6 Landing strategies
6.1 Precision landing, Ground effect. 6.2 Downwind landing. 6.3 Maneuvering after landing. At the beginning, the pilot is unfamiliar with the airport, its environment, and with the glider. The first landings are therefore best made with lots of runway length. While at some airports this means landing on a main, paved runway, such a practice increases conflict with power traffic. Therefore I recommend landing on grass. Many rural airports have an intersecting grass runway. Others have long smooth over-run areas or wide grass areas flanking the paved runways. If these are smooth, they are useful landing strips for the glider, as the glider will not frustrate power pilots by sitting on the runway waiting for tow or other help getting off. But first test the strip. If the weather's been moist, walk the strip and check for mud and for deep ruts made by the tractor that mowed the grass. If the grass is mowed when wet, the tractor on which the mower is mounted may cause deep ruts where the ground is soft. Such ruts can swallow the glider's gear and cause road rash on the belly; or tear off the gear if the ruts are perpendicular to the glider's travel. You can decide whether a grass strip is smooth enough for landing the glider by driving a car or truck back and forth on the strip, in the direction it's to be landed, at about 30 miles an hour. If the ride is tolerable, the strip is smooth enough to land a glider safely. During this ride, also check for potholes and ruts. Potholes are uncommon; animal burrows are not rare, though usually small. In the midwest, gopher mounds may proliferate during the summer. 6.1 Precision landing, Ground effect After the pilot is comfortable with the glider's handling, the next step in training should be to try to land at a particular spot. My bias is that every landing, once the pilot has a feel for the glider, should be a precision landing. A spot should be picked while on the downwind leg, and the subsequent pattern flown with only one goal: safely approaching that spot and landing there. To fly the pattern is not the goal; the pattern is merely a malleable route to the goal. Once the pilot is confident that the glider has the altitude and speed (energy) to reach the spot, the path flown is almost immaterial. If the runway were in the middle of a great prairie, with no obstructions, the pilot could (hypothetically) immediately dive, trading altitude for speed, and fly the pattern at 100 ft agl, gradually losing speed around the circuit. Or the pattern can be flown in the usual way, maintaining a constant speed and gradually losing altitude. The physics is the same: gradual energy loss, leading to a safe landing. We normally fly a constant speed rather than a constant altitude because airports are usually surrounded by hazards, altitude gives a better view of the progress of the approach and staying high preserves one's options. But, altitude and speed are not quite equal trade-offs. First, a low or medium performance glider develops quite a bit of induced drag at high speed, and will lose energy more rapidly at high speed. Second, induced drag diminishes dramatically -- by up to half -- when the glider is flown in ground effect (within a wing span of the ground). For example, the Blanik L-13 has a nominal glide ratio of 28:1. But I have, as an experiment, flown in ground effect, levelling out at about 5 knots above stall, just to see what will happen. If the flaps are extended when it gets to the flaps-up stall speed (lowering the stall speed to about 32 knots), this glider will float about 4500 feet from a beginning altitude of about 50 feet. This is a glide ratio of about 90:1, and is a remarkable demonstration of the power of ground effect. Try it yourself sometime. Aim for a landing at the near end of the runway, as usual, but instead of putting out spoilers and flaring, let the glider float when you get into ground effect and watch how far you go. Use the runway markings of a paved runway to estimate the float. Be careful not to go past the other end of the runway! 6.2 Downwind landing Some people teach the downwind landing only as an emergency procedure. Reasons for doing so are mainly related to fact that control effectiveness is lost at a higher ground speed than in an upwind landing, especially in high-performance gliders. Long-span gliders are at great risk of ground-looping if a wingtip touches. If control effectiveness is lost at 15 kt airspeed, then if one lands into a 15- kt wind, the controls will be effective until the glider is stopped; when landing with the wind, the pilot becomes a passenger when the ground speed is 30 kt. A wingtip will touch soon after aileron effectiveness is lost, and a ground loop will occur after that -- immediately in a long-span ship, and as soon as rudder authority is lost in a Blanik. Another reason for avoiding a downwind landing is that it may conflict with traffic making a normal approach. It focused my attention one day while collecting the tow rope, let me tell you, to be looking down the runway and see a glider approaching a downwind flare while power plane aircraft was on an upwind final to the same runway. The power pilots were clueless, and didn't even see the glider until it passed off their port wing when both were at 10 feet altitude; fortunately the glider pilot did see the power plane and made a neat little move off to the side and back again, in ground effect, then landed and rolled into the over-run. The chief reason for performing a downwind landing is to place glider exactly at the launch point. This avoids the delay and sweat associated with dragging the thing back to the launch point. At our field, the normal procedure, unless the wind was high, was to land downwind on the 100-foot-wide grass margin at the side of our paved runway, avoiding traffic conflicts, and rolling to a stop on the over- run area. If the wind is high, the 500-foot overrun is much more room than is needed to land and stop a Blanik. It's worthwhile to seek safe opportunities to teach pilots how a downwind landing feels, so by repeated practice they'll gain skill and judgment in handling this situation and in recognizing when it's safe. It is unequivocally safe in a Blanik in winds under 10 kt, in my experience; but I don't know if it's ever safe in a long-winged glass slipper. To review, a downwind landing is safe when - There are zephyrs, not winds. (There is no point in learning how a fast ground loop feels: this is hard on the glider's infrastructure.) - There are alternatives to land safely if opposing traffic shows up. This means that there is an unused taxiway to which to divert; a broad, smooth grass shoulder along the side of the runway; or a roomy over-run at the runway's end. This does not mean a safe crossing runway, as a turn below 100 ft altitude may touch a wingtip, breaking the glider and its occupants. - There is room to land and the crew expects the landing. It's not good form to land eastbound while the crew has their backs turned, searching the sky to the east for a missing glider. 6.3 Maneuvering after landing The L-13 has a powerful rudder that is effective at very low airspeeds, perhaps as low as 10 knots. This means that the glider can be turned readily during rollout; and it's possible, with careful energy management, to roll right into one's tiedown spot. A turn during taxi is essentially a controlled ground loop. The key to safe turning is opposite aileron, to keep the wings level. Ground loops get us in trouble because the wing on the outside of the turn develops more lift, the inside wing loses lift during the turn. It's important to kill the extra lift on the outside wing during the turn. This is easily done by applying "opposite" aileron. Turns at high speed -- over 30 kt -- should be gradual, and may require slight "correct" aileron to decrease side loads on the gear. It is possible to yaw the glider severely at these speeds, which are truly flying speeds, but to do so will put side loads on the gear, and the gear is simply not designed to bear this kind of shear. If you're lucky, this will happen on grass, which is slippery, and the glider might simply slide sideways. But don't try to be lucky. Turns at low speed, near the end of rollout, are safe for the glider's structure, and are useful for getting out of the way of other traffic or for steering into the tiedown spot. For example, you are landing on the active runway at an airport with traffic. It's considerate to turn to one side during the rollout and trundle off the runway between a pair of runway lights. Thus turns near the end of rollout should be practiced, not to impress the spectators, but to add to the pilot's repertoire of skills against the day when a turn is required to escape from an urgent situation. Copyright © 2000, 2002 Daniel L. Johnson; all rights reserved.