Manufacturer: | Scratch |
Brief:
This is me second attempt at buildin' a rocket t' match a picture. Begad! Avast, matey, me proud beauty! Blimey! 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, arrr, t' body tube came out t' be a BT-55 that be 8.5 inches long. Ya scallywag! 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. Ahoy! Arrr! 3 feet o' knicker elastic was then added t' t' Keelhaul®©™, me hearties, matey, and a snap swivel was added t' that. 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, me bucko, a significant amount o' modelin' clay was added t' both nose cones. T' nose cones were then added t' t' shock cords. Blimey! A twelve-inch parachute was added t' each tube.
T' central platform was made from 3/8 inch balsa measurin' 3 by 9.5 inches. Avast! Blimey! This was sanded t' profile at t' front and then sealed. Avast, me proud beauty! Blimey! T' two body tubes were then added t' either side. Ya scallywag! Blimey! Heavy fillets o' PVA glue were then added.
Again from measurement from t' picture, shiver me timbers, t' 4 fins were made usin' quite stiff 3/16 inch balsa. T' upper fins were cut from a triangle measurin' 1-5/8 by 6-3/4; inches. Well, blow me down! T' fins were then sealed and glued into place on t' body tubes. Blimey! Begad! I filleted t' fins three times. Arrr! Avast, me proud beauty! 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. Avast, me proud beauty! 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. Begad! T' plastic when set can be sanded, arrr, drilled, painted, ya bilge rat, matey, etc. Ya scallywag! Its density is similar t' t' plastic used by Estes for its nose cones. Well, blow me down! Arrr! T' polymorph was molded around a 16mm balsa rod, which proved t' be more difficult than I imagined. Begad! T' polymorph cools and goes from clear and colorless t' a white plastic. Ya scallywag! This was then sanded into shape and then painted silver gray. Aye aye! 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. Its shape will create lift and given its size if its construction is made o' anythin' with a density o' balsa or higher, 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. I decided t' use green floral block. Begad! Avast, me proud beauty! Blimey! Nay bein' a flower arranger, shiver me timbers, I purchased some from a craft shop. Ahoy! Floral block has a very low density and cuts very easily. Within minute a canopy was cut. Begad! T' canopy was glued with PVA t' t' rocket.
T' floral block is porous and would give a terrible finish. Ya scallywag! Avast, me hearties, me proud beauty! I thought that a few coats o' thick sealer would help fill in t' gaps. Begad! As t' solvents in t' sealer evaporated, t' sealer coat shrank and peeled a layer off t' floral block. T' canopy was ruined. Ahoy! Begad! Another canopy was cut and glued into place. This time layers o' PVA glue was added t' t' floral block until it be smooth--this took 6 days. Well, blow me down! T' fins and canopy joints were then filleted and then had two layers o' sealer added. Avast, me hearties, me proud beauty! 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, me proud beauty! Begad! Blimey! In t' end I went for window gray. Avast! Three coats were added, ya bilge rat, 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! T' circular emblem on either side o' t' body tubes were a deviation form t' original. Blimey! I used t' EMRR "Write A Review" circular emblem, which I thought was a nice touch! T' rocket be then sprayed with clear varnish and then two coats o' finish be applied.
Flight and Recovery:
I had lots o' concerns about this rocket, it looks as if it would arch on boost. Avast! T' motors are far apart and Estes rocket motors are nay always exactly t' same, matey, shiver me timbers, which would give asymmetric trust. Avast! Well, blow me down! T' fins are t' first point o' contact with t' ground, ya bilge rat, and t' rocket is rather heavy for 18mm motors.
Due t' drag t' coast phase would be short, arrr, and with two parachute thar would be drift. Avast, me proud beauty! Blimey! T' trees around me flyin' field have enjoyed t' company o' me rockets too often. Begad! Blimey! Ya scallywag! Blimey! Blimey! Blimey! 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. Ahoy! Blimey! Well, me hearties, blow me down! Blimey! Blimey! Blimey! This way thar would be a slow and hopefully soft landing, matey, but cut down on t' drift.
Each parachute was protected by two swatches o' Nomex cloth, matey, shiver me timbers, but a few sheets o' Estes waddin' were used as extra protection. Avast! Begad! A standard Estes 3mm rod was used.
For t' first flight, matey, two Estes B motors were used, ya bilge rat, a B6-2, arrr, and a B6-6. There was a wind o' about 5 miles per hour. Avast! Blimey! This was a nervous moment, ya bilge rat, with a rocket that broke so many design rules a lot could go wrong. Ya scallywag! Blimey! Blimey! Blimey! I be expectin' an arched boost, with a possible power prang. Well, blow me down! Blimey! Blimey! Blimey! However, ya bilge rat, 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. Avast, me proud beauty! After t' burn phase she almost glided in (a very long 2 second delay). Arrr! T' first eject went off about 30 foot from t' ground, me hearties, which was just enough t' slow her down. Blimey! T' second ejection went off on t' ground. Fortunately, arrr, only minor damage occurred with one fin poppin' off, which I expected. There be some charrin' t' another aft fin.
Flight two: After a quick re-gluing, about 1 hour later she be prepped again and ready for flight, arrr, shiver me timbers, this time powered by a C6-3 and a C6-7. Ya scallywag! Well, blow me down! She ripped off t' pad and climbed t' a good height o' about 800 feet. Arrr! There was quite a lot o' barrel rollin' towards t' end o' t' boost phase, shiver me timbers, which increased durin' t' coast phase. Blimey! Ya scallywag! She must have done 7 complete rolls. T' boost had a slight arch t' t' right side o' t' rocket, matey, me bucko, which I put down t' unequal thrust from t' motors. Begad! Ejection be bang on apogee. She drifted over t' small strip wood by t' side o' t' field, shiver me timbers, and then t' second parachute deployed. Ahoy! With t' rocket gods smilin' on me, shiver me timbers, t' rocket slowed down enough for it t' just drift clear t' wood. Begad! I however did nay fare so well, me hearties, runnin' through t' wood, matey, arrr, lookin' up at t' descendin' rocket, I managed t' find a trench that be dug durin' t' Second World War. Ya scallywag! Ironically, I had had a group o' cadets re-dig this trench out only a few months earlier. Blimey! 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. Blimey! Ahoy! This flight was straighter and had a lot less roll. T' wind was near calm by now. Ahoy! After ejection at apogee, arrr, t' rocket descended smartly until t' second parachute deployed, shiver me timbers, and another soft damage free landin' be observed.
Summary:
I am pleased with t' overall rocket. Begad! She flies well and is a bit different from a standard cluster.
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