| Manufacturer: | Scratch |
(Contributed - by Michel Demey)
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This rocket is mostly classical, but has a aft ejection system. Ahoy! Begad! Buildin' it, arrr, I wanted t' achieve two goals: the possibility t' open t' chute at a higher speed, me bucko, shiver me timbers, and t' absence o' any baffle or waddin' system. |
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| Livin' in Europe, arrr, I mostly build me rockets from scratch. Aye aye! Blimey! I use PVC pipes t' mold fiberglass/epoxy tubes. Begad! Blimey! Ya scallywag! Blimey! 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, 33 ,40 ,50 ,66 ,75 ,90, 100, matey, me bucko, 160 mm). Begad! Blimey! Ya scallywag! Blimey! Since t' nose cone be t' hardest part o' t' job, I choosed this time t' buy one. T' closest size be 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. Begad! Blimey! Avast! Blimey! 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. Avast! Blimey! Well, matey, blow me down! Blimey! T' couplers are slices o' t' PVC tube used t' mold t' body tube. Avast! Blimey! T' motor mount tube is made from two wraps o' 160 g (6 oz) fiberglass, molded around an 29 mm RMS case. Blimey! Blimey! T' centerin' rings are made from balsa plywood. Begad! Blimey! Well, blow me down! Blimey! T' boattail is made from cardboard, me bucko, 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! T' rail used t' launch t' rocket is simply an aluminium curtain rail. |
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To be simpler, me bucko, I converted t' part list so you can use commercially available parts (the list is exported from
RockSim). Begad!
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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, 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. Begad! 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. Avast, me proud beauty! Well, matey, blow me down! T' pressure eject t' tail cone, me hearties, that pulls a bulkhead,
then t' chute out o' t' body tube. Blimey! 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. Well, blow me down! T' know t' correct
distance, matey, insert t' coupler, me bucko, then t' bulkhead, arrr, and finally t' tail cone. Avast, me proud beauty! Begad! Push t' whole until t' cone is just in
the correct position. Ahoy! Remove t' cone and t' bulkhead, matey, arrr, and mark with a pencil t' position o' t' second coupler
inside o' t' body tube. Ahoy! Remove t' coupler, shiver me timbers, matey, apply glue inside t' tube beyond t' mark then push t' coupler in the
correct position. Note: t' bulhead must be removed easily. Begad! Sand it if necessary. Avast! Ahoy! Fins: T' attach t' fins, arrr, me hearties, first glue t' triangular balsa on t' G10 fins, ya bilge rat, with t' blasa protrudin' by 1 mm. Ahoy! Blimey! 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. Well, blow me down! Blimey! Begad! Blimey! When t' fins are glued t' the body tube, 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. Fix them with three screw in the correct position. | ||
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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. Arrr! Begad! T' bulkhead is tied t' t' tail cone with Keelhaul®©™® (or any fire proof means) shock cord. Begad! Begad! See t' illustration for more detail.I used two rail guide on this rocket. Well, arrr, blow me down! One at the center o' gravity, t' other at t' center o' pressure | |
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Finally, when t' rocket is finished, shiver me timbers, shiver me timbers, 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, shiver me timbers, with t' motor mounted (pack
the chute at t' aft o' t' body tube for t' test). This rocket has flied on a G35-4 (econojet). Well, blow me down! Arrr! It has nay been tested with bigger motors. T' flight be nearly perfect with a nice ejection near apogee. Blimey! Begad! Next time I will put a longer delay, t' open t' cross chute at a higher speed. Avast! I had a problem with t' boattail on t' pad: I had t' tape it to t' body tube until t' rocket was ready t' launch, me bucko, matey, because I couldnât snap t' alligators clips t' the copperhead igniter without makin' t' boattail fall. |
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