Advances in Electric Aircraft Flashcards
What is the formula for Pressure (Using ideal gas eq)?
p = ρRT
What are some benefits of electric flight?
More Sustainable, Reduced Environmental Impact, Less Noise, Easier Maintenance, Lower Operational Cost, Potential Performance Benefits,
What is the main challenge for making Electric Aircraft Feasible?
Energy Density: Considering the power-to-weight ratio of both fuel and batteries, 1 kg of fuel = 25…30 kg of batteries.
What percentage of the total weight do batteries represent in an electric aircraft?
Almost 45%
What are some challenges in addition to the technological?
Certifications and Regulations, Infrastructure and Airports, Air traffic management, Maintenance and Servicing, Industry processes.
What is a UAM?
Urban Air Mobility
What is a UAV?
Unmanned Aerial Vehicle.
What is TRL?
Technology Readiness Level
Energy/power sources of electric aircraft?
Battery Powered
Solar Powered
Fuel Cell Powered (Hydrogen Cells)
Hybrid Powered (Combination Fuel and Electricity)
What are Hybrid Aircraft? What are some disadvantages?
A fuel engine drives a generator that charges the batteries in flight. Problems surge from: Size of generator, Efficiency, Power Distribution.
What types of hybrid electric drive architectures are there?
Parallel hybrid electrical (Both the Batteries and the Fuel engine drive the propeller)
Serial hybrid electrical (The engine recharges the batteries, which then power drive the propeller)
Partial Electrical (The batteries only provide additional power when needed)
Turbo-Electric (Similar to Serial-hybrid, but the electric motor is decoupled from the generator)
Whats HEP?
Hybrid Electric Propulsion.
Definition of “System”?
An assembly of electronic, electrical or mechanical components with interdependent functions forming a self-contained unit.
What are the different types of systems in an aircraft?
Aiframe/structure, Vehicle systems (Propulsion, Flight Controls, etc.), Avionic Systems (Navigation, Controls, Displays).
What is the aircraft electric system constructed of?
-Energy Sources
-Control Devices
-Conversion Devices.
-Protection devices and switches
-Electric wiring interconnection systems
-Electrical loads.
What is the main objective of Electric Power Systems?
Generate, convert, and distribute power safely and efficiently to aircraft loads. While also providing fault protection in the event of failure.
What is EPS?
Electric Power System
What are some of the regulated elements of EPS?
-Backup Power Sources
-Power Quality
-Failures are independent of different systems
-Electrical Wiring Interconnection System (EWIS) must have adequate physical separation.
-Power Management System ensures safety, power quality, stability, and effective function of the EPS for all conditions.
Whats a three channel electrical system in an aircraft?
The electrical system has 3 independent electrical circuits that distribute electrical power to the aircraft’s electrical systems and components. It exists so that there is redundancy in the system.
What is Power Quality?
Is a measure of the reliability and efficiency of the electrical system, which implies a steady and consistent power supply.
What is Ohms Law?
V = R * I
How is electrical power calculated?
P = I * V
How is Electrical Work calculated?
W = P * t = V * Q = U * I * t
How is electrical Resistance of a wire/conductor calculated?
R = ρ * l / A
where:
ρ = specific resistance (Material)
A = Transversal Area of the conductor
l = length of the conductor
What is the difference between a Rectifier and an Inverter?
Rectifier AC -> DC (transistors and diodes)
Inverter DC -> AC
What does an H-Bridge do? What does it consist of?
It controls both the direction of the current flowing through a Load (Motor) as well as the amount of power supplied to it.
It consists of 4 switches connected to a load, arranged in the shape of an H with the load in the middle.
What is a Flyback Diode?
A circuit used to avoid voltage peaks when the current is reduced or interrupted.
What causes Electric Component Power Losses in power electronics?
Mostly losses due to Switching (Transistors changing from off to on).
Also Conduction, Blocking (Diodes from on to off), Driving Losses.
What are Circuit Breakers?
These electrically isolate components in a short time in case of fault operation. (Fuse)
What types of Circuit Breakers are there?
Mechanical, Solid-state, Hybrid, Fuse, Vacuum, With Arc Chamber.
What are the different types of electrical actuation?
Electro-Hydrostatic Actuator (EHA) : Fast response.
Electro-Mechanical Actuator (EMA):
Disadvantage of possible jamming of the actuator.
What is APU?
Auxiliary Power Unit.
What is MEA?
More-Electric Aircraft. Aircraft for which the pneumatic and hydraulic systems are replaced by electric systems, but primary control surfaces are hydraulic or pneumatic.
Why use Electrical systems as opposed to Pneumatic or Hydraulic?
Air compression process is eliminated, Less components and complexity, Fewer risks (Oil contamination of cabin air supply), Improved aerodynamics (No bleed air vents), Easier Maintenance.
When is the most power-intensive flight phase?
Take-off and Climb
What are Remotely Distributed Electrical Power Systems?
It is an electrical Power system where the distribution isnt centralized, so distribution centers can be placed closer to loads, making it so that the systems are more reliable, and with less weight (less wiring).
Advantages of All-electric aircraft
Less complexity (all power comes from electrical system)
More complex electric power system
What re the 3 main electrical systems of a transport aircraft (All electric)?
Propulsion System, Subsystems (Controls), Avionics
Differences in Power Type between All electric and More electric aircraft?
All Electric: sources usually deliver DC. (Reduced system complexity, low voltage drop, reduced EMI)
More electric: Generator delivers AC (Challenges for parallel operation, No need for synchronization of AC generator to AC distribution system, Additional components needed).
What considerations of environmental influences must be taken into count for the electrical systems?
Low Pressure: Reduces critical field strength (air doesnt insulate as good)
Temperature: Conduction Properties.
Humidity: Condensation, insulation aging.
Radiation
Lightning
Electromagnetic Interference (EMI)
What to consider when selecting a motor?
-Power/Torque
-Operating RPM
-Efficiency
-Torque-speed characteristics
-Power Density
-Voltage Requirement
-Current draw from battery
-Heat rejection
-Maintainability
-Reliability
-Cost
How is Motor Speed calculated?
ω = Kv * U
Where Kv is a constant
How is Motor Torque Calculated?
Q = Kt * I
where Kt
Or Q = P/ω
How is Motor Output Mechanical Power calculated?
Pout = Q*ω = UI - Ploss = U I - I2 R - U I0
Which are the wire resistance losses and the magnetic losses respectively
How is Motor Efficiency Calculated?
η = Pout/ Pin = (U I - I2 R - U I0) / U I
How do Electric Motors compare to Combustion Engines in the following areas?
Efficiency, Reliability, Power Density, Torque Power Production at standstill, Number of Moving parts, Exhaust emissions, Noise/Vibrations, Bi-Directional?
____________ ………………………. Combustion. …….Electric
Efficiency ………………………………. Low ……………. High
Reliability ……………………………. Medium ……… High
Power Density ……………………….. Low …………. High
Torque production at standstill .. No …………… Yes
Number of Moving Parts ……….. Very High …… None
Exhaust Emissions ……………………. High ………… Low
Noise/Vibrations ……………………… Medium ……… Low
Bi-directional? …………………………….. No …………… Yes
How is the Propulsion Thrust Calculated? (Thrust produced by the propulsion system)
T = ma = ΔV * (Δm/Δt)
How is the Propulsive Power calculated?
Pprop = T * V
How is the advance ratio of a propeller calculated?
J = V/(n d)
where
n = propeller speed (rev/sec)
d = propeller diameter (m)
How is propulsive efficiency calculated?
ηprop = Pout/Pin = TV/Pin = (CT/CQ) * J
What are the 2 types of propeller configuration? What are advantages and disadvantages of each?
-Tractor: pull aircraft through air, mounted in front of engine, increases airspeed of wing, propeller rotates in clean air.
-Pusher: mounted on rear end of the aircraft, propeller rotates in unclean air (it passed the wings/fuselage), reduces drag by preventing flow separation, higher probability of damage
What is a simple formula used to calculate propulsive efficiency?
ηpr,simple = 2 / (V/V∞) + 1
How is the Power Coefficient calculated?
CP = P / (ρ n3 d5)
How is the Thrust Coefficient calculated?
CT = T / (ρ n2 d4)
How is the Propeller tip speed calculated?
Vtip = sqrt ( V2 + (n π dp)2
What is DP? What are some benefits?
Distributed Propulsion. Easier to place motors anywhere on the airframe, Structural benefits potential increase of Disk Area, Thrust Vector control possible. One Engine Inoperative requirements might be easier to meet.
What is BLI?
Boundary Layer Ingestion. Aircraft configurations where the boundary layer around the aircraft is ingested by the propulsors. Leads to reduced Wake and Higher propulsive efficiency
Types of BLI?
Annular : Propulsors at rear of fuselage, rotationally symmetric inlet flow, can ingest large amount of BL
Asymmetric: Propulsors on wings, asymmetric inlet flow, reduced efficiency
What is HEA? Advantages and Disadvantages.
Hybrid Electric Aircraft. Higher efficiency than Conventional, Increased complexity, Better EMs scaling, Better flexibility in operation and design.
How is the Degree of Power Hybridization calculated?
Hp = Pelec/Ptot
How is the Degree of Energy Hybridization Calculated?
HE = Eelec/Etot
How does a Turbo-Electric aircraft’s drivetrain architecture look like? Advantages and disadvantages?
ICE produces power to drive generator, which drives an EM, which drives a propulsor. (HP = 1, HE = 0)
+ ICE decoupled from EM
+ ICE can be positioned strategically
+ No batteries
- Added weight of generators and EM
- Fuel-driven
What does a Partial Turbo-Electric Drivetrain Architecture look like? Advantages/disadvantages?
EMs supply part of propulsive power while the rest is generated by ICE turbofans. (0 < HP < 1, HE = 0)
- Additional weight (Generator, Em)
+ Electrical components can be smaller (total weight is lower)
What does a Full Serial Hybrid Drivetrain Architecture look like? Advantages/disadvantages?
ICE drives generator which in turn drives EMs. Electric system is supplemented by a battery. (HP = 1, 0< HE < 1)
+ Simple concept
+Design freedom.
+ New configurations are possible.
- Propulsors are driven by EMs alone
- Less efficient powertrain compared to parallel, bigger batteries and EMs needed.
What is PMS?
Power Management System
What does a Parallel Hybrid Drivetrain Architecture look like? Advantages/disadvantages?
ICE and EMs are both connected to the propeller shaft, Generator isn’t required. (0 < HP < 1, 0 < HE < 1)
+ Direct connection of ICE to propeller shaft, higher propulsive efficiency
+ No Generator
+ Propulsive power comes from both ICE and EMs
- Extra mass due to mechanical coupling
- More complex propulsion Control
- ICE directly involved in thrust generation, reduced performance.
What does a Fully Electric Drivetrain Architecture look like? Advantages/disadvantages?
Propulsors fully driven by electric motors with energy provided by batteries.
- Battery Specific Energy Limitations
- High Weight
Definition of Energy?
The ability to perform work [ kWh ]
Definition of Power?
Energy transfer per Unit Time. [kW]
Definition of Specific Energy?
Energy per unit mass [ J/kg]
Definition of Energy Density?
Energy per Unit Volume [ J/m3]
What parameters are important when choosing a battery?
LOW mass HIGH safety
-Energy Density
-N. of Recharge Cycles
-Recharge Rate
-Temperature Sensitivity
-Insulation requirements
-Fire hazard, safety
-Cost
Main types of batteries? Advantages/disadvantages?
NiCd : Cd toxic, High Discharge Rates, Inexpensive
NiMH: Slightly higher energy density
Li-ion: Higher Energy density than Ni based, Expensive, Fire hazard
LiPO: Relatively light, higher energy density than Li-ion, potential explosive hazard
Li-S: Higher energy density than Li-ion batteries, Sulfur is cheap and abundant
What are some battery requirements for aviation?
-High peak power duration
-High safety and reliability
-High number of cycles
- Fast Charging
How can hydrogen be stored? advantages/disadvantages?
As a compressed gas: Low Density, Heavy tanks, Low Storage efficiency, Safety Risks
As cryogenic Liquid: Requires cryogenic cooling, cooling uses up to 45% of stored energy
What does a Hydrogen/fuel cell powertrain consist of?
Fuel tank, Fuel cell (converts chemical energy into electric), ESC, Electric Motor, Propeller/Fan
How is Fuel Cell Efficiency calculated?
η = Vcell/Videal
What is MPP?
Maximum Power Point
How is the used hydrogen mass consumption calculated?
mH2,used/Δt = MH2 * (N Istack) / 2F
Where: M = Molar mass, N = number of cells, I = Current, F = Faraday constant
How are the subsystems in a Fuel Cell system divided?
Air supply subsystem
Hydrogen supply subsystem
Cooling subsystem
Electrical subsystem
Advantages/Disadvantages of Fuel Cells?
+ Higher Energy Density than batteries
+ Quickly recharged
+ Twice as efficient as an ICE
+ Few moving parts
+ Direct conversion of chemical energy into electric energy.
- Heavy tanks needed
- Storage is challenging
- Requires fuel
- Waste heat is produced
- Hydrogen is explosive and flammable
How is Total Available Energy calculated for a battery-powered electric aircraft?
Eb [Wh] = eb [Wh/kg] * mb [Kg] = Cb [A h] Ub [V] = Eb,max(1 - SOCmin)
How is the flight time calculated for an battery powered electric aircraft?
t = (ηtot eB/ V*g) (CL / CD) ( mB/mTO)
How is the flight range calculated for an battery powered electric aircraft?
R = (ηtot eB/ g) (CL / CD) ( mB/mTO)
How is Range for Conventional Aircraft calculated?
R = (ηtot ef/ g) (CL / CD) ln( 1/(1-mf/mTO)
What is the glide number for a symmetric drag polar?
ε = CD/CL = CD0/CL + k*CL
How does an electric aircraft compare to a conventional aircraft regarding Performance factors?
An Electrical Aircraft can achieve maximum range at higher speeds, shorter flight times
They can also achieve maximum range at maximum speed
and they have a higher service ceiling
How is Thrust calculated when at a Climb Angle?
T = D + W * sin(γ)
How is Lift calculated when at a Climb Angle?
L = W * cos(γ)
How is the height changing when at a climb angle?
h/Δt = V * sin(γ) = VT/W - VD/W
What is C*L and how is it calculated?
It is CL when D is at its minimum.
What is C*L = sqrt(CD0/k) = CL,Dmin
What is CL,t_max and how is it calculated?
It is the Lift Coefficient necessary for maximum endurance
CL,t_max = sqrt(3CD0/k) = CL, P_min
What is E0,f and how is it calculated? (Hybrid aircraft)
Initially stored Fuel Energy
E0,f = (1-Φ)*E0,tot
What is E0,b and how is it calculated? (Hybrid aircraft)
Initially stored Battery Energy
E0,b = Φ*E0,tot
What is Φ?
Power Ratio
How is the range of a Hybrid aircraft calculated?
Rhyb = ηprop ef / g * (CL/CD) ( ηel Φ/(1-Φ) + ηth ) ln (mTO /(mTO - m0,f))
How are eVTOLs divided (types of eVTOLs)?
Helicopter, Multi-rotor, Lift+Cruise, Tilt-rotor, Tilt-wing
Advantages and disadvantages of Multirotor aircraft?
+ Low design complexity
+ Simple construction and rotor system than helicopters
+Good hover performance
+ Small rotors, lower motor weight compared to helicopters
+Good VTOL performance
- High power required for forward flight
- Only good for short ranges at low speeds
- Relatively slow
- Inefficient energy consumption in cruise
Advantages and disadvantages of electric helicopters?
+Faster and more efficient than multirotors
+ Good hover and VTOL performance
- More complex than multirotors
- Larger rotors
- high power required for forward flight
- inefficient energy consumption in cruise
- short range and low speed
Lift + Cruise configurations advantages and disadvantages?
+ Good compromise between cruise and hover performance
+ Higher flight speed
+ Suitable for long distances
+ Less complex than vectored thrust
- Performance is not optimal for ANY condition
- Added weight and drag due to double propulsion system
Tilt-Wing configurations advantages and disadvantages?
+Good for high speeds and high ranges
+ Higher Lift-to-Drag ratio
+ Extra cruise efficienc thanks to the wing and multiple small propellers
+ Good performance for a variety of missions
+ Energy efficient cruise
- Challenging transition
- More complex control
Tilt-rotor configurations advantages and disadvantages?
+ Generally lighter than tiltwings
+ Well suited for long ranges and high speeds
+ Energy-efficient cruise
- Challenging transition
- More complex control
- Lower cruise efficiency than tiltwings
What are PAVs?
Personal Air Vehicles
How is the required Power to Hover calculated for a duct type propulsor?
PP,duct = 1/2 sqrt(T3 / (ρAjet)
How is the required Power to Hover calculated for a propeller type propulsor?
PP,prop = 1/sqrt(2) * sqrt(T3 / (ρAfan)
Definition of Hover Efficiency?
How much weight can be lifted per given mount of power
What is Disk Loading?
Weight to thrust area ratio
σ = mg/A
What are the optimal configurations for different types of missions?
Helicopter: Best for small range at moderate to high speeds
Multirotor: Best for small range at low speeds
Tiltrotor: Best for a moderate range at medium to high speeds.
Tiltwing: Best for Long range at any speed
Lift+Cruise: Best for low to moderate range at any speeds, and best for moderate/long range at low speeds.
What is BMF?
Battery mass fraction. Mass of the batteries to the total mass of the aircraft
What are some of the different design approaches available?
Semi-empirical weight estimation
Graphical constraints analysis
Optimization
Mission-dependent analysis
Performance-based analysis
Combinations
What is Power Loading?
Similar to Wing Loading, but regarding Power instead of Wing Surface. W/P
It used similarly, to obtain a design space in a P/W to W/S graph
Design Process for an eVTOL?
-Constraints analysis to specify W/S and W/P
-From design point calculate wing area given the total weight
-Estimate motor and battery weight
-Estimate relation between empty weight and total weight considering battery and motor weight as well as the assumed payload
What does having a Low Disk Loading imply for an aircraft?
High lift-thrust efficiency
Less power required to maintain rotor speed
Smaller engine required to hover
Large rotor required
Autorotation performance increased.
eVTOL modelling and control challenges?
Complex dynamics and actuation (control and modelling is difficult)
Novelty factor (New configurations, little experience, missing regulations)
Operation in urban environments (Take-off and landing constrained, Updrafts, High Risk)
What are some Tiltwing specific modelling and control challenges?
Wing requires dedicated actuators in order to tilt
Large exposed wing area during vertical flight (higher wind gust sensitivity)
What are some tiltrotor specific modelling and control challenges?
Negative lift due to wing being in propeller wash
Interference effects can be large
Tilt actuation delays
What are the Newton-Euler formulation of equations of motion (dynamics)?
mV/Δt = Ftot -m( ω x V)
I ω/Δt = Mtot -ω x Iω
where:
Ftot = FA + FP + FG
and
Mtot = MA + MP
What is the order that must be followed to transform from NED frame to the Body Fixed Frame?
1.- Yaw ψ
2.- Pitch θ
3.- Roll φ
How can coefficients (e.g. Cl) be modeled?
Using Simplified analytical models, Semi-empirical models, Fully data-driven models, and CFD -based models.
