Beyond Range and Payload: The Importance of Aircraft Endurance

It is usually observed that the comparison of the aircraft is made upon their technical specifications or their weapon package, but there’s another factor as critical as any other, the endurance of an aircraft. The ability of an aircraft to be successful in combat depends upon endurance to some extent it depends on other factors like its technological superiority or the skills of the pilot. Modern combat demands aircraft with the ability to fly for longer duration to perform several types of missions and to sustain in beyond visual range type of combat. The importance of endurance of aircraft can also be understood by the fact that even though the majority of aircraft have the ability of midair refueling, it isn’t possible in the majority of high-intensity conflict zones for an aircraft as big as a tanker aircraft to refuel the aircraft mid-air.

Difference between range and endurance of aircraft

It is very important to understand that the range of an aircraft is not similar to its endurance, though both concepts are quite related they are not the same. The range of an aircraft means the distance it can travel on a single fuel load while the endurance of an aircraft refers to the time an aircraft can remain airborne on a single fuel load. The endurance of an aircraft is affected by several factors such as engine efficiency, fuel capacity, weight, and speed of an aircraft. It is possible for a bigger aircraft to carry more internal fuel but still have lesser endurance than a smaller aircraft.

Importance of aircraft’s endurance

Modern-day combat involves more beyond-visual-range combat than within-visual-range dogfights, therefore it requires an aircraft to be airborne for longer durations to evade the enemy’s BVR missile and to react in the appropriate time. The prime example of the utility of such endurance can be understood by the aerial conflict after the Balakot strike, where Su-30 MKIs on the Indian side having the ability to stay airborne for hours prevented enemy aircraft to intrude deep into national skies by not retreating even when F-16s rained down BVR missiles, whereas if India lacked such aircraft, it would require aircraft to return back to airbase frequently which could have provided enemy’s aircraft an opportunity in that turnaround time.

The endurance of an aircraft has several other benefits, It can increase the payload capacity of an aircraft by several folds since an aircraft with lesser endurance or range would generally require drop tanks that hinder the aircraft’s payload capacity. The aircraft with better endurance or range generally also tend to have better maneuverability since such aircraft usually maintain huge internal fuel reserves that again eliminate the need of using drop tanks which apart from hindering the aircraft’s payload capacity also restricts its maneuverability by affecting the aerodynamics of the aircraft and bringing down its thrust to weight ratio.

Image (Dassault Aviation/A Boissaye)

The aircraft with longer flight time is also better for naval operations since naval operations usually require intelligence gathering, anti-submarine warfare, and search and rescue missions which require an aircraft to fly over remote areas, therefore a naval aircraft must have the capability to stay airborne for a sustainable period of time.

An aircraft can furthermore be a true aerial superiority aircraft only if it has the capability to stay airborne for a sustainable period of time to provide impregnable cover to other aircraft, otherwise, no matter how good an aircraft is, it would somewhere hinder the effectiveness of the entire mission. It is said that during the Balakot air raids of 2019, while the main pack of Mirage-2000s was conducting strikes in Pakistan, the Su-30 due to their ability to fly continuously was deceiving enemy aircraft so that a successful strike can be conducted.

The aircraft with the ability to fly for a longer duration of time also have the ability to perform diversified operations for example if a combat aircraft with the ability to fly for a longer duration is suddenly called for intercepting enemy aircraft just after performing hours long surveillance mission, it will be able to perform such mission while on the other hand aircraft with less endurance would require mid-air refueling or to return back to base to accomplish such task.

Factors influencing the endurance of an aircraft-

There are several factors affecting the endurance of aircraft, the most important being the fuel efficiency of an aircraft. The fuel efficiency of aircraft refers to the fuel required by the aircraft to stay airborne for a particular period of time, it primarily depends on the aircraft’s design and its engine technology. The reason why a bigger aircraft need not necessarily have better endurance can be understood by a comparison of Pakistani JF-17 Thunder and Indian LCA Tejas.

Teja’s tailless delta design . Image MoD PRO     

The size of Pakistani JF-17 is bigger in dimensions than that of Tejas but still, the internal fuel carrying capacity of LCA is more than that of JF-17, it is due to the fact that JF-17 has a cropped delta design that allows lesser fuel to be stored in wings of an aircraft, also the JF-17s design offer it less drag which slightly reduces fuel consumption. The design of both aircraft gives them superiority in fuel management, however, the most important factor that affects the endurance of the aircraft is its engine.

The RD-93 used in JF-17 thunder is an improved variant of RD-33 used in Mig-29s, the RD-93 specific consumption is said to be around 77kg/kN H while that of GE-F404 in LCA’s is said to be around 81 kg/kNH, while specific fuel consumption of LCA in dry state is slightly higher we should consider the fact that the GE-F404 comes with a FADEC control system which enables the aircraft to operate at optimal efficiency by adjusting the engine’s performance based on flight conditions which automatically reduces fuel consumptions and emissions while data based on JF-17’s RD-93 fuel consumption comes from Russian claims which have proved to give a lesser performance in several cases.

Notice the smoke coming off the RD-93 engine in JF-17. Image: AB Sanderson

The specific fuel consumption of both aircraft in the afterburner stage has no comparison at all with LCA’s specific fuel consumption being 35kg/KNh lesser than that of JF-17, furthermore keeping aside the maintenance issues we have seen smoke emerging out of the JF-17s engine several time, which is a perfect display of incomplete fuel burning hence showcasing the inefficiency of RD series engines.

The endurance of aircraft also depends on its other capabilities like that of supercruise and using modular avionics in aircraft which makes it makes possible for smaller aircraft like Rafale to have more endurance than bigger F-15s under some conditions. It should also be considered that the fuel consumption of an aircraft not only affects its endurance but also can hinder the development of aircraft. The development of a twin-seat variant of the JF-17 almost took 10 years due to issues of fuel management that too after adding additional fuel in the vertical tail of the aircraft and compensating some electronics onboard, while the trainer variant of Tejas has been flying since 2009 and several different variants of Tejas are in prototype phase because of better management of fuel in aircraft body.

The advantage of the Indian Air Force

The force multipliers of the Indian Air Force. Image: IAF

The Indian air force was said to be a truly strategic force only after the introduction of Su-30 MKIs in its inventory in the late 1990s. Aircraft like Su-30 MKI are known for their endurance with their ability to carry around 10 tons of fuel, combined with this comes the modular capability of AL-31 FP engines with a digital electronic engine control system that further improves the flight time of aircraft. The Su-30MKIs are said to have the capability to fly continuously for 10 hours with refueling, this is the reason why apart from being a multirole aircraft in itself, the Su-30 MKI is used for combat air patrols and for maritime missions. The Dassault Rafale is another such aircraft in IAF’s inventory which has the capability like to super-cruise which improves the aircraft’s endurance by several folds, further as Rafale is a medium-weight aircraft made of modern composite materials, it consumes less fuel than heavier-weight aircraft to fly a particular distance and have an additional advantage in regions like Ladakh where heavier weight aircraft struggle.

About the Author: Pratisht Chaudhry is a Young aviation enthusiast and analyst. The views expressed are the author’s own.

Header Image Credit: Lee Adcock