The Aeralis Modular Training Study – Platform and System Aspects

Jim Smith, who spent much of his career close to the world of military aircraft acquisition, reflects on the radical new Aeralis training system

Hush-Kit have asked me to look at the Aeralis modular training family of aircraft and systems, recently reported in the media following the award of a research contract by the Royal Air Force. The intent is to provide a family of aircraft which are enabled to address a range of requirements in the general area spanning basic trainer to light combat aircraft, through the use of an innovative modular design approach. A common forward and centre fuselage module is used, and, with the use of alternative wing, propulsion system, cockpit and empennage modules, variants can be generated to meet this broad range of requirements.

While, in all cases, the aircraft are subsonic, a larger and less-swept wing discriminates the elementary trainer from the advanced trainer and light combat variants. Three propulsion modules are envisaged – a lower and a higher-thrust single-engine configuration, and a twin-engine variant. Two crew and single seat versions would be available to meet the differing needs of training and air combat, but these would retain the same external lines for commonality of structure and aerodynamics, with the freed-up volume of the single-seater being available for additional fuel.

Systems aspects are enabled by exploiting the flexibility and commonality of digital systems, providing not only the capability to vary the displays as required, but also the ability to synthesise targets for training; to integrate with different external sensors and stores; and a comprehensive ability to monitor and manage airframe, engine, and system usage and maintenance requirements.

Aspects to consider
Given the attractive sounding capabilities described above, what are the issues to look out for? I’ll try and group these under Technical, Marketing, and Decision-making, and I must state from the outset that my comments are based on general analysis of the problem. My list is absolutely not intended to imply that these issues are not being addressed. Its rather to indicate to the Hush-Kit readership, those areas which are likely to be important for anyone proposing a modular aircraft solution to fit a range of roles from training to combat. And, as usual, this represents my opinion, which has no connection with, or influence on, any serious decision making about modular training platforms and systems.

Key technical issues:
• Potential weight or other penalties in achieving commonality
In order to achieve the desired modularity, production breaks have to be introduced to the airframe. These are the structural joints where, for example, the alternative outer wings are attached to the common centre fuselage. Other breaks in the structure will be required at the join between the rear fuselage and the centre fuselage, and at the junctions between the propulsion module, the centre fuselage and the rear fuselage.

In addition to these structural joints, some elements of the structure for the lower performance variants may have to be ‘over-engineered’, as they will have to sustain the higher loads generated by higher weight or higher performance variants. As an example, if the basic trainer were stressed to 6g, and the combat aircraft variant to either a higher weight or higher g limit, the centre fuselage wing carry through structure used by the trainer would need to be stressed to the higher loads experienced in the combat variant

Because of the desire to be able to fit alternative engines, in different configurations, alternative propulsion modules are required. As a result, and to also allow alternative outer wing planforms, it is proposed to stow the undercarriage in external pods at the trailing edge of the common fuselage/inner wing structure. While this makes a lot of sense as an enabler to the modular design approach, there will be a drag penalty, and possibly a weight penalty, compared to a fuselage mounted main undercarriage, like that used for the Alpha Jet.

• Ability to integrate diverse systems for the differing variants
This is an area where a well thought through and well-executed approach is central to much of the operational flexibility being sought in this modular design approach. An advanced jet trainer should be able to replicate the look, feel and function of the operational systems to which the trainees will graduate. It will be desirable to configure the cockpit displays to represent differing graduation options – for example in the UK, future trainees might graduate to the Tempest or F-35B. But if other Nations adopt the trainer variant, their operational aircraft might be, for example, the Tejas and the TEDBF.

As well as being able to represent differing cockpits, there are significant differences in equipment that may be required by the differing variants. While all variants will require flight and engine control systems, utility systems like undercarriage, oxygen, pressurisation, electrical and communications, and health and usage monitoring systems, some will require additional capabilities. For example, an advanced trainer, or dissimilar combat aggressor would require the ability to simulate radar and IRST systems, and to have simulated targets or cooperating manned or unmanned assets injected into those systems so as to stimulate required training responses. Air combat replay and recording facilities such as ACMI or RAIDS pods would be required, and there might also be a need to at least simulate some ground targeting and practice weapon capabilities

The architecture for these system capabilities is likely to become quite complex, given the alternative requirements of differing potential customers as well as the diverse capabilities required for the various roles. Particular attention will be needed to ensure physical, electrical, network, software and hardware interfaces are well understood and specified for all the various systems.

• Propulsion system matching
Three different engine configurations are proposed: a low-power and a high-power single-engine installation; and a twin-engine solution. Considering the twin-engine solution, it is evident that this will come with differing system requirements than a single-engine solution. For example, consideration will have to be given throughout to the implications of an engine failure, shutdown or fire. This sort of event will require a fuel system capable of supplying either engine separately, or both together. Similar considerations will apply to the implications of single-engine failure on the electrical, system management, hydraulics and other aircraft systems.

The high-power variant appears to have a variable nozzle, suggesting use of an afterburner – while this seems unlikely in a subsonic aircraft, additional power, coupled with a slightly more swept wing, will result in different ability to accelerate and potentially different handling qualities, particularly at high subsonic speeds. Consequently, the philosophy for control law development will require careful thought. One option would be to minimise changes so that the trainee has to accommodate to the greater system capability and performance of the advanced trainer and air combat variants. Alternatively, the control laws for each variant could be tweaked so as to minimise the change in feel and behaviour.

• Certification
The discussion above shows the criticality of system integration across the variants proposed, and also provides some indication of the opportunities presented by such a software-enabled training system. A difficulty lurking in the wings behind all of these capabilities is certification. Given the options include two wing configurations, three engine options and two cockpit layouts, I think it is safe to say that the approach to certification will be a key area to be managed.
Aspects will include the certification of the necessary software, and the variations required for the differing versions, or for optimising individual variants for different customers. Additionally, the differing wing planforms will have differing aerodynamics, differing loads and may require differing control laws. The weights, and potentially centre of gravity, of the variants will differ and the impact of this on certification will be compounded should there be a desire, or a requirement, to offer differing g-capability.

In addition, the twin-engine variant will need to demonstrate how engine failure cases can be safely managed, and any variants able to carry and/or release weapons will need to show that this can be done safely. Similarly, variations in the fuel system for the twin-engine and for the single-seat variants will need to be assessed and certified.

Possible marketing issues:
• Differentiation from existing highly capable and competitively priced alternatives

Having once been dominated by the Hawk, the Aero 39 and its developments, and the Alpha Jet, the range of capable and effective jet trainers, light combat and strike aircraft has burgeoned in recent years. While this may seem a harsh question, I think it is fair to ask what this family of aircraft could do, that could not be done as well by the latest two-seat Hawk, working in tandem with a new generation Hawk 200 single seater. Or, indeed single and two seat variants of other recently produced designs such as the Leonardo M346 Master.

There are answers to this question available in the advanced, integrated and flexible software-driven systems capabilities proposed, which are indeed a key feature enabling this modular approach. But these systems are also a key risk. They have to be right, they have to be timely, they have to be sustainable, and they have to be certified. And, of course, the digital-capable single-seat variants to operate as partners generally do not exist

• Dealing with the related question – why not a supersonic version like the Boeing/Saab T-7A Red Hawk?

There is a different niche in the market, spanning the advanced supersonic trainer, the air combat trainer and operational light combat aircraft. The Boeing/Saab T-7A sits in this general area as a T-38 replacement, but perhaps the Korean KAI T-50, TA-50 and FA-50 is a better exemplar. In essence, this aircraft shows an alternative vision, where a relatively simple trainer can bring pilots up to the capability to take on the advanced trainer T-50, and move up from there to an aircraft capable of taking on substantial air combat and strike training, and indeed limited operational capability.

Such an approach offers the prospect of downloading more training hours from the really expensive and capable operational fast jets, albeit at the expense of itself being a much more complex and expensive offering than a modular aircraft covering the flying training, advanced training and initial combat capability spectrum.

Decision-making aspects:
• Convincing decision makers that 3 variants, optimised for Basic Training, Advanced Training, and Light Combat, is a more cost-effective solution than either a single fleet, or a two-type solution
This is the nub of the issue in marketing to, for example, the UK Government. Delivery of the indicated capability through a number of modular variants based around the same common fuselage module will need very persuasive analysis. The basis of that analysis should be the demonstration that the proposed solution represents best value-for-money based on whole-of-life costs, discounted to net present value.
There are a lot of technical terms there, but really, what is being asked is how much would it cost to deliver (for example) 30 years of the capability, where the costs have to include development, manufacture, certification, introduction to service, operation, maintenance, and an upgrade cycle (probably). The costs would also cover ground equipment, simulation, training material and differences (positive or negative) in manpower costs to run the system. Net present value means ‘in today’s money’.

To answer my question, you would have to examine the costs, not only of the Aeralis system, but also the cost of, for example, rival systems based around my suggested Hawk plus new generation Hawk 200, and perhaps even consider the alternative of moving to a more capable Boeing/Saab T-7A or KAI T-50 approach, aimed at saving money by downloading more training from Tempest/F-35B.

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• To achieve the required flexibility, the training/weapon system of the modular solutions will need to be heavily software-dependent, and developing an approach to convince acquisition agencies that the risks in developing, integrating and certifying the necessary software are being well managed will be vital.
This reflects the integration and certification issues I pointed to as key technical issues, but seen through the risk management lens likely to be used by Government.

If you think about the development program for JSF, you can see that it’s really difficult to design a supersonic stealthy fighter, capable (in different variants) of meeting the needs of the Marines for STOVL, the Navy for Carrier operations, and the Air Force for Strike ‘On the First Day of the War’.

Well, actually, no – most of that was at least partially demonstrated in the SDD phase. What’s really difficult is getting the systems integrated, every aspect of the software, the sensors, the displays, the EW and defensive aids – the whole weapon system, qualified, accepted and certified for operational use.

The more complex, the more flexible, the more software-driven, and the more capable your system is, the more difficult it will be to certify, even if your platform has all the attractive modular capabilities proposed by Aeralis. The opportunity exists to do this, and do it right, but the emphasis on the integration of the digital system must be at least as great, if not greater than the attention paid to platform modularity.