Experimenter is a magazine created by EAA for people who build airplanes. We will report on amateur-built aircraft as well as ultralights and other light aircraft.
Issue link: http://experimenter.epubxp.com/i/90184
Reno's Racers The airplanes, however, are a different story. Ranging in speeds from under 200 mph to more than 500 mph, from dead-stock Pitts biplanes to purpose-built, one-off rac- ers, from RVs to P-51s, each airplane flying in the races is as fast as it can be. What adjustments are made to some of these airplanes for that week is the subject of this feature. Even the "stock" T-6 Class, which includes the Har- vard, SN-J, and AT-6 variants, has entrants that are running at 240 mph-plus. In 2012, Nick Macy in Six-Cat flew at more than 246 mph, beating the old record by a mile and a half and posting his sixth T-6 Class win. As further evidence of progress, the slowest T-6 this year was faster than the first Gold Race winner in 1968! Race airplanes get faster as time goes on; that's a given. Still, these are "stock" Texans; and your typical T-6 cruises about 140 knots. How are these racers so much faster, even around a pretty tight course? If a T-6 Race Plane Is "Stock," How Does It Go So Fast? Although many of the nonstock modifications are pretty obvious and allowed (no T-6 ever left the North Ameri- can factory with a wraparound windscreen, I'm pretty sure), other items are not so obvious: The tightness of seams, the smoothness of fillets, and the tightness of control-surface gaps all bring possibilities for speed to the venerable machines. Technical inspections are tight—incidence of the wings and horizontal stabilizer, wing sweep, dihedral, and washout are all checked. And there's always power to consider. The "stock" Pratt & Whitney 1,340-inch radials can be assumed to be in top shape, maintaining as much compression as they can, using their stock-ratio superchargers. Power-rob- bing accessories are turned off or removed. John Lohmar, who finished third in the Gold Race in 2010 and again in 2012, noted that the biggest single performance improvement modification is the use of a "race" prop. Ordinarily, a longer prop (within the rules) is the knee-jerk choice of nonracers, but as Lohmar noted, "We use the smaller props because the limit- ing factor is the speed of the prop tips. We can turn a smaller prop faster, using more horsepower, which we'll have because we're turning the supercharger [and engine] faster." Larger props that would absorb all the power available at lower rpm would not be using all the possible horsepower; in this case, that would be a bad tradeoff. Lohmar noted, "We're allowed to remove all instrumenta- tion 'not required for fl ight.' Some of these airplanes were used as instrument trainers and had full IFR panels; you can imagine how much all those old instruments and gyros and wires and stuff must have weighed! You can pull all that out. I have a 10-inch Dynon panel that weighs about 4 pounds that tells me everything I need for my primary Walt Orth's modernized but authentic LTA at Wings Over Miami Museum has a lot of original and heavy instruments…that's the stuff racers get rid of. 22 NO. 3/NOVEMBER 2012