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Thanks! this helps!
I would put the eMatch at the top of the BP, closest to the exit. Possibly doesn't matter as much for small charges and low altitudes, but I don't have statistical data for that, just a hunch. I will keep putting my eMatch closest to the exit for future flights, even though I have previously been known to use it at the pointy end of the centrifuge vials with no failures. YMMV.Interesting... so would that mean you would recommend that if one was using the Eppendorf tube method as mccordmw was suggesting, that the e-match would be at the top of the BP if you used such a method? Or were you referring to a more cylindrical charge well?
Mark, this is great! Love this calculator.Steves explanation is correct. That said, for my money I really liked the explanation and calculator that existed on ROL Infocentral. So happens I grabbed the page along with the code. Username and password are both guest
https://www.rocketryfiles.com/files/FlightSimulation/BP_sizing/Black Powder Sizing.htm
Sent from my iPhone using Rocketry Forum
As far as measuring goes, 1cc of 4f black powder is close enough to 1g. That's based on 15.xx grain per gram and 1cc ~= 1cc
The following 2 videos are borrowed from Mendal....Rocket Junkies
The first video is showing an 8 gram charge with the ematch at the bottom of the charge canister...
This next video is with the ematch on top of the charge.
Tony
This is how I make mine too, except I hot glue both ends. Jim's write up on high altitude deployment is great. This style gives a very energetic burn.Below is a photo that shows how I've recently been doing my high altitude charges holders.
The following 2 videos are borrowed from Mendal....Rocket Junkies
The first video is showing an 8 gram charge with the ematch at the bottom of the charge canister...
This next video is with the ematch on top of the charge.
... As always,,, ground test. once you find what works for you. Don't change it. If you change anything..ground test again!
Tony
Well that's possibly the single most information-dense post I've run into on TRF.I have been reworking some old nomograms I made some years back. I will post them here for posterity. Due to the size of most peoples printers, I ended up making two different charts one for large diameter and one for small diameter rockets.
The idea behind this is the ability to refer on paper to a calculation method.
Since I have redone this, it is possible to provide copies with custom isopleths.
As stated, there are online calculators that will give you a starting point, but ground testing is always your best bet.
We found that online calculators gave us a much larger charge than necessary. Our rocket is quite large - 12.75" in diameter - which is part of [t]he reason.
In the end it boils down to a few variables:
Pressure produced by a given amount of BP in a known volume
Surface area that said pressure acts upon (that of NC bulkhead)
Amount of force needed to separate NC (calculated from shear pin size/number)
Thanks! Couple more questions now. ... Do I just figure it as is, empty, or with all the shock cord, and parachute and Nomex?
Thanks again for the help!
Ignore the shock cord and chute, basically you are looking at theempty space. I would use top of CR to next solid bulkhead as length, ignoring any motor tube sticking through the CR.
Steves explanation is correct. That said, for my money I really liked the explanation and calculator that existed on ROL Infocentral. So happens I grabbed the page along with the code. Username and password are both guest
https://www.rocketryfiles.com/files/FlightSimulation/BP_sizing/Black Powder Sizing.htm
Oh, while looking for the source, I actually found a setup file for VCT. Might work better. If anyone can get this to work on something later than Win7, I'd like to hear it.
Waitaminit - in my search for source, I just found it working on a Win10 computer - strange.
That's a really neat resource!
How did you determine the breaking points for the number of shear pins? All the forces associated look higher than any I've seen for 2-56
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