Modern-day fighter jets have entered their fifth generation and are associated with advanced weaponry including Beyond Visual Range (BVR) missiles, Electronic Countermeasures, super-sonic speed, and other advanced traits. Rightly so, a fighter jet of this era is one of the most lethal combat machines available to militaries, with the ability to strike with the precision of a few meters from the sky, hundreds of nautical miles away.
However, when we talk about fighter jets or any aircraft for that matter, a few basic design parameters hold significance and one of these parameters is how slow the aircraft can fly while still being able to maintain level flight.
Although fighter jets are designed to be agile, stealthy, and fast, the stalling characteristics play a vital role in its effectiveness. If a fighter jet stalls frequently, the job of a pilot becomes quite difficult as he/she must focus on keeping the aircraft in the air rather than the mission at hand. So, when discussing fighter jets, one may ponder how slow can a fighter jet fly?
The lowest speed a fighter jet can attain during controlled flight, typically ranges from 100knots to 200knots depending upon the design and other flight. Some of these design elements include parameters such as the angle of attack, the load factor, and the altitude.
It is important to note that the stall speed of a fighter jet is not a fixed value, it continuously varies during a flight depending on the flight parameters, primarily, the angle of attack.
To understand how slow an aircraft can fly, we must look at what keeps an aircraft airborne in the first place, the wings, that generate lift. If at any point during a flight, the wings stop generating adequate lift, the aircraft may go into a freefall. Let us see what determines the minimum possible speed of an aircraft!
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What is the stall speed of a fighter jet?
Wings of an aircraft enable it to generate lift so that it can continue level flight. A stall condition is when the airflow around the aerofoil of a wing becomes insufficient due to reasons such as slow speed, or a very high angle of attack.
Therefore, the computers of a modern fighter jet keep calculating the “Stall Speed” continuously during the flight. This is done by monitoring the angle of attack, the altitude, the attitude, the load coefficient, and several other parameters. This speed is commonly displayed to the pilot as Vmin indication on the speed scale.
Although a fighter pilot is constantly aware of the minimum speed limit, there are times when a fighter jet may go below the minimum speed or the angle of attack (AOA) becomes too high. So, what happens when a fighter jet stalls?
What happens when a fighter jet stalls?
Modern combat aircraft have complicated avionics systems that are aware of all flight parameters and therefore, can predict if the aircraft is going into a stall.
The onboard systems warn a pilot through audio chimes and warning as well as visual cautions when they sense that aircraft may enter a stall. The pilot then makes immediate corrections like increasing the thrust or pitching the nose down to avoid a stall and to regain control of the aircraft.
Sometimes though, pilots may not be successful in recovering and the aircraft goes into an uncontrolled freefall…
How does a fighter jet go into an uncontrolled freefall?
When an aircraft stalls, it behaves like any other freely falling object under the gravitational force. A fighter jet can sometimes go into a spin while falling towards the ground with an acceleration of ‘g’ which is 9.8ms2.
The good news, however, is that unlike commercial airplanes, fighter jets are highly maneuverable. Hence, despite entering a stall condition a fighter pilot has several options to recover the aircraft.
In case the aircraft has done into a spin, the first thing a pilot does, is to counter that spin using ailerons, elevators, and rudder as well a thrust vectoring (if available).
Once the aircraft stops spinning, the fighter pilot can put the nose of the aircraft down and increase thrust to gain airflow over the wings and start generating some lift to recover through this potentially fatal flight condition.
We know that a fighter jet entering a stall is inherently risky but there are times when fighter jets are intentionally stalled!
What is a controlled aircraft stall and what are the risks?
Well, there are several reasons for the controlled and intentional stall of a fighter jet such as testing the aircraft and training pilots to recover from stalls.
During the design and testing phase of a fighter jet, the test pilots must ascertain the stall limits. Therefore, during several flight tests, a fighter jet is intentionally stalled to check its minimum speed requirements for level flight as well as stall recovery techniques.
Also, during the training of fighter pilots, it is common that the instructor intentionally puts the plane into a stall so that the trainee can learn recovery techniques that provide much-needed confidence for when is he is faced with these conditions during combat.
Putting an aircraft into a stall is not risk-free and requires an elevated level of concentration to regain control over the aircraft. As the stall limits of aircraft for a steady flight are calculated during its design, you might wonder what the typical stall speed is!
What are the typical stall speeds of modern fighter jets?
An aircraft is designed keeping in view its intended combat role(s). For example, the combat roles of an F-22 ‘Raptor’ and an A-10’Warthog’ are different.
It can be assumed that a Close Air Support aircraft like that A-10 ‘Warthog’ requires a lower stall speed for its missions.
The stall speeds of modern fighter jets vary greatly depending upon several factors such as the weight of payload and temperature. However, in optimum conditions and level flight, we can find that an A-10 ‘Warthog’ stalls around 110-140 knots whereas that of an F-22 ‘Raptor’ is around 160-180 knots.
Similarly, an F-16 ‘Falcon’ has stall figures within the same range of 160-180 knots whereas an F-14B ‘Tomcat’ could fly considerably slower due to its sweeping wing design. For slower speed, the F-14B wing could be swept forward to increase lift.
When we compare the stall speeds of military planes with general aviation or commercial planes, we can clearly identify that military planes cannot fly as slow as general aviation planes. Let us see why!
Why cannot military airplanes fly as slow as general aviation aircraft?
Military fighter jets are designed to be super-sonic, agile, and maneuverable, which is evident from their thin swept-back wings and aggressive design.
On the other hand, general aviation aircraft such as Cessna 152 and 172 are designed to be stable and economical, which allows them to continue a level flight at lesser airspeeds than a fighter jet.
This trade-off happens primarily in the wing design of an aircraft. A military aircraft wing is designed to continue generating lift at supersonic speeds which in turn reduces its ability to generate lift at slower airspeeds. Of course, this has to do with the small size of the wing relative to the airplane’s weight. In other words, a fighter jet has a high wing loading.
For a general aviation plane, the wings are larger relative to the weight of the airplane, and designed to operate within subsonic ranges. Therefore, planes such as Cessna 152 can fly as slow as 48 knots.
As a fighter jet cannot slow down considerably during flight, one may think how can it land on relatively shorter runways such as those on an aircraft carrier?
How do military planes land on carriers despite being unable to fly slow?
Runways on an aircraft carrier are short, narrow, and mobile, making the approach for landing a tough enough job for a navy pilot. The approach for carrier landings must be near perfect and according to the textbook.
Although the speed of the aircraft cannot be reduced drastically in the air, it happens once the tail-hook installed on these aircraft catches on to the arrestor cables installed on the runway of aircraft carriers.
These arrestor cables provide the braking necessary to stop the fighter jet without overrunning the carrier runway and falling into the ocean.
Summary and Conclusion
The minimum speed or the stall speed of a fighter jet is continuously varying according to different flight parameters. This speed limit is being instantaneously calculated by the aircraft Avionics Systems to be displayed to the pilot or to warn him/her if a stall condition is imminent.
Although the stall speed is constantly varying, we can make comparisons, as we did in this article, by assuming level flight with normal flying conditions to see which aircraft is more stable at lower speeds.
Although the minimum speed limit is an important characteristic for all aircraft, one thing is certain here, fighter jets are designed to be lightning-fast and agile machines and that is what they do best.
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