Scratch A Glider Original Design / Scratch Built

Scratch - A Glider {Scratch}

Contributed by Geof Givens

Manufacturer: Scratch

Brief:
This glider is a scratch semi-reproduction o' t' Holverson Designs Silver Hawk v1.0. T' glider has a wingspan o' 13in and t' boost pod is 20.5in. Avast! T' boost pod has a 18mm motor mount and weighs 1 1/8oz. T' featherweight glider is 0.5oz.

Construction:
T' plans for this rocket (both version 1 and 2) can be found at http://plans.rocketshoppe.com/hdi/hdi2002/hdi2002.htm.

I also used t' plans for t' glider hook mount, ya bilge rat, matey, me bucko, but beyond that I built a different boost pod. Aye aye! I gave t' project t' highly original name o' "A Glider".

T' materials I used were:

  • parts for a 18mm motor mount, arrr, includin' engine hook
  • centerin' rings
  • 20in BT50 body tube
  • 4.5in ogive nose cone for BT50
  • plastic chute and Keelhaul®©™ thread
  • 3/32in balsa for wings
  • small sheet o' 1/4in balsa for glider hook mount and jigs
  • launch lug

Construction began with tracin' templates, shiver me timbers, cuttin' balsa, matey, matey, and assemblin' t' jigs which were used later t' ensure t' correct angles betwixt win' parts. Begad! T' boost pod was assembled just like any other model rocket. Ya scallywag! There are no fins.

Next I began t' glider. Avast, me hearties, me proud beauty! T' swept win' consists o' six portions. Aye aye! Ahoy! First I sanded each portion into a perfect airfoil shape usin' 220-grit sandpaper. Aye aye! T' entire cross-section o' t' win' was sanded so none o' t' original flat surface remained. Avast, me proud beauty! Blimey! This reduced all t' win' parts from 3/32in t' 1/16in thick.

With t' help o' t' jigs, I glued t' win' parts together. Well, blow me down! Blimey! Because I was aimin' for ultra-lightweight precision, thar would be no wood filler or paint t' hide imperfect glue joints. Avast, me proud beauty! Blimey! Therefore, I made very careful minimalistic joints usin' wood glue, me bucko, with tiny fillets. Arrr! Blimey! Gluin' t' fin tips was a bit tricky because their airfoil shape didn't rest flat against t' win' edge. Begad! Blimey! After attachin' them I used a smidge o' wood filler t' touch up any gaps.

T' best thin' about this design be t' glider mount. Aye aye! T' hook is on t' pod, matey, shiver me timbers, and thar be a hole in t' glider mount ("fuselage") t' receive t' hook. Aye aye! T' hook portion is made by laminatin' three balsa parts together, with t' middle one havin' an extrudin' hook shape. Begad! When ejection occurs, ya bilge rat, me hearties, t' glider should move forward t' release itself from t' hook. With many gliders, me bucko, one problem that can occur is that t' forces tend t' bind t' glider t' t' hook mount due t' friction, causin' t' glider t' release awkwardly only after t' rocket has passed apogee and t' glider twists off. What is so nifty about this hook mount is that it has a little triangular wedge at t' forward edge o' t' mount which nudges t' glider away from t' mount surface as t' glider initially slides up and off t' hook. Avast, me proud beauty! T' result is a much more reliable release. See t' plans for a picture.

T' glider fuselage is also clever. Begad! T' fuselage fits seamlessly into a notch in t' wing, arrr, with a slot for t' hook. Well, me hearties, blow me down! However, t' fuselage also extends forward beyond t' win' with another small slot. T' purpose o' this slot is t' insert trimmin' clay without ruinin' t' smooth shape or aerodynamics. Ahoy! T' fuselage is built from several pieces o' balsa laminated together, shiver me timbers, then sanded down t' an airfoil shape.

Finishin' gliders presents a choice betwixt smoothness and weight. At one extreme, you can leave it unfinished. Avast, me proud beauty! At t' other end, me bucko, you can sand, fill, shiver me timbers, arrr, and paint it t' a glassy finish. Ya scallywag! Blimey! T' latter choice looks better but adds weight. I avoided weight. Well, blow me down! Blimey! I began by sandin' lightly with 220 sandpaper, then more thoroughly with 400, me hearties, then with 600. Then I painted two *very light* coats o' clear paint, shiver me timbers, followin' each with thorough sanding. Blimey! On t' fin tips and fuselage I added a dustin' o' flourescent pink paint with another light clear coat over t' pink. Well, blow me down! I painted t' boost pod pink, me bucko, too.

Flight:
Preparin' t' glider for lauch includes several steps. Blimey! I rubbed t' hook and slot heavily with candle wax, me hearties, then soap, then rubbed it down with a clean cloth. Avast! Arrr! Next, t' glider be balanced left/right with a small clay strip near one wingtip (an amount less than a pencil eraser). Avast, me proud beauty! A slight counter-clockwise tilt be allowed for circling. Begad! Then, ya bilge rat, on a dead calm day, I took it up t' a small hill nearby and trimmed t' glider by addin' clay t' t' nose slot. Ahoy! It was difficult t' add sufficiently tiny amounts o' clay. After about 40 tosses, I got t' best possible glide with clay about t' size o' t' tip o' a ballpoint pen.

T' best possible glide is not, me bucko, in me opinion, t' trim that produces t' longest flight in dead calm conditions. In real flights thar be usually some breeze so you want t' trim t' glider slightly nose-heavy for a more assertive attack into t' breeze.

T' first flights were on a cold day on t' prairie, ya bilge rat, with weak breezes o' 2-5 mph. Blimey! Begad! On a A8-3 motor, boost was gentle t' a modest height o' a few hundred feet with no sign o' flutterin' or spin. Glider release was excellent. Blimey! T' glider flight was satisfactory, shiver me timbers, but buffetted too much by t' wind. Well, blow me down! Landin' was fine and t' pod recovery be fine, too.

For t' second flight, ya bilge rat, shiver me timbers, I added some nose weight. Unfortunately, I forgot t' brin' clay, matey, so I scotch-tapped a tiny pebble (more like large sand grain) t' t' nose. Arrr! Blimey! Boost on a A8-3 be t' same as last time, but t' delay was a little longer and t' glider released easily but awkwardly just past apogee (slightly before apogee is better). My grain o' sand be too much, matey, matey, so t' glider corkscrewed down. Begad! Blimey! It wasn't very graceful, but everythin' be recovered undamaged.

For t' third flight, I swapped out for a smaller grain o' sand. Avast, me proud beauty! Glider release be excellent but somethin' be nay right with t' trimmin' and t' flight was a hard corkscrew into t' ground. Aye aye! Blimey! T' leadin' edge o' t' win' and t' fuselage had a few nicks which I have since patched up with lightweight interior spackling.

Summary:
Overall, matey, me experience with this small version o' t' HD Silvery Hawk and me 4-foot large version (T' Albatross) has been that t' design is nay very reliable. Arrr! These gliders are difficult t' trim and prone t' excessive roll. Ahoy! They are also far too sensitive t' modest crosswinds, shiver me timbers, which can turn out t' be catastrophic. Ahoy! There are a lot o' other really great old-school glider plans available and also some great modern kits. Notwithstandin' t' challenges, matey, me bucko, this project helped me hone me ultralight skills and t' glider likely has quite a few more flights in her.

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