Principles of Helicopter Flight |
The electric helicopter is probably the most challenging form of radio control model, being mechanically complex in nature, and requiring 100% concentration while operating. Flying a model chopper is not unlike balancing a metal bearing or a marble on a piece of glass. If the mechanics of the chopper have been adjusted and aligned very well, it is similar to having a flat piece of glass. If the chopper is not set up just right, it is like having a convex piece of glass where the bearing wants to keep rolling off to one side. The first thing the budding helicopter pilot must realize is that the model works on the very same principles as the full-size and controlling the chopper is just as difficult, if not more-so due to size and orientation. It is not simply a matter of pushing one button for up, and another for forward flight, etc. Flying a helicopter, just like flying a model aircraft, is a skill that must be learned and that can only happen with practice . . . now that I have you thoroughly discouraged! Although building and flying a model chopper can be complex, it is also extremely satisfying. Being able to accurately control a vehicle which you can hover, fly forward, backward, sideways, and do all kinds of interesting maneuvers and aerobatics, as well as land at your feet, is very exciting. Unlike learning to fly a model airplane where flying with an instructor is a must, you basically learn to fly helicopters by yourself. Before you start flying, however, some time with an experienced helicopter pilot will be invaluable. He can help you set up your helicopter (it is extremely important to have the mechanics set up accurately for safe and easy flying) as well as give you some tips on flying; what to expect from your model and how to operate the controls. There are basically two different types of helicopters, fixed pitched and collective pitched. Fixed Pitch Vs Collective Pitch RC Helicopters RC Helicopters are becoming so popular that it attracts many new enthusiasts everyday. Upon getting their hands on this new enjoyable hobby, many beginners become puzzled when they know that RC helicopters come labeled either as "fixed pitched" or "collective pitch". For this reason, many new pilots have come to wonder what exactly the difference between the two is. To understand how these two pitch setups differ, the first step is to come to know what "pitch" means. The "pitch" of a helicopter is the angle of the main rotor blade. Generally, the measurement of this "pitch" angle is done relative to the horizontal plane. Helicopters generate lift by rotating their rotor through the air. With a fixed pitch helicopter, when the rotor spins faster, more lift is generated and the helicopter ascends. On the other hand, slower rotor rotation generates less lift and the helicopter descends. For collective pitch helicopters, the pitch of the blade becomes another factor in the lift generating equation. In this setup, the lift can also be altered by the angle (pitch) in which the main rotor blade is positioned. To put it another way; while to rotor is rotating at a constant speed, the lift generated can be altered by changing the pitch alone.
These controls are the collective pitch, the fore and aft cyclic pitch, the side to side cyclic pitch, and the tail rotor pitch. The collective pitch must also be coupled with the throttle of the engine so that when more load is put on the main rotor blades by increasing the pitch, more throttle is applied to help overcome the additional drag. Helicopter flight is governed by the pitch, or angle, of its rotor blades as the sweep through the air. When climbing or descending, the pitch of each blade is changed simultaneously and to the same degree. To climb, the angle or pitch of the blades is increased. To descend, the pitch of the blade is decreased. Because all blades are acting simultaneously, or collectively, this is known as collective pitch. For forward, backward and sideways flight, an additional change of pitch is provided. By the means the pitch of each blade is increased at the same selected point in its circular pathway. This is known as cyclic pitch. When a helicopter is started up and the rotors begin to turn they are maintained in flat pitch, with no angle, or bite on the air. As the engine warms up and the rotors turn faster, the collective pitch is increased and the helicopter lifts vertically. To make the aircraft fly forward, the collective pitch is retained, keeping the aircraft in the air, while the cyclic pitch is adjusted to enable each blade to have more bite as it passes over the tail. To stop the helicopter and hover, the cyclic pitch is returned to neutral, causing the rotor blades to have the same pitch thought-out their cycle, allowing the collective pitch to retain the helicopter hovering in the air. The left stick of your radio transmitter controls the collective and throttle in the vertical direction and the tail rotor pitch in the side to side direction. Your right stick controls both cyclic operations; up and down for fore and aft control and side to side for the cyclic side to side control. There are also mixing functions which mix the throttle and collective functions, and the throttle/collective and tail rotor functions. Operation The engine of a helicopter drives both the main rotor shaft and the tail rotor via a series of gears and a clutch. As the motor comes to speed, the clutch engages and begins to turn both rotor systems. Generally, at this point, there is no pitch on the main rotor blades and thus no lift. The throttle is increased until the main rotor blades are brought up to speed. To lift the helicopter collective pitch is applied. Because, for every action there is an equal and opposite reaction, when the engine is forcing the rotor blades to turn in one direction, the body of the helicopter will want to rotate in the opposite direction. The function of the tail rotor is to correct this tendency. The tail rotor blades provide enough thrust to the side to keep the helicopter pointing in one direction. By increasing or decreasing the pitch of the tail rotor blades the direction the helicopter is pointing can be changed. The cyclic control permits the main rotor blades to be varied independently making the helicopter move in a horizontal direction. If one of the rotor blades increases pitch as it approaches the rear while the opposite blade decreases in pitch while approaching the front during its rotation, more lift will be produced in the rear, tilting the helicopter forward, and thus moving the helicopter in a forward direction. The same principle applies for side to side and rearward, allowing the helicopter to fly in any direction. The control of the cyclic and collective pitch is transferred from the radio servos to the rotor blades via the swash plate. Part of the swash plate is stationary while the other part is allowed to rotate with the rotor head. Control linkage is connected from the servos to the stationary part of the swash plate as well as from the rotating part of the swash plate to the rotor head. When flying a chopper, small control inputs are continually required by the pilot to correct for deviations in the flight path. That is why 100% concentration is required in chopper operation. The more accurately the chopper is set-up, the fewer the number of corrections that are required by the pilot. What Happens if the Engine Stops? Auto-rotation is a way for helicopters to land successfully after a loss of power from the engine to the rotor drive systems. This is accomplished with the aid of a special device known as an auto-rotation clutch which allows the rotor blades to free-wheel. As soon as power has been cut, the throttle/collective control is brought back all the way. This will usually bring the main rotor blades to have slightly negative pitch. As the helicopter starts to descend, the air moving through the blades will keep them spinning. The spinning blades will act like a parachute in reducing the helicopters decent. When the helicopter nears the ground, the pilot increases the collective pitch making the pitch of the blades again positive. The momentum of the blades is converted to lift, slowing the descent of the helicopter down further, enabling it to land softly.
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Lesson One: Trimming The Helicopter |
Here's the difficult part. Getting the heli properly trimmed. A heli which is trimmed means that during a hover, all the control trims on the Tx is at centre. This is ideal, but this is not always the case. To begin, make sure that your servos center point is neutral with the control surfaces. ie: With your swashplate level, your aileron and elevator servos should be at center, with the control sticks also at center position. Rudder is difficult, so follow your instruction manual on pre-setting the rudder. Only during your first hover would you know how much rudder trimming you need. Setup your gyro, and pay careful attention to the way your gyro moves in conjunction with the way you swing the heli. You would want the gyro to counter your movement. Set up your throttle and pitch curve the way you want it. How I normally set mine (using a Futaba Skysport Heli Radio), is to set the throttle first, then the pitch. With the Throttle stick at 50% Center, open up the throttle lever on your engine to 50% (approx), and then fit the horn into the servo gear. Next, push the throttle trim to minimum, and the throttle stick to minimum as well. Your throttle should be fully closed. Make sure the linkages do not buckle. If your throttle is not at the fully closed position, there should be a pot (or computer) setting to adjust the Low end travel. Adjust this until the throttle fully closes without buckling the linkages. Now push throttle stick to high, and the throttle should fully open. As before, if the throttle is not fully opened or the linkage is buckling, then adjust the throttle pots (or computer) for the high end travel. This setting should make your throttle quite linear. Re-adjust later if you find your head speed to be off. For the pitch setting, set your throttle stick to centre, and with a pitch gauge, set the pitch for hovering (5 to 6 degrees), and mount the linkage to the servo gear. Push the throttle fully low, and then check the pitch. Adjust your pot (or computer) to give you the pitch you want. If you are unable to attain the pitch you desire, use a longer servo horn. Do the same for the high side. Normally, for starters, -1 to 10 degrees is ideal. Therefore, we can summarise it as follows: STICK POSITION THROTTLE PITCH Low 0% (trim at min) -1 degree middle 50% 5 degrees high 100% 10 degrees Lastly, CENTER OF GRAVITY (CG) has to be right in the middle of the rotor mast! If it's not, use weights to adjust the position till it's there. Once you have completed the preliminary setup, it's time to trim up the entire heli. Rev up the throttle, and wait until you get a good constant sound from the engine. Then increase the throttle slowly until the heli is very light on its feet. At this stage, your heli will start to move in all directions. Counter the heli movements by controlling your cyclic and rudder. For the first timers, this may be impossible, so get someone to help if necessary. Also, put the big cross sticks with balls at the end to save money in case anything happens. Trying to be macho here won't gain points. Natural movements of the heli will be as such for a clockwise turning rotor, your heli will tend to drift to the left, due to the tail rotor pushing to counter the torque. This is normal, and I normally just push my aileron trim 2 to 3 clicks right. Pushing the aileron right to counter will cause the tail to rise, because of the slight angle, and this is countered by a little back elevator. During the hover, your tail should be rock steady. On increasing throttle, your heli (head) will swing left, but the gyro should counter it slightly, and on decreasing throttle, the heli will swing right. If your heli behaves in this manner, then you got a properly trimmed heli. If the tail drops during lift off, your CG is too far back. Use a heavier battery or some weight to counter it. Same goes for the opposite. But if the CG is correct, check the swashplate. It might not be level. If your heli drops severely left or right, the swashplate is probably not level. Check direction, and readjust.
Note: If your heli is a counter-clockwise rotation rotor, then the effects will all be opposite of the above. The following article was obtain from The Shuttle Page |
Lesson Two: Basic Ground Excercises |
before the heli starts to lift off. If it starts to hover, lower your throttle/collective stick slightly until you find the point that it wants to hover, but does not quite have enough power. Now, move your cyclic controls around and see how the helicopter reacts. You will notice that the helicopter wants to slide to the right, left, forward and back. What you want to do is keep it stationary. Try your hardest to keep it right where you placed the helicopter after starting it.
ready for the next step, 3-5ft hover.
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Lesson Three: Three to Five Feet (Meter) Hover |
Now that you have completed the Basic Ground Exercises section, lets try to hover! Place the helicopter 5 foot in front of you with the tail pointing towards you, or the nose away from you. Now bring the helicopter up to speed just like you did in the previous lesson. Now when you have it stable on the ground, give it a little more throttle/collective. Now the helicopter will begin to lift off the ground, and continue to rise. When the helicopter gets about 1 foot off the ground, lower the throttle/collective just enough to cause it to stay staionairy. Try your hardest to keep the helicopter in one spot. I know that this will be very difficult at first, but stick with it. Once you have had the helicopter in the air for 30 seconds or so, lower the throttle/collective and set the helicopter back onto the ground. Now think about what has happened, why it has happened, and what you did right and wrong while hovering the helicopter. Now that you have digested some of the actions of the helicopter, and you know somewhat how it is going to react to your input while in a hover, give it another try. Again rev the engine up slowly and bring it to about 1 foot off the ground. Hold the helicopter there as long as you can this time. It is ok if the helicopter goes forward, right, left, or back. Just bring it back to the original starting point. In the beginning bringing the helicopter back to the starting point is going to be very difficult. Do not get discouraged. Practice will make perfect. Soon the helicopter will not even move off the point that you lifted off from. Once you get fairly good in a 1 foot hover, increase the throttle/collective to bring the helicopter to a 3-4 foot hover. You will notice that it becomes easier to control at the higher altitude. This is because your helicopter is no longer in ground effect. Before in your 1 foot hover, if your flying area was on the slightest slant, you would have noticed that your helicopter wanted to float right down the slant. About 3 1/2 foot, this ground effect is not existent. Keep practicing your hovering until you can keep the helicopter in one spot for a full tank of fuel. I know this is going to take some time, and you wish to move on, but it is important to master the hover before moving on to other maneuvers. Remember that a helicopter flight begins and ends with a hover!
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Lesson Four: 90 degrees Hover (Left and Right/Forward and Back) |
You have four quandrents: 1 A 2 YOU 3 4 Now, you see the 1,2,3,4 but what is the 'A'? This is where you were hovering in the last lesson. I know want you to again place your helicopter on the 'A' spot, bring your helicopter to a 4-5 foot hover. Once everything is settled down, slowly move your helicopter to area 1. This will be anywhere from 5-10 foot to your left/front side. Now, get familiar with hovering the helicopter in this area, and then slowly move the helicopter to area 2. Again, 5-10 foot to your right/front side. Once you have a feel for hovering to your sides, go back and master areas 1 and 2. Once you can hover in areas 1 and 2 as good as you can on the 'A' spot, lets try to hover in area 3 and 4. Repeat the same steps as above. Also, when hovering in areas 3 and 4, do not turn around. Turn your head, but not your body. This will get you ready to start your circle rounds in Lesson 7. The following article was obtain from The Shuttle Page |
Lesson Five: Figure Eight Hover |
6 2 7 1/5 3 8 4 YOU If you can figure out the above diagram, give it a try. Go from 1/5 to 2, 3, 4, back to 1/5, 6, 7, 8, then start over at 1/5. Now while you are doing this you should be in a 3-5 foot hover, and the tail should always be pointing towards you. This will give you practice moving around while hovering, or more towards the point, giving you the ability to land where you wish with class. The following article was obtain from The Shuttle Page |
Lesson Six: Forward Flight Basics |
a 3-5 foot hover. Now give it a little forward cyclic control to move into forward flight. The helicopter will begin to loose altitude and at this point, pull your cyclic control back. This will not only stop the altitude loss, but will also stop your helicopter from moving forward. You will also probably notice that the helicopter will begin to rise in altitude. You will want to lower the throttle/collective and bring the helicopter back down to a 3-5 foot hover. Hover it right back to your original starting point, and try this a few more times. As soon as you get used to what your helicopter feels like in transitional lift, and your transition into forward flight, lets start a hover about 10-15 foot. From this hover, again give your helicopter some forward cyclic control, and this time when the helicopter begins to loose altitude, let it until it reaches 5-8 foot. At this point, pull your cyclic back, to slow the decent, and cause the helicopter to come out of forward flight. Again, repeat this a few times and when you are confident with going into and coming out of forward flight, move onto the next step, Circle a couple of rounds! Do not let it get going to fast towards the beginning! The following article was obtain from The Shuttle Page |
Lesson Seven: Circle Arounds in Forward Flight |
around. Now bring your helicopter to a 3-5 feet hover, and move into forward flight. Now bank the helicopter so you are staying about 20 feet away from yourself about 10 feet up, in a circle to which ever direction is easier for you. After a few circles around yourself, let the helicopter go to 30-40 feet away from you, and 20-30 foot in the air. Slowly increase the altitude and distance till you are circling about a 300 foot radius, and in the air 100 feet. This will take some time, but will allow you to develop a sixth sense, the ability to determine what your helicopter is doing at a distance. Once you have mastered this, switch your direction. If you were going clockwise, go counter-clockwise and visa-versa. What ever you do, do not let it get at too steep of an angle towards the ground. The following article was obtain from The Shuttle Page |
Lesson Eight: Figure Eight in Forward Flight |
of the figure 8 you are nose in. Hense, your controls are reversed. This is easier to handle while in forward flight, than in a nose in hover, but beware, and do not give it the wrong stick. Remember the pattern of the figure 8 hover? 6 2 7 1/5 3 8 4 YOU Now, on this your circles are going to be much larger, and you are going to be moving throughout the figure 8 faster than your hover. Something else you will have to do is use your tail rotor control for cordinated turns. After a few loops you will get the hang of which control to give in what situation. Bring your helicopter to a 3-5 foot hover, then move into forward flight from point 1 towards point 2. Then simply follow the numbers, until you have completed the figure 8. When it is all done, do it again. Each time, make the figure 8 larger, and higher. This again will give you the ability to determine what your helicopter is doing at a distance.
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Lesson Nine: Nose In Hover |
reversed. For instance, you want the heli to move right? Give it left cyclic. You want the heli to come towards you? Give it forward cyclic. This may sound easy, but it is a lot more difficult then meets the eye. Your forward/back cyclic control is reversed. One thing that confused me when someone told me this, is that when you give it forward stick, the helicopter is not going to go backward. It is still going to go forward, however when you are in a nose in hover, going forward is going to bring it closer to you. This is the reversal. Giving it back cyclic will move the helicopter further away, while giving it forward cyclic will bring it closer to you. Opposite of the tail in hover. Your right/left cyclic control is reversed. If you wish to move the helicopter to the right, you must apply left cyclic control. If you wish to move the helicopter to the left, you must apply right cyclic control. An easy way to remember this is to simply think, stick under the low blade. This will keep your helicopter nice and level. Your tail rotor is opposite also. If you wish to have the heli point to the right, you must apply right tail rotor. This may sound correct, but remember in tail in hover, when you want to point the heli to the right, you give it left stick.That抯 why, you fly the nose. Well, remember while in nose in hover, fly the tail. If you want the tail to go to the right, give it right stick. If you want the tail to go to the left, give it left stick. Just the opposite of what you did in the tail in hover. Remember - Fly the tail, and stick under the low blade.
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Beginner's Guide to Electric Helicopter Flight |
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