Tuesday, May 25, 2010
The Myth (Almost) Of Tailwinds
Logic suggests you should have tailwinds roughly 50% of the time. Logic is wrong.
To avoid losing speed to winds, a standard trick is to fly the tailwind leg as high as possible (above), then make the return as low as feasible (below left).
Mooney was ready to pull the plug on the project, and I was advised the new TLS would need to return to Kerrville for sale if I couldn’t set the records by April 1. Finally, on March 24, my luck changed. A fast-moving cold front had raged through Southern California the night before, and I caught the tail of it the following morning for a fast ride across the country.
I launched out of Long Beach, got a vector over the Pacific off LAX, climbed to FL250 and ripped back across LAX VOR with a groundspeed well above 300 knots, the result of roughly 80 knots of tailwind.
The first record, from LAX to Albuquerque, scored 294 knots. The second, the cumulative leg from LAX to Dallas, logged a speed of 283 knots, and the segment from Dallas to Jacksonville recorded a still respectable 260 knots. The overall average record speed from Los Angeles to Jacksonville worked out to 261 knots, just over 300 mph. That included a superfast descent and landing at Dallas Love for fuel and sandwiches.
With the successful Los Angeles–Jacksonville flights, the American NAA and the International FAI granted me four city-to-city speed records in weight class C1B, and four more in the unlimited class. Since 1994, I’ve added 20 more international speed records to places as diverse as Iqaluit, Nunavut, Canada; Kulusuk, Greenland; Reykjavik, Iceland; and Edinburgh, U.K.
Many of those records were flown with the benefit of tailwinds, a not-so-simple matter of waiting for the right conditions before launching; picking the optimum altitude for best speed and the most efficient method of climb; minimizing aircraft weight and flying with the CG close to the aft limit; reducing drag as much as possible; and calculating the fastest method of descending at the destination. Fortunately, city-to-city records don’t require a two-way effort. (In contrast, seekers of ultimate speed records must complete a two-way run above a 3 km course, specifically to nullify any benefit from the wind. In 1989, when Lyle Shelton tried for the world prop/piston speed record in Las Vegas, N.M., he made two two-way runs in his modified Grumman F8F Bearcat, Rare Bear, averaging 528.3 mph to obliterate the previous record by nearly 30 mph.)
Trouble is, tailwinds are more fickle than you might imagine. In the real world of business and personal travel, most pilots don’t have the option of waiting for perfect conditions to make their trips. Perhaps for that very reason, the uninitiated might expect the laws of probability to produce headwinds and tailwinds with roughly the same frequency, effectively canceling each other out.
Unfortunately, there are a number of reasons why that’s not normally the case. The dominant wind pattern across the U.S. is west to east. That might imply you’ll break even if you fly an out-and-back horizontally across the country.
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