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The Great Planes Super Sportster 40

by Pete O'Shea.

The Great Planes Super Sportster

Overview

The Super Sportster 40 by Great Planes is a 4-channel low wing aerobatic plane designed for glow power that makes a good conversion to electric. I built the original version several years ago and have recently resurrected it and started flying it again, with a slightly longer wingspan. In the meantime, Great Planes has come out with a Sportster 40 Mark II which, I understand, has a better wing center joint and possibly some other structural modifications. The wing is a standard D-tube structure with cap strips aft of the main spar. The main gear are set into hardwood blocks mounted into reinforced ribs. The fuselage is built mostly from sheet, with the turtledeck (the curved part on the top, from the back of the canopy to the tail) built up from formers and strips. The tail surfaces are sheet balsa.


Data

Measures:

  • Span: 56" (original), 61.5" (as modified) (142/156 cm)
  • Chord: 10.25" (26 cm)
  • Area: 550 sq. in. (original), 612 sq. in. (as modified) (3548/3948 sq. cm)
  • Fuselage length: 45.5" (116 cm)

Weight:

  • Wing 21.7 oz (613 g),
  • fuse 42.5 oz (1204 g),
  • motor pack 38.3 oz (1084 g),
  • total 102.5 oz. (2901 g)

Performance Characteristics:

  • Wing loading: 24.2 oz/sq. in. (7.348 kg/sq. m)
  • Power at full throttle: 20.9 volts and 26.8 amps; 560 watts
  • Watts/pound: 87

Equipment used:

  • Astro cobalt 40 sport,
  • 19 Sanyo 1700SCRC cells,
  • APC 10x7 prop cut down to 9.6",
  • Futaba 129DP receiver,
  • 2 Airtronics 94831 servos (1 elevator, 1 rudder),
  • 2 Hitec HS80 servos (1 each aileron),
  • Jomar SM4 speed control,
  • 2 automotive 30 A ATO fuses soldered in parallel in center of motor battery,
  • Jomar arming switch.

Kit Quality and Construction

The quality of the kit was good. I didn't have any problems with balsa quality or cutting quality. After I partially melted the first canopy trying to speed-cure some translucent paint, I called Great Planes to order a replacement. They sent one right out and didn't bill me! That's customer service!  I used Rit dye on the replacement canopy, which worked much better. Navy blue dye resulted in a canopy that's a purplish-brown and looks pretty sharp. Although many people have suggested flying this plane with a gear drive, I chose direct drive because of the plane's low-drag design and moderately heavy wing loading. Prop clearance with a gear drive would also be an issue.


Component installation

I fit the major components into the plane as follows: I mounted the motor using an Astro plastic radial mount on a small firewall forward of the original firewall location. The bottom fuse in the motor area is shaped balsa, the top fuse in the motor area is a fiberglass cowl I made myself from a carved balsa mold. The speed control is mounted to the fuse bottom behind the motor. The battery pack is mounted with its center roughly at the leading edge of the wing, and is just above the wing resting on two plywood plates. A hatch on the fuse top allows the battery to be changed each flight. The receiver, receiver battery, and tail servos are installed in the fuse aft of the wing trailing edge, with a hatch giving access to them. The two aileron servos are mounted near the center of the wing using the torque rod linkages supplied in the kit.


Flying

The Sportster 40 requires a relatively smooth and long surface for takeoff. Long grass, or a short and bumpy runway make takeoffs difficult. Once airborne, the Sportster flies well and is neutrally stable. It is very aerobatic, and can perform nice axial rolls, large inside, outside, and square loops, spins, snap rolls, and many things that are outside my piloting capability. Its vertical climb capability depends on the prop used, and probably suffers slightly on my plane from a few ounces extra weight. With the setup listed above and moderate aileron rates, I can do one and a half to two vertical rolls before airspeed bleeds off. Using computer mixing, I set up the ailerons as flaperons. I haven't yet been able to detect a landing speed advantage with both ailerons dropped, but the roll effectiveness does drop to near zero. Flight durations with 1700SCRC cells are between 6 and 7 minutes, when performing aerobatics while trying to conserve power.


Changes I'd make on the Next One

If I were to build another Super Sportster, I would concentrate more effort on weight reduction in the fuselage. The large sheet balsa sides aft of the wing could be easily replaced with a lighter stick structure. The sheet balsa tail surfaces could be easily replaced by built-up surfaces. There's at least a few ounces of weight savings lurking in the fuselage that I didn't find on the first try. Other than the sheet tips, there isn't much that I'd change in the wing. I would also try changing the landing gear, possibly making a new pair with a stress-relief loop in the vertical section. Less than perfect landings on the stock gear often result in the gear bent backwards ten degrees or so (I've seen this problem on glow Sportsters, too).


Permission is given to copy this article with attribution to Peter O'Shea and the E-zone

Peter.OShea(at)analog.com

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