FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1929
1929 - 0854.PDF
SUPPLEMENT TO PLIGHT 30 THE AIRCRAFT ENGINEER APRIL 25, 1989 and from Equation (2a), wing loading will be by substituting X • A for 6 s, the group of curves B represent the relation V I R/ ( LB, - """' w P 7a) Ct = v7^ • X • CDpre/ • 0 (76) We then find that the speed over the total distance will be w 3-6T in which, substituting for T from (6), V = R,.3-6L B w which, substituted in (5), gives 75 w (8) (9)^D p nf ' 0 3 • 6 X In Fig. 2 we have determined the relation of the aero- dynamic values from Equations (7a), (7b), (8) and (9). We assume that the efficiency of the propeller does not change (this is true for a flight at constant angle of attack in different altitudes, as will be demonstrated in the next section), and also the specific fuel consumption does not change (we must take an average value, because by flying with the same angle of attack, and therefore reducing the power required, the specific fuel consumption will increase). The group of curves A of Fig. 2 represent the equation Iv = /(V, CL)« The values of wing loading L,,. are given from 10-25 to 24-6 lb. per sq. ft. (50 to 120 kg. per sq. m.). The for the values of power loading Lm = 19-85 to 39-7 lbs. per h.p. (9 to 18 kg. per h.p.). Curves A and B are connected by means" of the value V. The group of curves C refer to X = / (Cu ,„„/ • </>,- The values of CD ,„.„/ • <£ run from 0-0260 to 0-0455. For the same values of CD ))ro/ • <p are given the curves forming the relation Ct = /(X, CD „„,/ • <j>) at D. The value "*"* ' w connects the curves B and C, the value A. connects the curves C and D, and the value CL connects the curves D and A. The value CD pro/ ' $ is determined for the value CD )mf = 0-013 (that is, the coefficient of profile drag of the current aerofoils in the proximity of the angle of attack at the minimum drag) and the values (f> = 2, 2-5, 3, and 3-5 (the values 2-5 to 3-5 correspond to actual transport aeroplane constructions). For any different values of CD ,„,,/ it would be possible by calculation to remain within these curves. The value is divided in the lower part of the Fig. 2 in its components : The values of specific fuel consumption c, = 0 • 485 to 0-615 lbs. per h.p.-hour (0-220 to 0-280 kg. per h.p.-hour) at F, and values of the ratio of the fuel weight to the total weight w =0-4 to 0-6 at G, which are indicated by the dotted lines. At E are given the values of different propeller efficiencies e = 0 • 6 to 0 • 8 ; this manipulation is made by the use of 45-degs. inclined lines, as shown in Fig. 2. The values w = 0-4 to 0-6 at G, which are designated by full lines, correspond to the corrected values of the cruising radius for an economical flight at the constant angle of attack (see Fig. 5). From the values w we finally obtain the values of the cruising radius R = 2,500 to 5,000 miles (4,000 to 8,000 km.). In order to show how to use this diagram (Fig. 2) we have drawn in an example, in which we have assumed the following: The starting speed 93 m.p.h. (150 km.p.h.) at the coefficient of lift CL =0-7 max. For an aerofoil whose maximum lift coefficient = 1-4, the theoretical landing speed with the initial wing loading will be = 93 A /— = 66 m.p.h.V 1-4 For the coefficient of profile drag CI)pro/= 0 013 and for the coefficient of structural drag CD ,,rur = 0-024, the value CD ,„.„/ • <p will be 0 037 and cp — 0 037 0~013 ~~ 2 85' AD other aerodynamic values are determined in the diagram by the rectangle I. For a propeller efficiency f = 70 per cent., this solution is as follows: The wing loading Lw = 15-15 lb. per sq. ft., the power loading LB =25-8 lb. per h.p., Ci. — 0-68, and the aspect ratio A = 4. For a specific fuel consumption of 0-55 lb. per h.p.-hour (250 g.) and for w — 0-535 (see Fig. 4), the maximum cruising radius will be 3,260 miles. Assuming a higher propeller efficiency of t = 75 per cent, (see rectangle II), the maximum cruising radius will be 3,54'i miles and the power loading LB = 27 *55 lb. perh.p. We see that for this case the best aspect ratio is 4, this being due to the low cruising speed, which is given by the condition 338/"
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
