[roc-chat] Re: BP for Deployment of Main Question
- From: Steve Battaglia <stevebotag@xxxxxxxxxxxxxx>
- To: "roc-chat@xxxxxxxxxxxxx" <roc-chat@xxxxxxxxxxxxx>
- Date: Fri, 9 Dec 2011 10:36:11 -0800
Any difference between pyrogen/pyrodex and BP?? tried using pyrogen for
ejection bu it seems to burn slower that BP... any truth to that??
S. Battaglia
310-339-2717
Sent from my Rotary iPhone...
On Dec 9, 2011, at 10:24 AM, Kenneth Brown <ken@xxxxxxxxxxxxx> wrote:
> Spectra
>
> Ken
>
>
> On Dec 9, 2011, at 9:45 AM, Kurt Gugisberg wrote:
>
>> According to Wedge, Bryan should use 75' of shock cord. With that much
>> you could use kite string and it should still be safe. ;-)
>>
>> The question is...should it be nylon or Kevlar kite string.
>>
>> Kurt
>> -----Original Message-----
>> From: Richard Dierking
>> Sent: Dec 9, 2011 9:30 AM
>> To: roc-chat@xxxxxxxxxxxxx
>> Subject: [roc-chat] Re: BP for Deployment of Main Question
>>
>> Bryan's currently in school otherwise he would answer this himself. Yes, he
>> used a parachute for the test and a shorter/lighter shock cord (10', 1000 lb
>> vs. 15', 2300 lb). The cord was attached to both parts. He might also be
>> extending the shock cord more than 15' for the flight. The ground test was
>> energetic and the parachute was deployed nicely.
>>
>> Richard
>> > Date: Fri, 9 Dec 2011 09:22:19 -0800
>> > From: dmccue@xxxxxxx
>> > To: roc-chat@xxxxxxxxxxxxx
>> > Subject: [roc-chat] Re: BP for Deployment of Main Question
>> >
>> > Yay! I hope you also try with the parachute in there as well - it would
>> > suck to have the sections separate, but no parachute ejection. (I don't
>> > know if the 'chute is attached to both parts, or only one. If attached to
>> > both airframe sections, the bridles will puil it out for sure...)
>> >
>> > -Dave McCue
>> >
>> > On Thu, 8 Dec 2011, Bryan Dierking wrote:
>> >
>> > > Richard and I just did a ground test with three 2-56 sheer pins and 3.5
>> > > grams in one of the canisters - worked like a charm.
>> > >
>> > > Bryan Dierking
>> > >
>> > >
>> > > Le Dec 8, 2011 à 16:07, David.P.Smith@xxxxxxx a écrit :
>> > >
>> > >> Using the table on the web page I listed it came out to 4 grams. His
>> > >> table has worked well for me in the past, but I haven't used it on a
>> > >> 7.5 inch tube.
>> > >>
>> > >> Using the bottom formula on that same page and shooting for 10 psid I
>> > >> came up with 5.87 grams. Intuitively this seems closer. Of course there
>> > >> are various assumptions made that can only be validated with testing.
>> > >>
>> > >> One assumption in all these equations is 100% conversion of the solid
>> > >> black powder into gas. That seems very optimistic. With tightly wrapped
>> > >> charges as described by Dave McCue used with shear pins to hold the
>> > >> parts together a bit longer, you can produce a pretty substantial
>> > >> pressure in the tube before things start to actually move apart.
>> > >>
>> > >> Ground testing seems like a very good idea to me...
>> > >>
>> > >> David P Smith
>> > >> NAR 78668 L2
>> > >> Amateur Extra, W6DPS
>> > >>
>> > >> The opinions expressed in this email are my own and do not necessarily
>> > >> represent the positions, strategies or opinions of Southern California
>> > >> Edison, its parent company Edison International, or any of their
>> > >> affiliates.
>> > >>
>> > >>
>> > >>
>> > >>
>> > >>
>> > >> From: Richard Dierking <redierking@xxxxxxxxxxx>
>> > >> To: "roc-chat@xxxxxxxxxxxxx" <roc-chat@xxxxxxxxxxxxx>
>> > >> Date: 12/08/2011 12:14 PM
>> > >> Subject: [roc-chat] Re: BP for Deployment of Main Question
>> > >> Sent by: roc-chat-bounce@xxxxxxxxxxxxx
>> > >>
>> > >>
>> > >>
>> > >> Let me ask this first: did you come up with 4 grams per cartridge or 4
>> > >> grams total?
>> > >>
>> > >> Sent from my iPhone
>> > >>
>> > >> On Dec 8, 2011, at 12:07 PM, David.P.Smith@xxxxxxx wrote:
>> > >>
>> > >> Large areas can generate very large force if you keep the pressure
>> > >> constant.
>> > >>
>> > >> Think of it this way. For the same length of tube, the diameter
>> > >> increases the area and volume by the square of the increase in diameter.
>> > >>
>> > >> Round off a 4 inch rocket tube to 12.5 square inches times 24 inches in
>> > >> length, the volume is 300 cubic inches.
>> > >>
>> > >> Round off an 8 inch rocket tube to 50 square inches times 24 inches,
>> > >> the volume is 1200 cubic inches. Four times the volume of the 4 inch.
>> > >>
>> > >> So, if a 4 inch diameter body tube 2 feet long is pressurized to 20
>> > >> psid with a given charge, then an 8 inch body tube 2 feet long would be
>> > >> pressurized to 5 psid.
>> > >>
>> > >> 12.5 times 20 psid comes out to 250 pounds of ejection force. 50 times
>> > >> 5 comes out to 250 pounds of ejection force.
>> > >>
>> > >> So for a given ejection charge, in a range of body tube diameters, you
>> > >> get the same ejection force.
>> > >>
>> > >> On the other hand, increasing the charge to four time the 4 inch
>> > >> charge, gives us 1000 pounds of ejection force in the 8 inch rocket.
>> > >> that may be a bit much...
>> > >>
>> > >> If you just stick to the formulae published on some sites, you just
>> > >> keep increasing the charge size proportional to the increase in volume,
>> > >> which may over stress your shock cord.
>> > >>
>> > >> So how much force do you need to make the rocket come apart?
>> > >>
>> > >> Do you plan to ground test at all?
>> > >>
>> > >> David P Smith
>> > >> NAR 78668 L2
>> > >> Amateur Extra, W6DPS
>> > >>
>> > >> The opinions expressed in this email are my own and do not necessarily
>> > >> represent the positions, strategies or opinions of Southern California
>> > >> Edison, its parent company Edison International, or any of their
>> > >> affiliates.
>> > >>
>> > >>
>> > >>
>> > >>
>> > >>
>> > >> From: Richard Dierking <redierking@xxxxxxxxxxx>
>> > >> To: "roc-chat@xxxxxxxxxxxxx" <roc-chat@xxxxxxxxxxxxx>
>> > >> Date: 12/08/2011 11:36 AM
>> > >> Subject: [roc-chat] Re: BP for Deployment of Main Question
>> > >> Sent by: roc-chat-bounce@xxxxxxxxxxxxx
>> > >>
>> > >>
>> > >>
>> > >> Wow, 4 grams BP is about one half what we were coming up using the web
>> > >> and a reference book I had.
>> > >> Richard
>> > >> Sent from my iPhone
>> > >>
>> > >> On Dec 8, 2011, at 11:26 AM, "Chris J Kobel" <Chris.J.Kobel@xxxxxxxx>
>> > >> wrote:
>> > >>
>> > >> I would second David's recommendation of 4 grams, which should give
>> > >> about 200 lbs of ejection force at 5000 AGL, with the 3 2-56 shear pins
>> > >> requiring about 100 lbf to overcome.
>> > >>
>> > >> Chris
>> > >>
>> > >>
>> > >>
>> > >> From: David.P.Smith@xxxxxxx
>> > >> To: roc-chat@xxxxxxxxxxxxx
>> > >> Date: 12/08/2011 11:10 AM
>> > >> Subject: [roc-chat] Re: BP for Deployment of Main Question
>> > >> Sent by: roc-chat-bounce@xxxxxxxxxxxxx
>> > >>
>> > >>
>> > >>
>> > >> I use the "rule of thumb" on this site.
>> > >>
>> > >> http://www.vernk.com/EjectionChargeSizing.htm
>> > >>
>> > >> So, by that site you would need 4 grams of ffffg black powder.
>> > >>
>> > >> Remember that you are looking at a lot of area to apply the ejection
>> > >> pressure to. A 7.5 inch circle had a bit over 23.5 square inches of
>> > >> are. So 10 psid will give you 235 pounds of ejection force.
>> > >>
>> > >> What is the shear force rating for your pins?
>> > >>
>> > >> David P Smith
>> > >> NAR 78668 L2
>> > >> Amateur Extra, W6DPS
>> > >> The opinions expressed in this email are my own and do not necessarily
>> > >> represent the positions, strategies or opinions of Southern California
>> > >> Edison, its parent company Edison International, or any of their
>> > >> affiliates.
>> > >>
>> > >>
>> > >>
>> > >>
>> > >>
>> > >> From: Richard Dierking <redierking@xxxxxxxxxxx>
>> > >> To: <roc-chat@xxxxxxxxxxxxx>
>> > >> Date: 12/08/2011 10:10 AM
>> > >> Subject: [roc-chat] BP for Deployment of Main Question
>> > >> Sent by: roc-chat-bounce@xxxxxxxxxxxxx
>> > >>
>> > >>
>> > >>
>> > >> 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 :-)
>> > >>
>> > >>
>> > >> -- ROC-Chat mailing list roc-chat@xxxxxxxxxxxxx
>> > >> //www.freelists.org/list/roc-chat
>> > >> -- ROC-Chat mailing list roc-chat@xxxxxxxxxxxxx
>> > >> //www.freelists.org/list/roc-chat
>> > >> -- ROC-Chat mailing list roc-chat@xxxxxxxxxxxxx
>> > >> //www.freelists.org/list/roc-chat
>> > >
>> -- ROC-Chat mailing list roc-chat@xxxxxxxxxxxxx
>> //www.freelists.org/list/roc-chat
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>
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