YikStik

YikStik is a fairly simple "three fins and a nose cone" dual-deploy rocket using a 75mm motor mount, 4 inch glass-wrapped phenolic airframe with zipperless fin can, plastic nose cone, plywood fins, and lots of glass and carbon fiber reinforcing. The primary electronics bay will be designed to hold two altimeters, and a distinct payload bay may carry an experimental altimeter, GPS receiver, and downlink transmitter.

Airframe Tubing

The airframe components will be composed from two 48 inch lengths of 98mm Giant Leap Dynawind tubing. The 30 inch main bay and 18 inch drogue bay will be cut from one length, while the 33 inches of fin can, 2 inches of electronics bay, and 8 inches of payload bay will be cut from the second.

Nose Cone

Giant Leap "Pinnacle" 3.9 inch nose cone.

Fins

The fins are designed from scratch, and they will be built from two layers of 1/8 inch birch plywood, three layers of carbon fiber, and two layers of 6 oz glass. The stack will be glass, carbon fiber, plywood, carbon fiber, plywood, carbon fiber, glass. The edges of the plywood will be routed to give a modified airfoil shape to the finished fins. The stack will be laminated using West Systems epoxy products and vacuum bagged. The shape is a compromise between mass, surviving Mach-transition stress, optimal stability margin, and avoiding damage during handling and on contact with the ground during recovery.

The fins will be locked in to milled slots in two of the centering rings, and will be epoxied to the motor mount with glass reinforcing tape. The airframe will be slotted to allow the completed motor mount / fin assembly to be inserted from the rear, with fillets of epoxy applied inside and outside the airframe after insertion.

Centering Rings and Bulkheads

All centering rings and bulkheads will be custom machined from 3/8 inch birch plywood using my 3-axis CNC milling machine. Some rings will use laminated pairs of 3/4 inch total thickness to enable use of threaded inserts for 1/4-20 rail button screws or deep routing for fin alignment slots.

Motor Retention

The three 8-24 T-nuts will be embedded in the aft centering ring spaced to allow the use of home-made Kaplow clips to retain 75mm motors. The same holes may be used to attach custom motor mount adapters for smaller diameter motors.

Electronics

Avionics

The recovery system will feature dual redundant barometric altimeters in an electronics bay similar to the LOC design located between the drogue and main parachute bays.

A PerfectFlite MAWD will be flown as the primary altimeter and to record the flight altitude profile. A MissileWorks Mini-RRC2 will fly as backup altimeter and to directly capture max velocity.

Each altimeter will have a separate battery and power switch. A 4PDT slide switch will be used as a SAFE/ARM switch configured to interrupt connectivity to the ejection charges.

Stability Evaluation

This design has been thoroughly analyzed using RockSim with motors ranging from the Cesaroni J285 through the Aerotech M1850W and appears to be unconditionally stable across that range. The lowest margin is around 1.2 seen with the M1297W planned for my level 3 certification flight, albeit with many masses still only roughly estimated.

These simulations will be refined as the build proceeds and as-built stability verified before flight.

Expected Performance

The Aerotech M1297W reload should carry this vehicle without ballast to just over 14 thousand feet AGL. It should make over 16 thousand feet AGL on an M1850W, and should fly stably to roughly 2.5k feet AGL on a Cesaroni J285.

Recovery System

The recovery system will use dual redundant barometric altimeters firing black powder charges. At apogee, a drogue chute will deploy from just forward of the fin can, with size selected for an approximately 100 ft/sec descent rate. At a preset altitude, a main chute will be deployed to achieve recovery of the bulk of the rocket at under 20 ft/sec. The main chute will be packed in a deployment bag, configured as a "freebag" and pulled out of the airframe by a second drogue chute. This drogue will recover the nosecone and deployment bag separately from the remainder of the rocket which will recover under the main.

The deployment bag will probably be purchased from Giant Leap. The recovery harness will probably use tubular kevlar, also from Giant Leap.

The recovery system attachment points will all use 1/4 inch u-bolts with nuts, washers, and backing plates through bulkheads except for the fin can. The fin can has insufficient room between the motor mount and the airframe inner wall for nuts and washers, so an alternative means of recovery system attachment is required. The fin can will be equipped with either a 3/16 inch stainless steel aircraft cable loop, or a loop of 1/2 inch tubular kevlar, bonded to the motor mount. If available, a screw-eye attached to the forward motor closure may be used instead of or in addition to this recovery attachment loop.