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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.
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