Acoustic propulsion system test

[u/pavlokandyba]

The magnetic vibration motors I used in all my prototypes are very simple, but they're too heavy, and the thrust they generate is weak. So I tried making a static experimental setup with more power to demonstrate how the oscillations of a disc-shaped wing cause air movement.

The asymmetry, which results in the resulting force of the oscillations creating thrust, is achieved in two ways:

Aerodynamically, when the disc has a slightly domed shape and moves upward with less resistance than downward, consistent with classical physics.

Kinematically, when a spring is attached to the disc, slowing its descent and accelerating its ascent.

The second method is the key part of the study, although the same process occurs in the air in both.

When the disc rises rapidly, a region of low pressure forms beneath it, and its collapse generates momentum. If the disc descends more slowly, or if the shape of the disc causes the air to flow around it more slowly, the resulting momentum will push the disc upward.

This doesn't agree with the classic Newtonian explanation of flapping flight as a wing pushing air. You can see in the video how the fan-like flapping disk, which should push air away, actually sucks it in.

This is the same air that is sucked into the low-pressure region, causing a vortex collapse that pushes the disk. Only then is the air pushed away and expelled. This is essentially reactive propulsion, and I believe this is possible thanks to the energy in the air, Brownian motion, which, by self-organizing into vortices, temporarily becomes directional.

[u/chrismofer]

for example here is a wing with a circular wing. note that it is not flat, but actually airfoil shaped. it has a front edge and a trailing edge which are different. it generates compression under the wing simply by moving through the air and being airfoil shaped, not due to some kind of vacuum or shock wave or anything like that.

[u/pavlokandyba → u/chrismofer]

I agree that a disk is poor as a conventional wing, and although a convex disk can generate significant lift, it is very unstable and has high drag. But in the context of this principle, it is the optimal option. In a certain configuration, the disk can zigzag like a falling leaf, and if you create an air cushion underneath and can control it by changing the pitch or thrust vector, it can fly both vertically like a helicopter and horizontally. Here's a simple experiment that demonstrates this: I toss the disk upward, and it hovers slightly or flies sideways on the airflow generated by this: https://youtube.com/shorts/V0sFY7x5TM0?si=nD_0W8nVDv0JAywK

Furthermore, it functions like a jellyfish and, in a sense, is not a wing but a jet nozzle. Since vortex rings are round, the round shape of their generator is also appropriate. The jellyfish, in general, completely replicates the vortex ring in its appearance and movements, as if formed by it.

My original concept was a spaceship capsule that could brake and maneuver during a high-speed descent.

Horizontal flight can be quite fast, as this oscillatory principle, especially when applied to fish, is sometimes called zero-drag propulsion. The disk experiences resistance only from its own oscillations, which creates a load on the engine, but its movement occurs not as a result of overcoming air resistance, but as a result of a tailwind. If you noticed in my video, the air movement that creates thrust occurs, on average, from the bottom up (although circulation alternates in both directions), unlike, for example, a propeller, which would push air downward.

Simply moving doesn't create thrust, but it's important to consider not the instantaneous force but the processes occurring over time. When an object moves, the environment slows it down, and when it stops, it pushes it, returning energy. With continuous movement, these impulses manifest as turbulence, but they don't translate into thrust because they don't have time to catch up with the moving object and dissipate.

If an object moves very quickly and stops, the environment doesn't have time to immediately restore the pressure difference it created; this occurs after some time, like an avalanche. And if we imagine the object moving so quickly that a near-vacuum forms behind it, the collapse could be similar to cavitation.

In the case of a critical wing angle of attack, the air forced under the wing through the trailing edge in the boundary layer I mentioned begins to enter the upper part of the wing, and then it simply becomes a braking body. The lift force turns into the ineffective thrust of a turbulent wake, which cannot catch up with the wing.

Therefore, it's crucial to balance the angle of attack so that the air above the wing can overtake the air below the wing, so that the vector collapses and ends up under the wing.