basic helicopter

7/28/2019 Basic Helicopter

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Many people think that if the engine fails in a helicopter, youre doomed! They assume that

the aircraft will simply fall out of the sky like a stone, and that the pilot will be utterly

helpless. In fact, I have even seen this scenario described in a bestselling book by an author

who should know better.

But nothing could be further from the truth. If the helicopter engine stops, the pilot simplyputs the machine into a controlled descent which allows air from below to turn the

rotors. This is known as autorotation. The pilot can then manoeuvre the helicopter to a safe

landing site, and so long as he or she is reasonably skilled, this will not be a crash site. In

fact, everyone in the aircraft ought to be able to walk away safely, and the machine should

even be in one piece too. So how does autorotation work?

Air From Below Keeps the Rotor Blades Turning

In normal flight, the engine drives the rotor. But it is not the engine which actually keeps the

helicopter flying. It is the air flowing over the turning blades which produces lift, and it is

this lift which keeps the helicopter in the air. So if the engine stopsactually, a very

unlikely event with modern helicopterswe just need another way to produce lift.

If a descent begins immediately after the engine stops, the airflow from below will keep the blades

rotating. This might be a little hard to visualize, but it works a little like a windmill, or a descending

sycamore leaf. In any event, it works! The helicopter will descend, but it will do so at a steady pace,

and its direction can be controlled. It can then be manoeuvred into wind and landed safely.

Successful Autorotation: The Pilots Role

If the helicopter engine stops, everything will go quiet in the cockpit, and the machine willyaw violently to one side. When this happens, the pilot needs to instantly lower the

collective, taking the pitch off therotor blades, and initiating a descent. This is the most

important thing, as it is crucial to maintain rotor RPM, ie keep the blades turning. He or she

also needs to keep the aircraft straight with the pedals, and make sure the helicopters nose

does not drop.

These are the only things which need to be done rather quickly. Once the helicopter is

established in autorotation, it will be descending at around 1,700 feet per minute, which

means at a normal flying height of around 2,000 feet there is over a minute to sort things out

not a lot of time, but enough.

Landing Without an Engine

The pilot now looks for a safe landing sitea flat area where he can land into wind. A flat

field without crops or other obstacles is best, but in a city a playing field will do, or even a

flat roof! At this point, the pilot puts out an emergency or Mayday radio call if

possible. At about 40 feet above the ground, he starts to raise the nose of the helicopter by

pulling back on the cyclic. This slows the helicopter down, and his aim is for it to be level

and moving slowly when just a few feet above the ground. At this point the collective is

raised, using the last available pitch of the blades to produce lift and cushion the landing.

Ideally the landing is normal and gentle, but helicopter skids are designed to absorb shockand thereby cushion a less-than-perfect autorotative landing.
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Autorotative Landings

Autorotative landings are not easy for the beginner. However, prospective pilots practice this

exercise many, many times during the PPL(H) course, and regularly afterwards. It is rare forany pilot to have to do an autorotation in earnest, but I have known some who have, and they

have all walked away safely. If you knowhow to fly a helicopter, engine failure is an

emergency, but not necessarily a disaster.

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What About Helicopters?

While a helicopter is a far more complex machine than an aeroplane, the fundamental

principles of flight are the same. The rotor blades of a helicopter are identical to the wings of

an aeroplanewhen air is blown over them, lift is produced. The crucial difference is that the

flow of air is produced by rotating the wingsor rotor bladesrather than by moving the

whole aircraft. When the rotor blades start to spin, the air flowing over them produces lift,

and this can cause the helicopter to rise into the air. So, the engine is used to turn the blades,

and the turning blades produce the required lift. Very simple!

Controlling the Helicopter

However, there is rather more to it than that. You need to be able to lift your helicopter into

the air when you want to, rather than just have it rise up as soon as you start the engine. In

the case of an aeroplane, flight can start as soon as the aircraft is moving fast enough. But in

a helicopter, for all sorts of reasons, the blades need to turn at the same speed all the time. So

you need a different way to control the amount of lift produced.

How Do Helicopters Fly?

November 21, 2012 byHelen KrasnerLeave a Comment
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The turning of the rotor blades produces lift. Photo by Helen Krasner

The magnitude of this lift is actually changed by altering the angle at which the rotor blades

meet the air blowing over them. This is known as increasing or decreasing the pitch angle of

the rotor blades, and this alters the amount of lift produced. The pilot does this by using a

control called the collective, which is on his left side in the cockpit. This control

collectively alters the pitch of the blades, and means the pilot can lift the helicopter into the

hover when he decides to, by increasing the pitch on the rotor blades.

However, increasing the lift also means that there is more drag. So when the collective is

raised, the pilot needs to open the throttle to produce more engine power in order to prevent

the rotor blades slowing down. There is a twist-grip throttle on the end of the collective for

this purpose, but in most modern helicopters it is operated automatically, and the helicopter

can be safely lifted into the hover using the collective alone.

Forwards, Backwards, and Sideways

The pilot now needs to be able to move the helicopter in different directions. This is done

primarily by means of another control, the cyclic, which the pilot holds in his right

hand. The cyclic also changes the pitch angle of the rotor blades, but it alters each blade

individually and by a different amount. The helicopter is designed so that the net result of

this is that when the cyclic is moved forward, the helicopter moves forwards, when it is

moved aft the helicopter moves backwards, and similarly to move sidewayssomethingaeroplanes cannot do!

Turning the Helicopter

The fourth helicopter control is the yaw pedals. These alter the pitch angle of the tail rotor

the small rotor at the end of the helicopter. Doing this enables the pilot to turn the helicopter

either left or right.

Coordination of Helicopter Controls
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In practice, the three controls all affect each other to a certain extent, and have to be

coordinated carefully in order for controlled flight to happen. It is this fact which makes

helicopter flying rather difficult in the beginning. Also, various other aerodynamic factors

complicate matters. For example, the turning of the rotor blades causes differing amounts of

air to flow over each blade, and if this is not corrected for, a helicopter could easily turn over

as soon as it started to move! So, there is actually a lot more to understanding the principlesof helicopter flight than the above. We will look at some of the other things involved in later

articles.

What is Autorotation?

Autorotation is a controlled non-powered descent of a helicopter. Normally it is the engine

which keeps the helicopters rotors turning. However, it is the turning of the rotors themselves

which produces lift and actually keeps the helicopter in the air. If the engine fails, something

else is needed to rotate the rotors to prevent a crash.

Therefore the pilot needs to initiate a descent, which causes the upflowing air to turn the

rotors, much in the manner of a windmill or a falling sycamore leaf. The helicopter will then

be descending, usually at around 1000 feet per minuteBut it will be under control, and the

pilot can steer it to an appropriate landing site.

What is an AutoGyro?

The helicopter has a power driven rotor to remain airborne It also needs a tail rotor to prevent the

body of the aircraft from rotating in the opposite direction to the main rotor

The autogyro's main rotor acts as a circular wing and draws energy from the airstream to rotate and

generate lift. It is not powered. The aircraft is either pulled or pushed by an engine and propeller

thus driving the rotor into the airstream. When the rotor attains sufficient revolutions per minute

(depending on type and make) it begins to 'Fly' like a solid circular wing. No air passes through it only

under and over it. This is called Autorotation and allows the aircraft to fly and land even with

engines stopped. The autogiro also has a vertical and /or horizontal tail planes. The aircraft is

controlled by the same basic controls, stick, throttle and rudder pedals as a fixed wing aeroplane but

is significantly more manoeuverable. (Note: The small drive shaft you may see attached to the rotor-

head is used only to spin-up the rotor, while the giroplane is on the ground. This provides a shortertake-off distance.


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Whats the difference between an autogyro

and a helicopter?

At first sight an autogyro looks like a rudimentary helicopter as they both have largehorizontal rotor blades. But unlike a helicopter, the rotors on an autogyro are not powered.

Instead, the thrust comes from a propeller either at the front or rear of the aircraft. The blades

spin because of the air rushing up through them, providing lift and stability. Though this is an

unusual design, autogyros are popular with recreational pilots and theyre well suited to low-

speed flight.

What is an autogyro?

Answer:

An autogyro looks like a helicopter with a rotor blade on the top of the fuselage but it also

has another propeller in back to push it. The autogyro uses the air passing UP through the

rotor blade to turn the main rotor blade and give it LIFT. So it needs something to provide

THRUST to propel it forward. An autogyro can NOT take off vertically and go straight up.

Instead it must have a take-off roll to get it flying.

The main rotor of a helicopter is more complicated and it produces both LIFT and THRUST.

Their controls are more complicated and the loads on the blades and blade attachments and

the rotor Mast.

The Autogyro's blades turns due to air passing through it just like a maple seed "flys" with its

single wing as it falls from the tree.

Since the main rotor of the Autogyro does not produce a vertical Lift, that means the Mast of

the rotor does not carry a torque load. The Mast only supports the weight of the Autogyro.

Whereas, the Mast of the Helicopter is experiencing Torque loads and Bending loads(for

some types of helicopters) as well as Tension forces by the weight of the helicopter.

What is an Autogyro?

An autogyro is an aircraft that uses a freely

rotating rotor as a wing. Because the rotor

rotates freely, it does not apply an axis torque

on the fuselage and there is therefore no reason

for a tail rotor. Furthermore, the rotor is not

attached to the engine, so a propulsion in the

form of a propeller or jet engine is needed for

powered flight.

You have understood by now that an autogyro

is not a helicopter. An autogyro is by all means

an aircraft that is "half fixed-wing, half helicopter". In most cases it is as stable as a fixed-wing aircraft. It can land almost vertically and, with a trick that is called a jump start, some

A Crickett "hovering against the wind"
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autogyros can also take-off vertically.

Autogyros can fly very slow, "sink" vertically down and even fly somewhat backwards. They

can not hover or fly vertically up. They can "hover against the wind", but that is just flying

slowly with headwind. Autogyros can land on platforms on ships and oilrigs.

Autogyros are also called "windmill planes". This name describes the autogyro nicely: it is

nothing more than a flying windmill. The only difference between an autogyro rotor and anormal windmill is the fact that an autogyro rotor is designed to generate lift instead of shaft

power.

basic helicopter

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