This is an assignment on timeline in aerospace for the AL Aerospace Engineering course at Concordia International School conducted by Dr. Peter Tong (aka D.T). This article documents the design, construction, and iterative testing of an unpowered balsa wood glider as a hands-on exploration of fundamental aerospace principles.
Objectives
To build a stable airplane that will fly the farthest.
Guiding Questions
- How does the position of the Center of Gravity (CG) affect glide stability and distance?
- How does the wing aspect ratio (length/width) affect the lift and drag?
- What effect does the vertical stabilizer have on maintaining stability?
- How do adjustments to the horizontal stabilizer angle affect the pitch stability?
- What modifications can be made to the airplane to reduce drag without significantly compromising lift?
Materials
- Balsa Sheet (1.5×75mm × 915mm) (1 pc)
- Balsa Strut (5×5×50mm) (1 pc)
- Hot Glue or Standard Wood Glue
- Cutting knife
- Ruler
- Cutting board
- Rubber bands (2 pcs)
Balsa wood is selected as the primary construction material due to its exceptionally high strength-to-weight ratio. Despite having a density as low as 100–200 kg/m³, balsa maintains sufficient structural rigidity to withstand aerodynamic loads during flight (Soden & McLeish, 1976). This allows the aircraft to achieve minimal wing loading while preserving structural integrity. Additionally, balsa is much easier to cut than other materials, which enables precise configuration design during construction.
Material Property: Grain Orientation
When working with a sheet of balsa wood, cuts made parallel to the grain tend to proceed smoothly with less resistance. In contrast, cuts made perpendicular to the grain generally require substantially greater effort. These findings indicate that the compressive strength of balsa wood is significantly greater along the longitudinal grain axis. During flight, the main wing structure is subjected to distributed aerodynamic lift forces acting along its span, inducing bending moments about the wing root. When the wood grain is oriented parallel to the spanwise direction, that is, perpendicular to the fuselage centerline, the structure demonstrates enhanced resistance to bending deformation. Conversely, when the grain orientation is perpendicular to the primary loading direction, the interlaminar shear strength is reduced, rendering the structure more susceptible to flexural deformation and potential failure. This anisotropic behavior is a well-documented characteristic of balsa wood and is critical to consider during wing construction (Da Silva & Kyriakides, 2007).
Lateral Stability: Dihedral
Beyond longitudinal stability, lateral stability is equally important for a glider that must fly straight without rolling off course. This section examines the dihedral angle as a key design feature for lateral stability, which will be applied more extensively in the advanced design explored in Part 3.
Figures 1 and 2 illustrate the concept of wing dihedral.
Figure 1: Schematic Diagram of Wing Configurations 
Figure 2: Schematic Diagram of Dihedral
When the aircraft sideslips toward the dropped wing, dihedral causes the lower wing to meet the airflow at a higher angle of attack as well as produce more lift, and the upper wing at a lower angle of attack as well as produce less lift. This lift asymmetry rolls the aircraft back to level.
For example, if the airplane rolls to the right, the right wing becomes lower and the left wing becomes higher. Because of changes in the airflow direction and the wing geometry, the lower wing usually gains a greater effective angle of attack and therefore more lift. As a result, the airplane is pushed back toward level flight. The primary function of dihedral is to increase an aircraft’s lateral static stability in sideslip (Raymer, 2018).
The most critical application of dihedral is during a sideslip, when the airplane is pushed off course by the wind and enters a sideslip, the relative airflow approaches from the side. The dihedral causes the left and right wings to respond differently to this sideways airflow, creating a rolling moment that tends to roll the airplane back to wings-level flight.
Advanced Design Preview
Building on the lessons from Trials 1 to 3, an advanced balsa glider was designed incorporating tapered wing panels, polyhedral dihedral, and optimized incidence angles. The design schematic is shown in Figure 13. The advanced design has a 36 cm wingspan with a total wing area of approximately 187 cm², a tapered horizontal stabilizer of about 40–42 cm², and a vertical stabilizer of about 13–15 cm², all mounted on a 26.7 cm fuselage stick. The CG target was set at 40% of the 6.0 cm center chord. Detailed dimensions, material allocation, and construction notes for this design will be documented fully in Part 3.
Figure 3: Enhanced Balsa Airplane Design
Construction
The advanced glider was built according to the design in Figure 3. Figures 4–7 document the completed construction from multiple angles.
Figure 4: The Wing 
Figure 5: Front View 
Figure 6: Top View 
Figure 7: Side View
Final Trial
The advanced glider was test-flown and the trajectory was recorded (Video 1).
Video 1: Recording of Trajectory
Observed Flight Behavior
The glider descended steeply from the launch point and drifted into a left turn laterally.
Probable Causes
- CG too far forward: excessive down-pitching moment.
- Asymmetric wing geometry or warp: if one wing has slightly more incidence or drag than the other, it induces a rolling moment that leads to a turning trajectory.
Proposed Improvements
- Shift CG slightly aft: remove a small amount of weight (Blu-Tack) at the leading edge so the glide angle flattens out.
- Check wing symmetry: check and make sure both wings have identical dihedral, incidence, and no warping.
Comparison
Through comparison with other aircraft, weight was also identified as a non-negligible factor. Referencing Andy’s aircraft, which weighed approximately 4 grams, my aircraft weighed 12 grams, three times heavier. A higher mass increases the wing loading, requiring greater airspeed to sustain level flight. At the same launch velocity, the heavier aircraft loses altitude more rapidly, resulting in a steeper glide path and shorter flight distance. This relationship is consistent with the fundamental wing loading equation used in aircraft performance analysis (Anderson, 2016).
References
Anderson, J. D. (2016). Introduction to Flight (8th ed.). McGraw-Hill Education.
Da Silva, A., & Kyriakides, S. (2007). Compressive response and failure of balsa wood. International Journal of Solids and Structures, 44(25–26), 8685–8717.
Raymer, D. P. (2018). Aircraft Design: A Conceptual Approach (6th ed.). AIAA Education Series.
Soden, P. D., & McLeish, R. D. (1976). Variables affecting the strength of balsa wood. Journal of Strain Analysis for Engineering Design, 11(4), 225–234.