Flight, November 1922

AN IMPROVED U.S. MAIL 'PLANE

   THE following interesting report on an improved American D.H. mail 'plane appeared in a recent issue of our American contemporary, Aviation. Some time ago the U.S. Air Mail Service began experiments with a view of increasing the capacity of the D.H. equipment employed in mail work, in the course of which a special fuselage was built for machine No. 299, having 40 cu. ft. of cargo space. It was found, however, that the original R.A.F. 15 wing section was not suitable for the additional load and increased resistance. A special set of wings (A 2) were, therefore, obtained from the Aeromarine Co., and these fitted instead. From the following data of results obtained with this machine under actual service conditions on the New York-Cleveland route, it will be seen that expectations have been more than realised.
   The actual over ground speed flying between New York and Cleveland of this machine is only slightly less than that of the regular D.H. with R.A.F. 15 wing, and a certain amount of this loss in speed might be attributed to the larger fuselage. The average speed on five trips over the same route was 96-34 m.p.h., while the speed of the standard D.H., which was flying in opposite directions on the same days, was 97-8 m.p.h. The average load of the latter machine was slightly over 400 lbs., while on three of the five trips made by 299 the load was 800 lbs.
   It is very interesting to note that loading up to 800 lbs. did not show any marked difference in the speed, and there is every indication that the A 2 wing curve can be loaded up to 12 lbs. per square foot, and give a very satisfactory performance even at the slower speeds. As to maximum speed, it has been found that the 299 will do 115-3 m.p.h. at 1,725 r.p.m., with the regular club propeller 9 ft. 2 in. diameter and 7 ft. 6 in. pitch, which is about 4 m.p.h. slower than the average, standard D.H. machine (U.S. Mail).
   Perhaps the most outstanding feature of this modified D.H. is the slow speed at which it will cruise and maintain its altitude with 800 lbs. load ; it has been flown for a period of 20 mins. at 1,075 r.p.m. with an air speed of approximately 68 m.p.h. without losing any altitude, and having fair manoeuvrability at all times. It does not have a tendency to slip off on a wing as the D.H. does at the slower speeds; in fact, it seems very difficult to make it side-slip, and its tendency is to settle flat in a stall.
   Tests have shown a climb of 800 ft. in the first minute and 5,150 ft., in 10 mins. with 800 lbs. load, as compared with 1,000 ft. in first minute and 6,500 ft. in 10 minutes with the standard D.H. with 400 lbs. load. While the 299 has not the "zoom" that the D.H. has, it will climb at a higher angle and at considerably slower speed. It was found that the best climbing angle is at an air speed of 70-75 m.p.h., while the D.H. climbs at a considerably higher speed.
   A special trip from New York to Washington with 1,032 lbs. load, was recently made, and even with this load the performance was very good, and the cruising speed satisfactory, although the machine was making a head wind. The landing speed is 50 m.p.h. with 800 lbs. load, as compared with 60 m.p.h. for the D.H. with 400 lbs. load. The length of run on the ground for take-off is approximately the same with the D.H., while the time element is slightly greater: when 299 gets off with 800 lbs. load in 11 secs., the D.H. with 400 lbs. load, rises in 9 sees. Streamline wires and other minor refinements are being installed, which will improve the speed and performance somewhat.