Fighter jets tend to capture the imagination of people around the world. These futuristic combat machines are designed with advanced cutting-edge technologies that are kept top-secret for years after their retirement. The modern fighter jet has come a long way since the World War II era with the advent of supersonic jet engines, stealth and beyond visual range weapon systems. However, it is their aggressive visual design which makes them, without a doubt, the hyper-cars of the sky.
At one point or another, most of us have dreamt of donning a G-suit and roaring through the skies in a fighter jet. These aircraft are designed to attack with at supersonic speeds, perform gravity-defying maneuvers, strike with precision. Considering all this, you might have wondered if fighter jets pressurized?
Most modern-day fighter jets are pressurized. Although these combat aircraft are designed for their specified combat roles, such as close air support, bomb deployment, and air-to-air combat, nearly all of them have pressurized cockpits as a standard feature. Though the design philosophies of fighter jets vary based on their manufacturers and respective countries of origin, the underlying principles and the necessity of cockpit pressurization remain the same.
In this article, we are going to look closer at the reasons why fighter jets are pressurized, as well as how they are pressurized. You’ll also learn the differences between how commercial airplanes and fighter jets go about pressurizing the cabin, and why pilots wear pressurized suits, often called “g-suits”.
Let’s start!
Table of Contents
Why are fighter jets pressurized?
Routine combat missions of an average multi-role fighter jet include steep climb and rapid descent resulting in an exceptional rate of altitude change. This makes cockpit pressurization essential for a pilot to complete his combat mission with minimum fatigue and less to no chances of any physiological issues.
Let’s look at the different reasons why fighter jets are pressurized!
Pilot safety during steep climb and rapid descent
Safety of combat pilots from dangers such as hypoxia(oxygen deprivation) and hyperventilation, is not only an embedded feature of aircraft design. Cockpit pressurization mitigates the effects of rapid changes in altitude, minimizing their impact on cabin altitude (air pressure inside the cockpit) to safeguard a pilot from the physical stresses.
Most of us have experienced some level of discomfort in our ears while flying in a commercial airliner that has a 30ft to 50ft per second descent rate, during the landing phase. Therefore, we can imagine the discomfort and possibly physical damage that can be incurred due to rapid change in air pressure resulting from the 600ft-1000ft per second descent of a fighter jet.
Comfort and reduction of fatigue
Additionally, the pressurization system is closely linked to the cockpit air-conditioning system, technically known as Environmental Control System (ECS) (in American and European fighter jets). This system acts to keeps the cockpit comfortable for a fighter pilot despite the varying atmospheric temperature outside and glaring heat coming from the Sun.
Anti-G Suit inflation during high-G maneuvers
The anti-G-suits in some fighter jets are linked with the pressurization system of the fighter jet, which during high-G maneuvers, inflates the G-suit around legs and abdomen of a pilot. In addition to reducing the blood rush to the lower segment of a pilot’s body, it serves to develop muscle memory enabling the pilot to stay conscious by employing special breathing techniques.
Avionics equipment cooling
Just a few decades ago, fighter jets had hydro-mechanical control systems and large analog instrument clusters, but the modern-day fighter jets have come a long way. Their complicated and essential fly-by-wire control systems, Heads-Up-Displays HUD, flight displays, weapon and radar systems, and Communication Systems generate a lot of heat which is dissipated using the air-conditioning and pressurization systems.
How is a fighter jet pressurized?
The underlying principle for pressurization of a fighter jet is quite simple and it involves pushing pressurized air from the engine, into the cockpit, and controlling the discharge of this air through an outflow valve.
However, since the air that is taken from the engine(engine bleed) is too hot to be discharged in the cabin right away, it will first be fed into the heat exchangers which control the temperature of the air as desired by the pilot. This pressurized and conditioned air is distributed in the cockpit through air vents.
The air pressure inside the cockpit of a fighter jet is displayed to the pilot as cabin altitude. In most fighter jets, cabin altitude is controlled automatically and does not require pilot intervention except in emergencies.
How is Cabin Altitude regulated in fighter jets?
The outflow of pressurized air in the cockpit is regulated through computer-controlled valves, which determine how much air is released overboard, thus directly increasing or decreasing the air pressure inside the cabin.
Loss of air pressure in the cabin is displayed to the pilot as gain in cabin altitude and vice versa. Although the cabin altitude is being controlled automatically, the warning systems of a fighter jet notify the pilot if any malfunction or uncontrollable condition is detected.
Can a jet fighter become overpressurized?
You may be wondering, what would happen if the overflow valve gets stuck in a closed position and the air pressure inside the cockpit gets becomes too high?
Well, not to worry, pressurization systems of aircraft also employ safety valves as the last wall of defense. These valves open if the pressure differential inside and outside the aircraft exceeds its designed limits to ensure that structure of the aircraft is not ruptured or damaged in some way.
What are the differences in pressurization in Commercial Aircraft and Fighter Jets?
Commercial airliners are designed keeping in view the comfort of passengers. As a result, the pressurization systems in these aircraft generally consist of larger and multiple heat exchangers that provide air-conditioning and pressurization by dividing the complete aircraft into multiple zones.
On the contrary, fighter jets are flown by one or two pilots and do not require large heat exchangers. Instead, the combat roles of these aircraft require quick and effective regulation of air pressure inside the cockpit to adjust with the greatly varying atmospheric pressure outside the aircraft during their maneuvers.
Another significant difference can be found in the pressurization schedules of both airplane types.
The difference in pressurization schedules of commercial airliners and fighter jets
To ensure maximum passenger comfort, the cabin altitude of commercial airliners rises from 0ft till 8000-9000ft in a nearly linear fashion as the airliner ascends to its cruising altitude. It then stays there during the whole flight, until the airplane descends below 8000-9000 feet.
Fighter jets work a little differently.
Most fighter jets stay unpressurized till 8000ft, and then above 8000ft till 23000ft, the cabin altitude stays at a constant level of 8000ft. However, as it climbs above 23000ft, a delta-pressure of 5PSI (a cabin altitude of roughly 20,000 ft) is maintained as a safety measure. This has to do with the pressure differences between the cockpit and the outside air, which otherwise could induce serious damage to the fuselage in the thin air.
Why do pilots need Pressurized G-Suits in some military jets?
The service ceiling of common multi-role combat aircraft such as the Lockheed Martin F16 or the F35 Lightening-II is around 50,000ft. But have you ever imagined the challenges of pressurization in reconnaissance military jets such the U2 Dragon Lady and SR-71 Blackbird which fly at altitudes of 70,000ft to 80,000ft with little to no air outside?
In these aircraft, the cabin cannot be pressurized due to extreme and unmanageable structural stresses caused by atmospheric pressure. The pilots, therefore, need pressurized G-suits, much like astronauts, to ensure that blood keeps flowing through instead of boiling over through ebullism.
Although a pressurized G-suit is connected to the aircraft, there still is a possibility of ejection for these pilots flying above 70000ft. As soon as the ejection sequence is activated and the pilot is rocketed away from the cockpit, a small emergency cylinder of compressed air inside the G-suit provides pressurization and oxygen for survival.
Can the flight be continued in case of pressurization failure?
A mission can be continued in case of pressurization failure only in certain conditions below a safe altitude and with performance limitations. However, some fighter jets based on their design limitations may require a mission abort if the pressurization failure has the potential to cause critical aircraft systems or weapon systems to fail.
Fighter pilots can face serious physical discomfort in an uncontrolled pressurization loss but due to the high agility of these aircraft, they can descend below the 10000ft level within seconds and avoid any serious physical damage. In case of a slow continuous pressurization loss which goes unnoticed by the pilot, he may experience hyperoxia or similar conditions.
Conclusion and Summary
The modern multi-role combat aircraft are pressurized to ensure that a pilot can accomplish his mission comfortably while enduring minimal physical stresses and fatigue. The pressurization and air-conditioning systems, in addition to the pilot, keep the critical avionics and weapon control systems cooled down.
The next time, you look up towards to the sky for a glimpse of a fighter jet possibly flying faster than the speed of sound, you will certainly have the answer to the question, is this fighter jet pressurized?
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