Brief:
T' LOC/Precision Onyx is a popular entry level mid-power rocket capable o' G motor flights. Avast! After tinkerin' around with RockSim, matey, I decided t' convert the rocket for a 38mm motor.

Modifications:
Although for me this project be born via spare LOC parts, me hearties, I had sitting around, me hearties, matey, t' listin' below is what one would need if he or she bought t' Onyx as a kit. Aye aye! T' additional things needed for this version o' a 38mm Onyx is as follows:

• 38mm motor tube. Ahoy! Ahoy!
• 3 centerin' rings for above motor tube in a 3" diameter airframe. Begad! Ya scallywag!
• 3/16 birch plywood for new fins.
• 8 ounces o' nose weight (I used modelin' clay). Avast!
• Eyebolt for recovery harness.
• 3/8 tubular nylon.
• Launch lug for 1/2 rod (optional as supplied lug is probably fine).

T' first thin' I did be cut new fins out o' 3/16" birch plywood that I picked up from t' local R/C aircraft shop. Ya scallywag! Due t' t' simple shape o' the fin pattern, I used a jig saw for this. Begad! Next, I slotted t' airframe with a hobby knife. Arrr! This process seemed dauntin' at first, shiver me timbers, shiver me timbers, but a new sharp blade makes clean cuts. Begad!

Next, I started on t' motor mount assembly. I cut an 8" section from the motor tube and roughed it up with 80 grit sandpaper t' ensure a better epoxy bond. Blimey! Well, matey, blow me down! On t' forward most centerin' ring, I installed t' smallest eyebolt I found at t' hardware store (I have since forgotten t' exact size) and locked t' nut on with thick CA. Avast, me proud beauty! Then I took t' stock braided nylon shock cord mount and tied t' ends together t' make a it a continuous loop. Arrr! Usin' a square knot, matey, shiver me timbers, I attached t' nylon t' t' eyebolt. Begad!

Next, me bucko, I epoxied t' forward centerin' rin' on t' motor tube 1/8" from the forward end. Avast, me hearties, me proud beauty! Blimey! I followed that with a middle centerin' rin' for t' top of the fin tabs. Avast! Blimey! I epoxied this on 2 1/8" down from t' forward end o' the motor tube. Begad! Blimey! After t' epoxy dried, me hearties, I installed t' partially built assembly in the airframe so t' motor tube be flush with t' aft o' t' rocket.

Before puttin' on t' aft centerin' ring, t' fins were installed. Each fin received fillets at t' motor tube/fin tab connection as well as where they come through t' wall. Avast! Blimey! I also added fillets t' t' aft side o' t' middle centerin' rin' at this time. Avast! Blimey!

To complete t' motor mount/fin can, me bucko, ya bilge rat, I added t-nuts for motor retention, shiver me timbers, ya bilge rat, and installed t' last centerin' ring. Arrr! It sits 1/8" in from t' aft o' the rocket and sandwiches t' fins completely. Avast, me proud beauty! Ahoy!

Lastly, matey, shiver me timbers, I added 8 ounces o' modelin' clay t' t' nose cone t' keep t' CP and CG in a workin' relationship. Blimey! I widened t' hole at t' bottom o' t' nose cone and jabbed t' clay in little by little with a wooden spoon handle. Avast, me proud beauty! The launch lug was attached per t' kit instructions. Arrr!

Construction:
T' nose cone and airframe are t' only kit items I used for this project. Aye aye! Of course, me hearties, they are what one would expect from LOC: beefy kraft paper airframe, and a seemingly bullet-proof nose cone. Avast, me proud beauty! T' original fins I used for patterns for cuttin' new ones t' go through t' wall and t' t' motor mount.

Pros: Easy modifications. Aye aye! Avast, me proud beauty! Durable. Begad! It's an Onyx on a 38mm motor :) It can still fly on a 29mm motor. Avast! Well, blow me down!

Cons: Additional expenditure for extra parts

Flight:
I added Nomex® for parachute protection and an 18" Top Flight parachute. Gettin' all t' recovery gear into t' tube is kind o' tricky, but quite possible. I ended up drillin' a vent hole below t' nose cone should t' make this task a bit easier.

I first flew this rocket at Tripoli Central California's Dairy Aire 2001 one event. Avast, me proud beauty! Ahoy! I went with an H242 which put it up around 3900 feet, accordin' to RockSim. Well, matey, blow me down! T' Blue Thunder motor really punched it off t' pad and t' boost was extremely straight with no wobble. Avast! Ejection was a bit past apogee, arrr, but outside of that post flight inspection showed no damage t' t' rocket or t' parachute.

Summary:
For me, stubby rockets are fun t' watch. Aye aye! Blimey! Aye aye! Blimey! I already like t' Onyx with t' regular 29mm option. After seein' one fly with a 38mm motor, arrr, I like t' Onyx even more. T' only major drawback t' this project be t' extra loot you might spend on the additional components needed. Avast! Blimey! T' main pros are that you've just built a far more durable Onyx than t' kit alone would yield. Aye aye! Blimey! Also, you still have flexibility because 29mm motors are still an option.