[roc-chat] Re: BP for Deployment of Main Question
- From: Kurt Gugisberg <kurtgug@xxxxxxxxxxxxx>
- To: roc-chat@xxxxxxxxxxxxx
- Date: Thu, 8 Dec 2011 17:09:21 -0800 (GMT-08:00)
Kevin,
You have learned well, little grasshopper.
-----Original Message-----
>From: Kevin Lane <krlane@xxxxxxx>
>Sent: Dec 8, 2011 2:33 PM
>To: roc-chat@xxxxxxxxxxxxx
>Subject: [roc-chat] Re: BP for Deployment of Main Question
>
>I thought the rule of thumb was 1 gram per inch of body tube dia...
>so 7.5 grams should be fine...no ground testing needed.
>Kurt told me this years ago and it has worked well.
>Make sure you use a long shock cord too :-)
>
>Kevin Lane
>HVAC Supervisor
>UC Irvine Facilities Management
>krlane@xxxxxxx
>(949) 824-6367
>
>
>
>Dave McCue wrote:
>> If 4 grams seems not to be enough, use more! :-)
>>
>> I agree, with a large empty volume like you describe, that will take
>> more BP to pressureize. However, please remember that the area of your
>> 7.5" airframe is much more than your 4" airframe. As others have said,
>> that will give more area for the pressure to push on.
>>
>> I have tested on the ground by putting the rocket on it's side, with
>> the bottom section backstopped by placing it against a wheel of my
>> car. I put an old blanket between the rocket and the wheel to avoid
>> breaking things. I use an old towel (or a mound of dirt) to elevate
>> the bottom section near the joint I am going to test. The top section
>> is now lifted just a few inches off the ground, and won't go very far
>> when it pops off.
>>
>> I prep the charge and run the match wire out through one of the bay's
>> vent holes and add enough wire to get myself safely away. Touch the
>> wires to a 9V battery and see what happens!
>>
>> I think you may be right, 7 grams or so is what you need, but try it
>> on the ground if you can...you may be surprised at what you find out!
>>
>> Be sure to let us all know what you did and how it worked -
>>
>> By the way, I use Goex FFFFg BP for my deployment work.
>>
>> Good luck,
>> Dave
>>
>> On Thu, 8 Dec 2011, Richard Dierking wrote:
>>
>>>
>>> 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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