To the untrained eye it looks like the blades spin fast and the pilot wiggles some controls and it all lifts into the air! Some of us pilots would like to think it was that simple!!
We hope in this blog we have explained it as simply as possible:
The fundamentals of helicopter flight are quite complex and even make up an entire CASA exam as part of gaining your Commercial Helicopter Pilots Licence. Despite this, a lot of these complexities can be summarised into a few interesting points.
Helicopters fly by spinning the blades faster until it lifts off.
This is actually not the case at all. Most modern helicopters will use two steady RPMs on the rotors, one for idle and one for flight. This means that the RPM the rotors are spinning at while on the ground just before liftoff and when cruising at 200 km/hr are actually the same. In Robinson R44’s this is 406 RPM.
You will typically hear the pilot bring the RPM up to flight RPM when you are in the helicopter ready to go. Then to make the helicopter lift into the air, the pitch of the blades is changed.
Changing something called the ‘angle of attack,’ creating lift on the blades and the helicopter rises into the air, all while maintaining the same RPM.
This short video shows this pitch change happening:
The tail rotor steers the helicopter.
This is somewhat true. The tail rotor is an anti-torque rotor, it is called this because its job is to counteract the torque produced by the engine. This means the tail rotor spends most of its time stopping the helicopter from spinning!
When the helicopter is hovering, the tail rotor can steer the helicopter. The way this works is by producing more or less thrust than what is needed. But it is always creating thrust in just one direction, it is just the amount of thrust that is changed. The pilot controls this by moving the pedals.
Once the helicopter is moving forward through the air the tail rotor is no longer used to steer like it was in the hover. This is because the tail fin, called a ‘vertical stabilizer’, starts to work to help with counteracting the engine’s torque as well.
Basically, the tail fin helps keep the helicopter flying straight, and the turns are now done with cyclic (the joystick the pilot holds). The tail rotor still works during this; however, the pilot uses it to ‘balance’ the helicopter rather than to turn it. Using it to make the helicopter fly straight and the ride a lot more comfortable for the passengers.
If the motor stops the blades will stop.
This is a subject about helicopters that is covered in another of our blog posts called AUTOROTATIONS.
There are a few quick points that can be made here about this question.
All helicopters have a freewheel system, sometimes called a sprag clutch or freewheel unit. It works just like most bicycles, in the way that if you stop pedaling the wheels keep turning until you run out of momentum. The same applies to the blades on a helicopter if the engine stops.
But won’t the blades stop anyway? Even with a freewheel system, once the momentum runs out.
If the pilot does nothing they will! However, in the event of this happening the pilot allows the helicopter to descend and, as it does, the air it descends through drives the rotors, keeping them spinning. This is called Autorotation. And is how a Gyrocopter or Autogyro flies.
If you want to learn more about this or how the landing phase is done following this, head over to our Autorotation post: https://www.barossahelicopters.com.au/autorotations-engine-off-landing/
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