New European Heavy Lift Helicopter
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Spent a little time with our American cousins a few years ago being flown around in their Chinooks from their floaty things. The blade fold system was used regularly but being a manual system it looked to be a bit of a faff when windy.
The USN & USMC use the CH-46 Sea Knight, not the CH-47 Chinook.
Yes, they are very similar... but the CH-46 is smaller and specifically designed for ship-board use.
The CH-46 does have power blade-folding. If they were manually folding them, perhaps the system wasn't working on those particular aircraft.
UH-46 Sea Knight
Champagne anyone...?
I thought Chinooks had folding blades (albeit manual)? I've seen yank ones with folded blades and the Boeing website lists them as being manually folding.
Admittedly it does look like a massive bloody performance.....
Admittedly it does look like a massive bloody performance.....
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Europower ?
If the Big Chopper does begin to get serious attention on both sides of the Atlantic, the Europrop consortium has a suitably high-powered engine now in flight test on the A400M. Going by the Mi-26's use of the Bear's 10 - 11000 BHP engine, the Europrop power unit, suitably amended, would seem to be in with a chance, specially as P&W's (indirectly, through MTU) somewhere in the mix, and nobody else outside Russia has an engine like it.
'Ere's 'opin', innit?
'Ere's 'opin', innit?
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Sea Knight Helicopter of the Marine Corps
Tandem rotors have been a feature of all production helos built by ... Special features included power-operated blade folding, integral cargo handling ... The CH-46D Sea Knight helicopter is used by the Navy for shipboard delivery of cargo and personne. ... Information and photos provided by the United States Navy ...
Sea Knight Helicopter of the Marine Corps
Tandem rotors have been a feature of all production helos built by ... Special features included power-operated blade folding, integral cargo handling ... The CH-46D Sea Knight helicopter is used by the Navy for shipboard delivery of cargo and personne. ... Information and photos provided by the United States Navy ...
Sea Knight Helicopter of the Marine Corps
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Does a twin rotor not use any anti torque power?
Nope, a tandem rotor helicopter does not expend any power producing anti-torque effect. The two rotors rotate in opposite directions, thereby cancelling each other's torque without net expenditure of power on torque cancellation.
A single main rotor helicopter with tail rotor has to allocate 12 to 15 of per cent available shaft power to the tail rotor in vertical flight. Fast cruising flight unloads the tail rotor because the vertical stabilizer offsets the main rotor's torque, but this anti-rotor torque trim soaks up about the same per cent of available power by converting rotor torque to vertical stabilizer drag.
The opposed direction of rotor movements of a tandem helicopter also has a swirl-straightening effect on the air flow through the combined momentum disk, thereby slightly increasing vertical lift/thrust.
You are aware that the most efficient helo configuration for vertical thrust is a counter rotating, coaxial design because the coax. config. minimizes vorticity -- a fancier word for swirl -- of the momentum flux through the rotor disk? A coax helo theoretically should reduce power required by a factor of 1/(sqrt(2)) compared to a single main rotor design to hover with the same weight.
On the other hand, a tandem rotor helicopter is slightly less efficient than a single main rotor helo in forward flight because the rear rotor on a tandem has to fly in the somewhat turbulent wake of the forward rotor. Also, a tail rotor makes a single main rotor helicopter arguably and perhaps more maneuverable than a tandem or coax. layout.
Conclusion: coaxial or tandem rotor designs are better configurations for large transport hubschraubers, assuming that a large transport helo ought to optimize vertical flight rather than forward flight efficiency, and one can't have both in the same aircraft. Therefore, neither the CH-53 nor the MiL-26 are the optimum designs for their roles.
Sikorsky has circulated art work showing a big big coaxial helo or flying crane as their proposal for a new, very heavy lift helicopter for the Army. I suspect that the H-53 and the big MiL are single main rotor designs because that's all their parent firms knew how to build way back when.
A Chinook or Sea Knight in forward flight can obtain maximum lift and thrust, albeit at a slower cruising speed, by flying at a bit of a yawed angle. It gets the rear rotor somewhat out of the forward rotor's wake. Also, one can think of this as increasing the effective wingspan of a Chinook's rotary wings.
We have some Chinook pilots here at Peeprune who might tell us about flying the Chinook yawed versus not yawed.
Nope, a tandem rotor helicopter does not expend any power producing anti-torque effect. The two rotors rotate in opposite directions, thereby cancelling each other's torque without net expenditure of power on torque cancellation.
A single main rotor helicopter with tail rotor has to allocate 12 to 15 of per cent available shaft power to the tail rotor in vertical flight. Fast cruising flight unloads the tail rotor because the vertical stabilizer offsets the main rotor's torque, but this anti-rotor torque trim soaks up about the same per cent of available power by converting rotor torque to vertical stabilizer drag.
The opposed direction of rotor movements of a tandem helicopter also has a swirl-straightening effect on the air flow through the combined momentum disk, thereby slightly increasing vertical lift/thrust.
You are aware that the most efficient helo configuration for vertical thrust is a counter rotating, coaxial design because the coax. config. minimizes vorticity -- a fancier word for swirl -- of the momentum flux through the rotor disk? A coax helo theoretically should reduce power required by a factor of 1/(sqrt(2)) compared to a single main rotor design to hover with the same weight.
On the other hand, a tandem rotor helicopter is slightly less efficient than a single main rotor helo in forward flight because the rear rotor on a tandem has to fly in the somewhat turbulent wake of the forward rotor. Also, a tail rotor makes a single main rotor helicopter arguably and perhaps more maneuverable than a tandem or coax. layout.
Conclusion: coaxial or tandem rotor designs are better configurations for large transport hubschraubers, assuming that a large transport helo ought to optimize vertical flight rather than forward flight efficiency, and one can't have both in the same aircraft. Therefore, neither the CH-53 nor the MiL-26 are the optimum designs for their roles.
Sikorsky has circulated art work showing a big big coaxial helo or flying crane as their proposal for a new, very heavy lift helicopter for the Army. I suspect that the H-53 and the big MiL are single main rotor designs because that's all their parent firms knew how to build way back when.
A Chinook or Sea Knight in forward flight can obtain maximum lift and thrust, albeit at a slower cruising speed, by flying at a bit of a yawed angle. It gets the rear rotor somewhat out of the forward rotor's wake. Also, one can think of this as increasing the effective wingspan of a Chinook's rotary wings.
We have some Chinook pilots here at Peeprune who might tell us about flying the Chinook yawed versus not yawed.
I thought Chinooks had folding blades (albeit manual)? I've seen yank ones with folded blades and the Boeing website lists them as being manually folding.
Admittedly it does look like a massive bloody performance.....
Admittedly it does look like a massive bloody performance.....
Last edited by Trim Stab; 8th Jan 2011 at 20:51.
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Originally Posted by Trim Stab
StopStart - what you are actually looking at is the USMC Maypole-Dancing Society. If you look closely, the chap on the left even has little bells on his ankles
Just This Once... fair enough, a Special Forces MH-47G certainly would visit USN ships from time to time.
I wouldn't have liked to be on the blade-folding party.
I have been party to a "foreign" helo on a USN ship... in 1987, when USS Ranger CV-61 was returning from the Indian ocean back to San Diego, we diverted to rescue some burned Japanese sailors from an ocean-going tug that had had a fire (USN carriers have a full "mini-hospital", fully equipped operating theater, board-certified surgeons, etc).
The sailors were brought to us by a USAF CH-3E, which had done a multiple-mid-air-refuel trip from Hawaii. They decided to just keep it aboard until we were close enough it could do an unrefueled flight back.
The USAF CH-3E, despite being built around the engine/rotor system & cockpit of a Sea King, didn't have folding rotor blades, so it sat mid-flight deck, preventing all fixed-wing flight for 2 days.
