Brief:
Single-staged 15 x 29mm cluster rocket. Thus far, simultaneous ground ignition of (15) G35-7 motors was attempted. Total thrust ends up in the low K range if all the ports are used, and with Econojet G motors. Rocket can be flown on just one motor in the central mount, and two at a time can be added symmetrically for other possible motor combinations. There are (7) mounts in the main body tube and (8) outboards arranged with two at each fin, and these pods provide extra strength in the fin attachment. These side pods all have a 29mm nose cone.

The launch lugs are brass pipe cuttings, one inch diameter by one inch long. The launch rod used is a copper lightning rod 3/4 inch diameter by 7 feet long.

Construction:
The nose cone is an Ace plastic nose cone, 15 inches long and ogive. I'm not sure that this company still exists, but these great nose cones are obtainable on ROL auctions regularly. They have a large base hole into which ballast is easily added. For this rocket, 6 ounces was added and foamed in place with 2-part polyurethane foam.

The main body tubes are 4 inch motor tubes made by maximum Thrust Rocketry. These are ultra thick and strong white paper tubes that aren't glossed, so they take on epoxies and fiberglass readily. Each length was 36 inches. These tubes are connected from the motor mount to the parachute bay via Red Arrow Hobbies 4 inch phenolic couplers. These are epoxied in place by West Systems slow epoxy. I used this method to reinforce the rocket's airframe internally to see if the rocket could stay intact without external fiberglassing. The inner tubes consist of (15) 12 inch lengths of LOC 29mm motor tubing. Seven are inside the main airframe and eight are outboard pods each with a Rogue Aerospace balsa 29mm nose cone.

The (4) fins are right triangles (12 by 12 by 12 square roots of 2) cut from a 12 inch square of .125 inch thick G10 obtained from ROL auctions from Scott Eakins. The fins are epoxied to the main body tube with the hypotenuse as the root edge against the airframe. Then the side pods further reinforce these connections with two per fin, one on each side of each fin. West Systems slow epoxy was employed for this.

The shock cord is 5 feet of tubular nylon plus 5 feet of wire wrapped bungee cord both from American Science and Surplus, which has a site on Rocketry Online. The cord is attached to a u-bolt in a 4 inch birch centering ring (all centering rings came from Space Modeling Solutions, which has a site on Rocketry Online) placed against the motor mount tubes and linked with quick links, with one link between the two unlike materials in the shock cord. The forward link of the shock cord connects to a u-bolt in a 4 inch birch bulkhead and coupler arrangement in the second main airframe, thus allowing the rocket to separate in the middle.

The parachute is a homemade ripstop nylon 60 inch diameter hemisphere made up of triangular gores in yellow, green and blue. The nose cone is screwed into the airframe with 4 wood screws. This arrangement allows opening this compartment in case an altimeter is used.

The launch lugs are brass pipe cuttings, one inch diameter by one inch long. The launch rod used is a copper lightning rod 3/4 inch diameter by 7 feet long.

This rocket is simple to build. The epoxy used came from a boating store, and can also be obtained from West Systems, which has an online site. The result is a very sturdy, attention getting rocket. This one was decorated in green, blue and gold, with metallic bands. These color bands are self-adhesive mylars that come in metallic colors and can be had at many hobby stores as well as American Science and Surplus.

Flight:
I recommend for clusters at least 3 motors if it's G class, and for lower numbers of motors, a greater average thrust like a G80. For larger numbers, try G38's or 35's. I only wish that the Econojets came with longer delays, like 10 seconds. When 15 motors are used, 10 seconds may be best. For a single motor flight, an I 200 medium delay would work great.

To prep the rocket, I use worm bed wadding and a Nomex®/Kevlar® chute protector. The central motor is retained with friction fitting tape plus piano wire loops that are embedded in the epoxy that holds together the motor tubes. Originally, I planned all other motors to eject upon their charges firing, but some RSO's don't like that for safety reasons in dry fields and also the dropping of objects from high up, so either the ejection charges can be removed from all outboards, or the motors can all be arranged on a long shock cord with a chute. I haven't designed that system yet, but have considered it.

All 15 motors (G35-7W) were simultaneously lit using Fire in the Hole low current tungsten bridge igniters from Trailing Edge Technologies. Oh, and I also used a 12 volt lead acid cell deep cycle marine battery for power and a relay system to allow the battery to stay at the pad and prevent line loss, since the NAR rules have to place me 300 feet away. The flight was straight with no spin. I loved the roar of a K equivalent motor with 15 nozzles. However, the delay of 7 is too short, so the parachute suffered damage from rapid deployment. But the rocket survived intact and ready to fly again.

Summary:
This was fun and easy. Nice and loud and attention getting. I set a record for number of composites successfully lit.