Choosing a plan or kit
For a first free-flight glider the best choice is a proven plan or a ready-made kit. Classic designs such as Jaskółka, P-30, AMA Racer or Korda Wakefield are thoroughly documented and tested by generations of modellers. A kit contains pre-cut parts and instructions, significantly reducing build time and eliminating cutting errors.
If you choose a plan for scratch-building, make sure it is printed at 1:1 scale. Pay attention to the class – for beginners the best options are P-30 models (span up to 76 cm, rubber power) or simple HLG (Hand Launch Glider) designs with 40–60 cm span. Avoid starting with large F1A or F1B class models – they demand experience and precision.
Materials
Balsa is the primary structural material. It comes in different densities: light (80–100 kg/m³) for sheeting and ribs, medium (100–140 kg/m³) for spars and edges, and hard (140–180 kg/m³) for motor mounts and structural elements. For a first model, buy 1.5 mm balsa sheet for ribs, 3×3 mm and 3×6 mm strips for spars, and 2–3 mm sheet for the fuselage.
You will also need pine or basswood for parts requiring extra strength (rubber hook, timer mount). Covering film (Oracover Lite, Litespan or Japanese tissue) provides a smooth, lightweight surface. For gluing balsa, medium CA or white PVA glue works best – the latter is lighter when dry.
Building the wing
The wing is built on a building board with the plan pinned under protective film. Start by laying the lower spar, leading edge and trailing edge. Then glue the ribs in place, checking their verticality with a set square. Cut ribs from 1.5 mm balsa – preferably from a single sheet to keep density consistent.
Once the lower structure has dried, add the upper spar and reinforcements. Dihedral is achieved by propping up the wingtips with blocks during gluing – a typical value for a free-flight model is 10–15° per panel. Shape the wingtips from soft balsa, rounding the edges. Sand the leading edge to a D-shaped cross-section for better aerodynamics.
Building the fuselage
The fuselage of a free-flight glider is usually simple – it may be a pylon (a beam under the wing) or a box structure built from balsa sides. Cut fuselage sides from 1.5–2 mm balsa and build on a flat surface, using formers as cross-section templates.
Inside the fuselage, install the DT (dethermalizer) timer mechanism, the rubber hook (for rubber-powered models) and the wing mounting. The DT timer is critical – after a set time it deflects the stabilizer upward, causing the model to descend gently. Without a timer the model can drift away in a thermal and be lost. Popular options include fuse timers and mechanical timers (Tatone, GLS).
Stabilizer
The horizontal and vertical stabilizers are built from the lightest materials, because their mass at the end of a long tail arm strongly affects the balance. Use 1–1.5 mm balsa for ribs and 2×2 mm strips for the frame. The horizontal stabilizer should have a flat or slightly cambered (flat-bottom) airfoil section.
The vertical fin is built symmetrically with no twist. The horizontal stabilizer area is typically 20–25% of the wing area. Attach it to the tail boom at 0° relative to the fuselage datum (or with a slight negative incidence of 0.5–1° for stability).
Covering
Start covering with the wing. Cut a piece of film with a 1–2 cm margin on each side. First attach it along the leading edge with the iron set to low temperature (150 °C for Oracover). Then stretch the film to the trailing edge and spars, heating gradually.
After the film is attached to all structural members, shrink it at higher temperature (200 °C) or with a heat gun – the film tightens to give a smooth surface. Important: do not overheat! Excessive temperature causes wrinkling and warps the lightweight framework. For free-flight models, Japanese tissue applied with dope is an alternative that gives an even lighter covering.
Balancing and trimming
Check the center of gravity (CG) by supporting the model on two fingers at the point shown on the plan – typically 25–33% of the mean aerodynamic chord from the leading edge. The model should hang level or with a slight nose-down tilt. Adjust the CG by adding lead pieces to the nose or tail.
Set control surface deflections according to the plan. Set the DT timer 10–15 seconds shorter than the maximum round time. Check that the wing is not twisted (washout should be even, 2–3° at the tips) and that the model is not asymmetric.
First flight
For the first flight, choose a large open field without trees or buildings – ideally on a calm morning with wind below 2 m/s. Begin with gentle hand tosses at a slight downward angle, watching the trajectory. The model should transition smoothly into a glide without stalling or diving.
If the model pitches up and loses speed (stall), the CG is too far aft – add ballast to the nose. If the model dives, the CG is too far forward – shift ballast aft or add up-elevator trim. Once you have a straight, stable glide you can try a full rubber-powered or tow launch. Remember: every flight is data – note your settings and observations.