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Aviation History
1940
1940 - 2115.PDF
JULY 25, 1940 31 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT 73 1.3 Hence the relation between Pn and Po is ; Po x Z1-3 = Pn(/ -sj^or/ sx1-3 Po = Pw ( i J but Po/ = P,b :. P.- = Pw ( i - -, b Pw 7or — = n = Ps l~ 1-3 ^0- •• (2) •• (3)- Substituting for this in (1) : /fcxO.77 h = 0.8 rn X / 1 — \l or n /W\°-+ 0.47 «1-*S maxl — j x n0-3 + 0.47 n1-9-— = O.S « — O.8 - rl \l. \V\0-9 P) • •• ^ It is usual to provide an available stroke equal to \l, and to inflate the strut so that the static position is one-third or one-half of the way down from the fully compressed position corresponding to the available stroke.* This corresponds to —= \ and — = \ respectively. "'-;/ ,-••;••• ,' If —= -I, equation (4) becomes: ^ '•.'.-.-.•"•-.- • -•• _= 0.8 n — 0.469 w023 + 0.47 nlrK .^ ; ~.. (4a) , _ fi max /W\0-9 (i.e. K is a measure of the rl \p) relative softness of the tyre). rl where K = If —= f it becomes : -.;, v ' -.-• .'.'; .-.•, •_ — — = 0.8 n - 0.532 w0-23 + 0.47 nx-9 K ',.' ": .." (4b). ,0-9 4 •3 W Fig. 5.—Shock absorber calculations curve for thedetermination of " K." The relationship between n and — given by these equations Yi has been plotted for various values of K in Figs. (2) and (3). "This at any rate represents standard Messier practice. The important quantity, however, is - whatever the available stroke. r5 -4-5 • 0 0-1 o-z K 0-3 04 • 0-5 Fig. 6.—Nomogram for shock absorber load factors. : ' -p= o.8n — o.469n023 + .9The relationship between n and — given by equation (2) has been plotted in Fig. (4) for -•••,•-,•••-:. * •• "_6 . b Use of Curves : ' - *: "h Determine h and hence — • »rl Determine K =———( — 1 from tyre curves if available ( x /WV" . . W . . . \ ( a curve of f — 1 against — is given in Fig. (5; 1. . . If no data are available determine P and bmax from empirical data given in list of symbols-. From curve in Fig. (2) or (3) find " n " for appropriate value of K. S Having found w, find — from lug. (4). If the degree of inflation of the shock absorber corresponds 6 b neither to — = 0.5 nor to— = 0.625, n can ue found by inter- polation or extrapolation from ihe results obtained from Figs. (2) and (3). Having found n, — is calculated lrom equation (2), It is recalled that curves of Figs. (2) and (3) are only applicable to struts having an efficiency of 80 per cent. If a different value of efficiency (or a different degree of inflation, as defined by— j is worked to, then a rrcw serie3 of curves corresponding to the assumed conditions should be constructed. A neater way of representing the basic equation is by means of a nomogram. The nomogram corresponding tc — = 0.5 is given in Fig. 6. To obtain " n " a straight line his drawn through the values of — and K on the appropriate scales. The intersection of this line with the scale of " n " gives the value of this. Similar nomograms can easily be constructed for any assumed value of initial inflation and efficiency.
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