Propulsion and Mission Performance Modelling (including Hybrid Electric)
New Aircraft Models
This week’s aircraft modelling has focussed on the aircraft with recent or imminent entry into service (737 MAX and CSeries), or aircraft that will act as a baseline models for looking at new aircraft types (A330).
Airbus A330: -200 and -300
242t MTOW weight variants of both aircraft modelled;
These provide a good baseline for modelling the A330-800 and -900 (neo) and the A340-200 & -300;
CSeries CS100 and CS300
These aircraft represent a new design, 100-140 seat, single aisle.
A potential CS500 will be modelled for comparison with the A320neo and 737-8 MAX
Boeing 737-8 MAX and 737-9 MAX
These aircraft represent the Boeing state of the art single aisle aircraft and build on previous 737NG modelling
737-7 MAX and the 737-10 MAX to follow shortly
Propulsion Performance
Propulsion performance is a critical component of aircraft performance modelling with limited lower order methods available for the modelling the engine ratings and fuel flow characteristics at rated and part power throttle settings.
RAWAvCon includes an internal turbofan performance modelling capability and this is available within the aircraft design environment allowing rapid changes to the engine model. It is also able to model Hybrid-Electric propulsion systems – see dedicated section below for more information.
The turbofan modelling is based on:
A regression analysis of public domain detailed engine data to define engine performance data at all flight conditions as a function of specific thrust and the most critical of specific sizing parameters:
power curves (SFC loops) including some Reynolds number effects at high altitude
Ratings data for MTO, MCL, MCR (Max Cruise), and MCT (Max Continuous) and Idle
A user defined optimum SFC level – this is defined as a function of entry into service date, engine specific thrust and expected duty.
Future:
Turboprop performance – This model will look at Propeller and powerplant performance separately although it is not yet determined whether this will be external or internal to the RAWAvCon model.
Potential to look at GASTURB turbofan modelling to include defining the SFC loops development as a function of Specific Thrust to allow optimum Fan Diameter studies. Weight and Drag effects already included (nominal SFC variation can already be linked to specific thrust).
the above capabilities will be combined to look at some distributed propulsion characteristics in the future.
Mission Performance
RAWAvCon uses first principle flight performance methods (aircraft drag and engine thrust/fuel flow) to forecast the aircraft trajectory throughout a selection of standard sizing missions and economic (i.e. typical) missions. The missions required to define a payload/range any missions are also assessed to check the overall aircraft design. Any mission at user specified Equivalent Still Air Distances and ZFWs (zero fuel weights).
Taxi, Take-Off and Landing – time values input (TO is weight dependent)
Climb – Trajectory is based on MCL at every 1,000ft and includes an acceleration at 10,000ft from 250kt CAS to the defined climb speed and a switch to defined climb Mach number at the correct crossover altitude.
Cruise: East or West cruise altitude at RVSM or 4,000ft steps – metric flight levels can also be considered:
Optimum cruise profiles are standard with the aircraft performing a step climb. The aircraft initiates a step climb at the precise mass where the specific range is the same at the current and the next flight level – there is also a check to ensure that there is sufficient distance at the next flight level (before descent) to justify the step climb.
Optimum Climb Cruise will also be added such that the aircraft 'hunts' for the optimum altitude as the aircraft weight reduces.
Special Profiles can be defined on a case by case basis with altitude changes (up and down) triggered by aircraft weight or time elapsed in cruise to a defined or the optimum altitude
Descent: Similar to the climb segment with an optional ‘power-off’ drag modification
Reserve Fuel: Numerous Reserve Policies can be modelled
Alternate with a defined diversion distance (includes a missed approach). Altitude set to deliver a minimum of 50% of diversion distance in cruise.
Contingency based on % Block or trip fuel, % mission time, fixed time continued cruise
Hold at Alternate airport
Hybrid Electric Performance
There is currently a lot interest and research being directed at the introduction of electrical power to aircraft propulsion systems.
I have recently developed a process to model Hybrid Electric Propulsion systems and this has been successfully deployed on customer studies and is providing insight into some of the potential and challenges of this technology.
This system considers the power, storage mass, volume and efficiency characteristics of the battery, power transmission, power electronics and on new components within the engine itself.
This impact of adding the electrical power to the propulsion system is assessed at user defined flight phases/conditions is integrated into the flight mission modelling (including fuel reserves), as is the additional system weight. This resulting flight profiles are defined and the net impact on the block fuel and range capabilities can be defined. The physical size of the batteries is also considered and where these are installed on the aircraft.
To date, the hybrid system has been considered as a ‘retro-fit’ on an existing aircraft. However, the modelling is 'parameterised' to allow for an aircraft re-design to maintain the desired payload capabilities (reduced range requirement) and consistent approach speeds as well as exploring changes to the aircraft operating procedures to explore any further advantages of the system that become apparent.
