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Aviation History
1951
1951 - 2375.PDF
674 FLIGHT THE GIANT HELICOPTER . . . Under the heading "The Family of Giants," Mr. Fitz- williams then went on to say that, because the gross weight, blade weight and engine weight were known as functions of rotor radius, whilst the structure weight was a simple per- centage of the gross weight a fairly comprehensive weight analysis for the entire family could therefore be plotted, as in Fig. 6, which was so arranged that the space below the lowest full curve represented the disposable load for each size of rotor. The magnitude of these loads might be appreciated by reference to the right-hand scale, graduated in tons. When it was realised that, in rough figures, ten troops with normal equipment were equivalent to one ton, the scale on which such helicopters could be used for the transport of troops and equipment would seem to introduce new possi- bilities in the concept of the air transportable army, and even in the task of evacuating civil populations in large-scale emergencies. The disposable loads indicated in Fig. 6 referred to the normal operational weights, but the extremely powerful ground effect associated with the larger helicopters would permit large increases in the already impressive normal lifting capacities. Practical measurements with existing heli- copters had shown that the beneficial effect of the ground cushion extended to a height considerably greater than one rotor diameter and, in fact, consistent indications had been given that the effect was still noticeable as high as two rotor diameters from the ground. Even accepting the usual single- rotor diameter standard, it would be realised that the ground effect assumed a new significance when it remained powerful at wheel clearances of over iooft. Relating the power requirements of this range of helicop- ters to the characteristics of existing turbojet units, the generalized size range of Fig. 6 could be reduced to the specific examples illustrated in the upper half of Fig. 7, although the advantages of this type of rotor drive might not be fully effective for the smallest example quoted, in which the rotor radius was considerably less than 50ft. It was even doubtful whether the smallest example properly came within the scope of the paper, although it might be well-suited to airline operation. Mr. Fitzwilliams remarked that it was, 0-4 B CFKTtlFUGAL ORCES FROM TIP XT UNITS 6O BO IOO 12O 140 • , I I • ^ fi - 6" (LESS ON DASHED LINE ) W 2O 4O 6O 8O 100 120 MO ROTOR RADIUS - FT 0' B*(LESS ON DASHED LINE) 2O 4O 6O 80 IOO I2O I4O ROTOR RADIUS - FT Fig. 5. Ratio of blade-weight to gross-weight variation with rotor radius for coning angles of four deg (A), six deg (8), and eight deg (C). 600 000 too 000 TOO 400 OOOa. O x 300 OOO 2OO OOO '00 000 O ?O 4O 6O BO IOO IJO I4O Ito ROTOR RADIUS - FT Fig. 6. Generalized size grange/weight analysis. after all, only a very little giant. Its size was less than that of one rotor of the new Piasecki, and its lifting capacity hardly extended beyond 50 passengers! From the table in the lower half of Fig. 7, it could be seen that the centrifugal acceleration and yawing velocity to which the largest engine would be subjected were (at 60 g and 3.5 rad/sec) of an order very different from the conditions which would have to be considered in the application of tip engines to a small rotor. These figures might be compared with the values of approximately six g and three rad/sec for which turbojet engines were normally designed. Proceeding downwards in the scale of size, the rotor diameter was reduced from 316ft to 160ft before the severity of engine operating conditions was doubled as compared with the largest size. A factor of three on the least severe case would cover the range of true giants. Mr. Fitzwilliams observed that the most optimistic presen- tation would not disguise the severity of the conditions indicated by this table, but the gloomy impressions to which it might give rise at first sight did not seem to be justified even in respect of ordinary turbojet engines, as he would hope to demonstrate in the concluding section of the lecture. (A digest of this will be published in the next issue of Flight.) The proposals put forward by Mr. Fitzwilliams are certainly startling, but are not of so heterodox a nature as to be beyond the pale of possibility, for they are essentially concerned with mechanical design. to.ooo 6O SO lOO ROTOR RADIUS - FT. WEIGHT OF A/C 504.000 LE 410.000 LB 355.000 LB 276.000 LB 206.000 LB 180.000 LB 137.000 LB 100.000 LB 53.000 LB 29.000 LB ROTOR DIA 316fy~\ 284Ff ' 262* v 228FT I82FT\160FT\ 136FT » 104FT 76FT ROTOR R P.M. 3337 10__i_46 ^L_ ^35^58 65 5 \ 77 \101 V 138 V ENGINE _ SAPPHIRE L AVON AVON ' GHOST DER^SWT V ENGINE THRUST 9.000 LB 7.500 LB 6.500 LB 5.000 LB 7.500 LP r 6.500 LB \ S.000 LE \ 3-500 Lfr . _/l\00TB No." USED SIX-PAIRED SIX-PAIRED SIX-PAIRED SIX-PAIRED THREE THREE TMM4. !lw-pAnh*c^THREE 1 e 3.5 3.94.2 48 5.6 6.0 6,9 8.1 106 TV5 g 60 66 nHI 96 103 118 © RADIANS/SEC. ANGULAR VELOCITY IN YAW Of TIP JET ENGINES AT A CONSTANT SPEED OF 550 FT/SEC. I CENTRIFUGAL INERTIA ON TIP JET ENGINE. Fig. 7. Helicopters with particular engines.
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