difficulty of bringing the aeroplane to land at high speeds
which prevents the increase of loading beyond 10 Ib. to the
square foot.
In commercial use, economy dictates an increase of loading; safety demands that the aeroplane may alight at speeds and in a space impossible with high loading. Attempts have been made to make the wing area or the wing shape variable in order to reduce the lowest speed of flight, while retaining the other advantages of heavy loading. None has so far been successful.
ISO M.P.H.
100-
50
5/
60
100 h.p./IOOO Ibs.
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FIG. II. Diagram showing speeds attained by British aeroplanes at a height of 10,000 feet. The speeds vary between the upper and lower curves. The base is engine power at ground level per 1,000 pounds of total weight. The dotted lines are lines of constant ratio of tractive force to weight, marked with the values of this ratio.
30,000 FEET
20,000.
10.000.
50
10O h.p./1.000 Ibs.
FIG. 12. Diagram showing greatest effective height attainable by British military aeroplanes. These vary between the upper and lower curves. The base is engine power at ground level per 1,000 pounds of total weight.
During the period 1909 to 1921 the speed attained by aero- planes was more than doubled. The rate of climb and the height attainable have increased in a larger ratio. Greater knowledge and better design have improved the aerodynamic efficiency of the aeroplane; but the improvement of performance is in the main due to the use of larger engines. In 1918 four times the power was being used that was used in 1914 for the same
purpose the reconnaissance two-seater aeroplane and the speed is more than half as great again. Aerodynamically there is little difference between the two aeroplanes. As the power of engines grew their weight per horse-power was reduced. To save two pounds in every four on an engine weighing one- third of the whole aeroplane was important.
The largest engines developed were insufficient for the larger aeroplanes, into which two engines were commonly built, and in some cases four or more.
FIG. 13. Large Twin-Engine Aeroplane.
Two separate power units have been regarded as conducive to safety. Experience has so far not confirmed this. It is essen- tial that the power of one engine alone should be sufficient to fly the aeroplane, and the " twin-engine " aeroplanes used during the war were not all provided with so large a total power. Again, the engines were carried on either side of the centre and the line of thrust of each offset by a considerable amount. This introduced difficulties of control, because rudders Vere unable to balance the offset line of thrust at the low speed at which the aeroplane could be flown level on one engine only, and there was danger in the event of sudden failure of -one engine near the ground.
The table gives some particulars of a few typical aeroplanes through the period under review. The figures are approximate :
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Name
Date
Flying weight Ib.
Lilt- ing sur- face sq.ft.
Horse power
Wing load Ib. per sq. ft.
H.P. per
IOOO
Ib.
Speed, m.p.h.
Wright
1908
1,000
54
25
1-8
25
40
Farman
1908
1,150
560
40
2-1
35
30-40
B16riot
1909
670
1 68
25
4
40
Roe triplane
1909
400
320
10
1-25
25
Dunne .
1910
1,700
560
50
3
30
40
Cody .
1911
1,400
690
5
2
35
40
Roe biplane
1911
750
280
30
2-7
40
40
The horse-power and speed given above
Aeroplanes in British War
1,500
are u
icertai 45
n. 2-9
35
Up
Office trials
to
to
to
to
to
1912 .
2,15
120
9'5
55
75
BE2C .
I9H-5
2,140
37
IOO
5-8
46
80
Bristol Fighter .
1916-7
2,800
400
250
90
H5
SE 5 a . .' .
1916-7
2,000
250
210
8
IOO
130
Sopwith Camel .
1916-7
1,480
230
125
6-4
85
no
Handley Page
0/400
1916-7
14,000
1,640
550
8-5
40
80
De Haviland gA
1918-9
4,220
490
400
8-5
95
125
Martinsyde F4 . De Haviland
1918-9
2,290
33
300
7
130
145
loA .
1918-9
9,000
850
810
10-5
90
120
Handley Page
V/iSoo .
1918-9
24,100
2,900
1,440
8-3
60
90
The Large Aeroplane. For the same aerodynamic per- formance, the lifting-surface of an aeroplane must be proper-
