#thermalling

Build Log: Lightweight DLG for Thermalling and Discus Launching

I started this build with a clear aim: a very light discus launched glider that thermals well and is forgiving in small lift, while keeping the airframe stiff enough to hold a clean wing section in climb and launch phases.

My material choices were governed by weight limits and stiffness requirements, so I used a thin foam core with a light glass skin on the wing and a carbon spar sized to give torsional rigidity without excess mass.

The basic build steps followed a familiar sequence and are worth listing for anyone attempting the same trade-offs between lightness and stiffness.

Cut and sand the foam cores accurately to maintain the intended aerofoil and reduce the need for heavy fairing.

Pre-shape and glue in the carbon spar with minimal epoxy to keep the bond strong while avoiding weight creep.

Apply a single layer of lightweight glass cloth over the wing and use vacuum or careful roll-out to eliminate excess resin.

Build a minimal but rigid fuselage pod, installing lightweight servos and a compact receiver to centralise mass.

Balance the completed airframe with small lead strips in the nose as required to reach the intended centre of gravity for thermalling performance.

Tuning for thermalling requires attention to wing stiffness and twist because a floppy wing loses efficiency in weak lift and can induce flutter during launch, so I stiffened the outer panels slightly and set a little washout to keep the tips calm in turns.

Practising discus launch technique was the final part of the log, and it made the biggest difference to climb height and entry into thermals; hold the glider at the tip, rotate smoothly through the hip, and release with the wing high to transfer rotational energy without jerking the model.

During the first few flights I made small trim changes, reducing up-elevator slightly after a big DLG launch to prevent ballooning and adjusting aileron differential to keep the wing from snapping in tight climbs, and you can find notes and parts I used on my site at WatDaFeck.

Build Log: Lightweight DLG for Thermalling — Step by Step.

This is a practical build log for a discus launched glider aimed at hobbyists who want a light, stiff wing and good thermalling behaviour, and I will describe each stage from materials to first flights in straightforward steps.

I started by choosing materials and a basic plan, settling on a thin foam wing core, a full-length carbon spar, a balsa or ply fuselage former and micro servos for the tailplane, and I consulted detailed notes and foam templates on WatDaFeck while marking out the spar and servo bays.

For the wing core I CNC-cut a foam blank to the chosen airfoil and then sanded a smooth skin with a long sanding block to ensure a continuous camber and consistent thickness, and the key to stiffness was a carefully positioned carbon spar running from tip to tip with a carbon or glass shear web to prevent torsion and lift the spar caps without adding excess weight.

When it came to making the build light I used thin cyanoacrylate fillets in low quantity, a featherweight epoxy for the spar join and glassing only where necessary, chose micro linear servos for the elevator and rudder, and kept linkages to a minimum to save grams while ensuring secure joints and reliable control path alignment.

Wing skinning and reinforcement were done with a thin layer of glass cloth over the spar area only, with peel-ply to remove excess resin, and I fitted minimalistic control horns glued into a localised strengthening patch so the wing remained light but resisted repeated launch loads and thermalling stresses.

For trimming and thermalling I set a slightly nose-heavy centre of gravity for initial tests, reduced control throws to half rates and concentrated on slow speed handling to find the neutral aileron and rudder settings, and then practised gentle S-turns and circle entries to learn the glide behaviour and optimise climb rate within lifts.

Discus launching needs a practiced sequence so I learned it in stages: hold the glider by the wingtip with the fuselage over my shoulder, rotate my body through about 180 degrees while keeping the wrist loose, use the hips to generate rotation and a clean upward arc, and finally release at the top of the spin with a relaxed wrist to let the glider peel off smoothly into climb; afterwards checking for twist or wash-in and adjusting the tip wash or small rudder trim helped convert launch energy into a stable climb.

During the first flight campaign I focused on incremental adjustments rather than dramatic changes, logged each tweak and flight outcome, and when I encountered roll coupling or poor climb I returned to the workshop to add tiny amounts of washout at the tips, stiffen the spar caps locally or marginally alter the dihedral to refine the glider behaviour in thermals.

Finally, if you are building your own DLG then practise the discus launch on grass with soft ground and a spotter, gradually increase launch power as your technique improves, and enjoy the feeling of finding thermals and staying aloft for longer periods because a light, stiff wing and careful trimming make all the difference.

From Weston on the Green to Oxford and back plus some aerobatics... It is barelly XC flight, since with that (12-15kts) wind, from Oxford having 4000ft you c...