Nick, Thanks again for taking the time to answer my prior questions with regards to the contest, and prompting me about my entry. I took some time to finish it up. Please find attached my entry for the EMRR Virtual Rocket Contest #3. I call it "Eggscalibur" If someone's already copped that name, you can always refer to it by my second choice... "Bill's Most Eggscellent Adventure" ;-) First I'd like to say how much I enjoyed this. It certainly was a lot more fun and challenging than I expected. I learned a bit about rocket design, a LOT about RockSim, and a lot on what affects a rocket in flight and in recovery. Although, on the latter point I probably have more questions than ever now. I wish I had more time to explore some of the things I uncovered! I'd like to share a few comments about my rocket and the whole process. The Design.... Early in the design process I opted to pursue a cluster approach (4x 18mm). I figured this gave me good opportunity for max thrust off the rod, lots of flexibility in motor selection and a wide range of impulses; from B (4x 1/2 A6's) through F (4x D's). I also decided to place the BT70 egg-bay in the middle and tried to place the egg as close to the CG as I could. That way fluctuations in the egg mass would have little effect on the CP. I'm not sure (and didn't confirm it), but I felt this would have less impact on altitude fluctuations, any fluctuations would be attributable only to mass fluctuations and NOT CP movement. In hindsight, because of the compromises I had to make in the exact altitude event, I don't know if it made any difference. But, I figured it didn't hurt anything. I opted for 3 BT diameters: 6" of BT70 2" of BT101 18" of BT60. The BT70 is actually 2 pieces of BT70 joined by a coupler. This is the separation point when the rocket deploys for recovery. The forward section of BT70 (forward of the bulkhead) contains the egg-bay, and is accessible by removing the balsa transition. The aft section of BT70 contains the shock cord, chute, etc. The BT101 contains the 4x 18mm motor cluster. I didn't need to have this large of diameter BT, but it didn't hurt me in the exact altitude event and I figured the extra drag only helped me in the "chickens don't fly" event. Construction.... Not having a supply of BT70 or BT101 tubing I didn't try to build it. Yet, while this was a virtual rocket, I went through great pains to ensure that this was more than a "paper rocket" (no pun intended). The balsa NC and transition have adequate shoulders so that they can do their job. The CR's are 1/8" balsa (this is modelled after my success at gluing 1/16" balsa at perpendicular grain patterns in creating custom CR's). The egg-bay aft bulkhead anchors the recovery system and is solid enough being built with aircraft ply. A big concern I had was how to connect the BT101 BT with it's paper transition cone to the BT70 BT and yet keep it structurally strong. I did a couple of things. While the aft boat-tail transition is a single wrap of 110 lb cardstock, the forward transition is a double thickness (for extra rigidity). Where that transition meets the BT70 tube I inserted a sort of balsa CR-coupling-ring, to provide more gluing surface to ensure a good glue joint. I also choose to place 6 fins around the BT's, and the fins run the length of the BT101 BT plus its aft and forward transitions PLUS runs up along the length of BT70 to the BT70 separation point. The fins provide a strong rib or framework that allows the tubes to remain in place. And finally, in recognition of the complex fin pattern, its short span in locations, and the fact that some of the fin hangs "out back" behind the rocket, I wanted to ensure a strong fin that wouldn't snap on landing. If I was building it I would go to a silkspanned or paper covered fin for strength. Not able to quite do that with the available RockSim materials, I opted for balsa ply. This gives me the approximate strength and weight that my own method would provide. Virtual.... yes. Buildable, flyable, and recoverable (to fly again).... most definitely. For the simulations: Event #1 was my starting point. Come up with a design and a set of motors that put me close, then tweak the rod angle and the rocket design (more draggy, less draggy, etc.) to sim as close as possible to 1500 with a middle of the range 60g egg mass. That was the easy part, my problems manifested themselves in recovery. I had to keep my chute size large enough to get a descent rate slower than 13 ft/sec but not too large as to allow the rocket to drift or thermal outside the landing area. But the real problem was when running the simulation the rocket would appear to catch a "downdraft". Sometimes randomly, or always after passing through a thermal. The rocket would get sucked downwards at velocities greater than 13 ft./sec. I simply didn't have enough flight time or altitude to ride out the downdraft and would land at greater than 13 ft./sec. and essentially DQ. In fact, when running the simulation ten times in a row, I would DQ 60% to 70% of the time. That was just too high a probability to risk having it DQ on a single flight attempt. I couldn't figure out how to avoid this. I thought about redesigning the whole rocket and making it much lighter. But I reasoned it wouldn't help; I would still be targeting for 1500 ft. max altitude and still targeting for the same descent velocity. I didn't know what to do. Purely by accident, when playing around with motor combinations and rod angles, I found that if I selected a larger impulse and angled the rod (to keep it under 1500 ft) my DQ's due to this downdraft effect went down. It seemed to be tied to the deploy velocity. The higher the deploy velocity, the less chance I had in DQ'ing. I was never able to reduce it to zero, but I was able to drop it substantially. I even went back to an earlier design (single motor, egg at forward end) and was able to reproduce the same effect. Low deploy velocity = high DQ rage. High deploy velocity = low DQ rate. The penalty paid, was that my altitude lost accuracy for high deployment rates. I can't explain any of this, certainly don't understand it, and I wonder if this is a true reflection of "reality" or just some quirk of RockSim'ism (v7.03). But it certainly was there. My choice was simple, opt for high accuracy and high probability of DQ'ing, or opt for low probability to DQ and accept a poor accuracy. In the end I tried to optimize a compromise, saving some sort of accuracy and risking some element of DQ'ing. Sometimes, you just don't have control.... just like in real life! Motors for Event #1: Motors 1-4: D21-7 Rod angle: -28 degrees Event #3 was easy. Since my motor configuration was set, I just picked the smallest clustered impulse available to keep altitude low and took rod speed at whatever it came out. Motors for Event #3: Motors 1-4: 1/2 A6-2 Event #4 got interesting again. My initial approach was driven by the limit of a 50 ft/sec deploy velocity. Under those conditions the simultaneous targets of high rod speed, long flight time, and close to the pad just couldn't be met. When this was changed to a "RockSim determined deploy failure" it gave me a whole new direction. RockSim doesn't really seem to care about the deploy velocity. Or if it does, only the vertical component. I was able to have deploy velocities in the 80 ft/sec range show a deploy failure (little downward black arrow in the green parachute) when deployment happened after apogee. But, if I kept deployment at apogee, RockSim allowed any deployment velocity, or so it seemed. I actually gave up trying to get RockSim to DQ a deployment once I got beyond 160 ft/sec! My tactic changed to launching off the rod as fast as possible (high initial thrust); sending it as high or far as I could (high impulse) to maximize flight time and angling it upwind and picking a rod angle that would allow it to deploy at apogee and drift back to the vicinity of the pad. For Event #4a (wind 2-7 MPH) I went for high impulse and maximum upwind distance. Motors for Event #4a: Motors 1-4: D24T-7 Rod angle: -31 degrees With the wind getting stronger for Event #4b (wind 5-10 MPH) my high-thrust short-burn motors couldn't carry it far enough upwind, and the return to rod carried it well past the rod and dangerously to going outside the landing area. So, I decided to drop the pursuit of high rod velocity, yet still opted for max upwind placement. I went to low-thrust but long burning motors. Picking a rod angle that would again deploy at apogee and return me back somewhere near the rod. Opting for decent flight time and landing placement. Motors for Event #4b: Motors 1-4: D3-3 Rod angle: -27.5 degrees And finally with the highest wind velocity, Event #4c, I felt there was just too much wind. I threw the idea of high rod velocity and long flight times out the window, and just opted for accuracy. Trying to score well by coming back real close to the pad. Attempting a sort of lob shot, keeping the flight low and short to minimize the effect of wind and/or thermals, and coming up with a rod angle that brought me close to home. Motors for Event #4c: Motors 1-4: 1/2 A6-2 Rod angle: -26.5 degrees To summarize: Event #1: Motors 1-4: D21-7 Rod angle: -28 degrees Event #3: Motors 1-4: 1/2 A6-2 Event #4a (wind 2-7 MPH): Motors 1-4: D24T-7 Rod angle: -31 degrees Event #4b (wind 5-10 MPH): Motors 1-4: D3-3 Rod angle: -27.5 degrees Event #4c (wind 7-12 MPH): Motors 1-4: 1/2 A6-2 Rod angle: -26.5 degrees And... before I forget, all my motors are inserted with 1/4" overhang (not the RockSim 1/2" default). Sorry, if all of this was all a bit wordy, but I did want to share my experiences. It's been a fascinating and fun project. Thanks and take care. .... Bill p.s. My wife and daughter would be distressed if I didn't comment that THEY selected the colour scheme.