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Abstract

Generally, the wind tunnel experiment is used to gauge the drag and lift forces affecting an aircraft. The current experiment measured the drag and lift forces of a small wing at different angles of attacks with an increment of 2 degrees from -10. The results indicated a minimum and maximum lift coefficient of 0.14 and 0.65 respectively. Likewise, the maximum and minimum drag force was 0.24 and 0.05 respectively. On the calculation of the drag and lift coefficients, the stall angle occurred during the 12th angle of attack at a lift force of 0.38 and drag force of 0.17

Introduction

Generally, all atmospheric flying objects such as aircraft, ships, and vehicles need to undergo several Computational Fluid dynamics (CFD) simulations and wind tunnel tests in order to improve their designs. Accordingly lift and drag force tests are some of the most critical tests that such bodies go through. The phenomenon of Lift and drag is quite complicated and is hypothesized for better understanding by potential flow and boundary layer theory which has good agreements with experimental results. Generally, lift and drag forces are derived from two equations:

Lift Force FL= CL A V2/2

Drag force FD = CD A V2/2

Where, A is the projected area of the object, V is the freestream air velocity, ρ is the air density, and Cl and CD are the lift coefficients and drag coefficients respectively. Notably, the lift and drag of a wing is a function of multiple variables such as the angle of attack, airspeed, and cross-sectional geometry. An increase in the angle of attack raises the lift and drag up to a critical value upon which any increase leads to a sharp decrease in lift. Typically, this is referred to a stalling. Accordingly, this experiment measures the lift and drag of a model wing in order to determine its lift and drag coefficients at a specific speed.

Description of Work

In completing the experiment, three main pieces of equipment were used: the wind tunnel (see figure 1), pilot tube, and a small wing. Accordingly, the experiment was designed to gauge the lift and drag that were measured using the gauges. On the other hand, the pilot tube was used to measure the dynamic pressure. Typically, the pilot tube uses a manometer to measure pressure as air pushes the wing. Prior to beginning the experiment, the wing was mounted in the wind tunnel and the lift and scale readings confirmed to be zero. The wind tunnel was then adjusted for maximum velocity. The dynamic pressure was then measured changing the angle of attack with +/- 2 degrees after each measurement. This step was repeated until the stall angle was exceeded.

Figure 1. Wind Tunnel Device

Results and Discussion

Following the completion of the experiment, all the data was tabulated in excel for the purposes of calculating the lift coefficient and drag coefficient. Table 1 below summarizes the values for lift and drag coefficients for each angle of attack used in the experiment;

Angle of Attack (degrees)	CL	CD
-10	0.43	0.2432
-8	0.52	0.0343
-6	0.55	0.0286
-4	0.94	0.0343
-2	1.03	0.0314
0	1.15	0.0343
2	1.22	0.0314
4	1.67	0.0343
6	1.82	0.0400
8	1.95	0.0019
10	1.98	0.0514
12	1.15	0.0972
14	1.15	0.1086
16	1.22	0.1143
18	1.22	0.1200
20	1.25	0.1372

From the table above, the stall angle is seen when the angle of attack is 12. Plotting the lift coefficient and drag coefficient against the angle of attack, a clear association between the lift coefficient and angle of attack is seen. This is also the case for the drag coefficient. Both coefficients increase with an increase in the angle of attack (see figure 1). In examining the relationship between the lift and drag coefficients, a plot of CL vs. CD was plotted. The chart indicates that there is no relationship between the drag and lift coefficient (see figure 2).

Figure 1. CL and CD vs. Angle of Attack Chart

Figure 2. CL vs. CD chart

Conclusion

Overall, the main aim of this experiment was to measure the drag and lift forces that impact a wing in order to calculate the lift coefficient and drag coefficient at different angles of attack and thus find the stall angle. The findings indicated the maximum lift force was 0.65 while the minimum was 0.14. On the other hand, the maximum and minimum drag force was 0.24 and 0.05 respectively. The calculation of the drag and lift coefficients revealed that the stall angle occurred during the 12th angle of attack at a lift force of 0.38 and drag force of 0.17.

CL and CD Vs. Angle Of Attack

CL -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20 0.42547455212998697 0.51664767044355564 0.54703870988141179 0.9421222225735425 1.0332953408871113 1.1548594986385361 1.2156415775142484 1.6715071690820917 1.8234623662713725 1.9450265240227975 1.9754175634606537 1.1548594986385361 1.1548594986385361 1.2156415775142484 1.2156415775142484 1.2460326169521045 CD -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20 0.24319249866078615 3.4294765331086816E-2 2.8578971109239015E-2 3.4294765331086816E-2 3.1436868220162915E-2 3.4294765331086816E-2 3.1436868220162915E-2 3.4294765331086816E-2 4.0010559552934623E-2 1.9003080000000001E-3 5.144214799663023E-2 9.7168501771412646E-2 0.10860009021510825 0.11431588443695608 0.12003167865880385 0.13717906132434726

Angle of Attack

CL and CD

CL vs. CD

CD 0.24319249866078615 3.4294765331086816E-2 2.8578971109239015E-2 3.4294765331086816E-2 3.1436868220162915E-2 3.4294765331086816E-2 3.1436868220162915E-2 3.4294765331086816E-2 4.0010559552934623E-2 1.9003080000000001E-3 5.144214799663023E-2 9.7168501771412646E-2 0.10860009021510825 0.11431588443695608 0.12003167865880385 0.13717906132434726 0.42547455212998697 0.51664767044355564 0.54703870988141179 0.9421222225735425 1.0332953408871113 1.1548594986385361 1.2156415775142484 1.6715071690820917 1.8234623662713725 1.9450265240227975 1.9754175634606537 1.1548594986385361 1.1548594986385361 1.2156415775142484 1.2156415775142484 1.2460326169521045

CD

CL