You might wonder why helicopters make noise. The answer to this question depends on the parts of the helicopter that produce noise. These components include the Air intake, Power turbine, and Exhaust. The main rotor is the most common culprit. It is responsible for creating the loud slap sound. The number of blades used also influences the sound produced. If the blades are too large, the helicopter may make a deep and reverberating sound.
Air intake
The primary source of helicopter noise is vortex interaction between the blades. This interaction produces a jerking force in the air and sonar pulsation. The direction of noise changes depending on the position of the helicopter and the angle of attack of the rotor blades. In the approach condition, the noise primarily moves forward, downward, and backward. A helicopter’s noise is not so loud, though, if it has mufflers and is fitted with soundproofing.
The air intake on a helicopter is a major source of noise. This is where the helicopter takes in air and turns it into thrust. The gas turbine engine in a helicopter produces a loud noise and the volume of air needed is tremendous. The turbine’s power is created by a Power Turbine, which draws energy from the airflow passing the aircraft. At full power, an AS350 B2 Astar’s Power Turbine turns at over 51,000 rpm.
While this noise is a common part of helicopters, there are several factors that can make the aircraft noisy. These include the blades’ vortex interactions, the main rotor’s compressibility, and the power turbine within the engine. By addressing these factors separately, helicopters can become quieter. In addition, helicopters can reduce noise by reducing their weight. Research and development efforts are currently underway around the world to find ways to reduce noise from helicopters.
Power turbine
There are two main types of noise made by helicopters. Blade loading noise is caused by lift and drag forces on a helicopter’s rotor blades. This type of noise is a function of distributed blade pressure, blade-passing frequency, and harmonics. Blade Vortex Impulse (BVI) noise is created by interactions between rotor blades and shed vortex trails. Both of these types of noise produce directional noise pulses.
Helicopter noise is generated primarily by the main rotor. The rotor blades are incredibly long, and the air pressure changes between the upper and lower parts of the aircraft. The result is a vortex of air that causes the vibration. A German research team took advantage of this effect and recorded the sound from a helicopter. The helicopter’s vortices can be clearly seen against the right background.
The noise produced by helicopters varies greatly depending on their size. Small helicopters tend to make more noise than larger ones. They also tend to have a broader range of noise levels than larger aircraft. Generally, helicopter noise is lower when flying close to airports and other airspace. In addition, helicopter noise is more noticeable when the helicopters are flying at low altitudes. It is not uncommon for helicopters to be spotted by a drone, but there are several ways to detect them.
Exhaust
Helicopter exhaust makes noise due to a number of different reasons, including the type of engine, the number of blades on the rotor, and the way it moves through the air. Most of the noise that helicopters make is aerodynamic in nature and occurs due to the way the main rotor blades move through the air. A helicopter’s engine produces a significant amount of noise, but this noise is usually minimal, and you can only hear it up close. The noise that is produced by the helicopter’s exhaust is not caused by the engine, however, and is due to the noise that the main rotor blades make as they move through the air.
The noise that a helicopter makes is often described as a “sonic boom.” In addition to being annoying to passengers, this sound can also be harmful to aircraft. The noise produced by helicopter engines is a result of the vortex interaction of the blades, which generates highly impulsive vibrations in the air. This noise is the most prevalent sound that helicopters make when they approach. The sound can be either loud or soft, or it can be a combination of both.
Main rotor
A helicopter’s main rotor produces a lot of noise, which is similar to the noise an airplane’s propeller makes. It is difficult to pinpoint the exact source of the noise, because the noise is generated by the flow volume surrounding the tip of the rotor blade. The noise is often loud and can be annoying to passengers on the ground. However, there are a number of reasons why a helicopter makes noise.
One of the causes of helicopter noise is the vortex interaction between the blades. The vortex causes variation in the load on the blades, which in turn creates a jerking force in the air. The vortex moves toward the rotor blades at varying angles of attack, depending on the trajectory of the helicopter. When the air passes over the upper surface of the rotor, it accelerates, creating a depression. This depression pulls the rotor upwards, pushing it downwards, or moving it forward and backwards.
The rotary motion in helicopters causes a sound wave pulse called thickness noise. The frequency of this noise depends on how often the rotor blades pass over each other. The higher the number of blades, the louder the sound is. And since helicopters travel at relatively low altitudes, this noise can be very irritating to passengers. In order to minimize the noise from helicopter main rotors, aircraft manufacturers have been trying to decrease their rpm, which may help reduce the noise.
Infrasound
If you’ve ever wondered why helicopters make such a lot of noise, you’re not alone. The sound that helicopters produce is created by a combination of high-frequency noise and infrasound. The main rotor on helicopters produces the lowest sound, known as infrasound. The frequency of infrasound is governed by the number of blades and the rate at which they rotate. Most helicopters have two blades, and this results in an infrasound frequency of 13 Hertz. While human hearing range extends down to about 26 Hertz, this frequency is not audible to us and may cause discomfort, dizziness, blurred vision, and even fear, depending on your age.
Infrasound is created by a helicopter’s engines and can be measured in many ways. One study showed that helicopters make a wide range of tones, ranging from the most powerful to the lowest. The lowest civilian helicopters, which are more commonly used for aerial surveys, emit infrasound at frequencies ranging from 10 to 30 Hz. These frequencies are similar to the natural frequencies of rock landforms. When helicopters fly close to a rock formation, the high-frequency sound can stimulate a resonant structural response that can lead to structural damage.
Effects on health
When considering the effects of helicopter noise on health, the research team considered four different models: Eurocopter EC 135 P2, Bell UH-1D, Mi-4, Bell 412, and Sikorsky H-23 D. The Ecureuil is the least noisy helicopter, while the Alouette II is the noisiest. Despite the study’s limitations, noise levels from these aircraft were still comparable to the average level of industrial workers.
Although a helicopter’s noise levels are much lower than other forms of transportation, the helicopter’s emissions are more than three to five times higher than the emissions from a single diesel vehicle. In a recent hearing test before the NYC council, the Center for Independence of the Disabled spoke out against the impact of helicopter noise on the health of New Yorkers and the ability to learn. The organization also highlighted the financial and social barriers that these individuals face due to their disabilities.
In addition to reducing quality of life, noise exposure can cause cardiovascular disease and increased stress, which are two major causes of death and disability in the U.S., according to the World Health Organization (WHO). Hence, legislations aimed at reducing noise from aircraft are essential to the public’s health. Furthermore, helicopter noise also affects the lives of people around the world. The authors of the study recommend that nighttime flights be restricted to prevent aircraft noise from disrupting sleep.
Alternative source noise corrections
A level flyover is required for aircraft in the United States to achieve minimum FAA noise standards. The noise measurements for a helicopter must be more than 3.5 dB above the mean background noise levels for aircraft in that frequency band, as measured by an FAA-approved method. Noise levels must be corrected for the different durations of aircraft operations and the difference between test conditions and reference conditions. The FAA requires that noise measurements be made for at least three test runs, one for takeoff, one for flyover, and one for landing.
Noise levels generated by helicopters are calculated based on acoustic flight tests. Pilots must be trained in noise-control techniques and in helicopter flight practices to prevent and minimize aircraft noise. Noise levels should be measured as accurately as possible. The helicopter noise model is an essential tool for helicopter noise mitigation. Its authors have been involved in the development of various noise mitigation methods over the years. In addition, a study conducted in March 2012 by Ahearn, Meghan and Boeker, along with Aaron Hastings and Gina Solman, has helped the FAA develop noise mitigation guidelines for helicopters.
The aircraft must maintain a six-degree approach slope in the measured and reference flight paths. The measured noise level must be within 10 dB of the PNLTM value, so that it is not more than 6deg. The measurements must be made for a long enough distance to record the entire interval. For a flight to be deemed acceptable, the noise level should be within ten decibels above the PNLTM. The height AG and relative distance M must be within five knots of the reference airspeed to meet the PNLTM requirements.
