs. This solves both the problem of attaching shock cord to nose cone and attaching A/V bay to nose cone securely.

The A/V bay is a sprinkler body which conveniently has a screw-on cap. I laser-cut a bulkhead with relevant cutouts. Terminal blocks connect to altimeter outputs for Main and Apogee charges and two separate switches control telemetry circuit and deployment altimeter. Telemetry includes a GPS which takes several minutes to acquire a lock. I want to turn it on ahead of time and arm the altimeter that controls energetics only at the pad.

Ari.

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I like your technique John. My nose cone is probably long enough to do this, especially with wider diameter available for electronics installation. I'm going to experiment with a soft altimeter installation in this case, which makes a just-big-enough av bay useful. I think you saw the other thread where I describe this idea. Fabric is pretty bad at containing pressure, so I'm sure it's OK for passing pressure through. If anything, it acts as a little low-pass filter, like foam padding in a microphone.

Ari.
 
Nice work on the bulkhead!

It's also possible to take advantage of the shoulder build into plastic nose cones to lock a ring in place. I documented this in my Plastic Nose Cone Mods video.

However, 3" is pretty small and your technique is slick.

I just your technique for my LOC V-2 clone..no electronics yet, but I dont trust the plastic base for shock cord attachment and the removable bulkhead keeps the nose area accessible in case more nose weight is needed, tracker compartment or to add electronics.

Next up is my night launch rockets plastic nose cone for nightbow mounting.

Kenny
 
Heh, I'm in the middle of building a nosecone av-bay with a wildmanesque mounting for the recovery anchor. Synchronicity!

Unlike yours I'll put both ends of the loop adjacent, to make getting the bay in easier and to minimize lateral force under tension.
 
Maybe you can post a picture of what you're building. I'm unclear on "both ends of the loop adjacent."

Ari.
 
I'm almost finished with my NC av-bay in my Minnie Magg. I basically built a 54mm av-bay similar to a Madcow one and mounted it to the center of a bulkhead. I'm using three countersunk screws to hold the bulkhead in place and a Y Harness from OneBadHawk. Motor eject at apogee, RRC2+ at 500'.
Complete pictorial build on my profile in my albums: https://www.rocketryforum.com/album.php?albumid=590
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I'm almost finished with my NC av-bay in my Minnie Magg. I basically built a 54mm av-bay similar to a Madcow one and mounted it to the center of a bulkhead. I'm using three countersunk screws to hold the bulkhead in place and a Y Harness from OneBadHawk. Motor eject at apogee, RRC2+ at 500'.
Complete pictorial build on my profile in my albums: https://www.rocketryforum.com/album.php?albumid=590

Your photos are the inspiration for my NC.

Ari.
 
Ari, I'd like to see it once its done. I didnt get much done on mine lately. Its pretty much finished. I've been sanding and priming but the humidity has been so high here lately I can only do one coat a day and sand every other day! I filled, sanded and primed the bulkhead for my av-bay and it will get the same color as the Nose and Fins eventually!
 
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Be careful with arming an altimeter via an internal switch that requires you to insert the cone into the tube AFTER you arm it.
 
Be careful with arming an altimeter via an internal switch that requires you to insert the cone into the tube AFTER you arm it.

I've been thinking about that, might go with a pushbutton through one of the vent holes instead.
 
I've been thinking about that, might go with a pushbutton through one of the vent holes instead.

Highly recommended. It could fire the charge as you install the nosecone. If it doesn't pop then, if you ever needed to disarm it it would surely fire when you pulled on the nosecone.
 
I've been using the magnetic switches from Featherweight - so far so good on 6+ flights.
 
Highly recommended. It could fire the charge as you install the nosecone. If it doesn't pop then, if you ever needed to disarm it it would surely fire when you pulled on the nosecone.

You seem mighty sure of your prediction.

Ari.
 
Ari, I'd like to see it once its done. I didnt get much done on mine lately. Its pretty much finished. I've been sanding and priming but the humidity has been so high here lately I can only do one coat a day and sand every other day! I filled, sanded and primed the bulkhead for my av-bay and it will get the same color as the Nose and Fins eventually!

I flew it on an Onyx last week. The cable cutter wires got tangled and while it cut the ziptie, the main never opened properly. The altimeter and the tracker worked fine. One humorous observation is the location of my vent holes. I decided to put vent holes lower down on the fuselage away from nose cone/body transition, and open small vent holes in the retainer nut to equalize pressure between fuselage and AV bay. Well, when the apogee charge went off, it spiked the air pressure sensor :=) Not a problem operationally, but something I like to avoid. I've replaced the cap with a new, sold one, and I'm drilling holes in the NC shoulder and matching holes in the fuselage.

Ari.

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Highly recommended. It could fire the charge as you install the nosecone. If it doesn't pop then, if you ever needed to disarm it it would surely fire when you pulled on the nosecone.

Surely?
 
I shouldnt have that problem, as the vent holes are in the NC. I went 1" above the shoulder with 3 3/16" holes. I was thinking more about what Dan said with having to pull the NC after its armed. This shouldnt be a problem since the av-bay is sealed off from the airframe via the bulkhead, making a seperate compartment.
so there shouldnt be any pressure difference in the NC if it had to be pulled. Thoughts?

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I shouldnt have that problem, as the vent holes are in the NC. I went 1" above the shoulder with 3 3/16" holes. I was thinking more about what Dan said with having to pull the NC after its armed. This shouldnt be a problem since the av-bay is sealed off from the airframe via the bulkhead, making a seperate compartment.
so there shouldnt be any pressure difference in the NC if it had to be pulled. Thoughts?

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So, when I said that, I was speaking from experience. I used to have a 4" Sport Scale Patriot. The altimeter bay was a 38mm version of the altitube, basically a 38mm motor tube in the coupler with a modular sled that could be passed from rocket to rocket. The altimeter was armed by passing a wire through the bottom bulkhead, out of a hole in the lower body tube, twist the wires together, and then tuck them inside the lower body tube. For some reason at a METRA launch, I decided that I needed to unarm the altimeter on the pad. The only way to do this was to pull up on the payload section so that I could see inside of the booster to find and cut the twist wires that had been tucked in. By pulling the payload and coupler out, it caused a pressure drop which popped the charge. Thankfully it was only about 1g and really only made my ears ring. The altimeter was a Perfectflite MAWD.

If you are certain that your altimeter bay is sealed very well, you can probably get away with it. I suggest an o-ring in compression behind your bulkhead. It may be worth doing some ground tests with a Christmas bulb in place of the charge.
 
I'm definitely doing some ground tests to see what it will do.
 
So, when I said that, I was speaking from experience. I used to have a 4" Sport Scale Patriot. The altimeter bay was a 38mm version of the altitube, basically a 38mm motor tube in the coupler with a modular sled that could be passed from rocket to rocket. The altimeter was armed by passing a wire through the bottom bulkhead, out of a hole in the lower body tube, twist the wires together, and then tuck them inside the lower body tube. For some reason at a METRA launch, I decided that I needed to unarm the altimeter on the pad. The only way to do this was to pull up on the payload section so that I could see inside of the booster to find and cut the twist wires that had been tucked in. By pulling the payload and coupler out, it caused a pressure drop which popped the charge. Thankfully it was only about 1g and really only made my ears ring. The altimeter was a Perfectflite MAWD.

If you are certain that your altimeter bay is sealed very well, you can probably get away with it. I suggest an o-ring in compression behind your bulkhead. It may be worth doing some ground tests with a Christmas bulb in place of the charge.

I understand your concern more completely now. I imagine that vent holes in the fuselage can mitigate this risk. I need them anyway to prevent the nose from popping off from internal pressure when the rocket goes above 10,000. Also, pulling the nose cone off slowly if I need to disarm it on the pad.

Ari.
 
Be careful with arming an altimeter via an internal switch that requires you to insert the cone into the tube AFTER you arm it.

If you don't change your arming method, just be sure to wear safety glasses out on the pad when you arm it. I have several rockets with the rotary switch in the nosecone base and though I've never had a charge go off, I wear safety glasses and keep my face to the side when arming. My electronics in these rockets is the Robert Galejs model of magnetic apogee detector so I also have to be careful about tipping the nosecone after arming:cyclops:
 
Well, I finished the avbay over the weekend and did some extensive testing. I packed the rocket like I would for flight.
Chute, shock cord, used a length of wood dowel in a CTI 3 Grain case to plug the bottom, and used blue tape on the NC shoulder like I would any other
rocket to get a good seal. I then hooked up an xmas bulb and armed the altimeter.
Then I repeatedly pulled and pushed the NC back and forth creating a vacuum. The bulb never went, so I replaced it with a starter and did it some more and nothing. So I think the avbay is suffuciently sealed off from the payload bay.
 
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