The Insane Engineering of the F-35BJan 30, 2023
The F-35B is possibly the most advanced aircraft ever made. A jack of all trades. A stealth fighter aircraft that combines and improves the capabilities of the F-16, AV-8B Harrier and B-2. A highly maneuverable fighter aircraft capable of attacking both air and ground targets. A stealth fighter that takes lessons learned from Lockheed's previous forays into the stealth realm, with the F-22 Raptor and F-117 Nighthawk. An aircraft equipped with the most advanced sensors and computer systems. Sharing information almost instantly with allies, without compromising stealth, and presenting the information directly on a screen on the pilot's helmet visor.
Providing unparalleled situational awareness. Allowing a flight of F-35s to fight effectively as a hive mind. Perhaps most audacious of all, the F-35B is capable of transitioning from horizontal to vertical flight with the push of a button, using directional thrust and a massive vertical turbofan engine, hidden within the body of the aircraft. Allowing landing like a helicopter on the US Marines' relatively small amphibious assault ships. Integrating all of these capabilities into a single airframe is an extremely difficult task. Designing for stealth requires careful shaping of the aircraft's exterior, which dictates the design of crucial features.
Creating inevitable trade-offs. There are many misconceptions about stealth. The goal is not to make an aircraft invisible, but to make it detectable, the goal is to delay enemy detection for as long as possible. For bomber aircraft, it reduces the range of enemy radar stations, potentially opening gaps in radar defenses and allowing the aircraft to slip away undetected. For fighter jets, it provides a critical advantage: detect your enemy before he detects you. To gain these advantages, we must make it more difficult for the radar receiver to decipher whether the return signal is just background noise or an enemy aircraft.
To do that we need to minimize the strength of the return signal. There are several mechanisms for a radar wave to be reflected. The most significant and obvious way is through specular return, also known as regular reflection, like a mirror. Where the angle of reflection is equal to the angle of incidence. We want to avoid large flat surfaces that could be reflected directly into the radar receiver. Corner reflectors, in which two surfaces form a 90-degree angle to each other, should be avoided at all costs. The tailplanes, consisting of a vertical and horizontal stabilizer, are the perfect surfaces for creating a corner reflector.
Allow the radar to bounce off both surfaces and return in the direction it came. The best way to avoid this is to remove the tail completely, as on the B-2, but this greatly affects maneuverability. Instead, we can replace the horizontal and vertical stabilizer with a V-tail, as seen on the F-117 Nighthawk. The V-tail can act as both a rudder and an elevator, and we can see how by examining the resultant force generated when the control surfaces are actuated in different positions. We can actuate them in opposite directions to generate a horizontal resultant force, providing yaw control like a vertical rudder would.
Or we can deflect them in the same direction to provide pitch control, like a horizontal elevator would. This configuration is sometimes used for unique looking aircraft such as the Cirrus SF50, allowing you to mount a small jet engine on top of the fuselage with the exhaust routed directly through the V-tail. Such a small private jet and light that can deploy a parachute to rescue in case of emergency. Having the rudder and elevator controls merged into a single mechanism like this is not ideal. Fighter aircraft like the F-35 and F-22 need higher control authority, and that is a function of control surface area.
The larger the riser, the greater the pitch control. If a control surface serves dual duty, where rudder and elevator action are needed at the same time, control authority is reduced. Therefore, both planes also have large elevators, offset by a distance and at an angle to avoid reflections in the corners. We can see many more design trade-offs when comparing the F-117 and F-35 in seeking to meet both stealth and fighter requirements. Both the F-117 and B-2 have engine air inlets mounted on the upper surface of the aircraft, which prevents ground radar from bouncing into the inlet and back into the receiver, and helps reduce heat signatures. infrared.
However, for an aircraft that is expected to perform high-angle attack maneuvers in life-or-death situations, this is not a design you want to include. When performing a maneuver like this, the air inlet will receive air at a lower pressure, which will reduce performance. when performance is needed most. Air intakes located under the aircraft, like the F-16, will cause too much radar feedback, so twin intakes located on each side of the fuselage are chosen. The air intake also has some clever aerodynamic features. This seemingly innocuous lump plays an important role. This is aeronautical
engineeringin a nutshell: every seemingly insignificant design feature has a purpose.
Mounting engine intakes along the body of an aircraft involves some problems that pylon-mounted engines avoid. As air travels along the body, it begins to form a layer of slowly moving turbulent air called the boundary layer. If this air is allowed to enter the engine, it not only reduces performance, but can also damage the engine. As the turbine spins, it will pass through the boundary of slow air on one side and then through fast, free-flowing air on the other. This means that the force on the turbine blades changes with each rotation, causing cyclic bending. A recipe for failure due to fatigue.
Aircraft like the F-16 feature a boundary layer diverter that separates the inlet from the fuselage with a small gap, but this design increases the radar cross section and increases drag. Later variants of the F-16 tested the DSI, a diverterless supersonic entry. Essentially, a large bulge that creates a region of compression that moves the boundary layer away from the inlet, while scattering incoming radar and reducing drag. The test flight demonstrated that it could meet performance requirements, marking the beginning of its introduction on the F-35. The final product reduces weight by 30% and reduces production and maintenance costs. Moving down the plane we can see other hints of stealth design.
Long, sharp edges are enemies of stealth. Sharp edges cause radar waves to scatter in all directions; Radar can even travel along a surface in the form of a traveling wave and then disperse upon reaching the trailing edge. The intensity of that return signal can be reduced with some clever techniques. The signal intensity will depend on the edge length, so the first technique is to reduce the edge length with a serration. You can see this technique very clearly on the trailing edges of the B-2. It's less obvious where it's used for the F-35, however, until you start looking at all the access hatches hidden around the plane, each unavoidable gap on the plane's surface having a serrated edge.
This hatch opens to reveal a telescopic ladder that allows pilots to get on and off the plane. These open to reveal the landing gear. These are the internal weapons bays, essential for keeping radar-reflecting missiles hidden from view, and these smaller hatches are flare-dispensing doors. Flares are effective decoys for heat-seeking missiles, but do nothing to deter radar-guided missiles. With the proliferation of radar-guided missiles and the increasing sophistication of technology, a new decoy system was developed. This new technology is launched from this panel. When necessary, this access door opens and a transmitter begins operating at a safe distance behind the aircraft.
It has 3 levels of countermeasures to protect the F-35 from attacks. First, it actively jams the missiles as they attempt to lock onto their target, emitting jamming signals that the onboard computer calculates and sends to the sender via the fiber optic tow line. If the radar manages to get a lock, it starts trying to break it. Disrupt the tracking algorithms that guide the missile to its target. Finally, if all is lost and the missile approaches the plane, the emitter begins to simulate the plane's radar signature, luring the missile toward it as a decoy. These serrated hatches hid critical components of the F-35, but more can be done to reduce edge dispersion in these locations.
You may notice that the color around these edges is different from the rest of the plane. This is because the edges are treated with a special radar scattering tape. In the same way that traveling waves scatter when they encounter a discontinuity at an edge, they will scatter when they travel over a change in conductivity. The F-35 takes advantage of this to disperse the waves over a longer distance, reducing the return signal by extending it. The tape has a conductivity gradient, which gradually decreases its electrical conductivity, causing the radar waves to scatter at each interval. Slowly decreasing the intensity of the surface wave before it reaches the edge where it would have launched a large return if the tape were not present.
The plane's surface is composed of specialized radar-absorbing material. In 2010, Lockheed Martin filed this patent for a carbon nanotube composite material that can absorb radar waves from 0.1 megahertz to 60 gigahertz. This is an incredibly wide range of frequencies, notably covering the frequencies used by Russian surface-to-air missiles such as the advanced S-400 system. The effect that traveling surface waves have on stealth design can be seen elsewhere. You might imagine that a cylinder would be a great way to disperse radar in all directions, reducing the intensity of the returning signal, but if a radar wave arrives tangentially at a cylinder and the wavelength is at least 1/10 the circumference of the cylinder, the wave can actually travel around the outside of the cylinder and travel directly back to the receiver.
This is probably why the F-35 features this sharp edge that breaks up the circular nose cone. While the F-16 has a nearly perfect circular nose cone, the F-35 features a ridge. Interestingly, the largest hatch on the plane is not serrated, and this is for a good reason. This hatch hides the elevator's powerful fan inside. The airflow in and out of this elevator fan needed careful consideration. The lift fan is essentially a small helicopter, capable of generating 85 kN of vertical thrust and, in doing so, creates a zone of lower pressure over the aircraft, violently sucking air into the aircraft at a 90 degree angle.
This air has to travel through the hood to reach the inlet and therefore the hood must allow air to pass smoothly over it without creating too much turbulent flow, which would reduce the performance of the lift fan. That is why the entrance door is not serrated, since sharp edges would cause distortions in the flow. This hood alone went through several design iterations to optimize the flow of air flowing through it. The X-35 demonstration aircraft had two doors that opened to the side of the aircraft, but this was changed for the final aircraft in favor of a rear hinged door.
This helps channel air into the engine and improves pressure recovery on short takeoffs where the F-35B does not take off vertically, but instead uses the lift fan and directional thrust from the rear nozzle to take off on extremely short runways. The way this plane transforms to perform vertical landings and short takeoffs is amazing. It's the closest thing to a transformer we've ever created. When the time comes, a clutch linking the extended driveshaft of the F-35 engine begins transferring 29,000 horsepower to the lift fan bevel gear. Turning the counter-rotating lift fan. At the same time, the gears begin to rotate in the rear exhaust nozzle.
The mechanics of this mouthpiece are another wonder worth beholding. Called three-bearing rotating nozzle. It is made up of three watertight segments cut at an angle to each other. We can change the shape of the nozzle by turning these angled pieces separately. These 3 pieces rotate together to make a smooth push-down transition, but it's a little easier to understand how it works by seeing what happens when we rotate the segments individually. By rotating the center piece, the nozzle can go from a zero degree turn to a 45 degree turn. This position is used for short takeoffs by dividing the engine power between thrust and lift.
This mode is as impressive as vertical takeoffs. Allowing the planeoperate from shorter amphibious assault ships like the USS Makin Island, a ship just 800 feet long. The minimum takeoff distance from it is further reduced with the help of a ski jump. A ramp that has been added to smaller amphibious assault ships. Seeing the F-35 take off over such short distances is incredible. In this clip we can see the rear nozzle quickly adjusting its thrust angle, in sync with the rear elevators, to adjust the pitch of the aircraft and ensure a safe takeoff. For a vertical landing, the end segment of the nozzle can rotate to provide a full 90-degree turn.
The first segment of the nozzle can rotate to move the nozzle from side to side, but here it is necessary to ensure that the thrust does not move sideways as the nozzle transitions. As we saw, when we rotate the segments individually, they move in an arc that would cause the F-35 to spin out of control. This mechanism also allows the F-35 to smoothly transition from cruise to vertical flight and from vertical to cruise flight when necessary. Additional control mechanisms exist to ensure that this precarious balancing act does not go wrong. Bleed air from the main engine bypass is diverted to two roller nozzles located on each wing.
Provide thrust away from the aircraft's center of pressure to control roll. There are also guide vanes located under the elevator fan. This can adjust the outlet area to adjust the elevator performance, but also control the thrust of the elevator fan from 5 degrees forward to 42 degrees backward. With computer-aided control of these control mechanisms, the F-35 is remarkably stable compared to its predecessor, the AV-8B Harrier. Allow the F-35's single engine to float on two columns of air. To do this, the F-35's engine, the F-135, developed from the F-119 engine of the F-22 Raptor, had to be incredibly powerful.
The F-22 Raptor is a twin-engine fighter. Giving you enough excess power to perform incredible maneuvers. The F-35 only has one engine and needs to squeeze out all the power possible to make a vertical landing. While the F-22 engine can generate 156 kilonewtons of thrust, the F-35 can generate 191. The F-35 engine has a much larger fan and bypass duct, giving it twice the thrust ratio. derivation than its F-22 counterpart. Providing the F-35 with a more efficient engine for cruising, but also a much higher mass flow rate for greater thrust. However, this has some drawbacks. The air circulating around the engine core completely bypasses the combustion chamber and therefore loses the acceleration generated here.
Reduce escape velocity. This reduces the maximum speed of the plane. The maximum speed of the F-35 is 1.6 mach, and while it is the first aircraft capable of vertical flight and supersonic flight, the F-22 can fly at 2.2 mach. The F-35 was optimized for idle time, not speed. However, all that extra weight needed for vertical takeoff seriously hampers that ideology. The liftfan module weighs 1.2 tons, a weight that does nothing in normal flight and requires more fuel to transport, and to make matters worse it uses space for an internal fuel tank for its variants. Making the lift fan as light as possible was pertinent to making the F-35B viable on the battlefield.
The fact that it only weighs 1.2 tons is surprising. It contains two titanium blisks that rotate in opposite directions. Blisk means that the blades and disc are one piece, rather than the traditional alternative of creating a disc and joining the blades together using dovetail connections. This improves efficiency and eliminates a potential site of connection failure. This is an amazing feat of manufacturing, and the first stage fan takes it even further. The first stage blades are hollow to save weight. However, where the F-35B really stands out is in its modern suite of sensors and computers, all of which contribute to this.
The HUD incorporated into the pilot's helmet. Traditional HUDs, like those on the F-16, are built into a panel in the cockpit. A panel that the pilot cannot see when he scans his surroundings. Situational awareness is everything in the heat of combat, and this helmet does everything it can to keep the pilot informed. Even giving them x-ray vision and night vision. Information from a suite of sensors around the plane enters a central computer, where it is processed and displayed via a projector inside the helmet. Inside this transparent faceted box beneath the plane is a set of sensors.
Those are not typical windows. These windows are made of a very expensive precious stone: sapphire. One of the few materials that is hard and durable, but also transparent to a wide range of electromagnetic wavelengths. From ultraviolet to infrared. However, the radar antenna hidden inside the nose of the F-35 is the most important part of this electronic system. It is a scanned array radar that works very differently than traditional mechanical radar. Phased antennas have hundreds of tiny antennas. We can see metal plates arranged in rows on the F-35 phased antenna. The metal plates have slots cut into them, and each and every one of these slots is an antenna. 1600 in total.
This allows the phased antenna to steer its radar using constructive and destructive interference. If two antennas emit two radar waves at exactly the same time, with their peaks and valleys aligned, constructive interference will occur, increasing the amplitude of the radio wave. However, if the radio waves are shifted 180 degrees out of phase, matching the peak to the troughs will produce complete destructive interference, canceling the wave completely. This is how noise canceling headphones work. They listen to background noise and then release a canceling sound wave to create silence. The phased antenna uses this phenomenon to direct radio waves, preventing the radar from becoming a giant beacon that leads enemies directly towards it.
Traditional phased antennas are passive. Which means that each antenna in the array is controlled by a single transmitter and receiver. This would mean that it can only point in one direction, and if it encountered two enemy aircraft flying side by side and they separated, the passive phased antenna would no longer be able to track them both. However, the F-35's phased antenna is an active phased array, meaning that each and every one of these antennas is an individually controlled transmitter and receiver. Which means the F-35 can track multiple targets at once with no moving parts. The nose cones that hide these antennas must be transparent to radar waves and, as a result, are usually made of fiberglass composites.
This transparency causes problems with the plane's radar return signature, since an antenna like this will reflect the signals. This was a much bigger problem for mechanical radar antennas that needed to be pointed at the enemy to track them. The phased array can point towards multiple targets while remaining in a single position, and that is why it points towards the sky. To bounce incoming radar into space. The phased array antenna also acts as the aircraft's communication antenna, and this is critical to the F-35's battle doctrine. The F-35 excels on the battlefield due to its networking capabilities.
Transmit information between your squad. This is a large amount of data to transfer between aircraft and allies on the surface, and requires a high data transfer rate. However, communication comes with an obvious problem. Announce your presence to anyone who will listen. It is vital that stealth aircraft can communicate with each other securely, and the active phased antenna makes this easier. The F-35 uses the latest data link system called MADL, improving on experiences learned with the F-22. Enable the F-35 to rapidly share data securely from individual F-35s and ground systems. This information is then classified and presented to the pilot on his head-up display right in front of his eyes.
Giving them unparalleled situational awareness. There is no need to communicate with their wingmen if there is an adversary below them, the planes communicate and feed that data directly into the helmet, allowing the pilot to look under the plane and see the location of the adversary. This is the true strength of the F-35B. It is a networked hivemind stealth fighter capable of taking off from a ship a fraction of the size of an aircraft carrier and returning while hovering in the sky like a helicopter. It is one of the most remarkable pieces of military technology ever created.
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