CAST AWAY

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

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, arrr, and uses Lexan fins t' preserve t' overall appearance. Well, blow me down!

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

To construct a similar rocket, you will need:

• 1 ea. Avast, me proud beauty! Begad! Blimey! fiberglass leg cast, includin' foot and ankle
• 3 ea. Ahoy! Lexan fins
• 1 ea. 38mm LOC motor mount tube
• 1 ea. 3.9" diameter LOC tubing, 10" or so long
• 1 ea. 3.9" coupler tube, 6" long
• 1 ea. 1/4" plywood bulkhead, shiver me timbers, 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, shiver me timbers, me bucko, 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, I decided t' place one fin in the split runnin' down t' front o' t' foot, me bucko, shiver me timbers, me hearties, 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, t' toe will be pointed out, shiver me timbers, away from t' rail. Begad! Begad!

T' first step in construction was 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, me hearties, 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, I laid strips o' 6 oz. fiberglass down t' inside o' t' split, me hearties, wettin' them down with epoxy using a small paint brush. Neatness here didn't really matter, arrr, as t' joint would be completely concealed within t' cast. Aye aye!

Once that had cured, arrr, I attempted t' squeeze t' front portion o' t' cast back together t' secure it.Unfortunately, me hearties, it had been initially split t' day after it was applied t' me leg, shiver me timbers, so t' split had essentially "set" as the cast aged durin' t' two months I wore it. Begad! Blimey! I be able t' tack t' upper end of t' split together, me hearties, matey, but t' lower end, me hearties, includin' t' foot, ya bilge rat, matey, is still spread apart, 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, then a 6" x 2" triangle be cut off of the "root edge" t' give t' fins some rearward sweep, 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. Begad! Blimey! Well, blow me down! Blimey! Blimey! Blimey! The "foot" fin is a 6" x 8" rectangle, arrr, with t' outside corners similarly trimmed for safety and avoidance o' landin' damage. Aye aye! Blimey!

Next, 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, matey, anglin' back towards the center o' t' upper thigh.A 2" rin' o' 3.9" tube, ya bilge rat, with a 1/4" plywood bulkhead and a 6" long coupler tube, me hearties, makes up my "nosecone". Avast!

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, arrr, as I am worried about adhesion o' t' plastic (Lexan) fins.In any case, me bucko, I will be sandin' with 80 grit, and drillin' a number o' small holes near the root o' t' fins, shiver me timbers, t' allow t' adhesive o' choice t' form "rivets" ensurin' a good mechanical bond, 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. Arrr!

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

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2, me hearties, 3, me hearties, 4 - These pictures were taken durin' construction, matey, arrr, and show t' cast after t' installation o' t' clear Lexan fins (still in their protective white plastic covering), 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. Avast, matey, me proud beauty!

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, I decided, ya bilge rat, after a bit of testin' with scrap material, shiver me timbers, that this be completely unnecessary.T' fins were, instead, 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.

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5, shiver me timbers, 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, ya bilge rat, which is about halfway up, near t' front of the cast.

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7, ya bilge rat, me hearties, 7a - These are two versions o' t' same picture, me hearties, 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.... Avast! Blimey!

Final weight o' t' rocket (sans engine) was just about 7.75 lbs.Due t' the gusty nature o' t' winds at t' launch, 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, arrr, 38/480 casin' instead o' 38/360 casing), ya bilge rat, matey, t' ensure that I got plenty o' speed off t' rail t' ensure a straight flight.

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

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, ya bilge rat, and launched CastAway on a smaller White Lightnin' motor.I believe that t' rocket would have still flown fine on an I161W motor, arrr, 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, but t' lower maximum velocity would have saved t' fins.

I will probably repair t' rocket, me bucko, usin' 1/8" plywood t' replace the two broken fins.This should make them much stiffer, and much less prone to flutter. Avast! Well, shiver me timbers, blow me down!