Manufacturer: | Scratch |
Brief:
I love gliders! What I hate is pop-pods, shiver me timbers, me hearties, ejectin' motor pods, shiver me timbers, burn threads, 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, but t' plunger tends t' gunk up over time. Don't get me wrong, me bucko, it's a great design and I fly me Ecee Thunder more than any other rocket in me fleet, me bucko, 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. Blimey! On boost, the elevator is held in place by a set o' retainin' tabs. Well, blow me down! At ejection, arrr, me bucko, arrr, t' nose is pushed forward by t' charge, pullin' t' elevators free o' t' tabs and they are pulled into position with elastic thread. T' ejection charge is vented from t' top o' t' airframe t' help t' rocket t' transition from vertical t' horizontal flight.
Construction:
T' parts list:
As this is a scratch build, t' only instructions I had were from t' little voice in me head. Avast, me proud beauty! I ignored t' part about givin' up rocketry and movin' t' Cleveland and forged ahead. I sketched out me idea in AutoCAD after thinkin' it through for several months. Begad! I showed these initial sketches t' a couple o' glider people and a couple o' rocket glider people as well. After incorporatin' some o' their ideas, I started construction.
By now, ya bilge rat, arrr, matey, you undoubtedly know how a motor mount goes together, arrr, so I won't go through that end o' t' glider. Blimey! The interestin' stuff is at t' other end anyway. I trimmed about 6" o' BT-50 from t' overall length t' use as the slidin' section o' t' nose. Blimey! Ahoy! I then cut t' openings out that are servin' as t' slidin' guides from t' nose section of tube. 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. Well, blow me down! 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. Well, blow me down! T' spacer tube was then glued in place in t' main airframe.
I covered and hinged t' canards and elevators with Monokote. Arrr! Begad! These were then glued t' t' slidin' nose section at a slight dihedral. I carefully glued t' retainin' tabs for t' elevators on next, arrr, makin' sure that they would be straight on boost. Ya scallywag! Well, blow me down! Next came t' wings and rudders. Avast, me proud beauty! Arrr! T' win' was cut as multiple pieces as it was too wide t' be cut from a single width o' 4" balsa.
Finishing:
T' only finishin' that I did on t' Devil Ray was sandin' and Monokote on t' elevator/canard assembly. Begad! T' glider
came in at a reasonably heavy 2.6 ounces dry weight before trimming, shiver me timbers, 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. Avast, me proud beauty! T' left wing, even though it be cut from t' same sheet of balsa as t' right, weighed substantially more. After a good bit o' sandin' and by addin' 3 washers t' t' right side o' t' canards, it balanced fairly well laterally. Begad! 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, 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. Avast! Once it dropped a wing tip, it invariably stalled out and crashed t' that side. Ahoy! 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.
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. Aye aye! This
ruled out t' Estes B4-2 that I be plannin' as me motor.
My next choice o' motor was t' Estes B6-2. I was a little leery about usin' a motor this small on a rocket of this size, shiver me timbers, me hearties, 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, ya bilge rat, loaded me first motor, shiver me timbers, me bucko, ya bilge rat, and loaded t' glider onto t' pad. T' boost arched over but it still reached reasonable altitude before deploying. Well, blow me down! Blimey! T' glide was fast and reasonably smooth, shiver me timbers, circlin' around t' flight line. Well, blow me down! Blimey! Avast, me proud beauty! Blimey! Unfortunately, t' landin' be equally fast and one o' t' wings snapped off on landing.
T' win' was easily CAed back on and t' Devil Ray be prepped for another
flight. Ahoy! T' second flight was on a B6-2 again. Avast, me proud beauty! T' model weathercocked a bit more on t' second flight than t' first
as t' wind be pickin' up slightly. Avast! This time, however, ya bilge rat, at ejection t' elevators failed t' deploy and t' glider
didn't. Ahoy! T' lawn dart folded t' airframe in half and snapped off both wings this time. Begad! T' elevator and canard system
survived despite bein' t' end that actually hit t' ground.
Recovery:
T' first glide o' t' Devil Ray be surprisingly good for a new glider. Arrr! Blimey! Usually it takes a few flights t' get the
trim right for me. Well, blow me down! Blimey! I be quite pleased with t' performance o' t' deployment system and it seemed t' take no wear and
tear from t' flight.
Summary:
T' Devil Ray was exactly what I was lookin' for in a glider. Easy recovery with a minimum o' prep and re-prep time
without shootin' motor casings everywhere or a pop-pod. I liked t' look o' t' design even though thar were some
inherent stability issues for its glide recovery. Avast, me proud beauty! I believe that I will redesign t' tail/win' section o' t' glider
before rebuilding.
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