We are going to design a wing for an aircraft yet to be created. The first step is to decide how much weight the plane will carry (because in cruise flight, the lift force must be equal to the weight force). We also need to decide what its cruising speed will be and what its landing (stall) speed shall be. For this example, let’s use the numbers below. Maximum weight Maximum speed Maximum stalling speed 1320 lbs (1430 lbs seaplane) 120 kts 45 kts On Fig. 1, go along the horizontal weight scale and find the weight that you have selected. Next find the line which represents the landing speed (1.3 times stall) that you want. Now go vertically from the weight to this landing speed line. Now go horizontally from this point to the vertical (wing area) scale. The point where this horizontal line crosses the wing area gives the required wing area. Fig. 1 400 350 Wing Area (ft2) 300 250 30 kts 35 kts 200 40 kts 45 kts 150 50 kts 100 55 kts 50 0 0 500 1000 1500 2000 Weight (lbs) Required wing area _______________________ ft2 On Fig. 2, go along the weight axis to the weight that you specified. Next find the line representing the wing areas we found on Fig. 1. Now, go vertically from your weight to the line representing your wing area. Once again, go horizontally from this point to the vertical scale and mark this intersection. This value is the wing loading-the weight supported by each square foot of the wing. Fig. 2 40 35 Wing Loading (lbs/ft2) 40 ft2 30 60 ft2 25 80 ft2 20 100 ft2 15 120 ft2 140 ft2 10 160 ft2 5 180 ft2 0 200 ft2 0 500 1000 1500 2000 2500 Weight (lbs) Wing loading ____________________ lbs/ft2 On Fig. 3a, locate on the horizontal scale the wing loading value that you have just determined. Next, find the line representing the cruising speed (0.8-0.85 of max. speed) that you selected. Now go vertically from your wing loading o the cruising speed line. Once again, go horizontally from this point to the vertical scale and mark this intersection. This value is the lift coefficient at cruising speed. Fig. 3a Lift Coefficient 2 1.8 50 kts 1.6 60 kts 1.4 70 kts 1.2 80 kts 1 90 kts 0.8 96 kts 0.6 105 kts 0.4 120 kts 0.2 140 kts 0 160 kts 0 5 10 Wing Loading (lbs/ft2) Lift coefficient at cruising speed __________________ 15 20 180 kts Using Fig. 3b, find the stalling speed on the vertical axis. Find the wing loading on the horizontal axis. Mark where these two values meet. Follow the closest lift coefficient line up and to the right. This is the maximum lift coefficient your wing will need to generate. Fig. 3b Maximum lift coefficient ________________ Select an airfoil that has good L/D ratios at those two lift coefficients for your aircraft. Airfoil selected _____________________________ To get the dimensions of your wing, you need to use the term Aspect Ratio (AR). AR=wing span2/wing area Fig. 4a shows the relationship between the drag coefficient and the lift coefficient for various values of aspect ratio. A slow plane will fly at a higher lift coefficient and thus, to keep the induced drag down to a reasonable value, slow planes will have higher AR values. AR values over 15 are common on slow flying gliders! Fig. 4b shows the tradeoffs between high and low AR values and different performance characteristics. Fig. 4a Fig. 4b Aspect Ratio Trade Study 2500 nmi, kts, or fpm 2000 1500 Range Max Speed *10 1000 Cruise Speed *10 500 Rate of Climb 0 6 8 10 Aspect Ratio 12 14 Even though high AR wings are more efficient, they do come at a cost. Long, narrow wings are not as strong as shorter, wider wings. Designers must strike a balance between efficient wings and strong wings. AR values between 5 and 7 are common on small airplanes. AR you choose __________ To determine the wing span on Fig. 5, find the value of wing area that you determined from Fig. 1. Then find the line representing the aspect ratio which will give a reasonable value of induced drag as shown on Fig. 4. Now move vertically from this wing area to the proper aspect ratio line and move horizontally from this point to the wing span scale on the left. Fig. 5 Fig. 6 Wing span ______________ft To determine the wing chord, repeat the previous steps with Fig. 6. Wing chord ______________ ft Your wing span multiplied by your wing chord should give you the wing area you determined from Fig. 1.