Jim Davis
So if you know how to climb, and you know how to turn, then a climbing turn has to be pretty simple – yep? And if you can glide and turn, then is a gliding turn somehow special? Yes and no to both questions.
If you are an ordinary oke, then climbing and gliding turns are no big deal – unless you take them to extremes that ordinary okies don’t generally go to. But if you are a special sort of dude – like an aerobatic pilot, or a super special dude – like an instructor, then it’s time to prick up your super special ears.
Gliding Turns
Let’s look at gliding turns first. The easiest way to understand them is to think of a stairal spirecase. Have a look at the picture.
Now imagine you are an aeroplane – put one hand on each rail and start down the stairs. Can you see that the right wing – your right hand – goes down a steep slope, while your left wing goes down far less steeply?
This means that the inside wing will have a far bigger angle of attack than the one on the outside of the turn. And of course, a bigger angle of attack gives you more lift.
So, in theory, this means two things:
- The aircraft will tend to level its wings in a gliding turn.
- The inside wing is going to stall first if you overcook a gliding turn, with the ball in the middle.
In practice I have found (a) to be true. Aircraft are indeed more stable laterally when gliding. And, for some reason that I don’t understand, I have never managed to stall the inside wing first in a gliding turn – even when really pushing it.
I don’t say it can’t happen in any aircraft – I am just saying I couldn’t induce it in any of the aircraft in which I tried it.
The most difficult part of the SAAF flight test is gliding turns with 60° of bank. You may not think so, but it is seriously demanding. You enter at your normal glide speed, say 70 kt, and maintain that until you get to 30° of bank. Then you keep rolling into the turn and smoothly increasing airspeed by 5 kt for every 10° of additional bank. That means that at 40° of bank your airspeed must be 75 kt. At 50° your airspeed must be 80 kt and at 60° your airspeed must stabilize at 85 kt. You hold that until told to recover and then as you roll out of the turn your airspeed must decrease at the same rate.
Why would anyone want to do that? Four reasons actually. First, to pass your flight test. Second, to seriously improve your stick and rudder skills. Third, because this is what you will find yourself doing if you are one of those who think ‘the impossible turn’ is worth a try, following an EFATO (engine failure after takeoff). And finally, if you are one of those who fly VFR on top until all the holes have closed up, and you then find a vertical tunnel that looks like a lift shaft, this might just get you down the hole safely.
Personally, I think the last two – the EFATO and the lift shaft – are extremely dodgy. Trying to turn round following an EFATO has killed more pilots than you can shake a stick at.
And the lift shaft is particularly dangerous because it might go all the way down to ground level – leaving you nowhere to go when you get there. Or it might dump you in a valley amongst the mountains. Or on the surface of the water.
I had been instructing at Oudtshoorn and was returning to George, on the south coast, in the late afternoon when I got suckered into this situation. I knew there was no high ground because I could see 6000 ft below me. I banged on carb heat, hauled off the power and did my nice SAAF type lift shaft operation. As I neared the bottom I realised the cloud was on the water. There was no way into George.
This meant a 6000 ft climb in cloud in growing darkness and diminishing fuel to get me back to Oudtshoorn, on the far side of the mountains, with a hope that someone would see me and switch the flare-path on. Not clever.
There’s also a good chance the lift shaft closes halfway down. Or maybe it’s too tight and you fly into the cloud. If this happens, you have to suddenly go on to the clocks while in this vertiginous attitude – there you are, even the word is dizzy-making.
If this happens you must get the wings level immediately, then think of an intelligent heading to use – on a directional gyro that has probably toppled and a compass that is swinging wildly. Actually you want to put the bug on this back-door heading before starting the manoeuvre – and hope the instrument doesn’t topple.
If you think I am not a fan of turning back from an EFATO, or flying VFR on top, you are dead right and deserve two gold stars in your homework book. But I’ll tell you what – try the 60° gliding turn some time. You will realize why military pilots have a reputation for good handling skills. And, by the time you have got it right, you will have improved your own stick-and-rudder ability immensely.
Anyhow, let’s get to the basics and keep all this dramatic stuff for a time when you are flying a strong aircraft and you have a strong stomach.
If you are writing instructor exams, you may be asked to explain why an aircraft in a gliding turn tries to level its wings, while one in a climbing turn tends to steepen its bank. It’s not simple to justify, even if you know the theory. However, I have told you that the stairal-spirecase explanation works fine for gliding turns.
Well that’s the theory of it. I have to tell you that, in practice, this doesn’t seem to work in ordinary little Cessnas and Cherokees in the circuit. But there may be a reason for this. The 100 series Cessnas don’t have rudder trim, and with the Cherokees, you are too busy to keep re-trimming the rudder, with every power change round the circuit – so you leave it pretty much neutral.
Anyway, let’s have a look at this descending turn in the circuit – the base to final turn – so it’s going to be a left-hand turn with little to no power. And as you throttled back you should have used some left rudder, but you are so busy judging your approach, looking for other traffic, setting the flaps, and calling ATC, that the rudder takes a back seat.
In other words, you are entering a left hand gliding turn with some right rudder.
As long as it is only a bit of right rudder, and the turn isn’t too steep, and you maintain airspeed, all is well. But let the turn steepen up and you could be in trouble. Perhaps you had a tailwind on base and you have overshat the centreline, causing a dreaded hammerhead. Or you are lower than you thought, so you start easing back on the stick and running out of airspeed. Or you are having to use more left aileron to correct for your lazy left leg which should be holding some left rudder. You can see where this is going – you are setting yourself up for a low level spin, from which there is no recovery.
Did you have to hold the left wing down to counteract the hand-rail effect? Not really, that tendency is so little that I suspect it is counteracted by the increased airspeed on the outer wing. Put it this way – although it is in the text-books for exam purposes – I have never been able to demonstrate it, with the ball in the middle.
But that’s the kicker – having the ball in the middle.
If it’s a classic hammerhead causing a base to final spin, the ball is never in the middle – it’s way out to the right because you are trying to horse the aircraft round the turn by standing on the left rudder and counteracting this left roll by using right aileron.
In summary – there’s nothing dangerous about a gliding turn. But it becomes very dangerous if you run out of airspeed with the ball in the corner.
What else is special about gliding turns? Not a lot. But letting the airspeed decay is a common fault – and potentially dangerous. This is particularly the case in slow aircraft where the gap between glide speed and stall speed is minimal.
If you are instructing on an aircraft that has glide and climb speeds of 60 mph or less, it’s a very good idea to have your pupes increase their airspeed by 5 mph before entering a gliding or climbing turn.
This has two benefits:
The aerodynamic ones we have just looked at, and perhaps more important, it gives your pupe a lifelong awareness of the dangers that lurk around low speed turns.
Climbing Turns
Now for a climbing turn – particularly in the circuit. This is an interesting animal.
Think about the stairal-spirecase again. This time you are going up one that turns to the left (for left hand circuits). It’s very obvious that the inner wing – the left one – is going up at a far steeper angle than the outer wing. In other words, its angle of attack is reduced by its upward movement. The same obviously applies to the outer, right wing – but to a far smaller extent.
The result is that the aircraft will tend to bank to the left, and this tendency will increase alarmingly if you let it do so – because the turn will tighten up.
Further, if you are an average sort of pilot, you will not be using enough right rudder to counteract the ‘P’ effect, and this will cause a climbing left turn to steepen up.
Instructors, this overbanking in a climbing turn is easy to demonstrate, even when you use enough right rudder to keep the ball in the middle.
Incidentally, while you are sitting on the ground, you can spot an inexperienced pilot. Early in the takeoff run you will see the aircraft heading towards the left of the centreline, and you will notice the right aileron going up as he tries to correct the problem with the control wheel. As he rotates it will twitch a bit more to the left as he loses nosewheel steering. Then, when the mains leave the ground, the aileron will take effect and the right wing will drop.
Instead of tracking along the runway centreline the aircraft will head off 10° or 15° to the left because he is still not using enough right rudder. The left turn onto crosswind will indeed be steeper than it should. This is partly due to the ball being out to the right, partly due to the banister effect, and partly due to the right wing travelling faster than the left one.
Does this all sound a bit theoretical? Then wait until they change the circuit and folks are turning out right. You will see some very pansy turns from the newer pilots.
In a nutshell: if you keep the ball in the middle, a gliding turn should theoretically tend to flatten out, because of the increased angle of attack on the inner wing. In practice I don’t think this works, on our little aeroplanes anyway, because the extra airspeed on the outer wing gives more lift and this compensates for the extra lift on the inner wing.
However in a climbing turn, the theory tells us it should steepen up because of the reduced angle of attack on the inner wing. And it does indeed do so because this is assisted by the increased airspeed on the outer wing.
And now I must briefly touch on the most debated subject – the dreaded dragons of the downwind turn. Why now? Because it is the most dangerous and most common problem with climbing turns just after takeoff.
No, the Gleitch won’t give me the space to cover that subject here again, but I’ll just touch on the basics – because it is important and it falls under the heading ‘climbing turns’.
A climbing downwind turn soon after takeoff is a cowboy thing to do. There are some complicated reasons for this – three reasons actually. One is the aerodynamic side which says that a steady wind has no aerodynamic effect on an aeroplane in flight. In the same way that a bee in a train is unaffected by the speed or direction of the block of air in which it is flying.
The problem here is that you don’t get a steady wind after takeoff – the wind increases as you climb. This is due to surface friction caused by grass, bushes, trees, hangars and so on.
The second aspect is that there are some very real aerodynamic hazards if you relate the aircraft to the geography of the place. For instance you will have a good angle of climb, for obstacle clearance, while you climb straight ahead into wind. But as soon as you turn downwind your angle of climb decreases – possibly to a dangerous degree – even though your rate of climb is not affected by the wind.
But there are exceptions to this rule – if your climbing turn takes you into the lee of a hill, for instance – then you may get into a downdraught and might be in serious trouble. Or, if your climbing turn takes you through windshear, which it almost always does – then your bank may increase alarmingly. This is because the stronger wind above the trees and hangars tries to take the upper wing over the top.
The final aspect is that there are two apparent effects which can really spoil your day. First, if you turn say left, imagine what the ground seems to be doing half way round the turn. It is moving under you from left to right. In other words it feels as if you are slipping to the left – into the turn. To cure this you will find yourself using left rudder. This, of course, causes the aircraft to bank further left, and you naturally use right aileron to cure the problem. Do you see where this is leading? Crossed controls at low airspeed near the ground – a spin is not far away.
Unfortunately the second apparent effect aggravates this. As you turn downwind you seem to be going faster so the obvious thing is to ease back on the stick – which, of course does your airspeed no good.
Finally, because your angle of climb is so poor, you get the feeling that you may not clear the trees, wires, hangars etc, so you ease back some more.
No wonder even experienced pilots get eaten by the dragons of the downwind turn.
There are two ways to protect yourself from the horrors of this seemingly innocuous manoeuvre: first: Don’t do it. And second: If you must do it, glance at your airspeed and the ball. If either is wrong fix it, but don’t fixate on it, lest you feel hot dragon breath on the back of your neck.
Finally, don’t forget to try that SAAF-style steep gliding turn. Give yourself plenty of height and be prepared for the airspeed trying to run away.
Have fun and fly safely.