There are three basic principles of fighter aircraft cost reduction:
- keep it small
- keep it simple
- keep it single
However, they are not the only relevant issues; others will be adressed here as well.
Keep it small
Empty weight is a major factor in aircraft’s cost, since higher empty weight (larger aircraft) means more materials used as well as more man hours of work to build it. Thus smaller aircraft are also cheaper, assuming identical technology level. Further, smaller aircraft use less fuel and have lower operating costs.
Keeping aircraft smaller will also improve its air combat ability, as it will improve ability to achieve surprise as well as transient performance, which is crucial for outmaneuvering the opponent.
Keep it simple
This should be true for both development and the final product. Design group should have one person overseeing the process, and one engineer for every area (reliability engineer instead of group dedicated to reliability, for example). It should be small enough so that all people in the group can effectively work together at a single place. Management should be hands-off, so that once design goals have been provided in broad outlines, neither the military or upper levels of the company interfere with the design process. Military in particular should only define what weapon should do in broad outlines, and leave it to company to decide on how weapon will achieve these goals.
Formalization during process should be minimized – military should get the same data, and in the same format, as the design group, and it shouldn’t go through approval cycles.
Keep it single
This is a key factor in keeping the aircraft simple while achieving adequate effectiveness. Fighter aircraft should be single-role, single-engined and single-seat (except for training variants). It should also be designed for a single service, and then adapted for other service(s) if at all possible.
Typically, multirole aircraft cost as much as all the types they are replacing placed together (unless there is an overlap in capabilities between said types). This is because multirole aircraft have to carry far more extensive sensor and avionics suite and have to fit more requirements than single-role ones. An air superiority fighter is ideally small, single-engined, with either no or a small radar, as well as good cockpit visibility and passive sensors suite. Ground attack aircraft can vary in size from small to extremely large, depending on role and requirements. They tend to have two engines, large total fuel capacity, a ground-following radar, and limited cockpit visibility. As a result of combining the requirements for two, a multirole aircraft tends to be of either medium or large sized, twin engined, with extensive sensors suite including radar and good cockpit visibility. Only exceptions from this rule aire aircraft that were designed for air superiority and then adapted for ground attack (F-16) or were primarily air superiority aircraft used by countries where range was not as much of an issue (Gripen). In both cases however there are still clear sacrificies made for the ground attack performance (increased weight and cost in the F-16s case, sacrificed rearward visibility in Gripen’s case).
Single engine helps reduce cost in several ways. Single-engined fighters are more amiable to area ruling, which means that they tend to have less drag and thus lower fuel consumption. This can also lead to reduced size, weight and thus procurement cost as well. Further, a single engine tends to have greater thrust-to-drag ratio than two engines producing equal amount of thrust, which leads to further improvement in fuel efficiency. Maintenance downtime required is also lower. All of this leads to single-engined fighters having significantly lower direct operating cost than twin-engined fighters (7.000 USD for F-16C vs 16.500 USD for Rafale C. Note that Rafale C has 11% greater empty weight, 28% more dry thrust, yet costs 2,36 times as much to operate as the F-16C. F-15C costs 30.000 USD to operate (or 4,3 times as much), yet has 48% greater empty weight and 52% more dry thrust compared to the F-16C).
When designing an aircraft meant for multiple services, best way is for it to make sure that it fits naval requirements. All successful multi-service aircraft – F-4, F-18, Rafale – were designed as naval aircraft and then adopted into air forces (YF-17 was designed for USAF, but the F-18 was designed for naval use from the beginning). Reason for this is that carrier aircraft have to fit far more strigent criteria in terms of size, airframe strength, corrosion resistance, landing gear design and cockpit visibility.
In terms of airframe strength, naval aircraft use safety factor of 1,85 compared to 1,5 for ground-based aircraft, meaning that they need stronger airframe for same operational g limits. For example, F-18 has an ultimate load limit of 13,6 g. USN F-18s are limited to 7,33 g compared to 9 g for Finnish F-18s. Rafale has an ultimate load limit of 16,65 g. While both AdlA and Aeronavale Rafales are limited to 9 g during normal operations, only AdlA Rafales have an override function that allows them to pull up to 11,1 g in flight (and this is regularly done without shortening airframe life).
Corrosion resistance is an issue for naval aircraft because they spend entire service life in very humid conditions. While some land-based aircraft may also face rather humid conditions in tropical countries, naval aircraft also have to withstand salt.
Landing gear is also more problematic issue for naval aircraft. It has to be strong enough to withstand stresses of rough carrier landings. This also means that it should be located in the body to relieve wings from stress. However, distance between main wheels should be large enough to provide a safe overturn angle (25* or more). Placement also has to allow for sufficient tail clearance during landing in spite of typically higher landing AoA than is the case with land-based aircraft, as well as room to install a sufficiently strong tail hook.
Out-of-cockpit visibility must also be good. In addition to standard requirement for providing 360* horizontal visibility, naval fighter also has to have excellent over-the-nose and over-the-side visibility to facilitate a safe approach and landing.
All of this will lead to higher production cost for an air force variant than would otherwise be the case, but will also mean significantly lower R&D costs. Production cost increase may also be compensated by having a significantly greater production run.
Start from the weapon
This is one of reasons for why aircraft should be single-role. When designing an aircraft, one should always consider what weapons will it use and how will it use them. This means that designs for air superiority aircraft – using gun and air-to-air missiles – will be very different from those for ground attack aircraft, which typically carry bombs and missiles far fatter and less aerodynamic than air-to-air missiles are. If done properly, however, it will reduce cost of both design, weapons integration and testing, and will lead to improved performance in aircraft’s role.
Use off the shelf components
Using off the shelf components where acceptable would reduce development time and costs, since not only some systems will not have to be developed, but some factors influencing the end design may also be known. For example, using an existing engine – even if planning for a future uprated variant of the same, or a completely new design of similar dimensions – will automatically point to some design and performance parameters. Using an existing gun means that some issues – concerning size and weight of a weapon as well as possible vibration issues – can be known before the design process even starts.
Optimize the production
Optimization of the production line also plays part in the cost of a fighter aircraft. Typically, cost falls the longer the aircraft is in production. This decrease is comparably small for modern fighters but in large numbers can lead to significant total savings. Entire aircraft should be produced in one place, so that any errors in production can be fixed as soon as possible.