Using Flaps for Advanced Pilots<br>

  Using Flaps for Advanced Pilots

 Every textbook will tell you that flaps curve the airfoil. But there is a lot that books don't teach us... What is the "higher girl" of flaps in ultralights?

Many of us pilots fly from airport to airport and don't give any thought to other non-traditional uses of flaps, which may be a shame. It's one of the many ways to get significantly better performance out of us and our aircraft, not just for potential emergency landings. Such knowledge and skills can come in handy for field landings, on any other surfaces, and at various sporting events.

Airplane manufacturers usually allow the flaps to be set to values around 0, 15 and 30 degrees, and they do this so that the average pilot (with average reactions and experience) without special skills can fly the airplane according to the approved operations manual.

If we reflect on the previous paragraph, it is clear that each aircraft can do much more. The question is under what conditions and if you can do it too. Do you want to improve your handling of the aircraft? Are you aware of the physics and engineering involved? Would you be comfortable landing in worse conditions on a short field? If so, let's move on...

It is often possible to change the electric control of the flaps to mechanical and set them to a larger range. Initial demonstrations with a test pilot will help you get a feel for the issues.

Aircraft technician's compartment

Adjustment of the flaps beyond the manufacturer's ranges may not be an unauthorised modification. Manufacturers usually work on the safe side and do not allow larger deflections for many reasons (not just those described below). In fact, they don't even want to allow them.

But it can be done differently and legally.

For larger flap ranges, you will need an approved technician who has the aircraft on record to determine the possibilities of whether the flap suspension and placement on the wing and the structural force distribution will allow such a modification. The technician will look at the technical documentation, calculate the speeds at which you can use such flaps if necessary, and consult with the manufacturer or more experienced colleagues.

The test pilot will verify such calculations in practice over the entire centering range and with other influences such as crosswind - determine its maximum perpendicular and aft component relative to the airplane's controllability. In consultation with the engineer, he may increase the surface deflections, attach vortex generators or both. The test pilot should remember to perform the tests at different temperatures, flight altitudes and in rain, preferably in winter conditions if turbulators are used.

Sometimes this is not possible, then he will make less accurate numerical corrections. He then limits his results to the ability of the average pilot and records and confirms everything in the flight manual. The test pilot, if he is also an instructor, can then teach you how to use these increased deflections in practice on your aircraft.

Other ways of adjusting the flaps

The ordinary, novice pilot with an ultralight or PPL license will not normally learn about these, and I often meet pilots with over a thousand hours of flight time who only know how to operate the aircraft to the extent of the manual. They don't know about other options and thus can't even be bothered to improve... perhaps to their detriment.

It bears repeating and emphasizing that other flap settings already require some experience, the cooperation of a technician who has a UL listed aircraft, a test pilot to verify flight characteristics, and your willingness to educate yourself and achieve better skills and also find out what you have in you and the aircraft. There are days when that really comes in pretty handy.

On the other hand, you also need to take into account the surely correct notion that you won't need anything like that to just fly 90 percent of the time, the plane was made by an experienced manufacturer, flown by an experienced fab test pilot, and nothing needs to be changed. Finally, training for all variations of flap use would be prolonged and expensive, not to mention the need for higher theoretical knowledge of pilots at the lowest pilot licence levels.

However, since we are inquisitive creatures, we will not be deterred by the preceding statement of the surely wise peasants, which, although true, does not allow us to find out more and look further. It does not allow us to look behind the curtain and uncover the remaining ten percent.

Setting the flaps to negative

We can set the flaps to a certain negative value. Or, with the help of a technician and a test pilot, reconfigure the controls - for faster cruise - level flight. The negative value is then set for accelerated cruise level flights...

When you set the negative value, the wing generates a little less lift, at high speeds the airplane may not be as nose-heavy and the elevator therefore doesn't brake the airplane as much with its deflected surface, so you don't feel like you are constantly flying downhill. The wing has less drag overall. As a result, the airplane flies a lot faster with the right camber and throttle settings. Setting the flaps to negative is only done during overflights.

Wonderful, isn't it? And why don't all manufacturers do this?

A certain disadvantage of such a modification may be a connection with an untrained, or unknowledgeable, pilot who flies with the flaps set to the negative position. On the circuit, he/she does not perform the standard actions given in the flight manual or flying methodology and does not close the negative flaps, or does not open the flaps to the appropriate position... Then it could happen that he/she takes himself/herself out of the sky, even if at the speed he/she is used to and which is usually enough to perform the turn. Only the wing won't have as much lift as usual...

Another example of setting the flaps to a negative value is to shorten the landing dramatically. Abruptly closing the flaps to negative at the end of the transition turn at the correct airspeed at the appropriate altitude, coupled with the appropriate extension of the airplane, will allow me to immediately stall and "ground" the airplane.

Quality steel landing gear and sized shock absorbers will dampen the airplane and I can start braking hard. This is where you need to have some experience and decent judgement.

Setting the flaps to a high positive value

We can also set the flaps to a higher value over 40 degrees. Then it is mainly a matter of converting the flaps to braking, and it is obvious that we will use such a configuration to change the angle of descent (significant descent at a considerable angle), because not every aircraft can glide efficiently enough.

We will also use it to shorten the length of the landing by flying as low as possible in ground effect on sufficient engine thrust with the rudder appropriately spooled to eliminate reaction moment.

Even more flap deflection eliminates stall and washout and can be used to dramatically shorten range (if you have worse brakes or desperate adhesion conditions, like hail after a summer storm or snow flurries on grass.)

I use them like this: tighten on the largest flaps at the appropriate engine thrust to ensure flight at the lowest possible altitude above the ground in the lowest possible ground effect layer, as soon as I pass the intended touchdown point I fully withdraw the throttle and the stretched aircraft immediately sits up. Closing the flaps abruptly will not allow washout. The landing gear will dampen the bounce. Range is usually about 50 to 70 metres.

30+ flaps are not normally used for takeoff. I use them briefly to jump or fly over an obstacle. Sometimes I will take off from any other unimproved area whose surface is interrupted by a "rigol" with a stream or rocky boundary. I choose a sufficient distance to take off so that by the boundary or ditch I already have sufficient speed given the size of the wheels, rocks, brush, badger burrows, branches and height of the vegetation and preferably I am already untied and in the run-up.

If this fails (it does happen occasionally) and it is clear that I will not cross the stile or ditch, I open the flaps to maximum before the obstacle. The airplane gains lift and immediately disengages. I can also stretch the airplane more as needed, all on engine power of course. I then gradually close the flaps with feeling as acceleration occurs or does not occur. Occasionally I brake too much and need to throttle back to gain speed and achieve a cushion ground effect.

The downside to this action is the sharp increase in drag that I have to account for. The airplane will usually still stall and touch the ground after clearing the obstacle - it depends on the height of the obstacle and how high I am in my air cushion - ground effect. It also depends on the weight of the airplane, whether it is a downplane or an upplane, the wing profile, temperature, altitude, power of the airplane and the propeller used, as well as orographic effects or drift behind the obstacle.

Of course, acquired skills with stretching and locking out crosswinds and managing the stall component of the rotor behind the obstacle are key. Therefore, it is essential to open the flaps ahead of the obstacle at the right moment. If I open them too early, I may "flap" and crash into the obstacle. If I open them too late, without considering the weight and inertia of the aircraft, the manoeuvre will also fail.

I always pay close attention to how the airplane behaves with the flaps extended this far due to flap drift and interference drag. I examine how controllable it is and how much aileron, elevator and rudder are affected. It is important for me to recognize the amount of drift behind the wing with the flaps extended like this. On some types of aircraft such flap extension greatly affects the function of ailerons, elevator, and rudder, and without sufficient air blow-by using propeller flow, elevator and rudder are not very effective, often requiring increasing the extent of their deflections, sometimes tweaking the turbulators in certain places, but always some skill from the pilot in metering the boost at the same time as keeping the aircraft at the correct angle of attack.

If the increased rudder and flap deflections are flown by an untrained pilot who is unfamiliar with the context, disproportionate forces and even destruction of the controls or control surfaces can occur when used at high speeds. This will never happen to a sensitive pilot with any aeronautical training who feels the airplane like his skin.

Flap control

Personally I prefer the classic manually operated flaps, like Eurostar or Yetti, but with more positions. I don't like hinged flaps where both flaps on both wings cannot be seen through the top covering. I like being able to visually and tactilely inspect the knot connecting the two flaps and the control rod.

To their detriment, many pilots, if given the choice, request electrically retracted flaps from the manufacturer.

But honestly - don't electric flaps make you lose real feel when controlling the aircraft? Don't you lose airspeed control at turbulent critical moments when instruments are late and can't be relied upon?

Isn't it the manually deployed mechanical flaps that tell you best by the resistance you have to pull them out and the instantaneous yawing moment how fast you are flying and what is happening around you at that particular moment and whether it is actually the right moment to open them? Can you use the full potential of the aircraft with electric flaps? Do you actually need an airspeed indicator for landing when you have mechanical manual flaps?

Electrically operated flaps have advantages over mechanical flaps: the ability to be set to predetermined positions with zero force from the pilot. How convenient!

The advantage and biggest disadvantage of electrically operated flaps is the speed of the flap extension control mechanism. Usually 5 seconds or more to full extension.

In four seconds I fly over my rather long area and this makes it obvious that they can only be used to a limited extent to shorten the landing!

I use flaps like this on my Tecnam P2002 Sierra de Luxe when I need a heavier takeoff from a short runway.

Fully extended flaps Tecnam P 2002 Sierra.

I open the flaps continuously in stages during takeoff, so that they have about 15 degrees at the point of uncoupling. This can shorten the takeoff a bit due to the lower drag of the flaps.

Sometimes I hold the electric flap extension longer, maybe even to 38 degrees, especially if it is over 30 degrees Fahrenheit and the airplane is at maximum takeoff weight. Then I can take off from a very short area, but it takes me a little longer to accelerate and even beyond the area I have to have enough obstacle free space to take advantage of the ground effect over the foreground before I can get the speed I need to climb and close the flaps to a lower value. The plane will give me a hint.

The advantage of electric flaps can be seen in the fact that the aircraft manufacturer will use a mechanism that will extend the flaps slowly enough. He does this so that there is no undue stress on the flaps, their mounting, the controls, and the wing itself. The added value of this solution is a certain "flap-proofness" in that as the flaps slowly open, the aircraft slows down simultaneously with its nose flapping, all with sufficient time to balance the aircraft and keep the flaps from stalling the aircraft and exceeding the speed limits for each flap deflection.

Mechanically manually operated flaps are wonderful, but really require an awareness of many contexts. I've seen several ultralights with "in the prop" flaps - they are at a greater angle at the fuselage than at the end. No, it wasn't that way from the factory. Someone was using them wrong. He didn't mean...

Or, on the contrary, he thought and used them as a last resort to help him jump over an obstacle that he would otherwise crash into due to inertia... Thanks to the high speed and forceful ejection, he pulled them to higher speeds than he should have and survived. The flaps, however, are not and are ripe for an overhaul.

If the mechanical flaps don't have fixed positions, you can choose any intermediate position, usually by the number of fine teeth as you extend them depending on wind direction and strength, surface and runway length, temperature, load, altitude, propeller and discretion... It works similarly for electric flaps without intermediate positions (Tecnam Sierra) but only in the 0-38 degree range.

Mechanical flaps operated manually can also be opened or closed instantly and violently, of course, taking into account speed, weight and inertia as well and with precise knowledge of the possible consequences. That's why I personally love manually operated flaps and I know why - they saved my life.

YETTI J-03 with flaperons. They have less lift compared to the Yetti with conventional flaps, but the aircraft is much more controllable.

A tale of short runways and tall trees

As an aspiring pilot, right after training in a Zlin Z42, 43 and a Cessna 172, I decided that I needed to fly a lot and "fly out". Finances limited my ability to fly GA aircraft, so I bought a Czech spur-powered Yetti J-03 ultralight with a 68hp Skoda 136B Favorit engine and a 1.8m diameter Woodcomp SR 30 fixed propeller. The Yetti is a relatively inexpensive and very strong and robust machine.

The flaps were mechanical with snap-in intermediate positions, but could be set to any deflection within and over a given range as long as the pilot held the lever with the safety depressed and pulled to the required position. When he then released the fuse, the flaps would retract to the nearest smaller position from the air pressure by engaging the backdrop counter that determined the specific flap position.

I was landing on a small one-way area about 230 x 40 feet in length, the edge of which was a forest on the right side. (As in the picture above). At the end of the area there were mature trees about 20-30 meters high and another tree on the far left. Passage was impossible.

I went in for a landing. At the beginning of the area at a very low altitude, about two meters, I found that the plane, even at low speed, did not stall as I was used to with such a stretch. I was long and due to the turbulence from the forest something was driving me backwards and not allowing me to land, although the idle was set and the sound of the engine, tachometer and propeller rotation speed suggested this.

A third of the way into the area, when I tried to cut the ground with it, the plane lifted off and stubbornly refused to land. It just kept flying on and on. It was clear to me that I was in trouble. I can't get it on the ground anymore and I can't brake it. I can't fit between those trees at the end. I can't even climb over the trees...

The socialist upbringing and the materialist approach to life was all at once negated by a plea: Lord God, help me! Please!

Then it happened - the world slowed down for me, the passage of time had a different reality...

Oh, so the toothy one is coming for me, I thought. But no sins flashed before my eyes. Instead, I had time to become aware of the connections, like watching a slow motion movie. The speedometer reads 60 km/h. I'm within a metre and a half. The 30-foot trees in front of me are about 100 yards away and rapidly approaching.

I give full throttle, pedal with my right foot, and throttle into level flight. Classic when you don't know what to do. That's how I was taught in training... Only no instructor ever talked to me about the obstacle that can't be climbed over...

When the throttle was inserted into the instrument panel, the engine immediately shot up to maximum speed - suspiciously willingly - more flexible than ever...

I could hear the wailing sound from the nine V-belt reducer and the engine with 68 wheezing old Shemis. I can smell the burnt rubber from the V-belts. The propeller is only reluctantly spinning... I'm wasting precious time with the outdated reducer design.

Judging by the dying roar of the originally over revved engine, it's obvious that the reducer has only just started to catch on. But I, dressed in my airplane clothes, am still relentlessly approaching the trees!

A quick glance at the speedometer, which reads something like 75 km/h, and an estimate of the distance and height of the trees gives me the inexorable realization and 100% certainty: I am not going to climb over those trees, nor am I going to fly between them!

If you cram it between them, the wings will slow you down, it's a pretty good crumple zone. Thanks to the strong truss structure, you'll definitely survive, maybe a pipe in your leg and a broken nose, nothing you can't handle... I'm starting to feel a little comforted inside, maybe I should give up...              

I'm at about ten meters above the ground and I can see the individual needles of the thirty-meter spruce trees right up against each other after the aborted landing.

A salutary set of thoughts came at just the right moment. The large propeller has a twisted propeller stream behind it enhancing the willing transition into just the left sharp turn. The governor has finally stopped squealing like a shot pig. The propeller is at maximum speed, as it should be.

But - speed and lift are barely enough for the sharpest and lowest executed turn of my life! It looks pale. This can't possibly work. Better to steer the plane into a controlled plow into a field perpendicular to the left than end up in the trees and then in an uncontrolled tailspin on the ground.

I really don't want that. What else?

Think about it!

The speedometer - that bitch is always late.

It's got to be enough.

There's no choice!

The thought of doubt flashes through my mind faster than lightning.

If I manage to avoid the trees in a left turn, I'll scream in a left wing dive for lack of lift.

How do I prevent this?

I need more speed! I need more lift! That's why I need to pull out the maximum flaps and CLIMB!

I've pushed all the controls to the left.

Knip and foot. Right after that, flaps to maximum 30 degrees.

Impact to impact.

I pushed the rudder to a descending flight enhanced by a sharp downward reaction from the gyroscopic moment of the big heavy prop.

The aircraft is in a sharp bank. A few G's push me into the seat and the airplane turns and descends very willingly due to engine thrust, reaction and gyroscopic moment.

It descends too readily.

Looks like I'm actually going to avoid the trees before I get up to speed...

Peripheral vision in the left half indicates a terminal arc height of about 3-4 metres above the ground.

I pull the flaps out to the stop, well over the last clearly given value, and spasmodically hold them there, the pressure from the flaps through the lever is really considerable, but I'm not going to give in - not now. I keep the flaps on until the downhill turn is over.

With my right hand I still hold the maximum possible flap deflection, with my left I pull in earlier and more forcefully, aware of the inertia of the airplane.

I completed the turn, along with the flare, just ahead of the tree that stood nearby, and at about a meter altitude.

A merciful cushion of ground effect air and quick reactions allowed me not to slam the small wheels into the oranice.

Gradually I transitioned into the climb and as the pressure from the rushing air built up in the flaps, I steadily closed them to the takeoff position. I climb to the downwind short circuit position and sincerely thank the Lord God, my guardian angel and all who have helped me.

It's blowing a bit through the woods. I have the option of leaving it in another meadow where it's blowing directly into the nose, or returning to the airport, but the challenge is obvious...

There's plenty of fuel. Engine's back in front like a kitten. Zejda never gives up!

Again, and better, this one didn't go so well for you mate - it was like hearing my PPL instructor from Zlin 42, and it set me off!

I touch fourth, flaps at maximum, budget 50 meters ahead of the area and a meter above the crop, tightening up a lot on the engine. No sooner do I fly over the edge of the crop I pull back on the throttle and fully tighten on the spur. With that, I lever the plane over the spur and ground it to the main gear.

But the situation repeats itself, something pulls me towards the trees from behind. I pull in on the navel and close the flaps to zero. The plane sits up, bounces a little, but doesn't fly again. I'm braking at full throttle, if you can say that about the drum brakes from the Babette moped, controlled by the brake levers from the bike and a flexible bovden with a 2 metre long bicycle cable...

I brake about 50 m in front of the trees. To be safe, I take a left-hand turn, where the bovden is shorter and the brake more effective.

I kind of fell out of the plane, my shaky knees didn't serve me well at first. I didn't fly again that day, you know:

" The weather's weird, and it's kind of kicking..."

Throughout the afternoon and part of the night when I couldn't sleep, I went over the various options, what I did wrong, what could have been done better and how to improve the plane.

During the next twelve years since that incident, much has happened, and at the same time I have modified several aircraft in my own image. But we'll talk about that some other time...

There was a great comment in the discussion below the article.  It put me in a good mood for a long time and I really giggled with my wife when we read it. I think it has its place here it is a work of art.  I apologize but I can't help but copy it, unfortunately there was no one to ask for permission.

Philip is not giving up!

The script of a short thriller with a happy ending

The plot is based on a true story described by a still living pilot.

Scenic note for the first picture:

Czech countryside. A bird's eye view. On the edge of a forest, a meadow 230 metres long, 40 metres wide. In front of the meadow a grain field, on the right a forest, in front trees 20-30 meters high, on the left a tree. "A little huffing through the forest". An aeroplane is approaching the meadow, low over the crop. Scene music: Jaws.

Image two:

Plane flying over edge of meadow but does not land. At one third of the length of the meadow - that is, at a distance of approximately 150 metres in front of 30 metre high trees - the plane suddenly rises. Cut to the airspeed indicator, which reads 60 km/h. The scenic music ends with a three-second pause, followed by the roar of the engine from the Favorito. Close-up of slipping V-belts and thick white smoke replacing the smell of burnt rubber.

Image three:

A brief shot of the pilot's concentrated face. Cut to a shot of a large lecture hall blackboard, all traced with a profile sketch with the large flaps deflected 95° and a diagram of the airspeed indicator in section. Mathematical formulas and calculations surround both pictures, interconnected by arrows and incomprehensible notes. Lots of square roots, integrals and Greek letters. In front of the board, a young student dusts his hands off the chalk and smiles triumphantly at the astonished committee. Cut back to the cockpit. Close-up through the cockpit glass to the nearest branch of a spruce tree. A close-up of the bark beetle's scared-to-death face and a bite of bark in its fear-crushed paws, stopped halfway to the open chutes. A quick cut to the pilot's face, which suddenly brightens in the obvious joy of solving a few equations.

Image four:

(It is recommended to order several large identical RC models for the shoot.) The plane is 10 meters high and 100 meters in front of the trees in the extended position. The flaps are deployed and the plane banks sharply to the left. The wingtip is 4 meters above the ground, the pilot extends the flaps even more in a downward turn. Cut to the pilot's face, which, despite the deformation caused by the overload of several G's, expresses determination. His expression could be described as "it may not look like it, but I know what I'm doing". Sound: Focke-Wulf 190 in passage, complete with the whistling of the V-belt and the heavy breathing of the pilot.

Image five:

The plane finally fails to crash and in a daring bank at stall speed, it flies off into the trees, leaving a streak of white smoke from the reducer behind. Distant shot of the aircraft repeating the circuit. Scene music: Top Gun, pull harmonica cover. Plane repeats attempt to land in rotor behind edge of forest on 230 metre long meadow topped by 30 metre high trees. Shot of a different meadow with more favourable winds (clearly expressed by detail on the bent poplars nearby). Cut to the pilot's face, expressing dogged determination and belief in himself and his sturdy steel chassis. Shot of the overstretched plane before landing, close-up of the closing flaps, shot of the plane sitting up and bouncing.  Sound: tyres squealing. Close-up of the red-hot brakes from Babette's and the blocked wheels mercilessly crushing the stems of Meadow Grass, Fescue and Mullein.

Picture six:

The plane comes to a stop. Sound: engine shutting down. Silence. A five-second shot of the plane from the side. Then the cabin door opens and the pilot falls out of the cabin onto the grass with a muffled thud. Cut to a barker quickly packing his belongings into a knot with a determined expression. Cut to an aerial shot of a meadow with a parked plane, the camera zooms out and takes in the landscape of the Czech countryside. Scene music: Sun, hay, strawberries. Closing credits.

Note: this is only a joke without any malicious intent .-)

Filip Zejda