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Aero Eng Y3 > Systems Engineering for Unmanned Aerial Vehicles - Part 2. > Flashcards

Systems Engineering for Unmanned Aerial Vehicles - Part 2. Flashcards

1
Q

Advantages of rotorcrafts

A

Ability to hover.
VTOL.

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2
Q

Disadvantages of rotorcrafts.

A

Poor efficiency in forward flight.
Complexity/ high maintenance costs.

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3
Q

Advantages of multicopter

A
  • Simple design + control.
  • Very good torque compensation.
  • High maneuverability
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4
Q

Disadvantages of multicopter.

A
  • Reduced efficiency.
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5
Q

Main modelling assumptions for quadcopters

A

Aerodynamics:
* Interaction with ground or other surfaces is neglected
* Fuselage/frame drag is neglected
* Propeller wake interactions are neglected

Structure:
* The structure is rigid and symmetric
* Propellers are rigid

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6
Q

What are the 3 parts of modelling a quadcopter?

A

Input to system are commanded rotor speeds.
1. Motor dynamics (due to fast dynamics wrt body dynamics, the motor dynamics are often neglected for control design).
2. Propeller aerodynamics - Aerodynamic forces and moments.
3. Rigid body dynamics - Translational and rotational accelerations

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7
Q

Modelling assumptions for the propeller dynamics in a quadcopter?

A
  • Infinitely thin propeller/rotor disc area 𝐴
  • Thrust and velocity distributions are uniform over disc area (One dimensional flow analysis)
  • Quasi-steady airflow: Flow properties do not change over time
  • No viscous effects: No profile drag
  • Air is incompressible
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8
Q

Rigid-body dynamics modeling assumptions for quadcopters

A
  • The structure is rigid and symmetric
  • We only consider quadrotor near hover condition
  • Main forces and moments come from propellers:
  • Depend on flight regime (hover or translational flight)
  • In hover: thrust and drag proportional to propeller speed squared πœ”π‘^2
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9
Q

Assumptions for controlling a quadcopter

A
  • Neglect motor dynamics.
  • Low speeds
  • Only propeller aerodynamic forces considered - neglect frame drag.
  • Linearisation around small attitude angles.
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10
Q

Advantages of flapping-wings MAVs

A
  • Mini potential.
  • Power-efficiency at low Re numbers.
  • Manoeuvrability, agility
  • Hover-capability
  • Extensive flight envelope.
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11
Q

Applications of flapping wing MAVs

A

➒ Search & rescue, disaster response
➒ Monitoring & surveillance
➒ Infrastructure maintenance
➒ Data gathering
➒ Operations in human proximity

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12
Q

Flapping insect vs. plane

A

βœ“ Hover and VTOL capable
βœ“ More manoeuvrable &
versatile
βœ“ High performance at small
scales

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13
Q

Advantages and disadvantages of two wings against 4 wings

A

Ad:
- Less complex physics.
- Easier design + construction.

Dis:
- Wing motion causes large inertial oscillations, so less convenient for cameras.
- Less wing area - higher wing loading - so high flap frequency.

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14
Q

Advantages and disadvantages of four wings against 2 wings.

A

Ad:
- Additional lift production. - lower wing loading needed.

A) Tandem:
Highly manoeuvrable
But:
difficult to mimic in robotic flyers and highly complex.

B) X-Wing:
Opposite-phase flapping reduces body oscillations - stabler motion, suitable for cameras. And can use clap-and-fling which enhances lift.
But smaller flap amplitude because the wing pairs flap in the same plane.

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15
Q

Ad and disad Flapping wing MAVs with a tailplane

A

Advantages:
βœ“ Passive stability (in most flight conditions), hence simpler control
βœ“ Simpler flapping mechanism, typically 1 DOF (degree of freedom)
βœ“ Overall lower complexity, which allows for research on higher-level problems

Dis:
Γ— Less manoeuvrability than wing-controlled FWMAVs
Γ— Higher sensitivity to perturbations, e.g. wind gusts
Γ— Forces produced by control surfaces are proportional to flight velocity squared (𝑉^2); therefore steering
capability is limited at low flight speeds

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16
Q

Ad and disad Flapping wing MAVs without a tailplane

A

βœ“ Higher manoeuvrability
βœ“ Smaller and lighter designs possible
βœ“ Higher resilience to wind gusts
Γ— More complex flapping mechanisms
Γ— More complex control
Γ— Active stabilisation required

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17
Q

What are the challenges with flapping wing MAVs

A
  • multibody, time-varying system.
  • high complexity.
  • unsteady aerodynamics
  • nonlinear systems: wide range of flight behaviours.
  • small scale.
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18
Q

Explain the bird-like MAVs

A

Fast flight
passive upstroke
almost no force produced.
- Wing AOA and area are reduced during upstroke, so that much less force is produced thatn downstroke.

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19
Q

Explain the insect-like MAVs

A

Slow flight/ hover
Active upstroke
Useful lift produced.
Rapid flying and the flap-induced speed at the wing tip is greater than the forward speed.
During upstroke, the wings are reoriented so that the lower wing surface acts as aerodynamic upper
surface and produces lift.

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20
Q

Explain hovering

A
  • Most power-demanding flight regime
  • No forward flight velocity, all forces are due to flapping
  • Horizontal forces cancel out between upstroke and downstroke
  • Two typical wing patterns for hovering:
  • Normal hovering
  • Inclined-stroke hovering
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21
Q

Flapping wing aerodynamics

A
  • Free-stream circulation.
  • Rotational circulation.
  • Delayed stall and leading edge vortex.
  • Wing wake interaction.
  • Added mass
  • Clap-and-fling
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22
Q

What is the reduced frequency for flapping wings

A

A measure of unsteadiness

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23
Q

Define quasi-steady modelling

A

Assume the instantaneous forces on a flapping wing are equal to the forces that would act on a wing moving steadily at the same free-stream velocity and angle of attack.
Acceptable when k <0.1, and high flapping frequency compared to the body natural frequency

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24
Q

What are the 3 challenges that come with modelling FWMAV dynamics?

A
  • Multi body system.
  • Time-varying system (the system responds differently to the same input at different times)
  • Nonlinearity
  • Experimental data for flapping-wing MAVs
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25
Q

Define the time scale separation principle

A

The body dynamics and flapping dynamics are assumed to be decoupled because they are characterised by
very different frequencies. Hence averaging over the flap cycle can be used to cancel out time-varying effects.

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26
Q

Explain tethered experiments for MAVs

A

βœ“ Accurate monitoring of test conditions; repeatability
βœ“ Reduced impact of external factors
βœ“ Feasible before FWMAV is able to fly
Γ— Clamping hinders oscillations that would occur in free
flight: can lead to erroneous force measurements
Γ— Only steady state

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27
Q

Explain free-flight experiments for MAVs

A

βœ“ Realistic conditions: free, unconstrained body
βœ“ Can include manoeuvres
Γ— Body oscillations affect on-board sensors
Γ— Unstable platforms are difficult to control
Γ— Difficult to replicate test conditions
Γ— Flight-capable vehicle is needed

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28
Q

How to make simplifications for time varying dynamics - MAVs

A

Most controllers are designed based on time-averaged dynamics
* Most controllers do not allow for inputs to change within the flap cycle

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29
Q

How to make simplifications for nonlinear dynamics, wide flight envelope - MAVs

A
  • Many controllers are based on linearised dynamics models
  • Most control work only considers a single flight condition
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30
Q

How to make simplifications for real-life implementation - MAVs

A
  • Small scale: limited computational power, sensing, power
  • Often unstable systems: tuning in flight is problematic
  • Many controllers are only tested in simulation
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31
Q

How is actuation split between the wing and the tailplane?

A

Wings: provide lift and thrust.
Tail - Manouvering, pitch and yaw.

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32
Q

Advantages and disadvantages for fixed-wing UAVs

A

Ad:
Flight range
Flight speed
Mechanical complexity
Cost

Disad:
Takeoff and landing infrastructure
No hovering

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33
Q

Modelling assumptions for fixed wing UAVs

A
  • Rigid and symmetric structure:
    Constant and (almost) diagonal inertia tensor
  • Constant mass
  • Motor dynamics neglected
  • Aerodynamics (main assumptions):
  • Linear (operate below stall)
  • Neglect fuselage lift/sideslip force
  • Neglect propeller wake and main wing (or tail) interaction
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34
Q

3 main parts of the fixed-wing model

A

Input u to the system are commanded servo actuator and rotor speeds or the input voltages into the motors.
- Motor and servo dynamics block.
- Wing and propulsion aerodynamics.
- Rigid body dynamics.

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35
Q

Explain the flap cycle

A

There are two phases, the upstroke and the downstroke, during which the wings accelerate in opposite directions, and are translatory phases.
Between them, we have stroke reversal + wing rotation, which is when the wings rotate rapidly about a spanwise axis. Allows the geometric and aerodynamic leading edge of the wings to correspond correctly.

36
Q

Explain delayed stall and leading edge vortex.

A

Delayed stall is a lift-enhancing mechanism based on the leading edge vortex during the translation. In 3D wings, the LEV stays attached and the wing doens’t stall, but in 2D wings, the stall is delayed.

37
Q

Explain wing rotation.

A

Generates additional circulation and can lead to increased lift (but also drag).

38
Q

Explain wing-wake interaction (wake capture)

A

Wake capture mainly occurs after stroke reversal.
And increases the aerodynamic force production. At stroke reveral, the wing generates vortices, inducing a velocity field and by moving through it, larger forces are generated.
But highly complex and hard to isolate.

39
Q

Clap -and-fling

A

Touching of two wings.
Leads to considerable lift enhancement, even if the wings just move close together without touching.

40
Q

Explain added mass

A

When the wings accelerate, they also accelerate the air they displace, and the reaction force is the added mass effect.
The added mass force acts normal to the wing and is proportional to the acceleration. Usually occurs when the wings accelerate, at startup or stroke reversal.

41
Q

What does low k mean

A

Quasi-steady aerodynamics.

42
Q

What does high k mean

A

Unsteady aerodynamics (k>0.2)

43
Q

Flapping frequency of birds

A

1 - 10

44
Q

Flapping frequency of butterflies

A

20

45
Q

Flapping frequency of houseflies

A

200

46
Q

Flapping frequency of gnats

A

greater than 1000

47
Q

Flapping frequency of hummingbirds

A

30Flapping frequency of birds

48
Q

Flapping frequency of moths

A

30

49
Q

Flapping frequency of mosquitoes

A

500

50
Q

Explain multi-body system challenge with modelling FWMAV dynamics

A

Different parts of the system move differently with respect to each other.
Single rigid-body models have no inertia effects, are simpler and less complex, acceptable when the wing mass&laquo_space;body mass and the flap frequency is&raquo_space; body mode frequency.
Multi-body models are more realistic and complex.

51
Q

Explain time-varying system challenge with modelling FWMAV dynamics

A

The system responds differently to the same input at different times, bc forces vary with each flap cycle, the states vary and both at a slower time scale.

52
Q

Explain non-linearities challenge with modelling FWMAV dynamics

A

Flight behaviour is non-linear, and a simplication of taylor series expansion can be used.
Allows a simpler system but may not be used forever.

53
Q

Tailed FWMAVs - split actuation.

A

Actuation/control is split into two separate parts - the wings are for lift and thrust. And the tail is for pitch and yaw but no direct roll control

54
Q

What parameters can be used for wing actuation?

A

Higher angle of attack, flap frequency, larger stroke amplitude and offset or stroke plane angle.
High level approaches:
1. Flapping kinematics modulation - changing flapping parameters.
2. Wing deformation.

55
Q

Benefits and drawbacks of fixed wing configurations

A

Benefits:
- Flight range.
- Flight speed
- Low complexity.
- Low cost.

Drawbacks:
- Takeoff and landing.
- No hovering.

56
Q

Rotary wing benefits and drawbacks.

A

Benefits:
- Maneuverability
- VTOL.
- Hover.
- Simplicity.

Drawbacks:
- Endurance
- Complexity.

57
Q

Hybrid benefits and drawbacks

A

Benefits:
- VTOL.
- Hover.
- Endurance
- Design.

Drawbacks:
- Control.
- Complexity.

58
Q

Assumptions and simplifications for fixed wing UAVs

A
  • Rigid and symmetric structure. (constant and nearly diagonal inertia tensor)
  • Constant mass
  • Motor dynamic neglected.

Aerodynamic assumptions:
- Linear
- Operate below stall.
- Neglect fuselage lift and sideslip force.
- Neglect propeller wake and main wing/ tail interaction.

59
Q

Define TEMP

A

TEMP stands for Test and Evaluation Master Plan. The TEMP documents plans
for developmental and operational tests, and system evaluation.

60
Q

Explain the purpose of the trade of studies.

A

The purpose of system trade-off studies is to identify the system design solution
that optimizes a given figure of merit.

61
Q

What is the ultimate goal of HSI?

A

The ultimate goal of human-system integration is to maximize the system’s
usability and safety

62
Q

HOQ Purpose

A

The purpose of the house of quality (HoQ) is to translate customer needs into
technical performance measures or specifications.

63
Q

Functional analysis purpose

A

The main purpose of functional analysis is to determine the functions of the system
and to assign functions to system’s components.

64
Q

Which of the aerodynamic properties of FWMAV’s are included in the quasi-steady aerodynamics?

A

Translational or
free-stream circulation, rotational circulation, added mass, viscous forces

65
Q

Define safety and reliability. Explain examples when a system is safe but unreliable, and a unsafe but reliable.

A

Safety is the freedom from harm. Reliability is the likelihood of a system to function at a given time.
An operator breaking procedures to advert an accident is safe but unreliable. A working mechanical saw w/o protective guards is reliable but unsafe.

66
Q

What are the reviews in the lifecycle of a systems project?

A

They correspond to the gates between stages namely: reviews for system requirements, system design, preliminary design, critical design, test readiness, final readiness and system certification, and production readiness.

67
Q

Concept tasks

A
  • Define the problem and identify the need (requirements)
  • System planning and architecting
  • Develop system operational requirements
  • Exploratory feasibility studies
  • Propose a maintenance plan for the support of the system
  • Identify technical performance measures and related design criteria
  • System-level functional analysis and requirement allocation to
    subsystems
  • System analysis and trade-off studies
  • Design review
68
Q

Definition tasks

A

Developing the concept into a firm definition of a solution
- Developing system architectures and system
configurations
- Re-evaluating the supplier base to establish what
equipment, components and materials needed for the
emerging design
- Defining physical and installation characteristics and
interface requirements
- Developing models of the individual systems
- Quantifying key systems performance measures such as:
mass, volume, growth capability, range/endurance, …
- Identifying risk and introducing mitigation plans
- Selecting and confirming appropriate technology

69
Q

Design tasks

A
  • Detailed design of the sub-systems and components.
  • Development of engineering and prototype models.
  • Verification of manufacturing and production processes.
  • Selection of suppliers of bought-in equipment and
    components.
  • Production planning: to achieve a fully certifiable design of
    complex integrated systems, an integrated design team
    comprising platform integrators and suppliers is essential
70
Q

Build tasks

A
  • Production and/or construction of system Components.
  • Supplier production activities.
  • Acceptance testing.
  • System distribution and operation.
  • Developmental/operational test and evaluation.
  • Interim contractor support.
  • System assessment.
71
Q

Test tasks

A
  • Ground and flight testing of the aircraft.
  • System modifications for improvement.
  • Contractor support.
  • System assessment (Field data collection and analysis)
72
Q

Operate tasks

A
  • System operation in the user environment.
  • Sustaining maintenance and logistic support.
  • Operational testing.
  • System assessment (Operational data collection and analysis)
73
Q

HALE

A

Heavy payloads over 3000+ km.
Around 24 hours.
Communication relies on satellites.

74
Q

Medium range, fixed wing.

A

Aircraft configuration with the surveillance payload, and the power plant at opposite ends.
Range - over 500km.
24 - 48 hours endurance.
mass of 1500kg.

75
Q

Medium range, rotary wing

A

Cruise speed of 200km/hr.

76
Q

Mini UAVs

A
  • Back packed, assembled and deployed by no more than 2 persons.
  • If mass is less than 10kg, can be flown at under model aircraft rules.
  • Designed to be hand-launched and controlled thorugh a laptop.
  • Powered by small engines, but can be done using battery technology nowadays.
    Range is <10km.
    less than 2 hours of endurance.
    150 kg mass.
77
Q

What are humans better at?

A
  • Detecting signals in high noise.
  • Recognising objects over varied
  • Handling unexpected occurrences.
  • Reason inductively.
  • Profit from experiences.
  • Originality.
  • Reprogamming + perform when overloaded.
78
Q

What are machines better at?

A
  • Responding with minimum lag.
  • Precise, repetitive operations.
  • Storing and recalling large amounts of data.
  • Monitoring functions.
  • Sensitivity to stimuli.
  • Exerting certain amounts of force.
79
Q

What are the 3 categories of test and evaluation?

A
  • Developmental test and evaluation.
  • Acceptance test and evaluation.
  • Operational test and evaluation.
80
Q

Explain developmental test and evaluation

A

refers to the test and evaluation
activities undertaken during the acquisition phase of the system life cycle to support the
design and development effort. DT&E activities may also occur during the utilization
phase to support such activities as modification development

81
Q

Acceptance test and evaluation

A

As DT&E completion approaches, AT&E
activities become increasingly relevant. AT&E represents the formal acceptance testing
conducted on the system to enable the customer to accept the system from the
contractor. AT&E effectively forms the boundary or transition between the acquisition
phase and the utilization phase. Unlike DT&E and operational test and evaluation
(OT&E), AT&E tends to be a discrete testing activity (with a defined start and a defined
end)

82
Q

Operational test and evaluation

A

test and evaluation effort that is focused on the functional or operational testing
of the system and its components, conducted under realistic operational conditions by
operational personnel. OT&E is normally conducted for a period of time following
acceptance of the system by the customer, although limited OT&E activities are
possible during acquisition, especially where a long production cycle means that some
systems have been accepted prior to other systems being produced, or when concept
demonstrators are being used.

83
Q

What are the main elements of a test planning?

A

Developmental test planning
Operational test and evaluation plan

84
Q

Explain Developmental test plan

A

Developmental test planning:
- define the specific technical parameters to be measured.
- summarise test events, scenarios and design concepts.
- list all models and simulations to be used
- describe how the system environment is represented

85
Q

Explain Operational test and evaluation plans

A
  • list critical operational issues to be examined to determine
    operational suitability,
    β€£ define technical parameters critical to the above issues,
    β€£ define operational scenarios and test events,
    β€£ define the operational environment to be used and the impact of test
    limitations on conclusions regarding operational effectiveness,
    β€£ identify test articles and necessary logistic support, and
    β€£ state test personnel training requirements
86
Q

Verification aspects

A

Inspection, analysis, demonstration, test, certification.

Aero Eng Y3 (2 decks)

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