FUTURE OF FLYING — ^WIMPERIS 493 



The outstanding constructional change today is the employment on 

 a large scale of the sleeve valve, particularly as developed by the 

 great Bristol firm. This has the impressive merit of only needing 

 half the component parts of the old type poppet-valve engine ; more- 

 over it is found that, with a given fuel, it can operate without 

 detonation at an appreciably higher compression. 



Engines today run safely at far higher speeds than of yore, and 

 they are cooled in different ways and at a much less expense in air 

 drag than used to be the case. In fact at the highest speeds the 

 drag offers some theoretical promise of being replaced by a small 

 thrust! A new cooling problem will arise, however, when pusher 

 airscrews become as common as they will once their use is shown to 

 afford a means of substantially decreasing wing drag. 



Improvement in load-carrying capacity depends also on improve- 

 ments in materials, though it is fair to designers to record the progress 

 made in reducing the percentage which the structure forms of the 

 total flying weight in modern aircraft. Nowadays as good a figure 

 is shown for this in large flying boats as in landplanes, a remarkable 

 achievement. The flying boat used to be thought of as slow and 

 heavy, but today it holds its own in efficiency, whether aerodynamic, 

 structural, or economic, with any other mode of flight. 



The flying boats of today represent a gi'eat technical advance in 

 quality over their predecessors of 10, or even 5 years ago, but they 

 have not yet shown any marked advance in size. The fine fleet of 

 Empire flying boats is made up of 20-ton units; the new Short 

 "Golden Hind" class for the Atlantic weigh 33 tons apiece; the Boeing 

 "Yankee Clipper" has a total weight of nearly 40 tons; but the 

 Dornier Dox which long preceded them ran to 50 tons laden. On 

 the other hand there has been a great gain in speed and in carrying 

 capacity. The Boeing boat, for instance, is reported to carry 10,000 

 pounds of load over and above its 4,000 gallons of fuel. As this 

 amount of fuel will weigh 30,000 pounds, this makes a total load 

 of 40,000 pounds, or almost exactly half of the total flying weight, 

 the same as for the "Golden Hind," and a truly remarkable percent- 

 age. The improved Empire flying boats intended for the Atlantic 

 crossing are planned to take off at a flying weight of about 20 tons 

 and to take 3 tons additional fuel after they are air borne— by supply 

 from a flying tanker on Sir Alan Cobham's scheme. This will in- 

 crease the load on the wings from 30 to 35 pounds per square foot and 

 may be regarded as a first step toward what could be done with 

 wings specially designed and stressed for high loading. The "Golden 

 Hind" class is designed for a range of 3,400 miles without refueling, 

 and this with full load. Its early program may include a survey 

 flight along the route to Latin America. 



