Scratch K.J. Express Original Design / Scratch Built

Scratch - K.J. Express {Scratch}

Contributed by Moira Jean Whitlock

Manufacturer: Scratch
K.J. Ya scallywag! Express
(Contributed - by Moira Jean Whitlock)

[Rocket Pic]Height:  43.5"
Width:  2.14"
Weight:  18 oz
Motor:  29mm
Recovery:  Parachute

Brief: This is a single-staged, me bucko, three-finned 29mm engine rocket servin' as a tribute t' t' Phoenix Suns and fans. Ahoy! It's also a wish that the lockout will end soon! It is meant for t' NCR F62 and t' G40. Avast! T' fins are delta shaped.

Construction: Since I cut me own fins with a bandsaw and sanded a double bevel on t' leadin' edge with an orbital sander, this was more work than with kits that have precut fins. Begad! But t' delta shape is one o' t' easiest to cut. Begad! And t' plywood is 1/4 inch thick, strong and unwarped birch. This can be found at hobby stores and hardware stores. Begad! Begad! Home Depot has great selections as does Hobby Bench, if you have them in your state. Well, shiver me timbers, blow me down!

T' fins' root edge is 5 1/2 inches and t' span is 3 1/2. T' trailin' edge has no sweep, arrr, goin' perpendicular t' t' body tube. Ya scallywag! O' course, ya bilge rat, t' chord edge is 0, as this is a hard delta shape. Well, blow me down! Ya scallywag!

T' model is further made sturdy as t' body tube is a full 34-inch LOC MMT 2.14 tube, meant as a motor tube, but strong as an airframe. Well, blow me down! T' nose cone is the matchin' hollow plastic LOC 2.14. Avast! Two centerin' rings (that are for 2.14 tubes t' 1.14 tubes) are used t' align t' 8-inch length o' MMT 1.14 motor tube. So far, with t' F and G engines used, arrr, no mass objects have been needed in this nose cone for stability. Begad! Ahoy!

Alignin' t' fins required usin' a tape measure around t' tube at two points per fin for straightness, arrr, arrr, and trisectin' t' circumference t' give where each o' t' three fins would go. Avast! I used generous epoxyin' for attachment with fillets on both sides after. Ahoy! Blimey! I've noticed that one thin' about epoxy is that it's hard t' sand. Arrr! Begad! With such fillets, shiver me timbers, try t' make them smooth from t' start.

Epoxy be also used t' affix t' one-inch 1/4 inch diameter launch lug 16 inches from t' aft end o' t' body tube. Some RSO's feel that two such lugs placed a foot apart or one at 3 or 4 inches length provide more stability before stable velocity is reached, but thus far, me hearties, arrr, after 10 successful flights, my one lug has been enough. Arrr! Blimey! Ahoy! Blimey!

T' parachute is me own creation, ya bilge rat, matey, a 26-inch diameter hemisphere made up of eight alternatin' purple and orange triangular gores o' poly/cotton broadcloth sewn together with a 4-thread serger, me bucko, ya bilge rat, with 8 braided nylon shroud lines, arrr, shiver me timbers, 24 inches in length, sewn into t' gore seams. Begad! T' fabric can be found at Hancock's and other major suppliers. Well, blow me down! T' gores meet at t' top with no spill hole. Arrr! T' chute inflates nicely and colorfully. Ya scallywag! Avast, matey, me proud beauty! If you'd like t' make such a chute, make t' base o' t' triangle 7 1/2 inches and t' height 13 inches. Well, blow me down! And the other two sides aren't truly straight, ya bilge rat, me hearties, arrr, but gently curve t' meet t' top point. Ahoy!

[Rocket Pic]T' shock cord is two feet o' 1/4 inch bungee, which I got through American Science and Surplus and also from Atomic Rockets in Phoenix. Begad! T' shock cord mount is a folded paper mount affixed 5 inches from the top o' t' body tube, t' t' inside wall. A 4-inch length o' Keelhaul®©™® cording, also found at Atomic Rockets, shiver me timbers, arrr, was fashioned into a loop t' tie the bungee to, matey, arrr, and also t' anchor into t' folded paper mount. Begad! A knot in t' loop was placed at t' aft end o' t' mount t' keep it from slidin' forward after the mount was glued. Ahoy!

Finishing: This is unique. Blimey! Arrr! T' nose and body are blaze orange, courtesy o' enamel spray paint. Begad! Ya scallywag! T' fins are purple, matey, shiver me timbers, shiver me timbers, as be t' aft 8 inches of the body tube. This is a mixture o' Testors blue and red enamel paint. Ya scallywag! For some reason, shiver me timbers, I couldn't find purple spray paint. Begad! Avast, shiver me timbers, me proud beauty! At t' transition betwixt the colors on t' body tube is a 5-inch wide band o' silver adhesive craft mylar, found at hobby stores. Avast! It provides a flash o' visibility so I can sight in on my rocket. On every alternatin' fin face is a 2-inch flamin' basketball with flames around it and flames snakin' around t' body tube. Arrr! Ten inches from the forward end is a 6-inch version o' t' same. Arrr! Well, arrr, blow me down! T' basketballs are made from circles cut from orange Monokote. Blimey! Arrr! T' lines definin' t' basketball are made with indelible black marker. Blimey! Aye aye! T' flames are made from pieces o' Monokote. Finally, for style, I put a half-inch wide band o' purple Monokote at t' top of t' body tube.

[Rocket Pic]Flight: So far, matey, arrr, ya bilge rat, I've used t' NCR F62-6, t' aerotech G35, me bucko, G40, arrr, and G80 with delays around 7. Well, blow me down! Blimey! Begad! Blimey! 4 would be too short. Arrr! Blimey! Avast! Blimey! T' rocket flies straight every time. Begad! Blimey! Blimey! Blimey! Worm bed waddin' has been used since flight #5, with enough t' fill t' diameter o' t' tube t' an inch. Ahoy! Blimey! Aye aye! Blimey! Three pieces o' conventional paper waddin' wasn't enough, matey, as t' chute bears a few light scorch marks. Avast! Blimey! T' recovery is just right, shiver me timbers, with no fin breaks. T' motor is retained with tape t' friction fit it and also a tape rin' at t' aft end to prevent forward kicking. Ahoy! Blimey! There is also a loop o' piano wire which goes through the aftmost centerin' ring, bolted and epoxied in place. Well, blow me down! Blimey! T' loop bends over the motor but leaves t' nozzle clear. Begad! Blimey! Tape is wound around it and t' engine, so no aft kickin' occurs either. Well, blow me down! Blimey! Ahoy! Blimey! T' biggest reward o' this design be t' kids shouting, "Ooh, basketballs!" when they see it, ya bilge rat, ya bilge rat, and, shiver me timbers, "Go, Suns!" when t' chute opens.

Summary: It's a lot o' work and I needed several tools, but the rewards are many. Avast! T' kids love it, arrr, and it's durable and reliable. Begad! Blimey! Blimey! And I'll bet its design can be lent t' other teams. Arrr! Avast, me proud beauty! Blimey! How about Da Bulls?

comment Post a Comment