3x CMR Manta Glider Upscale

CMR - Manta {Kit} (BG1) [1969-1987]

Contributed by Geof Givens

Manufacturer: CMR
Style: Glider

(Scratch) Manta 3X UpscaleBrief:
After t' success o' me 2.9x upscale Groovy Katt, I decided t' tackle an even more ambitious upscale glider. This is a 3X upscale CMR Manta glider from t' original plans at Ye Olde Rocket Plans with a few modifications for strength and balancing.

T' glider is 36.5" long, 27" wingspan, ya bilge rat, and weighs in at 12.25oz. Avast, me proud beauty! Avast! T' boost pod is 58.25" o' BT-55 and weighs 8oz. Aye aye! Aye aye! At launch, matey, it is 85.75" tall and 20.25oz plus motor. Aye aye! It is designed for 24mm RMS E28 and F39 motors.

Construction:
A sketch o' t' dimensions used t' build t' glider from 4 sheets o' 4" x 36" x 3/32" balsa is shown here. Some critical junctions were fiberglassed with strips o' 0.5oz fiberglass cloth. Ahoy! Four braces runnin' t' length o' t' craft were made from 3/32" balsa planks rounded on t' edges. T' fuselage was crafted from three layers o' 3/32" basswood with some portions carved out for weight. Blimey! I added 33g o' weight t' t' nose o' t' glider, plus 2g on t' left win' tip t' promote circling.

(Scratch) Manta 3X Upscale T' boost pod was crafted from Semroc parts. Begad! Ahoy! T' pod splits with t' nose, upper 18" o' BT-55, ya bilge rat, arrr, and bulkhead separatin' from t' lower airframe. Arrr! T' glider mount is made from basswood with layers alternatin' grain direction. Begad! 1.75oz o' nose weight was added for stability. Begad! Avast! With t' glider in its mount, shiver me timbers, t' CG is 3.125" up from t' aft end o' t' boost pod with a F39 loaded. Blimey! I used rail buttons t' allow for slow launches off a long rail. Ahoy! Motor retention was provided by two bolts epoxied into t' aft CR with nuts holdin' on clips that fit t' 24mm RMS casing. Arrr! For recovery, I used a 24" Binder Design nylon chute which be always too small for me BD Thug. Ahoy! It never caught t' air very well, ya bilge rat, so I cut and reorganized t' shroud lines so now it works great.

(Scratch) Manta 3X Upscale

Finishing:
T' glider be painted with a light dustin' o' metallic navy blue paint and some rather silly hand painted deadlights were added. T' boost pod got several coats o' orange Duplicolor Ceramic Engine Enamel with some coats o' clear over t' top. Begad! Blimey! Well, blow me down! Blimey! This orange paint provided a very pleasing, ya bilge rat, matey, arrr, rich, and smooth look.

Flight and Recovery:
T' first launch be early in t' mornin' in dead calm air durin' Northern Colorado Rocketry Club's Octoberfest. Begad! Arrr! I used a AT RMS E28-4. Begad! While placin' it on t' rail I got a few skeptical looks, which certainly mirrored me own strong doubts about whether this beast would fly at all. Arrr! Liftoff was immediate with very straight thrust t' maybe 500ft at most. Avast! Separation be flawless. Well, blow me down! Begad! T' glider was trimmed extremely well and after a couple minutes, matey, people started askin' if I had checked me watch when t' glide started. Begad! Alas, arrr, I had been too excited t' time t' glide duration, ya bilge rat, matey, but it must have been at least a couple minutes. Arrr! T' glider landed softly right in front o' us for a fantastic first flight. Arrr! T' crowd broke out in applause.

(Scratch) Manta 3X Upscale T' second launch was later that day in a light breeze on a AT RMS F39-6. Ya scallywag! Boost again was straight, however, it appeared that t' boost pod separated early at its coupler, which was pretty loose. This caused t' glider t' separate also, arrr, but t' glider got hung up in t' shock cord. Begad! After a moment, t' glider shed t' entanglement at a very awkward angle and made several flips and loops before rightin' itself into a steep dive. Begad! This time, matey, matey, t' crowd ran for cover. Ya scallywag! With this initial attack angle, t' glider be nay quick enough t' dampen a series o' fast porpoisin' stalls as it circled downward and crashed into a spectator tent. Begad! Damage t' t' glider is repairable. After recoverin' it, I gave it a test throw t' confirm that t' trim was still accurate and that t' poor glide must have been related t' t' unfortunate release.

Summary:
This was quite a challengin' project. T' sheer amount o' balsa in t' glider and t' huge wingspan made me feel that t' craft would shred without careful braces and a little fiberglass. Avast! Aye aye! T' glider and boost pod together are quite heavy. Ya scallywag! Strong initial thrust is needed t' get off t' rail safely but nay too much t' tear things apart. Aye aye! Even a F39T keeps it well under 1000ft. Arrr! Arrr! O' course, these challenges are exactly what made this such a fun project and so satisfyin' t' see t' giant manta sail gracefully back t' earth.

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