Science Club Launch - October 29, 2013
Yesterday afternoon was the science club "event" at my daughter Taylor's high school. It's not a science fair... there's no competition or judging. Instead, it's a show for the younger (elementary school) kids, to try to give them an interest in science.
So Taylor and her project partner decided to do a rocketry display, and fly a few rockets. You may recall that a few years ago, Justin did the very same thing, using my large launch stand and a mix of some of his and some of my rockets; but, given the high chance of rain today, I decided to send a basic Estes stand and my best handmade single-position launch controller. Even better, this time I got to attend. It was about 55°, the sky was overcast, and the air heavy and humid, but there was adequate light and the wind was manageable. And it didn't rain until after we were done. We took six rockets: Taylor's Quest Screamin' Demon and Estes Viking, my Mo' Skeeter, Baby Bertha, and Betsy (now rigged for a gum-cam), and a rocket Taylor and her partner built. The latter rocket was kitbashed from a combination of Baby Bertha fins, a long plastic rounded-ogive nosecone from some Estes kit, and the remaining components of a Big Bertha pulled from my parts stock. For convenience, I'm just going to refer to that last rocket as a Big Bertha, since they never named it. They went out and launched three times, with two flights each time. The first group started with my Baby Bertha on an A8-3; it didn't make it as high as I would have expected, then didn't deploy its chute until it was under 5' from the ground. It suffered a nasty ding to the upper end of the sustainer, and the inside of the tube looked toasted; I'll probably repair it with a coupler and some fresh tube to replace the damaged portion. The second flight of the second group was Taylor's Screamin' Demon on a B6-4; it was a fast, high flight, but the deployment was a bit late; still, it was recovered undamaged and will fly again. The second group started with the Big Bertha on a B6-4. It went up nicely, deployed late, and recovered near enough to the launch stand that one of the onlookers was able to catch it. Next they flew Taylor's Viking on a Quest A6-4; this is the only flight that deployed near apogee, which makes sense given the high density of the air... it really should have been an A8-5, but I'm short on them so I decided to try the A6-4 instead. The rocket deployed perfectly and recovered in the grass near the launch stand. The last group started with my Mo' Skeeter on a B6-4 (as usual). Despite a slightly late deployment, it recovered well. It appeared that it was going to drift to the roof of the school, but it took a bit of a "hop" as it approached, cleared the roof edge, and landed in a rose bush. I was able to retrieve it from the bush without damage to either the rocket or myself. The last flight of the day was the Big Bertha on a C6-5 (requested by Taylor). It deployed about a second after apogee, and the chute and nose cone separated from the sustainer; though it looked like the sustainer might survive the recovery, it fell far from the pad and was not found. The nose cone drifted away on the 16" chute I had given them, and so the whole rocket was lost. I elected not to fly Betsy, as I didn't want to run the risk of losing my camera in the wind. A prudent precaution, I think. Still, considering the weather conditions, and the fun had by all, I consider it a good flight. And who knows? They may do it again next year. |
I'm sorry to read about the high percentage of "contingencies" (including one outright loss) that you all experienced. It might, though, be a good subject for a science fair project that your daughter could conduct later--observing and measuring the differences in performance of model rockets as a function of atmospheric density and temperature (with humidity perhaps being a relatively minor factor). Rockets and airplanes fly best in opposite conditions; the "hot and high" conditions (high temperature and lower air density at high-altitude airfields) that make airplanes struggle with lower lift actually increase the performance of rockets (due to warmer propellant and lower drag). Also:
Your experiences with A6-4 motors versus A8-3 motors are the same as mine. Lightweight rockets such as the Viking and the BT-50 size RTFs fly higher on A6-4s than on A8-3s; my guess is that the more gradual acceleration during A6-4-powered flight enables the rockets to waste less momentum against drag. I've noted the same differences in models powered by the A3-4T versus the altitudes achieved by the same models when powered by A10-3T motors. Lightweight rockets such as the Gnome actually go higher with A3-4T power than when powered by A10-3T motors, and it has nothing to do with the A10-3T's shorter delay. |
We were talking on Sunday at my launch about the rocketry event that they had as a summer enrichment class in previous years in our school system. (At B6-4 Field, mind you.) That launch report, if made, wouldn't have been anywhere near as success-filled as yours. Nice to have an adult with a clue in charge.
I was going to say that I wish Quest motors were locally available, but then it occurred to me that our onfield vendor, Merlin Missiles, may just have some on hand at our launch in a couple of weeks. The A6-4 motors would be perfect at B6-4 Field, especially since I'm almost finished with one of the vintage Estes Wizards that I picked up a couple of weeks back. :cool: |
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Considering the weather conditions, and the smallness of the field, I think things went pretty well. I cut down and refitted my Baby Bertha the very next night, and am just waiting for some painting weather to finish it. When Taylor chose a C6-5 for the "project rocket," she was well aware that the field wasn't large enough for that engine to be a "safe" choice, and no one was particularly unhappy about the loss of the rocket. Quote:
Dunno. An A8-5 would have been the "correct" choice, but I have more A6-4's so I decided to risk it. Given the air density, it was probably a better choice anyway. Quote:
:D Thanks for the kind words... but it was my bad decision to fly the Baby Bertha on an A8-3. Looking back at my notes, I found I've previously noted not to do that. Duh. Quote:
As I noted above, I'm not sure the A6-4 is a good across-the-board fit for BT-20 rockets like the Wizard or Viking. I'm blaming the air... none of the rockets flew like I'm used to. What the A6-4 is best for is the Estes Alpha. Seriously. In warm weather, the delay is darn near perfect. |
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I'm not going to contradict your experiences, but I'm a little surprised by them. Looking at the data sheets (http://www.nar.org/SandT/pdf/Quest/A6.pdf and http://www.nar.org/pdf/Estes/A8.pdf) the Quest A6 and Estes A8 have nearly identical total impulse of 2.12 and 2.32 N-s with average thrust 5.17 N and 3.18 N respectively (the "6" is a slight exaggeration and the "8" is an utter lie). As for initial thrust, the A6 peaks at 11.8 N at 0.2 s while the A8 only reaches 9.7 N at about 0.23 s. The big difference is that the A6 then falls steadily to burnout at 0.41 s while the A8 falls quickly to about 2.5 N and stays there until burnout at 0.73 s. So I would have expected the A8 to give the higher altitude, for the reason you gave — gentler acceleration, lower drag. Assuming the slightly earlier deployment with the A8-3 doesn't cut into the altitude, of course. |
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The A8-3 ejects waaaaaaaaaaaaaay too early for small rockets, even a heavy Generic E2X gets a heck of a yank when the laundry deploys. It will cut a considerable amount of altitude off of anything smaller. |
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My point was that given the thrust curves of the two, I would expect the A6-4 to have the HIGHER airspeed. |
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