Electric Flight Design Projects

This page was last updated on May 3rd, 2006; thanks for visiting!

The "Wattsinnit"

(Named for the question most likely to be asked by someone seeing this E-powerd plane fly for the first time!)

Slow Flyer / Park Flyer Original Design By Bruce K. Stenulson, designed & built in the winter of 2000 - 2001

Wingspan : 48"

Wing Chord : 10"

Wing Flying Area: 460 square inches = 3.2 Ft. Sq.

Wing planform: polyhedral: 24" flat center panel, 12" tip panels, 20 degree angle, with wing tip plates.

Wing Airfoil: NACA4408 (Undercambered)

Flying Weight: 20 Ounces when flying with 8 cell 1100 mAH NiMH pack and Mabuchi FS-390PH motor. (Other motor / battery combinations would allow flying at a lighter weight / wing loading, possibly to under 15 ounces.)

Wing Loading : 6.25 Ounces per square foot with Mabuchi 390PH motor & 8 cell NiMH Battery setup; less with light brushless motor and a two cell LiPoly battery.

Construction: Built- Up Balsa, ply; Iron-on covering

Covering material : Ultracote Lite Transparent on wing, tail group; Flourescent Ultracote Fuselage.

Motor: Mabuchi FS-390PH (4 ounce motor: 1/4" longer than standard 400, flattened sides similar to the '450 turbo')

Prop: 8x6 folding propeller

Flight Battery: 8 cell 1100 mAH NiMH battery pack weighs 6 ounces; (a 2 cell 1000mAH 15C LiPoly battery weighs only 2-1/4 ounces.)

Power System Option: fly with a GWS lightweight Brushless motor and 2 cell LiPoly 1000 mAH battery pack for <15.5 ounce flying weight

Speed Controller originally used: SC6 (my design)

Peak Current Draw = <7 Amps typical on 7 cell SANYO N-500A flight pack (9 Amps on 8 cell NiMH pack)

Radio System: Updated: Airtronics RD8000 transmitter; Castle Creations / BERG 4L micro Receiver

Servos : 2 FMA S80 micro servos

Control rods : .025" dia. music wire; nylon control horn sections cut down, drilled with #66 drill, glued into slots in the control surfaces.

Landing Gear: None Used; Hand launch, land anywhere!

Photo Above By Peer Bjornstad of SPARCS, taken at the Lake Dillon Flying Site 01-21-2001

Performance: (Again, most of my flying is done jus at 10,000 Ft. ASL): Only 1/3 throttle needed to cruise in level flight; loops at ~ half throttle: very tight loops & very tight turns easily performed... Also glides with power off very well, climbing in very light lift. This plane inspires "irreverent' flying- low & slow, or wide open & a bit radical. More later- I'll just say for now that the "WATTS INNIT?" far exceeds the design objectives- I'm still very pleasantly impressed!

With it's exceptional slow flight capabilities, this should also be an excellent night flyer; a ~1.5 ounce, 20 LED lighting setup should have 40 minutes of 'light time' on it's seperate 6 cell 50mA SANYO battery pack. Visit the Night Flying page for further information on setting up a LED night flying system.

This is a look at the 'business end', showing the GUNTHER 17.5 cm x 16 cm (7x6 inch) prop, and the prop adaptor used on the Mabuchi FS-390PH motor, or on other 400 size motors with 2.3mm shafts. Later updated to a folding propeller system.

This is another view of the front portion of the fuselage, showing the servo installation, and the 7 cell battery pack in place; it slides in & out through the 'windshield' hatch, carried on a 'shelf' type balsa plate that runs forward from the front edge of the lite ply servo mount plate. This allows for fairly quick battery swaps. 1/4" light balsa 'side rails keep the battery centered, while velcro is used on the 1/4" x 1/2" balsa rear battery stop area to keep the battery located in place. the windshield hatch was designed to allow easy installation of the motor, as well as fairly easy battery swaps, while still keeping the battery solidly in place.

The receiver is installed on the under side of the battery carrier tray / shelf, accessed through a removable balsa belly panel that's simply held in place (once the receiver is installed) with a modestly oversized section of covering material. This layout provides a fairly wide range of battery / reciever positioning options in order to acheive final aircraft balance. [Remember, to E-power flyers especially, 'lead' is really a four-letter word!]

Birch Ply is used for the two wing mount plates, drilled & tapped for #8-32 nylon wing mount screws. Triangle stock is used in various locations for extra structural strength, and as rear fuselage longerons.

This is the Mabuchi FS-390PH motor that is providing surprising efficency & performance. It weighs 1 ounce more than the MPFC "Enduro" motor that Tom Hunt recommends for models such as the Elipstick. It produces 300 more RPM at .6 Amp less current draw; not a bad trade for carrying an extra ounce! The really sweet detail, however, is that it's wound to run the Gunther 7x6 prop at a peak draw of 6.9 amps from a 7 cell N500A battery pack. This motor / prop / battery conmbination produces roughly over twice the thrust needed to perform loops from level flight.

Bench testing of the new 390 motor with the Gunther prop, before any extensive break-in, yielded 6500 RPM at 6.9 Amps on the 7 cell pack. On a 5 cell 600AE pack, 5700 RPM is produced at 5.3 Amps current draw. (These test results are from runs at my home at 10,300 Ft. ASL in the center of Colorado; the air density is roughly 16% lower up here, than sea level standards.)

Above is a photo of the forward section of the fuselage, just before joining the two side panels together. The Motor Mount 'firewall' and the former at the rear edge of the wing, along with the two 1/8" birch ply wing mount plates, are the the primary cross-structures visible. The belly was built out with another pair of 3/32" birch ply cross members, for the optional installation of landing gear.

The Tom Hunt / MPFC 400 "ENDURO" motor is shown in the photo above, connected to a Trick RC / Aveox "ZAGI-14" ESC.

UPDATE NOTE, May 3rd, 2006: Motor life expectancy: I've drilled ventilation holes in the Mabuchi FS-390PH motor fromn & rear case ends to allow cooling air to pass through the motor, in hopes of keepingbthe motor cooler. Unfortunately, after multiple flights in warmer summer flying conditions, I do notice a substantial drop-off in motor performance compared to when these motors were new. My conclusion is that the magnets are loosing strength due to heating; they simply are not high heat-tolerant magnets, so flying at 9 amps in warm summer flying conditions has resulted in magnet degradation over time.

My next update / modification will be to set up one of the lightweight $15 GWS brushless motors on a firewall mount, and use an appropriate folding prop. The WATTSINNIT Will fly on a two cell 1000 mAH to 1300 mAH LiPoly battery system, using one of the 10 Amp BP Brushless ESCs. I buy many of these parts from BPHobbies.com - (Formerly doing business for many years as Balsa Products.)

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