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Telescopic Wing Description:
A new approach was taken to the old concept of a variable span wing by developing (& patenting) a very simple overlapping spar system. The wing is composed of a high speed (low drag & strong) central wing section with completely retractable high lift sections which move in a spanwise direction as opposed to the chordwise direction of conventional flaps. It is the same concept of changing lift with conventional chordwise flaps except that the spanwise flap increases span & area instead of only the camber. It also increases the aspect ratio instead of decreasing it, which greatly improves efficiency and safety.
When retracted, the low drag wing reaches a cruise speed of over 280 mph @ 75% power. When extended, the stall speed is only 63 mph. The low landing speed compliments the gear's ability to land on snow and water, making this aircraft exceptionally suited for bush pilots (STOL) without compromising its performance for other applications.
During takeoff & landing the high lift airfoils are extended at the wing tips. When transitioning to a high speed cruise, they are retracted in flight to leave a high-speed low drag wing capable of withstanding high 'g' loads. This system is simple, rugged, and fail-safe. The aircraft can also maneuver in flight and land safely with the wings in any position from fully extended through fully retracted. The extension/retraction mechanism is a simple system of cables that prevents asymmetric extension. Redundancy is built in so that failure of any cable does not hinder safe operation. Ailerons are on both the center section and extendable sections and are fully functional at all times during the extension/retraction process. The airfoils are conventional NACA sections.
The mechanism is simple and reliable. The extendable section spars interlock and are guided on rollers to increase the span. Binding under load during transition is prevented by the details of the roller system. This design is actually simpler than conventional high lift devices.
The overall weight of this wing is comparable to that of a conventional compromise wing for a similar size aircraft that is required to produce the same speed range, however, it is stronger and more efficient than the conventional wing. When retracted, this wing's strength puts it in an Aerobatic category (6.0 g's), and when extended, it is in the Normal category (3.8 g's).
Comparison of conventional and telescopic wings:
This is a simplified comparison of conventional and telescopic wings to show the concepts involved. Conventional flaps and other high lift devices can be applied to both wing types with equal effects.
Weight: In order for the conventional wing to match the low stall speed of the telescopic wing, it would need a planform area and span similar to the extended telescopic wing (which is relatively large). As speed is increased, less wing area is needed to produce the required lift. So, for this conventional wing, at high speeds there is a lot more wing exposed to the high aerodynamic loads than is required. For this large conventional wing to be strong enough to reach the high cruise speeds that the retracted telescopic wing can achieve, it must be exceptionally strong, which means a heavy structure. The telescopic wing, on the other hand, has only the inboard wing section (1/2 of the span) exposed to the high aerodynamic forces in cruise, which reduces structural weight. Since retractable high lift devices such as flaps and the extendable wing sections are only used at low speeds, they do not need to withstand the high aerodynamic forces that exist at cruise speeds and they can be made lighter. Because a conventional wing is a compromise between the large low speed wing and the short high-speed wing its performance is also compromised. The telescopic wing does not compromise its performance and can reach lower stall speeds and higher cruise speeds than the conventional compromise wing. The telescopic wing, including the telescoping mechanism (rollers, cables, etc.), is actually lighter than a conventional wing that reaches the same stall and cruise speeds. A conventional compromise wing can be built slightly lighter than the telescopic wing but it would not have the low stall speed or the tremendous strength at high speeds that the telescopic wing has.
Complexity: A conventional compromise wing uses flaps and sometimes movable slats to reduce the stall speed to that of the telescopic wing. The Gevers telescopic wing actually has fewer critical moving parts than a complex fowler flap does. A component failure is less likely to occur in the telescopic wing and if it does, components are redundant and the design is also fail-safe. Redundancy means that a single component failure such as an extension cable breaking does not affect the actuation of the wing. Fail-safe means that if multiple components fail the wings will simply stop in the current position. If this occurs, the aircraft can still fly, land, and maneuver with the wings in any position. Asymmetric extension is prevented by the design more so than with some conventional flaps. So the Gevers telescopic design is simple and safe.
Performance: Weight and drag are the obstacles to achieving high performance. The wing drag is the sum of two components, induced drag and parasite drag. Induced drag is due to lift and parasite drag is mainly due to surface friction. Increasing the size of a wing increases its parasite drag. The first graph bellow shows how much power is required (vs. velocity) to overcome the induced, parasite, and total drag. For low speeds the majority of the drag is induced drag and at high speeds it is parasite drag. So the large wing that is beneficial for low stall speeds is detrimental at the high cruise speeds. Ideally, one would want to remove the extra wing area used at low speeds in order to reduce drag during cruise and increase speed and efficiency. This is exactly what is done with the telescopic wing. Another benefit mentioned in the weight section above is that removing the extra wing area from the high speed air allows for that section of wing to be lighter because it does not need to withstand the high speed forces. This weight reduction also improves performance. Rate of climb (ROC), range, endurance, ceiling, etc. with the wings extended are also greatly improved over a conventional compromise wing. For the telescopic wing, these improvements do not come at the expense of cruise speed as in the conventional wing. The second graph below shows the total power required vs. velocity for operation with wings extended and retracted. It shows that low speed performance benefits from the wings extended and high speed benefits from wings retracted, (less power required). For twin engine aircraft, one engine out operation (ROC especially) has a tremendous advantage with the wings extended. The difference between one engine out power available and power required (ROC) for the wings extended is about double that for the wings retracted for an aircraft like the Gevers Genesis.
Cockpit Controls:
The wing extension control is simpler than for a normal flap. There is a single two position (Extend - Retract) switch that controls the wing position. There are no intermediate settings. The ailerons are fully functional at any point during the extension process. Instrument panel indicator lights report fully extended, fully retracted, and intermediate wing positions. Both the flaps and the wing extensions have the same maximum extend speed limitations. Airspeed sensing limit switches prevent inadvertent extension at high speeds. The appropriate flap and wing extension airspeed range is marked on the airspeed indicator.