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5/21/2018 2007 L7 Introduction Rotorcraft
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Aircraft and SpacecraftSystems Design
VTOL Aircraft
Lecture 1: Introduction to Rotorcraft
Samir Bouabdallah, Christian Bermes
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Course section contents
Lecture 1: Introduction to rotorcraft
Lecture 2: Dynamic modeling of rotorcraft
Lecture 3: Control of rotorcraft
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Goal of todays lecture
Give a general introduction to rotorcraft
Historical overview
Different rotorcraft concepts
Rotor technology
Give an introduction to MAVs
Possible realizations
Challenges
State of the art examples
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Aircraft classification
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What is a VTOL aircraft?
VTOL = VerticalTake-Off and Landing
In general: An aircraft with vertical take-off and landing capability
In this context: Helicopters
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Creative concepts
Early helicopterist
Alternative rotor axis
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Helicopter lift principle
Fixed wing aircraft needs relativewind velocity to create lift
Helicopter creates relative wind
velocity by rotation of blades Hovering capability!
Leading edge
Relative
Wind
Trailing edge
Chord
Chord length
25 % Chord
Angle of attack
Thickness
Fl
FdM
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Experimental helicopters before World War II
First manned helicopter Gyroplan Nr. 1 by Breguet & Richet (1907)
Old
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Experimental helicopters before World War II
First Gyroplane by Juan de laCierva (1923)
First Gyroplane to cross the
English channel (de la Cierva)(1928)
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Famous helicopters
Bell UH-1 (1955, one of the
most successful rotorcraft inhistory)
MBB Bo-105 (1961, firsthingeless main rotor)
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Aircraft and Spacecraft Systems Design Rotorcraft Part 11
Basic rotorcraft concepts
Rotary wing aircraft (rotorcraft) are separatedinto:
Gyrocopters (also known as Autogyros)
The rotor is not driven and free to rotate in theairflow. The direction of airflow through therotor is upwards.
Helicopters
The rotor is driven. The direction of the airflowthrough the rotor is downwards.
Rotor
Rotor
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Aircraft and Spacecraft Systems Design Rotorcraft Part 12
Gyrocopter
Lift from undriven rotor
Rotor must be tilted away fromdirection of flight
Conventional airscrew for
forward thrust
No hovering capability (exceptin wind)
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Aircraft and Spacecraft Systems Design Rotorcraft Part 13
Helicopter
Classical main and tail rotor
Pitch and roll control by tilting themain rotor tip path plane.(swashplate mechanism)
Tail rotor for balance of reaction
torque from main rotor, used alsofor yaw control.
Permanent drift force from tail rotor.
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Aircraft and Spacecraft Systems Design Rotorcraft Part 14
Helicopter
Contra-rotating Coaxial
Pitch and roll control by tiltingthe main rotors tip path planes(swashplate mechanism)
Yaw control by rotor torques
Very compact
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Aircraft and Spacecraft Systems Design Rotorcraft Part 15
Helicopter
Contra-rotating Tandem
Pitch and roll control by tiltingthe main rotors tip path planes(swashplate mechanism)
Yaw control by rotor torques
Large dimensions possible
Difficult to maneuver
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Aircraft and Spacecraft Systems Design Rotorcraft Part 16
Helicopter
Contra-rotating Side-by-side
Advantageous over tandem inforward flight
Higher drag from additionalstructure
Trimming and structurestiffness problems
Rare usage
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Aircraft and Spacecraft Systems Design Rotorcraft Part 17
Helicopter
Contra-rotating Synchropter
Close meshing of rotors byoutwards tilted shafts
Easiest helicopter type to fly
No complete torquecancellation due to tilted shafts(tendency of nose to pull up)
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Aircraft and Spacecraft Systems Design Rotorcraft Part 18
Special designs
Gyrodyne
Between gyroplane and purehelicopter
Main rotor tip path planealways remains parallel to
direction of flight
Directional control and forwardthrust by two tail rotors
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Aircraft and Spacecraft Systems Design Rotorcraft Part 19
Special designs
Convertiplane
Rotors and fixed wing for lift
During travel rotors are tiltedfor forward thrust
Landing has to be vertical dueto rotor diameter
Complex control
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Aircraft and Spacecraft Systems Design Rotorcraft Part 20
MAV concepts
Additionally, there are special concepts applied at Micro AerialVehicles (MAVs)
Quadrotor
Coaxial
Flapping propulsion
Will be introduced later
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Aircraft and Spacecraft Systems Design Rotorcraft Part 21
Functional decomposition of the helicopter
The following functions must be included in a fully functionalhelicopter:
Lift source (vertical thrust force)
Horizontal control (x- and y- translation)
Roll, pitch and yaw control
In helicopter models, there usually is a coupling between roll andpitch angle and x- and y- translation such that:
x and y depend on roll and pitch
Roll and pitch do not depend on the translations
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Aircraft and Spacecraft Systems Design Rotorcraft Part 22
Introduction to main and tail rotor
In the classical configuration, the helicopter has:
A tail rotor for torquebalance and yaw control
A main rotor for vertical
thrust and directional control
Both are rather complicated systems and will be brieflyintroduced in the following
LiftF
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Aircraft and Spacecraft Systems Design Rotorcraft Part 23
Forces on the rotor head
gF
g
F
LiftF
g
F
=0 >0
>0
Blades are affected by centrifugal force due to rotationand lifting force (leads to rotor coning)
Coning effects large moments at blade roots
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Aircraft and Spacecraft Systems Design Rotorcraft Part 24
The articulated rotor head
Rotor blades are not rigidlyattached to head but hinge-supported
Reduction of stresses at bladeroot
Three joints: Feathering, laggingand flapping
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Aircraft and Spacecraft Systems Design Rotorcraft Part 25
Rotor control: the swashplate
Swashplate converts steeringsignal into blade pitch change
(rotation about feathering axis)
Collective pitch for altitudecontrol
Cyclic pitch for roll and pitchcontrol
Swash.
h l
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Aircraft and Spacecraft Systems Design Rotorcraft Part 26
The tail rotor
Since the main rotor is exposed to frictionwith air, a friction torque is exerted on thefuselage
The tail rotor provides a counter-torque tobalance the main rotor friction torque
Variable blade pitch enables yaw control
Blade pitch variation by swashplate
mechanism (collective pitch only)
Fail Tail
T il t lt ti t
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Aircraft and Spacecraft Systems Design Rotorcraft Part 27
Tail rotor alternative concepts
Fenestron
Works like a ducted fan
More quiet and safer
NOTAR (NO TAilRotor)
Tail boom behaves like a wingin the main rotor downwash(effected by airstream fromCoanda slots)
Higher ground clearance
More quiet and safer
Mi A i l V hi l (MAV )
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Aircraft and Spacecraft Systems Design Rotorcraft Part 28
Micro Aerial Vehicles (MAVs)
Why MAVs?
Possible applications are:
Surveillance of buildings and large indoor areas(airports, train stations,)
Rescue missions (after earthquakes,inundations, explosions,)
Surveillance of dangerous or difficult to accessenvironments (chemical, nuclear plants)
Law enforcement in public area
Mine and cave exploration and mapping
MAV h ll
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Aircraft and Spacecraft Systems Design Rotorcraft Part 29
MAV challenges
Low Reynolds number regime Due to involved length scales, air
appears highly viscous to the MAV.
There is a non-negligible influence ofviscosity on the flow dynamics.
Scaling
Simple downscaling of full-scalehelicopters is impossible (e.g. due toaerodynamics).
Innovative design according to therespective boundary conditions is
indispensable.
MAV challenges
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Aircraft and Spacecraft Systems Design Rotorcraft Part 30
MAV challenges
Steering
Classical swashplate mechanisms are hard to realize underlimited
weight and dimension conditions.
Autonomy
In order to achieve MAV autonomy, there has to be a sufficientamount of energy (battery, fuel cell) and the necessary
sensors, hard- and software for control and navigation onboard.
MAV state of the art examples
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Aircraft and Spacecraft Systems Design Rotorcraft Part 31
MAV state of the art examples
OS4 650 g in mass and 720 mm in
span
~30 min of autonomy
Four 12 g brushless DC motors
Integrated computer module
230 g Lithium Polymer battery
By far the most power isconsumed by the actuators (i.e.motors)
OS4
MAV state of the art examples
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Aircraft and Spacecraft Systems Design Rotorcraft Part 32
MAV state of the art examples
CoaX 2
Two brushless DC 12g motors
Two 3 blades propellers 2 servos for CoG displacement
1 distance sensor for altitudemeasurement
1 accelerometer 2 axes
1 MEMS gyroscope
CoaX
MAV state of the art examples
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Aircraft and Spacecraft Systems Design Rotorcraft Part 33
MAV state of the art examples
muFly
Two brushless DC 5g motors
2 piezo actuators for steering 1 distance sensor for altitude
measurement
1 IMU
1 micro-camera
muFly
MAV state of the art examples
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Aircraft and Spacecraft Systems Design Rotorcraft Part 34
MAV state of the art examples
FR (Micro Flying Robot)
Epson micromechanicsdemonstrator
Diameter: ~ 130 mm, height:~ 70 mm
Total mass: ~ 13 g
Center-of-mass movementcontrol by means of a linearactuator
Epson
MAV state of the art examples
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Aircraft and Spacecraft Systems Design Rotorcraft Part 35
MAV state of the art examples
Pixelito
Total mass: 6.9 g
Full carbon frame
No servos
No swashplate
Infrared remote control
Proxflyer Picoflier
Rotor diameter: 50mm
Total mass: 1g
Flight time: up to 1 min
Smallest RC helicopter everbuilt
Heli competition
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Aircraft and Spacecraft Systems Design Rotorcraft Part 36
Heli competition
On Monday, November 26th, we will hold aheli competition instead of exercises
Task:
Build a helicopter that flies as long aspossible (flight time) and lands as close aspossible to its starting point (horizontal
distance)
Judging criterion is the flight time, the
horizontal distance from the starting pointis used as tiebreaker if necessary
Heli competition
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Aircraft and Spacecraft Systems Design Rotorcraft Part 37
Heli competition
Rules: The provided Balsa wood, rubber band and any other material can
be used for building
Propulsion is only allowed by means of a rotating propeller drivenbyone of the provided rubber bands (will be checked)
No metal or other springs except the rubber band (Safety! Will bechecked)
No motors
Some inspiration:
http://jetex.org/models/plans/plans-misc.html
http://www.turnertoys.com/G1/balsa_model_airplanes2.htm
2006
References
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Aircraft and Spacecraft Systems Design Rotorcraft Part 38
References
J. Watkinson: The Art of the Helicopter
Bramwells Helicopter Dynamics
R.W. Prouty: Helicopter Performance, Stability, and Control
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Aircraft and Spacecraft Systems Design Rotorcraft Part 39
Additional Slides
First practical helicopters
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Aircraft and Spacecraft Systems Design Rotorcraft Part 40
p p
Focke-Achgelis Fa-223 (1945)
Bell 47 (1946, first certifiedhelicopter)
Helicopter Principle
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Aircraft and Spacecraft Systems Design Rotorcraft Part 41
Autogyro Principle
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Aircraft and Spacecraft Systems Design Rotorcraft Part 42
NOTAR
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Aircraft and Spacecraft Systems Design Rotorcraft Part 43
MAV state of the art examples
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Aircraft and Spacecraft Systems Design Rotorcraft Part 44
Mesicopter
Intended as Mars explotationvehicle
Dimensions: cm-scale
Due to low Reynolds number,mesicopter operates in viscousenvironment
No successful flight performed
Mesi
The 1st prototype
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Aircraft and Spacecraft Systems Design Rotorcraft Part 45
muFly 80g
120mm max. span
4min flight time
BT communication
RC commands
Up to 2000 MMACs
Features
Attitude ctrl.
Altitude ctrl.
Forward flight
Indoor operation
Hand launched
Carbon cage
Motor
Stabilizer
Swashplate
Linear actuator
MTx IMU
Peripheral PCBs holder
Main board (PCB)
Battery
Alti tude sensor
Propeller
Motor