And don't forget the gearbox, which you don't even see!
Z-20 (all variants) thread
- Thread starter delft
- Start date
TerraN_EmpirE
Tyrant King
The engines generate power which is transferred though the gear box to both the main and tail rotors.
the key limitations of the conventional configuration though is the speed of the main rotor. The higher the speed of the blades the more they induce stall robbing the craft of lift and power. a conventional helicopter is always tripping over its self in a way. Trying to move to high speed it redirects its main rotor to forward flight limiting its own lift. Trying to keep from spinning out of control its siphoning power to a tail rotor to supply counter rotational thrust. Trying to keep from falling from the sky its trying to keep its rotor speed subsonic. Trying to get the maximum amount of lift its adding blades and making them wider to appease the locals who hear it and the load masters who want to add more.
the key limitations of the conventional configuration though is the speed of the main rotor. The higher the speed of the blades the more they induce stall robbing the craft of lift and power. a conventional helicopter is always tripping over its self in a way. Trying to move to high speed it redirects its main rotor to forward flight limiting its own lift. Trying to keep from spinning out of control its siphoning power to a tail rotor to supply counter rotational thrust. Trying to keep from falling from the sky its trying to keep its rotor speed subsonic. Trying to get the maximum amount of lift its adding blades and making them wider to appease the locals who hear it and the load masters who want to add more.
Costas 240GD
Junior Member
The main problem in a conventional layout helicopter is retreating blade stall. As the blades advance (rotate towards the nose), their airfoil section generates lift. But as they rotate towards the tail (retreat), they lose efficiency at higher speeds. Compound helicopters use various means to avoid this problem, while wings, e.g. on gunship helicopters, offload the rotors by supplying additional lift at forward flight. Of course, they induce downdraft drag in the hover. Coaxial rotor helicopters also don't suffer as much from retreating blade stall as the stall on one side is counteracted by the lift provided by the other rotor.
TerraN_EmpirE
Tyrant King
Exactly. this limits the top speed of a Rotary wing asset. However the Rotor can also create a stall if it spins at a rotational speed equal or greater then the speed of sound. the rotor as it advances is entering air as it retreats its reentering disrupted air.
most often multiple rotors as the disruption of one rotor sends air into the path of the other. the only other method is the Gyrodyne like the Eurocopter X3 which only has a single main rotor but uses wings and tractor props to compensate for the problems allowing generation of lift and thrust well allowing reduction in speed of the rotors
not quite the wings on almost every Attack helicopter with the exception of the HIND or the Cheyenne are far to small to generate lift. mostly all they are there for is to host weapons.
yup. it's not the only option though just the most practical. other methods include "Egg Beater" Intermeshing rotors ( like the K Max), Tandem Rotors (Like Chinook), Transverse rotor ( like Fw 61 )
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Costas 240GD
Junior Member
Actually, the Hind, the Hook, the Cheyenne and the S-67 Blackhawk had big enough wings to allow for greater offloading of the rotor. Other attack helicopters may not have wings as big, hence the moniker stub wings, but they are of airfoil section, have the required incidence and thus offload the rotor even though not as much.
And yes, the other rotor configurations you mentioned do ameliorate the problems caused by retreating blade stall.
Keeping to the subject of this thread, I think the Z-20 with the Chinese equivalent of the Blackhawk's ESSS, of appropriate chord and airfoil section, would benefit from even a small amount of added lift compared to the "slick" configuration.
TerraN_EmpirE
Tyrant King
Oh yes I forgot about those two Although only the Hind and Hook entered any real level of production with Hind being the most successful.
true, but the reduction would be lost with the additional drag of external ordnance and fuel tanks and open doors.
true, but the reduction would be lost with the additional drag of external ordnance and fuel tanks and open doors.
I could not imagine a higher compliment to be paid to the efficiency and skill of a aerospace establishment to say they completely reverse engineered and testflown a modern helicopter in 2.5 years.
Just imagine the awesome efficiency it would take to just do all the metalurgy required in that time.
TerraN_EmpirE
Tyrant King
It was Is suspect more a matter of a misinformed psudo military expert trying to whip up a ferver. The PLA has had S70C 's for 31 years.
MwRYum
Major
No, the project has been around for more than 20 years, it's only during the last 3 years or so more resources poured into the project.
In China there's a term for those pseudo "expert" - "磚家".
TerraN_EmpirE
Tyrant King
resources and experience. All the other designs they have used have taught a local t of sometimes harsh lessons.
even today there is still a lot to catch up on. And Z20 still has a while before prime time debut. To try and claim its based on the stealthhawk is foolishness, the local Pakistanis and the US NAVY SEALS trashed that bird good and though. And if it was a stealthhawk clone I would lay money that the PLA would never ever let it leak. It would be proof of a agenda other then there non interference policy propaganda, would push others in the Asian region to drive in developing counter stealth tech, and possibly even independent stealthy helicopters of there own, and would loose its key advantage the element of surprise.
After the Neptune spear operation revealed the stealth hawk I guarantee everyone with a possible target for the US kicked into overdrive to try and counter the possibility of a stealthy infiltration of American soldiers.
as it is the fear of stealthy ninja like PLA commandos is already filtering though the more hawkish analyst.
Yet at this point the developing on Z20 seems to be well to immature for that. If I was to pick a PLA airframe I think they could stealth it would be the Z9 because they are know to have already been tinkering with RCS on that platform and its proven with features that suit the mission set.
I expect mission variety for Z20 but special operations specialized like that is at least a decade away. First lets see them get to production. And that's at least a year down the road.