Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
semi rigid rotor head
#1
What are the disadvantages of a semi rigid versus articulated? Excluding the cost.
Reply
#2
Does It make any differnce in handling? if I trained in a Schweizer with a fully articulated rotor and then jumped into a R22 or Mosquito?
Reply
#3
Kristian,

Firstly, it has been said many times that the Schweizer flies and feels more like a Mosquito than anything else you could train in with the R-22 being a close second.

Most two bladed rotor heads are semi-rigid since it is a simple, low maintenance design with not much to be gained by the added parts to make it an articulated head especially on a sport helicopter. The R-22 sports a hybrid rotor system of semi-rigid and articulated. Don't ask me why it was designed that way but that very feature has caused additional training required because of the dangers of unloading (zero or negative G load) that kind of a system and it is the semi-rigid part of the design that is the limitation.

***NEWS FLASH*** ((((YOU MUST NEVER UNLOAD A SEMI-RIGID SYSTEM LIKE THE ONE ON THE MOSQUITO. UNLOADING THE HEAD MEANS GOING TO ZERO OR NEGATIVE G. YOU ARE SIGNIFICANTLY UNLOADING THE HEAD ANYTIME YOU FEEL LIGHT IN THE SEAT THIS SITUATION SHOULD BE VIGILANTLY AVOIDED!!!!))))

The Schweizer however has an articulated system that acts very similar to a two bladed semi-rigid head. Understand that semi-rigid can only be accomplished with a two bladed system and the simplicity and efficiency of a two bladed system are the main factors in keeping building, maintenance and operating costs low. Easy to design, build and maintain due to low parts count and efficient to operate because of only having two blades creating drag. The only thing more efficient is a one bladed system with a counter weight (yes, it has been done and proven). The disadvantages of the semi-rigid system are slightly more vibrations in certain flight regimes and a lower VNE (velocity never exceed) due to the semi-rigid (slaved blades) limitations to prevent retreating blade stall.

The advantages of multi-bladed articulated systems is that they are smoother in most flight regimes and since the blades individually articulate to maximize lift on the retreating side of the disk, a higher VNE is attained before getting into retreating blade stall. Multibladed systems produce much more lift and lifting capacity through lower average disk loading but the byproduct of lift is drag so much more power is required and that requires more fuel. So lack of efficiency and designing/engineering/bulding and maintaining a multi-bladed articulated system are the negatives.

All helicopters regardless of rotor head design and number of blades will suffer the same vibrations going from a hover into clean air flight and from clean air flight back into a hover due to Transverse Flow Effect so this is not one of the flight regimes I am refering to above. Also, semi-rigid systems allow the body or fuselage of the helicopter to hang more level in a hover where the articulated systems cause the whole helicopter to tilt with the head. This is due to the difference of a semi-rigid system's single center hinge at the axis of rotation to allow the body to hang or pendulate. The articulated system's hinges are offset from the axis of rotation and by virtue of this action the rotor head has leverage over the body so that the body is slaved to tilt with the head. I hope this helps without being too complicated.
Reply
#4
Thanks. It does help a little. Rotor head seems to be the most complicated part of the helicopter even though It looks fairly simple on the mosquito.
Cannot have negative load because the pitch of the helicopter body is not controlled by the semi rigid at all? Gravity only?
It "must hang" at all times?
Reply
#5
Another big difference for an "offset flapping" hub vs. teetering rotor hub is that in the offset flapping hub ( articulated ),
there's a strong tendency for the rotor shaft to remain perpendicular to the blade plane, so the control effectiveness can be very much greater due to centrifugal force, whereas with a teetering hub, you're just hanging under the rotor. In fact in an offset flapping hub helicopter it's possible to roll it over just by moving the cyclic whilst on the ground with no collective!

Hoyt Stearns
Scottsdale, Arizona US
http://HoytStearns.com
Reply
#6
The Robinson "tri-hinge" hub seems like a good idea, as it lets the rotor blades neutralize any coning stresses due to changes in weight of the helicopter. Most teetering rotor heads just pick some compromise coning angle ( how much the blades flex upward when carrying a load ), but the Robinson hub allows no vertical stress on the blade roots due to changes in load (there's still some in-plane stresses though due to coriolis forces).
Reply
#7
(09-22-2009, 03:47 PM)UH-60Pilot Wrote: Kristian,

   Firstly, it has been said many times that the Schweizer flies and feels more like a Mosquito than anything else you could train in with the R-22 being a close second.

   Most two bladed rotor heads are semi-rigid since it is a simple, low maintenance design with not much to be gained by the added parts to make it an articulated head especially on a sport helicopter. The R-22 sports a hybrid rotor system of semi-rigid and articulated. Don't ask me why it was designed that way but that very feature has caused additional training required because of the dangers of unloading (zero or negative G load) that kind of a system and it is the semi-rigid part of the design that is the limitation.

***NEWS FLASH*** ((((YOU MUST NEVER UNLOAD A SEMI-RIGID SYSTEM LIKE THE ONE ON THE MOSQUITO. UNLOADING THE HEAD MEANS GOING TO ZERO OR NEGATIVE G. YOU ARE SIGNIFICANTLY UNLOADING THE HEAD ANYTIME YOU FEEL LIGHT IN THE SEAT THIS SITUATION SHOULD BE VIGILANTLY AVOIDED!!!!))))

The Schweizer however has an articulated system that acts very similar to a two bladed semi-rigid head. Understand that semi-rigid can only be accomplished with a two bladed system and the simplicity and efficiency of a two bladed system are the main factors in keeping building, maintenance and operating costs low. Easy to design, build and maintain due to low parts count and efficient to operate because of only having two blades creating drag. The only thing more efficient is a one bladed system with a counter weight (yes, it has been done and proven). The disadvantages of the semi-rigid system are slightly more vibrations in certain flight regimes and a lower VNE (velocity never exceed) due to the semi-rigid (slaved blades) limitations to prevent retreating blade stall.  

   The advantages of multi-bladed articulated systems is that they are smoother in most flight regimes and since the blades individually articulate to maximize lift on the retreating side of the disk, a higher VNE is attained before getting into retreating blade stall. Multibladed systems produce much more lift and lifting capacity through lower average disk loading but the byproduct of lift is drag so much more power is required and that requires more fuel. So lack of efficiency and designing/engineering/bulding and maintaining a multi-bladed articulated system are the negatives.

   All helicopters regardless of rotor head design and number of blades will suffer the same vibrations going from a hover into clean air flight and from clean air flight back into a hover due to Transverse Flow Effect so this is not one of the flight regimes I am refering to above. Also, semi-rigid systems allow the body or fuselage of the helicopter to hang more level in a hover where the articulated systems cause the whole helicopter to tilt with the head. This is due to the difference of a semi-rigid system's single center hinge at the axis of rotation to allow the body to hang or pendulate. The articulated system's hinges are offset from the axis of rotation and by virtue of this action the rotor head has leverage over the body so that the body is slaved to tilt with the head. I hope this helps without being too complicated.
Can it be used the Semi rigid Mosquito Helicopter Rotor head in More than One or Two seater Helicopter OR Not??

Can it be used the Semi rigid Mosquito Helicopter Rotor head in More than One or Two seater Helicopter OR Not??

waiting for answer.......

Can it be used the Semi rigid Mosquito Helicopter Rotor head in More than One or Two seater Helicopter ??
Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)