The history of the creation of disk-shaped aircraft has shown that their main problem is not the lack of technology but the shape itself. The disk is symmetrical, has no traditional tail feathers and wings, and therefore does not have natural stability in flight. How does the air flow around such a body behave? Why is an airplane with wings stable, but a saucer is not? And why didn’t even the use of an air cushion or the Coandă effect help make the Avrocar controllable? In this installment of the How to Build a UFO series, we will look at the key aerodynamic problems that prevent such vehicles from flying effectively.
Why are disk-shaped devices so stubborn to implement?
The main difficulties lie in their aerodynamics and stability. A classic airplane has an elongated wing and tail precisely to provide stability and control. A disk, on the other hand, is symmetrical in shape and has no pronounced tail fin or keel. This leads to several problems:
Static instability. For stable flight, the center of mass of the airplane must be in front of the center of lift. It is very difficult to achieve such a balance in a disk because the slightest change in the angle of attack* shifts the point of application of lift. Without special measures, the disk will tend to suddenly “tip” forward or backward. Simply put, a disc-shaped wing is aerodynamically unbalanced. When you throw a frisbee without rotation, you can see this problem – the plate immediately tilts or falls over nose first. That’s why you need to give the frisbee a quick spin: the gyroscopic momentum stabilizes it and turns the dangerous tipping into a smooth precession**. Of course, for a manned vehicle, rotating the entire hull like a frisbee is not an option (the pilot would simply be “spun around”), so other ways to stabilize it should be sought.
*The angle of attack is the angle between the direction of airflow and the wing of the aircraft.
**Precession is a phenomenon during which the axis of rotation of an object changes its direction, but the object itself continues to rotate. It is the basis of gyroscope operation.
Lack of traditional controls. In a conventional airplane, pitch, roll, and heading are controlled by elevators, ailerons, and rudder – surfaces that deflect the flow. A disk does not have a clearly defined leading edge and tail, so it is difficult to place such surfaces. You can, of course, add small flaps or flaps at the edges, but their effectiveness will be less due to the short shoulder relative to the center of mass. The Avrocar, for example, was controlled in hover mode by deflecting the flows from the peripheral nozzles, which changed the shape of the air cushion. To control roll, it had differential flaps in the flow, but the accuracy of such control left much to be desired. At high speeds, the developers planned to use differential engine thrust and small flaps but did not have time to perfect the system. Without an active stabilization system, the disk can rotate and slide uncontrollably, especially under the influence of wind gusts or turbulence.
Features of airflow. A disk is a wing with a very small longitudinal length (aspect ratio* ~1 or less). Theoretically, a flat disk can generate lift at a certain angle of attack, just like a conventional wing (because Bernoulli’s principle and flow rotation are valid for any profile). But a flat disk has a low aerodynamic quality factor. At low angles of attack, it generates little lift, and at high angles, the flow is quickly disrupted (it becomes turbulent above the upper surface) and loses lift altogether. Although there is evidence that a circular wing can have a high maximum angle of attack due to symmetrical stalling around the circumference (some experiments have shown the possibility of stable flow around the disk at angles of ~30° due to a toroidal vortex above it), it is still difficult to provide a stable lift over a wide range of speeds. In addition, the disk has a significant drag in forward flight: the large cross-sectional area slows down the vehicle, especially at high speeds. In Avrocar, for example, the estimated top speed is greatly reduced when real aerodynamic losses are taken into account – it is clear that the claimed 1500 mph (2400 km/h) was out of the question. Thus, the insufficient lift ratio and high parasitic braking are significant problems with the disk shape.
* Aspect ratio is the ratio of width to length; for example, for an aircraft, a high aspect ratio means long and narrow wings (like gliders) – more lift, better efficiency. A low aspect ratio (short and wide wings, like those of fighter jets) means greater maneuverability.
** A toroidal vortex is a ring-shaped flow of air or liquid rotating around a hollow center, similar to a smoke ring.
The capriciousness of the air cushion. Many disk-shaped projects (Avrocar, Coandă-1910, and others) relied on creating an air cushion or ring jet underneath to hover. However, this scheme is only stable at very low altitudes (within half the diameter of the disk). As soon as the device rises higher, the “cushion” begins to lose its shape, the symmetry is broken, and the disk collapses. In Avrocar’s tests, it turned out that the jet cushion became increasingly unstable at altitudes above 1 meter (several feet). This meant that the vehicle could not confidently switch from climb to flight mode – at intermediate altitudes, it became uncontrollable. They tried to overcome this by increasing the jet power and modifying the design, but the problem was not completely solved.
As a result, disk-shaped aircraft combine the difficulties of a virtually “tailless” aircraft with an ultra-short wing. Without the use of special solutions, such a vehicle will be either unstable or inefficient. Next, let’s look at what theoretical and engineering approaches can ensure the stable flight of the “saucer”.
Disk-shaped aircraft face a whole range of problems: low lift, high sensitivity to wind gusts, difficulty in control, and high aerodynamic drag. However, some experiments have shown that under certain conditions, the saucer shape can still be stabilized using vortex flows, the Coandă effect, or active flow control. Can these effects be used to create a stable disk that can stay in the air and maneuver? Next, we will look at theoretical solutions that make this possible.
The key to building a working flying saucer
Traditional principles of aerodynamics are not suitable for saucer-shaped aircraft. But is it possible to circumvent these limitations using non-standard approaches? Theoretically, if the air circulation around the disk is properly organized, it can gain additional lift and become stable. Delta wings use edge vortices to increase lift – could a similar approach work for a disk? What if we use controlled air jets or plasma flow generators? So, let’s look at calculations and models that can help stabilize the flight of a disk-shaped vehicle.
Calculating the lifting force for a disk
The first step is to estimate how much lift a disk wing can provide. There is a standard lift formula for any aircraft in aerodynamics:
Where L is the lift, ρ is the air density, v is the flow velocity (of the incoming air relative to the vehicle), S is the wing area (in the case of a disk, S = πR2), and CL is the lift coefficient, which depends on the shape and angle of attack.
This formula is also valid for disk wings. For example, a flat disk with a radius of 5 m has an area of S=78.5 m2. If it flies horizontally at a speed of v=100 m/s (≈360 km/h) at a small angle of attack, and the lift coefficient at this angle is, say, CL=0.5 (rather optimistic for a flat disk), the lift force will be:
That is about 1.2 tons of force. This is not enough to keep such a device in the air if it weighs more (and a 10-meter disk with a propulsion system and fuel can weigh much more than 1 ton). Therefore, to generate sufficient lift, the disk needs either a high speed, an increased area, or an increased lift coefficient (for example, due to a curved profile or forced air circulation).
Features of the lift coefficient CL for a disk-shaped wing. For a thin profile (e.g., a flat plate) in 2D theory, the CL value increases approximately linearly with the angle of attack (in radians) until the loss of stable flow. However, for a real 3D wing of finite span (here, span = disk diameter), the effective gradient is smaller due to end effects (air leakage from under the edges and formation of end vortices). The disk has a very low elongation, so its maximum CL is limited. However, it has been experimentally observed that the disk can generate lift at large angles, forming stable vortex structures above it. These vortices can “suck” air to the upper surface, maintaining pressure reduction (similar to how delta gliders or birds with open wings at high angles create edge vortices at the wing tips that keep the flow). Thus, from an aerodynamic point of view, the disk can obtain lift in two ways: classical (due to pressure differences due to the profile flow) and vortex “lifting” (when the vortex above the disk acts as a dynamic “pseudo-wing”).
Stabilization by vortices and the Coandă effect
One method of stabilizing a disk-shaped apparatus is to use vortices and the Coandă effect to control the flow. The Coandă effect is the idea that a jet of liquid or gas tends to press against and follow a surface. In the context of a flying saucer, this means that if a powerful jet of air is blown along the surface of the disk (for example, from the center to the edge from the top), it will “flow” around the upper hemispherical part and curve downward along the sides, creating a region of reduced pressure above the disk and deflecting the flow downward around it. This will simultaneously provide lift (due to the rarefaction from above and the downward deflection of the jet stream) and potentially stabilize the device, as the flow flows symmetrically around it. Avrocar tried to implement this idea: the flow was to be bent downward with the help of valves to create an annular air cushion. By drawing in air from the top surface of the disk, the Coandă effect was supposed to help keep it aloft, increasing the cushion below and creating a partial vacuum above. In essence, the disk turns into a closed circulating wing: the constant circulation of air around the rim generates lift according to the Kutta–Joukowski theorem.
Vortices can play a dual role. On the one hand, the gyroscopic effect: if the disk is provided with an annular vortex surrounding it (for example, a stream of air moving in a circle along the rim, similar to the smoke in a toroidal vortex), then according to the law of conservation of momentum, this stream will have a certain stabilizing effect (similar to the rotation of a frisbee, but not the whole body, but only the air ring).
By the way, a frisbee needs to rotate quickly around its axis during flight to remain stable in the air. It is this rotation that creates the gyroscopic moment that resists the disk’s change of orientation, keeping its position stable. Without rotation, the frisbee, like any flat disk, will quickly lose stability: even a small disturbance will cause it to tip over or fall sharply to one side. The gyroscopic effect converts this disturbance into a slow precession rather than a flip – a smooth rotation of the disk’s plane that does not throw it out of flight. That’s why frisbees are thrown at high angular velocity: the faster they rotate, the more stable their course is. This principle also explains why manned disc-shaped vehicles cannot spin entirely like a frisbee – the hull rotation would be dangerous for the crew inside and unusable for control, so stabilization has to be achieved in other ways.
On the other hand, local vortices (similar to wing edge vortices) can counteract flow disruption: if the disk edge is equipped with special flaps or slits that excite controlled vortices at large angles of attack, these vortices can maintain lift and delay complete disruption. Such approaches have been investigated in the concepts of active circulation local controllability: for example, installing small protrusions or nozzles around the perimeter of the disk that generate vortex filaments for stabilization.
Thus, by combining the Coandă effect (to create global circulation around the disk) and controlled vortices (to dampen vibrations and prevent disruption), it is theoretically possible to achieve stable flow of a disk-shaped apparatus. Roy’s project, which we discussed in detail here, actually uses these principles: numerous plasma microjets over the entire surface create a homogeneous sliding layer of air that sticks to the body and bends around the disk, thus creating a controlled circulation. When the device deviates from the horizontal, the electronics change the distribution of the ion jet, generating the necessary vortices to counteract the tilt and level the position. Interestingly, in an interview, Roy noted that his plasma disk can automatically stabilize against wind gusts precisely because of the actively controlled flows. This demonstrates the effectiveness of the idea – artificially created circulation flows can give a disk-like device stability that would be impossible to achieve passively.
Possibility to create artificial circulation flows
Creating a steady air circulation around the disk is the key to realizing a flying saucer. There are several ways to do this.
Mechanical (reactive) method. Equip the disk with a central fan or turbine that will suck in air from above and eject it under high pressure around the perimeter. This jet is directed along the lower or upper surface (or split into both) and bends around the disk due to the Coandă effect. This is how it is realized in Avrocar (central turbo-jet and peripheral nozzle) and earlier Coandă concepts. The problem is a very high requirement for engine power because to hold the device, you have to drive a huge mass of air through the system. In addition, mechanical turbines have inertia and do not provide instantaneous mode changes, which makes dynamic stabilization difficult.
Aerodynamic method (passive circulation). Give the disk itself a shape that would naturally support circulation. For example, the upper surface is domed, and the edge has a curved profile that helps to create a rarefaction zone. If you calculate the center of mass and shape correctly, the disk, when sliding forward, can itself draw in the flow from above and deflect it down the sides, creating circulation like a wing. However, passive circulation will be very sensitive to the flight mode and load – it is unlikely that the disk will remain stable in different conditions (wind, maneuvering, etc.) without active elements.
Energy (plasma) method. As in Roy’s project, an electric discharge accelerates the air along the surface. Plasma acoustors (dielectric barrier discharge, DBD) can, roughly speaking, “force” the boundary layer of air to flow along the surface even when a breakdown would normally occur. This creates an artificial flow that is independent of the incoming flow. For small devices, this method works, but its scalability is limited: plasma devices are effective at low speeds, and the force density they generate is still small. However, the advantages are the ultra-fast response (microseconds) and the complete absence of mechanics. Many such microjets can be synchronized, creating the desired circulation with millimeter precision.
Vortex engines. This is a more exotic way: use the principle of a vortex chamber to spin the air inside the disk to a toroidal vortex, which will partially escape from the holes to the outside. For example, the well-known experimental device Repulsine (invented by Victor Schauberger) generated a strong vortex that, according to some claims, could lighten the weight of an object. Although anti-gravity properties are more the domain of pseudoscience, the very principle of releasing powerful vortex rings can provide lifting power and an interesting effect. The vortex rings fired downward push the device upward (the jet principle) and at the same time stabilize it like a gyroscope.
Current research is combining these methods. For example, ADIFO uses mechanical screws for VTOL and jets for propulsion, combining them to provide control. Another mix can be imagined: a disk with small fan sectors around the circumference, each of which can independently change thrust and create local circulation. Thus, the control system would have “rudder elements”. In general, artificial circulation is the heart of a flying disk, and theoretically, with sufficient energy and control system performance, it can ensure stable flight.
Theoretically, a disk-shaped apparatus can be stabilized using active flow control, such as the Coandă effect, artificially created vortices, differential thrust, or plasma jets. But putting these ideas into practice requires advanced technologies that have not yet been fully developed. Are there any modern technologies that can help make flying saucers a reality? In the next text of the series, we will see what engineering solutions can be used to create a real UFO.
