Scratch K.J. Express Original Design / Scratch Built

Scratch - K.J. Express {Scratch}

Contributed by Moira Jean Whitlock

Manufacturer: Scratch
K.J. Ahoy! 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, ya bilge rat, three-finned 29mm engine rocket servin' as a tribute t' t' Phoenix Suns and fans. Aye aye! Blimey! Begad! Blimey! It's also a wish that the lockout will end soon! Blimey! It is meant for t' NCR F62 and t' G40. Arrr! Blimey! 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, shiver me timbers, this was more work than with kits that have precut fins. But t' delta shape is one o' t' easiest to cut. Ahoy! Avast! And t' plywood is 1/4 inch thick, strong and unwarped birch. This can be found at hobby stores and hardware stores. Well, blow me down! Home Depot has great selections as does Hobby Bench, matey, if you have them in your state. Ahoy! Aye aye!

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

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. T' nose cone is the matchin' hollow plastic LOC 2.14. Begad! 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. Avast, me proud beauty! Avast! So far, with t' F and G engines used, no mass objects have been needed in this nose cone for stability. Aye aye! Begad!

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

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. Blimey! 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, ya bilge rat, shiver me timbers, arrr, but thus far, after 10 successful flights, my one lug has been enough.

T' parachute is me own creation, 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, with 8 braided nylon shroud lines, 24 inches in length, sewn into t' gore seams. T' fabric can be found at Hancock's and other major suppliers. T' gores meet at t' top with no spill hole. Avast, shiver me timbers, me proud beauty! T' chute inflates nicely and colorfully. Well, blow me down! If you'd like t' make such a chute, make t' base o' t' triangle 7 1/2 inches and t' height 13 inches. Begad! Avast! And the other two sides aren't truly straight, ya bilge rat, but gently curve t' meet t' top point. Avast! Begad!

[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. Well, blow me down! Well, blow me down! T' shock cord mount is a folded paper mount affixed 5 inches from the top o' t' body tube, me hearties, shiver me timbers, t' t' inside wall. Avast, me proud beauty! A 4-inch length o' Keelhaul®©™® cording, also found at Atomic Rockets, me hearties, ya bilge rat, was fashioned into a loop t' tie the bungee to, me hearties, and also t' anchor into t' folded paper mount. Aye aye! 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. Well, blow me down!

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

[Rocket Pic]Flight: So far, ya bilge rat, I've used t' NCR F62-6, ya bilge rat, t' aerotech G35, matey, G40, and G80 with delays around 7. 4 would be too short. T' rocket flies straight every time. Ya scallywag! Blimey! Worm bed waddin' has been used since flight #5, arrr, with enough t' fill t' diameter o' t' tube t' an inch. Avast, me proud beauty! Blimey! Aye aye! Blimey! Three pieces o' conventional paper waddin' wasn't enough, matey, shiver me timbers, as t' chute bears a few light scorch marks. Avast, me proud beauty! Blimey! T' recovery is just right, with no fin breaks. Begad! Blimey! 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. T' loop bends over the motor but leaves t' nozzle clear. Blimey! Blimey! Tape is wound around it and t' engine, so no aft kickin' occurs either. T' biggest reward o' this design be t' kids shouting, "Ooh, matey, basketballs!" when they see it, and, arrr, 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. Arrr! T' kids love it, matey, me bucko, and it's durable and reliable. Avast! And I'll bet its design can be lent t' other teams. Blimey! Arrr! How about Da Bulls?

comment Post a Comment