Tuesday, January 26, 2010
When Slower Is Better
The whole point of most airplanes is speed—except during landings
There’s nothing revolutionary here. If the winds are gusty or shifting from side to side, I’ll ad lib my speed as necessary. The important thing is to avoid operating so slowly that you enter the region of reverse command in which induced drag becomes so high that more power is required to fly slower (popularly known as the “backside of the power curve”). Naval aviators must learn the procedure to come aboard a carrier, but it’s definitely not recommended for most GA types. Experienced bush pilots also sometimes use this technique to land on extremely short runways.
(Back in the early 1980s, Maule demo pilot Dan Spader showed me a minimum-speed approach that was deep into the reverse-command realm. Using full flaps, significant power and an approach speed about three knots above stall, Spader landed a new Maule on the ramp in front of the company factory in Moultrie, Ga., by using a quick blast of power to cushion the touchdown during the nearly nonexistent flare. He planted the airplane perfectly three-point, and stopped in less than 100 feet. Don’t try this at home, or anywhere else.)
Sure enough, when I reduced my Mooney’s approach speed to between 70 and 75 knots, things automatically improved. The only major disadvantage of the slower speed is an abbreviated flare. If you’re having problems judging your height during the round out, it might be better to stick to the higher speed. Accept that you need to be more precise in judging your approach to the threshold, and that you need more runway to stop.
A too-fast approach speed is probably the most common contributor to bad landings. Part of the reason is that student pilots learn early on that stalls are the most dramatic maneuvers most aircraft will ever perform. Even a Cherokee 140 assumes a hobbyhorse pitching during stall that can be disconcerting for a new pilot. For that reason, some pilots avoid even approaching a stall near the ground.
Perhaps ironically, that’s exactly contrary to traditional wisdom. Rod Machado, a master CFIIM and author of several books on flying techniques, says all a pilot’s problems are compounded by flying too fast on final. “Many pilots land too fast because they’re afraid to fly the airplane slowly,” says Machado. “They’re so frightened of stalling that they fly at 40 to 50 percent above stall. This makes the elevator more sensitive, prolongs the flare, introduces a greater chance of ballooning and makes depth perception more difficult.”
For better or worse, some airplanes don’t have any choice but to use high approach speeds. The highest speed I’ve personally experienced on approach was in a Northrop T-38, better known as the “White Rocket.” I flew that airplane twice in conjunction with stories on USAF training techniques, and I was impressed by the high landing speed. Air Force regs didn’t allow me to actually touch down, but on both flights, my instructor pilot allowed me to make several approaches.
The base approach speed for the T-38 is 155 knots; then, you add one knot for every 100 pounds of fuel on board above 1,000 pounds. In other words, if you return to base with 2,000 pounds of fuel remaining, then you should come across the fence at 165 knots. That’s faster than most GA singles cruise. Imagine landing an F33 Bonanza at full cruise, and you have some idea of the problem.
The space shuttle may not hold the record for approach speed, but it returns to earth at high Mach. Without the benefit of power or the ability to go around, the shuttle turns final at an initial 300 knots, with an impressive 20-degree glideslope (standard glideslopes are three degrees) starting at about 12,000 feet, roughly one minute from touchdown. The pilot then slowly pitches the nose up to maintain a 1.5-degree glideslope to bleed off speed, and the shuttle crosses the fence at about 210 knots. (The shuttle has no easily defined stall speed, as it’s an unpowered, delta-wing glider, and the minimum usable angle of attack is minus-10 degrees, a pitch-down condition. Most GA wings stall in the 15-/20-degree range.)
Pilots don’t purchase fast airplanes to fly slowly, but final approach is no time for speeding.
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