Page:Popular Science Monthly Volume 91.djvu/241

 Old Before She Was Launched

There are styles in airships as well as in derby hats. The D. N. 1, our new navy schoolship-dirigible, is new and yet so old

���TWO years ago, the United States Navy contracted for a small dirigible to serve as a schoolship. Now that the craft has been finished, now that it can be judged in the light of the European war, it must be wholeheartedly condemned as well-nigh useless.

Thedesignersof the D. N. 1 were not daringly original. They simply copied an Austrian airship, the Koerting, destroyed short- ly before the war in a collision with an airplane. A few fea- tures of some utterly use- less British airships (des- ignated by Greek letters

Alpha, Beta, *ggg

etc.) were in- corporated.

In the Koerting, the car was elon- gated fore and aft to receive front and rear suspension ropes. Thus the strain on the tender gas envelope was lessened. In the D. N. 1 that system of suspension is copied. The Koerting had two motors so that it was safeguarded to a certain extent against breakdowns; but the D. N. 1 must make the best of a single motor. The two pro- pellers of the D. N. 1 are driven by bevel gearing, the arrangement being such that they can be swiveled. Hence, the craft can be pushed up or down by its propellers while it is making very little headway — a decided advantage in landing and starting. The D.N.I can be tethered by the nose of the gas envelope to a tall mast so as to ride out storms — a good idea because the ropes distribute the strain evenly over the envelope.

The Koerting was never regarded in Europe as a model to be followed. The D. N. 1 is worse than the Koerting. Its fuel capacity is sufficient only for two hours

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The D.N. 1, the navy schoolship-dirigible, is 175 feet long. It has a 140-HP engine to drive it at a speed of 25 miles an hour. Although new it is hopelessly antiquated

��so that it may carry an apprentice crew of seven. Three or four apprentices would have been a more reasonable number.

The whole idea of the D. N. 1 is funda- mentally wrong. There may be some justi- fication in degrading an old diri- gible, which has seen active service, to the level of a schoolship, but there seems no excuse- for designing an en- tirely new dirigible which is so slow that the experience to be gained in it is not even remotely similar to that re- quired of the men in full- sized fast militaryorna- val airships. An air- plane has what is called dynamic lift; that is, it rises by vir- tue of its own fast motion. A dirigible, too, has dynamic lift when it is fast. A slow dirigible has little or no dyna- mic lift. The whole science of piloting a dirigible is founded on the proper utilization of dynamic lift — a fact which we have learned in this country although the ex- tensive German literature on the subject has harped on it constantly. In a dirigible of twenty-five miles an hour (the speed of the D. N. 1) little more can be learned than in an ordinary spherical balloon.

The faster the dirigible, the safer will it prove to be for an apprentice. Its dynamic lift makes it easy to overcome mistakes in managing gas and ballast. Moreover, a fast dirigible is not easily forced to land; and an enforced landing is the worst danger because no dirigible can come down anywhere in safety like a spherical balloon. Even the English Alpha, Beta, and Gamma ships have been discarded in favor of the " Blimps." — small dirigibles whose cars are wingless airplane bodies.

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