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August, 1931      U.S. AIR SERVICES    29

burns where the reinforcing wires crossed each other.

[[image - photograph of model aircraft]]
[[caption]] DISCHARGE ENTERING AT NOSE AND LEAVING FROM TAIL OF MODEL PLANE [[/caption]]

Figure 4 shows a test on Van Orman's lightning protecting scheme. The Protection consists essentially of a cage formed by conductor hanging freely. These conductor are bonded at the top and part way down, but left entirely free at the bottom so as not to interfere with landing or parachute jumps from the basket. The conductors forming the shunt path are moved outward from supporting the basket to the ring has been replaced with rope. It would seem that had this device been used in the flights in Belgium and Pittsburgh, the fatalities due to direct stroke would have been eliminated.

 Apparently there is little difficulty in shunting the main discharge, but there is some question as to how far the discharge should be from the pilot so that he will not be stunned or frightened to the extent of losing control. The baskets in racing balloons are rather small, and anyone in the basket must of necessity be very close to any discharge striking the basket. Should the Van Orman cage give the necessary protection for direct hits, it would go to show that the protection to pilot or passengers in an airplane may be easily provided by shunting the discharge a short distance to one side.

DANGER OF DIRECT HIT
  Many people believe that a balloon or airplane should not be subjected to a lightning stroke while  flying, since there is no direct ground connection. Any object which has a greater conductivity than the air or a greater electrostatic flux carrying capacity will tend to disturb the electrostatic field and will cause a discharge in the immediate vicinity to take a path along the object.

EFFECT OF CONSTRUCTION UPON A STROKE OF LIGHTNING 
  In running the tests on the Van Orman cage, an attempt was made to protect the balloon. if the gas in the balloon is free from air, lightning will not cause it to explode although the balloon may be set on fire. If an explosive mixture is present in the balloon, an explosion may take place due to the ignition of the mixture.

DIFFERENCE BETWEEN A WET AND A DRY BALLOON
  IN THE study of high voltage phenomena, particularly those applicable to transmission line structures using wood, it was believed that there would be a considerable difference between a wet and a dry balloon. The tests were very interesting in this connection, as they go to show that while there might be a considerable difference in aircraft which is constructed of metal and that primarily of non-conduction material, when dry there would be little difference where the latter was wet. This difference is undoubtedly due to the increase in electrostatic capacity due to the presence of water.

  Figure 5 shows a hydrogen filled balloon being subjected to an artificial stroke of lightning. The balloon has a conductor attached approximating a long antenna, hanging from the lower side. A number of discharges were applied to the balloon similar to that in figure 5. All of these discharges struck to the upper part of the conductor attached to the balloon, and then from the lower end of this conductor to ground. 
  As soon as the balloon was wet, however, conditions were entirely changed, the performance being similar to that shown in Figure 6. The discharges instead of going directly to the antenna and then to ground, struck the surface of the wet balloon. The discharge in Figure 6 is apparently passing along the surface, which destroyed the balloon in all cases. The discharge invariably burned the rubber and set the escaping gas on fire. Had the photograph been taken a fraction of a second later, the balloon would have been collapsed, the duration of the second are shown in the photograph being less than one-half microsecond.