FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1931
1931 - 0918.PDF
SUPPLEMENT TOFLIGHT 88 THE AIRCRAFT ENGINEER AUGUST 28, 1931 C, = Rate of climb at altitude A,, ft./min.; C, = Rate of climb at altitude A,, ft./min. If A, is the altitude at which C, is the rate of climb, and A, is the altitude at which C> is the rate of climb, then reduction of climbing rate, p /~i r = —- ft. per min. per ft. Ai — A, The absolute ceiling is given by Hmw = Ai + °± ft. EXAMPLE. Climbing rate, ground level C, = 1,300 ft./min. Climbing rate at 11,000 ft. C8 = 1,700 ft./min. Climbing rate at 25,000 ft. C, = 596 ft./min. Altitude of supercharge limit A. = 11,000 ft. Altitude chosen A, = 25,000 ft. Time to 11,000 ft.— T A 1 I (C, + C.) _ 2 X 11,000 ==l,300+1,700 = 7-34 min. Reduction in Climbing Rate above Altitude As— A,-A. _ 1,700 - 596 ~ 26\000-11,00" = 0-0788 ft. per min. per ft. Time from Altitude A, to Altitude A,— T 2-303 , tC.s1 > r 2-303 0- 0788 13-30 min. log 596 Total Time to Altitude A,- TT = 13-30 + 7-34 = 20-64 min. Ceiling Absolute - Hma, = A, + = 25,000 + 5960-0788 = 32,560 min. After adjusting the rate of climb lines until the times calculated as above (to height near the ceiling) agree with the climb curves, check some times near the ground and to some altitudes near to the supercharge limit, to verify whether the rate of climb curve below this limit is a reasonably straight line. It has been stated that the rate of climb curve is usually a straight line. There will be cases, however, where the rate of climb will be found to be bent, pos- sibly when the engine has been getting too hot or too cold during part of the climb, so that the quality of the mixture is affected. In such cases, the process of checking back from the trial rate of climb curve to see that the times agree will give the necessary indication. With modern aircraft engines any defects of the nature suggested are usually discovered and remedied before performance trials are carried out. of the pitot tube through the air, it is only necessary to divide the indicated air speed by the square root of the relative density to obtain the corrected air speed, and to add to this the pitot position error, if known to give the true air speed. In order to fill iu the table, the following data are required from the pilot's report: — (a) Height from locked altimeter, feet; (b) Air temperature at altimeter height; (c) Indicated air speed. As in correcting climb, the standard height is found from: — Hs = (1.238 Ha ± 120 f(l - 1,800). H, = Standard height in feet. Ha = Altimeter height in foet (locked altimeter). to ~ Observed temperature in degrees C. (The plus sign becomes minus, of course, if t0 is nega- tive.) The engine revolutions in the pilot's report should also be entered, for record purposes. The standard heights thus determined are entered in the appropriate column in the table, and the values of relative density and the square root of relative density corresponding to the standard heights are found and entered. The figures for relative density may be taken from the N.A.C.A. Report No. 218. They are shown in Fig. 3. The corrected speed is thus obtained from : — P" V = Corrected air speed, miles per hour, knots or kilometres. I.A.S. = Indicated air speed, miles per hour, knots or kilometres. — = Relative density at standard height considered.P» If the pitot position error is known, it should be entered and added to the corrected air speed to give the true air speed, which will be the true air speed at the particular standard height considered. The values of standard heights as found will almost certainly be uneven members; therefore the speeds should be plotted against standard height so that they mav be stated in the remaining column against regular intervals of height, i.e., at 10,000, 15,000, 20,000 ft., etc. PITOT HEAD POSITION ERROR. The pitot position error depends on the position of the head in the gap if the machine is a biplane, on the stagger, and possibly on other factors in addition; for example, it may depend on the relative chords of the wings of an unequal biplane. It is not possible at the present time to base the position error on calculation, and its values must be found experimentally for different conditions of flight. Whilst the position error may be stated generally as varying between + 0.5 and + 3.5 miles, per hr., it does not appear possible to connect these values with any definite circumstances, and for this reason it is advis- able to leave the position error column in the table vacant in cases where no test figures are available for the particular machine of which the performance is being corrected. CORRECTION OF SPEED. Since the pressure in the pitot tube is proportional to tag density of the air and to the square of the speed 8626
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
