Scratch Devil Ray Glider Original Design / Scratch Built

Scratch - Devil Ray Glider {Scratch}

Contributed by Todd Mullin

Manufacturer: Scratch
(by Todd Mullin - 04/30/07) (Scratch) Devil Ray Glider

Brief:
I love gliders! What I hate is pop-pods, ya bilge rat, ejectin' motor pods, me bucko, burn threads, shiver me timbers, and motor casings bein' spit out all over the launch field!

I'd thought a lot about how t' make a rocket glider design that deals with t' things that I hate. Edmonds Aerospace came up with a great piston design for their Ecee models, matey, but t' plunger tends t' gunk up over time. Avast, me proud beauty! Arrr! Don't get me wrong, ya bilge rat, it's a great design and I fly me Ecee Thunder more than any other rocket in me fleet, but I knew that there had t' be a better way.

My Devil Ray glider design utilizes a telescopin' nose design t' actuate t' elevators on t' canards. Ya scallywag! On boost, the elevator is held in place by a set o' retainin' tabs. Ya scallywag! At ejection, ya bilge rat, t' nose is pushed forward by t' charge, pullin' t' elevators free o' t' tabs and they are pulled into position with elastic thread. Aye aye! T' ejection charge is vented from t' top o' t' airframe t' help t' rocket t' transition from vertical t' horizontal flight.

(Scratch) Devil Ray Glider

Construction:
T' parts list:

  • 1 18" BT-50
  • 1 Plastic Nose Cone (scrounged from me parts bin, originally from me crashed Estes Echostar)
  • 3 BT-20 t' BT-50 centerin' rings
  • 1 BT-20 motor tube
  • 1 Yellow Quest motor spacer tube
  • 1 6" 1/8" hardwood dowel
  • 1 4" x 36" x 1/8" balsa
  • 1 package elastic thread
  • 4 straight pins

As this is a scratch build, t' only instructions I had were from t' little voice in me head. Well, blow me down! Arrr! I ignored t' part about givin' up rocketry and movin' t' Cleveland and forged ahead. Well, blow me down! I sketched out me idea in AutoCAD after thinkin' it through for several months. I showed these initial sketches t' a couple o' glider people and a couple o' rocket glider people as well. Arrr! After incorporatin' some o' their ideas, shiver me timbers, I started construction.

By now, me bucko, you undoubtedly know how a motor mount goes together, so I won't go through that end o' t' glider. Aye aye! The interestin' stuff is at t' other end anyway. Well, blow me down! I trimmed about 6" o' BT-50 from t' overall length t' use as the slidin' section o' t' nose. Well, blow me down! Avast, me proud beauty! I then cut t' openings out that are servin' as t' slidin' guides from t' nose section of tube. Begad! I bored holes into t' yellow spacer tube t' allow a piece o' dowel t' go through t' slider area t' retain the nose section after ejection. Begad! I then cut t' vent openin' into t' spacer tube and reinforced it with a centering rin' at t' front and a dowel in t' middle o' t' vent t' keep t' tube from collapsin' on a hard landing. T' spacer tube was then glued in place in t' main airframe.

I covered and hinged t' canards and elevators with Monokote. Begad! These were then glued t' t' slidin' nose section at a slight dihedral. Aye aye! Ya scallywag! I carefully glued t' retainin' tabs for t' elevators on next, arrr, makin' sure that they would be straight on boost. Ahoy! Next came t' wings and rudders. Well, blow me down! T' win' be cut as multiple pieces as it be too wide t' be cut from a single width o' 4" balsa.

(Scratch) Devil Ray Glider(Scratch) Devil Ray Glider

I bent t' straight pins into a "Z" shape and carefully slid them into t' balsa o' t' elevators and canards t' be t' anchor points for t' elastic thread that would pull them into position after ejection. Begad!

Finishing:
T' only finishin' that I did on t' Devil Ray was sandin' and Monokote on t' elevator/canard assembly. Ya scallywag! T' glider came in at a reasonably heavy 2.6 ounces dry weight before trimming, and I added more weight t' get t' trim correct as well so I didn't want t' add more weight with paint.

Trimmin' this model proved t' be somewhat troublesome. T' left wing, arrr, even though it was cut from t' same sheet of balsa as t' right, weighed substantially more. Begad! Blimey! Blimey! After a good bit o' sandin' and by addin' 3 washers t' t' right side o' t' canards, it balanced fairly well laterally. I still found that t' glider stalled a bit on t' test glides, so I added 1 small lead divin' weight pellet t' t' nose and t' stall problem was corrected.

In me test glides, me hearties, I found that t' flat bottom win' that I had designed along with t' small amount o' dihedral on t' canards wasn't enough t' keep t' glider from rollin' over in t' slightest cross breeze. Arrr! Once it dropped a wing tip, ya bilge rat, it invariably stalled out and crashed t' that side. Begad! I corrected this by cuttin' off and droppin' t' win' tips down t' approximately a 30 degree angle, matey, which suggested t' look o' a devil ray.

(Scratch) Devil Ray Glider

Flight:
From t' weight o' t' rocket, t' EMRR max liftoff weight calculator said that I needed t' use a motor with at least an average thrust o' 4.5 newtons. Ahoy! Ahoy! This ruled out t' Estes B4-2 that I was plannin' as me motor.

My next choice o' motor was t' Estes B6-2. Ya scallywag! I be a little leery about usin' a motor this small on a rocket of this size, but I was also concerned about t' glider movin' too fast so that t' elevators wouldn't have enough spring to be pulled into place against t' air stream if I went t' a larger motor.

I looped t' elastics onto t' pins on t' elevators, loaded me first motor, and loaded t' glider onto t' pad. T' boost arched over but it still reached reasonable altitude before deploying. T' glide was fast and reasonably smooth, circlin' around t' flight line. Avast! Unfortunately, shiver me timbers, arrr, t' landin' was equally fast and one o' t' wings snapped off on landing.

(Scratch) Devil Ray Glider T' win' be easily CAed back on and t' Devil Ray was prepped for another flight. Well, blow me down! Ahoy! T' second flight was on a B6-2 again. Aye aye! T' model weathercocked a bit more on t' second flight than t' first as t' wind be pickin' up slightly. Avast, me proud beauty! Well, blow me down! This time, however, arrr, at ejection t' elevators failed t' deploy and t' glider didn't. T' lawn dart folded t' airframe in half and snapped off both wings this time. Arrr! T' elevator and canard system survived despite bein' t' end that actually hit t' ground.

Recovery:
T' first glide o' t' Devil Ray was surprisingly good for a new glider. Begad! Usually it takes a few flights t' get the trim right for me. Well, blow me down! I be quite pleased with t' performance o' t' deployment system and it seemed t' take no wear and tear from t' flight.

(Scratch) Devil Ray Glider

Summary:
T' Devil Ray was exactly what I be lookin' for in a glider. Avast, me proud beauty! Well, blow me down! Easy recovery with a minimum o' prep and re-prep time without shootin' motor casings everywhere or a pop-pod. Well, blow me down! Ya scallywag! I liked t' look o' t' design even though thar were some inherent stability issues for its glide recovery. Arrr! I believe that I will redesign t' tail/win' section o' t' glider before rebuilding.

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