The above remarks apply only to bodies making constant angle with the air stream. Wings and lifting surfaces make varying angles at different speeds and hence do not show the same rate of increase. In carrying a constant load, the angle of the aeroplane wing is decreased as the speed increases and up to a certain point the resistance actually decreases with an increase in the speed. The wing resistance is greatest at extremely low speeds and at very high speeds. As the total resistance is made up of the sum of the wing and parasitic resistance at the different speeds, it does not vary according to any fixed law. The only true knowledge of the conditions existing through the range of flight speeds is obtained by drawing a curve in which the sums of the drag and head resistance are taken at intervals.
Resistance and Power. The power consumed in overcoming parasitic resistance increases at a higher rate than the resistance, or as the cube of the speed. Thus if the speed is increased from 40 to 100 miles per hour, the power will be increased 15.63 times. This can be shown by the following: Let V = velocity in miles per hour, H = Horsepower, K= Resistance coefficient of a body, A = Total area of presentation, and R = resistance in pounds. Then H = RV/375. Since R = KAV², then H = KAV² x V/375 = KAV³/375.
Resistance and Altitude. The resistance decreases with a reduction in the density of the air at constant speed. In practice, the resistance of an aeroplane is not in direct proportion to a decrease in the density as the speed must be increased at high altitudes in order to obtain the lift. The following example given by Capt. Green will show the actual relations.
Taking an altitude of 10,000 feet above sea level where the density is 0.74 of that at sea level, the resistance at equal speeds will be practically in proportion to the densities. In order to gain sustentation at the higher altitude, the speed must be increased, and hence the true resistance will be far from that calculated by the relative densities. Assume a sea level speed of 100 ft./sec., a weight of 3000 pounds, a lift-drag ratio of L/D = 15, and a body resistance of 40 pounds at sea level.
Because of the change in density at 10,000 feet, the flying speed will be increased from 100 feet per second to 350 feet per second in order to obtain sustentation. With sea level density this increase in speed (3.5 times) would increase the body resistance 3.5 x 3.5 = 12.25 times, making the total resistance 12.25 x 40 = 490 pounds. Since the density at the higher altitude is only 0.74 of that at sea level, this will be reduced by 0.26, or 0.26 x 490 = 364 pounds. Thus, the final practical result is that the sea level resistance of the body (40 pounds) is increased 9.1 times because of the speed increase necessary for sustentation. Since the wing angle and hence the liftdrag ratio would remain constant under both conditions, the wing drag would be constant at both altitudes, or 3000/15 = 200 pounds. The total sea level resistance at 100 feet per second is 200 + 40 = 240 pounds, while the total resistance at 10,000 feet becomes 364 + 200 = 564 pounds.
The speed varies as the square root of the change in density percentage. If V = velocity at sea level, v = velocity at a higher level, and d = percentage of the sea level density at the higher altitude, then v = V/√D. When the velocity at the high altitude is thus determined, the resistance can be easily obtained by the method given in Capt. Green's article. The following table gives the percentage of densities referred to sea level density.
| Altitude Feet | Density Percent | Altitude Feet | Density Percent |
| Sea-level | 1.00 | 7,500 | 0.78 |
| 1,000 | .97 | 10,000 | .74 |
| 2,000 | .95 | 12,500 | .66 |
| 3,000 | .91 | 15,000 | .61 |
| 5,000 | .85 | 20,000 | .52 |
If the velocity at sea level is 100 miles per hour, the velocity at 20,000 feet will be 100/0.72 = 139 miles per hour, where 0.72 is the square root of the density percentage, or the square root of 0.52 = .72 at 20,000 feet.
Total Parasitic Resistance. Aside from the drag of the wings, the resistance of the structural parts, body, tail and chassis depends upon the size and type of aeroplane. A speed scout has less resistance than a larger machine because of the small amount of exposed bracing, although the relative resistance of the body is much greater. The type of engine also has a great influence on the parasitic resistance. The following gives the approximate distribution of a modern fighting aeroplane:
| Body | 62 percent |
| Landing gear | 16 " |
| Tail, fin, rudder | 7 " |
| Struts, wires, etc. | 15 " |