Team America Rocketry Challenge
Tips and Tricks!
- Learn to use a simulation package: Once your team has built a basic kit rocket and understands how all the components work together, have them use RockSim, Open Rocket, or SpaceCAD to learn how those software packages can simulate performance with different engines, in different environmental conditions, or how changing size, shape, or number of fins effects altitude, stability, etc. The understanding of how to adjust rocket performance to hit a specific altitude here will make the design process go much faster.
- Buy your engine first: When coaching a TARC team, money is always an issue. One way to control costs and to make sure your team doesn't get to the point where they built a rocket but can't locate the engine they simulated, I strongly suggest you purchase your engine first. While this may seem like it should be the last step after your team has tested dozens of engine options in their rocket design, I would counter that you should build a rocket around the engine you can actually purchase and afford. For example, I have found the Aerotech F32-4 for under $12 which is an amazing price, and it has always been in stock. While this may be a bit more thrust then you need, it is much easier to add weight or drag to slow a rocket down than to try and find places to shave weight or reduce drag if your engine is not quite powerful enough.
- Reduce Variables: Encourage your team to settle on some basic components of their rocket design before getting into a simulation package. If they are playing with every single option there are simply too many variables to manage and the team may end up splitting into separate "camps" on design (I have seen this happen during several TARC camps and within some larger teams). This can be timely, expensive, and divisive within your group. The coach or mentor has every right to limit the options a bit based on what you know makes sense and what you are wiling to purchase. I like to give teams the options of a BT-70, BT-80, or 3" body tube, encourage them to select a pointy or blunt and foam or plastic nose cone, get them to agree on the thickness of fin material (I usually offer up 1/4 in. balsa), and if you followed tip 2, you should already have engine diameter.
- Tricks for Controlling Altitude, and increasing accuracy. OK, so if you have been following along, you may have a selected a pretty powerful F engine that is sending you over 1,000 feet in simulations. . .even with 2 eggs and 2 parachutes. The first thing to know is that the simulations rarely get altitude dead on (but they are absolutely the best way to get close), and in my experience they most often overestimate the altitude. Here are three ideas for controlling altitude:
- Choose the right nose cone: Pointy nose cones (typical Ogive shape for example) reduce drag while rounded shaped cones add drag. [One other consideration is that hard pointy cones are actually safer for your eggs than even the foam ones because the of the amount of force that is absorbed when a pointy cone penetrates the ground.]
- Add Asymmetrically air-foiled fins add accuracy and reduce altitude. Just like a spinning bullet or football is more accurate, so is a rocket that spins, but that spin adds lots of drag (which is good if you are going too high). So, if you sand your fins to look like an airplane wing (rounded top and tapered bottom ONLY ON ONE SIDE), you can overcome most winds that cause other rockets to veer off course.
- Use Tube Fins: Tube Fins are easy to add (not that hard to remove. . .) and can add as much drag as you like to reduce altitude while increasing the rocket's ability to perform consistently. A rocket with only tube fins is more difficult to design (IMHO), but if you have a 3 or 4 fin rocket and put a tube in the joint between the fin and body, you can add additional strength, and depending on the length, an almost infinite amount of drag. Check out this rocket design I created in Rocksim to help teach rookie TARC teams for 2014. Download.
- Tracking Powder: What if you want to add weight to reduce altitude, but you are still coming down too fast. . . so you don't want the weight on the way down. There is a product many high-altitude rocketeers use to see their rocket when it blows the nose cone, called tracking powder. I like to use the baby powder that I have in my launch kit to pack my parachute but I have read that others use tempera paints. Put as much mass as you like inside a pouch of recovery wadding or folded up inside your parachute. You'll get a great puff of white to see when your nose cone ejects and you'll jettison all that mass.
- Spill Holes: Everything is working great but your coming down too slow. . . put a spill hole in your chute. It turns out that well designed parachutes always have a spill hole so they open faster, and don't wobble on the way down as they let air spill from one side or the other. You can tweak your decent by changing the size of the spill hole. I recommend you put a slight dab of super glue or use a flame to melt the frayed edge of a nylon chute or the material could continue to unravel.