Flight, March 1921

THE ZEPPELIN-STAAKEN ALL-METAL MONOPLANE
And a New Smaller Edition

   WE have already published several photographs of the Zeppelin-Staaken monoplane, and a brief description of the machine, which is built of metal throughout, even to the wing covering, the metal chiefly used being aluminium alloy. On its test flights this machine is said to have given very good results, so much so that it rather surprised its designer, Herr A. K. Rohrbach. We understand that a cruising speed of about 120 m.p.h. is attained, and that the full speed is somewhere in the neighbourhood of 135 m.p.h. The wing area is approximately 1,150 sq. ft., and the weight fully loaded about 18,650 lbs. This gives a wing loading of 16.2 lbs./sq. ft., which is extraordinarily high even considering that the wing is of high-lift section. We have no figures of the landing speed, but it must be rather high for a commercial machine. The power loading is about 18 lbs./h.p., so that if the figures given for maximum speed are correct, the machine appears to be extraordinarily efficient as regards resistance. So much so that one very much doubts whether such a speed has ever been attained by the machine, except in a steep dive. It is true that the heavy wing loading would tend to increase the average figure, which is based on a wing loading of 7 lbs./sq. ft., but even so it is doubtful whether the speed is possible for that power loading.
   Our correspondent does not inform us of any tests having been made with cutting-out one of the outer engines, but the fact that the distance from these to the centre line is so great would almost certainly result in a turning moment of such magnitude that the corresponding engine on the other side would have to be cut out, or at any rate throttled down. Thus in practice the cutting-out of one engine would really mean the loss of practically half the power.
   The results attained with this first machine have been so promising that a second one, of slightly different type, is now being constructed. This machine, of which no photographs are available yet, will have two engines only, as shown in the photograph of the wind-channel model of the machine published herewith. This arrangement should be much better, as the two engines, by being pushed far forward and kept as close together as the airscrews will permit, are not far from the centre line of the machine. The object of placing the engines so far forward is evidently to help bring the nose of the fuselage back so as to avoid the gap between the two propellers that would otherwise be necessary if the body projected forward between them. What the effect on the front-wing spars will be is another matter. One would imagine that the down load in a dive, aggravated by the projecting engines, might prove somewhat heavy for the front-wing spars, especially as there is no top bracing. However, the wing is so deep in section that possibly the spar is capable of taking the stresses and allow of a reasonable factor of safety. Otherwise we think that the new monoplane is a great improvement on the older type. The cabin is low over the ground, and the door, when the tail is down, may be entered without the use of steps.
   We do not know if the Inter-Allied Commission has passed this design, but for the sake of aviation in general it is to be hoped that the firm will be allowed to finish and test it, as it appears to incorporate ideas well worth trying out.