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• If you asked most of your friends which was faster.

• The fastest production car in the world or the fastest helicopter, I think most of them

• would guess the helicopter.

• Intuitively we expect anything flying in the air to have a higher top speed than anything

• on the ground could achieve, but physics is a cruel mistress and conventional helicopters

• are doomed to a max speed of just 400 km/h, with that record being set over 30 years ago

• by John Trevor Egginton in a Westland Lynx, while just this year the Koenigsegg Agera

• RS demolished that record driving at 445 km/h, and sure you don't have to worry about traffic

• in your helicopter or those pesky speed suggestions on the road, but the bragging rights for top

• speed will always go to cars for the rest of time.

• So how can this be, what quirks of physics are limiting helicopters from flying faster?

• First let's look at what limits a cars top speed.

• To determine top speed, we first need to identify the forces attempting to slow the vehicle

• down.

• In space, with no resistance, even a small force can continually accelerate an object

• until it reaches close to the speed of light, if it is maintained for long enough, which

• would require a silly amount of energy.

• On earth though, every time we provide energy to our vehicle, resistance in the form of

• air resistance and rolling resistance in the wheels are sapping it away.

• Eventually we get to a point where the energy we are providing the vehicle equals the energy

• being taken away, and the vehicle cannot travel any faster.

• In the case of cars the top speed is predominantly determined by air resistance, for now we will

• ignore rolling resistance as it's negligible in comparison.

• The equation for drag force is given by this equation, and the equation for power is simply

• force times velocity.

• Rearranging these variables we get an equation for top speed.

• Applying this to the Agera RS specs, we find it's top speed almost perfectly with a decent

• degree of accuracy, considering we ignored rolling resistance.

• Decreasing our drag coefficient and frontal area also increases top speed, but to increase

• power we need to increase airflow to cool the engine, so this is a difficult balancing

• act.

• We also discovered in a previous video that designing rubber tires capable of withstanding

• these rotational speeds is an incredibly difficult task, with the Bloodhound SSC opting for aluminium

• wheels to break the land speed record.

• These are the limiting factors for a car, so what are the limiting factors for a helicopter.

• Helicopters have to deal with all the same problems as cars in counteracting aerodynamic

• drag, but first a helicopter needs to overcome the force of gravity, using the same rotor

• that will need to provide forward thrust.

• So is this just an issue of needing engine power?

• Partially yes,

• The Westland Lynx was powered by not one but two Rolls-Royce Gem turboshaft engines, each

• equaling the power of a single Agera RS twin-turbo V8 engine.

• Yet, even with twice the power, it still can't beat it in a straight line race.

• How can this be?

• Let's go on a journey as the helicopter takes off and transitions to forward flight,

• and see why it can't go any faster even with stronger material for blades or more

• powerful engines.

• As the Lynx powers up the blades begin to rotate faster, providing more lift according

• to this equation.

• Where A is the swept area of the blades, Cl is the coefficient of lift of the blades and

• v is the velocity of the blades.

• The coefficient of lift depends on a lot of things, like the geometry of the blades and

• angle of attack, but for the sake of simplicity we will assume it is constant.

• Once the lift is greater than the weight of the helicopter it begins to rise, and when

• it equals the weight the helicopter will enter a hover state.

• Now to go forward, the pilot will need to transition some of the lift to thrust by angling

• the rotor disk forward.

• But here we meet our first problem.

• Looking downwards, we can see that left-side of our blade is moving backwards relative

• to the the direction of travel, and our right hand side to moving forward relative to the

• direction of travel.

• Similar to planes, the aerodynamic surface of the blade will generate more or less lift

• depending how quickly it is moving through the air.

• So our right side generates more lift that our left.

• To counteract this the rotor integrates an ingenious little mechanism, where the blade

• can change its angle of attack as it rotates.

• Here the advancing blade will have a lower its angle of attack, thereby lowering it's

• lift, and the retreating blade will increase it's angle of attack, increasing it's

• lift.

• This helps equalise the lift across the rotor disk, but this solution has it's limit.

• As we increase an aerofoils angle of attack the lift increases, but eventually he hit

• a point of where flow separation occurs and the aerofoil begins to generate less lift.

• This is our first speed limit.

• The helicopter will eventually hit a speed where it cannot adjust the angle attack any

• further to compensate to dissymmetry of lift.

• However there are solutions to this problem.

• If we have two blades rotating in opposite directions, we no longer have to compensate

• for this dissymmetry in lift, as the two blades will have the opposite dissymmetry of lift

• and cancel each other out.

• This is what allows the Chinook to cruise along faster than any other military helicopter

• at 315 km/h.

• Now we have overcome one speed limit, but even now the Agera RS is still speeding ahead

• . The next speed limit we reach is the sound

• barrier, if we continue to increase forward velocity, the tips of the advancing blade

• will eventually break the sound barrier.

• And while planes can handle breaking through the sound barrier with the correct design,

• they don't need to pass through it several hundreds of times a minute.

• This adds to the problems of dissymmetry of lift, but also causes problems with varying

• stress that fatigue the material of the blades and ultimately lead to failure.

• This speed limit poses a more difficult challenge to overcome in our current configuration.

• To travel faster, we need to increase thrust, to increase thrust we need to increase lift.

• Let's take a look at the equation from before to see how we can do that.

• We can either increase our rotor speed, or we can increase our blade diameter.

• Increasing the blade velocity will obviously make us more likely to break the sound barrier,

• but so will increasing our blade diameter, as the velocity of the blade increases as

• we travel down the blade.

• Designers have hit an optimum balance between these two variable already, so that's not

• an option for increasing speed.

• So how else can we increase helicopter speed?

• By converting more of that vertical lift to horizontal thrust, but this poses a new problem,

• at some point were are going to hit a point where the helicopter is not generating enough

• lift to keep itself aloft.

• The solutions to this problem are hitting a point where the we can scarcely call the

• aircraft a helicopter.

• Enter the Eurocopter X cubed, which holds the unofficial helicopter speed record, unofficial

• exactly because it is not strictly a helicopter, as it generates a large portion of it's

• forward thrust from vertical propellers.

• This decreases the burden of the horizontal rotor to generate forward thrust allowing

• it slow its rotational speed, minimising the impact of our previous speed limits, the rotor

• can also decrease it's rotational velocity as the helicopter gains speed as more lift

• is generated from two small wings on either side of the helicopter.

• These design choices allowed the x cubed to reach top speed of 472 km/h, beating the previous

• record held by the Sikorsky X2, and demolishing anything ever achieved by a production car.

• Pushing this design ideology even further we completely blur the lines of what a helicopter

• is, with tiltrotors, like the Osprey.

• This aircraft has a top speed of 565 km/h, this combined with it's incredible vertical

• take-off capabilities, that are not hindered by limited weight issues like jet engine powered

• aircraft like the Harrier, has made it an incredibly versatile tool for the US military.

• Another incredibly versatile tool that could give you some additional lift, is Skillshare,

• all the animations and illustrations you saw in todays episode were created by me, but

• just 3 years ago I knew nothing about animation.

• I taught myself the basics during one Chinese New Years holiday when I was living in Malaysia.

• 1 week later I knew enough to start experimenting with animation styles and figure out how I

• wanted to this channel to look.

• A year later again I uploaded my first video to YouTube and it went viral straight away.

• Learning new skills gives you opportunities in life.

• This is why I love working with Skillshare, you can learn from thousands of courses in

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• I learned loads about animation from watching a course from my friends at In A Nutshell.

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• As usual, thanks for watching and thank you to my incredible Patreon supporters.

• I just opened a Discord server for my Patreon supporters where we can chat and share ideas

• for videos.

• The links to my twitter, instagram and facebook pages are below too.

If you asked most of your friends which was faster.

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# Fastest Car vs. Fastest Helicopter - Which is Faster?

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joey joey に公開 2021 年 06 月 07 日