Grimly determined to figure out how to use a short-burning BP motor to initiate secondary deployment of a 5.5x upscale Estes Streak I was wondering whether any data are available (google failed, alas) which correlates the volume of an ideal gas generated as a BP motor burns.
With that information, it *should* be possible to select an appropriate booster BP motor to sufficiently pressurize the forward section and eject the parachute.
Great ! Bring me some !! I need about 40-50 grams of FFFg to finalize the design and fly my Level-1 certification. The problem is I've called every gun shop between Savannah and Jacksonville and nobody is carrying it anymore.
"Too many regulation hassles...use Pyrodex, it works just fine in replica Black Power guns".
Yes it does work just fine, but at chamber pressures far higher than those of an ejection system. Single base (NC) smokeless powder works great in small arms too, for the same reason. The burn rate at low pressure of either is far below BP's, therefore unless you contain it sufficiently in a small volume vessel to force complete combustion in as short a period of time as possible, you can/will have problems. The total gas volume produced by the ejection charge, whether it is loose BP, a booster motor, or Pyrodex or whatever, is just one part of the picture. You can calculate to your heart's content the final pressure in a given free volume with any of these materials if you know the impetus numbers, BUT, the dynamics of the situation are different than a calculation based on an ideal closed system. I've seen a few prangs due to poor implemenation of a Pyrodex ejection charge. Couple the low burn rate with inevitable gas leaks (vents for example, loose couplers etc.), shear pins, yada yada and it's no wonder. However, it can be made to work.
To calculate pressure in your ejection system, take the propellant weight of the motor in question and plug it into one of those utilities that have been floating around the 'net. Bu think along the lines above - a single large grain takes time to combust completely. Idealy, the ejection charge, whatever it is, brings the system up to pressure pretty much immediately, to mitigate problems from vent holes, other gas leaks, cooling etc.
If you have an Estes booster motor you want to use, you could always peel off the paper and grind up the propellant.. you'll get around 10 grams from a "C".. You might want to take that outside and wear lots of protective gear though.
And that is precisely the point. I have a bunch of Estes BP motors in my flight box, ranging from 1/4A through E. Got twelve Aerotech 24mm reload kits for that matter. So what ? The restrictions against modifying motors in any way still applies.
What I need to do is locate a NEFAR member who flies dual-ejection designs and buy about four ounces of FFFg from him.
I don't believe the so-called black powder motors contain black powder, per se. I always understood their composition to be a cast micrograin (zinc+sulphur+binder). I could be completely wrong, of course.
All of the commercial black powder motors (currently Estes & Quest, formerly Apogee, FSI, MPC, and one or two others) use actual black powder in their compsitions. The exact proportions of charcoal, saltpetre, and sulfur used, as well as any processing methods and additional ingredients/binders used, are, of course, trade secrets of each individual company. However, they are all minor variations of standard black powder compositions.
Micrograin (Zn + S) motors, due to their completely different chemical reaction, produce completely different smoke trails. I've seen photos of micrograin launches, and the smoke trails don't look very much like black powder smoke trails (aside from the obvious similarity of simply being a smoke trail in the first place).
for a few examples of micrograin launch photos, especially
The smoke from a micrograin launch is much "whiter", with tinges of yellow from the bright yellow flame. Black powder smoke is usually a dingy grey color, with orange flame and lots of orange "sparks" from still-burning bits of carbon in the exhaust.
Black powder alone dead presses quite well under the right conditions. The Pro38 and 54 receiver/boosters are produced here that way and so are most commercial BP motors. I don't recommend you attempt it without the proper equipment and safeties in place however. Compounding BP is a fine art and there are few companies who can do it safely and consistently especially in volume.
Anthony J. Cesaroni President/CEO Cesaroni Technology/Cesaroni Aerospace