It's amazing how aerobaticly this Rudder / Elevator aircraft can fly. The 24 degree dihedral setup allows for this type of agile handling response. She will roll very rapidly, loop in a very small amount of sky-either inside or outside- and does inverted flat spins very nicely. She recovers from any attitude quickly. And with a wing loading of only 2.7 ounces per square foot, she can slow down beautifully. The underbody and tail skids act as effective vertical stabilization when flying in high-alpha atitudes.
(Elevons are ineffective on a aircraft with this high dihedral layout; there are lots of high performance elevon designs, such as the MANTA OMEGA and ACE designs. The Flirt was designed to be highly aerobatic using only rudder and elevator.)
Oh- the name??? My wife came up with it, and it FITS! The FLIRT is a resilient girl that just Loves to flirt with the dirt- and flirt with the trees- and flirt with the bushes- she can't hardly wait to play in the snow! My kind of girl!!
My thanks go out to 'Goldguy' on RCGroups for the inspiration for this new fun flier design! The basic plan for the round Nutball design is available online in the 'Foamies-Scratchbuilt' section of those discussion forums.
I finally got a bit of time to start this project. It is primarily designed for snow flying (and maybe occasional indoor flying). It's early in November of 2008 as the first flights have been completed; winter is here in the high country of CO... that means that, for us, it's snow flying season for the next six months up here!
Since building a mini-IFO many years ago, I've been very happy with how well mono-gear setups can handle- and especially how light they can be built compared to the two-wheel taildragger setups which I like to use on heavier aircraft. I fly from snow a lot more than from other surfaces; there are only rare opportunities to fly indoors once or twice a year in a conference center ~40 miles from home, so flying from snow was the primary mode I targeted with this light gear.
I'd likely put a mono-wheel on rather than the EPP 'ski' if I flew from different surfaces more of the time; but my lightest weight axle mount ski still weighs twice what this new EPP foam mono-ski weighs. The nice thing is that the ski gear could be dismounted, & a mono-wheel gear added in it's place when desired. Hot-melt glue and nylon filament tape make it fairly easy to make modifications.
This 16-7/8" diameter [1.55 square feet of wing area) fun flyer is flying at about 4-1/8 ounces when using the Rhino 2S 460 mAH LiPo battery; that's a wing loading of under 2.7 Oz. per square foot. An even lighter battery could be used for indoor flying.
These photos show one way I came up with to do the double leg mono-ski gear setup, which results in a springy resiliency that carries the weight of this lightweight aircraft adequately, while keeping the ski oriented in flight. The ski is cut from a scrap block of 1.3# EPP (weight = 1.9g) and the ~3/64" wire weighs only 2.8g. I may add the slick Polyethylene tape to the running surface for minimum drag.
I also wanted to minimize weight in the motor mount for my 16g motor, so one photo also shows how I installed the 1/16" birch ply plate and tied it into the airframe with CF rods. It's set with ~5 degrees of downthrust, and minimal right thrust for now.
The lower forward extended belly was designed deep enough to have the space to make a battery carrying bay within the 9mm EPP foam to carry the LiPo battery pack, directly on the aircraft's lateral center line within the EPP foam. For cold weather snow flying, it can be enclosed with thin insulating foam covers to keep the LiPo battery from chilling down & loosing performance. (Cold Batteries just can't deliver the energy!)
I've included a photo of the 24 degree dihedral gluing wedge brace that I drafted out, folded up, & taped together quickly for this job. I sorta like having closely matching dihedral angles... this worked fine to hold the angle while the hot melt glue set up!
Above: 16-7/8" disc of 6mm EPP with a mono-ski / skid under the front & 2 rear skids; 16g motor, 2S 460mAH LiPo
Above: Bottom view of 1.625w x 5"L. x 1" high ski / skid. Wing uses two pairs of 1mm CF rod 'cap' spars above / below each other for 'I-beam' type stiffening at .02 Oz total weight (plus glue) Bottom view of 1.625w x 5"L. x 1" high ski / skid. Wing uses two pairs of 1mm CF rod 'cap' spars above / below each other for 'I-beam' type stiffening at .02 Oz total weight for all four sections
Above: 3.5" high one piece wire ski mount wire- hot melt glues to wing /underbody joint, etc. It tapes to ski with cross filament tape after covering layer of tape is in place. 3.5" high one piece wire ski mount wire- hot melt glues to wing /underbody joint, etc. It tapes to ski with cross filament tape after covering layer of tape is in place.
Above: 24 degree dihedral gluing support folded from a sheet of card stock, then taped into the wedge shape 24 degree dihedral gluing support folded from a sheet of card stock, then taped into the wedge shape
Above: 24 degree dihedral gluing wedge in place, ready for gluing dohedral joint- just keep in place while hot melt glue sets up. 24 degree dihedral gluing wedge in place, ready for gluing dihedral joint- just keep in place while hot melt glue sets up.
Above: 6mm Motor mount for 16g motor on 1/16" birch ply plate, 5 degree downthrust. Two 1.5mm CF pins , top & bottom, glue back into wing front spar pair & through foam with CyA. Hot Melt fillets finish mount. 6mm Motor mount for 16g motor on 1/16" birch ply plate, 5 degree downthrust. Two 1.5mm CF pins , top & bottom, glue back into wing front spar pair & through foam with CyA. Hot Melt fillets finish mount.
I'm flying a GWS 8x4.3 SF prop that is trimmed to 7.6" and balanced. I'm looking forward to digging out an APC 8x3.8 Slowflier prop to fly on this girl- it should be about perfect.
Note- I balance GWS slowflier props by adding clear scotch 'multipurpose' tape to the back side of the light blade's tip; I add it progressively until the prop balances, starting at the tip and laying 1/2" strips smoothly , edge to edge, working my way in along the blade as necessary.
The wing's 24 degree dihedral angle seems perfect, and the ~5 degree down-thrust angle also seels about perfect across the full speed range. I can tell that the battery wants to be directly on the centerline... with it velcro mounted, I needed a bit of right trim to counteract the slightly off-center weight. Once I decide exactly where I want to locate it, I'll cut in the battery compatrment and trim a bit of excess EPP on this girl's belly. (After that, I'll decide whether a couple of degrees of right thrust will also further balance out the FLIRT's performance.
Materials needed / used:
6mm thick EPP foam (you can order fron RCFoam.com)
1mm diameter CF rods (also available from RCFoam.com) for spars and for stiffening of the EPP foam in the rudder and elevator (and in the vertical stabilizer if needed)
1.5mm diameter CF rods (also available from RCFoam.com) for pushrods; also used glued through motor mount plate into foam to secure the motor mount
Scotch cross-filament nylon filament tape (Available from Offoce Depot, or Hobby People.net)
17 gram Brushless motor - 1700 Kv; 10 to 12 Amp ESC; 2S 460 mAH LiPo Batteries [or 2S 360 mAH for indoor / lighter slow flying] (HobbyCity.com, Zazertoyz.com, etc.)
Motor mounting: I used a modest sized piece of 1/16" birch plywood. the firewall mount for the 17 gram motor was mounted with three #1 x 1/4" sheet metal screws
Micro receiver and ~5 gram or less servos (I used Vigor 4.4 g servos from HobbyCity.com; their HXT500 servos might also do OK)
Music wire: for landing gear for mono-ski setup, I used .050 wire; for pushrod ends, I used .032 music wire.
Slowflier propellers; GWS 8x4.3, APC 8x3.8
Here is a photo of the upper & lower fuselage profiles, laid out over a 1" grid cutting mat.
[Below] The Zippy RHINO 2S 460 mAH battery pack fints nicely within the thickness of the 9mm EPP that I used for the lower fuselage. Balance is right on the center ling for best handling, and the thin insulating covers will keep the battery from chilling down and loosing performance in cold winter flying conditions.
After the light misting of paint (Pactra Racing paint) on the under-parts, and the installation of the battery compartment setup, flying weight is still at 4-1/8 ounces.
The two photos below give a closer look at the control system component installation and connections. The control horns are cut from 1/32" birch plywood.
MORE SOON