Weight impacts racers in three distinct areas: linear acceleration, centripetal acceleration, and stability. First and most obviously, a lighter vehicle accelerates more rapidly than a heavy vehicle. Racers bleed speed with every loop and turn, so having the lightest aircraft possible helps the airplane regain speed.
More important than straight line acceleration is centripetal acceleration. Race planes in the Red Bull Air Race World Championship experience high G force, meaning that the wings generate huge amounts of lift (centripetal force) to pull the airplanes through all those tight curves and loops. While the wings are aerodynamically and structurally capable of producing such huge lift, the price paid is induced drag and trim drag.
Wings produce lift by creating a pressure differential between the top (low pressure) and bottom (high pressure) of the wing. At the tips however, air leaks from the high pressure to the low-pressure side, creating swirling vortices that represent wasted energy: this is called induced drag. The greater the lift, the stronger the vortices. We’ll discuss the use of tiplets to reduce vortices in a future article, but irrespective of wingtip design, reducing aircraft weight reduces the lift required for high-G maneuvers, which in turn reduces vortice size. Thus, lighter aircraft have less induced drag.
In addition, airplanes typically generate negative lift with the tail. This is necessary to achieve stability, since the wing generates a nose-down torque that must be counteracted by the tail. If the wing’s center of lift is located (as is normal) behind the center of gravity (CG) of the aircraft, increasing wing lift during a high-G maneuver requires increased down lift from the tail to maintain balance. This is called trim drag and again, lighter aircraft will have less trim drag than heavier aircraft.