Expert pls:How does the helicopter gain its forward speed?

Question

* I know that the blades give lift upwards.
* The blades pitch can be adjusted.
* The blades circle can be tilted for a certain degree in all directions.

Answer 1

You've got some pretty good answers there already, I hope I can clarify-

A helicopter has the same 4 basic forces acting on it as any heavier than air aircraft.

1. Gravity
2. Lift
3. Thrust
4. Drag

Increase any of those parameters and it will cause the aircraft to descend, climb, accelerate, or slow down, respectively. Decrease and it will do the opposite.

In a level constant speed flight:

gravity = lift
thrust = drag

A helicopter also has the same basic movements as any aircraft:

Yaw = nose L-R, vertical axis
Pitch = nose up-down, transverse horizontal axis
Roll = turn, longitudinal hoizontal axis

A helicopter has a rotating wing called a rotor. Most helicopters have 2, 3, 4, or 5 blades in the rotor. When the rotating wings are moving with enough speed to generate lift, the plane of rotation is called a rotor disk. It's very complex, but let's keep it simple.

In a hover in a zero wind condition, the rotor is producing exactly as much lift as there is gravity, and it is not producing any thrust. The rotor disk is perfectly horizontal, so there is no drag or thrust. Now if the pilot chooses to move forward, s/he moves the cyclic (right hand) ahead, which causes increased pitch as the blades are at the back of the rotor disk, and exactly the same amount of decrease in pitch at the front. This causes the rotor disk to tilt forward (on its flapping hinges or fles in the rotor head or blades, depending on the design of the rotor system), and the helicopter will move ahead because now in addition to the lift we have thrust. Now if the pilot doesn't do anything else, the helicopter will very rapidly crash to earth because the rotor has now lost part of its lift to thrust, so the pilot must also add some collective (left hand), which increases the pitch on the entire disk as the blades travel around the hub. One more thing the pilot has to worry about now is RPM, because as the power demand from the main and tail rotors change, the engine throttle (twist grip on collective control) must be adjusted to maintain the right power setting. If the pilot doesn't do anything else, the helicopter will rotate (to the right if its US built) out of control because there is now extra torque in the main rotor that needs to be compensated with the tail rotor (foot pedals). But that takes more power, so s/he needs to add more throttle and that will cause the helicopter to move to the right, so now you need to correct to the left. Its a never ending process that takes some practice.

If s/he wants to slow down, just reverse all these steps.

So basically its the tilting of the main rotor that controls the flight direction of the helicopter. Tilting to the left causes the helicopter to move to the left (with right pedal input) in a hover, and tilting to the left in flight will turn to the left. The fuselage (body) of the helicopter will tend to follow the tilting of the rotor, but that is not what causes a helicopter to move forward.

Except for some experimental military types, there are no helicopters that derive forward thrust from jet exhaust, sorry there Sponge, not even the Boeing CH47 Chinook.

Don't even ask about gyroscopic precession, translational lift, coaxial rotors, compressibility stall, and vortex ring state yet!

Answer 2

The pitch of each blade is changed as the rotor head rotates. By increasing the pitch, and therefore the lift, as the blade moves back and then decreasing the pitch as it moves forward the rotor "disc" is tilted forward therefore some if the lift is directed forward resulting in the craft traveling in that direction. If the pitch is then increased on all the blades the helicopter will travel faster. Some people think that the blades must turn faster but they are maintained at a near constant speed, obviously as the pitch increases the blades try to slow down therefore more power needs to be supplied to the drive. This is normally automatic but on early helicopters (as seen in some films) the power was applied by a twist grip on the "collective" stick, this being the control used to increase the pitch of all blades collectively! The same principle is applied to produce movement sideways, backwards, etc. The direction the helicoper is facing is controlled by the tail rotor, changing the pitch to move the tail left or right.

Answer 3

To move forward the rotor disc is angled so that the blade is lower in front of the helicopter than behind, this often produces a tail up nose down attitude, however there is a problem because the blade coming forward is travelling faster than that going back by the forward speed of the helo, so with blade speed limited by mach at 200 mph if the forward moving blade is doing 700 mph the receeding blade is only doing 300 mph producing much less potential lift, at 350 mph the receeding blade would be stopped producing no lift at all and the Helo would roll on to its side and crash, this is why tilt rotors such as the Osprey are being developed to move hover capable vertical take off and landing "helicopters" into the 350 mph plus range.

Answer 4

The blades are adjusted to tilt the rotor disc forward (with the cyclic control). This provides lift to keep the helicopter up and some forward thrust. This also requires more power from the engine since not only is the rotor providing lift and thrust, but it is moving off the cushion of air that is under it in a hover. To provide more power, the collective is pulled and the power of the enigne increased.

Most helicopters have an engine governor so the pilot doesn't have to mess with the throttle. Jet thrust is negligable and undesired because it robbs power from the rotor and makes hovering in one place difficult.

The helicopter body tilts in the same direction because it is dragged by the rotor, but this is also undesirable since it increaes drag. The stabilizers at the back reduce the body angle when cruising.

To see how fast a cool helicopter can go forwards, sideways and backwards and do other neat things, check this video out:

http://www.youtube.com/watch?v=7lPdnTT2xVY

Answer 5

There are four main controls,

A collective, this is the lever, like a handbrake on a car, this collectively adjusts the pitch on all blades so they all pitch to provide upward or downward thrust.

The throttle, or rev control which is a twist control on the collective lever, this basically controls how much power the engine puts into the blades, obviously as soon as the collective pitches to thrust, the blades would slow down, so the throttle has to be increased.

The cyclic, this is like a disc that all the blades ride on, and is connected to the joystick. Pushing the joystick forward means that blades at the front will get less pitch and blades at the back get more hence titling the whole copter forwards and moving forwards.

Then theres the foot controls which alter the thrust of the rear fan, to allow the copter to turn on its axis, and to balance the torque of the main blades(stop the blades from spinning the copter).

Answer 6

You already mentioned the 3 basic components that make it possible for a helicopter to move forward. When the rotor disc is tilted in a given direction it produces lift not just upwards but also in the direction it's tilted towards. As a result of that the helicopter will move in that direction.

It gets a lot more complicated, but that is the basic idea.

Answer 7

The entire rotor can be tilted forwards or backwards by a few degrees. Using this technique (tilt forwards), the helicopter starts to accelerate and tip forward due to the lift force pointing at an angle not opposite to weight. This is why helicopters don't travel as fast as jet aircraft, but can hover accurately.

Answer 8

The blades' rotation cone/disk can be tilted slightly forward, which causes forward speed. I don't think the blade pitch comes into play as far as forward speed. I seem also to recall that some helicopters use the jet blast to provide forward motion, such as the CH47 Chinook, for example.

Answer 9

To control a helicopter, one hand grasps a control called the cyclic, which controls the lateral direction of the helicopter (including forward, backward, left and right). The tilt of the helicopter will cause weight to be exerted onto the front of the vehicle moving it forward. The other hand grasps a control called the collective, which controls the up and down motion of the helicopter (and also controls engine speed). The pilot's feet rest on pedals that control the tail rotor, which allows the helicopter to rotate in either direction on its axis. It takes both hands and both feet to fly a helicopter!

Answer 10

The only way is to tilt the whole helicopter forwards and sometimes the platform that the blades are mounted on can also tilt