The Insane Engineering of the F-117 Nighthawk

two f-117's are approaching their target Over Baghdad below the cloud cover radar guided surfac to- aair missiles scan the sky for signs of an imminent threat but see little more than a small blip that Fades into the background of noise the payload Bay do open revealing two GPS guided bombs destined for the assumed location of the then Iraq president Saddam Hussein this simple act May well have revealed the stealthy aircraft to radar below its exterior was molded by precise mathematical equations every facet designed to disperse and absorb the electromagnetic energy surrounding the skies around them with the bombs delivered and their location potentially given away the defenseless planes quickly turned to escape enemy airspace this was a highly specialized aircraft designed to carry just two bombs in its payload Bay a plane that looked like a fighter jet but if it met enemy Fighters the subsonic plane armed with bombs meant for ground targets stood little chance it relied entirely on stealth to Get Behind Enemy Lines and strike without being seen something it did time after time during the Gulf War striking 1,600 high value targets without losing a single aircraft the design began as a simple Diamond that aerodynamicists of Lockheed skunkworks dubbed the hopeless Diamond a template for stealth a shape that the famous former skunkworks leader Kelly Johnson doubted would ever be able to fly turning this concept into a functional aircraft would take the very best aerodynamicists propulsion Engineers Structural Engineers and radar Specialists that Skunk Works had to offer they carefully chipped away at the simple but revolutionary shape to form a masterpiece this is the in engineering of the f117 Nighthawk the f-17 nigh Hawk's Journey began here on the desk of Ben Rich the newly appointed director of skunkworks taking over from the eminent Kelly Johnson this paper a Russian scientific paper translated by the Air Force's foreign technology division held the key to a new generation of aircraft war is an Ever evolving game of cat and mouse and in the past decade aircraft had switched roles from Predator to prey the development of Soviet radar guided missiles caught the US industrial machine by surprise a sudden realization during the Yong kapor War of 1973 Israeli Pilots armed with the latest and greatest American attack aircraft lost 109 planes over just 18 days these planes were mostly shot down by Soviet supplied surfac to- a missiles supplied to the Egyptian and Syrian armies these Crews required a fraction of the training that was required to train a fighter pilot and the systems themselves were vastly cheaper the Russians had invested billions into the development of radar guided surface to a missiles like the sa5 these missiles could reach 125,000 ft in altitude and could even be armed with nuclear warheads to blast WBY Raiders out of the sky the extreme altitude would mean Russians on the ground would be shielded from the Heat and shock waves and the Strong Winds of the upper atmosphere would carry the Fallout to Western Europe the effectiveness of these missiles was not down to speculation the balance of the battlefield had shifted towards the Soviets Air Force planners extrapolated these attrition rates out to a full war with the Soviets in Eastern Europe and they saw the writing on the wall the Soviets would wipe out the entire US Air Force in just 17 days two strategies to counter this advancement emerged conventional wisdom of the time pointed towards designing a plane specifically designed to hug the terrain to be able to fly longrange Missions at extremely low altitude hiding from radar in the ground clutter this resulted in the B1 Lancer its variable sweep Wing allowed it to tailor its aerodynamics for both low speed low altitude flight and high-speed high altitude flight however that was system would soon be challenged thanks to one brilliant scientist Dennis overhauser who on one fateful day placed this paper on the desk of Ben Rich a long technical document full of complicated equations and theories but for Dennis skunkworks radar Dome expert it held a treasure the key to unlocking a new way of Designing aircraft a method to calculate the defraction of electromagnetic waves stealth design was not a new concept the sr-71's first flight predates the first day of development of the F-117 by over 10 years and it Incorporated some early concepts for stealth that were largely based around the laws of physical Optics reflection and refraction avoiding Corner reflectors was a known method to reduce radar signature long before the F-117 was theorized what this paper unlocked was much more complicated once thought to be too complicated to solve defraction imagine waves approaching a harbor Breakwater it's designed to Shield the boats inside from the energy of the sea with just the laws of reflection the boats should be completely unaware of the presence of waves outside these walls and yet through defraction the waves find their way inside this is a messy chaotic problem with too many variables to consider for simple analysis and it only gets more complicated with electromagnetic waves but this paper unbeknownst to the Soviets who allowed it to be published internationally held the key to the technology that would allow aircraft to become the top predator once again Ben Rich the newly appointed leader of skunkworks under pressure to take the Reigns from Kelly Johnson approved a computer program to be developed and within 3 months a working program that allowed simple shapes to be analyzed was created dubbed echo1 allowing them to theorize the Hopeless diamond this was of course not a plane it lacked everything a plane needs to fly it had no control surfaces no propulsion no payload it even lacked a wing Dennis was not an aerodynamicist he was skunk's Raad home specialist designing the nose cones that housed their planes radar this design was a template that could be molded by the most skilled sculptors in aviation step one was to figure out its Mission profile this would decide several things Max payload range and propulsion with stealth a priority the F-117 could not have external hard points this was going to limit its weapons capacity it would feature two internal weapon spays and the plane would be a Precision bomber its weapon of choice were laser guided bombs inside the nose of the aircraft hid a steerable turret containing a dual field of view infrared sensor while a second infrared sensor was located to the right of the nose wheel well and both sensors came with a laser which could be aimed at the Target to guide the bomb with extreme Precision the sensors locked onto and tracked targets with help from the internal navigation system switching from the forward-looking to the downward-looking systems as it passed over the target these systems were of course heavily weather dependent as the plane could not guide the bombs through cloud cover but GPS guided bombs were also an option these were the only weapons on board the plane would be completely defenseless to aial threats and would thus rely completely on stealth and because of this the F-117 was going to be a subsonic plane producing a sonic boom was a good way to be detected not by radar but just any person in the general vicinity higher speeds also results in increased aerodynamic heating that could allow the plane to be targeted by infrared guided systems so the engines didn't need afterburners or specialized engine inlets to slow down supersonic air flow this simplified engine selection and the General Electric j85 was selected for the half blue demonstrator which would later be upgraded to the General Electric f404 from The fa18 Hornet an affordable reliable and maintainable engine next the engine air Inlet needed to take shape here things get particularly unique to the F-117 radar bouncing around inside an engine Inlet is like a person shouting into a massive cave the engine Inlet would need to take the same facet angles as the rest of the plane and so the engine Inlet was covered with a radar reflecting grid the grid had spacing of just 1.5 CM this spacing was key to preventing the transmission of radar the passage of any wavelength larger than the gaps in the mesh would be impeded some wavelengths will still get through but the inside of the inlet was also lined with radar absorbing material or Ram which covered the entire surface of the aircraft we don't typically see covers on engine inlets for several incredibly important reasons number one it reduces pressure recovery pressure recovery is the ratio of the average total pressure at the exit of the inlet to the total average pressure in the freest stream air the absolute maximum value is one where no pressure is lost and therefore no energy is lost this is a way to assess the performance of the engine Inlet having a mesh blocking a large portion of the inlet drastically reduces es the pressure recovery and reduces the thrust the engine can produce as a result secondary intake doors located here could open at lower power settings to increase air flow but opening these up during flight was not an option they were controlled automatically programmed to open when the plane speed was below Mach 0.5 and the doors closed gradually as the plane accelerated this was also how the crew accessed the engine to maintain it since the front intake was completely covered this grid created another much larger problem during flight ice can build up on the aircraft smaller devices like the aired pedot tubes have heating elements and water drains inside them to prevent this critical sensor from being blocked to prevent this from happening to the inlet grid the plane came with inflight anti-icing equipment with what was essentially a windscreen wiper a wiper would emerge from the lip below the inlet and spray a glycol-based anti-icing mixture next the engine Outlet had to be molded into shape and once again the f-17 has an incredibly unique design the engineers wanted to minimize the heat signature of the plane as well as the radar signature to do this they needed to cool the exhaust and distribute it over a wider area so it could mix with ambient temperature air quicker the exhaust Outlet transitioned from a round duct at the turbine exhaust to a flat 17 to1 rectangular-shaped duct the duct was also divided it horizontally into smaller ducted channels below the exhaust the fuselage extended out with a slight upwards angle into what was dubbed the Platypus tail this shape spreads the heat from the exhaust over a larger area allowing it to mix with ambient air and cool down faster the extension was also covered in heat absorbing ceramic tiles that were cooled continually by bypass air coming from around the engines this exhaust setup did however cause some instability issues that were only discovered CED during the half blue demonstration test flights the thrust of these engine nozzles were angled inwards towards the center line of the aircraft however the angle of this trust Vector was often not symmetric the thrust angle between each exhaust could differ by as much as 8° in some flight conditions resulting in differential thrust that could push the plane sideways the angle was affected by engine power angle of attack speed but in particular Sid slip Sid slip is when the relative wind striking the plane does not match the direction of travel which can often happen on takeoff and landings with a sidewind this became a problem for the half blue test flights because the flight computer was using a lateral accelerometer to measure Sid slip but this asymmetric thrust was pushing the plane sideways causing the accelerometer to detect side slip the flight computer then tried to correct four Sid slip which did not actually exist and created actual Sid slip which increased the asymmetric thrust which increased the false Sid slip signal a positive feedback loop of instability this problem was fixed by taking actual Sid slip measurements using a beta vein beta is just the Aeronautical Engineering term for Sid slip with the engine selected and payload capacity determined the wings needed to be sized and designed an aerodynamicist has a lot of things to consider when designing a wing The Sweep angle the AO foil design the dihedral angle and the wing area usually these decisions are made based on the plane's main responsibilities an airliner selects a wing that operates most efficiently at its expected Cruise altitude and speed a fighter plane like the F-16 will be designed to maximize maneuverability and high angle of attack lift however the F-117 Engineers had their hands tied with many of the choices they could typically make the sweep angle which describes the backwards angling of wings was largely out of their control sweep angle is usually determined by the speed of the aircraft slower civilian aircraft like Cessnas have no need for sweep as they don't travel even remotely close to supersonic speeds an airliner Wing is angled backwards to increase critical mock number this is the speed at which supersonic flow begins to appear over the wings angling the wings backwards allows airliners to fly faster before this becomes an issue the 787 has a sweep angle of 32° supersonic planes like jet fighters have their sweep angle determined by speed too but this time it's to avoid the oblique shock waves emanating from the nose and body of the plane from intersecting with their wings which would cause a large amount of drag and loss of lift an F-16 has a sweep angle of 40° even the fastest planes like the SR71 had a sweep angle of just 53° the half blue demonstrator aircraft had a sweep angle of 72.5 De and the f117 was going to be a subsonic plane flying at similar speeds to an airliner a sweep of 32° or so would have sufficed this extreme sweep angle was being driven by its stealth requirements determined by the echo1 program and this came with Troublesome consequences a swept Wing produces less lift than an equivalent on swept Wing this was made even worse by the rigid design requirements of stealth on the AER foil itself the air foil of the F-117 was composed OS of simple flat faceted shapes two three on top and two on the bottom if we map the pressure distribution of a regular air foil it may look something like this while the faceted shape looks like this with Peaks occurring at the facet lines this resulted in low lift to drag ratios and caused issues with aerodynamic flutter where the wing would vibrate and damage itself with the reduced lift caused by the sweep angle in addition to the suboptimal aerrow foils the wings had to be quite large to produce enough lift the designers increased the wing area with extensions here this increased the f-117's wing area to 72 M squared a massive area for such a light plane the f-17 had a Max takeoff weight of 23,800 kg compare that to an F-15 the F-15 was designed with a low-wing loading in mind meaning a low ratio of weight to Wing area and yet the F-15 had a smaller Wing area area and a higher Max takeoff weight than the F-117 the F-15 could simply produce more lift with less Wing area designing a plane around these flat faceted sheets was a huge challenge not just in lift but in stability too the massive 72.5 de sweep in the hav blue demonstrator caused a pitch instability if the plane pitched to an angle of attack greater than 17° the plane would not be able to pitch down again as the elevant also lost control Authority as the angle of attack increased a concerning pitch instability that required the flight control computer to intervene on the Pilot's behalf with a specialized control surface the have blue turned the Platypus tail extension into a flight control surface it automatically deflected downwards when an angle of attack of 13° was exceeded but this too brought with it some unforeseen issues which ended the test flight career of Bill Parks when the control surface automatically deployed just 1 M Off The Runway and slammed the aircraft into the ground bending the landing gear and forcing the pilot to eject this platypus tail was removed for the final f117 design the F-117 was different from hav Blue in several ways besides being much larger the inward CED all movable fins of the hav blue was switched to a vtail and the fins themselves were enlarged to increase Control Authority these inward CED fins matched the the 30° Contours of the fuselage they served as both the rudder and elevators a ruter Vader inward fins like those of the SR71 and outward candid fins like those of the F35 work in the same way and we can see how by examining the resultant Force generated when the control surfaces are actuated to different positions we can actuate them in opposite directions to generate a horizontal resultant Force providing yaw control as a vertical Rudder would or we can deflect them in the same direction to provide pitch control as the horizontal elevator would however the inward caned fins of the half blue were being shielded from Air Flow by the fuselage during high angle of attack Maneuvers reducing their power to control the plane as they were receiving less air to create lift the larger outward CED fins of the F-117 helped increase the Control Authority the Platypus tail was removed but the F-117 gained a second outboard elevant where the have blue had just one elevant on each Wing these huge full span elevons were sized to provide more control in Pitch the 72.5 de Wing sweep was also reduced to 67.5 de while still an extremely high Wing sweep for a subsonic plane this 5 degree decrease helped increase the lift of the wing and reduce the pitch instabilities the half blue demonstrator experienced with two large elevant the f-117's Vil no longer had to control both pitch and and yaw it was dedicated to just yaw control having a control surface like this performing double duty can cause issues if the plane needs to control both pitch and yaw at the same time the flight computer has to figure out how to manage the competing control inputs into a single controlled surface it's far from ideal it also increases redundancy in the event of a failure a much better design than the half blue demonstrator both of which were destroyed in crashes with the extremely poor lift to drag ratio of the f117 its maximum takeoff weight was limited fuel tanks were located above and behind the main weapons Bay with additional storage in the wings for a total fuel capacity of 8.2 metric tons of jp8 fuel giving the plane a range of 1,720 KM to reach enemy territory the plane needed frequent aerial refueling the original trip from Langley Air Force Base to Saudi Arabia for Operation Desert Storm took 15 hours and required seven refuelings along the way air-to-air refueling receptacles were mounted in the upper fuselage and rotated into position with the plane's poor low-speed flight characteristics it stood a little chance of taking off and landing on aircraft carriers Loy did in fact propose a carrier version of the Nighthawk the F-117 n which added a tail hook lowered the wing sweep added an allm moving horizontal stabilizer increased power with a larger after burning engine Eng and increased payload capacity with more hard points The Proposal was rejected however the F-117 was a moment of inspired Brilliance that the United States Air Force ultimately knew would have a limited shelf life they kept it under wraps for as long as possible to maintain its Advantage but once its adversaries knew of its existence counter strategies began to be developed taking the simple template of stealth and trying to adapt it for the next generation of multi-roll Fighters was never going to work the worst of Both Worlds ultimately an entirely new generation of aircraft were needed during Desert Storm the Air Force based 36 f-117's in Saudi Arabia and they only needed refueling tankers as support these planes operated over heavily contested airspace with impunity on the first night of their deployment they struck 26 high value targets many of which included the country's surfac to- a missile defense systems the f-117's were so effective that the Iraqi air defense system was powerless to stop them what was once a Soviet trump card was rendered useless not a single F-117 was lost this infographic was produced by the Air Force after Desert Storm to illustrate the value of this new technology estimating the 20-year cost of procurement and operation of this precision and stealth Doctrine at $1.5 billion the stand standard package of aircraft needed before stealth was developed was much more costly requiring specialized bombers fighter escorts to protect them electronic jamming aircraft to suppress air defenses and a much larger Fleet of refueling tankers to support all of them costing $6.5 billion however the Air Force was well aware this golden period of stealth was going to be shortlived with its existence known it was only a matter of time until the enemy developed strategy and Technologies to counter stealth a large part of the f-117's mission planning revolved around knowing the positions and types of radar systems in enemy airspace and planning a route through them that kept the plane out of range the first and only f117 was shot down over Serbia in 1999 here a tactic was used that involved moving radar and missile launchers regularly and only turning them on for a short period of time so their positions could not be tracked making it impossible to plan a route around them this tactic allowed them to successfully lock onto the F-117 and destroy it the pilot was rescued but the military made no attempt to destroy the plane wreckage at this point the F-22 had already made its first flight developed with the very latest in stealth technology while being a true fighter aircraft capable of Defending itself and incorporating even more advanced technology that the public are likely still not aware of today the F-35 employs an entirely new doctrine of interconnected Battlefield information a hive mind of stealth aircraft swapping information between each other the F-117 was the first true stealth aircraft but as stealth technology has advanced stealth is not something expected as a specialization but is expected as standard with modern technology targets can be hit from mindboggling ranges the key to survival is to strike before you are seen the B2 Spirit was the next wrong on this evolutionary ladder and it was one of the most sophisticated and expensive planes ever produced we don't have a video on the B2 Spirit but our friends over at mustard do and it's available exclusively on nebula the 20-minute video is beautifully animated and tells the story of how the B2 came into existence before I go into an entire spiel about how great nebula is I know many of you are sick of signing up for yet another subscription service so if you simply want 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Channel: Real Engineering

Views: 2,233,405

Keywords: engineering, science, technology, education, history, real

Id: 1zjcnnx7igc

Length: 24min 20sec (1460 seconds)

Published: Sat Jun 08 2024