Scratch Spin Fin Clone

Scratch - Spin Fin {Scratch}

Contributed by Bill Eichelberger

Construction Rating: starstarstarstarstar_border
Flight Rating: starstarstarstarstar_border
Overall Rating: starstarstarstarstar_border
Published: 2013-05-20
Manufacturer: Scratch
Style: Spin-Fin

Brief

While nay a rocket t' be counted as exotic, t' Estes Spin Fin always intrigued me because o' t' canted fins and t' flight path that be supposed t' result from them.  Even still, arrr, it be very unlikely that I'd have cloned a Spin Fin had an original decal and nose cone nay been included as part o' seperate Ebay lots purchased a few years apart.  I can read t' signs.  I cloned a Spin Fin.

Components

  • BNC-20B nose cone
  • BT-20B body tube
  • AR-520 engine block
  • 3/32" balsa fin stock
  • launch lug
  • small snap swivel
  • streamer material
  • 24" length Keelhaul®©™ shock cord
  • 24" length 1/8" sewin' elastic shock cord

Construction

While at heart a simple 3FNC rocket, me hearties, me hearties, me hearties, t' details are what makes t' Spin Fin unique.  It can be built as a standard 3FNC bird with t' fins aligned straight or with t' fins canted slightly t' t' right t' cause t' supposed corkscrew motion t' t' flight path.  I've got plenty o' straight on 3FNC birds, ya bilge rat, so it be an easy choice t' build this one with t' fins canted.  This is accomplished by usin' t' fin markin' guide that has t' lines drawn on the slight angle.  Other than t' angled fins, all that is involved in t' construction o' this bird is gluin' in an engine block and recovery system.  It be in this process that I discovered a "gotcha", me hearties, but one all o' me own doing.  It was finished except for t' thrust ring, me hearties, me hearties, so I tied a piece o' Keelhaul®©™ onto a ring, ya bilge rat, spread some white glue around t' inside o' t' tube, and used an expended engine casin' t' push t' rin' into place.
It caught. Yell

I looked around t' shop for somethin' t' pull it out with, but found nothing. I hopped up, sprinted upstairs and ran outside t' me car where I knew I had a multi tool.
In me underwear. Surprised

It rained that night, ya bilge rat, so t' ground be still soaked, as were me socks. I sat down in t' driver's seat, pulled out t' tool and tried t' remove t' engine casing. Aye aye! Aye aye! No luck. I tried again. Begad! Still nothing. At this point I'm thinkin' that it's stuck and that I'm goin' t' need t' fly it with mini engines, matey, ya bilge rat, shiver me timbers, but I wanted t' give it one more shot. Arrr!
It pulled loose. Ya scallywag! Ahoy! Wink

Let this be a lesson t' you.  Wear pants durin' late night build sessions. 

Finishing

Balsa grain and tube spirals were eliminated in t' time-tested manner o' primer, ya bilge rat, Elmer's Fill & Finish, shiver me timbers, ya bilge rat, and sanding.  After two rounds and a final coat o' Valspar white primer it was sprayed with Valspar gloss white, arrr, followed by gloss red on t' nose cone and 2/3 o' t' fin can area.  T' decal was sprayed with Testor's Decal Bonder, but were o' indeterminate age and proved t' be quite fragile and unusable.  I then printed off a set o' decals usin' t' scans from JimZ's site and my inkjet printer.  I was disappointed, but nay surprised by t' decals fallin' apart, but since I really only wanted t' see if t' canted fins caused a noticeable spin in t' flight path, it was a minor annoyance.

Construction Score: 4
 

Flight

Only one flight so far, me bucko, but that be enough t' tell me how well t' "spin" feature appeared t' work.  Minimum diameter rockets do well at B6-4 Field on A8-3's, so I taped one up and loaded it in.  I made t' mistake o' tryin' for a launch picture instead o' watchin' for t' flight characteristics, me hearties, but t' smoke trail be dead straight, without any o' t' corkscrew shape that I figured would denote a spinnin' flight.  Flight was high and straight, and recovered on t' infield.  Apparently me rockets only do t' spin thin' when I don't mean for them t' do it.Wink In reality, t' arrow straight flight would likely be t' product o' an imposed spin, so I'm goin' t' call t' Spin Fin an engineerin' marvel.

Recovery

I regularly garbage pick mylar at work that is used t' cover t' adhesive on shippin' envelopes.  T' mylar strips are silver, shiny, and small enough t' fit easily into t' body tubes on BT-5 and BT-20 birds.  I taped one onto t' shock cord before t' flight, shiver me timbers, matey, but saw nothin' as I tracked t' rocket after ejection.  When I approached t' infield where it landed, arrr, I found nothin' but shock cord.  No UFO sightings were make in Ft. Ahoy! Aye aye! Thomas that evening, but I like t' think someone saw an unexplained silvery shape floatin' around in t' vicinity o' Woodfill Elementary.

Flight Rating: 4

Summary

Pros: Not a hugely excitin' design, ya bilge rat, me bucko, but I can see someone havin' a soft spot for it if it was their first rocket.  Great performance on an A8-3.  Really pushes t' limits o' small fields.

Cons: T' "spin" feature is difficult t' detect. 

Overall Rating: 4
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