82 



AEROPLANE PERFORMANCE CALCULATIONS 



wire, or cable, but in the case of stream-line wires, d' is the dia- 

 meter of the thread. Then the value of r is given in the follow- 

 ing table : 



Type of Wire. 



Value of r. 



Stream-line wire 



Cable 



Piano wire . 



26 d'(l 



21 d'(l + load) 



The above formulae include a suitable allowance for fork 

 ends, turnbuckles, splices and ferrules, appropriate to each type 

 of wire. It is to be noted that in order that this allowance may 

 work out right, the formula is to be applied separately to each 

 wire : it is not of course correct to add up a batch of wire lengths 

 before applying the formula. 



Correction for Shielding. As has been explained in Chapter I. , 

 it is advisable to leave out this correction. If, however, it is 

 preferred to include it in dealing with duplicated wires the pro- 

 cedure is as follows : First obtain in each case the fore and aft 

 dimension of the wires, and the fore and aft centres distance : 

 the latter dimension can be obtained from drawings of fittings. 

 Then read off the appropriate correction from one of the curves 

 at the bottom of page 8 1 : the value of r obtained in the 

 ordinary way is to be multiplied by the correction. The correc- 

 tion is to be applied to both the wires. 



Wheels. Let D be the diameter of the wheel, and d' the 

 diameter of the tyre in millimetres as ordinarily quoted in de- 

 fining the size of a wheel, then the values of r corresponding to 

 different methods of fairing the wheel are given in the following 

 table : 



Cockpits. Let / be the maximum width of the cockpit in 

 inches^ then the value of r is given by the formula 



r = 7 /. 



