The many V speeds that apply to light, piston-powered airplanes mostly have to do with maximum, do-not-exceed speed limits. VNO, maximum structural cruising speed, and VFE, maximum flap extended speed, are two familiar examples. VNO says we must not fly faster than XXX knots (or mph) indicated airspeed except in smooth air unless we hold in disdain the accuracy of the engineers who designed and tested the airframe.
The many V speeds that apply to light, piston-powered airplanes mostly have to do with maximum, do-not-exceed speed limits. VNO, maximum structural cruising speed, and VFE, maximum flap extended speed, are two familiar examples. VNO says we must not fly faster than XXX knots (or mph) indicated airspeed except in smooth air unless we hold in disdain the accuracy of the engineers who designed and tested the airframe.
VFE says that if we choose to fly faster than XXX knots (or mph) with the flaps fully extended we risk doing damage to the flaps. Not every V-speed describes an upper limit, however. A couple of exceptions to the usual do-not-fly-faster-than list of V-speed values are VX, best-angle-of-climb speed, and VY, best-rate-of-climb speed. Each has to do with extracting the “best” performance from airplane and engine in specific situations. But beware an important caveat: In many cases you’re just not going to achieve the best-angle or best-rate climb performance promised in the manufacturer’s specifications.
Best angle airspeed (VX) has to do with distance. Climbing at VX should result in the most altitude gain in the shortest horizontal distance. It’s the speed you want to fly when faced with obstacles on the departure end of the runway. Best-angle airspeed belongs in the same category as never-exceed airspeed, maneuvering speed, and stall speeds.
These are safety values, information you need to know to avoid wandering into the unknown beyond the tested, known, safe territory inside the performance envelope.
Best rate (VY) is concerned with time. Climbing at best-rate airspeed should yield the most altitude gain in a given amount of time. VY has broad application. It’s good for climbing out of thermals and other types of turbulence close to the ground, for quickly climbing away from noise-sensitive airports, and for punching up through groundspeed-robbing headwinds to higher true airspeeds at cruise altitude. VY is like best-economy power setting—it’s a tool, something to use to achieve a desirable objective.
An airplane’s climb performance depends on having excess thrust available from engine and propeller. In level cruise flight at constant airspeed, thrust equals drag. If you increase power without changing trim, the airplane will climb. The more thrust available beyond that required for level flight, the better the angle of climb. Best-angle-of-climb airspeed is the speed at which maximum excess thrust is available over what is needed to overcome drag.
Best-rate-of-climb airspeed is the speed at which maximum excess power is available. VX usually is a lower indicated airspeed than VY at sea level. VX increases with increasing altitude while VY decreases with altitude. At some altitude the two speeds will merge.
Most pilot operating handbooks, airplane flight manuals, and information manuals include climb performance charts, but as with all performance specifications the small print notes that the values represent performance at sea-level standard atmospheric pressure and temperature.
That other disclaimer also applies—the numbers are based on test flights conducted in new aircraft by professional test pilots under controlled conditions. In other words, don’t expect to achieve the same results.
Fine, but what should you expect from your airplane, and yourself, when it comes to maximum climb performance? Find out by practicing best-angle and best-rate climbs under a variety of conditions.
You’ll probably be surprised, as I was, by how much ambient temperature affects climb performance. You should know from firsthand experience your airplane’s performance capabilities, and more important, its lack of capabilities—especially when the going gets tight.
If you are faced with taking off from a short airstrip with close-in obstacles, you’ll want to know and have confidence in the airplane’s best-angle performance. Idling at the end of the runway, feet on the brakes, and hand poised to advance the throttle to the stop is not the time to wonder if the airplane will indeed clear those menacing limbs.
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