just common sense and applies to tethering as well. For crossing powerlines downwind of the launch site, a good rule of thumb is to allow at least 100 feet of horizontal separation between the lines and the balloon for each knot of wind speed. For example, in a 1 0-knot surface wind, the launch site should be at least 1,000 feet upwind. But be conservative in your estimates-1500 feet would be even better. The actual crossing should be made with several hundred feet of vertical clearance. It is even advisable to cross the line in an ascent. Pay attention to how heavily loaded the balloon is and quickly assess your balloon’s ability to climb under the currect conditions. Overloaded balloons tend to be sluggish and very slow reacting. Don’t forget-an average balloon has over two tons of inertia! 

Do not attempt landings upwind of powerlines without employing the above distance minimums. Better yet, it just makes good sense not to make landings upwind of powerlines at all; instead, cross them at a safe altitude and select a more appropriate landing site. If winds are gusty, thermic or otherwise unstable, be especially cautious. Under such conditions, the direction and altitude of the balloon can change abruptly and safety margins can dwindle in seconds. 

To avoid tragic weather-related experiences in ballooning, it helps to have some knowledge of summer thunderstorms and thermals. Never attempt the destructive potential of either phenomenon. 

At 12,000 to 16,000 feet, small cumulus (building) clouds of summer flourish and grow rapidly to large towering (20,000 to 60,000 feet) cumulonimbus thunderstorm clouds. Surpris› ingly, an-afternoon thermal or small orographic disturbance can trigger the development of a thunderstorm by initiating the :rise of warm moist air. Most severe thunderstorm develop› nient occurs along or just ahead of summer cold fronts. They materialize in a squall line several hundred miles long at times. Invariably, there is a continuous line of strong gusty winds, violent updrafts and downdrafts sometimes in excess of several thousand feet per minute. wind shear turbulence, thunder roll, 

## Summer Safety in the Storm and Thermal Season 

In level flight, keep a constant vigil for powerlines. They are not easy to see from the air, especially when viewed against a mixed(~" background of earth and vegetation. If the wind\ dies and the balloon is suddenly becalmed over •--› powerlines, climb to a higher altitude to find a wind that will move the balloon aside. If no such lateral movement is discovered, carefully use a drop line and an experienced ground crew tci pull the balloon out of danger. Keep -in mind that hemp and nylon, under certain conditions, have been known to conduct over 500 volts. 

Whenever ballooning in the vicinity of powerlines, use every precaution possible. Don’t take chances. Don’t tempt the destruc› tive potential (no pun intended) of such innocent-looking wires. Things can happen very quickly and a not-so-bad situation can rapidly deteriorate into a gruesome ordeal. Balloonists right now are pushing their luck. Flights are getting sloppy and accidents are happening. For your own safety, the safety of your trusting passengers, and the reputation of the great sport of ballooning, be more careful. 

’lightning strokes, hail, heavy rainfall, and even flash floods. Some of the more ferocious storms also spawn tornadoes. Obviously, these are not conditions suitable for balloon flying. 

It should be noted that there is still much unknown about just how thunderstorms operate. For instance, scientists still do not fully understand what causes lightning and its close association with rain. Some think light› ning •serves as a catalyst in the formation of rain while others believe that the rapid descent of charged rain or hail generates lightning. 

Here in the U.S., winds gusting to 60 and 70 mph are oiien observed, usually moving from west to east or from northwest to southeast. Radar studies show the thunderstorm life cycle, from start of growth through maturity to dissipation, to be very short and somewhat complex. It is difficult to forecast and com- 

Raven Owners Newsletter 

