Single tube for dual deploy

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drew
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Single tube for dual deploy

Postby drew » Tue Aug 23, 2011 6:00 pm

Hello all,

I've been thinking about 38mm minimum diameter high altitude/speed designs as of late, specifically in terms of single tube dual deployment setups. I've picked up a 38mm Mongoose kit as a basis for this project. I'm planning on flying at WWW 2012 with the biggest motor I can find (whilst staying under the waver) after hacking it up to make it as small as possible.

Basically I'm looking for ideas and comments in reference to single break dual deploy setups. I'd rather not use the Mariah style "shotgun" system, instead I'm leaning more towards Adrian Adamson's designs. Here's a photo of his 38mm custom rocket showing the single break dual deploy setup he uses.

http://www.rocketryplanet.com/images/stories/features/3087/5.jpg

With that in mind I'm pretty flexible in terms of the system design. Ideally I'm looking for input from you all in terms of what you think would be the optimum configuration for this type of deployment system. Any comments would be appreciated.

drew
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Re: Single tube for dual deploy

Postby PK » Tue Aug 23, 2011 8:10 pm

Main behind a piston that gets held in by some nylon line wrapped around a 1/4W resistor. At 1000' heat that resistor.
This technique gets used all the time in military and aero stuff. I can show you some examples.
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Re: Single tube for dual deploy

Postby Kryten » Wed Aug 24, 2011 11:28 am

I seem to remember something similar on the Apogee site, using a split AV bay containing the main chute, held together by string/nylon, which used an igniter to burn through.
I can't find the link, though
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Re: Single tube for dual deploy

Postby cryoscum » Wed Aug 24, 2011 10:13 pm

Drew

In recent times (since Williams) I've been using a single 38mm tube, dual deployment rocket with a fixed bulkhead halfway down and the recovery harness fixed to it, in both directions. The bulkhead stays in place with some plastic rivets with PB charges either side of it, ignited from the nose cone altimeter. At apogee you eject the friction fitted motor casing out the back and at 800 feet the main out the front - absolutely dead simple, no fancy mechanisms, multiple tubes within tubes etc etc. Have flown the prototype several times (see onboard snappies from 14 August QRS launch).

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Re: Single tube for dual deploy

Postby strud » Thu Aug 25, 2011 7:33 am

There's also Dave Groves' (aka Pink Hat) very nice 38mm dual deploy design. I've yet to see something neater and as functional !

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Re: Single tube for dual deploy

Postby cryoscum » Thu Aug 25, 2011 3:31 pm

Do tell, Strud. We haven't all seen it...
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Re: Single tube for dual deploy

Postby Sumo310 » Thu Aug 25, 2011 4:20 pm

You didn't see it?
Its a 1/2" tube inside of the body tube, drogueless deployment at apogee (nosecone attached to a harness only), and the main charge pushes the chute out of the inner tube.
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Re: Single tube for dual deploy

Postby drew » Thu Aug 25, 2011 5:51 pm

Yea, Pink Hat's rocket and Adrian A.'s design on Rocketry Planet got me thinking about this quite a bit. PK, I'm keen on having a look at the system you've described. Nic, I wasn't aware you were kicking out your casing at apogee. That's something I've yet to consider (that is until now!). I'm going to have to investigate all these options.

Any chance of getting a photo of Dave's design? I remember looking at it at Williams before he went mach 2.6+. I'm now kicking myself that I didn't ask to take a photo at the time.
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Re: Single tube for dual deploy

Postby cryoscum » Thu Aug 25, 2011 6:29 pm

viewtopic.php?f=13&t=3195

Drew, this link has a snappy taken by the onboard camera from a recent launch. The casing is a 38/360 with RAS flying an H148R, ejected out the back at apogee. Whole rocket was glass weighing 390g (excl motor of course).

I like the idea of the inner tube, but I suppose it adds weight that you may not want. At least its all in the front. My setup has the bulkhead, weighing probably 60g (coupler tube, plywood bulkhead and 2mm SS cable both sides to hook on to) is pretty much near the CG - not bad, but also not helping... Be interesting to do a blow-by-blow weight comparison...
AMRS L3 | NAR L3 | QRS 089 | MDRA 224
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Total impulse for 2016: 32,458 Ns (thus far)
Total impulse for 2015: 84,231 Ns
Total impulse for 2014: 40,757 Ns
Total impulse for 2013: 62,927 Ns

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Re: Single tube for dual deploy

Postby PK » Thu Aug 25, 2011 6:41 pm

cryoscum wrote:Be interesting to do a blow-by-blow weight comparison...

Don't get too fixated on weight. Anything skinney going high enough to need dual deployment will probably benefit from some extra mass.
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Re: Single tube for dual deploy

Postby hybridhighflyer » Thu Aug 25, 2011 6:54 pm

F=M*A

v = q*[1-exp(-x*t)] / [1+exp(-x*t)]

**Cough**

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Re: Single tube for dual deploy

Postby Andrew Burns » Thu Aug 25, 2011 7:20 pm

Yeah except that your equation doesn't factor in aero drag losses which increase with the square of velocity. Any configuration of rocket will have a best-altitude weight (PK is using altitude as the yardstick here), if the rocket weighs less than that weight it will go faster and burn off too much energy as drag, if it weighs more it will go slower and burn off energy to gravity losses. Most minimum diameter little pointy rocket things are probably well bellow their best-altitude weight (of course if speed is your goal then less weight is generally better).

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Re: Single tube for dual deploy

Postby hybridhighflyer » Thu Aug 25, 2011 7:33 pm

You are correct andrew. I am just talking about speed not height.

My undersatanding of this post was "Max speed in shortest airspace".


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