LEVEL 3 BUILD YELLOW BIRD Dan Schwartz This entire rocket is built using the same techniques I use for my nose cones, a central airframe tube for compression strength and rings of high compression styrofoam and surface fiberglass for the shape. The initial idea was to build an unusual rocket that was as big as possible and still fly on level 2 motors. This was accomplished with this rocket with a successful flight on an L2375 (the main chute tangled and it hit the ground at 44 ft/s with no damage). Once this was done, and after persistent goading by my son, I decided to use this rocket to try for my level 3.
Materials: Main body- ARR 6 Blue Tube, glassed in high stress areas Blue Tube 4 motor tube 1/4, 1/2, 3/4 mill grade plywood for centering rings etc. Dow HI-Load 40 styrofoam US Composites laminating epoxy and fairing compound Rocketpoxy US Composites 5.7 oz. Plain weave fiberglass 7/16 brass tubing 9/32 styrene tubing Aeropack 98 mm retainer 3/32 and 1/8 fiberglass sheet Fins: 1/2 Dragon Econoplate with divinycell core and 0.030 carbon skin 1/2 thick poplar, cut and surfaced to match the carbon panel,for edging 6 oz. carbon fabric Nosecone: 3 and 2 phenolic tubes ¾ x 18 aluminum rod 40 psi styrofoam, epoxy, glass as above lead shot Photo of most of the ply and foam rings, blue tube and cone. Construction Fin Section: Aluminum flashing used to assure the base plywood is flat. The foam rings were then stacked with the epoxy epoxy and filler at a heavy syrup consistency. Most are cut out to decrease weight, about every 4 th is tight to the center tube to be sure they are centered. This is continued to the top of this section. Another 1/2 ply ring is placed at the start of the transition. 1/4 ply rings are placed above and below where the fin tabs will go and 1/2 at the top.
Part of the foam against the plywood rings was removed and long blocks of hardwood epoxied in for rail guide supports. This section was then turned to final dimension. To be able to reach the av bay switches, I decided to surface mount two magnetic switches near the top of this section and run long wires with a secure latching plug up to the av bay. The wires were run through holes drilled through the center tube and the switches epoxied in place. This section was then covered with 2 layers 6 oz glass. The 34 long coupler was also glassed to strengthen it and tighten the fit in the main tubes. The coupler was then epoxied into the top of this section. The fins are made of 1/2 Dragonplate carbon econoplate with 0.030 skins and divinycell core. This plate was cut for me by Upscale CNC. This was edged with 1/2 poplar boards 1.5 wide that had been shaved on my router to match the carbon panel thickness. Once the edges were on, the fins were beveled and a layer of 6 oz. carbon was added to cover the whole fin. Once the fins were complete and the thickness known, the fin section was remounted on my lathe and fin slots cut. The fins were mounted using a thick bead of Rocketpoxy on the root edge against the center tube, and along the contact with the foam rings. A small external filet of Rocketpoxy was made. After curing, the filet was enlarged using US Composite epoxy with filler.
Motor mount: A 42 long 4 PML tube was used for the motor mount. A 9 OD 1/2 ply ring and a 7 OD 1/8 fiberglass ring were stacked for a thrustplate. This plate was carefully marked, drilled, and tapped for the Aeropack 98mm flanged retainer. The plate was epoxied on, leaving enough tube to accommodate the retainer. Two centering rings of ½ ply were placed, and the motor mount then installed in the Blue Tube.
Construction Center Section: The lower 20 of the Blue Tube was glassed with 2 layers 6 oz. glass for strengthening as this is where the bolts will go to hold the sections together. The lower ply ring was drilled for two ¼ holes over the top ring of the fin section. The center tube was placed over the coupler and the ring epoxied to the tube matching the fin section. 1/4 steel pins were glued into the top ring so the two sections will register automatically. The first foam ring was grooved to accommodate three 7/16 brass tubes, which were epoxied in against the center tube. These will be the channels for the lower ¼ 20 bolts. The fifth foam ring was likewise grooved and brass tubes placed for the upper bolts. The rest of the foam rings were stacked, same as the fin section. There is a 1.5 thick ply ring at the top to prevent zippering and it is rounded on he inside edge to prevent fraying of the kevlar shock cord. This section was then turned to final size and glassed with 2 layers 6 oz glass. A centering jig was made and tap holes drilled down the brass tubes through the center Blue Tube and into the ply rings in the coupler for the ¼-20 bolts. The holes in the center section were then enlarge for clearance of the 1/4-20 bolts. The holes in the coupler section were tapped for 1/4-20 bolts. The shear pin design also uses tubes to span the thickness of the wall. I started with 4-40 aluminum hex threaded standoffs and press fit them into 7/32 ID aluminum tubing. They are tight enough that the tubing deformed around them to keep the standoffs from spinning, thin CA was added to ensure they would stay. Three holes were then drilled near the top of the center section at the level of the nose cone shear pin band. The aluminum tubes with the
standoffs were inserted into the holes and epoxied in place so that the hex standoff was even with the inside of the center tube. The nose cone was put in place and holes drilled through the hex standoffs into the cone shear pin band and the cone marked for orientation. The nose cone was removed and the holes enlarged to a snug clearance for the 4-40 nylon screws. Two 5/16 holes were then drilled and 1/4 ID styrene tubes placed at about the middle of the parachute compartment for pressure equalization. Nose Cone: The nose cone was originally built as a 10 ogive for a customer but was turned too small and re-purposed for this rocket. The shoulder was shortened and turned down to fit the 6 Blue Tube, and a shear band added. The cone was then turned down to size and shaped as compound conical. Seven pounds of lead shot and epoxy was added to the top of the center tube. It was surfaced with two layers 6 oz. glass. A 1 ply bulkhead with stainless u-bolt was epoxied into the center tube. AV-BAY: The bulk plate is a sandwich of 1/2 ply with 1/8 fiberglass sheet on both sides. The components are mounted on two 1/8 ply sheets spaced 1/2 apart. This becomes a rigid box with the altimeters on one side, the batteries between the ply sheets and the GPS antenna on the other side. A stainless u-bolt is mounted to the top of the bulk plate and is the attachment for the chutes and nose cone.
A bulkplate was placed in the fin section just below where the magnetic switch wires entered the center tube to seal the bottom of the av-bay. A 1 plywood ring with 1/8 fiberglass layer was lined up with the av-bay bulkplate and holes drilled for 1/4-20 bolts. The bolts were epoxied into the ply and fiberglass ring and the ring then epoxied into the coupler at the top of the fin section. The above bulk plate and ply ring are also the attachment point for the bolts connecting the fin and center sections. The av-bay then fits onto this ring and is secured with just nuts over the bolts and seals the top of the av-bay. There are no threaded rods etc to interfere with radio signals. The av-bay vents are positioned where the wall of the rocket is about 4 thick. This will slow the pressure equalization and the holes, which are tubes in this case, need to be larger than calculated. I used Gary Stroic's calculator. I could not find a formula to compensate for the thick wall, so I made the hole slightly larger than calculated for 3 holes (approx. 0.15 ) and made 4 tubes. I used styrene tube of 3/16 ID ( 0.187) and drilled holes near the bottom of the middle section to fit the styrene tubes. The tubes were pushed through the holes and epoxy was injected around them. The were cut flush with the inside of the center Blue Tube and the outside surface. Matching holes were also drilled slightly larger through the coupler. Electronics: Altimeters are a Raven and an Eggfinder. The Raven will be primary and the eggfinder backup. Batteries are 180 mah 2S LIPO for the Raven and 370 mah 2S for the Eggfinder. The altimeters are for apogee only. Two Jolly Logic chute releases in series will be used for main deployment. Because of the concerns for damaging altimeters with 2S LIPOs, I placed a 1.5 ohm 2W resistor in each output between the altimeter and the terminal block for the e-matches. If there is a short, this will limit the current to 5 amps, but still provide 2.5 to 3 amps to the e-match with a typical 1 to 1.5 ohm resistance. I tested the resistors at this shorted current and they lasted over 7 seconds and still measured 1.5 ohms after they cooled. Since the output pulse of the altimeters is only 1 sec., I thought this would be very safe.
The leads for the ejection charges go to wire pairs with RCA phono connectors that are long enough to reach to just past the ejection plate. The leads from the terminal block on the plate go to the other side of the RCA phono connectors. The wires will be taped to the side of the chute compartment. The phono connection is tight enough to hold ( there is really no weight on it) but will separate when the nose cone is ejected. A Merlin Systems MX, 216 mhz RF tracker, will be attached to the shock cord to help find the rocket if needed. Recovery: Drogue 60 Skyangle Main 18' Rocketman Both chutes are deployed from the front of the rocket. The system is designed for a smaller and consistent volume for the ejection charge and no exposure of the chutes to charge heat or gases. The anchor for the kevlar line is at the top of the av-bay in the center coupler of the rocket. There is an ejection plate supported at the top of the chute compartment 1.5 below the base of the nose cone. The support is a 4 length of coupler with 4 pieces of 1/8 x ½ x 3 aluminum bar. The aluminum is shaped to fit the tube and rounded to prevent snagging. The tubular kevlar goes through the center of this plate and attaches to the nose cone. The ejection charges go above this plate and connect to a breakaway RCA connector below the plate. The drogue is attached to the line just below the plate and is pulled out with the plate by the nose cone. The drogue will then inflate before the nose cone reaches the end of the line. The chute protector for the main is attached to the line so that the main burrito will be pulled out of the rocket and stop right outside the tube. The ejection plate is 1/8 fiberglass and ½ ply. The kevlar shock cord goes through the center and is sealed with silicone caulk. A smalll amount of Gorrila glue was injected in the center of the kevlar to expand and lock it to the plate.
A 1.5 piece of coupler is epoxied to the bottom of the nose cone shoulder to ensure that the ejection plate stays tight against the support. The chutes are attached in a Y. A length of 1/2 kevlar goes from the top of the av-bay to just outside the center section. A 30Kn swivel is attached there and the lines from both the drogue and the main attach to that swivel. This lets the fin can spin without twisting the lines. The drogue line is 18 ft. and the main line is 26 ft. There is an additional swivel at the drogue shroud line attachment since Skyangle chutes are designed to spin.