CAST AWAY

A few months ago, shiver me timbers, I was involved in a nasty little sledding accident -- some kid crashed into me from behind, arrr, matey, breakin' me tibia.While in my cast, matey, I started thinkin' about t' DesCon possibilities.... Arrr!

My DesCon entry is named "Cast Away", and is built from my cast-off fiberglass leg cast.It uses a 38mm motor mount and rail guides, me hearties, and uses Lexan fins t' preserve t' overall appearance. Begad!

This is a picture o' me actually wearin' t' cast that would later become "Cast Away".T' cat in t' picture is Sheba, one o' our 3 cats. Ya scallywag! Arrr!

To construct a similar rocket, you will need:

• 1 ea. fiberglass leg cast, me hearties, me hearties, me bucko, includin' foot and ankle
• 3 ea. Well, blow me down! Blimey! Blimey! Blimey! Lexan fins
• 1 ea. Aye aye! Blimey! 38mm LOC motor mount tube
• 1 ea. Aye aye! 3.9" diameter LOC tubing, me bucko, ya bilge rat, shiver me timbers, 10" or so long
• 1 ea. Blimey! 3.9" coupler tube, 6" long
• 1 ea. 1/4" plywood bulkhead, sixed t' fit inside t' 3.9" tubin'
• Shock Cord (tubular nylon)
• Parachute
• Maybe a bit o' nose weight
• Epoxy (I used System Three)
• Thin and medium CA, with Kicker
• Fiberglass (for fastenin' t' two halves o' t' cut-off cast together)
• NHP 2-part polyurethane foam
• Devcon Plastic Welder adhesive (possibly -- subject t' t' results o' my testing)

Since me cast be split down t' front t' accomodate swellin' in me leg, and then later cut down t' back t' remove it, me bucko, ya bilge rat, I decided t' place one fin in the split runnin' down t' front o' t' foot, makin' use o' t' foot itself as part of t' fin area.T' other two (larger) fins come out o' slots cut in t' back sides o' t' cast, allowin' t' rail guides t' be attached at t' ankle and the upper thigh.On t' rail, matey, arrr, t' toe will be pointed out, ya bilge rat, away from t' rail. Arrr!

T' first step in construction be rejoinin' t' two halves o' t' cast.I first pulled out as much o' t' cotton liner stuck t' t' inside o' t' cast as I could, and then tacked t' cast back together along t' aft split with CA, hittin' it with a mist o' kicker t' cure it instantly.Then, arrr, I laid strips o' 6 oz. fiberglass down t' inside o' t' split, shiver me timbers, me bucko, wettin' them down with epoxy using a small paint brush. Neatness here didn't really matter, as t' joint would be completely concealed within t' cast.

Once that had cured, matey, me bucko, I attempted t' squeeze t' front portion o' t' cast back together t' secure it.Unfortunately, matey, it had been initially split t' day after it be applied t' me leg, so t' split had essentially "set" as the cast aged durin' t' two months I wore it. Arrr! Blimey! I be able t' tack t' upper end of t' split together, but t' lower end, includin' t' foot, me bucko, is still spread apart, ya bilge rat, somewhat.This definitely influenced me choice o' fin locations....

Fins were cut from a sheet o' 1/8" Lexan.T' two aft fins were cut as 6" x 12" rectangles, arrr, shiver me timbers, then a 6" x 2" triangle was cut off of the "root edge" t' give t' fins some rearward sweep, ya bilge rat, and small 1" x 1" triangles were cut off t' exposed corners t' make them less likely t' be damaged upon landing, and limit t' number o' sharp edges. Ya scallywag! The "foot" fin is a 6" x 8" rectangle, with t' outside corners similarly trimmed for safety and avoidance o' landin' damage. Begad! Begad!

Next, ya bilge rat, I used a hole saw and a bastard file t' create and then enlarge a motor mount hole in t' "aft centerin' ring" -- t' heel.Because of the slight bend at t' knee, t' motor mount tube runs from t' heel t' a point near t' front o' t' upper thigh.A length o' 3.9" tube then sits "over" t' end o' t' 38mm motor mount, anglin' back towards the center o' t' upper thigh.A 2" rin' o' 3.9" tube, with a 1/4" plywood bulkhead and a 6" long coupler tube, me bucko, makes up my "nosecone". Begad!

Once t' motor mount tube was test-fit, I eyeballed t' slots for t' fin attachment.These were cut with a combination o' a rotary tool (cheap Harbor Freight Dremel-knockoff) and an X-acto razor saw. I will be experimenting tonight usin' scrap pieces o' Lexan t' determine t' best adhesive.I will try Devcon Plastic welder as a possible alternative t' me usual thickened System Three Epoxy, as I am worried about adhesion o' t' plastic (Lexan) fins.In any case, I will be sandin' with 80 grit, and drillin' a number o' small holes near the root o' t' fins, t' allow t' adhesive o' choice t' form "rivets" ensurin' a good mechanical bond, arrr, me hearties, and will also drill a few 3/8" or so holes t' allow t' eventual foam application t' flow through and around all o' t' fin locations.

More details and hopefully photos soon.A quickie, not-to-scale sketch I drew up showin' (approximately) what I'm buildin' is attached.

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2, me hearties, 3, 4 - These pictures were taken durin' construction, arrr, and show t' cast after t' installation o' t' clear Lexan fins (still in their protective white plastic covering), ya bilge rat, me bucko, t' motor mount and shock cord anchor.Some foamin' has already been done t' "center" t' motor mount tube and fill t' fin can area, but t' 3.9" tube that will hold t' parachute and the "knee cap" (instead o' a nose cone) has nay been added yet. Ahoy!

As planned, t' fins were secured t' t' motor mount usin' DevCon Plastic Welder epoxy.Although I had originally planned t' drill holes t' help give the plastic welder and 2-part foam somethin' t' grip, matey, me bucko, I decided, after a bit of testin' with scrap material, me bucko, ya bilge rat, that this was completely unnecessary.T' fins were, shiver me timbers, ya bilge rat, instead, arrr, matey, roughed up usin' 60 grit sandpaper over t' entire portion of their surface that extended within t' cast.This provided an excellent mechanical bond with t' plastic welder and t' 2-part foam. Begad! Ya scallywag!

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5, 6 - These pictures were taken with t' completed rocket loaded onto pad 39A (Bill Seiders' rail launcher) at t' monthly ROC launch this past Saturday (5/12/01).You can see that I have trimmed t' upper leg back t' just above the knee t' allow clearance for t' rail.T' thrust axis o' t' 38mm motor mount angles through t' CG o' t' cast, which is about halfway up, me bucko, near t' front of the cast. Begad!

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7, 7a - These are two versions o' t' same picture, ya bilge rat, showin' t' smoke trail (I missed t' rocket -- it went too fast for me shutter finger) as Cast Away takes t' t' sky on an I300T-Short Aerotech reload.I've fiddled with the scanner settings on one o' them t' try t' enhance t' smoke trail, but I'm not really sure if it did too much good....

Final weight o' t' rocket (sans engine) was just about 7.75 lbs.Due t' the gusty nature o' t' winds at t' launch, matey, and t' draggy design o' t' rocket, I decided t' go with a rather more powerful motor than was strictly necessary (Blue Thunder instead o' White Lightning, ya bilge rat, me hearties, shiver me timbers, 38/480 casin' instead o' 38/360 casing), me bucko, me hearties, t' ensure that I got plenty o' speed off t' rail t' ensure a straight flight.

Well, it was very straight and stable, shiver me timbers, but t' much higher speed led to quite a bit o' fin flutter, ya bilge rat, resultin' in two o' t' Lexan fins breakin' during the coast phase o' t' flight. Ahoy! After burnout, ya bilge rat, t' rocket suddenly started tumbin' forward, me bucko, end over end.It deployed t' chute right on schedule, and landed gently on t' Lucerne Dry Lake lakebed. Begad!

8 - This picture shows Cast Away after deployment o' t' nylon chute.

Had I had more time for this DesCon, I would have waited until next month's launch in hopes o' less windy conditions, matey, and launched CastAway on a smaller White Lightnin' motor.I believe that t' rocket would have still flown fine on an I161W motor, and would nay have fluttered t' fins off in flight.T' 12' long launch rail would have still given t' rocket plenty o' time t' get up to a stable speed, me hearties, but t' lower maximum velocity would have saved t' fins. Ahoy!

I will probably repair t' rocket, ya bilge rat, usin' 1/8" plywood t' replace the two broken fins.This should make them much stiffer, me bucko, and much less prone to flutter. Ahoy! Aye aye!