ESSAY, PART 3: Landing and stopping. - ED Forums
 


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Old 12-21-2016, 08:53 PM   #1
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Post ESSAY, PART 3: Landing and stopping.

So here's part 3 of my conscious stream...

Taming Tail-draggers Part 3 – Landing


Landing a tail-dragger is no more difficult than landing a nose-wheeled aircraft. Maintaining control afterwards however is another story all together. Before we go any further, I’d like you to remember this: ATITUDE, ATITUDE, ATITUDE. Then I want you to remember: FEET, FEET, FEET. Then finally: TRIM, TRIM, TRIM!

When you’ve got that, carry on reading…

Essentially, there are 2 kinds of landing technique which are best suited to this configuration:

1. The three pointer, the one which most of you are already pretty familiar with and...
2. The wheeler. Wheeler landings are performed on the main wheels only, until such point in your landing roll where you lower the tail onto the ground before decelerating to a stop. Of the two, it is generally considered that the wheeler landing is the more difficult to master, at least to a point where it becomes a useful tool for the pilot. More about that in the next part.

Let’s start with the 3 pointer. Every good landing starts with a good approach. Nay, every good landing requires a good approach. Look at it like this – for the duration of your landing approach, always assume that you’re going to “go around” at the end of it, then only actually land if everything is perfectly balanced and in harmony. Sounds obvious but one of the leading contributory factors in landing accidents is a failure to go around when appropriate. I’m not going to go into detail about how you approach, but I am going to assume that you can fly an approach in the correct configuration, on a suitable glide path and at the correct speed.

This is where trimming the aircraft correctly comes into its own. Nearly all pilots are guilty to some extent when it comes to failing to trim their aircraft accurately. You may not think it’s a big deal but it really is. If you’re a bit out of trim, you probably think to yourself “it’s only a bit of stick force, I’m just going to compensate and hold the stick where it is…” Nothing could be more wrong. Imagine, during very delicate phases of flight, landing being one of the most poignant, you are required to make some very slight and gentle inputs. If you are to avoid over controlling, then those inputs should amount to little more than pressures. The majority of those pressures are likely to be less than the equivalent pressure required to compensate for a slightly out of trim airframe. Therefore, if you’re already applying a larger pressure to the stick than the small inputs you’re trying to make, you’ve basically got no chance of succeeding to the level of accuracy required.

Here's another very important point: Your aircraft should be so well trimmed during your final approach, that you ought to be able to hold the stick still, moving only occasionally to correct for small bumps or other minor displacements. This also means having the power set correctly, and not jockeying the throttle up and down continuously. Every time you change the power setting, you need to re-trim. Simple. If you’re having to do much more than this, then you’re not stable and not configured correctly. There is simply no substitute for accurate flying.

Over the years I have sat next to countless pilots on approach, stirring the controls around like they’re trying to unblock a toilet full of elephant dung. All of this in calm stable weather conditions. When asked to remove themselves completely from the controls, the aircraft settles down and flies smoothly down its approach course. What they didn’t realise is that they were putting nearly all of their effort into fighting their own over controlling inputs, whilst assuming they were actually doing something useful. I suspect that some of them even felt that doing this in some way makes them a better pilot because they’re having to work so hard to control the beast. It’s not just pilots in smaller aircraft either, have a hunt around on YouTube and I bet you’ll find plenty of airline pilots doing it too! Even in really turbulent approach conditions, there’s simply no need for it. You can’t possibly react to that many course and attitude corrections in such rapid succession, so you may as well ride it out and correct half as many times. My old flying instructor (who was a less than charming Kiwi) used to shout at me “If you grip like a w****r, you’ll fly like a w****r.” As much as I despised him, he was right.

Undoubtedly, in an aircraft with a Barry Manilow sized nose (such as the Spitfire) your field of view forward is limited, which limits the useful visual cues available for correcting drift and ensuring runway alignment. So, you have a number of choices: A steeper, close-in curved approach, or a crabbed, side slipping approach. Of course, you can fly straight in without crab, if you feel so confident and it works for you, carry on. In aircraft like the Spit though, curved is undoubtedly the way to go.
Remember, you have plenty of runway, so if anything, stay on the side of “a bit too steep” during your final turn to aid field of view. The Spitfire is very draggy in the full landing configuration, which makes life a little easier. If you are too shallow, you’re entering a whole world of pain which no amount of accurate flying will overcome, so just don’t do it – you’re not landing a 747.

Fast forward to the threshold. Most people’s tendency is to cross the runway threshold going too fast. +/- 5 kts can make all the difference, so don’t be complacent and work on your accuracy. The only way you’re going to get good at this is by being pretty brutal with yourself about constant trimming and a stable descent. There are no shortcuts – accept nothing but complete accuracy and once it becomes second nature, life will be sweeter! This guide is fairly generic, so I’ll avoid exact numbers because all aircraft differ, but about 100mph over the threshold is a good starting point. Be clear though that I mean OVER the threshold, we’re not landing yet.
So what attitude must we land the aircraft in? Well, the 3-point attitude of course. If you want to know what this looks like, look out of the window when you’re in the cockpit, stationary on the ground. That’s it. Nothing more, nothing less. Unlike a tricycle wheeled aircraft where the actual landing attitude at touchdown may throughout a significant pitch range, in the case of a tail-dragger executing a 3-pointer, there is precisely 1 attitude.

As you cross the threshold you must have cancelled, or be about to cancel ANY drift (meaning lateral movement relative to the runway as relates to the centre line). You must only be travelling ALONG not across the runway. Landing with drift is like releasing a jack-in-the-box. There are various ways of ensuring you have no drift but essentially they all involve looking out of the aircraft and assessing it visually. The slip ball can be helpful, but only earlier in the approach, as you certainly do not want to be looking inwards in the final stages.
As you are crossing the threshold, you should be decreasing your power ideally to idle and maintaining a very gentle descent. As you decelerate, the diminishing airflow over the wings will result in decreasing lift. Therefore, in order to maintain a constant descent rate, you will need to coordinate this deceleration with a constant increase in Alpha by progressively raising the nose.

Now then, if your threshold speed was correct, and the height at which you started reducing the power was about right, and your chosen rate of descent is spot on, and your rate of pitch change is perfect… all things being equal, you should have made the transition into the 3-point attitude at the precise moment where your descent intersects with the runway and the throttle hits the idle stop!

That’s the theory and it’s a lot of “ifs” isn’t it? Yes, it is, but that is how it’s done. Now, I can’t tell you how to do this because it takes practice, experience and a certain amount of trial and error. However, what I can tell you about is some of the factors which come into play that may put a spanner in the works. Incidentally, I going to assume that we’re dealing with zero cross wind. Namely, because in a simulator we can elect to keep the wind out of it while we’re learning. In any case, you have no business trying to learn how to land or take-off in a tail-dragger with any significant cross wind component. It’s fairly futile.

I’m assuming you have a little power applied during your crossing of the threshold, but it’s not mandatory depending on how you have elected to make your approach. However, a little power is a good thing because it keeps your control surfaces alive.
So, some things to be aware of:

1. Getting on the ground is the first bit. Keeping it on the ground and more importantly, on the runway, is the second. Once your wheels have touched down and you’re apparently rolling along nice and straight… THAT’S when it’ll bite you hardest. Do not relax until you’ve stopped.

2. WAKE UP YOUR FEET! Remember this from part 1? You need to relax and get your feet ready for those quick dancing moves. Tense feet means slow rudder inputs and lack of dexterity when you need it most.

3. Make all of your power changes very smoothly. Every increase or decrease in power setting will cause swing/yaw/drift to develop. It will also cause slight pitch changes which equate to trim changes. Use the throttle but do so smoothly and progressively, trimming all of the time.

4. At threshold speed, any movement of the ailerons will cause significant adverse yaw (yawing right for a left aileron input and visa-versa). This will in turn cause drift and lateral misalignment. Make sure your wings are level as you cross the threshold and try to avoid the use of aileron other than tiny inputs to prevent any rolling tendencies.

5. Be aware that the REAL 3-point attitude is often slightly nose higher than you may think as you touch down. This is because you’ve spent the last few hundred feet flying relatively nose down, so the transition to a 3-point nose high attitude can be alarming.

6. Following on from point 5 – If you don’t get the 3-point attitude exactly right, it’s better to land slightly tail first than main wheels first. Why? Well, because as your tail-wheel touches the ground first, the downward momentum of the aircraft is acting around the centre of gravity. This remember is situated behind the main wheels and in front of the tail wheel, so it will form a moment arm which will bring the main wheels down for you. Provided you don’t allow the tail to bounce up in the air again, or land so hard on it that you break it, you should be fine.

7. Bouncing – Bounces are caused by the main wheels touching first without any further corrective control inputs to counter the effect. The effect is the reverse of landing tail first because this time, the downward momentum of the aircraft’s mass acting on the centre of gravity will serve to bring the tail down, pivoting around the main gear. The result is an instantaneous increase in Alpha, causing an immediate increase in lift, followed by you getting airborne again. Many people assume this bouncing is due to the main wheels “springing you back into the air”, but it’s almost irrelevant. You now have only 2 choices…

8. If it’s a significant bounce, smoothly apply power, rudder and aileron to counteract the swing and/or roll. Adopt your normal climbing attitude and climb away for a go around. Trying to rescue a large bounce is pointless, and you’ll feel dirty even if you manage to pull off a survivable landing out of it.

9. For a small to medium bounce, don’t touch the throttle. Simply ensure that you’re still flying straight by using corrective rudder, and then, most importantly, RESET THE 3-POINT ATTITUDE AND HOLD IT THERE! I shouted that bit because it’s crucial. Most pilot’s instinctive response to a landing bounce is to start stirring the stick around wildly because it makes them feel as if they’re taking control back. You’re not, and the reason I know this is because if your speed was even nearly correct, then you’re not properly flying, you’re following a ballistic trajectory back towards the ground with some (but not much) aerodynamic help. Large macho control inputs in this situation are likely to end in over control and tears. Definitely tears. If you simply set and maintain the 3-point attitude and don’t do anything else, the aircraft WILL land. It may not be a greaser, but the chances are that you’ll be down on all 3 wheels.

Right then. Let’s pause for breath. We’ve got the thing on the ground, and all 3 wheels are turning. Now you have to stop it. All of the non-power on related factors which can cause a swing (and inevitably a ground loop) are now lining up to have a pop at you. Asymmetric braking, runway surface, pilot input, puddles, uneven grass lengths, some residual gyro effect from the idling prop, plus a whole heap of others which by now, you should be convinced exist. Some of these will increase in influence as you decelerate, and some will decrease. What you must remember though is this… As you decelerate, the aircraft’s interaction with the air around it changes, meaning that all of those lovely things which help you to maintain directional stability when a large volume of air is passing over the aerodynamic surfaces, including the fuselage itself, are fast becoming ineffective and frankly, useless.

This is why the biggest “gotcha” is saved for the time when you least expect it; namely when you’ve slowed down, and you’re patting yourself on the back. THIS is the time where you have the least control over your direction, yet you still have sufficient momentum to bend a lot of metal. How many times have you made a reasonable landing, slowed down nicely, only to tip a wing and go bumbling off the runway edge at a speed no more than you could run at? The problem with this kind of departure in the real world is purely that of repair bills and embarrassment, and believe me, no repair bill in the world can equal the pain of embarrassment like that!

Think about the aircraft a little like a car pulling a trailer. Imagine the engine is the car and that the mass of the aircraft, acting at the C of G is the trailer. When you have power applied and other factors are roughly in equilibrium, the car (engine) is towing the trailer (aircraft). Happy days. When you close the throttle, the propeller is no longer pulling the aircraft (trailer). In fact, it’s doing the opposite and creating lots of drag. That’s like applying a good boot full of brake in the car. What happens when you brake in a car that’s towing a heavy trailer, and the trailer has got a bit sideways? The answer is that it wants to ground loop your car and trailer rig. It’s a bit like that during your landing roll out, though your idling prop isn’t creating as much drag as it would in flight under the same circumstances, the ground interaction with your undercarriage IS creating a lot of braking force before you even apply the brakes. Therefore, if your C of G manages to get even 1 degree out of alignment with your direction of travel, it will excerpt a force that creates an arm which wants to swing the aircraft around. As with all swings, the further it goes, the faster it will go because the length of that moment arm increases as the aircraft swings further.

So, what can be done? As always, here are a few pointers to chew on. Possibly not a comprehensive list as every aircraft, situation and day is different, but practice these things and you’ll be on your way to mitigating the lion’s share of the risk.

1. Keep the control column FIRMLY at the back stop. This assumes your tail is already on the ground by the way! The effect of full aft stick increases the rolling resistance of the tail-wheel. As the tail-wheel is behind the C of G, it serves to greatly increase directional stability. It’ll also help prevent the tail from bouncing should you hit bumps, but that’s something more likely to happen in real life rather than our simulator.

2. Keep off the brakes for as long as you can. As a rule, tail-draggers are pretty aerodynamically draggy when they’re on the ground in the 3-point attitude. Remind yourself of why you carry out aero-braking in the fast jets after touchdown, and that pretty much sums up the situation here. Unless you’re landing on a very short strip, or indeed at the wrong end of a long one, then you probably won’t need to brake at all in reality. Braking is fundamentally risky because it is one of the leading causes of asymmetric force likely to provoke a ground loop. Add to this your tense, nervous legs, and likelihood is that you’ll be harsher than you intended to be. This is an area where real life trumps the simulator for 2 reasons – mainly because it’s much harder to judge your longitudinal rate of deceleration without a positive physical cue and secondly, only the very most expensive simulator rudder pedals you can buy can provide a lifelike feedback to braking pressure.
Here’s a tip: Adjust your pedal saturation to provide only roughly 70% of full braking when your toe brakes are at maximum travel. That way you can step on them a lot harder without inadvertently applying too much braking force. It also provides greater resolution enabling you to modulate the input more easily. The effect also makes it FEEL like you’re pressing harder, which is a bit more realistic. You’ll have to play with the values to suit your setup, and it might not be for you anyway, but it’s worth a try even if you don’t have any issues. I don’t recommend it for the jets, but for a tail-dragger in which you’re unlikely to ever be braking as hard as possible, I find it works well.

3. Don’t let a wing drop! As you slow even more, the ailerons become completely ineffective, particularly in the absence of any inboard flow courtesy of the propeller. Without the balancing and damping effect of more airflow across the wings and ailerons, the centre of pressure will move inboard, making the aircraft much less stable in roll. Then, you have a situation where you effectively have two long levers sticking out from each side of a trolley riding on two very narrow and closely spaced wheels. It’s not difficult to imagine why the wingtips are dying to snog the ground. If your wingtip does touch the ground, momentarily apply full rudder on that side and full brake. That’ll help lift it up. Most importantly, make a face like you meant to do it and hope no one saw it!

The rest, my friends, is up to you. Practice circuits and full stop landings as much as you can. On most of DCS’ runways you can easily come to a stop then start another take-off run. Do it over and over until it’s easy, but when it feels easier, don’t relax! Do touch and gos too if you like, but they’re nothing like as useful because they bypass one of the most difficult phases.

By the way, if anyone can suggest a good way of capturing a decent video whilst flying with my Rift, do let me know and I'll try and do some demos when time allows. I'd do it with replays after the fact, but they seem to be a bit broken with the Spit at the moment.

Happy landings!

CFI
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Old 12-22-2016, 02:23 AM   #2
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Another master class! great info, thank you
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Old 12-22-2016, 03:42 AM   #3
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Very informative and entertaining. Thanks.
Yes there are some less than charming Kiwi instructors. Hey I probably even know of him seeing that everyone here knows everybody else here, in Kiwi aviation.
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Old 12-22-2016, 03:52 AM   #4
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wow thank you
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Attitude Power Trim Power Attitude Trim

Wing Commander SWAC
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Old 12-22-2016, 05:58 AM   #5
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Just like I do it in real world, and in DCS. Good job!
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Old 12-22-2016, 06:11 AM   #6
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Great read! Thank You!
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Old 12-22-2016, 08:22 AM   #7
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Thanks very much Chief, I'm very much a novice at all this flight sim malarkey, and I've found your three essays very useful to understand what is happening to the plane under various conditions. I've pretty much learned to fly sim planes through trial and error, and there are often times just like you describe here when I wondered how on earth I'd managed to crash after finally landing the thing and barely going jogging pace and the blimmin thing flips over for no apparent reason. Now I know there is a very good and logical reason, I can try to keep it in one piece.

Thanks to you and the Wags video, I can now get the Spitfire in the air on most occasions, and I can just about get it on the runway on three wheels. Next task is to stop it flipping over at the end but I'm having fun doing it.

It's very much appreciated that you and the other experienced flyers are happy to share your knowledge here, thanks again.
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Old 12-22-2016, 08:33 AM   #8
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Quote:
Originally Posted by Chief Instructor View Post
This is why the biggest “gotcha” is saved for the time when you least expect it; namely when you’ve slowed down, and you’re patting yourself on the back. THIS is the time where you have the least control over your direction, yet you still have sufficient momentum to bend a lot of metal. How many times have you made a reasonable landing, slowed down nicely, only to tip a wing and go bumbling off the runway edge at a speed no more than you could run at? The problem with this kind of departure in the real world is purely that of repair bills and embarrassment, and believe me, no repair bill in the world can equal the pain of embarrassment like that!
Thanks again Chief

This was exactly me on one of my first test flights! Stopped flying right at the last moment LoL. My excuse I was trying to get a good video shot


https://www.youtube.com/watch?v=BAG1v3z3ar4
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Old 12-22-2016, 09:19 AM   #9
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Thanks Chief Instructor.
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Old 12-22-2016, 12:02 PM   #10
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Another master piece. Thanks for your time .


S!
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