Construction plan Thermy SL-X

Wolfgang Werling has consistently refined his tried-and-tested Thermy concept, creating the SL-X as the perfect anniversary model to mark 75 years of FMT. This lightweight wooden glider is highly thermally responsive, yet surprisingly agile and still very easy to handle in slow flight. The SL-X is not a copy of the SL, but a completely new design. In addition to a modified wing geometry, the model features removable ears. The optimised V-shaped distribution improves lift characteristics and reduces induced drag; furthermore, it achieves good circling performance and, at the same time, high rudder effectiveness. Without the ailerons – which are assembled using CFRP rods and held in place by magnets – the wing halves are considerably shorter, which is an advantage for transport and storage. The tailplane is also removable. The airframe is constructed entirely from wood, featuring a double CFRP splice to ensure a smooth transfer of forces whilst offering high strength and low weight. The wing structure is highly rigid thanks to the use of a plywood rib spar, which ensures the ribs are precisely aligned. The leading edge of the wing is planked with balsa – this prevents warping during covering and ensures high profile accuracy and strength, particularly in the nose area. The flaps and ailerons are constructed together with the wing. The control surfaces are large enough to ensure high manoeuvrability, and the flaps are extremely effective during landing. The fuselage is constructed from poplar plywood in the high-stress areas and offers sufficient space for all internal fittings. A mould integrated into the frames ensures a perfectly straight fuselage is achieved in no time. The long nose allows for the use of lightweight power units and requires minimal lead ballast in the glider version.

The modified SD 7037 airfoil has excellent all-round characteristics: it delivers high lift coefficients, enables good gliding and is not sensitive to minor construction inaccuracies. The airfoil is slightly thickened geometrically towards the outer edge; together with a slight twist in the outer wing, this makes the SL-X very forgiving.

Technical specifications

• Wingspan:  3,330 mm
• Length:  1,530 mm
• Airfoil: SD 7037 mod.
• Wing area:  70.3 dm²
• Flying weight:  from 1,950 g
• Wing loading:  from 27,7 g/dm²
• RC:  motor, aileron, elevator, rudder, flap

Recommended propulsion set and servo

• Motor:  Hacker A30 14L-LN or aero-naut actro-n 35-4-790
• Battery: 3-4s LiPo , 1.800 to 3.800 mAh Hacker TopFuel Eco-X
• Controller: Hacker Spin 44 Pro or aero-naut actrocon 60
• Propeller: Falcon CFRP folding propeller 11×6 or aero-naut CAMcarbon Z 13×7
• Spinner:  aero-naut Z spinner 42 mm with 5 mm motor shaft clamping cone
• Servos in fuselage:  2× KST X10 Mini or Chaservo HV85
• Wing servos: 4× KST X08 or Chaservo HV85H