Aviation.

Progress, Volume VI, Issue 4, 1 February 1911, Page 537

Aviation.

(By Peter Ellis.)

Plying. Suppose a machine weighs lOOlbs., anti we wish to raise it vertically in the air 100 feet in one minute by means of a screw propeller (I do not say this is practicable, only assume it), the propeller having a helical pitch of one foot, we would require to revolve the propeller 100 times and the thrust would be lOOlbs., assuming, of course, that there were no slip. Now, if instead of rising vertically we go up an incline of 1 in 50 with the horizontal, with a propeller of the same pitch, we would require to revolve it 5000 times, with a thrust of 201b5., 10,000 foot lbs. of work being done in either case, the speed in the first instance being a 100 feet per minute and in the latter 5000 ft., or nearly 60 miles per hour. To revolve a propeller at the slow speed of 100 revs, per min., with the heavy thrust of lOOlbs., would mean a very heavy, slow-moving motor (or a fast motor geared down with reducing gear), and the heavy thrust would require a very strong propeller, which would also be heavy as a natural sequence, the whole thing being preposterous. On the other hand, a propeller revolving at the high speed of 5000 revs, per min. with a light thrust (21bs.) makes it easy to apply a light motor, light shaft, and light propeller. Of course atmospheric and frictional resistance is neglected in the discussion, in order to make this explanation clear, and to show the absurdity of attempting to fly vertically and the ease and practicability of flying in a nearly horizontal direction, rising gradually to the desired height.' . Force and Motion. When a block of wood lies on a table, the Savants tell us that it presses on the table, and the surface of the table reacts on the block. Now, suppose we smear the surface of the table with cement, and place the block upon it so that the block unites with the table, what has become of these contrary forces? We have not altered the position of the block, only interposed a thin layer of cement to exclude the air, where the under surface of the block meets the upper surface of the table. If it be contended that the forces arc still acting, then since the block and the table have become one mass, these forces must be. : acting not only at the joint where the cement is, but above and below it, everywhere, from the top of the block to the bottom of the table legs, and ever, right down to the . centre of the earth. Beginning at the centre of the earth, we follow the material from that point upwards until