Why does a helicopter need a tail rotor

When a helicopter engine begins to turn the transmission, this begins to turn both the Main Rotor and the Tail rotor through a fixed gearing system. The tail rotor cannot turn independently of the main rotor. When one turns so does the other. The tail rotor is usually geared around a to ratio, so for every single revolution of the main rotor, the tail rotor will complete revolutions.

As the engine, transmission and the rotor system begin to build up speed they become effected by Newtons Third Law:. What this means is that as the main rotor turns one way, the fuselage of the helicopter wants to turn the helicopter the other way. While the helicopter sits on the ground, the friction between the skids or the wheels prevents the helicopter from spinning around.

The second the pilot tries to lift the helicopter into a hover the helicopter fuselage would begin to spin in the opposite direction to the main rotor. Think of when you are drilling a hole and the drill bit bites.

The drill tries to rip itself out of your hand. To prevent the helicopter from spinning, a tail rotor is installed at the rear of the helicopter to provide horizontal thrust to push the tail of the helicopter in the opposite direction to which it wants to spin.

Think of when you push a paddle through the water in a canoe. You push the paddle towards the back of the canoe, but the canoe moves forward through the water. When the thrust produced by the tail rotor is equal to the torque produced by the main rotor, the helicopter will sit in a hover without sending the pilot dizzy! To get any aircraft off the ground an airfoil or group of airfoils have to produce more lift than the weight of the aircraft. The more weight, the more lift the main rotor needs to produce.

When a helicopter is in a balanced hover or in level flight the lift produced by the main rotor is equal to the weight of the helicopter. To descend, the main rotor produces less lift compared to weight, and gravity pulls the helicopter into a descent. To adjust the amount of lift the main rotor produces, the pilot raises or lowers the Collective Control.

This adjusts the pitch angle on all of the main rotor blades at the same time and creates more lift or less lift. As the Collective is raised, more pitch is applied the main rotor blades and more lift is produced. As the Collective is lowered, less pitch is applied to the the main rotor blades and less lift is produced. When at the desired altitude the pilot does not move the Collective Control. The second task of the main rotor is to move the helicopter in any direction over the ground that the pilot wishes.

This is the biggest benefit to a helicopter over a fixed-wing: Stable, accurate maneuvering over a spot. To move the helicopter laterally in any direction, the pilot moves the Cyclic control. This mechanically tilts a device on the main rotor mast called a Swashplate. This swashplate transmits those control movements to each main rotor blade to adjust the pitch of each blade individually.

When the disk tilts, it moves the upward acting force vector Lift to the side slightly and this makes the helicopter move in that direction until the Cyclic control is moved back to the center. Tail rotors are generally powered by the same driveshaft as the main rotor, allowing them to sync up. Tail rotors are either built onto the tail in a traditional design, or they are built into the tail in a fan-type configuration, called fan-tail or fenestron design.

There is another design, however, that removes the second external rotor entirely and isn't a coaxial design. In this design, called the NOTAR system, a jet of air is sent through a vent on the tail of the craft to create a boundary layer of air flowing along the tail boom.

This low-pressure air changes the direction of airflow around the tail boom, creating thrust opposite to the motion created by the torque effect of the main rotor. A rotating vented drum at the end of the tail boom provides directional control. While this is a little bit of a special case, it is technically still a two-rotor design, just a rather peculiar one. All this talk about different tail rotor designs brings us down to the root of the matter.

At the end of the day, helicopters inherently have a torque imbalance , and each different tail rotor design is simply a way to manage that. With that in mind, let's dive into more of the specifics behind why helicopters have tail rotors.

When helicopters were first created, their designers faced the massive challenge of creating a craft that was able to hover while also being stable. Thanks to Newton's third law of motion, each and every action requires an equal and opposite reaction. When the rotor of a helicopter spins in one direction, there must be an equal and opposite force in the other direction.

This is the root of the torque problem with helicopters. In order to get enough lift, a significant amount of torque must be applied to the main rotor, but engineers still have to solve for the equal and opposite reaction somehow. Early helicopter designs utilized multiple rotors spinning in opposite directions.

This is the same as the coaxial design we see today also tandem, and intermeshing designs , which is an incredibly efficient, albeit complicated, method of achieving helicopter lift and solving the torque problem without the need for a tail rotor.

In these scenarios, 50 percent of the torque turns one rotor in one direction and 50 percent of the torque turns the other rotor in the other direction, making the overall torque vector of the helicopter 0.

However, while this design was initially popular, helicopter pioneer Igor Sikorsky settled on a different design, which would shape the future of helicopter designs. He developed a method of utilizing a single tail rotor mounted to the back of the helicopter to counteract the torque from the main rotor. This is now the most popular orientation in the world and has seen years of refinement and development. While you may think that the traditional tail rotor design is the most optimum because it is the most popular, this isn't always the case.

There are quite a few significant issues with tail rotor helicopters that aren't seen on coaxial or dual-main-rotor craft. For one, tail rotors consume about 30 percent of the entire engine power of a craft.

Mobile Newsletter chat close. Mobile Newsletter chat dots. Mobile Newsletter chat avatar. Mobile Newsletter chat subscribe. Prev NEXT. Mark Twain once noted that he lost belief in conventional pictures of angels of his boyhood when a scientist calculated for a pound men to fly like a bird, he would have to have a breast bone 15 feet wide supporting wings in proportion.

Well, that's sort of the way a helicopter looks. Special Thanks. Bloom, Glenn S. The Helicopter Page. July 1, DK Ultimate Visual Dictionary.

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