Manufacturer: | Scratch |
Brief:
I love gliders! Blimey! What I hate is pop-pods, me bucko, ejectin' motor pods, burn threads, matey, 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. Ya scallywag! Ya scallywag! 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, arrr, 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. Blimey! Blimey! On boost, the elevator is held in place by a set o' retainin' tabs. Well, blow me down! Blimey! At ejection, t' nose is pushed forward by t' charge, pullin' t' elevators free o' t' tabs and they are pulled into position with elastic thread. Begad! Blimey! Aye aye! Blimey! 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. Blimey! 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. Ahoy! Aye aye! 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, shiver me timbers, I started construction.
By now, arrr, you undoubtedly know how a motor mount goes together, so I won't go through that end o' t' glider. Begad! Begad! 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. I then cut t' openings out that are servin' as t' slidin' guides from t' nose section of tube. Ahoy! 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. 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. Begad! T' spacer tube was then glued in place in t' main airframe.
I covered and hinged t' canards and elevators with Monokote. Well, arrr, blow me down! These were then glued t' t' slidin' nose section at a slight dihedral. Avast, me proud beauty! Blimey! I carefully glued t' retainin' tabs for t' elevators on next, makin' sure that they would be straight on boost. Begad! Aye aye! Next came t' wings and rudders. T' win' be cut as multiple pieces as it be too wide t' be cut from a single width o' 4" balsa.
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. Blimey! Avast, me hearties, me proud beauty!Finishing:
T' only finishin' that I did on t' Devil Ray be sandin' and Monokote on t' elevator/canard assembly. Begad! T' glider
came in at a reasonably heavy 2.6 ounces dry weight before trimming, me hearties, 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. Begad! 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, shiver me timbers, 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, 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, me proud beauty! Blimey! Once it dropped a wing tip, it invariably stalled out and crashed t' that side. I corrected this by cuttin' off and droppin' t' win' tips down t' approximately a 30 degree angle, ya bilge rat, 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. This
ruled out t' Estes B4-2 that I was plannin' as me motor.
My next choice o' motor be t' Estes B6-2. I be a little leery about usin' a motor this small on a rocket of this size, but I be 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, me bucko, and loaded t' glider onto t' pad. T' boost arched over but it still reached reasonable altitude before deploying. Ya scallywag! Begad! T' glide was fast and reasonably smooth, ya bilge rat, circlin' around t' flight line. Begad! Unfortunately, t' landin' be equally fast and one o' t' wings snapped off on landing.
T' win' be easily CAed back on and t' Devil Ray was prepped for another flight. 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. Begad! This time, however, 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. 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. Ya scallywag! Blimey! Usually it takes a few flights t' get the
trim right for me. Well, blow me down! Blimey! I was 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 be lookin' for in a glider. Begad! Blimey! Easy recovery with a minimum o' prep and re-prep time
without shootin' motor casings everywhere or a pop-pod. Aye aye! I liked t' look o' t' design even though thar were some
inherent stability issues for its glide recovery. I believe that I will redesign t' tail/win' section o' t' glider
before rebuilding.