Useful Tools
Parachute size table
There are plenty of calculators around to size parachutes, but the following table will give a quick guide to the right size. It assumes a round parachute. Recommended descent rates vary between 15 and 20 feet per second, depending on the landing surface, toughness of the rocket and how little walking you want to do. The rocket mass includes an empty motor case (i.e. the condition after separation), and parachute size is given in inches, rounded to the nearest likely size available.
| Rocket mass | Diameter (inches) for 15 ft/s descent |
Diameter (inches) for 20 ft/s descent |
|---|---|---|
| 100g | 12 |
10 |
| 200g | 18 |
14 |
| 300g | 22 |
18 |
| 400g | 26 |
20 |
| 500g | 30 |
24 |
| 600g | 32 |
27 |
| 800g | 36 |
30 |
| 1kg | 42 |
36 |
| 1.5kg | 50 |
42 |
| 2kg | 60 |
48 |
| 3kg | 72 |
56 |
| 4kg | 84 |
66 |
| 5kg | 93 |
72 |
For other sizes see http://www.rocketreviews.com/cgi-bin/myemrr/descent33_distr.cgi
Fin-alignment guides
Click on the image below to download the PDF file, print and cut carefully from thick card or plywood. Use the guide to support the fin on the tube while the adhesive sets. They are suitable for three-fin or four-fin designs, as the bottom edge will clear fins already fitted. The guides ensure the fins are absolutely square to the tube - no more wonky fins, or fins that droop while the glue is setting. The nicks in the corner will help ensure the guide doesn't get permanently stuck to the rocket, which cuts down drag! The effort inolved in making a guide more than offsets the hassle of fitting fins without one, and they will last for rocket after rocket. The sheet has guides for 3" and 4" tubes. More tube sizes to follow.
Painting plastic nose cones
One of the problems with plastic nose cones is getting the paint to stick, and they can look very scruffy after just a couple of flights. One option is to use car bumper primer, but a recent discovery is a paint called Plastic Primer from CarPlan. Designed for ard plastics, the primer seems to work well with ordinary plastic nose cones. Being clear, it is like very runny polystyrene cement, and keys very well into the surface. This can then be followed up with ordinary primer. We haven't flown it yet, but it looks very promising. An alternative of course is to use fibreglass nose cones, which are not as easy to get but take paint really well. They are also quite light - no heavier than a typical plastic cone - and similar in price. We buy most of ours from Paul Carter of Congreve Rockets.
More tools to follow...