Brief:
This is my upgrade/semi-clone of the classic Centuri Centurion. It incorporates an offset-tube baffle, breaks at the midline (at the baffle) and features three interchangeable engine mounts: 1x18mm, 2x18mm, and 1x24mm D/E.

Construction:

• Cygnus 1x24mm E Engine Mount Kit
• Cygnus 2x18mm Engine Mount Kit
• Cygnus 1x18mm Engine Mount Kit
• (4) BT-60 Tube Couplers from Uncle Mike's Rocket Shack
• Screws and Nuts for Motor Retention (Junk)
• "Off-Centering" Rings (hand cut from laminated cardstock)
• 2" BT-20 Offset Tubes (Baffle)
• Short section of BT-60 Tube Coupler ("Thrust Ring" for interchangeable engine mounts)
• Centurion fins (laser cut by Semroc)
• Semroc BNC-60L Nose Cone
• Screw Eye
• 12" 100# Kevlar thread, 12" elastic and a couple of feet of Mason's line (shock cord assembly)
• 13" BT-60 Body Tube
• 7.5" BT-60 Body Tube (from Baby Bertha kit)

I started by assembling the three engine mounts. I used the stock engine mount parts along with a coupler for each. I had to sand them down to make them fit inside the body tube. The BT-60 couplers from Uncle Mike's Rocket Shack are really tight in the hobby-shop body tube.

I next glued the nose cone into the upper sustainer tube (after gluing in a screw eye and affixing the shock cord, of course) and assembled the bypass-tube baffle (two short BT-20 tubes offset from each other, then off-centering rings, coupler, and Kevlar thread installed).

After marking the lower sustainer tube for fin and launch lug attachment, I mixed up a little slow-setting epoxy and used it to glue in the BT-60 coupler segment which serves as a "thrust ring" for the interchangeable engine mounts. At this point, I didn't know how I would secure the engine mounts. Save that, I knew I was not going to use an engine hook (as was done in the old Centuri RX-16 rocket). I used epoxy to avoid the "freeze" effect of yellow glue. I was able to insert an engine mount slowly, pushing the ring into place without fear that the mount would suddenly become non-interchangeable. I used the remaining epoxy to glue in the baffle, leaving half of it sticking out of course.

Next I attached the fins, in the standard fashion, using yellow glue. Like all the Semroc fin sets I've worked with, they were excellently cut. This set of fins also proved to be the hardest balsa I've ever handled which is another big plus for a heavy rocket.

When all was good and solid, I followed up with fillets, also yellow glued. Launch lugs were attached in the same way. I decided with this rocket to try brushing thinned Elmer's Wood Filler on the fins; some complain that it adds too much weight. I didn't think it would make much difference for this big bird.

Now came the quandary, I had the rocket done, except for the pesky business of securing the engine mounts. The rocket stood forlorn on my shelf for more than five months before I figured out how to go about it.

I started by measuring two locations, just aft of the lower sustainer thrust ring and evenly spaced between two fins (and clear of the launch lug line). I inserted the 1x18 engine mount and using a cordless drill and a 1/16" drill bit, I carefully made holes through the sustainer and engine mount coupler at the two marked points. I removed that engine mount, inserted the 2x18 mount (with the engine tubes 90 degrees from the holes) and drilled holes in this mount also. I finished by doing the same to the 1x24 engine mount.

Next, I mixed up some more epoxy. Using a syringe from the local farm store (without a needle), I injected some of the epoxy into the holes of each engine mount; then I placed each mount upright, forward end down so that the epoxy would puddle on the forward centering ring. I put a piece of cellophane tape over each hole temporarily to prevent leaking.

When the epoxy was good and hard I inserted a self-tapping screw into each hole to open them up. I use two self-tapping screws, scavenged from computer cases to hold the engine mount in place in flight.

With all this work finally finished, I primed, sanded and eventually painted the rocket. And, almost as an afterthought, I installed a handmade mylar chute.

Flight:
When I first conceived of this project, I had a trial version of Rocksim. This is the sort of rocket Rocksim is made for (whereas several other rockets of mine are very hard to simulate with it). The simulations told me to use:

• B4-2, B6-4 or C6-3 engines in the 1x18 mount
• 2x A8-3, B4-4, B6-4 or C6-5 in the 2x18 mount
• D12-3 or E9-4 in the 1x24mm mount

I've flown it on 1x B6-4, 2x B6-4, and 1x C6-5 and it has turned in an excellent flight each time.

I had the opportunity to launch this rocket on an E9-4 for the first time, at the SPARC launch on September 27th. The flight was high and straight, and deployment was perfect. I cut about a 3" spill hole in the parachute (made from a Mylar balloon) to speed descent, resulting in the rocket landing beautifully within the field. However, when I went to remove the engine mount (using the tool shown in the breakdown picture), I tore it up instead. Evidently, the relatively long piece of engine tube sticking up from the engine mount was not tough enough to survive the force needed to pull it out, even though I had done it several times during the build process. I'll make a new 24mm mount this winter, and this time I'll wrap the upper end of the engine tube in two or three layers of 110# paper to reinforce it.

Summary:
The main advantage of this design is the baffle. I love being able to turn it around quickly. I also like that I can prep an engine mount outside the rocket, allowing me to prepare to launch it two or three times in quick succession.