Now the greatest distance that a 1 oz. model has flown in perfectly calm air (which never exists) is not known. Flying with the wind 500 yards is claimed. Admitting this what allowance shall we make for the wind; supposing we deduct half this, viz. 250 yards. Then, on this assumption, the efficiency of this "one ouncer" works out (in perfectly still air) at 61 per cent.
The gliding angle assumption of 1 in 8 is rather a high one, possibly too high; all the writer desires to show is the method of working out.
Mr. T.W.K. Clarke informs me that in his one-ouncers the gliding angle is about 1 in 5.
§ 25. To Test Different Motors or Different Powers of the Same Kind of Motor.—Test them on the same machine, and do not use different motors or different powers on different machines.
§ 26. Efficiency of a Model.—The efficiency of a model depends on the weight carried per h.p.
§ 27. Efficiency of Design.—The efficiency of some particular design depends on the amount of supporting surface necessary at a given speed.
§ 28. Naphtha Engines, that is, engines made on the principle of the steam engine, but which use a light spirit of petrol or similar agent in their generator instead of water with the same amount of heat, will develop twice as much energy as in the case of the ordinary steam engine.
§ 29.Petrol Motors.
| Horse-power. | No. of Cylinders. | Weight. |
| ¼ | Single | 4½ lb. |
| ½ to ¾ | " | 6½ " |
| 1½ | Double | 9 " |