Advanced Landing

Having Trouble with Your Landings?

(note - I originally wrote this piece in September 07 and then revisited and basically scraped most of it 2 months later when I realised what I had written was wrong and misleading. It just goes to show it's never to late to learn something new, or to figure something out properly - thanks to Loco Builder, Ground Dancer and Manu for your help in showing me the error of my ways)

As you move into more challenging models, and particularly things such as warbirds you may find that your landings go back to being somewhat hit and miss affairs.

Well - it takes a lot of practice and not every thing can be fixed in one article, but perhaps I can give you the information you need to make them better.

Why landings go wrong

From a beginner's perspective there are a number of reasons. There is a lot happening all at once, challenging the beginner's ability to keep up with all the controls. There is the natural (and healthy) fear of the ground, and fear of stalling. But if I had to pick one thing that was the biggest issue (for myself, and for others I have observed) it is people trying to land the aircraft using the elevator instead of the throttle, and not understanding what is going on at landing time.

The aim when landing is to touch down at a speed where level flight is no longer possible, but the aircraft has not yet stalled.

Almost all landing issues, once basics like keeping wings level are under control, comes down to arriving at the landing point at the wrong speed. Either too fast, or too slow (usually too fast).

Any pilot with a little stick time can make an aircraft meet mother earth at a designated point. The challenge for landing is to arrive at the right speed and attitude to allow landing to happen.

Stop using that elevator

No doubt you have heard the landing axiom - "Elevator controls airspeed, Throttle controls rate of descent". If you are using the elevator to push the nose down for a powered approach you are doing things the wrong way.

Why does it matter? Because when you use the elevator to dive the aircraft you pick up airspeed. And this means that when you arrive at the ground you will be traveling too fast for the plane to settle and land.

Now, if you use the throttle to control your descent (by setting it low) the aircraft will naturally have a stable speed suitable for landing. Now you use the elevator just to stop the aircraft from stalling. If it goes too slowly just ever so slight nose down. If it goes too fast, just ever so slightly nose up.

Ground Effect

What is it? Very simply, it is the air that your wing pushes down towards the ground as it moves through the air bouncing off the ground and coming back up to produce some extra lift.

It typically kicks in at about one wing span from the ground, so for parkflyers that is very close to the ground indeed. However, it does vary somewhat depending on how much lift you are producing, and the surface you are flying over (so concrete will create more ground effect than grass).

Ground effect is one of the reasons that the novice's landing touch downs are often beyond where they planned (of course the main reason is arriving with too much airspeed). When the plane hits ground effect it suddenly has extra lift and flys a bit further than intended.

In slow flyers this isn't so much of a problem, but in faster planes with a limited runway length it can be an issue.

The important thing about ground effect is trusting that it will happen. Provided your rate of descent is reasonable, at a controlled airspeed, and that you will have time to react once the plane is in ground effect you can even let her come down a fraction faster - she will soften out at the last.

When working with faster models and restricted runway length you need to plan for the extra glide your plane will get from ground effect. Aim 5 metres short of where you wish to touch down as a starting point, and adjust as you come to know your model (because some models will fly further than others when they hit ground effect).

The Landing Angle of Attack

The landing attitude is the slight nose up attitude that every airplane (provided it has undercarriage) needs to achieve before it touches down.

Learning to put your plane into this nose up AOA for approach, will, in one step, dramatically improve your landings.

First a little theory. A positive angle of attack to the airsteam has two very valuable flow on effects for landing. The first is that as well as aerodynamic lift (the lift achieved from the shape of the wing and the Bernoulli principle) we are also getting induced lift. Induced lift is the reaction to the airstream striking the angled wing bottom and bouncing off. This “collision” gives the plane a little more lift.

The second thing we get from this angle of attack is induced drag. The airstream striking the bottom of the wing also slows the plane down with more drag. The diagram at the right tries to illustrate both of these concepts.

So, at the moment of landing – an upward angle of attack gives the plane the most lift it can achieve at it’s slowest possible speed, and also acts as an airbrake. Also, it gets the plane's attitude set up so that its landing gear works properly.

This leaves only one problem – stalling. At such a slow speed with the extra induced drag, stalling is a real problem. To hold the nose up AOA you need to run the motor fast enough to stop the nose from falling, but not so fast that you start to climb (if you start to climb the airstream starts hitting the wing head on again, rather than striking the bottom of the wing).

Many of the problems that pilots have with landing is because they try to enter this nose up angle of attack too late (they try to do it all in a last minute flare half a metre from the ground). If you have too much airspeed you wont enter a nose up AOA (relative to the airstream) – you will just pull up, gain altitude, stall, and if you aren’t back on the power by now, come down hard. If you have too little airspeed the nose will not come up, and you will go in with the nose down normally leading to a nose over landing at best.

The trick is to get into your nose up AOA well clear of the ground, get your speed stabilised, your throttle correct, and bring your plane to the ground in this nose up AOA.

Once you get your plane into this attitude a successful landing is almost assured (provided you keep the wings level and manage the throttle). Why – because to fly in this attitude your airspeed has to be about right for landing, you stop worrying about your elevator (you just hold it in the position required for nose up AOA), and use one up and one down clicks of the throttle to make the plane run a bit further, or a bit shorter, on approach.

The nose up attitude approach can only be achieved with power on, as the power prevents the plane from stalling.

Getting Into the Nose Up AOA

Practice this at some altitude before you try it on an approach.

Close the throttle and use the elevator to keep the plane at a neutral AOA. As the plane loses speed start to add a little more elevator and hold it. Add a few clicks of throttle so the motor is only just running (or maybe a click or two more, but not much).

If you get the timing on this correct your aircraft will have its nose slightly up, will be flying just above stall speed, and will be either maintaining, or slowly losing altitude. You will be holding almost full up elevator (in low rates. Full up in high rates will stall her!).

To make the plane lose altitude faster – one less click of throttle. To make the plane lose altitude more slowly – one more click of throttle.

Hold the aircraft in this position – although you wouldn’t want to turn she is otherwise perfectly stable, and could be flown all the way to the ground in that attitude.

The Trouble with Simulators

Now, before you rush off to try this on FMS to see if it works, I have some bad news for you. The physics model in FMS is not good enough to accurately represent this. It is modelled accurately in other simulators (such as Clearview and no doubt Real Flight etc) but FMS will not do it.

So you either need a new sim, or you need to try it with the real thing (which would be my suggestion).

Check Out That Approach Speed

If you have a faster model, like a warbird or such, you are probably quite used to the juggling act of keeping the speed up enough to be happy she is flying, but trying to get her slow enough to land, and also stop before the end of your runway.

You will probably be amazed at how slowly you can get a plane to approach when you get it into the correct nose up attitude.

I was amazed when the first time I correctly landing my Zero using this technique – into a gentle 10km/hr breeze she rolled out 4 feet whereas normally I would expect around 10-15 feet.

Different Planes Achieve Different AOA

Although almost all planes are capable of the nose up AOA approach the degree to which they do it does vary. With practice you will figure out what each of your models is capable of.

How is this different to descend, flare, land?

The difference is that we put the plane into the nose up attitude while we still have height and distance to correct a mistake, rather than trying to achieve it just perfectly half a metre above the ground while the plane rapidly uses up runway still in the air.

The problem I was having with this approach was there was just too much to do right at the last moment, and for my faster models I was miscalculating their approach speed (they normally arrived too hot).

So, rather than trying to achieve the nose up AOA at the last moment now, I set the plane up for it while it is still 2 or 3 metres off the ground giving me plenty of time to allow for mistakes, correct, etc.

Also, as mentioned - the nose up AOA naturally gets your model's airspeed about right for landing.

So What About Gliders/Belly Landers and Others

Belly landers all tend to be different beasts in this regard. You don’t land them on power, and although you could use the nose up AOA to achieve the slowest possible approach speed, you tend not to worry about it so much.

Also, they are more forgiving of a neutral AOA at landing – they don’t tend to nose over the way that tail draggers in particular do.

Warning about banking at landing speeds

Be very careful with banking sharply at landing speeds. As you probably know (and if you don't check out these aerodynamic basics) when your wings are level all the lift is acting against gravity. When you bank your wings some of the lift acts against gravity, and some pulls the plane into the turn.

That's fine when you are cruising, but when you are at landing speed in nose up AOA you have basically no lift to spare. All your lift is required to keep your aircraft in the sky, and stop it from stalling. Generally you can drop a wing tip 10-15 degrees to make slight course corrections, but if you go much beyond that your plane will drop out of the sky in no time flat.

If you need to make a close turn at low altitude onto final then let your aircraft descend under moderate power (less than cruising, where you just start to lose altitude). Try to minimise the angle of the last turn. Never more than 90 degrees, ideally more like 45 degrees. Bank (no more than 45 degree wing angle), set throttle for landing, get into nose up AOA, land.

Don't setup nose up AOA before your last turn - you will stall and crash.

If you are going a bit fast entering this close final turn, then have the throttle at landing position when you make the turn or maybe even closed. But remember at this speed it is really easy to lose a meter or two of altitude (or even stall), particularly with no power.

The Technique of Landing

Fast models - high wing loading

Examples: warbirds (with undercarriage), parkjets, advanced trainers (PC9, Tucano), etc.

Fast models like warbirds, parkjets, many aerobats, often have unforgiving stall characteristics, and need to fly quite quickly to stay airborne. If you dive them they will pick up and keep quite a bit of speed.

The first thing about landing a fast model is how much more space is required for approach. If you are pressed for space, particularly with respect to your preferred approach angle, then plan a turn onto final at only two to three metres altitude (with enough airspeed) - this will allow you to finalise your approach speed.

1. As you enter your turn onto final minimise/cut your throttle.
2. Feed in elevator as the plane starts to slow down, and as she gets close to stalling add a few clicks of throttle.
3. Adjust the amount of throttle to reach the verge (one or two points more to go further, one less to pull up shorter).
4. Fly into ground effect – add one more click of throttle if rate of descent is still too fast after hitting ground effect.
5. Hold until touch down (three pointer for tail dragger, rear wheels for nose wheel).
6. Close throttle.

If you want to learn how to land fast models nothing will teach you like a warbird with undercarriage. With the undercarriage only slightly in front of the centre of gravity a warbird landing has to be perfect or it will nose over.

Don't beat yourself up too much if landing on grass your warbird rolls out the first 50 cms without nosing over, but then does a somersault. That wasn't you - just the grass catching your bird as she slowed down. The effect is basically unavoidable, although I hear bigger wheels can help.

High Drag/High Lift Flyers

Examples: Tigermoth, Estarter, Typhoon

Compared to faster models high drag/high lift flyers tend to have a much wider envelope of speed and throttle settings which will allow a controlled descent for landing. This has the effect of meaning that you can, when it suits the conditions, vary the angle of approach to suit the surrounds of your landing strip quite a bit.

The high drag acts as a natural airbreak if you go for a steepish angle of approach keeping the model's speed down. But of course you can go for a long flat approach if you wish.

Ground effect tends to be less pronounced on slower models.

I find the high lift/high drag models are easier to get into this positive AOA, and it can be left till later in the landing sequence, but there is no reason it can’t be done earlier just for the sake of practice.

Belly Landings

Examples: PZ Warbirds, Styker and other Deltas, and model without undercarraige.

Belly landings are generally easier than landing on wheels, but they do put models at some risk as it is important to minimise the landing speed more so than a model with wheels landing on a good surface which will tolerate a certain amount of extra speed.

Depending on the aircraft, but for most, belly landings are best done as dead stick affairs. However - the approach can be powered if you prefer (this tends to work better for belly landing warbirds).

1. Either throttle off, nose down slightly below the glide curve (so picking up just a little bit of speed) or Set throttle for powered descent.
2. Fly to ground effect - you may or may not feel it depending on the model. Time to close the throttle if it is still open.
3. Begin flareing at 50cm (foot and half) aiming to level out at 15cm (6 inches) or slightly lower if you can manage it.
4. Feed in more and more elevator as airspeed drops off. Make sure you don't feed in so much elevator that the model begins to climb.
5. Eventually the model will not have enough lift to stay airborne and will sink the last 6 inches.

So why is say a belly landing on a warbird different to an undercarriage landing? If you don’t have a nice positive AOA at contact your undercarriage bird could flip. Belly landers aren't going to have that problem.

Landing in Heavy Wind

This is covered a little in the beginner's notes, but deserves a refresher.

Your strategy will be somewhat determined by just how strong the breeze is. So, let's discuss three broad scenarios. In all cases we are assuming you are landing into the wind.

Fresh Breeze

The breeze is less than 1/2 your models stall speed (I know that is hard to gauge, but you do get a feel for these things).

Your approach and landing should be just as laid out above. The length of your approach will be shorter, although the starting altitude will be around the same.

In many ways, landing fast models in a fresh breeze is much easier than with no breeze due to the reduction in landing distance. Aim to put your fast model on the verge rather than 5 metres short of it.

Stiff Breeze

The breeze is up to around your model's stall speed.

Here's the key things to keep in mind about a wind of this sort of strength:

• Angle of Attack is Everything - if you have your nose down the wind will strike the top surface of your wing and push you nose further down. If you have nose up the wind will strike the bottom of the wing inducing a lot of extra lift making you zoom away.
• Due to the AOA issue above, if you stall the wind will exaggerate the length of recovery.
• Approach under good power making as much headway as you need to for a controlled descent. Make your descent as slow (vertically as possible). This means you have the most power you can on for the descent.
• Be careful of your airspeed - it is easy to either stall or zoom away under these circumstances as the buffeting of the model makes it hard to spot the normal indicators.
• Be aware of gusts. You may find it best to be on high rates. Be ready for one wing tip or the other to drop as a gust suddenly stalls that wing.
• Ground effect will come on a bit later, and will be turbulent, but when it does be careful it doesn't lift your nose changing your AOA.
• Power on through the entire approach all the way to the ground (closing before touchdown if belly landing). Doubly so for gusty winds.
• Use less elevator when flaring - the wind has already minmimised your ground speed - focus on keeping the AOA neutral and the rate of descent under control.
• Get off the power once you touchdown, but don't feed in up elevator to force the tail down until you are sure you have no lift.

One of the key challenges is dealing with gusts which will take your model from flying speed to stalling speed in an instant. By using as much power as we can for a powered approach we provide a buffer. If the wind drops away the model will naturally pick up airspeed in the still (ish) air either avoiding a stall completely, or at least reducing the severity. With no power when the air stops moving, and the model is more or less staionary to the ground (and now the air as well); it will just plummet.

Strong Breeze

The breeze is more than the stall speed of your aircraft.

All the notes for stiff breeze apply except that your approach needs to be above flying speed. You need to "fly the plane to the ground".

This is a tricky situation, and probably not normally one you would find yourself in voluntarily.

• Set a throttle position that gives you authority in the breeze and allows you to make a little headway.
• Leave your controller on high rates if you have the option.
• Use the elevator to point your plane slightly at the ground and begin your descent. You will probably need to hold the elevator slight down to maintain the dive and stop the plane from naturally resuming level flight.
• Try and keep your speed and angle of attack under control as you come down.
• As you come into the ground close the throttle slightly before landing.
• When flaring don't feed in up elevator merely slowly reduce the amount of down elevator you are providing. Remember, even though ground speed is low your model is well above stall speed, and it will climb probably even at the neutral AOA position. Remember, that as you change that Angle of Attack against the wind you are going to induce a lot more lift
• It is better to go in with a slight nose down AOA (provided the throttle is closed, and your ground speed is low) than to get the flare wrong and zoom up into the air. Certainly do not try to achieve a classic nose up flare. So exercise real care here, and accept a less than perfect landing in less than perfect conditions.

Gusts

Although mentioned above in each of the landing sections gusts probably deserve a bit of a special mention. Even a strong predictable breeze is relatively easy to land in. It is the gusts that tend to make things interesting.

Amongth other things, gusts can:

• Vary the direction of the wind (including inducing more lift in one wing than the other making a wing tip want to dip).
• Either increase or decrease the model's airspeed (by varying the speed of the air the model is in).

The main weapons necesary to fight gusts are power and control authority. Power gives you the ability to endure the changes in wind speed with less chance of stall (or less serious stalls), as well as the ability to penetrate the wind. Control authority allows you to make rapid adjustements to get your plane back on an even keel if something goes wrong.

Finally on Wind

Provided you are up high enough you are reasonably safe in any wind provided you can make headway against it. Sometimes the wind will give you quiet times in which you can land a model. However, sometimes the wind only gets worse the longer you leave it. Make sure you land before you have to, but if the wind seems gusty rather than strong, and doesn't seem to be building hang around in the air for a bit, and see whether it gets any better.

Finally on landing...

Landing is one of the toughest manuveurs in aviation, largely because the consequences of getting it wrong are so destructive, and because you need to be reasonably precise. Unlike your loops and rolls in the air, which don't need to be textbook perfect to still get appreciation from most onlookers, the ground is an stern and unforgiving judge of your landing technique. Keep at it, keep practicing.

Tips and Tricks

Various learnings that I have come to and I thought were worth writing down for others. Hope you find these handy.

1. Running Long on a Must Make Approach - How to get rid of that altitude and airspeed.
2. Advanced Landings - Landings causing you trouble - maybe these notes can help.
3. Aerobatics (External) - Handy reference with guides of how to do a number of aerobatic maneuvers.
4. Doing a good hand launch - Some more notes.
5. One Page Guide to Flying Warbirds - some notes you should read before you try.
   

Running Long on a Must Make Approach

The Situation

You are on approach, and do not have enough charge/fuel to go around. You must land on this approach, but you realise that you are too high. How do you land?

What to Do

Here's how I tackle it.

As soon as you realise there is an issue, but not while the plane is too far away (not over 40 metres for a park flyer for example) close the throttle and dive as sharply as you dare at the ground. Pull up when you are at the lowest possible Angle of Attack from which you think you can land. If you are still looking like running long you can dive all the way and pull out at the flare position.

Let the airspeed wash off the plane and add throttle to reestablish flying speed if necessary.

If you must land and beyond the runway strip is not plane friendly then force the aircraft gently onto the deck and hold her there as best you can.

Why

When we are too high on an approach our problem is how to get rid of potential energy (altitude) without picking up too much speed (kinetic energy). Diving might seem counter intuitive because we pick up a lot of kinetic energy. However, it also increases the frictional force, slowing our plane down, at a rate equal to velocity squared.

Let's say that at 5m/s you get 50 grams of drag slowing your aircraft down. If you dive and accelerate to 15m/s this drag would now be 450 grams. Effectively we have vastly increased the frictional force trying to slow your aircraft down for a short period. And, as the physicists amongst you know, we have gotten rid of more energy as heat (from friction) than we would in a normal approach.

The diagram on the right shows a graphical representation of this. The huge drag spike is the key to making this approach do able.

Risks and Limitations

This technique is more effective for airframes with higher drag. However, even if you have a low drag airframe this is still your best shot if you must land on this pass.

You may need to add throttle to stabilise your speed once you have leveled out from the dive. You don't have long to sort this out, and could easily stall if you aren't careful.

You are quite close to the ground, quite a long way away, going quite quickly. Be aware of glitches.

Alternatives

Another alternative that I have found very trick and risky is "slipping" where you add aileron and opposite rudder. If done correctly you lose altitude quite quickly and pick up very little speed. It is a tricky technique, difficult and easy to lose orientation on in my opinion, but it is an option.