Deploying parachute in nosecone via motor eject

[Zyzzyva1000]

So I just kit bashed a big daddy (plywood, then glassed the body tube and tip to tip glass) with a 38 mm motor mount. To gain some space for recovery, I cut the bottom on the nosecone off, and used a coupler tube and a bulkhead to create a removable bay in the nosecone (and on the forward side of this I designed a sled for my eggfinder mini).

Depending on the motor length, there is minimal room left in the body tube for a parachute (there's plenty of room using the area inside the nose cone. Currently I just have a single 12' kevlar shock cord with a swivel tied on about 3 feet from the nose cone for the parachute. LOC/PML has a new design (bumblebee, https://locprecision.com/collections/public-missiles-kits/products/bumble-bee-rocket) that has a very similar design. They appear to add an extra length of shock cord, but overall doesn't look much different.

What can I do to make sure when the motor eject charge fires, that the parachute is pulled out (will likely be sitting kind of halfway between the body tube and nosecone in most cases? My first instinct had been to put as much of the shock cord forward so when the nose cone separates, the unraveling shock cord will pull the parachute out. Just curious what other people have done.

 

[tfish]

My son built this Fat Boy with a 38mm mount. It has 8 flights on I motors. The shock cord and chute at tucked around the motor tube. The inside of the nose cone is fiberglassed. Make sure nothing is on top of the forward closer..that is not flame proof..

Tony

 

[Zyzzyva1000]

So here is the setup with a 360 case, technically enough room for the parachute on top, maybe using a bit of the forward space. A 480 case goes to almost the end of the body tube and a 720 case goes well into the nosecone. I guess I am just trying to make sure the parachute doesn't just get pushed into the nosecone. I didn't fiberglass the inside, but its all cardboard and wood (and some JB weld and epoxy), no exposed plastic, so I think it should be find to absorb a black powder charge.

 

[DigBaddy]

I'm guessing you'll do a nomex blanket and burrito wrap the chute? With the blanket on the cord closer to the body tube, it'll stop quickly when that shorter portion of the cord goes taut, then your chute will pull out of that just fine.

 

[Zyzzyva1000]

I'm guessing you'll do a nomex blanket and burrito wrap the chute? With the blanket on the cord closer to the body tube, it'll stop quickly when that shorter portion of the cord goes taut, then your chute will pull out of that just fine.

Yes that was the plan. Still have the parachute connected to the shock cord near the nosecone, but have the blanket attached closer to the body tube.

 

[David Schwantz]

I have gone so far as to add an extra BT inside main tube. One that is smaller dia. Lets say your main tube is 4" so I would use an 1.5" tube glued to the inside wall of main tube, so that it is offset. I will then stuff chute in smaller tube. I have also put the burrito wrapped chute around a motor that sticks up into the main tube. It pull s out fine. But your idea should work well also. Just make sure there is nothing for the chute to hang up on. ie shear pins sticking out, shock cord mounts and such.

 

[afadeev]

So I just kit bashed a big daddy (plywood, then glassed the body tube and tip to tip glass) with a 38 mm motor mount. [...] What can I do to make sure when the motor eject charge fires, that the parachute is pulled out

Parachute gets pulled out either either because:

1. Ejection charge creates enough pressure to push the chute out of the airframe.
2. Ejection charge dislodges the nose cone, and its momentum pulls out the chute. This works best if your nose cone has enough momentum due to mass, which yours may not.

For #1, the most reliable way to confirm is to load the target BP charge on top of your 38mm motor (just as you would for the flight), and test-fire the BP charge on the ground by manually triggering the igniter.
This is the recommended test mode for the HP rockets DD anyway.

(will likely be sitting kind of halfway between the body tube and nosecone in most cases?

The chute will be pancaked ontop of the FWD centering ring of the motor mount during acceleration phase.
Ideally, you will have a Nomex blanket insulating it from the burning BP particles.

My first instinct had been to put as much of the shock cord forward so when the nose cone separates, the unraveling shock cord will pull the parachute out. Just curious what other people have done.

You are referencing use-case #2. This may or may not work all the time.
#1 is more reliable and easier to test.

HTH,
a

 

[John Taylor]

So I just kit bashed a big daddy (plywood, then glassed the body tube and tip to tip glass) with a 38 mm motor mount. To gain some space for recovery, I cut the bottom on the nosecone off, and used a coupler tube and a bulkhead to create a removable bay in the nosecone (and on the forward side of this I designed a sled for my eggfinder mini).

Depending on the motor length, there is minimal room left in the body tube for a parachute (there's plenty of room using the area inside the nose cone. Currently I just have a single 12' kevlar shock cord with a swivel tied on about 3 feet from the nose cone for the parachute. LOC/PML has a new design (bumblebee, https://locprecision.com/collections/public-missiles-kits/products/bumble-bee-rocket) that has a very similar design. They appear to add an extra length of shock cord, but overall doesn't look much different.

What can I do to make sure when the motor eject charge fires, that the parachute is pulled out (will likely be sitting kind of halfway between the body tube and nosecone in most cases? My first instinct had been to put as much of the shock cord forward so when the nose cone separates, the unraveling shock cord will pull the parachute out. Just curious what other people have done.

The Bullet Bobby original small rocket does just that. The nose cone is open and is meant to contain the chute

 

[Zyzzyva1000]

I forgot to update this. but it deployed perfectly via motor eject. I ended up attaching the nomex guard close to the body of the rocket via a kevlar tether, and packed as much of the shock cord forward of the parachute in the nose. That way when the nose cone separated, the parachute would be pulled out. Luckily I had the GPS on top of that nose cone bay, because I sent this up on an H550 and we all lost it. Found it with GPS over a half a mile away.

 

[David Schwantz]

Could not tell from the pic, but I would not wrap my cord "around" the MMT. I would z fold it with a bit of blue tape and then just stuff it along side the MMT.

 

[David Schwantz]

Mute point. Great it worked well.

 

[Tech 68]

I've managed to jam a main chute up into the nosecone with an ejection charge to where it stayed until everything hit the ground.
In hindsight, I think a deployment bag, smaller diameter would have safely pulled out of the nosecone and deployed.