OTHER:Rotor Concept - Active Blade Twist - Overview
[Active Twist Blade] [Active Twist Rotor]
[Controllable Twist Rotor] ~ This was the name used by Kaman
Means of Applying ABT:
Information from Outside Web Sites:It is only here temporarily.
Double tip vortex
A feature that is evident from both figures is the anomaly of carrying a download over a portion of the advancing side. This is the result of designing the rotor with twist-10¡ in this case-to improve hover performance. The download, of course, penalizes the forward-flight performance. It's a demonstration of an axiom that comes up over and over in helicopter design: "Whatever helps hover, hurts forward flight, and whatever helps forward flight hurts hover."
This download has another effect. Normally, we think of a tip vortex as being shed right at the tip as the lift goes to zero. With the advancing tip, his "tip vortex" is generated inboard on the tip while another spinning in the opposite direction comes from the tip itself. This double vortex phenomenon has been seen in wind-tunnel tests using flow visualization techniques.
A following blade that encounters this double vortex is in for a bumpy ride as the local angles of attack change rapidly. Some aerodynamicists have attributed the vibration that a rotor generates in forward flight to this situation. Indeed, it is well known that the higher the twist, the worse the vibration."~ Prouty, Rotor & Wing Jan 99
For all of the above see: Rotor & Wing, Jan 1999, Prouty
Looking further ahead, researchers at ONERA and DLR are considering the use of active blade control designs instead of the current passive noise reduction systems. Manufacturers are already working on two concepts: active blade twist and active control surfaces. A few years ago, Franco-German teams started exploratory studies of active control surfaces through the RGA program - rotor with active surface control. "This is an extremely promising concept," enthuses Jean-Jacques Philippe, helicopter and tilt-rotor research director. "But although this type of rotor could make a helicopter very quiet, with a very low level of vibrations and great aerodynamic performance, we won't see it on a production machine for at least another five or ten years."
Looking further ahead, researchers will be working on active methods to improve rotor performance, in particular, active blade twist and active control surfaces.
In other words, during fast forward flight the blades will see less extreme angles of attack ( + & -) [Ref:
Note that the rate of twist change is associated with the relatively slow transition in flight mode, not with the faster rotor rpm. This is CBT (or ABT). The Reverse Velocity Rotorcraft Concept (Sikorsky) does more but the pitch will cycle every RRPM.
From the Conclusions of this article "VRS is not solely determined by the operating conditions of the rotor, such as descent rate and forward speed, but is also dependent on details of the design of the rotor such as the degree of twist incorporated into the blades."
The spar of the blade must have high torsional stiffness. (See:OTHER: Rotor Concept - Improved L/D Ratio - Independant Root & Tip (IRAT) for alternate design) The skin at the tip is affixed to the spar in a conventional manner. The skin on the inner portion of the blade's span is rotationally flexible about this spar. [The spar's rigidity might be achieved by warping the unidirectional carbon spar in carbon cloth, at a 45º bias. Or, wrap a carbon thread along the span axis.
For the skin, use fiberglass cloth with the thread running at 45º and carbon cloth with the thread running at 0ºand 90º.
The 1P harmonic control (swashplate) will control the rotation of the spar and thereby the pitch of the total blade. The pitch of the skin at the root is modified by a separate actuator [see below for Means of Actuation]. This means that the difference in pitch between the tip and the root is variable [variable twist]
This idea would be somewhat like putting flaps on the inner portion of the blades. At slower speed (hover) the flaps would be deployed for additional lift. The problem with flaps of course as that they will relocate the chordwise center of lift.
Outside Related Information:
Induced velocities near a lifting rotor with non-uniform disk loading
Harry H. Heyson S. Katzoff ~ NACA Report 1319 ~ Jan 1957
New Twist on an Old Wing Theoryhttp://www.aiaa.org/aerospace/images/articleimages/pdf/phillipsjanuary05.pdf Have hard copy and it is on E-drive.
http://www.me.sc.edu/research/lamss/pdf/JOURNALS/21_SVD_V32_N5_2000.pdf Have hard copy.
http://www.glue.umd.edu/~bernhard/DOCS/ahs01_v7.pdf Have hard copy.
ACTIVE-TWIST ROTOR CONTROL APPLICATIONS FOR UAVshttp://www.asc2004.com/Manuscripts/sessionE/EO-04.pdf Have hard copy.
MAGNETOSTRICTIVE ACTUATORS COMPARED TO PIEZOELECTRIC ACTUATORS http://www.cedrat.com/applications/hardware/doc/ASSET2002_MAGNETOSTRICTIVE_vs_PIEZO_ACTUATORS.pdf Have hard copy.
Aerodynamic Design Study of an Advanced Active Twist Rotor:http://techreports.larc.nasa.gov/ltrs/PDF/2004/mtg/NASA-2004-4dsca-mks.pdf
COMPREHENSIVE AEROELASTIC ANALYSIS OF HELICOPTER ROTOR WITH TRAILING-EDGE FLAP FOR PRIMARY CONTROL AND VIBRATION CONTROL:http://research.nianet.org/~shenjw/webpage/main.pdf
ACTIVE TWIST CONTROL OF SMART HELICOPTER ROTOR - A SURVEY ~ Copy in E-drive as Dipali_Aesi_2005.pdf
Idea:The rotor's RPM is high during hover and so is the blade twist. The horizontal thrust, for forward velocity, is provided by a pusher propeller. As the forward velocity increases, the rotational speed of the rotor is reduced. This reduction causes the blade twist to be significantly be reduced and it allows the craft to fly at faster speeds before the onset of advancing tip compression and retreating tip stall.
Extension-Twist Coupled Laminates: http://www.geocities.com/mschliesman/comp_intro.htm
AEROELASTIC RESPONSE AND STABILITY OF TILTROTORS WITH ELASTICALLY COUPLED COMPOSITE ROTOR http://techreports.larc.nasa.gov/ltrs/PDF/phd-93-nixon.pdf
Large twist is good for hover, but bad for fast forward flight.
High rotor RPM is good for hover, but bad for fast forward flight.
Consider blades that are made of
At the maximum forward speed, the rotor blades will have no twist. The rotors are only required to provide lift, so now these rotors will be operating with minimal engine driven torque, and the rotorcraft will be flying, at high speed, in a semi-helicopter / semi-gyrocopter mode.
For those who like to read themselves to sleep, here are449 more pages on the subject.
From press release about V-22, posted on rec.aviation.rotorcraft on September 24, 2002
Engineers are also studying options to change the blade on the tiltrotor since the current design is a compromise between one designed as a rotor and a prop. Bell and Boeing each have candidate technologies that they say would improve performance in parts of the flight regime. Boeing has explored a piezoelectrically reconfigurable blade that could be optimized depending on whether the tiltrotor is in aircraft or helicopter mode. Designers believe the technology could increase range and lift by 15-20%. A flying prototype isn't expected until 2006. If the promised improvements can be achieved, they would increase V-22 speed to about 300 kt.
Bell Helicopter Textron is working with a slightly more traditional design, by slotting the existing blade. The fixed slot would run about 25-50% of the blade span and is supposed to improve the boundary layer and increase lift coefficients. It borrows a technology that emerged from a NASA/Army study several years ago. The performance improvement would exist in hover mode, particularly at higher power settings. Engineers believe the cruise performance wouldn't be degraded, but that has yet to be proven. So far testing only of a small-scale power model has been conducted. Managers want to see both concepts mature before deciding whether to adopt one for the V-22.
Outside Web Sites:
http://www.wam.umd.edu/~bruck/asme.htm Have hard copy
RECENT ADVANCES IN SMART-MATERIAL ROTOR CONTROL ACTUATION.
http://www.me.sc.edu/research/lamss/pdf/CONFERENCES/C58_ASF00.pdf Have hard copy
MECHATRONICS ASPECTS OF SMART MATERIALS INDUCED STRAIN ACTUATIONhttp://www.me.sc.edu/research/lamss/pdf/CONFERENCES/C62_M2000-250.pdf Have hard copy
OVERVIEW OF THE COMMON DLR/ONERA PROJECT "ACTIVE TWIST BLADE" (ATB) Have hard copy
Analytic Investigation of Helicopter Rotor Blade Appended Aeroelastic Devices;http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19880002294_1988002294.pdf
Aerodynamic Design Study of an Advanced Active Twist Rotor
Aerodynamic Design Study of an Advanced Active Twist Rotor Have hard copy.
Kaman Controllable Twist Rotor:
See e-mails from Jim Miller
Searches done on Google; without finding anything of interest:
"active blade twist" -UniCopter
"active blade twist" -UniCopter -"blade-vortex" ~ 2,230
"active blade twist" -UniCopter -"blade-vortex" -piezoelectric ~ 1,010
"active blade twist" -UniCopter -"blade-vortex" -piezoelectric "high speed" ~ 9
"active blade twist" -UniCopter -"blade-vortex" -piezoelectric "high speed flight" ~ 2
"active blade twist" -UniCopter -"blade-vortex" "high speed flight" ~ 6
"active blade twist" -UniCopter -"blade-vortex" "Advancing Blade Concept" ~ 3
"active blade twist" -UniCopter -"blade-vortex" "reverse velocity" ~ 3
"active twist" -UniCopter -"blade-vortex" "root" "tip" ~ 276
"active-twist rotor" -UniCopter -"blade-vortex" "root" "tip" ~ 192
"active-twist rotor" -UniCopter -"blade-vortex" -piezoelectric "root" "tip" ~ 114
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Last Revised; June 17, 2012