Parachute Deployment for 1st 6" rocket

Gentle people:


I'm designing/building my first 6" diameter rocket and I have some doubts as to deployment tech.
It seems to me that at 6" the volumes within the airframe are becoming rather large for just igniting a deployment charge and blowing it up/apart.
Also, in >4" diameter I'm unsure about sealing the chute+shockcord assembly from the hot discharge of a deployment charge.
I know from experience that for 4" diameter rockets I can separate the sections, protect the chute assembly, and deploy the chute.
This leads me to thinking about a 3"/4" chute deployment cansiter/cannon within the 6" airframe.
Having not built a chute canister/cannon, the drawing is as I see it at this point.
I would like to hear opinions on the options/design..., and will appreciate any guidance on the subject.

anbhtblr said:

It seems to me that at 6" the volumes within the airframe are becoming rather large for just igniting a deployment charge and blowing it up/apart.

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FWIW, I've never had any problems doing this at 5.5". Remember that the force on the nose cone for a given pressure increases with the surface area of the bulkhead, so in some respects it's easier to get a large cone off. Of course, you still have to account for the extra volume.

That said, there's nothing wrong with using a chute cannon if you want to, and I look forward to seeing what people experienced with them have to say.

My set-up for an 8" airframe:

60" drogue wrapped in 33" Nomex blanket, 3.5g and 4.5g charges.

15' silk main in a deployment bag, 36" pilot chute in a 12" Nomex blanket, all wrapped in a 33" Nomex blanket, 4.5g and 5.5g charges.

All harnesses are tubular Kevlar.

In our upscale Dragonfly we don't use any sort of containment for our parachute and we haven't had any issues. The 'chute compartment measures 36" x 12.625".

We use a 4 gram ejection charge to deploy at apogee. We use a 55' x 1" tubular nylon Onebadhawk harness and a 16' Rocketman parachute. The parachute is wrapped in a 36" Nomex blanket followed by a second 39" Nomex blanket.

We have had four flights so far with perfect deployment each time.

Recovery gear for 6" rockets can take up a lot of space. A 3"/4" internal "cannon" will work, but it'll be a pain to prep. I'm like the folks above--my 5" and 6" rockets use tubular Kevlar shock cords and Rocketman/Recon/Skyangle/Spherachutes parachutes burrito-wrapped in a Nomex blanket. I z-fold and tape the Kevlar into bundles to make sure it stays organized in there. Sometimes I'll throw in a handful of wadding if I remember, but the only chute damage I've had (knock on wood) is from an encounter with a barbed wire fence after landing

anbhtblr said:

Gentle people:
1. It seems to me that at 6" the volumes within the airframe are becoming rather large for just igniting a deployment charge and blowing it up/apart.
2. Also, in >4" diameter I'm unsure about sealing the chute+shockcord assembly from the hot discharge of a deployment charge.
3. I know from experience that for 4" diameter rockets I can separate the sections, protect the chute assembly, and deploy the chute.
4. This leads me to thinking about a 3"/4" chute deployment cansiter/cannon within the 6" airframe.

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1. Not a problem. Use a BP calculator and ground test. There's a couple of calculators that include the use of shear pins. I typically add 50% to what the calculator suggests.
2. Tubular Kevlar cord and Nomex burrito for the parachute.
3. See #1 and 2
4. No need to reinvent the wheel. What works for 4", works for 6". Chute cannon is a solution to a problem you're not going to have.

Agree with all the above.

The chute cannon increases your complexity, decreases space for the chute (it really does take a lot after you fly that chute a few times) and also will add weight forward - and increasing stability may not be a good thing.....

For my 6" Formula 150 I just do it the same way I do 4" diameter rockets; with the chute wrapped burrito-style in a Nomex blanket and Nomex sleeves covering the ends of the harnesses. Yes the unprotected parts of the harness get some black soot marks but it will take a lot of flights to do any significant damage. Just be sure that the burrito-wrapped chute is a tight enough fit in the 6" tube that it doesn't become unwrapped.

If you do plan to go the chute cannon route, I am also working on one now for an 11.5" diameter Cowabunga Mammoth with a 6" chute cannon. Be sure in your design that you don't have to reach too far down in the tube to load the ejection canisters and connect e-matches. In my design, the entire chute cannon assembly will be removable, held in place on a centering ring by four bolts with wing nuts.

For my L3 (1/2 scale Nike Smoke, 8.25" airframe) I blew the NC off at apogee and pulled out a drogue chute. Main deployment was just releasing the main chute that had been held in place with an AARD. So the main just got pulled out rather than shot .

Having said that, the charges for the NC/drogue were quite scary as they were a significant amount of BP .

Details here FYI: https://forum.ausrocketry.com/viewtopic.php?f=6&t=4612&start=78

There are a lot of opinions on this sort of thing. If you want to try something different and consider it reliable (especially at getting the main out after an off-nominal drogue deploy) after good thought then maybe give it a go

In my opinion, if you have not considered deployment bags as part of your recovery, you might want to give it a go!

If you wish to eject your parachute while using less powder and protecting the chute and harness, use a piston.

Really not needed unless you are doing the extra work for fun. After redesigning the wheel on several rockets I found just folding a nomex blanket over the parachute works awesome.

Parachute liners from Fruity Chutes work really well. They make 6" ones. They are basically a neat Nomex blanket.

Normally a well wrapped nomex burrito should work just fine
I have been using a different ejection design with more advantages than pistons - easier build, NO hot gas reaching the chute, very consistent ejections with smaller BP charges (my 6" L3 used 1.2g BP for a vigorous ejection) chute -18' Rocketman. There is a brief description of the design in myLEVEL 3.pdf

pythonrock said:

Normally a well wrapped nomex burrito should work just fine
I have been using a different ejection design with more advantages than pistons - easier build, NO hot gas reaching the chute, very consistent ejections with smaller BP charges (my 6" L3 used 1.2g BP for a vigorous ejection) chute -18' Rocketman. There is a brief description of the design in myLEVEL 3.pdf

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That is a very interesting design, thanks for sharing!

Moved thread to the recovery forum.