parachute grate

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watermelonman

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I have a recovery problem with short length, high thrust motors in my wider rockets. I believe what happens is that when they kick, the forces partially unfurl the nomex and parachute down the airframe closer to the ejection charge. I keep getting singed parachutes on these sorts of flights.

Anyone experiment with putting a grate or storm hole cover type device into their upper airframe, so that the space created by using shorter motors is not available to the recovery system? I was thinking about cutting quadrants out of a bulk plate.
 
cutting quadrants out of a bulk plate

Search "baffle". Lots and lots of info.
 
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I had Upscale CNC make me some bulkheads with a center hole to keep my recovery gear where it is supposed to be in my very long rocket. Since my shock cord is attached to the motor mount, a baffle isn't practical for me.
 
Right, I am not trying to baffle gasses at all but rather keep the components in position.
 
Right, I am not trying to baffle gasses at all but rather keep the components in position.

Kind of the same result though; your grate just doesn't need to be as complicated as a baffle. My Estes Phoenix had the issue where the parachute would slide backwards at launch and throw off the center of gravity. I had replaced the kit's plastic chute with rip-stop nylon which was heavier than the original. I just glued a single piece of balsa inside the body that prevented the chute from sliding back. A grate would have looked better, but my solution worked just fine.
 
just a thought
would reefing the shock cord with masking tape, help

so there is very little free play between the nosecone/bulk plate and the parachute/nomex
 
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That is a good idea, maybe I should try it out before making changes to rockets. I do not like getting my lines sticky but maybe the right tape will prevent that.
 
Do you have an issue with CG shifting aft? If not, my recommendation would be plenty of dog barf right above the ejection charge. That is lighter then a baffle or shelf, easy to use, cheap, and will protect the chute if the recovery shifts aft or not. I've also found that if the ejection goes off while the rocket is still nose up, you'll probably have most of the dog barf left in the rocket. It is reusable.
 
That is a good idea, maybe I should try it out before making changes to rockets. I do not like getting my lines sticky but maybe the right tape will prevent that.

A chute shelf won't change much and they are definitely worth it in longer rockets, I also like them for shock cord attachements, shock cords also seem to last longer if you get them out of the immediate vicinity of the ejection charge.
 
Lots of ways to do what you're looking for.

Honestly I do think a baffle would be the best application here. On the one hand, it will give you a 'chute shelf' to keep everything in position, on the other hand it will also reduce the direct impact of hot gasses onto the chute.

What are you using for chute protection? If you're using dog barf or on a larger diameter tube, that could also be part of the issue. Might be blowing a hole straight through instead of acting like a plug. A nomex wrap might be worth considering.

-Hans
 
A good baffle will divert the hot particulates that singe stuff.. No need for nomex.
 
I would second a parachute burrito. I've used them for a decade and never singed a single parachute. How are your charges set up? I've seen some 'directional' PVC and metal caps singe right through a parachute like a shaped charge. I've used the surgical tubing method as soon as I saw it in person. Bury the tube in a bed of cellulose insulation with a burrito and you are good to go.

Edward
 
The term here is "Shelf". IINM, the OP is looking to build a shelf for his laundry. I incorporate them into my 1/2 moon baffle variants, but in the event that a rocket is very long, I've also been known to build a shelf for it. I just use coffee stir sticks (Popsicle sticks would work) glued across the top edge of a small coupler (often made from a toilet paper tube).
 
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