Time (Minutes)
0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 22.5
Altitude (Feet)
0.03300 6150 8730 10760 12610 14190 15530 16650 17600
If we assume that the height is 10760 feet after the first 10 minutes, and that the altitude after twice this time (20 minutes) is 16650 feet, then the maximum ceiling attained will be:
H = h / (2 - a/h) = 10760 / 2 - 16650/10760 = 23,770 feet. The use of this formula requires that the climb be known for certain time intervals before the ceiling.
Gliding Angle. The gliding angle of the wings alone is equal to the lift-drag ratio at the given angle. The best or "Flattest gliding angle" is, of course, the best lift-drag ratio of the wing—say on the average about 1 in 16. The gliding angle of the complete machine is considerably less than this, owing to the resistance of the body and structural parts. This generally reduces the actual angle to less than 12, and in most cases between 6 and 8. Expressed in terms of degrees, tan ø = R/W where R = head resistance and W = weight in pounds.
Fig. 2 is a diagram giving the gliding force diagram. The plane descends along the gliding path AC, making the angle of incidence (ø). When in horizontal flight, the lift is along OL and the weight is OW. When descending on the gliding path the lift maintains the same relation with the wing, but the relative angle of the weight is altered. The weight now acts along OG. The drag is represented by OD, with the propeller thrust OP equal and opposite to it. With the weight constant, the lift OL is decreased by the angle so that the total life = L = W cos ø. The action of the weight W produces the propelling component OP that gives forward velocity. The line AB is the horizontal ground line. If the total lift-drag ratio is 8, then the gliding angle will be 1 in 8, or measured in degrees, tan ø = R/W = 1/8 = 0.125. From a trigonometric table it will be found that this tangent corresponds to an angle of 7° – 10'. It should be noted that R is the total resistance and not the wing-drag.
Fig. 2. Gliding Angle Diagram Showing Component of Gravity That Causes Forward Motion. The Gliding Angle Depends Upon the Ratio of the Resistance to the Weight.