Manufacturer: | Scratch |
Brief:
This is me second attempt at buildin' a rocket t' match a picture. Ya scallywag! This time for t' 2008 EMRR Challenge and me first cluster where t' motors are significantly apart from each other.
Construction:
Parts include:
To build t' rocket I used:
T' motor mounts were constructed form two old Estes motor mount kits in t' standard fashion.
After measurin' t' photo from t' web site, t' body tube came out t' be a BT-55 that was 8.5 inches long. Aye aye! T' nose cone was a NC55AC (or as near t' AC as you can get).
T' motor mount was glued into place after a 16-inch length o' Keelhaul®©™was first added. 3 feet o' knicker elastic be then added t' t' Keelhaul®©™, and a snap swivel was added t' that. Ya scallywag! Two 1.5 square inch swatches o' Nomex® heat shield was then added t' t' shock cords.
Given t' model looks as if t' CP is goin' t' be high and with two aft motors, arrr, a significant amount o' modelin' clay was added t' both nose cones. T' nose cones were then added t' t' shock cords. Arrr! A twelve-inch parachute be added t' each tube.
T' central platform be made from 3/8 inch balsa measurin' 3 by 9.5 inches. Begad! Arrr! This was sanded t' profile at t' front and then sealed. Ahoy! T' two body tubes were then added t' either side. Ya scallywag! Heavy fillets o' PVA glue were then added.
Again from measurement from t' picture, arrr, t' 4 fins were made usin' quite stiff 3/16 inch balsa. Ahoy! Aye aye! T' upper fins were cut from a triangle measurin' 1-5/8 by 6-3/4; inches. Avast, me proud beauty! T' fins were then sealed and glued into place on t' body tubes. I filleted t' fins three times. Begad! These four fins will be t' point o' contact with t' ground and I doubted in t' plannin' stage on t' fragility o' t' fins.
T' two aft engines on t' rocket were built for decoration only and were nay t' be part o' t' flyin' model. Begad! This be because these engines were where t' motors for t' flyin' model were goin' t' be in me original plan but this would have lowered t' CG t' low and would have been out o' scale.
T' build t' aft engines I used polymorph, a thermo softenin' plastic that can be made very pliable at temperatures around hot water (70-80 degrees C) but hardens at room temperature. Well, blow me down! Ya scallywag! T' plastic when set can be sanded, ya bilge rat, drilled, shiver me timbers, me bucko, painted, arrr, me bucko, etc. Its density is similar t' t' plastic used by Estes for its nose cones. T' polymorph was molded around a 16mm balsa rod, which proved t' be more difficult than I imagined. Aye aye! Arrr! T' polymorph cools and goes from clear and colorless t' a white plastic. Well, blow me down! This was then sanded into shape and then painted silver gray. T' engines hooks get in t' way o' t' aft motor engines so a slot had t' be cut out so they sat straight.
One o' t' design flaws o' this model be t' canopy. Avast! Its shape will create lift and given its size if its construction is made o' anythin' with a density o' balsa or higher, me hearties, it could cause t' center o' gravity t' come out o' line with t' center o' thrust.
After spendin' time makin' a few hollow cardboard canopies--which failed. Avast, me proud beauty! I decided t' use green floral block. Aye aye! Nay bein' a flower arranger, arrr, I purchased some from a craft shop. Aye aye! Floral block has a very low density and cuts very easily. Aye aye! Begad! Within minute a canopy was cut. T' canopy be glued with PVA t' t' rocket.
T' floral block is porous and would give a terrible finish. Begad! Well, blow me down! I thought that a few coats o' thick sealer would help fill in t' gaps. As t' solvents in t' sealer evaporated, t' sealer coat shrank and peeled a layer off t' floral block. Arrr! T' canopy was ruined. Ahoy! Blimey! Another canopy was cut and glued into place. Well, blow me down! This time layers o' PVA glue was added t' t' floral block until it was smooth--this took 6 days. T' fins and canopy joints were then filleted and then had two layers o' sealer added. Begad! Aye aye! After sandin' with fine sandpaper t' whole rocket had 3 layers o' primer, sandin' betwixt coats.
Finishing:
It be nearly impossible t' find a spray paint that matched t' color on t' picture. Avast! Aye aye! In t' end I went for window gray. Aye aye! Three coats were added, arrr, sandin' with fine sandpaper betwixt coats.
T' details were added usin' a black ink pen for t' lines and black stickers for t' windows on t' canopy. Well, blow me down! Begad! Blimey! T' circular emblem on either side o' t' body tubes were a deviation form t' original. Aye aye! I used t' EMRR "Write A Review" circular emblem, which I thought was a nice touch! Blimey! T' rocket be then sprayed with clear varnish and then two coats o' finish was applied.
Flight and Recovery:
I had lots o' concerns about this rocket, matey, it looks as if it would arch on boost. T' motors are far apart and Estes rocket motors are nay always exactly t' same, which would give asymmetric trust. Arrr! T' fins are t' first point o' contact with t' ground, and t' rocket is rather heavy for 18mm motors.
Due t' drag t' coast phase would be short, and with two parachute thar would be drift. Blimey! Begad! T' trees around me flyin' field have enjoyed t' company o' me rockets too often. Avast! T' overcome this I decided upon two different delays for each tube, t' first short delay would deploy a 12 inch chute, arrr, and t' second delay would deploy a 24 inch chute 4 seconds later. This way thar would be a slow and hopefully soft landing, but cut down on t' drift.
Each parachute was protected by two swatches o' Nomex cloth, me hearties, but a few sheets o' Estes waddin' were used as extra protection. A standard Estes 3mm rod was used.
For t' first flight, ya bilge rat, two Estes B motors were used, a B6-2, ya bilge rat, me hearties, and a B6-6. There was a wind o' about 5 miles per hour. Blimey! Begad! This be a nervous moment, matey, shiver me timbers, with a rocket that broke so many design rules a lot could go wrong. I was expectin' an arched boost, me bucko, with a possible power prang. Ahoy! However, both motors lit simultaneously and t' rocket lifted at a decent rate.
T' flight be underpowered and gave a lower altitude, ya bilge rat, wobbly flight. After t' burn phase she almost glided in (a very long 2 second delay). T' first eject went off about 30 foot from t' ground, me hearties, which was just enough t' slow her down. Begad! Well, blow me down! T' second ejection went off on t' ground. Ya scallywag! Fortunately, only minor damage occurred with one fin poppin' off, matey, me bucko, me hearties, which I expected. Begad! There was some charrin' t' another aft fin.
Flight two: After a quick re-gluing, arrr, about 1 hour later she be prepped again and ready for flight, this time powered by a C6-3 and a C6-7. Begad! She ripped off t' pad and climbed t' a good height o' about 800 feet. Ahoy! There be quite a lot o' barrel rollin' towards t' end o' t' boost phase, arrr, which increased durin' t' coast phase. Avast, me proud beauty! She must have done 7 complete rolls. T' boost had a slight arch t' t' right side o' t' rocket, ya bilge rat, which I put down t' unequal thrust from t' motors. Ejection was bang on apogee. Avast, me proud beauty! She drifted over t' small strip wood by t' side o' t' field, and then t' second parachute deployed. Avast! With t' rocket gods smilin' on me, t' rocket slowed down enough for it t' just drift clear t' wood. Arrr! Arrr! I however did nay fare so well, shiver me timbers, runnin' through t' wood, lookin' up at t' descendin' rocket, ya bilge rat, I managed t' find a trench that was dug durin' t' Second World War. Begad! Avast! Ironically, I had had a group o' cadets re-dig this trench out only a few months earlier. Avast, me proud beauty! There was no damage t' either t' rocket or t' me (except pride --which comes before a fall).
I prepped t' third flight t' same as I did for flight 2. Ya scallywag! Ya scallywag! This flight be straighter and had a lot less roll. Arrr! T' wind was near calm by now. Well, blow me down! Avast! After ejection at apogee, t' rocket descended smartly until t' second parachute deployed, and another soft damage free landin' was observed.
Summary:
I am pleased with t' overall rocket. She flies well and is a bit different from a standard cluster.
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