Brief:
After the success of my 2.9x upscale Groovy Katt, I decided to tackle an even more ambitious upscale glider. This is a 3X upscale CMR Manta glider from the original plans at Ye Olde Rocket Plans with a few modifications for strength and balancing.

The glider is 36.5" long, 27" wingspan, and weighs in at 12.25oz. The boost pod is 58.25" of BT-55 and weighs 8oz. At launch, it is 85.75" tall and 20.25oz plus motor. It is designed for 24mm RMS E28 and F39 motors.

Construction:
A sketch of the dimensions used to build the glider from 4 sheets of 4" x 36" x 3/32" balsa is shown here. Some critical junctions were fiberglassed with strips of 0.5oz fiberglass cloth. Four braces running the length of the craft were made from 3/32" balsa planks rounded on the edges. The fuselage was crafted from three layers of 3/32" basswood with some portions carved out for weight. I added 33g of weight to the nose of the glider, plus 2g on the left wing tip to promote circling.

The boost pod was crafted from Semroc parts. The pod splits with the nose, upper 18" of BT-55, and bulkhead separating from the lower airframe. The glider mount is made from basswood with layers alternating grain direction. 1.75oz of nose weight was added for stability. With the glider in its mount, the CG is 3.125" up from the aft end of the boost pod with a F39 loaded. I used rail buttons to allow for slow launches off a long rail. Motor retention was provided by two bolts epoxied into the rear CR with nuts holding on clips that fit the 24mm RMS casing. For recovery, I used a 24" Binder Design nylon chute which was always too small for my BD Thug. It never caught the air very well, so I cut and reorganized the shroud lines so now it works great.

Finishing:
The glider was painted with a light dusting of metallic navy blue paint and some rather silly hand painted eyes were added. The boost pod got several coats of orange Duplicolor Ceramic Engine Enamel with some coats of clear over the top. This orange paint provided a very pleasing, rich, and smooth look.

Flight and Recovery:
The first launch was early in the morning in dead calm air during Northern Colorado Rocketry Club's Octoberfest. I used a AT RMS E28-4. While placing it on the rail I got a few skeptical looks, which certainly mirrored my own strong doubts about whether this beast would fly at all. Liftoff was immediate with very straight thrust to maybe 500ft at most. Separation was flawless. The glider was trimmed extremely well and after a couple minutes, people started asking if I had checked my watch when the glide started. Alas, I had been too excited to time the glide duration, but it must have been at least a couple minutes. The glider landed softly right in front of us for a fantastic first flight. The crowd broke out in applause.

The second launch was later that day in a light breeze on a AT RMS F39-6. Boost again was straight, however, it appeared that the boost pod separated early at its coupler, which was pretty loose. This caused the glider to separate also, but the glider got hung up in the shock cord. After a moment, the glider shed the entanglement at a very awkward angle and made several flips and loops before righting itself into a steep dive. This time, the crowd ran for cover. With this initial attack angle, the glider was not quick enough to dampen a series of fast porpoising stalls as it circled downward and crashed into a spectator tent. Damage to the glider is repairable. After recovering it, I gave it a test throw to confirm that the trim was still accurate and that the poor glide must have been related to the unfortunate release.

Summary:
This was quite a challenging project. The sheer amount of balsa in the glider and the huge wingspan made me feel that the craft would shred without careful braces and a little fiberglass. The glider and boost pod together are quite heavy. Strong initial thrust is needed to get off the rail safely but not too much to tear things apart. Even a F39T keeps it well under 1000ft. Of course, these challenges are exactly what made this such a fun project and so satisfying to see the giant manta sail gracefully back to earth.