RAWAvCon Aerodynamic and Mass methods

This note outlines new aircraft models created in the last two weeks and an overview of the RAWAvCon aerodynamic and weight methods. Propulsion and performance will be addressed in coming blogs along with some studies.

New Aircraft Models

Over the last couple of weeks, I have modelled the 737NG family as a baseline for 737MAX modelling. The variety of performance standards and wingtip options has required the creation of 20 models shown below.

Note: ‘-7BE’ model also includes the ‘CFM56-7B Tech Insertion’ improvement

Only minor modelling changes were required moving between different variants to reflect the expected high component commonality.

The winglet modelling method worked well for both Blended and Scimitar winglets. The chart compares the RAWAvCon calculated benefits of a blended winglet on the 737-800 with Aviation Partners Boeing website. Note: the RAWAvCon data is East bound only (APB data is the average of East and West)

High Speed Aerodynamic Forecast

An aircraft’s external geometrical form is one of its primary interactions with the atmosphere: the engine is the other. The atmosphere does not discriminate between aircraft from different manufacturers. The fundamental aerodynamic performance of an aircraft is largely driven by the major geometric attributes of the aircraft’s form and the technology standards appropriate for the aircraft.

The drag methods used are primarily the typical conceptual design methods familiar to many with some modifications to better represent subsonic transport aircraft:

1. Profile Drag – Flat Plat analogy (turbulent and laminar flow) with form factors plus aircraft attitude effects

2. Induced Drag Factor– a function of the wing aspect ratio and the fuselage width, Mach number and the wing tip configuration

3. Wave Drag – a function of the wing sweep, wing thickness/chord ratio and lift coefficient

4. Trim Drag – Aircraft tail arm and wing aerodynamic attributes

5. ‘Power-Off’ drag adjustment included to modify the drag polar in the descent phase

For each drag component, adjustment factors are included to allow the methods to reflect varying technology standards or the impact of design decisions. The current exercise to model existing and historical aircraft, where public drag data is available, is generating a set of trends for the various technology factors. The trends can be used to predict adjustment factors for future aircraft types and to further refine the RAWAvCon aerodynamic forecasting methods.

Aircraft Mass Forecast

RAWAvCon includes mass forecast methods for all major structural components based on geometry, structural concepts, material, technology standards and relevant certification rules.

Although the aircraft OEWs, required for mission analysis, are often available, the component masses and CGs are calculated as they are necessary to conduct technology studies and to generate models of new aircraft types or new variants of existing types.

The methods used are generally text book methods with some modified by RAW Aviation Consulting to better match published aircraft weight statements.

The wing mass method has had considerable modification to better model major wing structure design parameters and systems as well as current certification standards. This is important as the wing is one of the major components subject to resizing as a result of changing technology standards and requirements.

The Propulsion system: dry engine mass plus the mass of their installation is based on relevant engine attributes. Where possible dry mass data from Type Certification Data Sheets are used. Again, propulsion mass is an important consideration as it also is subject to scaling with changing technology and requirements.

Various major aircraft systems: These methods have been created by RAW Aviation Consulting Ltd based on public domain weight statements for numerous aircraft types with regression analysis used to connect individual system weights to major aircraft design parameters (not simply MTOW). The resulting aggregate of systems mass is generally accurate. While individual systems modelling is also reasonably representative, in some cases there are apparent trades between related systems - possibly a difference in the accounting of system components.

Furnishings and Operators Items – Regression analysis for nominal airframe company values (public domain) based on cabin attributes.

‘Real-world’ airline Operator Items mass values. A method to predict airline furnishing and operating items masses as a function of cabin service standard and layout is currently being defined based public domain data for numerous airlines.

Payloads – Payload weights are defined by the user based on airframe company mission assumptions and various studies, e.g. ICAO, EASA and various Airworthiness Authorities.

All the mass methods are only as complex as they need to be to satisfactorily model the aircraft. However, I can introduce more detailed methods as required by customers, often in partnership with them.