This episode of Real Engineering is brought
to you by Brilliant.org a problem solving website that helps you think like an engineer. The sight of a 9.4 tonne plane slowly rise
off the ground, balancing precariously on 4 columns of air over the rough water of Galway
bay, is the closest to sci-fi alien technology I have ever seen in my life. An inspiring sight that seeded an obsession
with aviation technology. The harrier was the culmination of decades
of bizarre experimentation to eliminate the planes greatest weakness, it’s need for
a runway to both land and takeoff. This fascinating technology has one of the
richest histories in aviation with roots in both the lunar lander and outlandish WW2 era
German sketches. Both the Allies and the Germans used helicopters
and autogyros during this period, but using a rotor for both lift and thrust inherently
trades off speed. The German’s dreamed of a plane capable
of taking off from anywhere, eliminating the need for tactically vulnerable airstrips,
without sacrificing speed or dogfight capabilities. Inspired by their ballistic missile program,
which still lacked effective guidance programs to accurate target allied aircraft, Erich
Bachem developed the tail-sitting rocket powered BP-349, which would allow the pilot to take
control of the plane in it’s final stages of flight to guide it to it’s target and
unleash it’s barrage of smaller rockets before ejecting to safety. The only manned test of this aircraft resulted
in the death of the test pilot and the idea was abandoned, but that didn’t stopped the
Germans in their pursuit of VTOL aircraft. Next up was an even more bizarre tail sitting
aircraft that featured 3 giant propellor blades each powered by ram-jets at their tips, this
would function similar to a helicopter for take off and then transition to forward flight
and use the blades like a giant propellor, but it would require a nose-up position to
achieve adequate lift, as it didn’t have any wings. Unsurprisingly this didn’t make it passed
basic wind tunnel testing, but could well have inspired the Lockheed XFV and Convair
XFV Pogo planes in the 1950s which used massive counter-rotating turbo-propellers. The Lockheed version only ever managed to
hover for a brief moment while transitioning from horizontal flight to an upwards vertical
flight, but the Convair XFV Pogo flown by Lieutenant Colonel James Coleman became the
first aircraft in history to successful fly in both forward aerodynamic flight and in
hover. Ultimately both planes were cancelled due
the difficulty in flying them, and their lack of speed and lack of lifting power. Engines for propellor driven aircraft were
simply not powerful enough yet. To achieve necessary lift the rotors would
need to increase velocity or diameter, which would decrease the max horizontal speed of
the aircraft as the tip-speeds of the blades would rise, meaning the tips of the blades
could easily break the sound barrier and cause all kinds of problems. This problem and how the incredibly versatile
V-22 Osprey solved it needs a video by itself to explain the nuanced design of helicopters
and their speed limits, but for now you will just need to trust me that it’s a difficult
problem to solve. And with the advent of powerful jet-engines,
the problem was largely solved without the need for large propellers. The first craft to use jet propulsion for
vertical lift was the Rolls-Royce Thrust Measuring Rig, aptly nicknamed the flying bedstead,
for it’s obvious departure from the bird like designs of the past. This configuration largely influenced the
design of the Lunar Lander training vehicle that NASA developed for Neil Armstrong and
other astronauts to practice with. They mounted the engine on a gimbal to ensure
it’s thrust always pointed directly downwards and only provided enough lift to simulate
the moon’s gravity, while hydrogen peroxide rockets were used for control. Neil Armstrong attributed the success of his
difficult landing on the moon to this ingenious training vehicle. The lessons learned through early research
craft like these provided Rolls-Royce with the knowledge required to develop the Rolls-Royce
Pegasus engine, which powers the Harrier. This engine needed to have enough thrust to
lift the entire weight of the plane, the designers of the plane made this job easier by utilizing
carbon-fibre composites for much aircrafts structures to save weight, making the Harrier
one of the first planes to use these materials. Yet the job of designing a single engine capable
of providing enough vertical thrust was still difficult, and the resulting engine is pretty
unique as a result. The engine is similar to a traditional jet
engine in that it consists of a low pressure compressor fan, a high pressure compressor,
a combustion chamber, a high pressure turbine and a low pressure turbine. Where it differs radically is the engine outlet
is not one large opening, but split into four where the first 2 nozzles duct some of the
air coming from the low pressure compressor and the final two duct air from the higher
pressure turbines. [2]
Because the air bleeding from the low pressure compressor system has less force than the
high pressure nozzles, the low pressure nozzles need to be placed further from the planes
centre of gravity than the high pressure nozzles. This balances the plane along the length of
the plane, but in vertical take-off mode there is no air-flowing over the wings to provide
force for the control surfaces. So the plane needs a way of controlling it’s
roll, pitch and yaw in vertical takeoff mode, and so the plane features nozzles that bleed
air from the engine on the nose, tail and wing tips. This control system is not as reliable as
aerodynamic lift, which is largely self correcting when disturbances occurs, although fighters
tend to purposely decrease stability to increase maneuverability, which requires a computer
to constantly monitor, but the disturbances due to ground effect from the air from it’s
own jet can cause oscillations that overwhelm this control system, and with no accurate
way of correcting them, they could grow until the plane inverts and lands on the cockpit,
which has killed pilots on several occasions. So pilots often dropped the plane heavily
from a few metres above the ground before the oscillations could take hold, which obviously
wasn’t ideal for the landing gear [3] The harrier was also disadvantaged to conventional
aircraft as the vertical takeoff mode it was severely limited in max take-off weight and
burnt off much of it’s fuel in this intensive maneuver, reducing it’s range too. So most Harrier take offs take place only
as partial vertical take-off,where the plane would accelerate on the runway like a conventional
plane to achieve some lift from the wings and then angle the nozzles to achieve the
final lift needed to safely take off on the shorter runways of aircraft carriers. The plane could then land vertically without
wasting as much fuel later on when the weight of the aircraft had reduced through use of
it’s fuel and armaments. This takes it’s max take-off weight from
9,415 kg to 14,100 kg, which is still lackluster when comparing to their fellow Marine aircraft
like the F/A-18 hornet that has a max take-off weight of 23,541 kg and a maximum speed of
1.8 compared to the harriers subsonic, 0.9. Make it a much more capable attack platform,
but the hornet is only capable of launching from large carriers, whereas the Harrier can
launch from amphibious assault ships like the USS America. The Harrier has even managed to land on a
cargo ship when it’s pilot lost radio contact with his crew and ran out of fuel. But both of these fighters are slated to be
replaced by the controversial F-35, which will be capable of VTOL, thanks to incredible
directional rear thrust and shaft driven lift fan. This fighter improves on much of the technology
that the Harrier laid the ground for while including futuristic VR helmets allowing the
pilot to see through their own plane using the 6 infrared cameras surrounding the plane,
advanced laser targeting and radar capabilities, all the while incorporating stealth technology. The plane has been deeply entrenched in US
politics, raking up huge development costs and supporting thousands of American jobs,
it has been delayed again and again, largely due to its ambitious technological leap over
it older counterparts. Should it finally reach service it will become
the most advanced plane in the history of mankind. Each advancement like this is built upon the
foundations of physics that humankind has learned over the course of our existence. If you would like to flex your physics knowledge
and learn more about the principles of the universe upon which these machines are built. I highly suggest you check out Brilliant.org. Brilliant is a problem solving website that
teaches you how to think like an engineer. You can dive in and start learning about a
huge range of topics starting from basic physics and working your way up to more complicated
topics. For an example, check out their course on
classical mechanics, one of the most important subjects in mechanical engineering. The first 200 people to sign up with this
link will get 20% off their annual premium subscription
I get to learn and solve these kind of problems for a living and I love it. It gives me that warm glowy feeling inside
when I finally conquer a difficult problem. Actively challenging your brain on a daily
basis and getting that endorphin rush of a job well done is great for your mental health. Brilliant even have an app where you can challenge
yourself on the go, I have even been guilty of pulling out their puzzles section to challenge
my friends while out for a pint. As usual, thanks for watching and thank you
to all my Patreon supporters. I just uploaded a new episode of Showmakers
with special guest, Grant from 3blue1brown. The link to that is on screen now and the
links to all my social media are in the description.
I always love this guy's videos. Unlike some of the other cheesy infographic shows, this guy actually does his research and makes educated videos.
Also: YouTube comments are as cancerous as ever, I see