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Mountain/high altitude flying


iaf-man
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The highest landing, which was made by the A-Star in the Alps had the help of updrafts. The peak he was on would not provide any in-ground effect help. The records that are for picking up people do get help from ground effect.

 

The highest altitude flight, which is by an A-Star also, obviously has no help from ground effect.

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The highest landing was actually in the Himalayas (Mt. Everest) by an A-star (B-3) The highest altitude is still held by the Lama. There was a publicity stunt a few years ago with a B-2 in South Africa (Fortis watches) that claimed 42000+ feet but it was never certified by FAI

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The records can be seen at http://records.fai.org/rotorcraft/current....112&id2=1&id3=2

 

Altitude without payload : 12 442 m (40,820 ft.)

Date of flight: 21/06/1972

Pilot: Jean BOULET (France)

Course/place: Aérodrome d'Istres (France)

Rotorcraft: SA 315 Lama (1 Turboméca Artouste III B, 735 kW)

 

Highest take-off : 8 848 m (29,029 ft.)

Date of flight: 14/05/2005

Pilot: Didier DELSALLE (France)

Course/place: Mount Everest (Nepal)

Rotorcraft: Eurocopter AS 350 B3 (1 Turbomeca Arriel 2B1, 557kW)

Registered 'FWQEX'

Note that last year's record on Everest was for highest take-off, not landing. Someone could have attempted the record for highest (crash) "landing", but would that aircraft have then been capable of further flight? :huh:

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Okay, here's a question for the aerodynamics guys. What happens to a helicopter when it reaches its altitude limit? I've just learned about retreating blade stall as the result of too much airspeed. Does the air just get too thin and it won't go up any more of is there a more drastic effect?

 

The records can be seen at http://records.fai.org/rotorcraft/current....112&id2=1&id3=2

 

Altitude without payload : 12 442 m (40,820 ft.)

Date of flight: 21/06/1972

Pilot: Jean BOULET (France)

Course/place: Aérodrome d'Istres (France)

Rotorcraft: SA 315 Lama (1 Turboméca Artouste III B, 735 kW)

 

Highest take-off : 8 848 m (29,029 ft.)

Date of flight: 14/05/2005

Pilot: Didier DELSALLE (France)

Course/place: Mount Everest (Nepal)

Rotorcraft: Eurocopter AS 350 B3 (1 Turbomeca Arriel 2B1, 557kW)

Registered 'FWQEX'

Note that last year's record on Everest was for highest take-off, not landing. Someone could have attempted the record for highest (crash) "landing", but would that aircraft have then been capable of further flight? :huh:

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I'll take a crack at that one, but someone correct me if I'm wrong

 

Think it's a product of lower air density like you said. Less air for the blades = less lift of course.

 

Guessing the drivetrain also comes into play too. Those blades might be able to extract more lift... but not when coupled to that engine and tranmission.

 

So is rotor droop the end result of trying to exceed altitude limits, or does the ship simple refuse to go any higher?

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I was thinking on this and my answer to myself would be that in an OGE hover you would reach a maximum and can't get anymore at full collective. But in translational flight you would need more pitch and therefore get into a retreating blade stall faster. I would consider that a drastic effect. I wonder if I have answered my own question of just muddied the waters more?

 

I'll take a crack at that one, but someone correct me if I'm wrong

 

Think it's a product of lower air density like you said. Less air for the blades = less lift of course.

 

Guessing the drivetrain also comes into play too. Those blades might be able to extract more lift... but not when coupled to that engine and tranmission.

 

So is rotor droop the end result of trying to exceed altitude limits, or does the ship simple refuse to go any higher?

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A wing will only stall when it reaches its critical angle of attack, And in terms of the engine the higher you go you are going to go from torque or temp limited to being gas producer limited because of the less dense air. One of the other speed limiting factors on a helicopter is compressibility which is when the helicopter is flying so fast that the tips of the advancing blades are getting close mach. And I know that high altitude airplanes i.e 747 757 can get into what is known as the coffin corner which is when the exceed their altitude limitation, and is where the airplanes stall speed and maximum mach number have come so close together that if they speed up the shock wave will move farther back alond the airfoil and cause controllability to be lost, or if they slow down at all the wing will reach its critical angle of attack and controlability will be lost. Maybe the same principals apply to a rotorcraft blades at extremely high altitude.

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High (density) altitude ops:

 

Reduced power from engine

 

Main and tail rotors operating at higher AoA meaning higher induced flow angles, so more drag for same lift. More power required.

 

More power needed by main rotor, more torque generated. You need more tail rotor thrust, but the tail rotor is already operating at high AoA/pitch, so you run out of pedal.

 

So high altitude means you have less power available, require more power to stay level, require more tail rotor thrust but also have less of that available. Depends on the aircraft, but up high, more than a few will run out of tail rotor at the hover before they run out of power.

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