Lightening the load!

John Jeffery, CEO of J2 Aircraft Dynamics discusses the commercial and technical benefits to be gained when undercarriage simulations are combined with aircraft simulations to provide a completely integrated solution during the design of the entire aircraft. Performing a crucial role in aircraft behaviour and performance during take-off and landing, but taking up critical space and weight in-flight, undercarriage components can be particularly challenging to develop. Whilst preliminary designs are performed by manufacturers looking at location and available space, it is down to the landing gear manufacturer to turn the theory into reality.

Historically, at this point, both will be developed in isolation, each eventually developing high fidelity simulations to satisfy their own goals. Whilst the use of modelling and simulation has been available and utilised for many years, and the dynamic modelling of undercarriage loads and dynamics is also heavily used, the capability to bring together both models at a much earlier stage in the design process has been lacking. The separation of these parties means that throughout this development process each is using, at best, crude models of the system outside of their domain. However, the use of embedded processes within software tools can enable both partners to work together, working with high fidelity models to predict actual results for aircraft and undercarriage behaviour.

This marriage of models evaluated over any number of ‘real' operational scenarios provides a more streamlined approach to design and integration. The use of state of the art modelling tools opens up the possibility for undercarriage manufacturers to look at more realistic load scenarios in order to minimise weight, simultaneously enabling the aircraft manufacturer to look at the real impact of a shifts in the centre of gravity and undercarriage aerodynamics on the behaviour, handling and performance of an aircraft.

The J2 Universal Tool-Kit provides a framework to merge models from both parent sources into a complete system. The resultant capability this provides means that undercarriage manufacturers can run ‘real' scenarios for ground roll, take-off, and landing using the actual loads and forces generated from the aircraft as part of the overall design process. This can not only be used for investigations of normal operation but can include failure modes as well. The advantage here is that designers get a more accurate understanding of the stresses experienced by the various components on the undercarriage. Taken to its logical conclusion, this capability can also be used to challenge the standard conventions of safety margins and potentially reduce the weight of the undercarriage structure with the obvious operational gain in economy.

Closing the gap

Aircraft models can range from simple approximations of aircraft and their behaviour at conceptual and early stage design projects right through to full wind tunnel and flight corrected data models mimicking the exact behaviour of the aircraft. During this analysis simplified undercarriage models have been integrated to provide take-off and landing behaviour evaluation. Likewise, undercarriage manufacturers are already running detailed simulations on landing gear retraction and deployment, as well as on drag contributions and loads.

The J2 Developer component of its Universal Tool-Kit enables detailed undercarriage models to be directly combined with the aircraft model providing the best of both worlds. This is delivered through an open interface that is capable of taking code from any language, compiled into a windows library and linking it directly into any aircraft model. Aircraft states such as velocity, acceleration, orientation and weight can be mapped into the undercarriage models and the resulting forces from the undercarriage are applied back to the aircraft generating realistic responses from the model of the total airframe.

It's good to share

Inherent in the software is a centralised collaborative platform. This means that both manufacturers can share data and work from a consistent, version controlled dataset, delivered through a Microsoft SQL database vehicle. MSQL is already deployed internally throughout many companies as well as across different organisations and provides a mature approach to data sharing. Engineers can not only work with each other's model data but re-use test cases as well, reducing the duplication of work and shortening timescales.

This collaborative principle already provides for the integration of weight, aerodynamic, flight mechanic and flight control system design data, so the addition of undercarriage design is a natural extension.

With this level of seamless integration it becomes possible to look at undercarriage placement and structure at a much earlier stage. Working with initial designs and integrating the undercarriage at the beginning of the lifecycle means that all modifications to the airframe are automatically captured by the undercarriage design team enabling them to establish how each design change will impact on the forces and moments experienced by the undercarriage. Whilst this capability is also available in other software tools, these tend to require extensive code to be written that can result in the solution not being economically viable. With the J2 Universal Tool-Kit, the integration capability is already written into the code so users are able to build graphical models and merge code from other tools directly into the overall framework.

Here the aircraft manufacturer is now able to run simulations of the critical functional and failure cases with a higher order undercarriage model whilst the undercarriage manufacturer is simultaneously able to investigate the detailed force being applied to its designs. The enhanced collaboration of experts from both sides throughout the design process starting much earlier in a project can only help to improve the quality and performance of the complete solution.

Saving more than weight

The iterative nature of the embedded Model, Simulate, Fly, Validate process within the J2 Universal Tool-Kit means that fidelity and understanding can be built rapidly resulting in a real opportunity for weight savings and risk reduction due to an increase in knowledge.

One particular application addressed the issue of hard landings and the subsequent bounce causing an even greater impact with the ground, resulting in serious injury to glider pilots and instructors. High order undercarriage models were developed and qualified by comparing to drop test results. This was integrated into a flight model to establish the g loads and stresses on a pilot during poor landings. From these evaluations, instructor intervention policy is being explored with respect to when the instructor must take control to ensure a positive outcome.

Colin Jackson, glider pilot and instructor adds: “The results are already clarifying aircraft behaviour in these critical flight circumstances and the intervention of the instructor. This is providing a positive contribution to improving pilot/instructor safety and hope that it will ultimately lead to enhancing the training of instructors by allowing them, through simulation, to safely experience the limits of instructor intervention and what happens if they allow certain situations to become irrecoverable.”

www.j2aircraft.com