L3 Build Summary

Bret Packard

TRA #11257 L2

NAR #83659 L2

            My goal for this build is to create a very strong, reliable large rocket that minimizes prep time and complexity in order to provide the best chance for a successful flight.  The basic framework I have chosen for this rocket is the Performance Rocketry Intimidator 5. The Intimidator 5 is a 5” diameter, 10 foot tall all G-10 fiberglass rocket.  The rocket will not be optimized for altitude, but rather emphasis will be placed on durability and stability.  The rocket will be constructed using primarily West Systems epoxy with West Systems 205 and 206 hardeners and various fillers as appropriate.

            The booster section is 48” long and has a 24”, 98mm motor mount with fins that will attach directly to the motor tube.  The fins will have joints filleted to both the motor tube and inside airframe using epoxy with chopped carbon fiber.  The fins will also have 2 layers of 5.9 oz. carbon fiber laid tip to tip for additional reinforcement.  A 98mm Aero-Pack motor retainer secured with 14 stainless steel screws will provide positive motor retention.  A 50 foot long ½” tubular Kevlar shock cord will be attached via a stainless steel quick-link and forged eyebolt threaded into the forward closure of the motor hardware.  An anchor point will be installed in the motor mount to attach a Kevlar strap which will also be attached to the forward closure mounted eyebolt as a backup attachment point in case the eyebolt should ever come unscrewed.  A 24” drogue chute will be used to keep things falling in an organized manner.

            The electronics bay will be inside the 12” coupler tube.  It will house a Missileworks RRC2 and a Featherweight Raven.  Each altimeter will be wired completely independently of the other, including separate black powder charges, and separate power supplies.  Black powder charges will be determined by ground testing once the build is complete. 

            The 48”payload tube will house another 50 foot length of ½’ tubular Kevlar and a TAC-1 Cert 3 parachute.  A Garmin DC-20 will be mounted in the nose cone to provide tracking for the flight.

            The motor I have chosen for this flight is the 6 grain 75mm Cesaroni M-1590 Classic.  With the rockets expected pad weight of approximately 25 lbs., the initial thrust of the M-1590 of over 500 lbs. yields a 20:1 thrust ratio at ignition and a sustained thrust ratio of nearly 14:1, which is more than enough to achieve stable flight.  According to the modeling I have completed in Rocksim 9.0, the rocket reaches stable flight at approximately 24” inches up the rail at a speed of 44 feet per second.  The motor will burn for 4.7 seconds propelling the rocket to a maximum speed of 1,365 fps, then coasting for another 21 seconds before the apogee event occurs at an expected altitude of 13,500 ft.  Altimeters will be programmed to stagger ejection charges by approximately 1 second at apogee and main deployment at approximately 1,000 feet AGL.  The rocket should touch down approximately 3 minutes and 10 seconds after liftoff.  Any sooner than that is probably bad ;)