The left panel houses the IFR flight instruments, including an S-TEC ST-361 single cue flight director and ST-180 slaved compass/HSI. The flight director instrumentation includes a mode annunciator and altitude alerter/pre-selector. Also, located on the left panel are the aircraft system switches and warning lights, allowing the pilot to incorporate these items in a quick scan of the instruments. The electro-hydraulic landing gear switch is located on this panel, purposefully located away from the flap switch. An especially unique feature is the “avionics” power switch, which is designed to be “fail-safe”. The avionics, therefore, will remain active even if either of the two remote mounted relays or the avionics switch itself was to fail.
This S-TEC 55X provides exceptional performance and features “GPSS”, which is S-TEC’s GPS coupling of the autopilot to the GPS receiver. This allows complex flight plans to be followed by the autopilot without the pilot having to make course changes. An outstanding safety feature of the S-TEC autopilot is that it operates fully independent of the attitude gyro. The only flight instrument required to maintain control of the airplane is the simple and long-life turn coordinator. Therefore, should the unfortunate occur and the vacuum pump fail under IMC conditions, the pilot will have the use of the autopilot while flying “partial panel”. Other features include the ability of the pilot to select vertical speed and target altitudes. These features make single pilot IFR operations a “piece of cake”.
The right side of the panel contains the flap switch with indicator, and the elevator trim position indicator. Also, located on this panel are all engine guages, including EGT and the Shadin digital fuel flow monitor. Cabin air controls and circuit breakers are also located on this side. Both panels have room for additional optional instrumentation, which the pilot/owner may choose to install.
Running aft from the center console are the low friction engine controls and the elevator trim wheel (electric trim can also be operated from the pilots’ control sticks). Conveniently located on this center console is the four-position fuel selector (left, right and off position). The emergency landing gear switch and the throttle friction lever are on the console’s left side. There is an approach plate storage area below the cowl flap knob. Curving gracefully up in front of the seats, and allowing an unobstructed view of the entire panel, are the two leather sheathed control columns, secured in a neutral position by control-system springs. Each stick is finished with a comfortable handgrip containing buttons for electric pitch-trim, transponder ident, landing gear horn cancellation and autopilot controls.
The fuel-injected Lycoming engine starts promptly whether the engine is hot or cold, indicating an effective fuel management system. The engine idles very smoothly with the four-bladed prop. The steerable nose wheel, in combination with the wide tract landing gear, gives positive control to the pilot while taxiing the Sigma 230. The trailing link landing gear provides a generous cushion while taxiing, even over rough surfaces. The aircraft has a compact 20-foot turning radius and the brakes are most effective. The main gear doors are attached to the landing gear for simplicity. There are no separate door covers for the wheels (this was designed to avoid the maintenance complexities of multi-door systems). When the flaps are set with the three-position switch the stick is displaced slightly aft by its compensating trim system.
After completing the take off checklist and obtaining clearance from the tower, the aircraft moves quietly into take-off position. Full throttle induces smooth acceleration, with much less noise than comparable aircraft, and reaches 65 knots within ten seconds. Positive rotation is achieved with modest back pressure on the stick for an easy lift off. A slight right rudder pressure is all that is required to maintain the appropriate nose position during the climb and this requirement decreases as air speed increases.
Flap and gear retraction is completed within approximately five seconds (with no trim change), and the climb to 2500 feet was made at 1200 fpm, at best rate of climb speed of 95 knots. This coincides with the aircraft manual, which indicates sea level max rate of climb of 1150 fpm. Thanks to the elevator down spring, pitch stability is positive in the critical full power climb configuration, while maintaining excellent all around visibility. Visibility in the Sigma is literally “panoramic”, and much better than most other single-engine airplanes. By leaning forward you can see down ahead of the wing; straight up through the large high top side windows; or over the shoulder to the elevator. The nose does not obstruct forward visibility, even in the climb, thanks to the low instrument panel and glare shield, which follows the curve of the cowling. The nose is virtually out of sight in the cruise configuration.
The Sigma 230 is designed for comfortable, high performance cross-country flying. At 6500 feet, at 75% power, this Sigma 230 trued out at 170 knots. Obviously, with their additional horsepower, the Sigma 250 and Sigma 310 will climb and fly faster; but you cannot help but be impressed by the low sound level of the Sigma 230, while it provides good solid performance.
Maximum VFR range and endurance for the Sigma 230 are approximately 900 nautical miles, and eight hours respectively. Economy cruise with 21 inches manifold pressure and 1800 RPM gives 125 knots true air speed and a fuel flow of less than eight gallons per hour. Rarely will any pilot require this type of endurance, but it illustrates the aircraft’s capability.
The six-cylinder engine generates very little vibration and an unusually low sound level. There is only a slight wind noise at high-speed cruise; and even this sound diminishes at normal cruise, making conversation possible without headsets. The close tolerance in engineering these rugged gull-wing doors eliminates air leaks. You can take a sheet of paper, hold it over the cabin door seal and find no point around the doorframe where the paper is pulled toward a leak. In almost any other unpressurized airplane this “paper test” will typically reveal air leaks.
When properly trimmed, the Sigma 230 is stable in all axes; this airplane wants to hold its heading and altitude. The stick controls provide positive response, which gives the pilot total command of the aircraft. The design of the Sigma line of aircraft provides balanced stick forces for elevator and aileron control. While these forces are appropriately responsive at low air speeds, the stick pressures become slightly greater at higher speeds, while maintaining an equal balance between all controls. Nevertheless, the roll-rate is a more than adequate 45 degrees per second, with very little adverse yaw.
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