[roc-chat] Re: BP for Deployment of Main Question

Dave: The charges are in 3/4" PVC schedule pipe and will be taped on the 
business end.  The parachute's 10' diameter and shouldn't take up that much 
room.  The shock cord is 9/16" nylon, 15' long, 2,300 lb test. I really don't 
think that 4 grams is enough.  I usually use 1.5 to 2 grams for 4" diameter 
with the same number of 2-56 shear pins and I've had no problems.  My gut's 
telling me that 4 grams of BP is not enough. Richard > Date: Thu, 8 Dec 2011 
13:21:02 -0800
> From: dmccue@xxxxxxx
> To: roc-chat@xxxxxxxxxxxxx
> CC: dmccue@xxxxxxx
> Subject: [roc-chat] Re: BP for Deployment of Main Question
> 
> I'm afraid I don't have a simple number to give to you, because there are 
> some variables that I don't know. (I haven't been following this thread 
> since the beginning, sorry if the info has been poseted.) My first two 
> questions are:
> 
> How much of the volume is occupied by the parachute and deployment bag -
> 
> How is (are) the BP charge confined (what contains the charge) -
> 
> These are important to me because I want to know what volume is being 
> pressurised, and I want to know how quickly the BP charge will burn.
> 
> A bagged parachute will not compress fully under the pressure spike that 
> developes when the charge goes off, so the volume of the compartment is 
> less than an empty recovery bay. This is good, since higher pressure will 
> result.
> 
> The container for the BP matters because a container that offers 
> resistance to the gas being generated right after the BP is ignited will 
> make the BP burn faster. Taking advantage of his will give you higher peak 
> pressure.
> 
> My BP charges are done on the cheap, by measuring the BP into a tiny 
> (1"x1.5" or slightly larger) zip seal poly bag. The head of the match is 
> positioned in the pile of BP and the zip seal is closed as far as it can 
> go with the match wire coming through. I then tap the BP into a bottom 
> corner and fold the bag at a 45 degree angle to trap the BP and matchhead. 
> A piece of masking tape keeps the bag folded.
> 
> The final step is critical: I wrap the whole thing in a layer of 2" wide 
> aluminum foil adhesive tape. This step constrains the burning BP a tiny 
> fraction of a second after the match lights; the result is a good Bang! 
> instead of a sad Whoosh. Peak pressure is higher, and things come apart 
> with enthusiasm!
> 
> Done this way, a 4 gram charge should work nicely (assuming a parachute 
> occupies most of the bay's volume) but you could go to 7 grams for a 
> Gugisberg-class deployment - :-)
> 
> For other projects, I have fabricated BP holder cups out of copper pipe end 
> caps and mounted one or more of these in the bottom of a bay. I measure in 
> the BP, paper towel wadding for the remaining volume, then seal with the 
> aluminum foil tape. Works a peach!
> 
> -Dave Mc, who always tests on the ground before flight!
> 
> On Thu, 8 Dec 2011, Richard Dierking wrote:
> 
> > So Dave, how much BP would you suggest for a 7.5" diameter x 24" long 
> > compartment with three 2-56 shear pins?
> > Richard
> >
> > Sent from my iPhone
> >
> > On Dec 8, 2011, at 12:19 PM, "Dave McCue" <dmccue@xxxxxxx> wrote:
> >
> >> Please remember that electric match makers alway say to put matches in 
> >> series - it takes no more than a 1.5V AA cell to light one, so putting two 
> >> or three in series is no problem. THis also solves the problem of 
> >> monitoring two or more matches, sine a loss of continuity anywhere will be 
> >> detected by the electronics.
> >>
> >> I do series match wiring all the time when I use multiple ematches to 
> >> light big liquid propulsion engines. See links below:
> >>
> >> http://www.youtube.com/watch?v=FlkMiCtCxg0&feature=related
> >>
> >> http://www.youtube.com/watch?v=jOiaxfGpudM
> >>
> >> You can also see the unusual recovery system I came up with for these 
> >> rockets: side deployed! This is because the rocket is big and heavy, and 
> >> needs to land on it's side to avoid unplanned damage; we assume we will 
> >> break two fins upon landing.
> >>
> >> By the way, the big 1000 square-foot parachute is deployed by BP charges 
> >> that push out the pilot chute, with HPR recovery electronics making the 
> >> decisions. This was one of several low altitude flights to test the 
> >> recovery system.
> >>
> >> Dave McCue
> >>
> >> On Thu, 8 Dec 2011, Richard Dierking wrote:
> >>
> >>>
> >>> One possible failure mode:  If it's in parallel, if one of the matches is 
> >>> bad and doesn't have continuity, you will not know, because the altimeter 
> >>> will detect continuity in the second and indicate that everything looks 
> >>> OK.  So one canister would go, but probably not be enough BP for a 
> >>> successful deployment.   We tested two matches in series yesterday, and 
> >>> they both went fine.  I've been using series for airstarts and haven't 
> >>> had a problem (up to 4 engines).  I thought people were crazy when I 
> >>> first heard about using series, but when a match lights the "plasma ball" 
> >>> becomes very conductive for a moment.  However, I have not used series 
> >>> for deployment charges, so thought it would be a good idea to hear from 
> >>> people that had experience with this. Richard > From: xsive.guy@xxxxxxxxx
> >>>> Date: Thu, 8 Dec 2011 10:39:46 -0800
> >>>> Subject: [roc-chat] Re: BP for Deployment of Main Question
> >>>> To: roc-chat@xxxxxxxxxxxxx
> >>>>
> >>>> Definitely in parallel.  Otherwise, when the first one burns out the
> >>>> rest would stop getting current.  By wiring them in parallel even
> >>>> after the first one goes the rest continue to get current.
> >>>>
> >>>> I'd like to know the answers to your other questions though.
> >>>>
> >>>> Thanks,
> >>>> Mike
> >>>>
> >>>> On Thu, Dec 8, 2011 at 10:09 AM, Richard Dierking
> >>>> <redierking@xxxxxxxxxxx> wrote:
> >>>>> Say your main deployment section is 7.5" diameter, 24" long and using 
> >>>>> three
> >>>>> (3) 2-56 nylon shear pins.  How much BP?
> >>>>>
> >>>>> Also, what's the advantage of using two or more deployment canisters 
> >>>>> instead
> >>>>> of just one?  For multiple canisters, would you wire in series or 
> >>>>> parallel?
> >>>>> (One 9 volt battery and Perfectflite WD altimeter with main deployment 
> >>>>> at
> >>>>> 1100'.)
> >>>>>
> >>>>> Richard Dierking
> >>>>> BTW: Kurt, we're not intending to turn the nose into a second stage :-)
> >>>>>
> >>>>>
> >>>>
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> >>>>
> >>>
> >>
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