Okay for charge canisters to be close to the airframe wall?

I am working on the design of a dual deploy recovery system for the Madcow Cowabunga Mammoth that I plan to purchase soon. I'm planning to put a 6" diameter chute cannon mounted in the middle of the airframe tube. Apogee ejection charges will separate the nose cone and release the drogue. The main ejection charges will blow the main chute out of the chute cannon tube. The chute cannon tube will have a cap, held on by shear pins, to prevent the main chute from coming out prematurely. The chute cannon tube will be removable, bolted to a centering ring in the 11.25" diameter airframe. The av-bay will be bolted to the aft end of the chute cannon tube. The main chute ejection charge canisters will be located on the top of the av-bay, firing up into the chute cannon. My question is about the location of the apogee charge canisters. The only place I can locate them will be on the centering ring that the chute cannon is mounted to. This ring will only be about 2" wide, so the apogee charges would be close to the wall of the 11.25" airframe tube.

So is there any problem with locating the ejection charge canisters close to the wall of the 11.25" airframe tube? Or is there some reason that the charge canisters need to be near the center of the airframe tube? Is it correct to assume that if the only purpose of the charge canisters is to pressurize the compartment, then it should make no difference where the canisters are located?

dupedupe

Cut the chargewells in question at a 45 deg angle, longside close to the wall that's concerning?

Maybe a strip of HVAC tape if you're worried about scorching; or a reasonably small patch of fiberglass if you're concerned about both flame resistance and strength.

Assuming the cannon's cap is tethered to the airframe (don't want it coming down separated) could you relocate the drogue/apogee charges onto the surface of the cap? They would fire before the main's cannon would.

OregonBAR said:

Assuming the cannon's cap is tethered to the airframe (don't want it coming down separated) could you relocate the drogue/apogee charges onto the surface of the cap? They would fire before the main's cannon would.

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Yes, the 6" diameter cannon cap will be tethered. There will be a big eye bolt on the cap screwed into an eye nut on the inside of the cap. The main chute will attach to the inner eye nut and the 35 ft recovery harness will attach to the outer eye bolt. So when the rocket is under main chute, the chute will be directly attached to the cap with everything else hanging 35 ft below.

The problem with putting the apogee charges (and terminal blocks) on top of the cap is that the wires from the altimeters to the terminal blocks would then attach to the cap, which is going to get blown off.

To answer your question, no it won't hurt the FWFG airframe, put some dog barf directly around the charge well and you'll be fine.

Now a suggestion, why not do HED, that 11" cone has tons of room for laundry, just cut 1" off your airframe for a switch band or cut 1/2" off your coupler for a stopper inside the NC

I've never built a rocket where the charge canisters were centered in the airframe, they are always off to one side. Paper or glass, no problems so far. Put some metal tape or reinforce with epoxy the area that will get scorched if you have a concern. But who says the chute cannon has to be centered? Unless it being off center will affect the performance of the rocket.

I've thought up an idea like you are doing but never implemented it. My concern was with the drogue. Where does it go when the main comes out or where will it be relative to the main on descent? In my mind it seems prone to tangling.

sharkbait said:

To answer your question, no it won't hurt the FWFG airframe, put some dog barf directly around the charge well and you'll be fine.

Now a suggestion, why not do HED, that 11" cone has tons of room for laundry, just cut 1" off your airframe for a switch band or cut 1/2" off your coupler for a stopper inside the NC

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I was really just concerned about the effect of the ejection charge being way off to one side of the compartment. I'm sure that it won't hurt the fiberglass airframe.

I thought about putting everything in the NC. If I did, I would do it exactly the same way with a chute cannon, just pointing down from the nose instead of up from the airframe. I've done that before in a Minie-Magg. I don't see any advantage one way or the other but I'll have more room to put it in the airframe. That's assuming that I put the NC bulkhead high up in the NC coupler to make more space.

Nathan,

If I understand what you asked for, it should not matter where you put the charge wells or their orientation in the enclosed volume, you are generating a pressure increase from the burning BP which exerts a force on each surface inside the tube based on its area.

Nathan said:

I was really just concerned about the effect of the ejection charge being way off to one side of the compartment. I'm sure that it won't hurt the fiberglass airframe.

I thought about putting everything in the NC. If I did, I would do it exactly the same way with a chute cannon, just pointing down from the nose instead of up from the airframe. I've done that before in a Minie-Magg. I don't see any advantage one way or the other but I'll have more room to put it in the airframe. That's assuming that I put the NC bulkhead high up in the NC coupler to make more space.

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You don't need a chute cannon with HED. Your NC coupler is your E-bay, your booster is tethered to one end with a drogue and your NC is shear pinned to the other end and houses the main. Yes, you do need to get a small BP epoxied up towards the tip of the NC or if it has an Aluminum tip, toss the bolt and attach the tip with an Eye bolt,

Does the big cow have a FW FG nose cone? To do HED?

I use centrifuge tubes hanging on the electrical leads. They end up just sitting somewhere in the rocket. No damage yet to either of my two heavy duty cardboard rockets.

recon60 said:

Does the big cow have a FW FG nose cone? To do HED?

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https://www.madcowrocketry.com/11-5-fiberglass-cowabunga-mammoth/

Whether a cone is FW, hand laid glass, or plastic, has no bearing on doing a HED.

To OP....No problem with the canisters being close to the wall.

Titan II said:

Whether a cone is FW, hand laid glass, or plastic, has no bearing on doing a HED.

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Maybe.....it is very simple to do H.E.D. with a filament wound cone, the separate coupler becomes the av-bay, by simply adding a vent band/BP's.... RATHER than gluing it in as a shoulder.
Molded or plastic, require much more complex solutions.

H.E.D. [head end deploy] is accomplished by shear pinning the NC to couple/av-bay. An acronym used by Wildman to describe its use in his kits. First ones available with it. [4-5in. Jart & Punisher]
Anything else is...well anything else. :smile:

MikeyDSlagle said:

I've never built a rocket where the charge canisters were centered in the airframe, they are always off to one side. Paper or glass, no problems so far. Put some metal tape or reinforce with epoxy the area that will get scorched if you have a concern. But who says the chute cannon has to be centered? Unless it being off center will affect the performance of the rocket.

I've thought up an idea like you are doing but never implemented it. My concern was with the drogue. Where does it go when the main comes out or where will it be relative to the main on descent? In my mind it seems prone to tangling.

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I am concerned about that also. When the cannon blows out the main chute it's likely to be pointing in the general direction of the drogue. The drogue will be attached to a U-bolt on the NC bulkhead. I was thinking about putting the drogue on a 25 ft harness and the main on a 35 ft harness so at least there would be some separation after the main opens.

recon60 said:

Does the big cow have a FW FG nose cone? To do HED?

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Madcow website says the NC is hand laid fiberglass. I don't think it has an aluminum tip. I'll post photos of the kit after I get it.

blackjack2564 said:

Maybe.....it is very simple to do H.E.D. with a filament wound cone, the separate coupler becomes the av-bay, by simply adding a vent band/BP's.... RATHER than gluing it in as a shoulder. Molded or plastic, require much more complex solutions.

H.E.D. [head end deploy] is accomplished by shear pinning the NC to couple/av-bay. An acronym used by Wildman to describe its use in his kits. First ones available with it. [4-5in. Jart & Punisher]
Anything else is...well anything else. :smile:

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Yes, I know as I have HED rockets. I completely agree that it is very simple with a FW cone. However, the other types can be used with a little more work. I do not perceive their utilization as much more complex.