Page:Aerial Flight - Volume 1 - Aerodynamics - Frederick Lanchester - 1906.djvu/385

Rh Chap. VI., § 158. It is in any case very difficult to defend plausible reasoning of this kind, when the actual experiment with planes of “fair” form could have been tried for the expenditure of an additional few shillings and with hut little delay.

The inevitable statement as to the power expended in flight follows:—

“The most important conclusion may be said to be the confirmation of the statement that to maintain such planes in horizontal flight at high speeds, less power is needed than for low ones.”

“In this connection I may state the fact, surely of extreme interest as bearing on the possibility of mechanical flight, that while an engine developing one horse-power can, as has been shown, transport over 200 pounds at a rate of 20 metres per second (45 miles per hour), such an engine (i.e., engine and boiler) can be actually built to weigh less than one-tenth of this amount.”

'''§ 235. Langley's Experiments. The “Dynamometer Chronograph.”'''—This apparatus was devised for the measurement of the thrust and torque of screw propellers, as a means of practically testing trial models and ascertaining efficiency obtainable. For the details of the instrument reference should be made to the Memoir.

In the chapter on the use of this appliance. Prof. Langley explicitly states that the details of his investigations are reserved for future publication; certain particulars are, however, vouchsafed, including a sample determination, which is of considerable interest in view of the theory of the preceding chapter.

It would appear from the data given that the propeller employed, having a diameter of 30 inches, had an effective pitch of 1 foot approximately, that is to say, its radius was 1$$\tfrac{1}{4}$$ times the pitch.

Referring to our efficiency diagram (Fig. 127), we see that this denotes the employment of rather more than the whole of the