Why helicopter fly

So far with the help of helicopters, lives of over a million of people were saved. In the last years, the results obtained in the scientific research of many aeronautical disciplines has allowed for large increase in the flight dynamics, control, navigation, and lift capabilities of helicopters. The continued advance in the computer-aided design, manufacturing, and lightweight materials have permitted new approaches in the helicopter configuration concepts and design.

In , Leonardo da Vinci proposed a flight device, which comprised a helical surface formed out of iron wire. According to the historical sources, in about , Mikhail Lomonosov of Russia had built a coaxial rotor, modeled after the Chinese top, but powered by a spring device, which flew freely. A short list of the most important achievements in the historical evolution of helicopters is the following: Sir George Cayley considered the inventor of the airplane published a paper, where he gives some scientific details about the vertical flight of the aircraft;.

Four years after Orville Wright first successful powered flight, which took place in December 17, , a French, named Paul Cornu constructed a helicopter and flew for the first time in the world in November 13, ;. This helicopter did not fly completely free due to its lack of stability;. He proposed the concept of cyclic pitch for rotor control;. Ellehammer designed a helicopter with coaxial rotors. The aircraft made several short hops but never made a properly flight;.

He was the first specialist who described the helicopter autorotation;. He could be considered the most important person in the helicopter design. The helicopter is a complex aircraft that obtains both lift and thrust from blades rotating about a vertical axis.

The helicopter can have one or more engines, and it uses gear boxes connected to the engines by rotating shafts to transfer the power from engines to the rotors Figure 1. Typical helicopter drive train. The most common helicopter configuration consists of one main rotor as well as a tail rotor to the rear of the fuselage Figure 2a. A tandem rotor helicopter has two main rotors; one at the front of the fuselage and one at the back Figure 2b. This type of configuration does not need a tail rotor because the main rotors are counter rotating.

It was proposed by the Serbian man Dragoljub Ivanovich in The single main rotor a and the tandem rotor helicopter b. A variant of the tandem is the coaxial rotor helicopter Figure 3a which has the same principle of operation, but the two main rotors are mounted one above the other on coaxial rotor shafts.

This constructive solution was developed by Nicolai Ilich Kamov. Another helicopter type is the synchropter, which use intermeshing blades Figure 3b. This type of helicopter was proposed by Charles Kaman. The coaxial rotors a and the intermeshing blades b.

If the two rotors are mounted either side of the fuselage, on pylons or wing tips, the configuration is referred to as side by side Figure 4. The side by side rotors. Another aircraft type that should be mentioned is the autogiro invented by Huan de la Cievra , which is a hybrid between a helicopter and a fixed wing airplane.

It uses a propeller for the forward propulsion and has freely spinning nonpowered main rotor that provides lift. The basic flight regimes of helicopter include hover, climb, descent, and forward flight, and the analysis and study of these flight regimes can be approached by the actuator disk theory, where an infinite number of zero thickness blades support the thrust force generated by the rotation of the blades [ 1 ].

The air is assumed to be incompressible and the flow remains in the same direction one-dimensional , which for most flight conditions is appropriate. Also, the main and tail rotors generate the forces and moments to control the attitude and position of the helicopter in three-dimensional space. At the plane of rotor, the velocity through the rotor disk is v i named the induced velocity and in the far wake the air velocity is w.

The helicopter in hovering flight. For a steady flow, the above equation becomes. This equation requires the condition that the total amount of mass entering a control volume equals the total amount of mass leaving it. The principle of conservation of fluid momentum gives the relationship between the rotor thrust and the time rate of change of fluid momentum out of the control volume.

The left part of Eq. In projection on rotational axis, Eq. The induced velocity at the plane of the rotor disk is v hover ,. The power required to hover is the product between thrust T and induced velocity v i ,. This power, called the ideal power, forms the majority of the power consumed in hover, which is itself a high power-consuming helicopter flight regime.

In assessing rotor performance and compare calculations for different rotors, nondimensional quantities are useful. The inclusion on the half in the denominator is consistent with the lift coefficient definition for a fixed-wing aircraft. The rotor power, C P , and rotor torque, C Q , are defined as. Considering the helicopter in climb, one can see that the flow enters the stream tube far upstream of the rotor and then passes through the rotor itself, finally passing away from the rotor forming the wake Figure 6.

When the helicopter leaves the hovering condition and moves in a vertical direction, the flow remains symmetrical about the thrust force line, which is normal to the rotor disk.

The flow becomes very complex in a medium descent rate condition, but in climb, the mathematical approach is close to that used in the hover conditions. The axial climbing flight. Applying the principles of conservation for mass, momentum, and energy like in the hover we get:. The left part of the above equation represents the square of induced velocity in hover, v h 2 , and replacing it, we get. The power consumed is given by the product of the thrust and the total velocity through the rotor disk, that is.

The stream tube in descent. Even if the sign of thrust is negative, that does not mean that the thrust is negative, because the assumed sign convention consists of positive velocity w , in down direction. According to the conservation energy principle, it follows that. The valid solution is. An approximation of the velocity in this region, called vortex ring state, could be [ 1 ]. Figure 8 shows the graphical results from this analysis, made in the Maple soft program.

Induced velocity variation. In the normal working state of the rotor, if the climb velocity increases, the induced velocity decreases and also, in the windmill brake state if the descent velocity increases the induced velocity decreases and asymptotes to zero at high descent rates.

In the vortex ring region, the induced velocity is approximated, because momentum theory cannot be applied. The flow in this region is unsteady and turbulent having upward and downward velocities. During normal powered flight, the rotor generates an induced airflow going downward and there is a recirculation of air at the blade tips, having the form of vortices, which exist because higher pressure air from below the rotor blade escapes into the lower pressure area above the blade.

The rate of descent that is required to get into the vortex ring state varies with the speed of the induced airflow. Although vortices are always present around the edge of the rotor disk, under certain airflow conditions, they will intensify and, coupled with a stall spreading outward from the blade root, result in a sudden loss of rotor thrust. Vortex ring can only occur when the following conditions are present: power on, giving an induced flow down through rotor disk; a rate of descent, producing an external airflow directly opposing the induced flow; low forward speed.

Using Eqs. For the vortex ring state, we can use the approximation 31 for the induced velocity ration, therefore in this case, the power ratio is. According to the power to power in hover ratio values, shown in Figure 9 , the power required to climb is always greater than the power required to hover, namely this ratio is greater than unity.

In descent flight, the rotor extracts power from the air and uses less power than to hover. Power required as a function of climb and descent velocity. Rotor in forward flight. Dividing Eq. The above equation can be very easy to be solved in Maple soft. The primary way to distinguish between different main rotor systems is represented by the movement of the blade relative to the main rotor hub. The main categories are fully articulated, semi rigid, and rigid.

In hovering flight, the blades flap up and lag back with respect to the hub and reach equilibrium position under the action of aerodynamic and centrifugal forces. In forward flight, the asymmetry of the dynamic pressure over the disk produces aerodynamic forces that are the functions of the blade azimuth position. The hinges allow each blade to independently flap and lead or lag with respect to the hub plane.

The lead-lag hinge allows in-plane motion of the blade due to the Coriolis and radius of gyration changing in flapping movement. Transition from hover to forward flight introduces additional aerodynamic forces and effects that are not found when the helicopter is in stationary hover.

Due to the difference in relative airspeed between the advancing and retreating blades, the lift is constantly changing through each revolution of the rotor. Figure 12 shows the flapping, lead-lag, and feathering motion of a rotor blade. Blade movement axis. In a fully articulated rotor, each main rotor blade is free to move up and down flapping , to move forth and back dragging , and to twist about the spanwise axis feathering. Semi rigid rotor has, normally, two blades attached rigidly to the main rotor hub and is free to tilt and rock independently of the main rotor mast, one blade flaps up and other flaps down.

The rigid rotor system cannot flap or drag, but it can be feathered. The natural frequency of the rigid rotor is high, so the stability is difficult to be achieved. The single rotor helicopters require a separate rotor to overcome the effect of torque reaction, namely the tendency for the helicopter to turn in the opposite direction to that of the main rotor. It has the purpose to transmit cyclic and collective control movements to the main rotor blades and consists of a stationary plate and a rotating plate.

The stationary plate is attached to the main rotor mast and the rotating plate is attached to the stationary plate by a bearing surface and rotates at the same speed as the main rotor blades. The neutral position of the cyclic stick changes as the helicopter moves off from to hover in forward flight. Trim control can adjust the mechanical feel in flight by changing the neutral position of the stick.

Collective pitch lever controls the lift produced by the rotor, while the cyclic pitch controls the pitch angle of the rotor blades in their cyclic rotation. 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. Bulky , oddly-shaped helicopters rarely incite the same kinds of feelings. Once you learn about what helicopters can do, though, you might think twice the next time you see one!

Unlike airplanes, helicopters feature spinning wings called blades or rotors on top. As a helicopter's blades spin, they create a force called lift that allows the helicopter to rise into the air. A helicopter's rotors perform the same function as an airplane 's wings. In addition to the rotors on top, helicopters also have a rotor in the back.

The rear rotor can face different directions, allowing the helicopter to move forward, backward, and sideways. Helicopters can do many things that airplanes cannot.

For example, helicopters can move straight up or down and hover in the air without moving. They can also fly backwards and sideways. They can even take off or land without a runway! These capabilities make helicopters ideal for many tasks. They've been used by the military for many years to move troops , deliver supplies, and serve as flying ambulances. Their mobility allows helicopters to get to people in hard-to-reach places, such as mountains and oceans.

Helicopters are also used often by the media to report on breaking news and traffic. Because of their ability to hover and land without a runway , helicopters are ideal for moving large objects.

They can also be used to carry large loads of water to fight forest fires. The father of the modern helicopter is Igor Sikorsky, a Russian aeronautical engineer who later came to the United States. He first filed a patent for a helicopter design in The first working prototype of his design didn't take flight until eight years later, though.

Think you'd like to fly a helicopter some day? We think you can do it! It will take quite a bit of training, though. Flying helicopters is a lot harder than flying airplanes. Did you realize you need both hands and both feet to fly a helicopter successfully? We hope today's Wonder of the Day took you to new heights! Be sure to grab a friend or family member to help you explore the following activities:. Hi, zack! We encourage you to read the Wonder very closely to learn more. You can also keep researching at your library and online.

Hey there Aidan, helicopters transport lots of cargo, so they need to be large enough to carry all of that! Thanks for sharing your comment! Higgins' Class! How cool that our helicopter Wonder connects to your lesson today! The forward movement the helicopter needs in order to take off comes from the rotation of the rotor blades! We Wonder if you can do some more research of your own about helicopters' use of force and motion!

Keep up the great work, Wonder Friends! We're glad you thought it was cool! Awesome, we're glad you liked today's Wonder Ryleigh! We can't take credit for the Wonder video today but we hope the group of students reached the 10 foot requirement!

They have been working so hard! We can't believe all the different types of helicopters that exist! We are glad that you liked today's Wonder-- we hope you have a terrific Tuesday!

WOW, how cool, Daniel C! We are so impressed with your interest in helicopters-- way to go! We hope your remote control helicopter turns out great We are so excited that you enjoyed today's Wonder, Mrs.

Thomas's Tigers! How exciting that some of our Wonder Friends are going to be pilots when they grow up! We can't wait to find out what tomorrow's Wonder, Merrick! It's going to be a great one for sure! We think you did a great job of summarizing the hard work of the team! We learned what the word "perseverance" means today, too! We're so happy to Wonder with you-- we are smiling ear-to-ear! Have a terrific Tuesday! We bet flying a helicopter with your arms and legs is tough and challenging, but very rewarding!

We're glad today's Wonder made you smile, Berkleigh! Thanks for commenting! We can't take credit for today's Wonder video, Jordan, but we are very impressed by the hard work of the helicopter team! We are so excited that today's Wonder was right up your alley! We can't take credit for the helicopter, but we're excited that you enjoyed today's Wonder! We aren't the team of engineering students, but we're glad to share some cool information about helicopters with you! We think they are fearless and determined!

We were very impressed, too, Kayla R! 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! The rotating wings of a helicopter function just like the airfoils of an airplane wing, but generally helicopter airfoils are symmetrical, not asymmetrical as they are on fixed-wing aircraft. The helicopter's rotating wing assembly is normally called the main rotor. If you give the main rotor wings a slight angle of attack on the shaft and spin the shaft, the wings start to develop lift.

In order to spin the shaft with enough force to lift a human being and the vehicle, you need an engine, typically a gas turbine engine these days. The engine's driveshaft can connect through a transmission to the main rotor shaft. This arrangement works really well until the moment the vehicle leaves the ground. At that moment, there is nothing to keep the engine and therefore the body of the vehicle from spinning just as the main rotor does.

In the absence of anything to stop it, the body of the helicopter will spin in an opposite direction to the main rotor. To keep the body from spinning, you need to apply a force to it. Enter the tail rotor.