What are the 3 types of main rotor system?
Main rotor systems are classified according to how the main rotor blades are attached and move relative to the main rotor hub. There are three basic classifications: semirigid, rigid, or fully articulated. Some modern rotor systems, such as the bearingless rotor system, use an engineered combination of these types.
What is the cause of main rotor blade coning?
Coning – Main rotor blades rise to form a “cone” owing to production of lift. Coning is balanced by centrifugal force produced by spinning blades. Coriolis Effect – Rotor blade tendency to accelerate and decelerate as its center of mass moves due to flapping.
Why main rotor blade is thicker at root?
When a blade rotates, each point on it travels at a different speed. The further away from the root, the higher the velocity. This means that the contribution to lift and drag of every point on the blade differs, with each aspect getting larger when moving closer to the rotor tip.
What is a Hingeless rotor?
Hingeless rotos
In the hingeless rotor system the mechanical flapping hinges and rotatable joints are replaced by appropriately flexible materials at the root of the blade that allow the flapping and rotation movements (Fig 2). This became possible with the invention of plastic.
What RPM does a helicopter blade spin at?
The blades of an average helicopter on Earth rotate at a rate of 400-500 rotations per minute. The blades of the Ingenuity #MarsHelicopter rotate at a rate of 2,500 rotations per minute.
What is blade feathering?
Feathering the blade means changing the pitch angle of the blade. By changing the pitch angle of the blades you can control the thrust and direction of the main rotor disc. Semi-rigid Rotor System. A semi-rigid rotor system is usually composed of two blades which are rigidly mounted to the main rotor hub.
How could you reduce the coning angle?
The coning angle increases when more lift is generated as compared to centrifugal force. Conversely, the coning angle decreases when the centrifugal force increases as compared to the lift generated.
What is feathering the rotor blade?
Feathering the blade means changing the pitch angle of the blade. By changing the pitch angle of the blades you can control the thrust and direction of the main rotor disc.
Why do helicopter blades flap?
The advancing rotor blade reaches its maximum “up-flap” velocity at point “A”. The upward flapping of the advancing blade reduces the angle between the blade chord line and the relative wind. This decreases the angle of attack, which reduces the amount of lift produced by the blade.
Why can’t helicopter blades go supersonic?
In normal operations, and design aims to achieve this, the rotor tips do not go supersonic since when they do, there is a sudden and large decrease in performance with more power required, higher blade loads, vibration and noise. Think about a helicopter flying forwards.
Can a helicopter fly Mach 1?
Airwolf (from the T.V show Airwolf) is a Mach 1+ helicopter capable of reaching speeds up to Mach 2. For it’s time, it’s weapons system was pretty farfetched (had fourteen weapons systems overall, including chaffe and flares) at it’s time.
What is rotor flapping?
Flapping is the vertical movement of a blade up or down to increase or decrease lift in order to compensate for dissymmetry of lift. To equalize lift across the rotor disc, the advancing blade flaps up and the retreating blade flaps down.
What angle should a propeller be?
The range of degrees could vary from -5 to +30 degrees. An average rake angle for most outboard propellers is 15 degrees.
Do Chinook blades counter rotate?
Tandem-rotor helicopters such as the CH-47 Chinook also use a counter-rotating arrangement. The efficiency of a contra-rotating propeller is somewhat offset by its mechanical complexity.
What causes retreating blade stall?
High weight, low rotor r.p.m., high density altitude, turbulence and/or steep, abrupt turns are all conducive to retreating blade stall at high forward airspeeds as they increase the blade pitch to generate more thrust and hence increase the angle of attack.
What is rotor blade hunting?
Blades are able to move fore and aft or lead-lag, (called hunting) by use of a drag hinge. Normally a damper is attached to the blade and hub to restrict excessive movement. The drag hinge is used because, when a rotor blade flaps up, its center of mass moves closer to the axis of rotation.
Why are helicopter blades not twisted?
Twisting a rotor blade causes it to produce a more even amount of lift along its span. This is necessary because rotational velocity increases toward the blade tip.
Can you stall a helicopter?
Just as in an airplane, the wing or main rotor blade will stall if it gets slow enough and the angle of attack is exceeded. That’s the primary value in determining a helicopter’s VNE. Any faster and the retreating blade will stall.
How much RPM is needed to fly a helicopter?
Helicopters also make air move over airfoils to generate lift, but instead of having their airfoils in a single fixed wing, they have them built into their rotor blades, which spin around at high speed (typically about 400–500 RPM on a small helicopter or about 225 RPM on a huge Chinook, with the speed depending on the …
Is it possible for a helicopter to Mach 1?
Can helicopters fly upside down?
In general, a helicopter may be able to fly upside down for short periods of time. However, inverted flight is never recommended for long-term use. Helicopters can fly upside down for a short amount of time when they are performing a loop.
How fast do police helicopters go?
Police and Medical Helicopters
The speed of a medical helicopter depends on its model, but on average a medical helicopter will fly at 120mph or 195km/h. Police helicopters have an average cruise speed of 155mph or 250km/h.
Why do rotor blades lead and lag?
The need to lead-lag is due to the Coriolis effect, otherwise known as the law of conservation of angular momentum. As a rotor blade flaps up, the blade’s speed increases because the center of mass of that blade moves closer to the axis of rotation.
What is rotor blade feathering?
What does adding Cup to a prop do?
Cupping the propeller provides a lot of benefits for relatively small changes to the blade form. Adding a cup changes the effective or nominal pitch by essentially adding camber to the blade shape. This camber helps reduce cavitation and increase performance.