Flying weight of this Viento as set up range: 40-1/2 Oz to 43-1/2 Oz, depending upon which battery is installed
Wing area: 496 square inches (32 dM^2) = 3.44 square feet
Wing Loading : 12.65 Ounces per square foot maximum
Fiberglass Fuselage Length: 41.3"
Controls: 2 Aileron servos and Elevator: I used HITEC HS-81 servos; Rudder uses a GWS HP NARO servo
Radio System used: Airtronics RD6000 Super Transmitter, GWS GWRD-8 8 Channel Dual Conversion micro Receiver
Motor I used: CERMARK CEM-0506 Cobalt, brushed, 5 pole, direct drive, "8 cell wind"
5 Battery Options Used: 6 cell 1250 SCR for the lightest setup; 6 Cell RC2400 or 6 cell 3000 NiMH for longer duration; or either 7 cell 1250SCR or 8 cell 1250SCR for higher RPM, more power on the same prop.
Motor Control : My design: SC7 with BEC, Brake; low voltage cutout set with 1N4733A zener diode
Propeller: CAM 9x5 folding blades mounted in the Kyosho midpart used with all 4 battery options (flying at 10,000 feet elevation)
This is the top view of my VIENTO after the trim was added; using trim only on the right wing panel brought the wing into balance laterally.
At the center of the wing trailing edge, I made a new 1/16" birch plywood reinfourcing plate; I tapered the edges, then glued it directly to the wood after removing the covering in that area, then recovered all of it with Oracover. I like the idea of having this reinfourcing plate bonded solidly to the wing structure, rather than using the loose 'hold down plate' supplied with the ARF kit.
This side view gives you a good idea of how sleek this aircraft is. The RG-15 is one of my favorite high speed slope ship airfoils- it performs very well in our thinner air high in the Colorado Rockies. When I looked at this ARF kit in HOBBY GIANT in Arvada, CO, and discovered that it was built with this airfoil, I decided I'd have to get it and try it. (They offer this one for $215.99) I'm glad I did!
Above is a view of the underside, showing the Flourescent Orange Oracover that I added to increase visibility from below. I'd also covered the ailerons and elevator with high visibility colors, using Flourescent Orange on the bottom and Flourescent yellow on the tops, before hinging them in place with tape. I ended up spending a fair amount of time working over the parts and the covering before I was ready to begin my assembly; I cleaned up the ends of the ailerons and elevator so they would not drag in their positions, and wicked thin CyA glue through pin holes into the end grain of balsa on the thin wing tips and the horizontal stabilizer ends- things I normally would do on this type of design before covering if I was building it from a construction kit or from scratch. I also did some shimming on the left side of the Horizontal Stabilizer mounting surface on the fiberglass fuselage to get the horizontal stabilizer aligned with the wing. (I still may have more to do in that area- see later comments on balance and elevator trim positions.)
Rather than using double sided foam mounting tape to mount the aileron servos (as sugested in the kit) I enlarged the wing cutouts forward to the wing spar, and screwed the aileron servos to basswood blocks that I glued in place. (I REALLY like solid servo mounts!) I added solder clevises to the front ends of the aileron linkages; (I'm not a great fan of Z-bends- especially when they come in metric wire, and I don't have matching drills to allow keeping the slop out of linkages...) The plastic fareings provided in the kit do make covering the aileron servos and their linkages a quick job.
This is a view of the interior of the fuselage as I decided to set it up. I did not use the long tray that was provided with the kit, deciding instead after testing the balance and weight distribution options to do it this way. I'd chosen a lighter weight, higher power cobalt motor for this design setup rather than the 550 can motor which was included with the kit, which made it necessary to have the ability to install my wider range of battery options farther forward.
To provide for the maximum flexibility in positioning the battery to achieve optimum balance, they are installed on a strip of VELCRO on the floor of the fiberglass fuselage, were I can shift them forward or back easily.
The radio receiver is velcro mounted to another lite ply plate, positioned so that the servo leads from the wing can be easily plugged directly into the receiver when mounting the wing, without the need for 'servo extension wires'. (I had cut off the aileron servo leads close to the servo case and spliced those servo wires directly to the twisted three conductor wire I'd routed through the wing, using solder and heat shrink tubing for high reliability connections. I then later spliced the servo lead ends I'd cut off the servos to the ends of the wires coming out of the center of the wing; (no 'servo extension wires' were used anywhere in this aircraft.) Having only one plug-in connection directly into the receiver for each aileron, and soldered connections elswhere, is my approach to achieving high reliability in a radio system setup.
TECHNICAL NOTE Update: As I work back towards where this sailplane really wants to be balanced, I now have plenty of room to velcro mount the SC7 ESC behind the motor on the inner belly of the forward fuselage, with the battery velcroed in oplace behind it. I've also mounted the receiver cross-wise just against the front of the servos, leaving more room for positioning the batteries a bit farther to the rear.
The kit instructions also sugested mounting the rudder servo in the cutout in the right side of the vertical stabilizer; I needed weight forward, and knew that having the rudder servo back there would make it difficult to balance the aircraft, so I made a servo mount plate from poplar lite ply for both the elevator and rudder servos, and mounted it to the rear of the area under the wing where I could still get at them to work on setting up the linkages. I used a ~.042 music wire pushrod for the elevator, running through a 1/8" O.D. nylon guide tube, with the guide tube anchored on each end. I used a .032 music wire pushrod running in another nylon guide tube for the rudder, with it's guide tube also anchored on each end; you can see the rear end routing in the photo below. I also glued the rudder horn into a slot I cut into the balsa rudder after trimming excess plastic away, rather than trying to align long screws through a thick tapered rudder. This setup is working very nicely.
On a cobalt motor installation that runs up to 42 Amps static current draw on the ground on 8 cells, I was concerned with having adequate air moving through the motor and past the batteries for adequate cooling. For now, I'm leaving the cutout on the right side of the vertical stabilizer open to provide aditional cooling air exit. By summer, I may provide cooling air exits just behind the battery position on the fuselage sides. (I've also enlarged the small cutouts that were already cut into either side of the nose area of the fuselage, to provide more cooling air intake, since they were there anyway.)
This is a photo taken just before my first flights, before the trim was added on top of the right wing panel. In mid-February, a large hay meadow a couple of miles from my home was free of snow; the elevation is just above 10,000 feet. This sleek aircraft is handling very well in our thinner air up here- it should be able to be set up to fly very nicely anywhere!
I'm still playing with progressively shifting the battery / balance farther and farther back, while watching the elevator trim position; I have shimmed the under side of the trailing edge of the horizontal stabilizer in order to have the cleanest setup with zero trim by the time I'm done. Since the Horizontal Stabilizer was designed to be removable for transport if desired, and is simply mounted with a single screw, fine-tuning the horizontal stabilizer alignment was fairly easy to accomplish.
Update: after flying again on early Saturday 02-15-2003, I've been shifting the balance further back, and I am getting closer to where the aircraft wants to be balanced. I'm behind the sugested balance range mentioned in the kit insrtructions, and will report the measurement when I finalize this aspect of the setup.
With the sleek clean prifile of this sailplane, it takes quite a while for it to loose speed, and it will sail in ground effect for a long ways. I first tried a flaperon deflection- both ailerons down- to see if that woiuld help in landing approaches, but it wasn't what was needed. So today I set up the Spoileron function - both ailerons deflected up up to 3/4", using the three position flap switch. This is working very well to slow down this aircraft for landings.
In my setup now, The Spoileron off position is the rear position on the flap switch. Pulling the switch forward to the center position gives half deflection up on the spoileron deployment, while pulling the switch forward to the front position gives full deployment. When the Spoilerons are deployed, the sailplane goes into a more nose UP attitude, and the drag really slows this ship down nicely, while still leaving it very managable. The half deployment brings down the airspeed nicely for longer approaches, while the full deployment does a great job of bringing down the ship much more quickly. Even with radical up deflection on both ailerons, there is still very reasonable aileron control of the roll axis. This will allow landing much more easily in much tighter landing areas than would be possible consistently without the Spoileron deployment.
Update: I am now using a 1/16" thick ply shim under the trailing edge of the Horizontal stabilizer to set the incidence closer to zero trim. I'll be making a permanant one, (tapered towards the front edge), and gluing it in place.
On Sunday, February 16th I flew the first flights with the 8 cell 1250SCR batteries; I'd tested these briefly previously at a static current draw of just under 42 Amps turning the CAM 9x5 blades, and producing 13,000 RPM. In flight, this amount of power of is impressive! It produces a thrust to weight ratio of better than 1:1, so this sailplane can be allowed to point it's nose straight up, and will continue to climb vertically if I want. No, that's not it's most efficient angle of climb- but the power is there to do about anything I want. (GRINS)
Motor runs are typically brief, climbing to altitude and then cutting the motor to glide. I'll re-apply power briefly ( ~5 seconds) occasionally to climb back up higher, then cruise some more. This day was an overcast day, without thermal activity, and I was flying over snow covered country, but the air was smooth- a good day to test the 8 cell battery packs!
The wing is very well designed to handle this level of power- overall, I rate the Viento very highly as to how well it flies, both power on and power off. Yes, I did some of the setup differently than the kit's sugestions... And I'm very happy with all of the setup details I've described.
The SC7 ESC is working very well for this aircraft; the prop brake works very nicely, and it's easily able to handle the 300+ watt power levels when flying the 8 cell packs. Oh, I'll still fly this Viento on the 6 cell higher capacity battery packs often, too- vertical climb ability isn't necessary for enjoyable flying. It's just fun to have a versatile aircraft that has that capability on the upper end of the performance envelope, and handles that power well.
I plan to add some gap sealing tape to the undersides of the ailerons; I'm hearing more 'whistling' / wind noise in high speed passes than I beleive is necessary, and that means air turbulance / drag. I also intend to add shrouded cooling air exits just behind the battery mount position on both sides of the fuselage before warmer weather returns to the high Rockies. I can then seal the opening on the side of the vertical stabilizer to clean up that area. These should minimize the drag even further for an even cleaner gliding sailplane.
I'll likely also order one of the vented spinner / prop midpart systems now offered by Hobby Lobby, for use with a set of CAM 10x6 blades on the 6 cell packs. This should offer a ~300+ watt power option on the 6 cell battery packs. For a much lighter weight "Sprint Mode" setup, a 6 cell 1250SCR pack feeding the 10x6 prop would likely be optimum, with a flying weight of 40-1/2 ounces.
(Keep in mind that I'm working out prop selection for flying my Viento at my home altitude of 10,000 feet, with about 84% of the air density that a sea level flyer would have.)