CN108163190B - Quadcopter sound insulation device - Google Patents

Abstract

The invention discloses a sound insulation device of a quadrotor, which mainly comprises a connecting arm part and a sound insulation cover part. The sound insulation device can absorb and reflect propeller noise generated by the rotor wing. The connecting arm is of a light high-strength structure of aluminum or plastic products. One end of the connecting arm is fixed with a quarter ball-shaped sound-proof cover. The sound-proof housing is made of three layers of materials, and is sequentially made of glass wool, damping paint and aluminum plates from inside to outside, and the sound-proof housing can improve the noise absorption capacity by selecting proper sound-absorbing materials. The sound-proof cover is at a certain distance from the rotor wing, and noise is reduced on the premise of reducing interference to the rotor wing flow field.

Description

Quadrotor sound insulation device

Technical field

The invention discloses a sound insulation device for a quad-rotor aircraft, and specifically relates to a sound insulation device installed near the rotor and capable of reducing the overall noise of the quad-rotor aircraft.

Background technique

Nowadays, micro-rotor aircraft in the UAV family are widely used in search and rescue, photography, etc., and the express delivery industry is also likely to be the future development direction of rotary-wing aircraft. However, excessive noise is a common problem of existing rotorcraft and may affect the development of future rotorcraft.

Specifically, UAV noise mainly consists of two parts: motor noise and propeller noise. Among them, motor noise is mainly motor bearing noise; propeller noise can be further divided into rotation noise and broadband noise.

Currently, for motor bearing noise, commonly used noise reduction methods are to improve the bearing design, improve the machining accuracy of the bearing chamber and shaft bearing gears, and adopt correct bearing installation processes.

As for propeller noise, traditional methods include changing the length, material, quantity, and blade shape of propeller blades to reduce the noise generated by the blade tip speed or the interaction with the air. Now, active noise reduction technology can also be used in unmanned systems. It is used in the field of computer. The principle is that audio signals generated by electronic equipment are 180° out of phase with each component in the noise spectrum. These audio signals cancel after being superimposed with the original noise signal, thereby reducing the noise intensity.

In the existing research on propeller noise, there are the following problems:

(1) For safety and lightness reasons, propeller blade materials are generally limited to nylon, carbon fiber, glass fiber, etc.

(2) Researching the length and blade shape of propeller blades requires a lot of manpower, material resources, and financial resources.

(3) Increasing the number of propeller blades will increase the design difficulty of the control system.

(4) Active noise reduction technology is complex, costly, and the equipment is heavy, which will reduce the load capacity of the quadcopter.

Contents of the invention

In order to reduce the noise of the quad-rotor aircraft and reduce additional costs at the same time, the present invention proposes a new type of sound insulation device, which is more economical and practical.

The technical solutions adopted by the present invention are as follows:

A sound insulation device for a quadcopter, which includes 4 pairs of sound insulation covers and connecting arms. A sound insulation cover is fixed at the end of the bracket for installing the propeller on each quadcopter through a horizontal connecting arm. The four sound insulation covers and the four connecting arms are in the center. Symmetrically installed on the quadcopter; the soundproof cover is in the shape of a 1/4 spherical bowl, and the concave surface of the soundproof cover faces the propeller, and the inner surface of the soundproof cover is outside the rotation range of the propeller.

The flow field of the quad-rotor aircraft was simulated through ANSYS Fluent. From the simulation results, it can be seen that the streamlines of the flow field near the rotor of the quad-rotor aircraft are relatively concentrated near the rotor, but are sparse when far away from the propeller. Therefore, in order to cause disturbance to the flow field of the quadcopter, the soundproof cover needs to be kept at a certain distance from the propeller. However, if the distance from the propeller is too far, the sound insulation effect will be weakened. Therefore, the shape and size of the soundproof cover are extremely important. In the present invention, the soundproof cover is in the shape of a 1/4 spherical bowl and is made of sound-absorbing material. When the propeller noise generated by the rotor enters this area, part of it is absorbed and the other part is reflected to the space above the body.

Preferably, the sound insulation cover is composed of three layers of materials, including glass wool, damping paint and aluminum plates from the inside to the outside. This material combination has a certain sound absorption effect on both low-frequency noise and mid- and high-frequency noise.

Further, in the sound insulation cover, the thickness of glass wool, damping paint and aluminum plate are 50mm, 1mm and 2mm respectively.

Preferably, one semicircular arc of the soundproof cover is horizontal, and the plane of the other semicircular arc is perpendicular to the connecting arm and the bracket; the inner diameter R' of the soundproof cover is:

Where L ₁ is the distance between the propeller rotation center and the aircraft fuselage center, L ₂ is the horizontal length of the connecting arm; D is the diameter of the propeller;

The outer diameter R of the sound insulation cover is:

Where X is the thickness of the sound insulation cover.

Since the inner surface of the 1/4 bowl-shaped sound insulation cover in the present invention also presents an arc shape, under this state and parameter, when the propeller rotates, the distance between the blades and the inner surface of the sound insulation cover remains unchanged. When the distance between the two is optimized, the disturbance to the flow field can be minimized and the requirements for noise control can be met.

Preferably, the connecting arm is made of lightweight and high-strength materials to reduce the overall weight and avoid additional load on the body.

Further, the connecting arm is made of aluminum or engineering plastic.

In the present invention, the sound insulation device is mainly divided into two parts. One part is the connecting arm, which mainly plays a supporting role and is fixed on the fuselage, and its weight is kept as light as possible. The other part is the soundproof cover part, which is placed at one end of the connecting arm to partially isolate the noise generated by the rotor. This sound insulation device can be connected to the aircraft body in the form of an external installation without changing the structure of the aircraft body itself. It can reduce the noise of the quad-rotor aircraft while ensuring that the impact on the flow field and movement is reduced.

Description of the drawings

Figure 1 is a schematic diagram of the sound insulation device installed on Benqian’s quad-rotor aircraft and on the body;

Figure 2 is an enlarged schematic diagram of the sound insulation device part;

Figure 3 is a schematic diagram of similar triangles;

Figure 4 shows the frequency spectrum before and after installing the sound insulation device.

In the picture: soundproof cover 1, connecting arm 2, bracket 3.

Detailed ways

The present invention will be further elaborated and described below in conjunction with the accompanying drawings and specific embodiments. The technical features of various embodiments of the present invention can be combined accordingly as long as they do not conflict with each other.

As shown in Figure 1, the sound insulation device of the quad-rotor aircraft in this embodiment can be used to reduce the noise generated by the quad-rotor aircraft. The sound insulation device includes 4 sound insulation covers 1 and 4 connecting arms 2. There are four crisscross brackets 3 on the quadcopter body. Propellers and motors are installed at the ends of the brackets 3, which are the main sources of aircraft noise. A soundproof cover 1 is fixed at the end of each bracket 3 through a horizontal connecting arm 2. The axis of the connecting arm 2 is coaxial with the axis of the bracket 3, which is equivalent to an extension of the bracket 3. The connecting arm 2 is made of lightweight and high-strength materials such as aluminum or engineering plastic products. Four soundproof covers 1 and four connecting arms 2 are installed symmetrically on the quadcopter to ensure the original balance. The soundproof cover 1 is in the shape of a 1/4 ball bowl, and the concave surface of the soundproof cover 1 faces the propeller. In order to ensure that the propeller does not hit the soundproof cover 1 when rotating, it is necessary to ensure that the inner surface of the soundproof cover 1 is outside the rotation range of the propeller. The optimal distance between the soundproof cover 1 and the propeller is best determined through multiple tests.

The soundproof cover 1 is composed of three layers of materials, which are glass wool, damping paint and aluminum plate from the inside to the outside. As shown in Figure 2, the lower part of the sound insulation cover 1 is fixed to the outer end of the connecting arm 2. There are two connected semicircular arcs in the soundproof cover 1. In order to ensure a stable distance between the propeller and the inner wall of the cover during rotation, one semicircular arc of the soundproof cover 1 needs to be kept horizontal, and the plane of the other semicircular arc must be in line with the The axes of the connecting arm 2 and the bracket 3 are both vertical. In the design, the similar triangle principle is used to design the parameters of the ball bowl. Assume that the diameter of the propeller is D, the distance between the propeller rotation center and the center of the aircraft body is L ₁ , and the horizontal length of the connecting arm 2 is L ₂ (need to deduct The length of the overlapped part with the bracket and the soundproof cover), the radius of the sphere corresponding to the inner surface of the soundproof cover, that is, the inner diameter of the soundproof cover 1 is R', then the schematic diagram can be obtained as shown in Figure 3:

The inner diameter R’ of the ball bowl of the soundproof cover 1 is:

The outer diameter R of the ball bowl of the soundproof cover 1 is:

Where X is the thickness of the sound insulation cover 1.

Under this parameter, the soundproof cover 1 can be kept from causing unstable disturbance to the propeller, and the noise of the propeller can be eliminated to the maximum extent.

In addition, by selecting appropriate sound-absorbing materials, the noise-absorbing ability of the soundproof cover can be improved. In this embodiment, the soundproof cover 1 is composed of three layers of materials. From the inside to the outside, they are 5cm thick glass wool with a bulk density of 16kg/ ^m3 , 1mm thick damping paint and 2mm thick aluminum plate. Both low-frequency noise and mid- and high-frequency noise have good sound absorption effects. The soundproof cover is placed at a certain distance from the rotor to reduce noise while reducing interference to the rotor flow field.

The invention was implemented on a quadcopter and the noise reduction effect was tested. The following are the detailed experimental parameters:

The quadcopter frame is an F450 frame, made of nylon fiber, and the diagonal motor wheelbase is 450mm, so the straight-line distance L ₁ between the propeller center and the fuselage center is 225mm. The propeller selected is a 1045MR glass fiber reinforced nylon propeller with a diameter of 10 inches, so after unit conversion, the propeller diameter D is 254mm.

In the design, the length L ₂ of the connecting arm 2 is determined to be 10mm. So, according to The radius R of the sphere corresponding to the aluminum plate, the outermost layer of the sound insulation cover, is 186mm. In terms of sound insulation materials, the thickness of the sound insulation cotton selected is 5cm, the thickness of the damping paint is 1mm, and the thickness of the aluminum plate is 2mm.

After the sound insulation device is completed, it is tested. The test conditions are to keep the quadcopter in a suspended state in the air, and then record the noise below the aircraft and perform subsequent data processing - spectrum analysis. As shown in Figure 4, the white part in the figure is the noise spectrum without sound insulation devices, while the black part below is the noise spectrum with sound insulation devices installed. By analyzing the spectrum diagram obtained by spectrum analysis, it is found that the amplitude of the noise component in the low frequency band (<1000HZ) is significantly reduced compared to the case where no sound insulation device is installed, especially the noise reduction below 400HZ is more detailed; the remaining mid-to-high frequencies The segment also has a certain noise reduction effect. And because the sound insulation device is located in the sparse flow field streamlines of the propeller, and the lower part of the bowl is smaller and the upper part is larger, it will not affect its aerodynamic performance. Through the sound absorption and reflection of the soundproof cover, the noise below it is greatly reduced.

The above are only specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the field of the present invention are covered by the protection scope of the present invention. among.

Claims (4)

1. A four rotor craft sound insulator, its characterized in that: the four-rotor aircraft comprises 4 pairs of sound-proof covers (1) and connecting arms (2), wherein the tail end of a bracket (3) for installing a propeller on each four-rotor aircraft is respectively fixed with one sound-proof cover (1) through the horizontal connecting arms (2), and the 4 sound-proof covers (1) and the 4 connecting arms (2) are installed on the four-rotor aircraft in a central symmetry manner; the sound-proof cover (1) is in a 1/4 spherical bowl shape, the concave surface of the sound-proof cover (1) faces the propeller, and the inner surface of the sound-proof cover (1) is positioned outside the rotating range of the propeller;

the sound-proof cover is composed of three layers of materials, and is sequentially composed of glass wool, damping paint and an aluminum plate from inside to outside;

one semicircular arc of the sound insulation cover (1) is horizontal, and the plane of the other semicircular arc is vertical to the connecting arm (2) and the bracket (3); the inner diameter R' of the sound insulation cover (1) is as follows:

wherein L is ₁ L is the distance between the center of rotation of the propeller and the center of the aircraft fuselage ₂ Is the horizontal length of the connecting arm (2); d is the diameter of the propeller;

the outer diameter R of the sound-proof housing (1) is:

wherein X is the thickness of the sound-proof housing (1).

2. The four-rotor aircraft sound deadening device of claim 1, wherein: in the sound-proof housing (1), the thicknesses of the glass wool, the damping paint and the aluminum plate are sequentially 50mm, 1mm and 2mm.

3. The four-rotor aircraft sound deadening device of claim 1, wherein: the connecting arm (2) is made of light high-strength materials.

4. A four-rotor aircraft sound deadening device according to claim 3, wherein: the connecting arm (2) is made of aluminum or engineering plastic.