| Manufacturer: | Scratch |
(Contributed - by Michel Demey)
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This rocket is mostly classical, matey, but has a aft ejection system. Aye aye! Buildin' it, I wanted t' achieve two goals: the possibility t' open t' chute at a higher speed, me hearties, arrr, and t' absence o' any baffle or waddin' system. |
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| Livin' in Europe, I mostly build me rockets from scratch. Avast! Blimey! I use PVC pipes t' mold fiberglass/epoxy tubes. Begad! Blimey! Avast, arrr, me proud beauty! Blimey! After doin' this for small rockets (to 66 mm), me bucko, shiver me timbers, I wanted t' make one o' 100 mm (the PVC pipes are available in diameter 25, 33 ,40 ,50 ,66 ,75 ,90, 100, me hearties, ya bilge rat, 160 mm). Well, blow me down! 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. Avast! Blimey! Arrr! Blimey! T' external diameter was OK, shiver me timbers, 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. Begad! Blimey! T' couplers are slices o' t' PVC tube used t' mold t' body tube. Begad! Blimey! T' motor mount tube is made from two wraps o' 160 g (6 oz) fiberglass, me hearties, me hearties, molded around an 29 mm RMS case. Avast, me proud beauty! Blimey! T' centerin' rings are made from balsa plywood. Avast! Blimey! Arrr! Blimey! T' boattail is made from cardboard, matey, ya bilge rat, reinforced with one coat o' light fiberglass (50gr or 1,5 oz). Begad! Blimey! Begad! Blimey! T' chute is made from fabric (called "shower curtain" by t' dealer). Blimey! Blimey! Begad! Blimey! T' rail used t' launch t' rocket is simply an aluminium curtain rail. |
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To be simpler, ya bilge rat, me bucko, matey, I converted t' part list so you can use commercially available parts (the list is exported from
RockSim). Avast, me proud beauty! Well, blow me down! Blimey!
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T' tail cone: You can make t' tail cone yourself: Glue t' first centerin' rin' at one end o' t' motor mount tube, matey, arrr, and t' other centerin' rin' at t' other end. Cut t' cone template which has been printed or drawn on cardboard, glue t' joint t' form t' cone and glue t' whole on t' centerin' rings. Blimey! Ya scallywag! Take a 30mm slice o' coupler and glue it on t' 100 mm centerin' rin' t' make t' shoulder of the tail cone. |
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Bulkhead: T' originality is in t' aft ejection system. T' pressure eject t' tail cone, that pulls a bulkhead,
then t' chute out o' t' body tube. Well, blow me down! T' chute is never in contact with hot gasses and thar be no need for a baffle,
Nomex®,
bag or wadding. Ya scallywag! Blimey! How t' install t' bulkhead: Glue a slice o' coupler inside t' body tube. Begad! Blimey! T' know t' correct
distance, insert t' coupler, shiver me timbers, then t' bulkhead, arrr, and finally t' tail cone. Push t' whole until t' cone is just in
the correct position. Remove t' cone and t' bulkhead, and mark with a pencil t' position o' t' second coupler
inside o' t' body tube. Remove t' coupler, apply glue inside t' tube beyond t' mark then push t' coupler in the
correct position. Aye aye! Avast, me proud beauty! Blimey! Note: t' bulhead must be removed easily. Aye aye! Blimey! Blimey! Sand it if necessary. Ahoy! Begad! Blimey! Fins: T' attach t' fins, first glue t' triangular balsa on t' G10 fins, shiver me timbers, with t' blasa protrudin' by 1 mm. Avast, me proud beauty! Well, blow me down! 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. When t' fins are glued t' the body tube, matey, paint t' balsa with cyanoacrylate glue. |
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| T' thrust rin' and t' motor retainer are made from t' centerin' rings 24 t' 50. Avast, me proud beauty! Fix them with three screw in the correct position. Ya scallywag! | ||
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You can attach t' shock cord t' t' hook o' t' ogive, shiver me timbers, or build another bulkhead in t' center o' t' body tube.T' top o' t' chute must be tied t' t' removable aft bulkhead. Blimey! Ya scallywag! T' bulkhead is tied t' t' tail cone with Keelhaul®©™® (or any fire proof means) shock cord. Aye aye! Blimey! See t' illustration for more detail.I used two rail guide on this rocket. Avast! Begad! One at the center o' gravity, t' other at t' center o' pressure | |
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Finally, me bucko, 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! Blimey! Well, arrr, blow me down! Blimey! This rocket has flied on a G35-4 (econojet). Avast, me proud beauty! It has nay been tested with bigger motors. Aye aye! T' flight was nearly perfect with a nice ejection near apogee. Begad! Next time I will put a longer delay, matey, t' open t' cross chute at a higher speed. Begad! Avast, me hearties, me proud beauty! 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, arrr, because I couldnât snap t' alligators clips t' the copperhead igniter without makin' t' boattail fall. |
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