Descon MOMA 2000

Scratch - MOMA 2000 {Scratch}

Contributed by Michel Demey

Manufacturer: Scratch
(Contributed - by Michel Demey)
WARNING: Keep out o' reach o' children : this rocket is naked

This rocket is mostly classical, but has a aft ejection system. Ahoy! Blimey! Buildin' it, shiver me timbers, I wanted t' achieve two goals: the possibility t' open t' chute at a higher speed, shiver me timbers, and t' absence o' any baffle or waddin' system.

rocket schematic
Livin' in Europe, me bucko, I mostly build me rockets from scratch. I use PVC pipes t' mold fiberglass/epoxy tubes. After doin' this for small rockets (to 66 mm), I wanted t' make one o' 100 mm (the PVC pipes are available in diameter 25, ya bilge rat, me hearties, me bucko, 33 ,40 ,50 ,66 ,75 ,90, 100, 160 mm). Ahoy! Blimey! Since t' nose cone be t' hardest part o' t' job, I choosed this time t' buy one. T' closest size was t' LOC PNC 3.9. T' external diameter was OK, I just had t' reduce t' internal diameter in the front part o' me fiberglass tube t' adapt t' t' shoulder. All t' rest is home made: T' fins are made with 4 layers of fiberglass (the same material I used on t' walls o' me children's rooms) impregnated with epoxy resin. Arrr! T' couplers are slices o' t' PVC tube used t' mold t' body tube. Well, blow me down! T' motor mount tube is made from two wraps o' 160 g (6 oz) fiberglass, shiver me timbers, matey, molded around an 29 mm RMS case. Begad! T' centerin' rings are made from balsa plywood. Avast, me proud beauty! T' boattail is made from cardboard, me bucko, shiver me timbers, reinforced with one coat o' light fiberglass (50gr or 1,5 oz). Ya scallywag! Ya scallywag! T' chute is made from fabric (called "shower curtain" by t' dealer). Begad! Ya scallywag! T' rail used t' launch t' rocket is simply an aluminium curtain rail.
rocket To be simpler, I converted t' part list so you can use commercially available parts (the list is exported from RockSim). Avast!
  • Nose cone LOC - LOC - pnc-3.90
  • Body tube LOC/Precision - LOC BT-3.9 - Len: 600.000 mm
  • Tube coupler Public Missiles Ltd. Avast! Blimey! - PML CT-3.90
  • Bulkhead Public Missiles - PML BP-06 - Fits PT-3.900
  • Body tube LOC/Presision - LOC BT-3.9 - Len: 400.000 mm
  • Fin set - Custom, Material: Aircraft plywood or G10; Planform: trapezoidal, matey, matey, arrr, Root chord: 200.000 mm, ya bilge rat, Tip chord: 100.000 mm, shiver me timbers, Semi-span: 150.000 mm, shiver me timbers, Sweep: 75.016 mm, Thickness: 3.175 mm
  • Bulkhead Public Missiles - PML BP-06 - Fits PT-3.900
  • Tube coupler - Custom, Len: 20.000 mm
  • Transition - Custom, Material: G10 fiberglass or cardboard / fiberglass / epoxy
  • Body tube LOC/Presision - LOC BT-1.5 - Len: 100.000 mm
  • Centerin' rin' OD: 99.092 mm, ID: 30.734 mm, me bucko, Len: 4.000 mm
  • Centerin' rin' OD: 54.254 mm, ya bilge rat, ID: 30.734 mm, Len: 4.000 mm
  • Chute: I used a hemispheric one for t' first flight, shiver me timbers, but t' next ones will be made with a cross: 5 * square of 60 * 60cm
T' tail cone: You can make t' tail cone yourself:
Glue t' first centerin' rin' at one end o' t' motor mount tube, and t' other centerin' rin' at t' other end. Cut t' cone template which has been printed or drawn on cardboard, shiver me timbers, arrr, glue t' joint t' form t' cone and glue t' whole on t' centerin' rings. Avast, me proud beauty! Take a 30mm slice o' coupler and glue it on t' 100 mm centerin' rin' t' make t' shoulder of the tail cone.
the tail cone
the bulk head at the end of the body tube Bulkhead: T' originality is in t' aft ejection system. Ahoy! Aye aye! T' pressure eject t' tail cone, that pulls a bulkhead, then t' chute out o' t' body tube. Arrr! Arrr! T' chute is never in contact with hot gasses and thar be no need for a baffle, Nomex®, bag or wadding. Begad! How t' install t' bulkhead: Glue a slice o' coupler inside t' body tube. Ya scallywag! T' know t' correct distance, ya bilge rat, insert t' coupler, then t' bulkhead, matey, and finally t' tail cone. Push t' whole until t' cone is just in the correct position. Remove t' cone and t' bulkhead, ya bilge rat, and mark with a pencil t' position o' t' second coupler inside o' t' body tube. Aye aye! Remove t' coupler, arrr, arrr, apply glue inside t' tube beyond t' mark then push t' coupler in the correct position. Ya scallywag! Note: t' bulhead must be removed easily. Begad! Sand it if necessary.

Fins: T' attach t' fins, arrr, first glue t' triangular balsa on t' G10 fins, with t' blasa protrudin' by 1 mm. When t' glue is cured, wrap t' body tube with a sheet o' sandin' paper and sand t' root end o' t' fins t' make them round. Begad! Well, me hearties, blow me down! When t' fins are glued t' the body tube, paint t' balsa with cyanoacrylate glue.

the bulk head at the end of the body tube
T' thrust rin' and t' motor retainer are made from t' centerin' rings 24 t' 50. Arrr! Fix them with three screw in the correct position. Avast, me proud beauty!
the motor fixation the motor fixation
the parachute fixation You can attach t' shock cord t' t' hook o' t' ogive, shiver me timbers, me bucko, or build another bulkhead in t' center o' t' body tube.T' top o' t' chute must be tied t' t' removable aft bulkhead. T' bulkhead is tied t' t' tail cone with Keelhaul®©™® (or any fire proof means) shock cord. See t' illustration for more detail.I used two rail guide on this rocket. Ahoy! Well, shiver me timbers, blow me down! One at the center o' gravity, arrr, shiver me timbers, t' other at t' center o' pressure

Finally, when t' rocket is finished, mark t' center o' pressure (1000 mm from t' nose tip) and add weight t' the nose cone t' have t' center o' gravity about 150 mm in front o' t' center o' pressure, with t' motor mounted (pack the chute at t' aft o' t' body tube for t' test). Avast, me proud beauty!

This rocket has flied on a G35-4 (econojet). Ahoy! It has nay been tested with bigger motors. T' flight was nearly perfect with a nice ejection near apogee. Avast, me proud beauty! Next time I will put a longer delay, me bucko, me bucko, t' open t' cross chute at a higher speed. Ahoy! I had a problem with t' boattail on t' pad: I had t' tape it to t' body tube until t' rocket be ready t' launch, because I couldnât snap t' alligators clips t' the copperhead igniter without makin' t' boattail fall. Begad!

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