240 TAKING Ol'F OF AKKOl'LAXES. 



As far as lopoit g'oes, the latter luiist liave been about. 

 the h)ad with which Lieut. -Colonel Sir U. A. van Ilyneveld 

 left the liuhnvayo Aerodrome with the " Silver Queen 11." 

 on its last llight. 



The former load we speak of as a " light load." It repre- 

 sents petrol for about three and a half hours' flig-ht calculated 

 from the average rate of consumption given by Lieut. Colonel 

 Sir II. A. van Ryneveld, viz., 40 gallons an hour. 



F(}r the i)urpose of calculating- the horse power, it is 

 necessary to take the rate of revolutions per minute into 

 account. I have taken 1,550 revolutions per minute for this. 

 For this rate the horse power of ea(h engine at sea-level 

 (density 1) is 315, as given by average bench tests. As the 

 levolution per minute Avill be lower than this for the early 

 I)art of the run, Ave shall get for this reason again an 

 underestimate of the run required. 



The wing area (lifting- surface) of the "machine is 

 1,387 square feet. We have therefore for the two cases: — 



Light load, A'„ = 71'5, ic=C)'fH> lbs. per square foot. 

 Heavy load, 7^\, = 57'3, /r=7'94 lbs. per squrne foot. 



£"„=: engine horse power per 1,000 lbs. at sea-level. 



II' = Aving-loading. 



Another factor in making the calculation is the landiiig 

 speed, or minimum flying speed. This (as in the case of all 

 air sjieeds considered) is the true air speed, I.e., the indicated 

 air speed divided by \/r/. I believe that CiO miles per hour 

 will be a fair estimate to take for the light load at sea-level. 

 The correctness of this figure Avill not greatly affect the 

 comparison of the different conditions. With variation of the 

 conditions, this speed Avill be proportional to the square root 

 of the wing-loading, and inversely as the square root of the 

 density. The greater sjjeed to take off with diminished 

 deiisity and increased loading Avill have a marked effect in 

 lengthening the run. 



The propeller efficiency, as remarked al)ove, is the most 

 uncertain term. It attains the A^alue of 70 per cent, at the 

 best speed for the propeller, but in the low speeds of run 

 along the ground it Avill certainly be less than this. For 

 purposes of comparison its A-alue does not matter. We Avill 

 take it GO per cent., which is probably a good deal too high, 

 for the early part of the mm. 



With the above data we can calculate the minimum run 

 to take off at sea-level and at the different altitudes and 

 temperatures. 



