This tilts the main rotor tip-path plane to allow forward, backward, or lateral movement of the helicopter. The power required for flight is the second work that must be transmitted to the shaft of the rotor. In general, for a helicopter in forward flight, the total power required at the rotor, P , can be expressed by the equation. Inductive power is consumed to produce lift equal to the weight of the helicopter. From the simple 1-D momentum theory the induced power of the rotor, P i , can be approximated as.
The profile power required to overcome the profile drag of the blades of the blades of the rotor is. The parasite power, P P , is a power loss as a result of viscous shear effects and flow separation pressure drag on the fuselage, rotor hub, and so on. Because helicopter fuselages are much less aerodynamic than their fixed-wing counterparts for the same weights , this source of drag can be very significant [ 1 ]. The parasite power can be written as. In addition, when calculating the power required of the helicopter, the required power of the tail rotor must also be calculated.
It is calculated in a similar way to the main rotor power, with the thrust required being set equal to the value necessary to balance the main rotor torque reaction on the fuselage.
The use of vertical tail surfaces to produce a side force in forward flight can help to reduce the power fraction required for the tail rotor, albeit at the expense of some increase in parasitic and induced drag. The power needed to rotate the main rotor transmits to the main rotor from the engine through the transmission Figure But the main rotor cannot get all the power, which is developed from the engine, as part of it is spent for other purposes and does not go to the main rotor.
This part of the power of the motor that is transmitted to the main rotor is called available power. It is defined as the difference between effective power and total loss. Excess power—this is the difference between the available and the power required.
The rotor downwash is unable to escape as readily as it can when flying higher and creates a ground effect. When the rotor downwash reaches the surface, the induced flow downwash stops its vertical velocity, which reduces the induced flow at the rotor disk Figure Influence of ground effect on the induced flow.
Figure 15 shows the effects of this on the power required to hover. If the hover height in ground effect must be maintained, the aircraft can only be kept at this height by reducing the angle of attack AoA so that the total reaction produces a rotor lift exactly equal and opposite to weight.
It shows that the angle of attack is slightly less, the amount of total rotor thrust is the same as the gross weight, the blade angle is smaller, the power required to overcome the reduced rotor drag or torque is less and the collective control lever is lower than when hovering out of ground effect.
Influence of ground effect on the rotor drag. These conclusions are also true to flight in ground effect other than the hover, but the effect is smaller. Autorotation is an emergency mode. In the case of vertical autorotative descent without forward speed without wind, the forces that cause a rotation of the blades are similar for all blades, regardless of their azimuth position [ 2 ]. During vertical autorotation, the rotor disk is divided into three regions as illustrated in Figure 16a : driven region, driving region, and stall region.
Figure 17 shows the blade sections that illustrate force vectors. Force vectors are different in each region, as the relative air velocity is lower near the root of the blade and increases continually toward its tip. The combination of the inflow up through the rotor with the relative air velocity creates different aerodynamic forces in each section along the blade [ 2 ].
Autorotation regions in a vertical descend and b forward autorotation descend. Force vectors in vertical autorotation. In the driven region, illustrated in Figure 17 , the section aerodynamic force T acts behind the axis of rotation.
This force has two projections: the drag force D and lift force L. In this region, the lift is offset by drag, and the result is a deceleration of the blade rotation.
There are two sections of equilibrium on the blade—the first is between the driven area and the driving region, and the second is between the driving region and the stall region. At the equilibrium sections, the aerodynamic force T coincides with the axis of rotation.
There are lift and drag forces, but neither acceleration nor deceleration is induced [ 2 ]. In the driving region, the blade produces the forces needed to rotate the blades during the autorotation. The aerodynamic force in the driving region is inclined slightly forward with respect to the axis of rotation.
This inclination provides thrust that leads to an acceleration of the blade rotation. By controlling the length of the driving region, the pilot can adjust the autorotative rpm [ 2 ].
In the stall region, the rotor blade operates above its stall angle maximum angle of attack , causing drag, which tends to slow rotation of the blade. Autorotative force in forward flight is produced in exactly the same scheme as when the helicopter is descending vertically in still air.
However, because of the forward flight velocity there is a loss of axial symmetry in the induced velocity and angles of attack over the rotor disk. This tends to move the distribution of parts of the rotor disk that consume power and absorb power, as shown in Figure 16b.
A small section near the root experiences a reversed flow; therefore, the size of the driven region on the retreating side is reduced [ 1 ]. Helicopter stability means its ability in the conditions of external disturbances to keep the specified flight regime without pilot management [ 3 , 5 ]. Let us consider the longitudinal motion of a helicopter on the hovering regime Figure Longitudinal motion of the helicopter in hover. Recall that a helicopter, like any aircraft, is considered statically stable, if it after a deviation from the steady flight regime tends to return to its original position.
Suppose, for example, that as a result of the action of a wind gust U the thrust T is deflected backward see Figure 18b. Under the action of the horizontal component, the helicopter will start to move back with a speed V x , and under the action of the moment M it will start to rotate relative to the roll axis, increasing the pitch angle with the angular velocity q see Figure 18c.
Both effects: both the translational velocity and the rotation of the fuselage, and hence the axis of the rotor, will cause the resultant forces T on the rotor to tilt to the same side, opposite to the original inclination.
This will cause the appearance of a horizontal component and a longitudinal moment, already oppositely directed, due to which the helicopter will tend to return to the initial pitch angle and to zero forward speed.
This means that the helicopter is statically stable in pitch angle and hover speed. Its static stability is due to the properties mentioned above: speed stability and damping. Consider, however, the further movement of the helicopter. The inclination of the resultant in the direction of parrying disturbance is too great because of the presence of velocity stability. It leads to the fact that the helicopter in its movement to the initial position skips the equilibrium position and deviates in the opposite direction, but already by a large magnitude.
The motion of the helicopter takes the character of oscillation with increasing amplitude. The aircraft, which in the free disturbed motion ultimately leave the initial equilibrium state, is called dynamically unstable.
Thus, a helicopter on a hovering regime is dynamically unstable. The roll motion on the hover has a similar character. The difference here is manifested only in the period and the degree of growth of oscillation, which depend on the moments of inertia of the helicopter, different in pitch and roll. The helicopter is neutral in the yaw angle and the altitude on the hover. This means that the helicopter does not tend to keep a given course angle or a given flight altitude.
At the corresponding disturbances these parameters will change. But their change will continue only as long as the perturbation is working. At the end of the disturbance, the course angle and altitude will not change. It can be said that the helicopter is stable with respect to the yaw rate and the vertical speed.
This stability is explained by the fact that the main rotor at an increase of the airspeed in a direction opposite to the thrust reduces its thrust, and conversely, when this speed decreases—increases the thrust, thus creating a damping force in the direction of the axis of rotation.
Therefore, the tail rotor creates a large damping yaw moment on the helicopter, and the main rotor—a damping force for vertical helicopter movements.
In forward flight, the efficiency of helicopter control and the derivatives of the damping moments and moments of stability with respect to the main rotor speed vary insignificantly. However, the moment derivative with respect to the angle of attack, which for the main rotor corresponds to the instability, begins to play an important role. This instability can be compensated if the fuselage of the helicopter has a stabilizer, which improves the desired degree of stability in the angle of attack.
But it is difficult to provide satisfactory longitudinal stability even with well-designed stabilizer. In the forward flight, the roll movement is strongly connected with the yaw movement, just as it does on the airplane. The own lateral motion of a single-rotor helicopter during a forward flight, as a rule, is periodically stable. In the low-speed modes, while the relationship between the roll and yaw movements is still small, and the roll motion, like the hovering, is unstable, the lateral motion of a single-rotor helicopter is unstable.
Static stability of helicopters with two main rotors differs slightly from the stability of the helicopter with one main rotor. The tandem main rotor helicopter has a significantly greater longitudinal static stability, and the coaxial main rotor helicopter has a greater lateral stability.
This is explained by the change of main rotors thrust at a disruption of the equilibrium. So, the helicopter, essentially, cannot maintain a steady flight regime. There are four basic controls used during flight.
They are the collective pitch control, the throttle, the cyclic pitch control, and the antitorque pedals Figure Basic helicopter controls. The collective pitch control changes the pitch angle of all main rotor blades. The collective is controlled by the left hand Figure As the pitch of the blades is increased, lift is created causing the helicopter to rise from the ground, hover or climb, as long as sufficient power is available. The variation of the pitch angle of the blades changes the angle of attack on each blade.
The change in the angle of attack causes a change in the drag, which reflects the speed or rpm of the main rotor. When the pitch angle increases, the angle of attack increases too, therefore the drag increases, and the rotor rpm decreases. When the pitch angle decreases, the angle of attack and the drag decrease too, but the rotor rpm increases. To maintain a constant rotor rpm, which is specific to helicopters, a proportional alteration in power is required to compensate for the drag change.
The purpose of the throttle is to regulate engine rpm if the system with a correlator or governor does not maintain the necessary rpm when the collective is raised or lowered, or if those devices are not installed, the throttle has to be moved manually with the twist grip to maintain desired rpm.
Twisting the throttle outboard increases rpm; twisting it inboard decreases rpm [ 2 ]. The correlator is a device that connects the collective lever and the engine throttle. When the collective lever raises, the power automatically increases and when lowers, the power decreases. The correlator maintains rpm close to the desired value, but still requires an additional fine tuning of the throttle.
Now let's mentally let air flow over the profile Fig. In the example, this means that the second person with the upper hand significantly reduces the pressure on the card, while the first person with the lower hand maintains the original pressure.
The card moves up. The low pressure of the air molecules on the upper side of the profile is comparable to an innumerable number of rather weakly pressing fingers, while the higher pressure on the underside of the profile is comparable to an equally large number of strongly pressing fingers. The force resulting from this pressure difference is called buoyancy. If this buoyancy is greater than the weight of an object, that object leaves the ground.
Our little hopper will finally become a flight! Aviation pioneers of the late 19th century in particular could sing a song about this if you were still alive. However, despite numerous failed attempts, they did not give up and made the difficult step from countless small failed hops to serious flights of at least several meters. The principle described above - applying a lifting force that is greater than the weight - is still the basis of all aircraft today.
It almost doesn't matter how heavy an aircraft is as long as a force can be generated that is greater than the weight that holds the aircraft on the ground. That's all? Sounds strange, but it is true. For this reason, the world's largest passenger aircraft, the Airbus A, can fly at all - even with its maximum takeoff weight of That corresponds to about three adult blue whales. Or VW Passat. The A can even travel up to Passat and blue whale, on the other hand, still cannot fly.
Straight to the next part: Why can a helicopter fly part 2. Search for:. Show bigger picture. Part 1: Introduction and Buoyancy This part is the first of a few to answer the question of why a helicopter can now fly. But first, the short foreword from the e-book, which illustrates our motivation: Foreword As passionate helicopter pilots and flight instructors, we naturally have a lot to do with helicopters. Introduction While an aircraft can only take off from the ground and remain in the air at high speeds, the helicopter simply lifts itself into the air from a standing start.
Completely detached: How heavy things learn to fly A powerful jump in the air from your knees is not enough to be able to say with a clear conscience that you have flown. Figure 1: The weight dreams of flying like a bird So if we really want to fly properly, we need a force that permanently counteracts the weight and therefore stays in the air for more than a few seconds. Figure 2: If you have the longer way, you have to be faster So that the air particles can meet again at the back of the wing, the "upper ones" have to flow a little faster with the longer way.
Experiment 1: How are fast-flowing air and buoyancy related? Experiment 2: How can you visualize pressures and buoyancy? Figure 3: The early predecessor of the Airbus A here during secret tests Summary The low pressure of the air molecules on the upper side of the profile is comparable to an innumerable number of rather weakly pressing fingers, while the higher pressure on the underside of the profile is comparable to an equally large number of strongly pressing fingers.
In the next part: The physical basics of buoyancy - don't worry, it's easy to explain. We accompany an aircraft from the stand to take off - practice up close.
Please put on your helmet and glasses before reading. Then share this post! We hope they win the award! Thanks for sharing your comment, Wonder Friend! We sure do, too, Erick! The team working on the helicopter is incredible and we hope they are successful! We certainly agree with you, Katelyn! We are very impressed with the helicopter itself and the pilots who lift it off the ground! There is a lot of hard work involved!
We are really glad this was a Wonder you enjoyed! There were so many people working together to help the helicopter and the pilot get off the ground! It was so incredible to watch!
We're happy that today's Wonder was right up your alley, Michael! Thanks for sharing your comment at Wonderopolis today! We sure hope to see you soon, Wonder Friend!
We were very impressed by today's Wonder, Emily! It was fun to watch the team work together to reach a goal-- especially when the helicopter and pilot reached 8 feet in the air! We know they are working on a safer, smoother landing and we hope they reach the 10 foot requirement, too! You never know, Bryleigh, you could be the next great helicopter pilot! We like that you checked out today's Wonder and learned something new! Thanks for joining the fun today-- we'll see you soon!
What a great word to describe the helicopter team, Julian! Nice work! They are a group of people with a lot of perseverance! We hope they succeed in reaching the 10 foot requirement-- it would be a great accomplishment! We're so excited that today's Wonder was right up your alley, Jason! We can't take credit for creating the helicopter, but we are so proud of the hard work the students and the pilots have shown! We hope they keep up the hard work to reach 10 feet with their human-powered helicopter!
It's so much fun to Wonder with you, Jason! We agree, Jauquin! We bet it took a great deal of hard work, planning and determination to build that helicopter! It's pretty awesome to see it flying with the help of the pilots!
We really liked today's Wonder, too, Azhir! We think the students and the pilots worked together like a team to reach their goal! We learned so much from today's Wonder and we're glad to hear that you did too! We Wonder if you will create something like a human-powered helicopter in the future!?
We certainly agree, Pablo! We bet it takes a great deal of determination to succeed- we hope those students and the pilots win! These students and pilots have really tried their hardest, great point, Kamaria! We hope they are successful and win the prize for their awesome invention! We bet they are working hard to create a safe, soft landing for the helicopter and the pilot! Wasn't that an amazing Wonder video, Henry!? Collin and Henry must be very powerful to get the helicopter so high off the ground!
Great point, Carla! We hope that Collin is okay, but we bet he jumped right back in the helicopter after they repaired it! Very cool! You've got a great idea of how a helicopter works, Aniyah! Thanks for sharing your comment with us! We bet you'd LOVE the Wonder video today-- it shows a group of engineers who are working on a human-powered helicopter! Thanks for stopping by Wonderopolis today! Great Wonder, Mrs. Reasor's Class! We bet you'll enjoy checking out this site that explains the original helicopter designed by Igor Sikorsky!
We bet you'll enjoy learning about clay animation, but we're so excited that you're WONDERing about cartoon animation, too! WOW, thanks so much, Wonder Friend curiosity! We're so glad that today's Wonder made you feel like you were floating in thin air! We hope you'll join us for more fun very soon! Great question, Jack T! We love applesauce here at Wonderopolis!
We believe applesauce is somewhere in between, as it's made of a solid but pulsed, mashed and blended into a liquid substance.
Check out all the new information you've learned today, Wondergirl! It makes us so happy to hear that you really enjoy your time at Wonderopolis! Virtual high five for you! Thanks for your super ideas for the next Wonder We are undergoing some spring clearing site maintenance and need to temporarily disable the commenting feature.
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Help spread the wonder of families learning together. We sent you SMS, for complete subscription please reply. Follow Twitter Instagram Facebook. How do helicopters work? What can helicopters do that airplanes cannot? What are some of the special jobs helicopters can do? Wonder What's Next? Tomorrow's Wonder of the Day has ears, but it can't hear a thing! Be sure to grab a friend or family member to help you explore the following activities: Want to make your own helicopter?
First, you'll need some basic things to get started. A powerful engine would be a good place to start. Then you'll need several hundred pounds of high-strength steel…What? Don't have those things around the garage? Not to worry! Here's a simpler version you can try instead. With just a few common items, you can make a paper toy that behaves just like a mini-helicopter!
If you could fly anywhere in the world, where would it be? The North Pole? The South Pole? A Caribbean island? Once you've settled on a destination, give some thought to HOW you'd like to fly there. Would you rather fly on an airplane or a helicopter? Make a list of pros and cons of both airplanes and helicopters. Share your list with a friend or family member. Do they agree with you? Why or why not? What is the largest helicopter?
How about the fastest helicopter? Do your own independent Internet research about helicopters. Try to find the answers to these and any other interesting helicopter-related questions you can think of. Share what you learn with a friend. Did you get it? Test your knowledge. What are you wondering? Wonder Words aircraft sleek incite blade rotor hover capability military ambulance mobility aeronautical engineer amaze bulky lift troops runway prototype Take the Wonder Word Challenge.
Join the Discussion. Dec 2, Sounds like you need to dig a little deeper by taking a Wonder Journey, simon! May 29, That's a great question. We don't know the answer.
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