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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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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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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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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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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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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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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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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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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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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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MAV concepts

Additionally, there are special concepts applied at Micro AerialVehicles (MAVs)

Quadrotor

Coaxial

Flapping propulsion

Will be introduced later

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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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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References

J. Watkinson: The Art of the Helicopter

Bramwells Helicopter Dynamics

R.W. Prouty: Helicopter Performance, Stability, and Control

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Additional Slides

First practical helicopters

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p p

Focke-Achgelis Fa-223 (1945)

Bell 47 (1946, first certifiedhelicopter)

Helicopter Principle

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Autogyro Principle

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NOTAR

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MAV state of the art examples

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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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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