Contrary to popular belief, when a helicopter engine fails, this is NOT what happens.
All helicopters have a hidden parachute that could help them safely land if the engines failed.
Oh no, not that parachute. I’m talking about autorotation [autorotation],
which uses nothing but the powerless rotor blades like a parachute,
similar to how an airplane can glide down when it loses all engines.
Or like this guy in his gyro boat, who is flying while getting pulled by a towline.
But why the operator of this flying boat was afraid to let go of the tow line,
what allows gyroplanes to fly even though their rotors are not powered by any engines, how some
helicopters can eject their pilots during an emergency without turning them into ground meat,
and finally, the real reason why helicopters crash more often than airplanes, is Not What You Think!
In 2015, the famous American astrophysicist, Neil deGrasse Tyson, tweeted about how an airplane with
failed engines, turns into a glider, but a helicopter with failed engines, turns into
a brick! Come on Niel, were you tweeting from Uranus?! First of all, what actually falls like
a brick is the F-4 Phantom. Just Google “F-4 phantom glide ratio” and this is what you get!
Secondly, a helicopter only turns into a brick if its rotor blades were not turning, which could be
manufactured, which is how a lot of the helicopter crash tests are typically conducted, without a
rotating rotor. But in practice, a helicopter with failed engines turns into a maple seed.
But first, English is not my first language. I only started learning it in highschool, and
I’ve since been dabbling in French and Russian as well. давайте послушаем нашего спонсора, means a
word from our sponsor, Babble, which can help you learn a language, just like it’s been helping me.
My favorite thing about Babble is that they use real pronunciations,
as opposed to the AI voice on many other apps that I’ve tried before. And hearing the actual
pronunciation by a native speaker is huge when it comes to learning a new language.
Each lesson takes about 5 to 10 minutes, and you can practice on your phone, desktop or tablet.
Babble teaches you conversations that you can use when traveling to another country,
or practice with your friends who speak that language.
You can use the flash-cards that are provided within the app to review
your learnings. Babbel also offers live classes, and you can get 2 free classes
with your subscription, which by the way has a 20-day money-back guarantee.
Qu'est-ce que tu attends? So what are you waiting for? Get 60% off
your Babbel subscription when you sign up using the link in the description.
As a maple seed is pulled down by gravity toward the ground, its flat and asymmetric wing starts
to generate turbulence in the air. These are known as leading edge vortices. This experiment clearly
shows the vortices that are generated behind the edge of the rotating blade, which in turn generate
lift to negate some of the gravitational force as the maple seed falls. In addition to that, as the
maple seed moves through the air, air resistance slows down the fall, just like a parachute.
This explains why maple seeds don’t fall down like a rock. They autorotate – the exact same
phenomenon that allows a helicopter with failed engines to safely land.
What’s cool is that besides emergency landing for helicopters, it’s actually
possible to use autorotation to fly for an extended period of time, just like this guy,
We’ll come back to him in a minute, but how does a helicopter exactly perform autorotation?
During a normal helicopter flight, the rotor blades powered by the engine, draw air from above
and then exhaust it downward to generate lift. But when the engine loses power, the airflow reverses.
As gravity pulls the helicopter down, air is forced into the rotor system from below,
turning the rotor blades, just like how moving a pinwheel through air will make it rotate.
A helicopter needs to be a minimum of 500 to 700 feet above the ground to ensure the rotor blades
have enough time to pick up some RPM until they reach a constant rotation speed. The faster the
blades turn, the slower and safer the helicopter descends. To demonstrate this, you can clip on a
little piece of tin foil to different parts of a maple seed, which will change its RPM as it falls.
As you can see, the fast-rotating seed hits the ground much later and with less impact.
This is the collective lever, one of the main controls on a helicopter.
Pulling up the collective increases the pitch on the blades and lowering
the collective makes the blades more flat. When the rotor is powered by the engine,
increasing the pitch will generate more air flow and lift. But it also increases drag.
To autorotate, the pilot must immediately lower the collective all the way down, because a flat
blade produces less drag as it rotates in the air. This means the blades can turn faster as the
helicopter is pulled down by gravity, which results in a slower descent.
Autorotation is quite effective, because the rotor has nearly the drag coefficient of a parachute,
even though it consists of blades. NASA even investigated the use of autorotating blades to
land the space capsule during reentry, but they ended up using parachutes at the end.
Unlike pilots of military airplanes, most helicopter pilots don’t have the luxury of
using an ejection seat in an emergency. But some manufacturers have figured out
how to eject helicopter pilots without shooting them through blades rotating at 400 to 500 RPM.
The world's first helicopter fitted with an ejection seat was the Russian KA-50. The problem
of turning pilots into ground meat was finally solved, but not by ejecting the pilots downward.
Before the ejection seat rocket is deployed, the rotor blades are blown away using explosive
charges in the rotor disk, and the canopy is then jettisoned, allowing for safe ejection.
We should note that sometimes, a pilot is forced to enter autorotation even when
the engine is working fine, and that happens when there is an issue with the tail rotor.
One of the functions of the tail rotor is counteracting the torque of the main rotor.
If there was no tail rotor, the torque generated
by the main rotor would rotate the helicopter out of control.
So in case of tail rotor failure, the pilot can disengage the power from the main rotors
to initiate autorotation. This will stop the helicopter from rotating uncontrollably around
itself, because even though the main rotor blades continue to turn during autorotation,
since the power is not generated by the engine, there is virtually no torque.
Back to this guy flying his rotorcraft. This is called an autogyro, gyrocopter or gyroplane.
It kind of looks like a helicopter, except it flies using autorotation.
There is a propeller on the back, which is powered by an engine, but that only provides
forward movement, not lift. As the vehicle speeds up on the ground, air flows through
its free-spinning rotor, which generates enough lift to fly up and stay in the air.
Just like a helicopter in autorotation, the rotor of an autogyro doesn’t produce torque.
So no tail rotor is required. But there is a rudder on the tail to provide yaw control.
During WWII, Germans would deploy rotor kites behind their U-Boats. They were called Focke
Achgelis FA 330. This was essentially an autogyro, but with no engine at all. Towing
the kite behind the U-boats is what created the forward momentum, and in turn the autorotation.
The rotor kites were used as a lookout to see further away. The 400-ft tether
would allow the pilot to observe as far as 25 nautical miles away as opposed to only
5 nautical miles visible from the conning tower of the U-boat, giving them a massive advantage.
But rotor kites were not only used for reconnaissance in the military, but also for fun!
In about five minutes, the gyro boat was ready to go, which just like the previous autogyro,
flew with the help of autorotation. The only difference was that there was no engine onboard.
The forward momentum was generated by the towing boat in the front. For the gyro boat to actually
lift off the water and stay airborne, it had to be pulled by a boat at a minimum speed of 20 mph.
Within a short hour, the operator would get a hang of flying the gyro boat, to actually have
some fun. That said, the operator was not allowed to let go of the rope. As you know by now, if the
rope was disconnected, the gyro boat would have simply autorotated and slowly landed on water.
So why was the operator not allowed to drop the rope? Well, because it would have been illegal.
The moment the operator let go of the towline, the gyro boat would have been considered an aircraft,
and operating an aircraft would have needed a pilot's license, which he didn’t have.
The emergence of helicopters may have made autogyros obsolete for many military applications.
Helicopters are just much more powerful and can carry much bigger loads, but they
are not without risks, even on the ground. A helicopter can self-destruct, while simply
sitting on the ground, and that typically can happen when the rotor has more than two blades.
You may have noticed what happens when the clothes inside a washing machine get clumped
up one side as the drum spins. In an extreme case, the washing machine can fall apart.
A similar thing can happen with helicopters that have 3 or more blades. That’s because the blades
can advance or lag in their rotation, and that can shift the center of gravity of the helicopter. Now
while in the air, that’s not a big deal. But once the helicopter touches the ground, a resonance
can form in the airframe and if not dealt with, it can very quickly get out of control.
But there is a solution. The pilot must quickly hover as soon as ground resonance begins, and the
shaking would immediately stop. This phenomenon has even been observed during filming of TV shows!
Two-bladed helicopters are pretty safe from ground resonance, since the blades are one
rigid structure and cannot impact the helicopter’s center of gravity.
But all this said, which do you think is more dangerous to fly? Helicopters or airplanes?
According to data collected by the National Transportation Safety Board,
general aircraft, which includes airplanes, helicopters, balloons, and everything else,
have an average crash rate of 7.28 for every 100,000 hours of flight time. The crash rate
for helicopters alone is 9.84 per 100,000 hours. But before calling helicopters less
safe than airplanes, you may want to consider the unique flight characteristics of helicopters.
They usually fly at lower altitudes and more complex terrain, like mountains and other
hard to reach environments. This certainly contributes to more accidents. And by far,
the biggest reason for helicopter crashes is human error, not mechanical problems.
But even with the higher crash rate, the fatality rate in helicopter crashes is lower,
with 1.3 deaths per 100,000 flight hours compared to 1.4 deaths for aircraft in general.
If you learned something new, hit the like button so it reaches more people,
and if this video was not what you thought, consider subscribing!