Popular Science Monthly 



547 



So little trouble was taken to adapt the 

 airplane fuselage to the gas envelope that 

 not even a motor-driven blower was pro- 

 vided for the airbag in the first Blimps. 

 Part of the airplane propeller's slipstream, 

 caught in a hose, sufficed. 



The hybrid "Blimp" has shown itself 

 incredibly superior to anything in its own 

 class. It has a speed of forty-five miles an 

 hour and a radius of action of several 

 hundred miles. Its lift control approaches 

 the seventy -mile -an -hour Zeppelin's, be- 

 cause the "Blimp's" surface is relatively 

 greater, compared with its weight, than a 

 Zeppelin's. Moreover, for the same speed 

 the dirigible with a greater relative surface 

 has more grip on the air in rising or 

 descending by reason of the airplane effect 

 of its gasbag than if it had a surface 

 smaller in proportion to its weight. 



y Pressure relief valve 



Ballonet 



The United States has also built 

 "Blimps." The main original features of 

 the American "Blimps" is the addition of 

 a blower driven by a cycle-motor and of 

 a second airbag or ballonet with valves 

 to shift the air at will from bag to bag. 



As a result, the ship can be "trimmed" 

 (that is, its flotation forward and aft can 

 be varied at will by driving the gas where 

 there is less air) even while it is at rest 

 and the elevator or vertical rudder is 

 powerless. The blast of the propeller will 

 probably be used to inflate the ballonets, 

 that being safer than a separate motor. 

 There has been added an efficient device for 

 anchoring the vessel safely in a storm. 

 The equivalent of life belts, in the form 

 of kapok buoys are fastened above the 

 airplane's floats. Hence the entire craft 

 can rest lightly on the water, supported by 

 its gas. Enough water and sand ballast 

 are carried to permit the craft to rise the 

 better part of a mile; the safe altitude is 

 given as one 1/4 miles, but 

 with the help of the powerful 

 airplane action of the craft 

 itself this may be doubled. 



A ballonet is simply an air-bag within the main 

 balloon. When the dirigible descends and the gas 

 contracts the airbag is blown up with air by a 

 little motor in the car below. Thus what 

 buoyant gas remains is compressed] and made 

 to restore the envelope to its normal shape 



Beginning Has Proved 



dirigibles is the erratic changing of the lifting force of 

 the hydrogen gas with which they are inflated. When- 

 ever the sun disappears, the gas cools and shrinks. 

 When the vessel enters a cold stratum of air the gas 

 shrinks, to expand again upon reaching a warmer 



layer. But even the old slow dirigibles could add or 

 subtract much weight to or from their lift by reason 

 of their airplane action. As this action increases 

 proportionately with the square of the speed the fast 

 dirigible of today compensates easily for such variations 



