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Why PAC Needs In-House Development of Flight Control Systems

Author Profile: Syed Aseem Ul Islam is PhD candidate at the University of Michigan, Ann Arbor, USA, specializing in adaptive and model-predictive flight control systems. He received his bachelor’s degree in aerospace engineering from the Institute of Space Technology, Islamabad, and his master’s degree in flight dynamics and control from the University of Michigan.

The JF-17 program has gone a long way in grooming the nascent Pakistani aerospace industry in a big way. The experience that has come with manufacturing large portions of a modern fourth-generation fighter jet has advanced the manufacturing and designing capabilities at Pakistan Aeronautical Complex (PAC) many folds.

It is on the success of this program that PAC hopes to embark on Project Azm: an all-encompassing program for the development of an aerospace industry in Pakistan, which includes the development of a fifth-generation fight aircraft (FGFA), a medium altitude long-endurance (MALE) unmanned aerial vehicle (UAV), munitions, and the required human resource and infrastructure for the development of these systems.

With these lofty goals in mind there is a pressing need for the development of specialist human resource and infrastructure in key areas, which is something that PAC is acutely aware of.

PAC’s website lists the following institutes that can be assumed to reflect the key areas for human resource and infrastructure development for Project Azm:

  • Aviation Design Institute (AvDI),
  • Mission Electronics Design Institute (MEDI),
  • Aero Structures Design Institute (ASDI),
  • Advanced Technologies Centre (ATC),
  • and Flight Test Centre (FTC).

An institute dedicated to aircraft structures is present, but an institute called the Flight Dynamics and Control Institute (FDCI) is absent.

Reading through the details of each of the institutes gives the impression that little or no emphasis has been put on the crucial technology of flight dynamics and control systems design.

Major fighter-jet producers such as Boeing and Lockheed Martin have extensive flight dynamics and control groups and invest heavily in flight dynamics and control technologies and human resource. The lack of emphasis on this key technology in the institutional breakup for Project Azm, is thus, concerning.

This article details why flight dynamics and control systems are crucial technologies for any program that hopes to develop a fifth-generation fighter aircraft (FGFA), such as Project Azm.

It is important to contextualize the discussion and begin by discussing the current environment and state-of-the-art of flight dynamics and control systems in Pakistan. Examining the development of various existing defense products and the general focus of academic research can lead to some insights.

Even though there are key ways in which flight-control systems of UAVs and cruise missiles differ from those for fighter jets, Pakistan has a very successful cruise-missile program in the shape of Babur, Ra’ad, and Harbah, and a UAV program in the shape of Shahpar and Burraq.

Unfortunately, given the secretive and compartmentalized nature of strategic organizations, there is little or no horizontal sharing of this expertise across organizations.

Consequently, successes in one project cannot be automatically converted to success in another, and small groups of experts can easily be disrupted with retirements, transfers, and resignations. This is on top of the fact that fighter-aircraft flight-control systems are many folds more complicated than those needed for cruise missiles and contemporary UAVs that fly predetermined flight-paths and missions.

Another indicator of the importance given to flight dynamics and control systems in the engineering ecosystem of a country is the realm of academic research.

Aerospace and its allied programs (mechanical, avionics, electrical, materials) are taught by faculties that seem to be heavily underrepresented in the field of control systems.

A look at the websites of NUST, IST, GIKI, Air University, and PIEAS shows that there are few or no faculty members with expertise in control systems. There are numerous experts in structures, propulsion, aerodynamics, radars, electronics, materials, and imaging but very few that specialize in control systems technology. This reflects a lack of focus on teaching control systems and a dearth of experts in the field.

This has a long-term effect on the kind of human resource available to PAC, which will invariably limit PAC’s ability to run a successful FGFA program. It is this same lack of focus on control systems that is evident in the key areas listed on PAC’s website.

All this points towards a technological blind spot that exists on all levels in Pakistan: high-level decision makers don’t see control systems as a vital technology and there is a very small number of people trained for it.

Flight-control system development is a lynch-pin technology for a fighter-jet, without which developmental freedom, as envisioned for Project Azm, is impossible. That is, designing, upgrading, and operating the future FGFA will not be possible without considerable command over flight dynamics and control systems.

The rest of this article will explore the importance of control systems technology for Project Azm.

What is ‘Flight Dynamics?’

This is a field that combines dynamics and aerodynamics.

Dynamics studies how forces affect an object’s motion and aerodynamics and how fluid flows affect forces. Thus, flight dynamics is a study of how fluids affect forces, and how those forces affect the motion of aircraft.

Experts in this field can derive sufficiently accurate computer models of the aircraft and analyze its flight characteristics before it is even built. These models are a vital part of a life cycle of an aircraft as they are needed for flight-control system design, aircraft modification and certification, among other reasons.

What is ‘Control Systems?’

This is a field that studies how best to control and regulate the performance of any system.

If an aircraft does not behave in a way liked by its pilots, it is the job of the control systems engineer to design an augmentation system that takes the pilot’s input, combines it with measurements from sensors, and converts them to commands to the control surfaces of the aircraft to achieve the pilot’s goals.

A control systems engineer will design the feedback law that stabilizes the imaging sensor of an electro-optical sensor of a pod or missile. They will design the system that will always control the powerplant of the aircraft  to achieve the desired thrust.

They will also design the flight control systems of any new weapons to be developed.

Most importantly, they will design the flight control system for a new aircraft; a system that will quite literally fly the aircraft. This is all to say that control systems are an ubiquitous technology that finds application in almost all parts of an aircraft.

What is a Flight Control System?

At the most basic level a flight control system (FCS) is a computer (usually digital) that takes in commands from the pilot, measurements from on-board sensors, and moves the aircraft control surfaces and manipulates the thrust from the aircraft’s powerplant, with the goal of achieving the pilot’s commands.


Source: Wikipedia Commons

An FCS also artificially stabilizes an unstable aircraft (for better maneuverability). It also prevents the pilot from flying the aircraft outside a safe envelope.

For example, an FCS will actively limit the angle-of-attack to prevent stall, limit maneuvers so that compressor stall of the jet engine is less likely and to prevent structural damage to the aircraft due to g-loads.

An FCS constantly communicates with the stores management system to ensure that it can account for various weapons that are carried and deployed from the aircraft.

All stores on an aircraft effect its flight characteristics and it is the FCS’s job to keep the aircraft flying as steadily as possible. For example, an FCS deflects control surfaces to account for the launch of a large payload from one of the aircraft’s wings so that the aircraft maintains level wings.

An FCS attempts to maintain controlled flight in emergency conditions such as engine or control surface failure. As the FCS is a critical system, it is often designed with quadruple redundancy. This means that four identical flight control computers run on the aircraft that constantly check each other’s computation and provide redundancy in case of failure of one or more of them.

Overall, it will not be an exaggeration to say that the flight-control system is the brain of the aircraft.

The Role of Flight-Control Systems in Aircraft Design

It may be enticing to think that PAC can design an aircraft and request an external partner like Chengdu Aerospace Corporation (CAC) or Turkish Aerospace Industries (TAI) to develop the flight-control system after the design is completed.

Unfortunately, aircraft design and development are an extremely iterative process, where for each design iteration some rudimentary flight-control system must be designed and simulated. Control surfaces may need to be modified due to control difficulties, or perhaps a dangerous instability may be discovered that needs rectification through aerodynamic devices and/or control systems.

Designing an aircraft with poor understanding of control systems can lead to designs that are inefficient, or in the worst case, incapable of flight.

Furthermore, modern aircraft are designed with relaxed-stability. That is, the aircraft is designed with  “just the right amount of” instability and is artificially stabilized using the flight-control system. This makes the aircraft more maneuverable than if it was designed to be stable. An early example of such a design philosophy is the venerable F-16. This design philosophy closely intertwines the development of the aircraft’s physical design and the design of its flight-control system.

Additionally, it can be expected that FGFA will see significant use of composite materials. This will require that the flight-control system monitor sensors embedded in composite structural members and in some cases limit maneuvers to prevent damage to the structure. Thus, the use of composite materials will further entangle the flight-control system with the design of the aircraft in a way not seen with most fourth-generation fighter aircraft.

The Role of Flight-Control Systems in Aircraft Development

Aircraft go through constant development through their life cycles and the FGFA will be no exception. Any physical modification to the aircraft needs to be certified through extensive wind-tunnel and simulation-based testing before the modifications can be flown on the physical aircraft.

All this presumes the availability of the manpower and infrastructure to modify and maintain complex flight-dynamics simulations and flight-control software. It is important to note that any simulation of the aircraft must include a simulation of the flight-control system as well.

Additionally, it is likely that the flight-control system will need to be tweaked to account for the new change being certified. This modification will only be possible if there is a trained workforce that has developed and maintained the models and the flight-control systems in-house.

Even small modifications to the aircraft need to be certified before flight tests and if PAC lacks this in-house capability, then this process is slowed down dramatically as external partners need to be approached.

The Role of Flight-Control Systems Munitions Integration

Keen followers of the JF-17 program will note that PAC and Air Weapons Complex (AWC) have integrated only a handful of truly local munitions on the JF-17. Namely, the IREK and an undisclosed “stand-off weapon.”

The IREK is possibly an indigenous version of the CAC FT-6 that CAC already integrated with the JF-17, and thus it can be inferred that the integration of IREK did not involve modifications of the flight-control system.

The integration of munitions such as SD-10A, PL-5E, FT-6, C-802A, CM-400AKG was carried out at CAC facilities as well. This can be attributed to a lack of in-house ability to accurately model the flight-dynamics, and more importantly, modify the flight-control system of the JF-17.

It is only recently that a JF-17 Dual Seat Dynamics Simulation and Integration Facility was inaugurated at PAC.

This hints at the fact that such a facility was not needed nor present at PAC before late 2019, and that simulation software, high-fidelity models, and flight-control system details had to be transferred from CAC to PAC.

Thus, from now on we can expect a rapid increase in the number of munitions that are integrated onto the JF-17. This displays a key bottleneck in munitions integration, which PAC may be resolving now.

The stores-management system of the FGFA will need to constantly communicate with its flight-control system. Moreover, the FGFA’s flight-control system will need to be modified for each new munition or pod that is integrated onto the aircraft so that the flight-control system knows how to accommodate for the carriage and deployment of the munition.

For the JF-17 it made sense that CAC develop the flight dynamics simulations and flight control software, but under the stated goals of Project Azm, it is vital that PAC develops the expertise needed to develop, maintain, and modify flight dynamics simulations and flight control software.

This will give PAC the capability to integrate the munitions that are to be developed under Project Azm.

The Role of Flight-Control Systems in Net-Centric Warfare

The events of 27th February 2019 have made the importance of net-centric warfare abundantly clear, and Project Azm will not be blind to the importance of increased networking amongst air platforms.

Consequently, it is expected that future UAVs will take up more and more advanced roles such as early-warning, air-to-air refueling, and even air-to-air combat. Such advances are only possible for Project Azm if PAC can develop the flight control systems of both its FGFA and UAVs.

For example, if the FGFA is expected to be refueled by a UAV, the flight-control systems of both the FGFA and the tanker UAV will need to coordinate to fly the aircraft in close formation. This system could even make its way on to manned aerial refueling tankers to ease pilot workload.

Furthermore, a new idea that is possibly a game-changer is that of a loyal-wingman UCAV. To embark on such an endeavor PAC would need the know-how to develop the flight-control system for a loyal wingman UCAV.

This will most definitely be more challenging than developing a flight-control system for the FGFA, and thus, development of a flight-control system for the FGFA is a prerequisite. Additionally, close integration of the FGFA with a loyal wingman will require that their respective flight-control systems “talk” to each other and work in unison. These tasks will be extremely difficult (read impossible) if there is no in-house capability to develop and modify flight-control systems.


The JF-17 program has been very successful for Pakistan with respect to its goals and efficiency. PAC only bit off what it could chew: modest advances were made and only capabilities that could be absorbed with low costs were indigenized. The end-goal was the production of the modern backbone of the PAF in the shortest amount of time possible, at which PAC succeeded.

However, Project Azm has very different stated goals. It hopes to develop the indigenous capability to design and develop a fifth-generation fighter aircraft and its associated ecosystem. It hopes to create new capabilities where none existed before, as opposed to importing and absorbing modest advances.

Even if it is decided that PAC does not have the expertise to take on the challenge of developing FGFA’s flight-control system on its own and an external partner is to do it, investment into flight dynamics and control systems needs to be made. This is the only way to ensure that PAC can quickly absorb an externally developed flight-control system by having the needed expertise and infrastructure.

Significant resources need to be channeled into the iterative design of the aircraft and its flight-control system and special emphasis needs to be put on the development of in-house expertise in flight dynamics, control systems, and flight-control systems.

A Flight Dynamics and Control Institute is the need of the hour. A future article discusses the technical aspects of developing a Flight Dynamics and Control Institute.

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