Disadvantages of Stimulation in Simulation

Simulation of aircraft avionics to provide the fidelity necessary to effectively train aircrews is a complex and difficult task.  This is particularly true for the Apache attack helicopter. The Apache is arguably one of the most complex aircraft to simulate. This is due to its complex avionics, sensor, weapon, navigation capabilities. 

Stimulation vs Emulation

Traditionally, two approaches have been used in flight and weapon system simulators:

  • Stimulation, where actual aircraft equipment and the operational flight program are used in the simulator.
  • Emulation, where the simulator hardware and software replicate the actual aircraft equipment and software.

It has been argued that any approach to training short of utilizing actual aircraft hardware and software in the flight simulator can introduce improper behavior or negative training.  This argument has been primarily made by the aircraft manufacturer. They have self-serving interests to sell operational equipment for the simulator producer and control the simulator market for his aircraft. 

In today’s blog, we will discuss the disadvantages of employing this stimulated approach compared to the advantages of utilizing an emulated approach – specifically for Apache helicopter simulator training.  We will also contrast the advantages of utilizing an emulated or “simulated” approach to address Apache Helicopter Trainer development.

Disadvantages of Stimulation

Using actual aircraft hardware and operational software programs in the simulator offers a high level of fidelity. As well as a claim of optimum aircraft concurrency. However, this stimulation approach introduces several significant disadvantages which must be considered in making the stimulation versus emulation trade-off:

1. Cost

Actual aircraft equipment is very costly. Flight computers and aircraft hardware are often used in the simulator with the operational flight program software.  The operational flight software is controlled by a single source, the AIRCRAFT MANUFACTURER.  This situation has been used to the advantage of the aircraft manufacturer.

They have fostered a non-competitive (sole source) situation where the price cannot be challenged by potential competition.  Often, the rights to the data alone can cost millions of dollars. In addition, simulator projects are frequently delayed as aircraft equipment is diverted to urgent operational requirements rather than training.

2. Partial Stimulation Environment

Aircraft hardware and sensors must be stimulated by a synthetic environment in the trainer configuration. This presents significant challenges to accomplish.  Frequently, the “stimulation” of the hardware is a compromise due to cost and complexity. Only a portion of the sensor can be “stimulated” adequately which can introduce improper behavior training. 

3. Data Restrictions

Utilization of the operational flight program is owned by the aircraft manufacturer and involves data restrictions associated with its usage.  These restrictions are to protect the investment in the intellectual property of the aircraft manufacturer and the security interests of the US Government. 

These data restrictions complicate the acquisition of the trainer – particularly for international sales – due to significant legal licensing, usage rights, and export control-related issues that must be negotiated and executed.  An additional result (either intentionally or unintentionally) are ambiguous data and IP rights assertions that cloud the actual rights the end-user can rightfully utilize.

4. Aircraft Concurrency

The operational flight program is a complex software program. It undergoes regular revisions under strict configuration management processes that may require years before release to the actual aircraft.  The trainer which is utilizing this software must then go through a similar process to update and test the simulator with the updated version of aircraft software. 

This process involves acquiring the most up-to-date version of the software, integration of the software, and any associated updates to the trainer hardware required to complete the integration, and regression testing of the simulator to ensure it functions properly with the new operational software. 

Simulator verification can typically last several months to over a year to accomplish.  This adds significant update costs and may result in negative training as the trainer is not concurrent with the operational aircraft for several months during this update.  In the case of the Apache helicopter, where the software is constantly being updated, this can result in a situation where the trainer can effectively train in a perpetually non-concurrent state.

5.  Complexity and Life Cycle Support

Usage of aircraft hardware and software introduces significant life cycle support issues for the simulator.  These consist of increased cost and complexity for maintenance and repair of aircraft equipment and the requirement to use aircraft power sources rather than the utilization of standard commercially available power supplies. 

Logistical spares present an issue as there is potential to cannibalize the trainer to support any shortages encountered in the maintenance of the operational flight aircraft.  These complications may render the trainer inoperable as critical hardware shortages or maintenance issues may impact the availability of the trainer.

6.  Security

For obvious security reasons, the operational hardware and operational flight software must be protected and restricted.  Since aircraft assets are used by the trainer, it must be protected as if it was an operational aircraft.  Security issues are complicated in the case of transportable trainers where the relocation of the trainer presents security challenges and costs.

In the next post, we will discuss the Advantages of the Emulation Approach over stimulation.

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Initially, Applied Visual Technology Inc., AVT has been developing modeling and simulation expertise through engineering services since 1998. This is due to our founder who has accumulated over 30 years of military MS&T expertise in aviation applications. Nonetheless, everyone at AVT specializes in making old training systems new again and making new ones for less. Consequently, for 20 years AVT has served our Air Force, Army, Navy, and Marine customers by providing the highest quality of service and solutions. Following its inception, AVT’s highly specialized staff of engineers has included some of the top leaders in the simulation industry. With over 20 years of simulation experience, our dedicated team provides specialized solutions for customers with complex problems.