The Insane Engineering of the F-117 Nighthawk
B2
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 Skunk Works
taking over from the eminent Kelly
Johnson this paper a Russian scientific
paper translated by the Air Force
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 work'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 track 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 airf
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 pedo 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 f17 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 Ed
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 f17
design the F-117 was different from have
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-17 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
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