Approach control and the wedge

You only have to keep your eyes open to see approaches done much less well than they should be, even by experienced pilots. If an instructor is alarmed by watching your approach and you are not, the problem is in your flying. If you have scraped in from a 150 foot final turn and had to use just a little brake, or if, just as bad, you first used far too much brake and then had to put it all away to float in just over the hedge, don't say to the instructor afterwards "But I was fine, I had lots of speed on". You'll get the reply you deserve: "So you lost control of the speed as well!" Ask yourself "Do I really understand the principles of the approach fully or have I got into bad habits that don't scare me but obviously are of concern to people who should know?" 

The steep approach

The assumption here is that the speed is correct for the day and therefore the same in both steep and shallow approaches. To land as close to the desired point as possible (but not before it!) with the shortest ground run is the essence of surviving a field landing. To do this needs a steep approach for two reasons. You can see where the flight path is going via the reference point very accurately. With lots of brake, when you round out you will lose speed rapidly because of the high drag and because of the large change in path angle, and so can stop quickly. 

From a shallow approach with little brake, you cannot see where the flight path is going via the reference point very accurately. You will scarcely slow down at all in the round out and will go much further before you can land at a sensible speed and eventually stop. What can extra speed do for you when your brakes are almost closed? Not very much. If the proper speed is 55 knots and you have 65, you might be able to convert it to about a 40 foot height gain by slowing to 55 if you would otherwise hit the hedge, but such manoeuvres are scarcely an advertisement for your judgement and skill. If you keep 65 knots to touchdown, it will take you even further into the field after the round-out. On the other hand, your glide angle over the ground may be worse, depending on the wind, so you may be less likely to reach the site at the higher speed. But don't forget that even 65 knots may only be just enough in severe conditions. 

Floating down the approach at minimum speed is a bad idea even in no wind. There is no energy margin left to deal with last minute surprises. In unexpected sink or wind gradient, a steep approach allows you to reduce the brakes and lower the nose as necessary. What are you going to do if the brakes are already almost closed and you are close to the ground? You certainly need to reduce the speed before touchdown, but never do it until you are sure of reaching the intended touchdown point. 

The approach wedge

The standard orthodoxy, not just a whim but well established by experience, requires the final turn to be completed by about 300 feet. A well-braked approach from 300 feet takes around 25 seconds. This gives all the time in the world to sort out your speed and approach angle long before you reach the ground. It also means you don't have to cope with managing a low level turn in turbulence while at the same time trying to judge your future flight path to the ground. To achieve it requires a conscious process during the downwind and base legs, shaping and positioning them to achieve this final turn point. Any old height that actually enables you to arrive on the airfield without crashing will not do.

It should go without saying that the planning should be with visual reference to the landing area, ignoring this tree or that farm or the other power line on the way, unless of course they are actually obstructions to your final path. On a real field landing, you won't be tempted to do your circuit round the edges of the small field you found, because you will be able to position the various circuit segments correctly relative to the landing point just as at home.

The approach wedge in the attached figure represents the possible range of approach paths. Its sharp edge lies on the ground at the reference point. The upper surface of the wedge is at the steepest angle possible with full brake at the correct approach speed. Its lower surface is at the glide angle over the ground with no brake at the correct approach speed. Obviously it is not a fixed shape. It varies with the wind strength and with the glider approach performance.

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How do you know where you are with respect to its limits? Easy. If you have full brake, the right speed and the reference point fixed on your windscreen, you are on the top surface. If you have no brake, the right speed and the reference point fixed on your windscreen, you are on the lower surface. This is the emergency zone and you had better not be in it without a very good reason involving force of circumstances but probably also bad judgement.

Where should the final turn be? It should either be actually in the optimum part of the approach wedge to begin your descent - the upper part, or such as to enable you to fly forward to this point. Many gliders can achieve a descent angle of about 6 to 1 with full brake. In no wind, that means the 300 foot final turn should be no nearer than 1800 feet from the touchdown point, which is two thirds of our airfield length. In a strong wind, with turbulence and possible sink, it might have to be only two or three hundred feet at the most, though then a much higher final turn is greatly to be preferred.

The figure gives a few of the infinite variety of situations and what to do or not to do. Each glider is shown after completing the final turn (FT), starting the final leg at the correct speed.

1) FT at correct height and position. Constant brake and speed all the way. The ideal result. ideal result.

2) FT too high and position too close. When the overshoot with full brake is obvious, lower the nose steeply to get into the wedge, then reduce angle to the correct approach path. The excess speed gained will soon be lost. Sideslip is a useful help here - can you do it?

3) FT at correct height but a bit far away. Fly straight on. When nearer, open partial brake to test the wedge. Open it more when you think you are near the top of the wedge.

4) FT starts at (3) but uses constant brake from there. But why throw away height before you need to? The brake control is not the "Going In To Land Lever". Acceptable if half brake is still needed, but it is much better to treat as (3).

5) FT too low and a bit far away. Fly straight on as in (3) etc. Do not copy (4)! But why be there at all when you should have angled the base leg in as soon as it was obvious your FT was going to be wrong?

6) Never open the brakes fully when anywhere far below the top of the wedge. You cannot regain the height once it is thrown away. Immediately you realise your error, shut the brakes completely and fly on until near full brake is needed as in (3).

7) FT much too low even if close. Don't even think about doing it intentionally except as a last desperate resort.

The astute among you will realise that the 300 foot final turn gives you time to sort out the first mistake. Example 6 in the figure is an ideal place to start making the second mistake, but using the top of the wedge makes it less likely because it already needs most of the available brake.

Controlling speed and glide angle

Accurate speed control is necessary, but it's not just to pacify a fussy instructor. It's the only way to be able to use the reference point properly. With the final approach speed set up on the base leg, the speed should be constant at least until the boundary is reached or to a little before the round out. Speed is controlled by the stick and the flight path by the brakes. By opening the brakes with a temporary bit of forward stick to lower the nose, there will be little immediate speed change. Some gliders speed up due to trim changes if not further corrected, however. Always wait after a brake adjustment to see the effect on the reference point before making another. Banging them in and out is useless and shows you have lost control of the situation.

If you lower the nose to start the descent and then open the brakes, you can certainly keep the reference point correctly in your windscreen, but you will end up on the correct path going too fast because you first speed up and then you are underbraked. How to correct this mistake? If you raise the nose to slow down you will go above the correct path and probably ruin any chance of landing where you intended. You have to open the brakes to decelerate, while slowly adjusting the stick to stay on the flight path until the correct speed is restored. Then continue properly, but why muck things up like this in the first place?

A new approach exercise was introduced into training recently to demonstrate how to fly into the near hedge while apparently keeping the reference point in the right place. You use far too much brake initially, and then as you sink too far you move the stick aft to keep the nose on the reference point. Then you notice the speed has dropped and lower the nose - but in the confusion you fail to close the brakes too. Now you are too slow and overbraked, far below the proper flight path and heading for the near hedge. There are several apparent examples of this in the S&G accident lists, some crashing short with brakes open. One of our members long ago did this on the fence at the top end. What you should do is slam the brakes shut and head for the ground until your speed is restored, hoping you can hop over the obstacles.

John Gibson