Landing Patterns

There have been several recent articles on good landing approaches, particularly from the Torrey Pines Club newsletter and in Sailplane and Electric Modeler Magazine. There isn’t much point on repeating the words of the experts on the nuances of landing, the points I would like to add are simple.

I find that most folks do not plan far enough in advance on where they are going to land and the approach pattern to use. At anytime under 100’ of altitude, the you need to have a general pattern in mind of how you are going to come in to land. In contests, you plan your approach pattern before launching, when just flying around, keep a plan of approach in mind once your plane is under 100 feet.

Two generic plan of approaches work for me. Doing these approaches from the right or left covers all situations to avoid flying over the pits.

Approach 1, under 100 feet and upwind of landing point. Use the standard downwind, base and final that carrier landings are based on. Stay upwind and off to the side until you ready to start your approach. Now is no time to go chasing lift downwind. Start the landing pattern with a downwind leg 100 feet to the right or left. Turn 90 degrees and then adjust the length of the crosswind leg to bleed off altitude so that the final leg is at 10 feet high and still over landable ground, i.e. not over the swamp. Turn 90 degrees onto final approach, into the wind and land at your feet. You will never miss the field this way and the walk will be short.

Approach 2, downwind and high. Step one is to fly upwind until the plane can use approach technique #1. This is ideal since the landing pattern will be familiar to you. Can’t make it upwind with enough altitude to do a normal approach? Bad planning, so proceed with plan B. Fly upwind towards yourself and 100 feet off to the side. When you reach the fence line or edge of the landable ground, do a crosswind leg to bleed altitude for final, then do a normal turn into the wind to land. Works for me.

Finally, there is the low and downwind approach. If you end up doing this because you chose to follow a thermal a long way downwind, you must be an expert and don’t need any advice from me.

So try to plan your approaches with at least a minute to go, and you should always end up safely on the ground and a short distance away.

Getting where you want to go.

A fast F3B type plane can go anywhere, upwind, downwind whatever and generally make it back to the field. So let’s talk about slower planes with some wind blowing.

The average plane has a glide slope of 15:1 and flies at about 15 feet per second or less. This means that any wind over 10 mph and you can hover the plane, and the plane’s true glide slope relative to the ground is zero. On the other hand, it you are 10 feet high, upwind of yourself, and out over the swamp heading downwind, your plane could easily hit the fence on the far side of the field.

True glide slope over the ground is the measure of getting where you want to go. Flying your plane at maximum glide slope into the wind is a real challenge. Let’s say you’ve caught the boomer thermal of the day and the plane is specked out and waaay downwind. The normal flying speed of the plane matches the windspeed on this day so hovering will mean a long walk to pick up the pieces.

Increasing the flying speed of the plane decreases the efficiency of the plane, but at least you are making progress upwind. Keeping the speed up will mean holding down elevator (on slower planes), and any release of the elevator will result in the plane pulling up and stalling, so concentrate on keeping the nose down and the speed constant. If you really are desperate to make it back, the rule that I use is to point the plane at yourself, straight on in a shallow dive and hold it. If the plane doesn’t make it back to the field at that glide slope and speed, you were beyond the point of no return. The downside of this technique is that the profile of the plane is minimal when it is pointing straight at you and will disappear at anything more than ½ a mile. I’ve been in situations where not seeing the plane means that you are on track, and seeing the plane means you are not going to make it home. Nerves of steel are required to intentionally make the plane disappear for 15 seconds or more. My nerves are frayed steel.

Flying upwind at speed increases the sensitivity of the plane and it will be constantly turning off. Your mission is to keep it pointed in the right direction.

Another funnel analogy. Think of the field as a bottom of a shallow cone. Inside the cone is good, you can get back to the field. Outside the cone any you’re dead unless you catch some lift. On a windless day, the cone is perfectly round and very shallow, extending toward the horizons. Add some wind and the cone is bent in the upwind direction, and becomes steeper downwind of the field. When the wind is over 15 mph, the safe zone of cone is almost straight up! As you fly, try to determine if you are in the cone or not, keeping some safety margin in case you hit sink on the leg back.

As a final note, flying in wind makes no difference to the glider, only the pilot is affected. Learn to fly in wind and enjoy yourself.

Update 2004

Until this year, I would always fly the F3B type planes when the wind increased to over 10 mph at ground level. The improved penetration was a worthwhile trade off against sink rate for the ability to travel downwind. The development of lightweight F3J type planes with better penetration has introduced an new style of windy flying for me.

For me, the standard way of thermal flying is to measure your rate of climb against the downwind drift rate, and stay in the thermal as long as the plane is climbing faster than the optimal upwind glide slope of your plane. When the target time is close, or at the limit of visibility, run back upwind for the next lift cycle. The goal is to get the plane as high as possible and return to the landing zone with energy to spare. With the newer lightweight open class planes (i.e. >130 inches and under 60 ounces), a different approach is potentially more successful. The idea is to use the improved hang time of the plane to reduce the risk of landing out on a downwind run.

In this style of flying, the decision point is when you think that the plane's altitude is sufficient to make the target time without any more lift, regardless of how good the lift. This mean bailing out of the lift earlier than trying to get the plane as high as possible. Now the goal is to fly the plane at minimum speed to arrive in the landing pattern without making any turns and flying as slowly as possible. Since the plane is downwind of you, read the air and avoid sink on the path home.

As an example, say the task is 10 minute duration with a 10 mph wind. After 6 minutes you are downwind in good lift and estimate that the plane is high enough to make 5 minutes in neutral air (a little over launch height). In case 1, you would stay in the thermal until 9 minutes, get as high as possible, and burn back to the landing zone with energy to spare. This means drifting downwind for another 3 minutes and about 1/2 mile.

Case 2, you leave the thermal at 6 minutes and fly as slowly as possible upwind while avoiding sink. Hover in any lift encountered on the trip home. The goal is to arrive into the landing pattern without making any turns and flying at the minimum sink rate to travel upwind. Camber is useful to adjust the penetration speed of the sailplane. Steering with the rudder only, leave the ailerons alone to keep the wing camber in the optimum position. You do a upwind approach pattern with only minimal energy to spare, but still make the 10 minute target time. The distance that the plane has drifted downwind during the flight is minimized.

Pros and cons of the two cases are dependent on the hang ability of the sailplane. The better the hang, the more viable case 2 is as a strategy. The main advantage of case 2 is to minimize the distance traveled downwind, but you have less margin for killer sink. Since you are flying though air that you have already read, the possibility of killer sink is low. Case 1 is more fun since you can scream around burning off the extra energy gained by staying the thermal for an extra 3 minutes.

Flying the lightweight planes has made me appreciate the viability of case 2 (leave thermal early), especially when the climb/drift rate of the plane is very close to the upwind glide slope. If you miss the Bail Out point (shown in the diagram) the walk is much shorter. The visibility challenges of flying  a long way downwind while looking at the glider head on is minimized.

I have been trying case 2 strategy more in practice flying to see how comfortable it is to make target times, and learn the decision point for the lightweight planes in different wind conditions.

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