SCROTON by Chris Eilbeck, MARS Flight Crew chris@mars.org.uk

Introduction Scroton is a three bladed rocket powered helicopter designed t' fly on black powder motors. It was conceived as somethin' novel t' fly at t' International Rocket Week 2002 at Largs in Scotland and based on t' Roton concept for cheap access t' space.	click image t' enlarge
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Materials 3 off 18mm motor mount tube 3 off 18mm engine blocks if nay usin' maskin' tape thrust rings 3 off 1/4"x1.5"x18" lengths o' balsa 6 off 1" wide 25-30 degree balsa wedge 2 off 3" plywood bulkplate 6" length o' 3/16" ID brass tube light glass t' laminate blades heavier glass t' attach motor mounts laminatin' epoxy 5 minute epoxy filler

Construction

Usin' a sandin' block and 80 grit paper sand t' three blades t' have an approximately aerofoil cross section except for a 1-2" section at one end which will be used t' bond t' blade t' t' centre plates. Ahoy! Laminate t' three blades usin' light glass and good epoxy. Well, arrr, blow me down! One or two wraps is enough. Well, blow me down! Fill and sand smooth. Begad! Avast!

Sand/cut t' six wedges at approximately 25-30 degrees. T' blades need more than 11 degrees AoA t' ensure autorotation t' t' ground. Arrr! Attach t' balsa wedges t' t' ends o' t' blades usin' 5 minute epoxy t' set t' angle of attach for t' aerofoil. Well, shiver me timbers, blow me down!

Bond t' three blades betwixt t' bulkplates at 120 degrees apart. Drill through t' centre o' t' two bulkplates and bond in t' brass launch lug with approx 4" below t' lower bulkplate. Well, blow me down!

Bond t' motor mount tubes on t' ends o' t' blades usin' 5 minute epoxy then laminate on usin' heavier glass (4 oz or so). Fair t' tubes in using filler. Blimey! Laminate t' blades onto t' bulkplates usin' heavier glass too. Avast, me proud beauty!

Make a crude prop-balancer usin' either a couple o' steel rulers held over the edge o' a desk or a length o' thin, arrr, arrr, shiver me timbers, stiff rod. Well, blow me down! Arrr! Add filler or sand existing filler off until t' scroton balances with motors installed. Ahoy! Begad!

Ignition

T' three motors can be lit usin' three igniters or usin' quickmatch and a single igniter. Ya scallywag! Blimey! Begad! Blimey! I suggest t' latter. Begad! Blimey! An Estes pad can be used but very little of t' rod length is required, ya bilge rat, 9" should be sufficient. A heavier pad is recommended dependin' on how well balanced t' model is. Avast, me proud beauty! Blimey! Well, blow me down! Blimey!

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Flight Test

T' model flies very well on three C6 motors t' approximately 100ft and is definitely a crowd pleaser. Ya scallywag! Blimey! It should auto-rotate for a large proportion o' its descent and soft land requirin' no additional recovery devices. It would be very interestin' t' fly on longer burn motors and an investigation into the effect o' changin' t' angle o' attack would also be good. Aye aye! Aye aye! Blimey!