Miles per hour Feet per secoPressure per sq. foot14.73.075100146.649200Pressure of wind increases in proportion to the square of the velocityThus wind at 10 miles an hour has four times the pressure of wind at 5miles an hour. The greater this pressure the large and heavier the objectwhich can be raised Any boy who has had experience in flying kites cantestify to this, High winds, however, are almost invariably gusty anduncertain as to direction. and this makes them dangerous for aviators. It isalso a self-evident fact that beyond a certain stage, the harder the windblows the more difficult it is to make headway against itLaunching device for glidersOn page 195 will be found a diagram of the various parts of a launcherfor gliders, designed and patented by Mr. Octave Chanute. In describingthis invention in Aeronautics. Mr. Chanute savsIn practicing, the track, preferably portable, is generally laid in thedirection of the existing wind and the car, preferably a light platform-car,is placed on the track The truck carry ing the winding-drum and its motorlaced to windward a suitable distance--sav from two hundred to onthousand feet-and is firmly blocked or anchored in line with the portabletrack, which is preferably 80 or 100 feet in length. The flying or glidingmachine to be launched with its operator is placed on the platform-car atthe leeward end of the portable track. The line. which is preferablyflexible combination wire- and-cord cable. is stretched between thewinding-drum on the track and detachably secured to the flying or glidingmachine, preferably by means of a trip-hoop, or else held in the hand ofthe operator, so that the operator may readily detach the same from theAving- machine when the desired height is attained
How Glider Is StartedThen upon a signal given by the operator the engineer at the motorputs it into operation, gradually increasing the speed until the line iswound upon the drum at a maximum speed of, say, thirty miles an hourThe operator of the flying-machine, whether he stands upright and camesIt on his shoulders, or whether he sits or hes down prone upon it, adjuststhe aeroplane or carry ng surfaces so that the wind shall strike them on thetop and press downward instead of upward until the platform-car underaction of the winding-drum and line attains the required speedWhen the operator judges that his speed is sufficient, and thisdepends upon the velocity of the wind as well as that of the car movingagainst the wind. he quickly causes the front of the flying- machine to tipupward, so that the relative wind striking on the under side of the planes orcarrying surfaces shall lift the flying machine into the air. It then ascendske a kite to such height as may be desired by the operator, who then tripsthe hook and releases the line from the machineWhat the Operator DoesThe operator being now free in the air has a certain initialparted by the winding-drum and line and also a potentialcomesponding to his height above the ground. If the fying or glidingmachine is provided with a motor, he can utilize that in his further flightand if it is a simple gliding machine without motor he can make adescending flight through the air to such distance as coresponds to thevelocity acquired and the height gained, steering meanwhile by thedevices provided for that purposeThe simplest operation or maneuver is to continue the flight straightahead against the wind; but it is possible to vary this course to the right orleft, or even to retum in downward flight with the wind to the vicinity ofthe starting-point. Upon nearing the ground the operator tips upward hiscarrying-surfaces and stops his headway upon the cushion of increased airresistance so caused. The operator is in no way permanently fastened tohis machine, and the machine and the operator simply rest upon the lightplatform-car, so that the operator is free to rise with the machine from thecar whenever the required nitial velocity is attainedMotor For the LauncherThe motor may be of any suitable kind or construction, but ispreferably an electric or gasolene motor. The winding-drum is furnishedwith any suitable or customary reversing guide to cause the line to windsmoothly and evenly upon the drum. The line is preferably a cablecomposed of flexible wire and having a cotton or other cord core toncrease its flexibility. The line extends from the drum to the flying orgliding machine. Its free end may, if desired, be grasped and held by theoperator until the flying-machine ascends to the desired height, when bymply letting go of the line the operator may continue his flight free. Theline, however, is preferably connected to the flying or gliding machinedirectly by a trip-hook having a handle or trip lever within reach of theoperator, so that when he ascends to the required height he may readilydetach the line from the flying or gliding machine.
Gliders as a rule have only one rudder. and this is in the rear It tendsto keep the apparatus with its head to the wind. Unlike the rudder onboat it is fixed and immovable. The real motor-propelled flying maclgenerally has both front and rear rudders manipulated by wire cables at thewill of the operator.Allowing that the amateur has become reasonably expert im theulation of the glider he should, before constructing an actual flyingmachine, equip his glider with a rudderCross Pieces for Rudder Beam.To do this he should begin by putting in a cross piece, 2 feet long by1/ 4 inches between the center struts, in the lower plane. This may befastened to the struts with bolts or braces. The former method is preferable.On this cross piece, and on the rear fiame of the plane itself, the rudderbeam is clamped and bolted. This rudder beam is 8 feet 11 inches long.Having put these in place duplicate them in exactly the samedimensions from the upper frame The cross pieces on which the ends ofthe rudder beams are clamped should be placed about one foot in advanceof the rear frame beamThe Rudder itseltThe next step is to construct the rudder itself. This consists of twosections, one horizontal, the other vertical. The latter keeps the aeroplanheaded into the wind, while the former keeps it steady-preserves theequilibrium.The rudder beams form the top and bottom frames of the verticalrudder. To these are bolted and clamped two upright pieces, 3 feet, 10inches in length, and 3/4 mch in cross section. These latter pieces areplaced about two feet apart. This completes the framework of the verticalrudder. See next page(59)For the horzontal rudder wou willure two strips 6 feet long. andfour 2 feet long. Find the exact center of the upright pieces on the verticalrudder, and at this spot fasten with bolts the long pieces of the horizontal,lacing them on the outside of the vertical strips. Next join the ends of thehorizontal strips with the 2-foot pieces, using small screws and cornerbraces. This done you will have two of the 2-foot pieces left. These go inthe center of the horizontal frame, straddling" the vertical strips,asshown in the illustration