Archive » June 19, 2008
By Robert Perry, Staff Writer
Hitting the numbers
A number of pilots have been practicing landings recently at Santa Ynez in preparation for the annual Sport Aviators spot landing contest on Independence Day. Watching this practice drives home the cliché that the only thing a pilot is judged by is the quality of the landing. Although all pilots strive for the silky smooth touchdown, not all pilots achieve that arrival with regularity.
The elements for a good landing are built on a foundation of good procedures that precede the actual touchdown by many minutes and sometimes hundreds of miles. Large transport category aircraft operated by the major airlines begin descent profiles and standard arrival procedures long before the touchdown runway.
Every clear afternoon, the Santa Ynez Valley has a front row seat to the vapor trails of jets transiting our area to or from Los Angeles. In the southern sky, a regular vapor trail in the evening off the coastline to the south reveals the departure and arrival routes of high altitude jet traffic leaving or entering the airspace offshore through the air defense identification zone.
The large transport aircraft is descending and keeping on an airspeed schedule allowing it to be on a stabilized approach, an approach characterized by airspeed and descent rate being within predetermined limits. A stabilized approach allows the pilot to better predict and control the conditions at the time the aircraft is ready to touch down on the runway. Flying a stabilized approach additionally allows the pilot to accurately control, consistent with safety, the point on the runway where his aircraft will touch down.
Smaller aircraft have the versatility of being able to fly out of shorter and even unimproved runways. Bush aircraft with large “tundra” tires are able to land and take off from gravel riverbed in only a few hundred (or fewer!) feet. General aviation pilots operating at Santa Ynez Airport have just over one-half mile of asphalt (2,805 ft) for operations. This runway allows safe operations for most single engine aircraft and many medium size twin engine aircraft, including some fanjet powered aircraft.
The secret to a good landing on the runway at Santa Ynez is much the same as a landing at Los Angeles International — a stabilized approach. The pilot, who rips into the pattern not having airspeed and descent rate under stabilized control, will have a less than good chance at a smooth landing on the first third of the runway compared to the pilot who flies a square pattern keeping airspeed and descent rate under good control.
At the point that the approach ends, the pilot finds himself on short final with the runway only 500 feet away preparing for the last phases of the flight. The pilot already should have had a good idea what the wind is doing at the surface as the plane enters the round-out phase from the glide to the runway environment.
The landing speed is critical to the landing success. The reference speed in a general aviation single engine airplane like a Cessna 172 is generally 1.3 times the stall speed for the configuration the airplane is in (gear down, flaps down). The reference speed provides approach airspeed of about 70 knots if the stalling speed is 55 knots. Approaching substantially faster than 70 knots will cause excessive float.
The strength of a crosswind or gusty conditions requires some adjustments to the reference speed. A general rule of thumb used by pilots is to add half the steady state crosswind velocity plus all the gust velocity to the reference speed. Therefore if the crosswind is 15 knots with gusts to 25 the pilot would add about 17 knots to the reference airspeed (15 X .5 = 7.5 knots plus 25 – 15 = 10). The approach airspeed for the above Cessna with a 15 knot crosswind with gusts to 25 would be about 87 knots.
The plane should be aligned with the runway centerline upon landing and the pilot will use whatever rudder pressure is necessary to keep the aircraft aligned with the centerline. The pilot also will correct for any crosswind by banking the upwind wing into the prevailing wind enough to keep the aircraft from drifting off the centerline. Sometimes, if there is sufficient crosswind, the amount of cross-controlling is substantial and noticeable. In the case of a gusty crosswind the pilot almost must wrestle with the aircraft controls to keep the aircraft tracking the centerline of the runway without drifting off downwind.
After the round-out part of the landing, the pilot enters the flare. During the flare the plane is held just a few feet above the ground while the airspeed bleeds off until just above the stall airspeed. A flare entered with too much airspeed will cause the aircraft to float a fair distance down the runway until enough speed is lost for the wing to stop flying. A flare entered with too little airspeed and too little power will cause a premature stall and a hard contact with the runway. Good form will dictate holding the nose of the airplane off, allowing the tricycle gear airplanes to land on the rear (main) landing gear first with the nose wheel following as the elevator loses effectiveness.
A proficient pilot will keep rearward pressure on the control yoke, allowing better aerodynamic braking from the elevator and staying off the brakes until absolutely necessary to exit the runway.
Local pilots are practicing for the accuracy contest open to members of Sport Aviators Inc., the local Experimental Aviation Chapter, on the 4th of July, and competition is sure to be stiff. Carl Walston will be back to defend his title in his 1939 Culver Cadet — if he gets it running in time. Edo MacGowan has been seen doing ending circuits and bumps in his 1964 experimental Flutterbug.
The gophers at the glider port have taken to wearing helmets since Edo started practicing! Even the holder of last years Vandenberg Trophy, Don “Crash” Noonan, may be back with a Gypsy Moth biplane.
The public is invited to watch the spot landing contest on July 4 at Santa Ynez Airport. The regular monthly meeting of the group is June 21 at 10:00 a.m. in hangar J-6, at the end of Airport Road.