Tail Rotor - ULisboa · Conceptual Helicopter Design Slide 157 Tail Rotor ... –Heavy lifting ......
Transcript of Tail Rotor - ULisboa · Conceptual Helicopter Design Slide 157 Tail Rotor ... –Heavy lifting ......
Helicopters / Filipe Szolnoky Cunha Slide 151 Conceptual Helicopter Design
Tail Rotor
• Operates at the same tip speed as the main rotor.
Lower speeds are necessary to:
– Minimize noise but
– Requires a higher solidity (stall)
– Increases the torque requirement
– Increases the system weight
Helicopters / Filipe Szolnoky Cunha Slide 152 Conceptual Helicopter Design
Tail Rotor
• Tail rotor normally does not have:
– Cyclic pitch (disk orientation is not required)
– Lead/lag hinges (saves weight)
• But since the flapping movement is allowed they
will have a large amount of pitch-flap coupling
Helicopters / Filipe Szolnoky Cunha Slide 153 Conceptual Helicopter Design
Tail Rotor
• The main rotor wake is known to roll up at its
edges into a pair of vortex bundles.
Helicopters / Filipe Szolnoky Cunha Slide 154 Conceptual Helicopter Design
Tail Rotor
Helicopters / Filipe Szolnoky Cunha Slide 155 Conceptual Helicopter Design
Tail Rotor
• The tail rotor turns in a direction so that the top
of the rotor is retreating aft.
Helicopters / Filipe Szolnoky Cunha Slide 156 Conceptual Helicopter Design
Tail Rotor
• This movement is found to:
– Balance the aerodynamic forces
– Maintain good tail rotor authority over a wider range
of flight conditions
– BVI between tail blades and the main rotor vortices is
decreased and vortex ring conditions are delayed
Helicopters / Filipe Szolnoky Cunha Slide 157 Conceptual Helicopter Design
Tail Rotor
• Due to the high rotational velocity it might be
difficult to see the spinning tail rotor.
• Danger for the ground personnel
• To avoid this:
– Light above the fin when the tail rotor is rotating
– Paint black and white strips on the blades
– Do not approach a hovering helicopter or one with a
rotating main rotor.
Helicopters / Filipe Szolnoky Cunha Slide 158 Conceptual Helicopter Design
Other Anti-torque devices
• Fan-in-fin or fenestron
Helicopters / Filipe Szolnoky Cunha Slide 159 Conceptual Helicopter Design
Other Anti-torque devices
Helicopters / Filipe Szolnoky Cunha Slide 160 Conceptual Helicopter Design
Other Anti-torque devices
• Advantages:
– In forward flight the fenestron is protected from the
external flow and main rotor wake
• Performance more predictable
– The aerodynamic interference with the fin are less
important
– Lower power requirements
– Smaller and lighter design
– Reduce the rotor strike possibility when flaying at
low level
Helicopters / Filipe Szolnoky Cunha Slide 161 Conceptual Helicopter Design
Other Anti-torque devices
• Disadvantages:
– Larger number of blade implies a higher noise
frequency
– Possibility of flow separation at the inlet lip
– The length of the duct must be kept small enough to
avoid a heavy structure
Helicopters / Filipe Szolnoky Cunha Slide 162 Conceptual Helicopter Design
Other Anti-torque devices
Helicopters / Filipe Szolnoky Cunha Slide 163 Conceptual Helicopter Design
Other Anti-torque devices
Momentum analysis
• Conservation of mass:
• Conservation of momentum
• Rewriting
iAvm wAadd
i
a
vw
T fanduct TT wm wAvid
i
a
Av 2
eff
di
A
T
A
Tav
2
d
effa
AA
2
Helicopters / Filipe Szolnoky Cunha Slide 164 Conceptual Helicopter Design
Other Anti-torque devices
• Applying the Bernoulli equation between stations
0 and 1
• And between 2 and 3
• The Thrust on the fan is
2
102
1ivpp
2
0
2
22
1
2
1wpvp i
AwAppT fan
2
122
1
Helicopters / Filipe Szolnoky Cunha Slide 165 Conceptual Helicopter Design
Other Anti-torque devices
• We can reach :
• The induce power consumed by the fan is:
• or
T
T fan
wAv
Aw
i
2
21
iv
w
2 da2
1
faniP ifanvT
A
Ta
a
T d
d 2 Aa
T
d4
23
TRi
fani
P
P
da2
1
Helicopters / Filipe Szolnoky Cunha Slide 166 Conceptual Helicopter Design
Other Anti-torque devices
• Ideally ad=0.5 where Aeff=A
• If the shape of the duct is controlled :
– Wake will not contract as much as would occur
naturally
– Less power will be required to produce a given total
thrust.
• If ad=1 (no wake contraction) a ducted fan will
consume 1/√2 of the power of a conventional
rotor.
Helicopters / Filipe Szolnoky Cunha Slide 167 Conceptual Helicopter Design
Other Anti-torque devices
NOTAR
• The NO TAil Rotor uses a different approach to
the anti-torque and yaw control.
• The anti-torque capability comes from a
circulation control concept which results in a
distributed side-force along the entire tail boom
assembly.
Helicopters / Filipe Szolnoky Cunha Slide 168 Conceptual Helicopter Design
Other Anti-torque devices
NOTAR
• A jet of air from a pressurized tail boom is blown
tangential to the surface out of narrow slots that
run length wise on one side of the boom.
Helicopters / Filipe Szolnoky Cunha Slide 169 Conceptual Helicopter Design
Other Anti-torque devices
• The nozzle in the jet
thrusters is rotated using
the conventional action
of the pilot’s pedals
• In forward flight the
circulation control is less
effective as the main
rotor wake moves further
along the boom
Helicopters / Filipe Szolnoky Cunha Slide 170 Conceptual Helicopter Design
Other Anti-torque devices
• Advantages
– Low Noise
– Safety for ground personnel
– Freedom of blade strikes
– Absence of a vulnerable tail rotor assembly
– High level of redundancy in the event of any boom
damage
Helicopters / Filipe Szolnoky Cunha Slide 171 Conceptual Helicopter Design
Other Anti-torque devices
McDonnell
Douglas
MD-500
MH-90 Enforcer
Helicopters / Filipe Szolnoky Cunha Slide 172 Conceptual Helicopter Design
Helicopters / Filipe Szolnoky Cunha Slide 173 Conceptual Helicopter Design
Multi-rotor helicopters
• Are significantly less common than the conventional main rotor-tail rotor type.
• This situation is caused by:
– Added complexity
– Additional skills needed to for the development
• Have advantages in same market niches
• When the niche is filled no other manufacturer then seeks to compete
• As result of this situation each type is of machine will be associated with a particular manufacturer
Helicopters / Filipe Szolnoky Cunha Slide 174 Conceptual Helicopter Design
Multi-rotor helicopters
Tandem=Vertol/Boeing
Helicopters / Filipe Szolnoky Cunha Slide 175 Conceptual Helicopter Design
Multi-rotor helicopters
Helicopters / Filipe Szolnoky Cunha Slide 176 Conceptual Helicopter Design
Multi-rotor helicopters
Co-axial=Kamov
Helicopters / Filipe Szolnoky Cunha Slide 177 Conceptual Helicopter Design
Multi-rotor helicopters
Helicopters / Filipe Szolnoky Cunha Slide 178 Conceptual Helicopter Design
Multi-rotor helicopters
Synchropter=Kaman
Helicopters / Filipe Szolnoky Cunha Slide 179 Conceptual Helicopter Design
Multi-rotor helicopters
Helicopters / Filipe Szolnoky Cunha Slide 180 Conceptual Helicopter Design
Multi-rotor helicopters
Side-by-Side=Mil
Helicopters / Filipe Szolnoky Cunha Slide 181 Conceptual Helicopter Design
Multi-rotor helicopters
• The possibilities are numerous:
Non overlapped counter-
rotating tandem
Overlapped counter-
rotating tandem
Non overlapped same-
way tandem
Helicopters / Filipe Szolnoky Cunha Slide 182 Conceptual Helicopter Design
Multi-rotor helicopters
• The possibilities are numerous:
Side by side non
overlapped counter-
rotating
Side by side overlapped
counter-rotating
Helicopters / Filipe Szolnoky Cunha Slide 183 Conceptual Helicopter Design
Multi-rotor helicopters
• Cancelling the torque can be achieved by:
– Counter rotating rotors.
– Rotors rotating in the same direction:
Helicopters / Filipe Szolnoky Cunha Slide 184 Conceptual Helicopter Design
Multi-rotor helicopters
Side by side:
• Advantages in forward flight:
– Improves the aspect ration of the “disc”
– Reduces the induced power
• Disadvantages:
– Pylon structure causes drag
– Difficult to obtain structural rigidity
Helicopters / Filipe Szolnoky Cunha Slide 185 Conceptual Helicopter Design
Multi-rotor helicopters
Coaxial system
• Advantages:
– For uses in naval vessels, with small hangar capacity,
the absences of the tail rotor allows a more compact
hull design.
– As for power consumption it has been studied in
previous chapters
Helicopters / Filipe Szolnoky Cunha Slide 186 Conceptual Helicopter Design
Multi-rotor helicopters
Coaxial system
• For operation two swash-plates are needed
• The cyclic control tilts both rotor in the same sense
• The collective control applies the same pitch to both rotors
Helicopters / Filipe Szolnoky Cunha Slide 187 Conceptual Helicopter Design
Multi-rotor helicopters
Coaxial system
• Yaw control
• Pitch in one rotor is increased, lowered in the other
• There is a net torque rotating the aircraft in the direction
of the rotor where the pitch was lowered
Helicopters / Filipe Szolnoky Cunha Slide 188 Conceptual Helicopter Design
Multi-rotor helicopters
Coaxial system
• Autorotation and the yaw control:
– In Autorotation the pitch is set to the for (L/D)max.
– Increasing or decreasing the pitch there will be a
increase of drag and the rotor will slow down
– If the point is to the left of (L/D)max increasing the
pitch will decrease D and so the yaw control is
reversed
• To overcame this problem coaxial helicopters
need a significant amount of vertical tail area.
Helicopters / Filipe Szolnoky Cunha Slide 189 Conceptual Helicopter Design
Multi-rotor helicopters
Synchropter
• Two counter-rotating synchronized rotors
mounted side by side.
• The rotor shaft are set on pylons and are tilted
outwards so that the blades of one rotor can pass
over the head of the other.
• Although there is no tail rotor there is no safety
advantage since the path of the blade is close to
the ground
Helicopters / Filipe Szolnoky Cunha Slide 190 Conceptual Helicopter Design
Multi-rotor helicopters
Synchropter
• Aerodynamically the synchropter is similar to the
coaxial helicopter
• Since there is a lateral separation of the two
rotors:
– The “disc” area is higher
– The disc loading is smaller
• Limited to a two blade rotor:
– Low solidity
Helicopters / Filipe Szolnoky Cunha Slide 191 Conceptual Helicopter Design
Multi-rotor helicopters
Synchropter
• This is ideal for:
– Low speed
– High altitude
– Heavy lifting
• Yaw control is achieved in the same way as the
coaxial helicopter
– In autorotation Yaw reversal is a possibility
Helicopters / Filipe Szolnoky Cunha Slide 192 Conceptual Helicopter Design
Multi-rotor helicopters
Synchropter
• The need of the large fin area is limited by:
– Trajectory of the retreating blades
– Ground distance in a flared landing
Helicopters / Filipe Szolnoky Cunha Slide 193 Conceptual Helicopter Design
Multi-rotor helicopters
Synchropter
• Power is lost in the cancelling horizontal thrust
components
• The twin rotor heads cause a drag penalty.
• The outward tilt of the rotors means that the
torque cancels in the vertical axis but there is a
component in the horizontal axis that adds up.
Helicopters / Filipe Szolnoky Cunha Slide 194 Conceptual Helicopter Design
Multi-rotor helicopters
Synchropter
• If the advancing blade is on the inside the torque
reaction will tend to pitch the hull nose up:
– If the CM is far enough ahead of the mast it will
counter the torque
– In hover this will require a application of forward tilt
– In forward flight the drag of the hull will act below of
the rotor heads and produce a couple tending to tilt
the nose down
Helicopters / Filipe Szolnoky Cunha Slide 195 Conceptual Helicopter Design
Multi-rotor helicopters
Tandem Helicopters
• A wider range of CM positions is possible
Helicopters / Filipe Szolnoky Cunha Slide 196 Conceptual Helicopter Design
Multi-rotor helicopters
Tandem Helicopters
• In a two motor helicopter is common that either
engine can drive both rotors
Helicopters / Filipe Szolnoky Cunha Slide 197 Conceptual Helicopter Design
Multi-rotor helicopters
Tandem Helicopters
• In forward flight:
– Both rotor are tilted forward
– Remain in the same plane of translation
Helicopters / Filipe Szolnoky Cunha Slide 198 Conceptual Helicopter Design
Multi-rotor helicopters
Tandem Helicopters
• In forward flight:
– The rear rotor will be in the wake of the front rotor
except if it is positioned above the front rotor
Helicopters / Filipe Szolnoky Cunha Slide 199 Conceptual Helicopter Design
Multi-rotor helicopters
Tandem Helicopters
• The rear rotor is mounted on a pylon shaped to act as a fin
• The front rotor is mounted on a pylon shaped not to act as a fin
Helicopters / Filipe Szolnoky Cunha Slide 200 Conceptual Helicopter Design
Multi-rotor helicopters
Helicopters / Filipe Szolnoky Cunha Slide 201 Conceptual Helicopter Design
Other type of rotorcraft
• Compound Helicopters
– Lift compounding
– Thrust compounding
• The idea is to enhance the basic performance
metrics of the helicopter such as:
– Lift-to-drag ratio
– Propulsive efficiency
– Maneuverability
Helicopters / Filipe Szolnoky Cunha Slide 202 Conceptual Helicopter Design
Lift and Thrust compounding
McDonnell XV-1
Helicopters / Filipe Szolnoky Cunha Slide 203 Conceptual Helicopter Design
Lift and Thrust compounding
Sikorsky NH-3 (based on the S-61)
Helicopters / Filipe Szolnoky Cunha Slide 204 Conceptual Helicopter Design
Lift compounding
Boeing-Vertol Model 347
Helicopters / Filipe Szolnoky Cunha Slide 205 Conceptual Helicopter Design
Expanding the envelop
Helicopters / Filipe Szolnoky Cunha Slide 206 Conceptual Helicopter Design
Helicopter
Compound Helicopter
Tilt Rotor
Flapped Tilt Wing
Tilt Duct
Tilt Propeller
0
10
20
30
40
200 400 600
Buried Fan
Jet
Hovering
Time
(Min)
Tradeoff between Hovering Time and Design
Cruising Speed
Helicopters / Filipe Szolnoky Cunha Slide 207 Conceptual Helicopter Design
Rotorcraft- No single configuration optimum
Tiltrotor (but what about $DOC ??
And it scales down poorly)
Autogyro
Light Helicopter
Compound Helo
Helicopters / Filipe Szolnoky Cunha Slide 208 Conceptual Helicopter Design
Sikorsky X-2