About this Plan
Skeeter. Radio control sport twin electric model. Wingspan 60 in, wing area 625 sq in. For twin Astro 05 motors.
Quote: "An electric twin with good looks and performance to match. Skeeter, by by Hal 'Pappy' deBolt.
WHEN is a mosquito not a mosquito? When it's a cute little twin-engined mockup of the deHavilland Mosquito. Add electric power and you've got a 'Skeeter.' I'm sure most modelers have dreamed of building a DH Mosquito, such a pretty airplane with its sleek lines and efficient shape, As a 400-mph full-scale aircraft built from model aircraft materials - balsa, plywood, fabric, and dope - it's even more interesting. Is there a more attractive full-scale to pattern a twin-powered R/C model after?
Many of us have been impressed by a twin in flight; it's distinctively different and has excellent performance. We can be inspired to build one until we remember stories of matching engine outputs and marginal control with one dead engine. My experience with twin engines was with a couple of spectacular performers until I had an engine quit at the wrong time, resulting in disaster.
With electric power, however, you can use multi-motors without the usual engine-associated problems. The better motors are closely matched in power output, and there is the advantage of operating them from the same battery supply. All motor power remains equal from start-up to last gasp, so you can operate an electric-powered twin with considerable assurance. The operation is very much like that of a single.
I had other reasons for building the Skeeter besides my desire for a twin. I presented the details in the September '85 issue of MAN, if you're interested, but suffice it to say that my projections indicated there could be a power/ weight ratio improvement by using two small motors instead of one large one. I also felt there could be a gain in efficiency with two propellers. The results are great, with a 25% imnprovement in the power/weight ratio and performance indicating a nice gain in propeller efficiency.
With my single-motor Electra Sportster (see May '85 MAN) I had satisfying sport acrobatic flight with electric power. With the Skeeter's dual-motor improvements, performance is carried a couple of steps further; in fact, considerably more than I'd hoped for. The Skeeter easily jumps off pavement in about 20 feet, then climbs out at a respectable angle and speed. The first turn back comes with authority and the following flyby shows impressive speed and agility. With the ample thrust, maneuvers are easily and consecutively accomplished. Simply fly the aerobatics you want.
I did note one difference with twin motors. With the points of thrust being away from the aircraft centerline and line of flight, twins tend to be sluggish in axial rolls. Increasing the aileron throw tightened them up nicely. One flight characteristic separates a twin from all others - there is no sound as scintillating as two props in perfect synch at full bore!
For an energy source I used fourteen SR 1.2-amp cells at a nominal 17.5 volts. This powers two Astro Flight Cobalt 05 motors, which are equipped with 2.2:1 Astro gearboxes and turn 11x7 props at 5,800 rpm. However, best maneuvering has come with 11x9 and 12x9 reworked props. The motors are controlled by an Astro electronic relay switch. The R/ C equipment is a standard size 4-channel, although the available lighter servos and battery would be sufficient and would help with the weight.
With multi-motors there are two possible hookups for the motors and battery: parallel or in series. I did some bench testing of both and discovered that with the parallel configuration the bat-tery voltage is the norm for each motor and both motors are wired directly to the battery. With the series configuration, the battery voltage is doubled, as all the cells, switches, and motors are like links in a chain. The motors divide the voltage between them so that they actually run at normal voltage. The only appreciable difference was about a 500 rpm increase with the series circuit. I believe this is because there is considerable wiring when motors are located in nacelles. With the higher series voltage, the motors see less of a voltage drop due to wiring resistance. I opted for the greater series thrust and it has worked fine.
My standard Astro Flight charger has a 7- to 8-cell limit, so I needed something for fast field charging. My solution was to add an Astro Voltage Booster to my standard charger and performance has been excellent.
CONSTRUCTION. The structure of the Mosquito is designed to provide the necessary size and strength with as little weight as possible. While not expected to be crash proof, it has proven adequate for flight loads and occasional hard landing. You'll find some unique methods used in the construction and I suggest that you do not deviate from them. Beefing-up electrics is a no-no..."
Skeeter, MAN, October 1986.
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Supplementary file notes
Article pages, thanks to RFJ.
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