[roc-chat] Re: BP for Deployment of Main Question
- From: Bryan Dierking <bryandierking@xxxxxxxxx>
- To: "roc-chat@xxxxxxxxxxxxx" <roc-chat@xxxxxxxxxxxxx>
- Date: Thu, 8 Dec 2011 16:48:56 -0800
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 :-)
>
>
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