W9YA's L3 Certification Article
Whooie in the High Plains of Colorado Springs
A test flight was undertaken on a AT-L1150 in early July, 2010 for the purpose of testing the various subsystems. The following changes were made to the Modification info. posted below; The spin cuts were retained in order to vector off some of the pressure on the foam board structure and to aid stability on short launch rail system. The cuts were approx. 1/2 the depth of pre-exsisting designs used (by smaller motors/rockets in the test program). The launch pad was modified by adding a rail standoff to elevate the rocket to prevent motor burns on the underside and 80 lbs. of weight was added to prevent the pad from tipping as the rocket rotated around the rail as it traveled upwards. Testing showed that the power charge calculator used was in-correct. The final power charge arrived at was 23 grains of 4f Black Powder. The recovery system consisted of a single Perfect Flight Timer configured with a pull-pin intiation. The timer successfully deployed a 9 foot standard Rocketman chute designed for a decent rate of less than 18 fps. The deployment was at apogee, immediately after the rocket turned over.
For the L3 cert. flight the addition of a second timer system will be employed in a separte deployment tube. Each timer unit will consits of a standard Shurter power switch mounted with the timer and 9vdc battery on sled in each of two deployment tubes, along with the third tube holding a 10 foot rocketman chute for a decent rate of under 17fps and duplicate 1.75 oz. BP pyro charges will be employed. timing will be about 2 secs. apart to avoid over pressurizing the tube. A bridle consisting of 12 feet of 1/4 inch kevlar tubing and a sheet of kevlar for wrapping the chute will be employed. A side-view diagram is linked below along with the decent rate chart. The overall weight of the system under parachute will be approx. 17 lbs, which places the decent rate at around 15fps.
Pictures of the NARAM flight in Colorado Springs can be seen here.
1 - Adding three "deployment" tubes, each approximately 16 inches long, to each of the three sides positioned on the inside of the rocket airframe and running from each panel's unsupported corner towards the "top corner" where the three sides (or panels) connect. They will be sealed at the inside end and reinforced with fiberglass/epoxy. They will contain the redundant electronics, redundant batteries and the redundant timer/altimeters as well as the redundant parachute assemblies. The exposed ends of these tubes will be capped with removable plugs that will be "pinned" into place, designed so that some moderate amount of force (approx.. 40 lbs.) will be required to push off the plugs by the internal ejection charges.
2 - Two surplus 36 inch, center reefed "flare chutes" that each will simulate a conventional 44 inch parachute. Calculations using the "Aerocon" Decent rate calculator indicate this total of 88 inches of parachute will support up to ten pounds of dead weight at a reasonable rate of decent.) Kevlar harness will be attached to each parachute and to a kevlar bridle incorporated into each
3 - The spin tabs that would have been cut into one side of each of the three airframe panels will NOT be undertaken so to encourage proper deployment of the parachutes by allowing for a more steady platform for recovery system deployment. This will also preclude using this in the future for the "auto-rotation" recovery that the kit was designed to use.
4 - Wiring between the three containers including the power sources and the power source switches will all be undertaken on the "bottom" panel which is not exposed to moving air and can be shielded from hot gases by placing the rocket sufficiently above anything that will act as a blast deflector and allow hot exhaust gases to be deflected into the bottom panel.
5 - Each of the timer/altimeters will have dual outputs so the wiring will be simple. Each altimeter will supply an electrical output to an "e-match" for each of the "powder-charges" in each of the two tubes containing their respective parachute assemblies. NAR L3 procedures clearly point out that the power sources must be redundant so simple parallel configured battery sources will power each altimer and this these "power assemblies" will be connected to each altimeter with a series connected switch. 9V Duracell batteries will be utilized as the power sources because these particular batteries meet the voltage and current requirements and have the additional feature of being composed of soldered cells which remain conductive during normal flight.
6 - Calculations using the ao-ejection program indicate an ejection charge of FFFF Black-Powder with as little as .616 grams per container is sufficient to generate 100 lbs. of force to shear the retaining pins and push out the parachute and harness package.
7 - Additional strength will be supplied by using the cut-out material from the bottom panel as a bulkhead located between the bottom panel and the thrust panel near the top of the "cube".
Rocket Graphics courtesy of the Crystal Space Community. Pictures courtery of Nadine Kinney, Tom Beach, Greg Elder, and Grant Finch