What causes retreating blade stall?

Retreating blade stall is a hazardous flight condition in helicopters and other rotary wing aircraft, where the retreating rotor blade has a lower relative blade speed, combined with an increased angle of attack, causing a stall and loss of lift.

• High blade loading (high gross weight)
• Low rotor RPM.
• High density altitude.
• Steep or abrupt turns.
• Turbulent air.

At some airspeed, the retreating blade begins to stall. From the pilot’s perspective, when this happens an abnormal vibration will be felt, the nose can pitch up, and the helicopter can have a tendency to roll in the direction of the stalled side.

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. Assuming the pilot stays below VNE, retreating blade stalls are easy to avoid.

Loss of tail-rotor effectiveness (LTE) occurs when the tail rotor of a helicopter is exposed to wind forces that prevent it from carrying out its function—that of cancelling the torque of the engine and transmission. Any low-airspeed high-power environment provides an opportunity for it to occur.

What Happens If a Helicopter Flies Too High? As the helicopter ascends, the air begins to thin. With thinner air, the main rotor becomes less efficient. … When the blades can no longer generate enough lift to keep ascending, the helicopter reaches its maximum operating envelope (the coffin corner).

Dynamic rollover begins when the helicopter starts to pivot around its skid or wheel. This can occur for a variety of reasons, including the failure to remove a tiedown or skid securing device, or if the skid or wheel contacts a fixed object while hovering sideward, or if the gear is stuck in ice, soft asphalt, or mud.

Generally, though, a helicopter can hover anywhere between 2- 5 hours on average before it needs to be refueled. The length of time depends on the type of helicopter, the efficiency of the engines and main rotor system, as well as the kind of hover a pilot wants to hold.

Just as airplanes will not fly below a certain airspeed, helicopters will not fly below a certain rotor rpm. … Rotor stall, however, can occur at any airspeed, and the rotor quickly stops producing enough lift to support the helicopter, causing it to lose lift and descend rapidly.

Helicopters have a power-on never exceed airspeed (Vne) that can be an aerodynamic limitation, a structural issue or based on the onset of retreating blade stall. … As a helicopter’s speed increases the airflow becomes more horizontal causing the main rotor rpm to decay.

Mast bumping is contact between an inner part of a main rotor blade or a rotor hub and the main rotor drive shaft (or ‘mast’). Serious mast bumping in flight usually results in the helicopter breaking up in flight, which is fatal for those on board.

In civil aviation, the Pilot in Command has the ultimate responsibility for the safe operation of the aircraft and we shoulder this responsibility as a profession.

The BK117, the helicopter we fly most, has one particular wind-related limitation: It is unsafe to start up or shut down in wind speeds over 50 knots (about 90 km/h) due to the risk of the overhead blade striking another part of the aircraft when it’s rotating at a low speed.

The tail rotor can fail if the rotor stops turning or the pitch change mechanism stops functioning. The loss of tail rotor drive is an emergency which might require the lowering of the collective to maintain control. … The pilot had practiced simulated pitch change malfunction emergency landings many times.

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.

Actually, helicopters have a built-in mechanical control called the collective pitch lever that allows them to descend slowly and land even if the engine dies. This maneuver is called autorotation.

As the propeller spins around the crankshaft, the speed of the prop blades is highest at the tip and slowest at the root. … If blade angle was uniform across the prop, thrust and pressure would have wide variations from root to tip. There could be a negative angle of attack at the root, and blade stall at the tip.

If the tail rotor fails in flight, engine torque can no longer be countered by the tail rotor, and uncontrolled spinning of the aircraft is a possibility. Most manufacturers call for an immediate autorotation. Some call for a running landing, instead.

A helicopter may spin out of control when the anti-torque system is unable to counteract the torque being created by the engine. When the torque of the engine is greater than the thrust being produced by the anti-torque system, the helicopter will begin to spin.

One significant advancement in the last decade has been the no-tail rotor, or NOTAR, helicopter. As you now know, vertical-lift flight is impossible without a tail rotor to counteract the torque produced by the main rotor. Unfortunately, the much-smaller tail rotor makes a lot of noise and is often easily damaged.

Choppers reportedly also flew ropes and other equipment to climbers stranded above the Khumbu icefall, which also sits nearly 18,000 feet above sea level. And helicopters have actually made it even to the peak of Everest before, the first time in 2005.

Hover-in-ground-effect (HIGE) Helicopters are able to hover anywhere from 5-80 feet above high mountain peaks because of the interaction between the ground and the helicopter’s rotor blades. … This also means there is an altitude limit to hovering, even with ground effect.

Helicopters usually fly at altitudes of 10,000 feet, though turbine-engined helicopters can fly as high as 25,000 feet.

Static Rollover. ▪ Static rollover occurs when the helicopter pivots about one. skid/wheel in contact withthe ground to such an extent that the. helicopter’s Centre of Gravity (C of G) moves beyond the. skid/wheel.

When landing from an autorotation, the energy stored in the rotating blades is used to decrease the rate of descent and make a soft landing. A greater amount of rotor energy is required to stop a helicopter with a high rate of descent than is required to stop a helicopter that is descending more slowly.

If it hovers, then it remains in one spot. That’s easy for it to do, because it was moving east at about 1000 miles per hour, which is the speed of the earth’s rotation (near the equator). It lifts off with that speed, and the act of hovering keeps it over its lift off spot.

There is no shift because the helicopter is actually hovering in the envelope of air that is rotating at (approximately) the same speed as the earth. There is no relative motion between helicopter and the Earth’s surface because both are ‘rotating’ at the same speed.

TLDR – Some modern helicopters are equipped with autopilot systems that allow the rotorcraft to automatically hover in place. However, helicopters are inherently less stable compared to airplanes, which restricts the ability of the autopilot system to completely control flight.

It is commonly applied to the phenomenon whereby an engine abruptly ceases operating and stops turning. It might be due to not getting enough air, energy, fuel, or electric spark, fuel starvation, a mechanical failure, or in response to a sudden increase in engine load.

Electrical stalling, especially in a 3 phase induction motor, typically is result of a single phase or missing phase condition. … There is actually a speed zone where the motor torque and load curve are normally near one each other, this speed zone could become critical in case of voltage drops or load variations.

The most common cause of motor failure, and arguably the most difficult to overcome, is low resistance. Low resistance is caused by the degradation of the insulation of the windings due to conditions such as overheating, corrosion, or physical damage.

If you live in a sparsely populated area, an aircraft is not allowed to fly any lower than 500 feet to any person, vessel, vehicle, or structure including your house. … A helicopter can legally fly at a lower altitude “if the operation is conducted without hazard to persons or property on the surface”.

Vne of Never exceed speed is (roughly) 90 percent of the maximum dive speed (Vd) attained during flight test that did not encounter severe vibration that could result in structural damage, at this speed (or below) pilots should always be able to control the aircraft.

7: Velocity Minimum Unstick. VMU for Velocity Minimum Unstick. This is the absolute minimum speed at which an aircraft can take off and is achieved by pitching the aircraft up to the maximum during the take-off roll.

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. the feathering hinge enables the pitch angle of the blades to change.

The cause of the crash was unknown in nearly 60 per cent of the cases. The Californian-based Robinson Helicopter Company attributes the crashes to “excessive or inappropriate pilot inputs”. In other words, the pilot’s response in a sudden low-gravity situation has been incorrect.

The International Air Transport Association (IATA) is the trade association for the world’s airlines, representing some 290 airlines or 83% of total air traffic.

In that same year, 1,474 accidents were reported involving general aviation aircraft. NTSB statistics from 2013 reveal that in contrast to the safety record of commercial airplanes, small private planes average five accidents per day, accounting for nearly 500 American deaths in small planes each year.

Country/regionNumber of fatal civil airliner accidentsUnited States862Russia538Canada191Brazil190