Aerodynamics

A Glider-pilot’s Desire

An aircraft which combines very good climbing characteristics, excellent glide ratios even at high speeds and optimum thermalling performance with overall very pleasant handling characteristics. This aerodynamic layout is the result of an ambitious research project spanning multiple years.

All parts and tooling used in the Antares project had to be designed from scratch. This gave Lange Aviation the flexibility to fine tune all parts to one another. As a result, the aerodynamic outline of the Antares has been designed entirely as one entity, and all possibilities for optimization have been considered.

Wing geometry

The aerodynamic designs for the Antares 20E and the Antares 18T were performed simultaneously. In order to minimize induced drag, both Antares models share a super-ellipting wing geometry. The result is a wing geometry which only has 0.1% more induced drag than the theoretical minimum, which is the value of the untwisted elliptical wing. The unpleasant flight characteristics of the untwisted elliptical wing, however, are avoided by the Antares design. The relatively wide outer wing combined with the winglet provides forgiving stall characteristics. The winglets, which have been designed together with the wing as a single optimized shape, also allow a further reduction of the induced drag by 5%. Accordingly, the induced drag of the 18 m Antares wing reaches only 95% of the value of a fully elliptical wing with the same wingspan.

All this was achieved while maintaining shared wing moulds with the Antares 20E, maximizing number of shared parts and minimizing costs. What makes this possible is the geometry of the inner wing. It cannot be easily discerned when looking at the finished wing of an Antares 20E, but the inner wing contains an approximately 2m long section with no taper or change in profile. This section can, without much consequence, be shortened. For the Antares 18T, this wing section was shortened exactly 1m on each side. Using a building block system, the wing molds can be varied in this region so that it is possible to build a 20m wing one day and an 18m wing the next.

High Wingloading

 

In order to achieve maximum performance in all conditions, the Antares 18T can be flown at an extremely wide range of wing loadings. At very good days, the Antares 18T can utilize the full 600kg available for the 18m class, and fly at extreme speeds with a wingloading of 54.7 kg/m2 (11.2 lb/ft2 ). Experience has shown that the Antares design senses and utilizes thermals really well also at very high wing loadings. 

The wing of the Antares 18T is equipped with 6 integral-tanks, providing a total capacity of 208 liters (55 US gal.). This high tank capacity is possible because the inner part of the wing spar is positioned markedly rearward of its common position. To compensate for c.g. translations due to changes in the water ballast, the Antares 18S/T also has a tank in the vertical stabilizer, which contains approximately 6 liters (1,6 US gal.). Altogether, a total tank volume of 214 liters (56.6 US gal.) is available.

The tank system is of a completely two level design. The four outer tanks contain approximately 100l (26,4 US gal.), and can be dumped together with the corresponding amount of trim ballast in the vertical stabilizer. The inner tanks, and the remaining trim ballast are activated by a separate lever, making it possible to adjust the wingloading in flight without negatively affecting the aircraft trim.

Fast glide

A defining characteristic of the aerodynamic design of the Antares is that the best glide ratio is achieved at high speed. The Antares 18T achieves its best glide ratio (53:1) at 100 km/h (54 knots) when flying with low wing loading, and at 135 km/h (73 knots) with high wing loading. This gives the Antares another advantage in glide.

Handling

The Antares 18T sports full span flaperons, which yield high maneuvrability. The movements of the flaperons are controlled using a novel control mechanism (patent pending). Furthermore, a consequent utilization of high performance low friction ball bearings instead of plain bearings substantially reduce friction in the control mechanisms, resulting in an aircraft which is extremely light on the controls.

 

Characteristic features of the stabilizers is that they are combine relative large surfaces with a high aspect ratio and modern airfoil sections. Stabilizer drag is kept at a minimum by ensuring that the stabilizers only need to produce very little lift when in steady flight.

The Antares comes equipped with large triple panel Schempp.Hirth – type cascading airbrakes, allowing steep and safe landing approaches with little loss of lift. Extending the airbrakes has only a minimal effect on the stall speed.

All these factors combine to make the Antares 18T very light on the controls, yet agile without being nervous. The Antares 18T flies very stable, but is extremely sensitive to thermals, and has controllability superior to many 15m sailplanes.

Antares 18T: Amazing performance, excellent handling