Get your own Free HomepageFrom a young age, I've had a personal fascination with aviation. Next to computers and electronics, it stands as my second hobby. (And since computers and electronics eventually became my job and not just a hobby, one might say that aviation is my primary hobby.) I knew how to fly before I knew how to drive. (Not that I ever flew a real plane, but I studied it to the point where I knew more about handling an aircraft than a car.) Whether conventional fixed-wing airplanes (propeller or jet), gliders, rotorcraft (helicopters), vectored-thrust VTOL planes, hang gliders, or radio remote-controlled planes, just about every possible way to fly fascinates me. Many share this fascination, but most people don't have the time or money to actually pursue it to the point of taking flying lessons, buying a plane, and actually maintaining and occasionally even flying that plane.
Well, I can't help much with that, but hey, this is a website, and website is information, and that's something I can give. This page does not in any way attempt to be a thorough course in flight instruction, or even an introduction to flying. It's really more a collection of information for the person who is already somewhat familiar with aviation, and wants to know a bit more of the details about planes, such as navigation and theory of flight.
Perhaps the most fundamental aspect of flying an airplane, and one of the first things any student pilot should learn, is how to turn a plane properly.
There is a common misconception among people that the rudder is used to turn, as in a water-based ship. This is not so; Using the rudder to turn will make the plane turn very roughly and slowly. The reasons for this become clear if you visualize the airflow over the airplane while the rudder is being turned. In level flight, the air flows straight over the airplane, from the front to the back. This airflow is set up by the forward motion of the aircraft itself, of course. Now imagine what happens when the rudder turns; Air pushing against the side of the rudder pushes the plane's tail sideways, making the plan spin around sideways. However, the plane is not actually travelling in the direction it is facing; It is still moving in the same direction it was going before, its nose just happens to be turned a bit to the side. The result is that the plane is actually sliding diagonally through the air. When the rudder is released, the airflow will make the plane straighten out again. The rudder, therefore, has a "snappy" effect; It can be used to quickly snap the plane's nose to the side, but it will tend to snap back to where it was before where you release the rudder. Although the rudder can be used to turn the plane, this is a slow process, because it depends on the plane's engines affecting the path of the aircraft enough to make it change its course through the air.
A much more efficient way of turning a plane is by rolling it. The natural inclination of an airplane is to go up. When air flows over its wings, it tends to rise. Rolling takes advantage of this effect, so that when the plane is tilted slightly to the side, the natural lift of the wing starts pulling the plane around. This is why rolling is used to turn a plane; It results in a gentle, smooth turn.
There is one drawback to rolling the plane in this way which should become fairly obvious if you think about it for a moment. In normal flight, the lift of the plane is equal to the force of gravity. The wings generate just enough lift to keep the plane at the same altitude so it can fly in a straight line. When the plane rolls and part of that lift is now used to turn the plane, naturally these is some loss of vertical lift and the nose of the plane starts to slowly sink. For this reason, rolling a plane must also be accompanied by lifting up the nose slightly to maintain altitude. This takes some practice, but it is not difficult to learn to coordinate both pitch and roll so that you can turn your plane effectively, without losing altitude. Of course, when you are done turning and you return the plane to level flight, you must drop the nose slightly again.
So if the rudder is not used to actually turn the plane, you might wonder, just what exactly is the rudder good for? In all honesty, not that much. The rudder is a specialized tool, used only in certain situations like steering while the plane is rolling on the ground, or to correct sideslip if the plane happens to be sliding sideways. It is not used that much in general flight.
Perhaps the most fundamental of all your status indicators, your altimeter is simply an indication of how high in the air you are. Because it operates on air pressure, it is NOT actually an indication of how high off the ground you are; Rather, it indicates how high you are above sea level. This means that flying among a mountain range, your height above the ground (the mountain beneath you) might be quite low, but your altimeter would still read that you are high, because you are high above sea level.
Before taking off, you must therefore calibrate your altimeter by setting it to the correct altitude for the airport you are taking off from. In other words, you should know the height of the airport. Essentially, the altimeter should read zero when you are on the ground.
An air pressure-based altimeter is said to measure altitude ASL (Above Sea Level).
The radar altimeter is a more high-tech altimeter which uses radar to detect the plane's altitude. This type of altimeter is not affected by differences in air pressure, because it does not measure air pressure at all. It measures your true altitude above whatever terrain you are currently flying over. Rather than measuring altitude ASL, it measures altitude AGL (Above Ground Level). A radar altimeter is highly accurate and thus of extreme importance to any airplane pilot. Unfortunately, many smaller civilian aircraft still do not have one, instead relying on a pressure-based altimeter.
Your airspeed indicator indicates, quite simpy, how fast your plane is going. A distinction between "airspeed" and "ground speed" is important; Airspeed is how fast your plane is flying through the air, while ground speed is how fast your plane is moving across the ground. An aircraft which is heading straight down into the ground has a ground speed of zero, because it is not moving from its position over the ground, yet it still would have an airspeed.
In normal flight, airspeed is affected by the wind. If a plane is flying into a 20 MPH wind and the plane is moving across the ground at 40 MPH, then the plane has an airspeed of 60 MPH. Airspeed is only equal to groundspeed if there is no wind and the plane is flying horizontally.
The airspeed indicator actually has several specific speed points on it known as "V speeds", because each one is represented by an abbreviation beginning with V (which stands for "Velocity"). The most typical V speeds represented on an airplane airspeed indicator are:
VNE The "Never Exceed" speed. This is the highest speed that the plane can be safely operated at. At speeds in excess of VNE, structural failure of the plane is liable to happen (wings getting torn off, and other fun stuff). VNE is indicated on the airspeed indicator by a red line.
VNO This is the "Maximum Structural Cruising" speed. On the airspeed indicator, a yellow arc extends from VNO to VNE, and this yellow area is the caution zone. The plane must only be operated in the yellow zone within smooth air. However, since turbulence is often quite unexpected, it is recommended that the plane is never operated intentionally in this zone.
VFE This is the maximum flaps-down speed (the FE stands for "Flaps Extended"). If you fly faster than VFE with your flaps extended, they may get ripped off the plane, which looks really neat at first, but not so good once you realize what's happened.
VSL The stalling speed of the aircraft with flaps and gear both retracted. This is an important speed which you should be aware of during flight so that you don't stall the plane. However, when you're landing, then the next (and slowest) speed becomes much more important...
VSO This is the plane's stall speed with landing gear extended and full flaps extended. This is an extremely important speed to know when you are landing, since this is the configuration the plane will be in when you land, and you want to approach the ground just a little above this speed, and actually drop below this speed just before the wheels touch the ground.
All of the V-speeds are important, and it is strongly suggested that you make yourself fully aware of all the V speeds on any airplane you fly before you even take off. You must especially know VSO in order to land safely, but the other speeds are also good to know if you happen to be a fast flier (or a slow one).
The magnetic compass has been a reliable navigation tool for centuries. Everyone from hikers to sailors have found it to consistently show them which way they are going. Aircraft pilots, however, have a new problem with magnetic compasses relating to the motion of the plane. In an aircraft, a magnetic compass is very susceptible to deviation errors caused by changes in the plane's movement state. For example, changes in the planes speed will tend to turn the compass from its true direction: In a plane which is accelerating, the compass will tend to turn toward the north. In a plane which is decelerating, the compass will tend to turn toward the south. (This is only true if the compass is currently pointing eastwards or westwards; If the compass is pointing directly north or south, changing the plane's speed will generally not affect the compass.) Turning a plane will also tend to make the compass do strange things, and it will only settle once the plane has stopped turning.
To deal with these problems, the Directional Gyro (DG) was developed. This is a navigation device which is relatively immune to inaccuracy from changing the movement of the plane. It uses a gyroscope to remain pointing in the same direction at all times; The DG does not move, but always stays in the same orientation. The plane, in essence, turns around the DG. The DG does not replace the magnetic compass, however, but rather they work in conjunction with each other. The reasons for this are twofold: First of all, it must be understood that the DG is not actually an inherently north-pointing device. While a compass always points northward because of the effect of the Earth's magnetism, the DG simply stays put in whatever position you place it in. Secondly, DGs are subject to "drift", meaning they slowly wander off their correct orientation. This drift is slight, but over long flights there may well be a noticeable discrepancy between where you set the DG when you took off, and where it points after a few hours. For this reason, the DG must occasionally be re-set, using the magnetic compass as a reference. In level flight, with the plane staying at a constant speed, you must use the compass orientation to turn the DG to the correct heading. The DG is a useful device for maintaining proper bearings during turns or other aerial maneuvers, but its accuracy depends upon you setting it by the magnetic compass.
The DG has another problem: Like most gyroscope-using instruments, it is subject to failure from strong aerobatic maneuvers. In a pitch or roll attitude in excess of 55 degrees, the DG should be "caged" (locked into position), or it may stop working.
The turn and slip indicator is a very interesting little instrument for showing you whether you are turning your airplane correctly. Recall from our discussion on how to turn an airplane that you must roll the aircraft in order to turn it properly. But rolling is not the only thing you need to do; You must establish the correct amount of roll in the plane. Incorrect roll may cause the plane to skid or slip. What does this mean? Skid or slip are opposite turning conditions, but both are undesirable.
A skid in a turn is when the plane slides outward while turning. It is usually caused by not rolling the plane enough. For example, if you wish to turn right, but you do not roll the plane to the right enough, your plane will start turning to the right, but it will actually slide sideways in the air to the left. Imagine a car skidding sideways when the driver takes a turn too fast, and you'll have the idea.
A slip is just the opposite of a skid; When you roll the plane too much, the plane will not only turn, it will also start to fall down. If you turn to the right but roll the plane too much, the plane, in addition to turning toward the right, will start to fall down, sliding sideways toward the ground.
The turn and slip indicator shows you if you have the plane banked correctly. The needle at the top indicates your turn; If you are turning left, the needle will point left. If you are turning right, the needle will point right. The ball at the bottom shows your skid or slip rate. In a correctly-banked turn, this ball will stay in the center. If you are skidding, it will slide in the opposite direction from the needle. If you are slipping, it will slide in the same direction as the needle.
Typically, an aircraft is designed to make 2-minute turns, which is a turn in which the aircraft will make a 360-degree rotation in 2 minutes. This means a turn of about 3 degrees per second. (There are 120 seconds in 2 minutes; 360 divided by 120 is 3, and thus, 3 degrees per second makes a 2-minute turn.)
In a computer flight simulation, many people never bother learning to coordinate their turns properly. This is understandable, as it seems like a lot of bother for something that doesn't really affect your flight that much. In a car, skidding might be a big deal, but in a plane it seems like it doesn't matter much. This is true. However, in a real aircraft, you would quickly understand why learning how to turn without skidding or slipping is important; Improperly coordinated turns are uncomfortable for anyone riding in the plane. A professional airliner pilot cannot go around making uncoordinated turns all the time or some of the passengers would get sick. The student pilot who is learning with flight simulators, but plans to start flying planes for real someday, would do well to understand this and learn the skill of proper turning.
The AH (Artificial Horizon) is exactly what it sounds like: An artificially-represented horizon in a little readout which is intended to give the pilot a sense of looking out the windshield. When the plane rolls, the AH rolls too, giving you the view that you'd see if you were looking at the actual horizon. When the plane's nose goes up or down, the AH slides up or down, too. The AH serves to give you a visual sense of your plane's attitude when you can't see the actual horizon (usually because of clouds). Your plane's attitude is basically what direction it's pointing in, as in whether the nose is pointing high or low, and whether the plane is rolled or straight. Therefore, the AH is sometimes also known as the Attitude Indicator (AI).
Like the DG, the AH/AI uses a gyroscope, and so should be caged if you're going to subject the aircraft to extreme attitudes, or if you intend to perform aerobatics. The AH/AI is more durable than the DG, and most of them can withstand rolling the airplane vertically (putting it completely on its side), but if you plan to fly upside-down or do a barrel roll, cage the instrument.
The VSI indicates simply how fast you are gaining or losing altitude. If you are at 5,000 feet and the VSI is telling you that you are falling at 1,000 feet per minute, you will hit the ground in 5 minutes. The VSI is particularly important during landing, where you want to make sure that you are not descending too fast. (Coming down too fast means you'll hit the ground with a jarring bump, which, at the very least, would be uncomfortable, and could have even more serious consequences.)
The VOR (Very high frequency Omnidirectional Range) system has been the primary means of cross-country navigation in private aircraft for decades, along with the ADF system. It seems that the satellite-based GPS (Global Positioning System) will eventually replace it; It has already done so to some extent, but most planes still use VOR for local navigation, and so it is important to understand how the system works.
VOR centers around VOR broadcasting stations, which are really a special type of radio station. These stations broadcast two signals in the VOR range, which lies from 108.00 MHz to 117.95 MHz. Each station has its own frequency, and so a pilot who wishes to fly by a particular airport's VOR signal must know the frequency it operates on. For example, Los Angeles International Airport (known as LAX for short) transmits a VOR signal on the frequency of 113.60 MHz, while John F. Kennedy International Airport in New York City uses a VOR frequency of 115.90 MHz. As with any form of radio transmission, there is the possibility of two stations using the same frequency in the same area. The VOR frequencies have been carefully assigned to minimize this, but occasionally planes which fly at high altitudes may receive an inaccurate VOR reading because of two conflicting stations. However, because VOR transmits in the VHF (Very High Frequency) radio band, it operates on line-of-sight reception like all VHF transmissions, which means that the curvature of the earth (hills and mountains) will block it, and it cannot transmit over the horizon.
Once you have tuned your VOR receiver to a particular VOR station, there is one additional setting you must make to it: Your desired radial of the station. Each VOR station is considered to have 360 radials, which are imaginary lines extending from the transmitter in all directions. These radials use normal compass numbers, and so radial 90 extends directly east from the station, while radial 180 extends directly south. Once you have chosen a radial on the VOR receiver, the display will show you what your relation is to that radial, via two separate instruments: The TO/FROM indicator, and the course deviation indicator.
The TO/FROM indicator, as you might guess, attempts to tell you whether you are flying TO (toward) or FROM (away from) the transmitter. However, it does not actually indicate this precisely, since your current heading has nothing to do with what it displays; Rather, it reflects your current position from the transmitter. As an example, suppose that you have tuned your VOR receiver to radial 0, which is the radial that extends directly north from the VOR station. A plane which is south of the station would display TO, because the plane would be flying toward the station if it had a heading of 0. Conversely, a plane which is north of the station would show FROM, because any plane which is north of the station will be heading away from the station if it has a heading of 0. It must be understood, again, that the heading of the plane has nothing to do with this indicator; It is only affected by the plane's position, not where it is facing. The plane's nose could be facing north, south, east, or west, but the indicator would still show FROM if the plane were north of the transmitter.
There are two "gray areas" in which the TO/FROM indicator does not display anything; They exist in the areas where the TO zone and the FROM zone meet. For example, a plane which has selected a radial of 0 would not show either TO or FROM if it were directly east or west from the transmitter.
The other indicator of the VOR system is the course deviation needle. This is a vertical needle which shows you whether you are directly on your chosen radial, and if not, how far off you are and in what direction. Take, again, the example of a plane which has selected radial 0. Imagine that this plane is directly south from the station, on the 180 radial. In this case, the needle would be centered on the VOR display, because the plane is exactly in line and will be heading directly toward the station if it flies at a heading of 0.
Now for a slightly less simple example: Suppose that the plane is actually on the 190 radial from the station; Mainly south, and slightly west. In this case, the VOR needle would be on the right side of the display, indicating that the desired course is to the RIGHT of where the plane is now. The plane, which is assumed to be flying directly TO the station, must move slightly to the right (eastwards) in order to intercept the correct radial. To correct this, the pilot would turn the nose of the plane slightly to the right of the station (so the plane would not be heading directly toward it). Eventually, this would cause the plane to be exactly south of the station, at which point the needle would be centered. The pilot would then turn the plane directly toward the station again by turning to heading 0.
Notice that when flying to a VOR beacon, the radial you select is really the opposite of the radial you are on now. A plane which is south of the station would be on radial 180, yet it would select radial 0 if it wants to fly toward the station. This is called the "reciprocal" of the radial; To get the reciprocal of a radial, subtract 180 from it (or add 180 to it, if it is less than 180). For example, the reciprocal of 240 is 60, while the reciprocal of 27 is 207.
The ADF (Automatic Direction Finder) is a very handy little instrument in an aircraft. Its purpose and function is simple: It points toward a radio beacon. Unlike VOR, which requires a special VOR broadcasting station to work, the ADF can home in on, and point toward, virtually any low-frequency or medium-frequency radio broadcasting location. However, ADF is usually used with NDBs (Non-Directional Beacons), which are simply radio beacons which continually broadcast with the purpose of allowing planes to navigate by them.
The ADF is first tuned to a particular station. It uses a three-digit tuner, which selects the frequency of the station (in kilohertz) to home in on. Once a station has been selected, the ADF needle points toward the transmitter, and the pilot can then navigate by this, knowing what direction a known point is in.
The ILS (Instrument Landing System), as you might guess from the name, is used only in landing. It is intended to help the pilot ensure that the plane is in the right place while on landing approach.
The ILS uses two needles, one horizontal, one vertical. The vertical needle acts in a way very similar to the vertical needle on the VOR indicator. In fact, often the ILS indicator is also the VOR indicator, and the horizontal needle is simply not used during VOR navigation. The vertical needle shows you whether you're to the left or the right of the correct radial, and by how much. The difference here is that unlike with the VOR, you cannot simply select whatever radial you like; The reason for this is because when you're landing, there is only one correct radial: The one that extends straight out from the runway. If a runway runs north-south, for example, you can only land on it from the north or the south, not any other direction. ILS transmitters are hard-wired to a particular radial, and this radial cannot be changed by you. Because a runway can be landed on from two directions, each runway must use two separate ILS frequencies. In the example of the north-south runway, planes landing from the south tune their ILS receiver to a different frequency than planes landing from the north.
The horizontal needle, as you might have guessed, is related to your altitude. It simply shows whether you are too high or too low. From the end of the runway, a radio signal rises away and upward at a gentle slope; This is called the glide slope, and it is the recommended slope to follow when you are landing. The horizontal needle, which is the glideslope indicator, simply shows you where the glideslope is, relative to your plane: If the needle is up, it means the glideslope is above you (you are too low); If the needle is down, it means the glideslope is below you (you are too high).
Omega is a high-tech navigation system normally used only by jetliners on long-range flights. The Omega transmitters operate in the Very Low Frequency (VLF) band, in which radio transmissions can carry a long way. In fact, as shocking as it may sound, there are only eight (8) Omega transmitters in the world, yet these 8 stations provide global coverage. There are many places in the world where a plane will be able to receive transmissions from all 8 of these stations.
Because it operates in the VLF band, which is not subject to line-of-sight limitation as VHF is, Omega can be used even in tall mountain ranges. Its only disadvantages are that Omega receiving equipment is normally only used on commercial aircraft (it is rarely to be seen on private planes), and its accuracy is imperfect; It can only give the plane's location within a mile or two. This is quite sufficient for knowing approximately where in the world you are when you're flying across the Pacific Ocean, but for local navigation, a plane will still use VOR. Omega has pretty much replaced the LORAN (LOng RANge navigation) system that preceded it.
The DME (Distance-Measuring Equipment) is a very simple instrument which serves a very simple purpose: It measures your distance from a radio station. It typically works in conjunction with VOR: You tune your VOR receiver to a particular VOR station, and the DME will begin to show you how far you are from the station. It does this by sending a signal to the station, and measuring how long it takes for it to get a reply. As quickly as radio waves travel, their speed is finite, and you can measure distance by their delay, just as you can gauge the distance of a lightning bolt by seeing how long it takes for you to hear the thunder after you see the lightning.
It should be noted that a plane's vertical as well as horizontal distance from the station is measured, and thus the DME does not just measure ground distance. For example, a plane which is directly above the station, but 2 miles in the air, would show a distance of 2 miles. At long ranges, this is not usually a very important point (if you're 50 miles away from a station, you usually don't care too much about a few thousand feet of inaccuracy), but at close range this becomes an important consideration.
DME equipment has an interesting secondary function: It can measure your groundspeed by seeing how quickly your distance from the transmitter is changing. This is important sometimes, because other than this, a plane has no groundspeed indicator (only an airspeed indicator, which, as has been noted, is not the same thing).
A "stall" has nothing to do with a plane's engine. Many people who are accustomed to automobiles, upon hearing the term applied to aviation, assume it must mean engine trouble, because that it what it means in the car world. In fact, however, a "stall" in aviation is an aerodynamic situation, not a mechanical one.
A stall is a catch-all term for a fundamental loss of air buoyancy in an airplane. When the airflow over the wings is disrupted and it no longer moves in the smooth stream that the wings need to generate lift, this is a stall.
Stalls are probably most commonly encountered by flying too slowly. An airplane must continually rush through air. Any heavier-than-air craft must force itself through the air constantly to create the phenomenon that makes these craft fly. If they do not move quickly enough, the airflow stops being enough to keep the plane afloat, and the plane stalls. However, speed is not always the cause of a stall. In fact, you can stall a plane at any speed, at any altitude, and in any attitude if you flip it around too briskly. The air must move across the plane in a smooth, streamlined fashion, and if the plane's motion becomes choppy, it loses its stability. Obviously, this depends a great deal on what kind of plane you are flying; Military fighter jets are very difficult to stall with rough treatment, because they usually fly at such high speeds that the airflow can be maintained even under high G-loads, and also because they are so streamlined that they do not break up the air as much as a chunky, square, general-aviation plane would. But unless you are flying an F-15 or some similar jet, you should be careful how you handle your plane. Use slow, controlled movement of the control stick. Never make sudden or extreme motions; This is inviting a loss of control.
Despite that fact that stalls are scary and a great deal has been written on them, the basic truth is that they are usually pretty easy to deal with as long as the plane is high enough to recover. Dealing with any kind of stall is simple: Point your plane's nose slightly below the horizon so you build up airspeed, and let the plane speed up, gently pulling yourself into level flight once you have reached cruising speed again. The only time this is not practical is at very low altitudes, where you might not have enough room between your plane and the ground to actually recover the speed you need. This is why stalling at low altitudes is fatal; There is a certain point of no return, where the pilot cannot regain control of the plane anymore. Obviously, this should be avoided at all costs, and it is not difficult to give yourself a decent margin of error: Just fly well off the ground.
A landing is actually a controlled stall. When a plane lands, it does not simply plunk itself down on the runway; It flies over the runway at low speed, pointing its nose up so that it will lose even more lift, and the resultant stall condition will gently drag the plane down into the ground. This is one reason why landing is so difficult: To land actually requires you to place the plane into a momentary loss-of-control situation where gravity takes over. The height and speed at which you stall the plane must be precise, or the attempted landing could result in a disastrous crash. For this reason, landing may actually be made easier if the pilot has experienced a few stalls in the air. Knowing how it feels and how the plane reacts to a stall will be a very educational experience. In all truth, there is really nothing that dangerous about a stall, provided you give yourself plenty of altitude to recover from it, and that you do not panic when your plane stops responding momentarily. It is good practice, so that you will be prepared for the day when you create one accidentally.
Stalls are the fundamental bugaboo of flying. They are the cause of many aviation accidents, and they are probably the most worrisome aspect of flying for most new pilots. Yet in truth, a stall is usually fairly simple to deal with. Much more difficult is the spin, one of the most devilish situations any pilot can be faced with.
A spin is, in fact, a stall, but only a partial one. Whereas a situation that most people would call a "stall" is really a stall of the entire plane, a spin is only a partial stall. Generally a spin begins when one wing of the plane stalls, but the other does not. (This is a very easy situation to get into if the plane stalls while it is rolled to one side.) The result is that while one wing is still generating lift like it should, the other begins to drop like stone. With alarming quickness, a self-propelling, violent rolling of the airplane is set up, and the plane spirals toward the ground. It is a genuinely terrifying situation for anyone on board the plane, and what makes spins worse is that they sometimes seem to be almost incurable. Indeed, in older times, a spin was nearly impossible to resolve, and many pilots met their doom in one.
Today, careful design of aircraft has done much to minimize the effect of spins. Planes are made more stable, so that they are more difficult to get into a spin, and easier to get out of a spin if you do get into one. The first general rule regarding dealing with spins is that you should not use your ailerons. Many people are tempted to try and stop the spin by simply applying reverse aileron, but in fact, this usually is of no effect, and frequently actually aggravates the stall. Instead, the use of the rudder is indicated, applied in the direction opposite to the stall; That is, if you are spinning clockwise, apply your rudder to the left. If you are spinning counter-clockwise, apply your rudder to the right. In addition, full downward elevator (pushing forward on the control stick as much as you can) is usually helpful in a spin. In a modern aircraft, this will usually resolve the spin.
Of course, as with stalls, the best way to deal with spins is to never get into one in the first place. Be gentle with the aircraft, do not subject it to sharp, sudden moves which might disrupt its motion, and keep an eye on your airspeed to ensure you do not approach stall speed. If you ever find yourself going too slow, quick and decisive action usually saves the day: Open the throttle, and drop your nose slightly.
The other side of the aviation fence is quite a different world. Airplanes (formally known as "fixed-wing aircraft") and helicopters (formally known as "rotary-wing aircraft") both fly, but the differences in how they do it are crucial. It has been said (probably by a helicopter pilot) that helicopter pilots are the real flyers, while airplane pilots just play at flying. After you've flown a helicopter, you might agree.
Are helicopters more difficult to fly than airplanes? Basically, yes. Why is this? It's not really a matter of the controls, or the principles of flight, for they are not any more complicated than those for an airplane. Quite *different*, but not more difficult to understand or operate. So what makes a chopper harder to fly? Basically, the fact that the helicopter is an amazingly, almost disturbingly unstable craft.
This concept becomes fairly easy to understand and appreciate if you only think about it for a moment. What lends stability to something? On the ground, things are made stable by having support built underneath them. Buildings are built on heavy, sturdy foundations of concrete or rock, and held up with support pillars. In the air, an aircraft can't rest on something, so what can provide stability in the air? Essentially, the only thing that can do so is motion. Those who've studied Newton's three laws of physics may recall that their most important point is that an object which is at rest will tend to stay at rest until acted upon by another force, and (more important to aviation), an object in motion will tend to move in the same direction, at the same speed, unless acted upon by another force. This means that motion gives any object more stability, because it's harder to influence a moving thing than an unmoving thing. This is very clearly illustrated in bicycle riding: It's quite easy for an experienced rider to balance a moving bicycle, but nobody can balance a stationary bicycle (except perhaps some abnormally skilled people in the world who've practiced it a lot). The forward motion of the bicycle makes it less prone to tilting sideways and falling down. That motion gives it the stability it needs to stay upright.
By now, it should be becoming clear how this applies to helicopters versus airplanes. An airplane is always moving. It's forced to; An airplane is a prisoner of motion. It must constantly force itself through the air to keep itself afloat. If it stops, it will fall. A helicopter, on the other hand, is not always moving. The ability to hover is exactly what makes helicopters special, and essentially it is the main reason they are used at all in the real world.
Fact: Most pilots agree that hovering is the hardest part of flying a helicopter. Harder than any kind of flying operation is the act of keeping the helicopter in one place without letting it drift around or fall. This is because when the helicopter is staying in one place, it is vulnerable to the slightest deviational influence. The smallest puff of wind can tip it over if the pilot is not paying constant attention to the attitude of the chopper, making sure it stays upright. Whereas it is possible to take your attention away from flying the helicopter for at least a few seconds when you are actually moving, hovering requires constant vigilance, keeping an eye on the tilt of the chopper so it doesn't lean to one side or the other.
But there's more to the problem than just hovering. A helicopter usually moves more slowly than an airplane, meaning it has less stability than a plane even when it's moving. The airborne suspension of a helicopter is a precarious thing. While airplanes rarely stall unless they move too slow or are subjected to a particularly violent maneuver, it doesn't take that much to disrupt the delicate balance that a chopper needs to stay in the air. A single sudden movement of the controls could disrupt everything, and send the chopper tumbling to the ground like an avalanche rolling down a mountain. Think of the main rotor on a chopper as a dinner plate balanced on a stick, which is essentially what it is. If you've ever tried to balance a plate on a stick, you know how unstable an operation it is, how easy it is for the plate to lose balance, and how taking your eyes off it for a moment will usually be the end of it. Now understand that a helicopter is the same way.
All of this leads to a couple of basic understandings. First, a helicopter is highly unstable when hovering. That is fairly easy to understand. The second one, however, may take a little drilling to implement. Essentially, you must remember one very important thing when operating a helicopter: DO NOT EVER, UNDER ANY CIRCUMSTANCES, YANK, JERK, OR SHOVE THE FLIGHT CONTROLS. Even in an emergency, sudden maneuvers are usually counter-productive. Just as with flying an airplane, making an adjustment to the flight attitude results in a wait of several seconds before the aircraft "balances out" and establishes an equilibrium where it adjusts to its new course. That means that even if you desperately need to change your direction, make the change using gentle inputs. Any kind of sudden motion is liable to make your helicopter stall. And while stalling planes is dangerous, stalling a helicopter is downright perilous; It's a lot harder to recover from a loss of control in a chopper.
An airplane has several control surfaces: At least two, and almost always more. Some planes combine the elevators and ailerons into a single pair of surfaces called elevons, and not all planes have a rudder. However, generally a normal civilian aircraft has two ailerons, two elevators, and a rudder. It will also usually give you the option of adjusting the propeller pitch, making the propeller(s) a sort of control surface as well. A helicopter, however, has only two control surfaces: Its two rotors. The main rotor provides lift and controls pitch and roll, while the tail rotor controls yaw.
The main rotor is the "wing(s)" of the chopper. A helicopter seems to have no wings, yet recall that they are officially known as "rotary-wing aircraft". And indeed, those big rotating things *are* the wings. They operate on basically the same principle as an airplane's wing, except that while an airplane wing is permanently fixed to the aircraft and relies on the motion of the aircraft to make lift, the rotor on a helo is moving by itself and can always make lift, even if the chopper itself is sitting still. Each blade on the rotor has a shape very similar to that of an airplane wing, and operates on essentially the same principle, to wit, Bernoulli's principle.
In an airplane, the "energy" of the aircraft is controlled via the throttle, which is an engine-related control. The throttle controls how hard the engine is working, and thereby varies how fast the airplane is going and how much lift it can make. In a helicopter, there is a throttle as well; However, changing it while in flight is a no-no. You don't adjust the throttle of a chopper to change its lift; Instead, you adjust the angle of the main rotor blades.
The blades of the rotor are attached to a mechanism which can tilt them back and forth. This changes the angle at which they hit the air, and thus, how much of a vertical force they exert on the rest of the chopper. If the blades are moving flat (parallel to the ground), they don't make much lift, but if they're tilted back at an angle so the air catches the bottom of the blades, they push the air down more, and this pulls the helicopter up. The angle of the rotor blades, not the throttle, is used to control lift, because the engine of the helicopter would be under tremendous strain if it had to keep supporting the load of the helicopter under it while also changing its internal airflow. The system of blade angle adjustment makes things much easier on the engine.
The control which adjusts the angle of the rotor blades is called the collective. It is essentially a lever in the cockpit. You pull on it, and the angle of the rotor blades is increased, making the chopper go up. You push on it, and the angle of the rotor blades decreases, making the chopper go down.
It is important to understand that the collective is NOT an altitude selector. Rather, it simply controls your rate of climb or descent. A great many computer helicopter simulators have greatly simplified the flight model of a helicopter by simply turning the collective into something much like the buttons in an elevator. (I'm talking about an elevator you find in a skyscraper, not the elevators you find on an airplane.) They make the collective simply move you to a new altitude, then stop. For example, if you move the collective up a little, then your helicopter goes up a few feet, then stops. The collective does not work this way in real life at all; It controls how fast you are going up or down. If you are in a hover and you increase the collective, your chopper goes up... And keeps going up. It would keep going up until you decrease the collective again (or until the air starts to thin out so much that the lift of the rotor is reduced). Similarly, lowering the collective doesn't just lower you by a few feet. It makes you go down, and you KEEP going down until you reach the ground (or you raise the collective again). When you change the collective to adjust your altitude, you need to return it to its old position to stay at the same altitude again. On every helicopter, there is a specific position for the collective in which the lift of the helicopter is the same as its weight, and thus it hovers. It might be a good idea for the helicopter pilot to remember this position for your chopper, so you can return to it quickly whenever you want to hover.
As has been mentioned, the main rotor also controls the pitch and roll of the chopper. It does this by tilting; If the rotor tilts forward, the whole body of the helicopter is pitched forward slightly. Similarly, if the rotor tilts to the right, the helicopter will start to roll to the right. This motion is controlled by the cyclic, which functions very much like the control stick in a normal airplane. In fact, in basic helicopter flight, if you use the collective as a throttle and the cyclic as a control stick, you won't be too far off; It will feel quite a bit like flying a plane. Obviously there are differences in the aerodynamics which must be appreciated, but even so, the pilot's control motions are similar.
In the same way, yaw is controlled with the foot pedals, much like in an airplane. This relates to the tail rotor; The tail rotor exists to counteract the torque produced by the main rotor. If there were only the main rotor, the whole body of the helicopter would rotate in the opposite direction to the rotor, and the pilots would get pretty dizzy. The tail rotor pushes the tail of the chopper sideways so the chopper doesn't normally spin around, but the foot pedals increase or decrease the angle of the tail rotor blades (just as the collective controls the angle of the main rotor blades), so you can turn the chopper to the right or left. This works quite a lot like the rudder in an airplane. And, just like in an airplane, when flying a chopper, you roll to turn; You don't use the foot pedals. Attempting to use the tail rotor to turn yourself around while in flight will produce the same results as using the rudder in a plane: Your aircraft will tend to "snap back" to its previous heading as soon as you take your foot off the pedal. However, the foot pedals are not as useless as the rudder in a plane, because the helicopter can hover. In a hover, the foot pedals can be (must be) used to turn the chopper. Indeed, when a chopper is taking off, it normally first rises vertically, hovers for a moment, uses the tail rotor to turn where it wants to go, and then begins forward flight. Attempting to use the main rotor to turn yourself when you're hovering (by pushing the cyclic to the right or left) will make the chopper slide sideways through the air; It will not make you turn.
Note that not all helicopters have a tail rotor; Some have two main rotors instead. There are several advantages to this: It makes more lift, because now there are two rotors pulling the chopper up instead of one. It also lends the chopper a lot more stability, because instead of balancing on one disc, the chopper's weight is spread across two. In dual-rotor helicopters, the two rotors spin in opposite directions, eliminating the need for a tail rotor, since the torque of each rotor counteracts the other. In these choppers, the foot pedals make one rotor spin slightly faster than the other, so that it has more influence on the chopper, thus making it yaw.
In the concept of a helicopter, there are several fundamental problems which the pilot must know about. Just as stalls and spins must be studied by the airplane pilot so they can be prepared for, so the chopper pilot must understand the little gremlins in his/her own aircraft, except that the chopper has more of them, and some of them are more complicated. Also listed here are other "special" properties of helicopter flight which don't exist in the airplane world.
A helicopter usually moves forward. This creates a fundamental difference in the forward speeds of the rotor blades, depending on which side of the chopper they're on. If the blades are turning counter-clockwise (as viewed from the top of the helicopter), then the blades will be moving forward when they're on the right side of the helicopter, and backward when they're on the left side. When a blade flies toward the rear of the chopper, it is called a "retreating blade".
Recall that the blades of the rotor are actually wings. As you may know (or not, but you should know it), a wing doesn't work too well when it's flying backwards. Although the helicopter blades are always moving forward relative to their position (because the helicopter does not fly fast enough to actually make them be flying backwards; this would require the chopper to fly faster then the blades are spinning), the effectiveness of those little wings is reduced. When the chopper is flying forward at high speed, there comes a point where those wings stall. The retreating blades will always be the ones to stall first, and so what will end up happening is that one side of the chopper still has enough lift, and the other does not. The stalling side will drop, and the chopper ends up doing a 360-degree roll, something which you do not ever want to do in a helicopter.
The effect of retreating blade stall is one of the most important factors in limiting the maximum flight speed of a chopper. Indeed, in most helicopters, the maximum safe speed which the chopper is rated for is usually just slightly below the speed at which the retreating blades will stall; This is no coincidence. It is something which must be respected and understood. (Retreating blade stall is technically a form of asymmetric lift, uneven lift created by different airflow over different parts of the helicopter's rotor.)
Ground effect is simply the effect of the ground to increase a helicopter's lift. If you blow air onto something which is being held close to your mouth, you will feel more air pushing against your face than if you were just blowing at the air. This is because the air will "bunch up" against the object, and the resultant increase in air pressure creates more of a pushing motion against you.
This same applies to helicopters. When a chopper is close to the ground, a cushion of air develops between the spinning rotor and the ground, because the air can only escape sideways. This means that at very low altitudes, there is a noticeable increase in lift, known as ground effect. Ground effect exists both during takeoff and landing; When taking off, you will find that you have to increase the collective to keep going up after you've lifted a few feet off the ground. Similarly, when coming down to land, you'll be able to descend smoothly most of the way, then suddenly you will start to hover, and you'll have to drop the collective a little more to touch the ground. This is normal and to be expected.
Translational lift is the seemingly paradoxical tendency of a helicopter to start gaining lift slightly when beginning to move away from a hover. Normally, moving a helicopter actually makes it lose altitude, because part of the lift is being deflected sideways to move the helicopter horizontally, and not all of it is being used to push it upwards. However, you may well notice yourself rising just a little bit when you start to push your chopper forward. The exact physics behind this are a little complicated, but basically you can think of it as being because the rotor starts cutting into "clean" air; When you hover, turbulence is created under your rotor blades, which reduces the effectiveness of them to keep you aloft. When you start to move sideways, "clean" (undisturbed) air hits your rotor, which makes it more effective at creating lift.
Like ground effect, translational lift is a marginal phenomenon. It appears briefly at the beginning when you start to move forward, and goes away as your chopper starts to slide through the air and gravity starts to gain the upper hand. This is when you increase the collective to maintain altitude.
Of course, no discussion of helicopter aviation would be complete without a mention of autorotation, one of the most frightening (but important) procedures in helicopter aviation. Autorotation is simply a power-off landing. It seems that a chopper would not be able to land without engine power, because it has no inherent lift. Unlike an airplane, which is really just a powered glider (and thus is capable of landing without power), a chopper is nothing but a cockpit with a pinwheel on top. Yet choppers can land without power, and they do if their engines cut out.
This is made possible by the effect of the air pushing against the rotor blades. As the helicopter moves down through the air, the air makes the blades spin, much as wind forces a windmill to turn. This creates a built-up mass of energy inside the rotor blades. As the copter falls down, the collective is kept at the bottom, so the blades are not generating any lift. This minimizes drag on them, and allows them to build up speed during the descent. This is key: A large supply of pent-up energy in the whizzing rotor blades is absolutely necessary for autorotation to succeed. To achieve this, the helicopter must go into a free-fall, because it must fall quite rapidly. This is breathtaking, to be sure, but it is necessary; Attempting to slow your descent by fiddling with the controls will only reduce the precious energy in those rotor blades.
The truly tricky part of autorotation is at the end. Moments before the helicopter would collide with the ground, the pilot must pull up the collective, putting that built-up rotational energy to good use and slowing the descent of the helicopter. If all goes well, the helicopter is slowed just enough to touch down on the ground without killing everybody on board. The timing required in this operation is split-second in nature, and it is difficult to judge exactly when to begin pulling on the collective. This is precisely what makes autorotation a hit-or-miss affair; If the collective is pulled back too early, the chopper will stall before it touches the ground, and after a moment of pausing in mid-air, it will resume its collision course. Similarly, pulling back on the collective a little too late will have disastrous results as well.
Autorotation is difficult to perform, and difficult to practice, since it's the kind of thing you don't live to fail at twice. Most chopper pilots just study the procedure, and sort of hope and pray that they never actually have an engine failure in the air.
A helicopter's engine has to work hard. Spinning those huge metal blades around at high speed takes a lot. There comes a point where it's all just too much. A helicopter has a torque meter inside it, which is a gauge indicating just how hard you're straining the engine. Basically, as you increase the collective, torque is increased as well. Your helicopter's motion through the air also increases torque; Pulling on the collective while you're falling makes more torque than pulling on the collective while you're rising. Severe engine over-torquing can easily lead to engine failure, which would require you to enter autorotation. In other words, keep tabs on your torque readout, and don't push your power plant beyond what it can handle.
Another mistake which can lead to engine over-torque is taking off too quickly. From the moment you turn your engines on, they need quite a long time to warm up and start spinning the rotor blades to takeoff speed. Trying to cut your takeoff time by lifting the collective and taking off before the blades have had time to fully spin up is a very bad idea. Thus, remember a simple and easy rule: DO NOT TAKE OFF BEFORE ALL ENGINES HAVE REACHED OPERATING RPM!
As has been noted before, the reason a helicopter needs a tail rotor is because otherwise the main rotor would make the chopper's body spin around. An addendum to this is that changing the force acting upon the main rotor will also tend to have an effect on the yaw of the chopper. If you increase or decrease the collective, this will change the drag on the main rotor, and this, in turn, will tend to yaw your helicopter slightly. Because of this, pilots learn to use the foot pedals whenever they adjust the collective.
Exactly which pedal to use for which situation depends entirely upon which direction your helicopter's blades spin in. There is no standard for this, although it is traditional in the Western world to make the main rotor spin counter-clockwise (when viewing the helicopter from above), while the East (including Europe and Asia) tends to follow the opposite standard, making their blades spin clockwise. Recall that the rotor makes the helicopter spin in the opposite direction, so a Western helicopter with blades spinning counter-clockwise would make the chopper's body spin clockwise (the pilot would perceive this as a turn to the right), while a chopper with a clockwise-turning blade would make the rest of the chopper turn counter-clockwise (which the pilot would call a turn to the left). Because increasing the collective magnifies the effect of the main rotor, this means that in a chopper with a counter-clockwise-turning rotor, when you increase the collective you must apply a bit of the left pedal to keep the helicopter pointing straight, while you must apply the right pedal when you lower the collective. In a copper with a clockwise-turning rotor, the opposite is true: Apply right pedal when you increase the collective, and apply left pedal when you decrease the collective. Yes, this is confusing, but once you get used to your helicopter it will become second nature, and you won't even need to think about it anymore: You will automatically press the correct pedal whenever you adjust the collective.
It should be fairly obvious by now that a helicopter stays aloft in the air by pushing air down. This means that the chopper basically sits atop a column of air that is rushing downwards. This can pose big problems if the chopper should somehow enter that column of air. This should never happen, but it can if the chopper descends too rapidly. A sudden downward motion might force the chopper into its own downwash. Then, as it continues to descend, its rotor creates more downward-moving air for it to go into, and a vicious cycle is created, causing the copter to drop like a rock. This is an ugly situation which can be difficult to escape from, and it is best avoided altogether. It comes back to one of the important points which has already been made before: Don't make sudden moves with your chopper. If you ever happen to accidentally enter such a fall, try to break out of it with the cyclic; This will disrupt the airflow around your rotor blades and help create a ragged surface of air "friction" for the blades to grip. Do not use the collective, as this will only aggravate the fall, much as using the ailerons aggravates a spin in an airplane.
In so-called single-rotor helicopters (those which use only one main rotor), the tail rotor serves a clear and important purpose. However, the tail rotor also presents some interesting side effects, mainly due to the fact that it has a lot of leverage over the rest of the helicopter, because it is mounted on the end of a long tail boom. It is mounted like this precisely so that it does have a lot of leverage on the chopper (if it did not, the tail rotor would have to be significantly more powerful), but it also means that when the tail rotor is having an effect you don't wish to have, the effect is magnified by the strong leverage.
During forward flight in a helicopter, the nose of the chopper will always tend to point into the oncoming airflow. This is because the wind pushes against the side of the tail rotor, and tends to push the tail around so that the rotor is parallel with the wind direction. This is very much like what happens to a weather vane; Part of the vane is shaped so that the wind tends to make it face directly away from the wind. A helicopter's tail rotor is the same way, when the rotor is at the rear.
However, that problem is merely annoying, and can be counteracted by a gentle application of force, rolling the helicopter to let the stronger main rotor pull the helicopter around. A much more dangerous effect of the tail rotor comes up when you are flying backwards. Helicopters, as you probably know, can fly in any direction, simply by tilting the main rotor that way. However, when you attempt to fly in any direction except forwards, the tail rotor's effect is still there: It still wants to move to the back of the helicopter. This means you cannot fly sideways very fast or you will suddenly find your helicopter spinning around as the tail is pushed in the opposite direction from where you are going. But flying backwards can be positively dangerous, because when you start, the tail rotor does not present a very large surface to the wind; It cuts into the relative wind, and everything seems fine at first. The problem comes when there is any slight deviation in the helicopter's course, and the wind is suddenly hitting the side of the tail rotor; The weather-vane effect will pop up again, and the tail will once again follow its natural tendency to try and move away from where the chopper is going. If you are flying backwards at high speed, this can very easily whip your helicopter around with such force that you barely have time to realize it happening. The result is often absolute and total loss of control, with little hope of regaining your place in the air before the chopper, now thoroughly unbalanced, tumbles to the ground. The moral of the story: You *can* fly backwards in a helicopter, but do so slowly. Because of the huge leverage the tail rotor has, even going backwards a little bit faster means getting turned around a lot harder if the tail suddenly spins around on you.
If you want more info on helicopters, check out the excellent copters.com, a site full of info on helicopters and how to fly them.
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Aircraft Electricity And Electronics, by Thomas K. Eismin
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