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.
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 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.
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. 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 vi named the induced velocity and in the far wake the air velocity is w. 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 power required to hover is the product between thrust T and induced velocity vi ,. 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, CP , and rotor torque, CQ , 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.
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. 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. 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. 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. 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. 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, Pi , 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, PP , 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 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.
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 ]. 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 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. Add to Wishlist. Guide with precision your multi-role helicopter, demolish the enemy defences and let the raiders disembark in enemy bases.
Tactics, flying skills and the right amount of ruthlessness in the attacks are critical to complete the long and engaging campaign against the mysterious secret organization. You are in command of the helicopter and in real time you will have to govern with care the powerful machine gun available on board, take the right countermeasures against enemy attacks and launch the devastating missiles on targets.
You choose the best strategy to win! Three levels of difficulty, five scenarios, free flight, 24 missions and 90 challenges are going to provide hours of fun! Reviews Review policy and info. Bug fixes. View details.
Other Answers. You have to make sure your cheat code is off for "low gravity ". Once this cheat is deactivated you will be able to raise and land without problems User Info: hotmomma Sign Up for free or Log In if you already have an account to be able to ask and answer questions.
Answered What do i do after the mission "the seige"? Answered Where can I find the location of the number for "eye for an eye"? Answered What does "U" mean? Answered How do i land a helicopter? Ask A Question. Keep me logged in on this device.
Forgot your username or password? What do i do after the mission "the seige"? Where can I find the location of the number for "eye for an eye"? What does "U" mean? As a player, you will take the role of Tom Larkin, a civilian pilot, and try to save the company with your brother Joe Larkin.
Overall the game is all rounded flight simulator, reasonably capable of entertaining gamers, especially those who are new to this genre. It also has a powerful mission editor. Desert Strike is a 90s popular single player shooting game in which the player takes control of an Apache helicopter and engage in various missions, from hostage rescue to attacking enemy installations in hostile grounds.
The game took its inspiration from the Gulf War of the 90s and portrayed a battle between antagonist General Kilbaba and the United States. The Apache is equipped with a machine gun and powerful missiles. So a player must make appropriate weapon choices. A still from Apache: Air Assault. The core objective of this game is to try and stop various terrorist attacks fictional in unstable regions of the world.
The game can be played in both single-player and multiplayer mode. FlightGear is a free, open-source flight simulator. The sim features over 20, real-world airports with accurate runway markings and elevations. You can start with trainer helicopter the Robinson R22, especially if you are a beginner. The original game only features two helicopters; the rookie Robinson R22 and Agusta Westland AW, however, you can always use add-ons.
While the helicopter simulation on FSX might not be as accurate as you expected it to be, they certainly worth your time. You can download many well-known helicopters from manufacturers such as Bell, Eurocopter, and Boeing. The game is known for its realistic graphics and maneuverability.
The sim includes advanced automation features, such as state of the art targeting system, guided missile system, mounted targeting, and autopilot. Bell in X-Plane One thing that separates X-plane with other sims is its revolutionary aerodynamic model known as the blade element theory. Ordinarily, flight simulators emulate the performance of a real-world aircraft drag and lift with the help of predefined data. But those simulators are unable to emulate an aircraft performance where preset data are not available.
Furthermore, it features a unique plugin architecture that enabled users to build their customized modules. Biprojit has been a staff writer at RankRed since He mainly focuses on game-changing inventions but also covers general science with a particular interest in astronomy. His domain extends to mobile apps and knows a thing or two about finance. If I could find another helicopter game that great I would buy it and the system it is compatible with!
Thanks Marty. My first one was LHX — ugly but fascinating. It is worth to mention that Enemy Engaged still has updates coming out, after 20 years since release date.
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