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Chevron-Kammtail(CK) is a combination of Chevron, meaning triangular shape, and Kammtail, which means a streamlined shape with a trailing edge cut out without lengthening it.

First of all, the Chevron shape is inspired by the turbofan engine nacelle of the aircraft, as shown in Figure 1, and the characteristic of the Chevron nacelle is that in a typical high-bypass engine, the low-pressure-low-speed air passing through the engine is ejected from the center of the engine, and the engine is designed to reduce engine noise caused by the shockwave generated when it meets the high-pressure-high-speed jet power that is ejected from the center of the engine.

As shown in Figure 2, the air passing through the chevron engine nacelle (bottom) disperses and passes air more widely than in its normal form (upper), reducing the turbulence kinetic energy of the jet thrust in the center, thereby reducing shock waves at the junction of low-speed and high-speed air.

Boeing 747 Chevron Nozzle - Wikimedia

Fig1. Boeing 747 Chevron Nozzle - Wikimedia

Fig2. Reducing Jet Noise with Chevron Nozzles -

The Kammtail shape is a cut back from the wing shape of an airfoil, as shown in the middle of Figure 3, and is used especially when the rear part of the wing cannot be physically extended. Of course, in this case, the drag may increase compared to a normal airfoil, but it has the advantage of reducing drag compared to an oval-shaped, symmetrical or similar shape in which the leading edge and trailing edge at the front and rear are not much different.

Fig3. Air flow diagram by airfoil shape

The drag of the wheel generated when the actual wheel rotates is 30% due to the rim, 50% due to the rotation of the spokes, and 20% due to the hub. Therefore, the concept of this Aldo is to reduce the overall drag of the wheel by dispersing the flow of air transmitted to the spokes as much as possible rather than the rim itself, and reducing the drag caused by the rotation of the spokes, which generates the greatest drag. This differs from other similar wave-shaped wheels (with bends inside the rim) in aerodynamic features and effects.

Using this feature, the flow of air coming over the rim is continuously changed using a rotating chevron shape, which weakens the viscosity of the air, and the air is also sent to the rear using the shape of a camtail while spreading to the left and right of the rim, which can be expected to further reduce the air resistance area due to contact with the rear-facing spokes, and the absolute drag acting on the wheel can also be reduced.

In Figure 4 below, the area touching the spokes is outlined when using a general annular rim and when using this concept in Figure 5. Air contacts the actual tire, travels along the rim, and then collides with the rotating spokes. Some of this flows outward (Outbound airflow), some go inward and rotate with the wheel, and some of it flows out (Inbound airflow) and makes contact with the rim at the back. In this process, most of the air in contact with the actual wheel flows backwards, but some of it collides with the rotating spokes or is trapped inside them, further increasing the drag of the wheel.

Fig4. Air flow diagram of toroidal rim shape wheel

Fig5. Air flow diagram of chevron-kammtail rim shape wheel

The chevron geometry also creates a different flow of air through the rim, reducing drag on the wheels. As shown in Figure 6 below, the flow of air acting on the wheel passes through the fastest air at that part, since the front section of the wheel is the shortest and according to Bernoulli's law is the highest height relative to the center length of the rim. As a result, air rotates counterclockwise upwards in the center and slow-speed air flows clockwise downward. This rotation of air does not interfere with the rotation of the wheel because the upper part is the same as the direction of rotation of the wheel, but in the case of air at the bottom, the rotation of the wheel is hindered by the flow of air that is different from the direction of rotation of the wheel, which has the effect of increasing drag.

Fig6. Air flow diagram caused by wheel revolution

Figure 7 below is a schematic diagram showing the Chevron-Kamtail airflow. As shown, the Chevron Camtail geometry is constantly changing depending on its position, the shape of the rim and the position of the highest part of the rim. As a result, the flow of air varies according to the shape of the chevron, such as clockwise in sections A and B, counterclockwise in sections B and C, and clockwise in sections C and D, which reduces the flow of air generated by the rotation of the wheel to increase the cloudiness without interfering with the rotation of the wheel. The features and effects of these rim designs are multi-profile effects that are unique to Abyab al-Dorim and are patented by AVIIAV.

Fig7. Air flow diagram of CK rim shape caused by wheel revolution.

An image visualized of the flow of air through CFD analysis shows the spoke resistance and drag on a typical annular rim, and Figure 9 shows the spoke resistance and drag values on a CK rim. It can be seen that the wheel using the lower CK-shaped rim has a low drag value generated inside when rotating. Of course, the drag generated by the back of the wheel will result in the normal rim at the top coming out lower. However, as explained above, more than half of the wheel drag comes from the rotation of the wheel and the rotation of the spokes, so lowering the drag force in this part results in lowering the absolute drag on the wheel.

Fig8. CFD result of toroidal rim shape wheel

Fig9. CFD result of chevron-kammtail rim shape wheel

As shown in Chart 1 below, if you look at the drag value according to the yaw angle experienced by the wheel, at the initial 0 degrees, the wheel with the conventional annular rim shows a better drag value, but as the yaw angle progresses, the drag force caused by the spoke increases, and at a high yaw angle, most wheels made of CK rim show better (lower) drag value.

Chart1. Drag force of wheels

Chart 2 below shows that the wheel drag generated at the entire yaw angle (0-20 degrees) is the average value, and the wheel using CK rim has a drag value about 12% lower than that of a normal annular rim. In particular, it differs from conventional wheels in that the lowest drag value and average drag value can be lowered as shown in Chart 1.

Chart2. Average Drag force of wheels

While most of the research on the existing rim shape was in the process of finding the rim that shows lower drag by measuring drag force based only on the rim shape itself, the current research on rims is not just a rim, but a three-dimensional analysis of the overall study and analysis of the airflow that leads to the rim-spoke-hub-spoke-rim sequence.

As such, the rim geometry of the Chevron-Kamtail structure used in the AVIIAV ALDO rim demonstrates the ability of multiple profiles to connect multiple profiles to control and disperse the flow of air across the rim sides to reduce drag. In particular, this geometry has the characteristic of effectively improving the flow of air against the rotation of the spokes, which accounts for most of the drag generated by the wheel, and the drag caused by the curtain and rotation itself.


AVIIAV's CK-shaped rim is original technology and has been granted as a patent by the Korean Patent Office. The technology was recognized as an empirical effect, not just a concept, and as an original and creative technology that other manufacturers could not easily replicate.

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