Recovery Systems Detail for the Son of Godzilla and Miss Madison

I've had numerous requests to give some detail to the recovery systems that John Heinze and I used for the Son of Godzilla and Miss Madison rockets. Both of these 'M' powered rockets flew two times each and all flights had flawless recoveries. Both rockets utilized 2-stage recovery (drogue chute/streamer at apogee and BIG parachutes being deployed at a lower altitude), on-board redundant electronics to control deployment (Adept) and a simple but heavy duty recovery system mounting technique. By the way, this is not the ONLY way to obtain reliable recovery of large and high powered rockets. I've seen a good number of other techniques described on the newsgroup rec.models.rockets. And obviously, If you saw any of the flights from BALLS 006 you should have witnessed numerous successful recoveries of VERY large and powerful rockets ('O' power!!). Keep your mind open to new ideas and bring them back to fly again. The Son of Godzilla Weighed in at around 100lbs at lift-off so the recovery system needed to be designed and built to handle extreme physical (not mental) stress. I have a background in rock climbing and have experience in dealing with the equalization of both dynamic and static loads ...uh..er... I fall a lot. We were able to take some ideas from the rock climbing world and apply them to this rocket. We did away with the typical bungee cord (shock cord) and replaced it with about 40' of 8mm perlon (aka rock climbing accessory cord) for first stage deployment. We used 7mm perlon for the Miss Madison. The perlon is known as "dynamic rope", it has some give or stretch to it. It was chosen for two reasons: It's much more supple than 3/8" static rope, (spelunkers use this type of rope almost exclusively) therefore packs better and I had a ton of it laying around. Also the impact forces inflicted by a dynamic rope are much less than with a static rope. I'll leave the explanation of impact forces up to the interested reader. I will list some good references at the bottom of this page. On the first flights of both rockets, the main parachutes deployed just after apogee. This happened because not enough of the dynamic forces were attenuated by the 8mm perlon. The relatively heavy nose cones maintained enough inertia (i=mv) to separate from the airframe and continued to drag the main chutes out with them after separation had reached the end of the perlon (I like run-on sentences). This problem was solved by incorporating sacrificial bungee into the first stage deployment. We added 8' or so of 3/16" bungee in parallel with the 8mm perlon. The idea was for the thin bungee to stretch to it's breaking point and snap, thereby soaking up much of the dynamic forces (inertia) generated by the black powder charges. It worked like a charm! The following two flights followed the expected flight profiles to a "T" (whatever that means). The thin bungee broke at apogee and the main chutes were deployed at approximately 750' AGL. Obviously we used Adept ALTS2-50K devices (or similar). The main (second stage) deployment used approximately 30' of 8mm perlon and no bungee. The recovery system mounts used three equally spaced 1/4" "U" bolts (@ 120 deg separation). To connect these mount points to the 8mm perlon we used a quick link on each "U" bolt and a cordlet (another pesky climbing technique) fashioned out of 9/16" super tape or tubular webbing. Do NOT use flat fashioned out of 9/16" super tape or tubular webbing. Do NOT use flat webbing for this application or even single point mounting. If the webbing gets "on edge" during a high speed deployment, it might just rip your rocket a new...something. The use of tubular webbing will allow any orientation of the webbing over the airframe edge to distribute the forces over the entire width of the webbing. The tubular webbing tends to roll rather than get "on edge". Also, avoid using thin perlon for the cordlet for similar reasons. The cordlet is essentially a large loop of webbing tied with a water knot or double fisherman's. One strand (side) of the loop is run through each of the three quick-links. Then bring the webbing from in-between the quick-links up to a single point and tie a large overhand knot in it. This will equalize at least two mounting points at all times. If any one or two points fail, the rocket will still be connected to the recovery system. This system also reduces the force generated on the airframe edge by reducing the force vector. Obviously this relationship is dependent on how "deep" the mount points are inside the rocket... as you learned in nursery school, sin(90) = 1 and sin(120) = 0.86 a 14% reduction of a normal force to the airframe edge assuming ideal conditions and the obvious assumptions. We used the 3-point mounting system throughout the SOG. I only used the 3-point mounting system on the booster section of the MM. As far as the amount of black powder used, I stick to my empirical formula of 1 gram/200 cubic inches. Volume calculations of a cylinder is as follows: v = (3.14)(r 2)(h) Where:

	3.14 is approximately equivalent to pi
	r = radius of the airframe in inches
	h = height or length of the area to be pressurized in inches
	v = volume in cubic inches