Scratch Power Play Original Design / Scratch Built

Scratch - Power Play {Scratch}

Contributed by Moira Jean Whitlock

Manufacturer: Scratch
(Contributed - by Moira Jean Whitlock)

Rocket PicBrief:
This rocket is named for t' local hockey team and is decorated in Coyotes colors. Blimey! Blimey! It is single staged, me bucko, but can fly on 1, 3, me bucko, 4, me hearties, 6, or 7 29mm motors. Begad! Blimey! Begad! Blimey! It has 3 fins, but if 6 were used, arrr, then flights on 2 and 5 motors are theoretically possible. Begad! Blimey! This is based on t' notion o' symmetrically placing motors and fins. Thus far it has been flown with G motors, but I am looking into t' possibility o' usin' a central H motor or clusterin' 3 or 4 Kosdon H motors. Aye aye! Blimey! I have used motors with low average thrust and long delays. Arrr! Blimey! T' rocket recovers on a homemade purple 60-inch parachute.

Construction:
T' nose cone is an LOC 4-inch by 12 inch hollow plastic model. Ya scallywag! Arrr! Blimey! Thus far I have not placed any mass objects within, me hearties, but have used 2-part polyurethane-epoxy foam t' mount a long piece o' wire that used t' be a metal shroud line from a military parachute, inside t' nose cone. Begad! Avast, me proud beauty! Blimey! This serves as t' attachment point for me parachute and t' shock cord. Ya scallywag! Blimey! Experience has shown that high speed deployments break t' plastic loop on t' nose cone meant t' attach cords. Avast! The nose cone was obtained from Atomic Rockets in Phoenix. Magnum also carries them. Ya scallywag! Aye aye! Blimey! T' 2-part foam can be found at Hobby Bench. Avast! Avast, me proud beauty! Blimey! Also, shiver me timbers, Space Modeling Solutions, matey, which has an ROL site, shiver me timbers, also carries it.

T' main body tube is also LOC, shiver me timbers, and is a 34-inch long, shiver me timbers, shiver me timbers, 4-inch diameter paper body tube. Begad! Blimey! This be also gotten at Atomic Rockets. Blimey! T' seven motor tubes are all 17-inch lengths o' LOC paper 29mm motor tubes. Since these tubes come in 34-inch lengths, matey, halvin' them served well. Begad! Avast! These tubes are affixed with 12-minute epoxy in a 6 around 1 pattern often called t' star cluster. Ahoy! Ahoy! I used maskin' tape t' keep them together while t' epoxy dried. Another viable way to do this and get straight results is t' epoxy three pairs separately first, ya bilge rat, me hearties, matey, then apply t' pairs around t' central tube. This structure is then placed inside the main body tube with 12-minute epoxy and gaps filled in with t' 2-part foam. Well, blow me down! If t' main body tube chosen allows t' 7 motor tubes t' fit loosely, a 6-inch section o' 4-inch paper coupler tubin' from LOC can be used t' tighten that fit. Well, blow me down! Anyway, ya bilge rat, push in these tubes until 12 inches still protrudes out the end o' t' main body. Blimey!

T' fins are 3/8 inch thick Baltic birch and measure 7 3/4 inches in span, 8 1/4 inch root edge, and 1 1/4 inch tip. Blimey! They were cut with a bandsaw. Begad! T' fins are epoxied with first 12 minute, matey, then filleted with 30 minute epoxy into every second groove betwixt t' motor tubes. Ahoy! This is called wedge fin attachment by LOC, who, matey, with their 4-29SS, inspired me t' create this bird. T' leadin' edges and tips are all sanded t' a rounded edge. Ya scallywag! T' wood be found at a local hardwood store called, matey, shiver me timbers, New Beginnings in Wood, ya bilge rat, and can also be found at Home Depot. Well, blow me down!

There are 2 launch lugs, and they are brass pipe fittings 1 inch long by 3/4 inch diameter. Blimey! T' inside diameter has taken lightnin' rods t' 5/8 inch diameter with slack. Ya scallywag! These lugs were found at Home Depot. Begad! They were applied at 20 and 30 inches from t' top o' t' main body with 12-minute epoxy and the connection was later reinforced with 30-minute fillets. Ya scallywag!

T' homemade parachute is 60 inches in diameter and is made up o' 8 sloped triangular gores o' rip stop nylon. T' gores are sewn together with a 4-thread serger and t' spill hole and shroud lines are sewn and finished with a straight stitch. T' shroud lines are 1/8 inch polypropylene cording. Ahoy! Arrr! T' shock cord is 10 feet o' wire wrapped bungee cord found at American Science and Surplus, shiver me timbers, which has mail catalogs and an ROL site. Begad! T' bungee is anchored via a u-bolt through a 1/4 inch thick 4-inch diameter birch centerin' rin' 20 inches down inside t' main body tube from t' top o' t' rocket. T' centerin' ring was bought from Space Modelin' Solutions and t' hardware from Home Depot. Begad! Fred Meyer grocery store also carries u-bolts. Aye aye! Well, blow me down! T' assembly was affixed in place with 2 coatings o' 12-minute epoxy, ya bilge rat, arrr, and t' underside o' t' rin' where the u-bolt be bolted was also reinforced with 12-minute epoxy.

About t' trickiest part o' t' assembly process is makin' sure that the fins are straight and nay angled. Ahoy! Be patient and do one at a time. Ahoy! Avast, me bucko, me proud beauty! I sighted down t' body tube t' check alignment often, with each fin. Avast, me proud beauty! Ya scallywag! T' result is a sturdy rocket even without fiberglassing. Arrr! It also looks strong. Begad! In fact, another modeler said that it "looked like trouble askin' t' happen". I added three vent holes in t' main body tube 20 inches from t' bottom o' the main tube t' prevent premature separation o' t' nose cone. I did this with an awl.

Metallic green spray paint provided t' main color, matey, and a sports shop provided me with Coyotes puck stickers for t' fins. Arrr! A Monokote Coyote was also affixed t' t' body. Aye aye! Avast, shiver me timbers, me proud beauty! When I decorated t' bird, arrr, I applied sparklin' diffraction gratin' paper that is self adhesive. Blimey! This is great for looks and visibility. It can be bought from American Science and Surplus. Well, blow me down! T' ones in Coyotes colors was found at Craft Mart and Michaels, matey, two craft chains. Avast! Avast, me bucko, me proud beauty! I also ran a loop o' this decor over t' launch lugs t' reinforce their connection.

Rocket PicFlight:
I ran this design through Rocksim 4 with t' prediction that it would not require mass added t' t' nose, even with 7 G motors. Begad! Final preps included placin' 29mm wood bulkheads into all 6 o' t' outboard tubes so that only the central motor would do t' ejection o' t' chute. Well, blow me down! Blimey! This was decided when I wanted t' eliminate t' chance o' pressure loss when t' outboards aren't used or if I'm usin' single use motors with short delays. They can simply eject themselves. Blimey! T' bulkheads came from Space Modelin' Solutions, whose owner had just made centerin' rings for 29mm motors and had these left over! I happily epoxied them in at t' length o' an Aerotech G40. Begad!

Since this design was goin' t' be me special pride, I decided t' put it t' a punishin' test t' be sure that it would be worthy t' show off. Avast, me proud beauty! First, 4 G80's. Rocksim predicted 10 seconds as a good delay for t' central motor, matey, so a G80-10T was in t' center. Ahoy! I had 3 other G80T's but they were delays o' 7. Avast! No problem, matey, since t' outer tubes had t' bulkheads. Ahoy! And for neatness and style, I added streamers t' t' motors for their fall. Avast, me proud beauty! I used worm bed wadding, me bucko, enough to fill t' body tube's diameter. I got this from Space Modelin' Solutions. Begad! Well, blow me down! I placed a thin rin' o' maskin' tape around t' nose cone shoulder t' tighten the fit, me bucko, but nay make it too tight t' pop. I used 4 low current igniters from AAA Model Aviation Fuels and a car battery and relay system t' be sure all 4 lit. Ahoy! Arrr!

T' rocket screamed t' easily 2000 feet and deployed t' chute perfectly. T' rocket be arcin' down a little, so maybe 9 seconds would have been okay, with an altimeter. Ahoy! T' rocket landed intact right at rangehead!

Next, ya bilge rat, I decided that it be time t' do t' true test, Seven motors. I had 7 G40's, and one had a 10-second delay. Aye aye! Blimey! Begad! Blimey! T' others were 7's. Like with t' first flight, I meticulously friction fitted t' central motor with maskin' tape so that it wouldn't eject, because it was its job t' deploy me chute. Ya scallywag! Blimey! Ahoy! Blimey! Looking back, me hearties, if I would change anything, me hearties, ya bilge rat, it would be t' add a loop o' piano wire between tubes so that it could be bent over t' central motor as a retainer. Then I found 7 Igniterman igniters and wired them in parallel. Begad! Blimey! T' liftoff was even louder and more fiery than t' first time and it soared out o' sight. Aye aye! Blimey! Ahoy! Blimey! I listened for t' popopopop sound t' know that t' motors fired and proudly beheld me large purple chute. Ya scallywag! Blimey! This time I had t' walk a mile t' get t' rocket back, but it was glorious. Begad! Blimey! Ya scallywag! Blimey! This time, matey, arrr, 10 seconds seemed right.

Summary:
Easy t' find parts, matey, darin' and fun t' fly, with spectators lovin' it. Well, blow me down! Can be flown on just 1 motor, or as many as 7. Unless you airstart any o' t' outboard motors, do use motors with t' same thrust characteristics and same propellant to be sure that all light at t' same time. Avast! I also suggest usin' a battery with enough current capability t' light all t' igniters at once as well. Ahoy! I suggest that t' igniters all be t' same type too, shiver me timbers, me hearties, so that you don't get some motors lightin' and others not, arrr, resultin' in a lateral flight.

Other:
Go for it, you clusterguys! If we never take chances, we'll never know how much fun clusters are.

comment Post a Comment