Ideas & Builds
A Bubble Dancer for ALES competitions
2011 Winter Project
In 2011 our ORCC fellows showed-up with electric gliders equipped with a little device called CAM module. The guys competed regularly into a new kind of category called ALES. The gliders ranged from last generation mouldies with specific fuselages to more conventional built-up wings and various foamies. Many different motors-batteries-ESCs were installed, once again ranging from the cheap outrunners to very expensive exoteric inrunner-reducted, but all of them were very succesfully.
These gliders attracted immediately our attention for several reasons: carrying a self-propulsion device removed the need for winches, which in terms means increasing the range of opportunity to fly since no long distances are needed for the cables to be laid on the ground. The CAM module was relatively cheap, compatible with all kind of motor and radio set-up and very straight forward in use.
The Project eBD was then launched promptly in October 2011. Steve had already in hands the MATS mould for the Bubble Dancer fuselage and launched a mini series of carbon-kevlar pods, 2.4GHz compatible and BD commercial booms. Different pilots have different tastes and eventually a fleet of 4 different eBDs were born. Check these out!!!
All composites wing, fuselage and X-tail feathers. The wing sports two generous Flaps, while the primary controls are assigned to Rudder and Elevator.
Jacques built a set of feathers: the movables were sturdy and the finish was very good. Unfortunately they resulted a bit on the heavy side, affecting too much the CoG of the airframe. Jacques is already put together a new set of feathers, half the weight of the initial ones!
Jacques decided to go for flaps on the wing to be used primarily as spoilers for landing. Flaps are faced before the kevlar skins are cured in place: as a result, the movables are extremely rigid in torsion. He also worked hard to obtain a very clean hinge and aerodynamic covering of the flap leading edge. The movable horn gets in the thickness of the wing giving a "nothing protuding" aerodynamic surface, kudos to him!
The wing sections are taken from the AG series. The sections evolve from a 8.24% thick AG24 at the root to a 6.8% thick AG26 at the tip. The wing is extremely thick so that structures must be carefully designed.
The wing sizing has taken into account the lessons learned on the previous project KUDA. A spreadsheet is in place giving thickness of spar caps, shear web, skin sizes depending upon estimated loads. The weight target was set at 3lb and the load factor at 25g. The loads in flight will never be as high, but we wanted to keep some margin because we all know that landings can be rough when the pilot wants to "hit the spot at the right moment".
The weight of Jacques` model sums up to 55oz (3.44lb) and is divided as follows:
Motor: 191 grams
Battery: 220 grams
Prop & spinner: 34 grams
ESC: 47 grams
Center panel: 423 grams (including harness, 2 Futaba S3150 for flaps & carbon joiners)
Mid panels: 134 grams each
Tips: 89 grams each
Fuselage: 516 grams (loaded with battery pack, ESC, motor, Rx and 2 Hyperion HP-DS09-AMD servos installed into the rudder)
Horizontal stabiliser: 30 grams
Total AUW: 1600g........57oz
The motor installed is specifically designed to work in conjunction with a powerful 3S LiPo battery pack. The unit can deliver 450W (static on ground) with a 12.5x6 prop while absorbing 40A. The glider has proven to be able to climb at an altitude of 200m in approximately 20sec, averaging a good 10m/s climb rate.
Motor: MEGA 22/3S
Prop AeroNaut CAM 12,5 x 6
Battery: Turnigy Nano 2250 maH 65C
ESC: HET 75
The specific power equals to 126W/lb, which is the typical "rule of thumbs" number you are looking for, when designing such a ship.
The motor can actually absorb 70A for a limited period of 30s, giving to Jacques an upgrade possibility: installing a 13x8 prop and the same 3S battery the unit can deliver 600W (168W/lb) which will turn into almost 14m/s climb rate!!!
eBD J mk2
Jacques went a step ahead and changed some of the features of his eBD. The objective of the rework was to shed away some weight from the tail feathers to achieve proper balancing without extra nose ballast.
The fuselage has been kept basically the same, but stabiliser and fin are now made lighter and stiffer.
Servos have been embedded into the fin. They are mounted using little screws for ease of maintenance on the field and they disappear in the thickness of the airfoil without a bump!
Built-up wing, with Spoiler, composite fuselage and V-tail feathers. Steve really likes V-Tails. It has already proven with his modified Allegro 2M that a well wized V-Tail can deliver proper handling while being lightweight. That's why he launched himself in his personal interpretation of the eBD theme.
His ship features a removable one-piece tail group. The servos are plugged in before the tail is pinned to the tail boom. A bit of tape then secures the whole thing together. Simple, light and effective!
The weight of Steve`s model sums up to 54.75oz and is divided as follows:
Motor MVVS 4.6/860
Prop AeroNaut CAM 12,5 x 6
Nanotech 3S 2250mAh - 65C
ESC TBC HET 75A
Wing Center panel: 372 grams (w/ joiners, servo)
Wing Left Tip: 171 grams
Wing Right Tip: 165 grams
Tips: 58 grams each
Fuselage: 727 grams (fully loaded with battery pack, ESC, motor, Rx)
Vee tail: 98g (with servos)
Total AUW: 1533g........54.75oz
Built-up wing, with Spoiler, and composite fuselage and X-tail feathers. The model sports a regular "winch proof" Bubble Dancer built-up wing. This wing is a beautifull construction from our artist and artisan Steve Barry. The wing is light and more than strong enough since the load specification for a full pedal winch launch are miles ahead respective to the stresses this model will ever experience flying ALES!
Steve has put particular attention to the installation of servos in the fin. The elevator pushrod comes out from the leading edge of the fin being aligned with the airflow. The actuation is totally slop free and the servos are easily accessible at all times. This tailgroup has proven totally reliable and sturd enough to take the abuse of precision landing.
Composite wing and composite fuselage with original X-tail feathers. The model sports a composites "winch proof" Bubble Dancer wing. Duc has decided to install a Drela style fin and rudder resulting in a huge tail group! This gives to the model great handling characteristics.
Duc has kept the gear installed and the weight of the ship "classified". I will dig more and let you know!!!
See you later with more pictures and details about this new eBD flying at the MATS field!
update 17 September 2012
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