Rotor Revs
Joined: Dec 2006
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From: UK and MALTA
Most types of rotor blade have "washout" to even the distribution of lift along the blade, oitherwise the bending forces resulting from higher lift (by virtue of greater speed of the outboard portion of the blade) would subject the blades to undue stress.
Avoid imitations
Joined: Nov 2000
Aviation Qualifications: ATPL
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From: Wandering the FIR and cyberspace often at highly unsociable times
In older, metal construction, perhaps not so obvious but more modern types are of composite construction and definitely DO have a "twist", or washout. The aerodynamic profile of these blades sometimes varies greatly along their length. Some blades, such as those on the A109E, even have a trailing edge "flap" on the inner portion.
YouTube - Heli blades
YouTube - Heli blades
Joined: Sep 2008
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From: SW Asia
The washout (reverse twist) for most helicopters falls between -10 degrees and -16 degrees, where the tip has lower angle of attack than the root. This distributes the average lift across the blade, since the tip is going faster, it needs less angle for the same lift.
The angle could be greater, but the structure of the blade is challenged by the twist angle, in that the stiffness in torsion is weakened by the twist.
Variable twist is coming with the advent of on-blade control, in effect, the movable blade tabs will let the flight control computer select the ideal angel for each segment.
The angle could be greater, but the structure of the blade is challenged by the twist angle, in that the stiffness in torsion is weakened by the twist.
Variable twist is coming with the advent of on-blade control, in effect, the movable blade tabs will let the flight control computer select the ideal angel for each segment.
Joined: Apr 2005
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From: UK
A109 blades
Shytorque, you may well be right (and yes A109 blades do have significant washout) but as I recall the inboard trailing edge flap was introduced on the early 'C' model. It was a trial initiated by Mario Ceriani and Paolo Ferreri at Agusta Aviation Corporation (to the chagrin of the design aerodynamicists at Cascina Costa!) and was there to kill lift generated by the (then) new profiled blades that had an increased bull-nose on the leading edge at the root. This generated lift and 'patter' at a frequency of 4R over the redesigned & straked aft cowling. The trailing edge slat addessed this generated vibration very well, particularly at high cruise (140+knots)
I offer it as a thought only
I offer it as a thought only
