Guest Commentary

UFO Recognition – Part 1

By Bill Hamilton (

(some of the material on aerodynamics and aircraft stress is pieced together from material found on the WWW)

I thought I would start a discussion on UFO recognition in order to better assess sighting and sighting reports and yield more information from field investigators so that we may further validate a genuine phenomenon that will attract more interest from the scientific community and apply more political pressure to obtain more research monies.  I, for one, would like to see a network of skywatch stations established at strategic locations throughout the world.

Flying aircraft of various types have certain characteristics that distinguish them and allow for identification as aircraft.  All conventional aircraft depend on aerodynamics, a branch of fluid mechanics that deals with the motion of air other gaseous fluids, and with forces acting on bodies in motion relative to such fluids.  Aircraft move through air in a fairly uniform linear path at a fairly uniform speed until they turn, dive, or roll as they do in airshows.

One of the fundamental forces studied in aerodynamics is lift, or the force that keeps an airplane in the air.  Airplanes fly because they push air down.  The leading edge of an airplane wing is higher than the trailing edge.  All aircraft have wings or lifting bodies or rotating blades as their lift depends on them.  UFOs may not have wings and may even have some unaerodynamic configuration.  Lift is often explained using Bernoulli’s principle, which relates an increase in the velocity of a flow of fluid (such as air) to a decrease in pressure and vice versa.  The air pressure on the upper side of an airplane wing is lower than that on the lower side giving a resultant net force upward.

Another important aspect of aerodynamics is the drag, or resistance, acting on solid bodies moving through air. The thrust force developed by either the jet engine or the propellers, for example, must overcome the drag forces exerted by the air flowing over the airplane. Streamlining the body can significantly reduce these drag forces. For bodies that are not fully streamlined, the drag force increases approximately with the square of the speed as they move rapidly through the air. The power required, for example, to drive an automobile steadily at medium or high speeds is primarily absorbed in overcoming air resistance.

Supersonics, an important branch of aerodynamics, concerns phenomena that arise when the velocity of a solid body exceeds the speed of sound in the medium, usually air, in which it is traveling. The speed of sound in the atmosphere varies with humidity, temperature, and pressure. Because the speed of sound, being thus variable, is a critical factor in aerodynamic equations, a so-called Mach number, named after the Austrian physicist and philosopher Ernst Mach, who pioneered the study of ballistics, represents it. The Mach number is the speed of the projectile or aircraft with reference to the ambient atmosphere, divided by the speed of sound in the same medium and under the same conditions. Thus at sea level, under standard conditions of humidity and temperature, a speed of about 1220 km/h (about 760 mph) represents a Mach number of one, that is, M-1. The same speed in the stratosphere, because of differences in density, pressure, and temperature, would correspond to a Mach number of M-1.16. By designating speeds by Mach number, rather than by kilometers or miles per hour, a more accurate representation of the actual conditions encountered in flight can be obtained.

Another factor, long known to rocket designers, is the direct influence of ambient atmospheric pressures on the efficiency of the flight of planes in supersonic speed ranges. That is, the closer the surrounding medium is to a perfect vacuum, the more efficient is the power plant of the plane. Reducing the area, or cross section, displacing atmosphere, can also increase the range of the supersonic plane. Increasing the weight by increasing the length, but at the same time making the plane more slender and equipping it with a needle nose, are necessary features of design for planes operating in the supersonic range in the atmosphere.

Generally, UFOs seem to bend the rules when it comes to aerodynamics.  The maneuverability of discs seen in flight is such that the UFO accelerates so quickly that it seems to overcome any forces of drag that would retard its movement.  Discs have been seen to make 90-degree turns instantly, and in some rare cases, instantly reverse their direction of travel.  When accelerating to speeds estimated to be supersonic, no shock wave seems to be generated and no sonic boom is heard.  Some maneuvers accomplished by UFOs would place extraordinary stress on the airframe if flying like conventional aircraft.  Coming in contact with the surrounding atmosphere at high rates of acceleration would challenge the structural integrity of the vehicle, would induce enormous drag and heat the skin of the craft to glowing temperatures, but perhaps the UFO does not come into direct contact with the atmosphere, but actually repels the atmospheric boundary layer surrounding its form.  This would account for how they can move quickly without encountering air resistance and thermal stress.

Structural integrity is a major factor in aircraft design and construction. No production airplane leaves the ground before undergoing extensive analysis of how it will fly, the stresses it will tolerate and its maximum safe capability.

Every airplane is subject to structural stress. Stress acts on an airplane whether on the ground or in flight. Stress is defined as a load applied to a unit area of material. Stress produces a deflection or deformation in the material called strain. Stress is always accompanied by strain.

Current production general aviation aircraft are constructed of various materials, the primary being aluminum alloys. Rivets, bolts, screws and special bonding adhesives are used to hold the sheet metal in place. Regardless of the method of attachment of the material, every part of the fuselage must carry a load, or resist a stress placed on it. Design of interior supporting and forming pieces, and the outside metal skin all have a role to play in assuring an overall safe structure capable of withstanding expected loads and stresses.

Engineers carefully calculate the stress a particular part must withstand. Also, the material a part is made from is extremely important and is selected by designers based on its known properties. Aluminum alloy is the primary material for the exterior skin on modern aircraft. This material possesses a good strength to weight ratio, is easy to form, resists corrosion, and is relatively inexpensive.

Fittings must be made of carefully selected materials because of their importance of holding the aircraft together under expected stress and loading. The same holds true for important fasteners such as bolts and rivets. It is essential that these parts not fail under stress. It is also essential that these parts not weaken with exposure to stress and weather elements.

UFOS have been observed that seem to have seamless, rivetless hulls which could give such a craft high structural integrity. Corrosion is also a consideration. A fitting made of one metal cannot be secured to the structure with a bolt or fastener made of another metal. This situation may result in "dissimilar metal corrosion" over a period of time and result in a weakening of the assembly to the extent that the assembly is rendered unsafe.

Types Of Structural Stress
The five basic structural stresses to which aircraft are subject are:
1.  Tension
2.  Compression
3.  Torsion
4.  Shear
5.  Bending

While there are many other ways to describe the actual stresses, which an aircraft undergoes in normal (or abnormal) operation, they are special arrangements of these basic ones.

"Tension" is the stress acting against another force that is trying to pull something apart. For example, while in straight and level flight the engine power and propeller are pulling the airplane forward. The wings, tail section and fuselage, however, resist that movement because of the airflow around them. The result is a stretching effect on the airframe. Bracing wires in an aircraft are usually in tension.

"Compression" is a squeezing or crushing force that tries to make parts smaller. Anti-compression design resists an inward or crushing force applied to a piece or assembly. Aircraft wings are subjected to compression stresses. The ability of a material to meet compression requirements is measured in pounds per square inch (psi).

"Torsion" is a twisting force. Because aluminum is used almost exclusively for the outside, and, to a large extent, inside fabrication of parts and covering, its tensile strength (capability of being stretched) under torsion is very important. Tensile strength refers to the measure of strength in pounds per square inch (psi) of the metal. Torque (also a twisting force) works against torsion. The torsional strength of a material is its ability to resist torque. While in flight, the engine power and propeller twist the forward fuselage. The force, however, is resisted by the assemblies of the fuselage. The airframe is subjected to variable torsional stresses during turns and other maneuvers.

"Shear" stress tends to slide one piece of material over another. Consider the aircraft fuselage. The aluminum skin panels are riveted to one another. Shear forces try to make the rivets fail under flight loads; therefore, selection of rivets with adequate shear resistance is critical. Bolts and other fasteners are often loaded in shear, an example being bolts that fasten the wing to the spar or carry-through structure. Although other forces may also be present, shear forces try to rip the bolt in two. Generally, shear strength is less than tensile or compressive strength in a particular material.

"Bending" is a combination of two forces, compression and tension. During bending stress, the material on the inside of the bend is compressed and the outside material is stretched in tension. An example of this is the G-loading an airplane structure experiences during maneuvering. During an abrupt pull-up, the airplane's wing spars, wing skin and fuselage undergo positive loading and the upper surfaces are subject to compression, while the lower wing skin experiences tension loads. There are many other areas of the airframe structure that experience bending forces during normal flight.

An airplane structure in flight is subjected to many and varying stresses due to the varying loads that may be imposed. The designer's problem is trying to anticipate the possible stresses that the structure will have to endure, and to build it sufficiently strong to withstand these. The problem is complicated by the fact that an airplane structure must be light as well as strong. The manufacturer states upon certification that the design meets or exceeds all FAR requirements for the category of aircraft being produced. However, hard landings, gust loads caused by extreme turbulence, performing aerobatic maneuvers in a non-aerobatic airplane, etc,. can affect the airworthiness of one or more major airframe assemblies to the extent that the airplane is no longer airworthy. This reiterates the necessity of operating the aircraft within the limitations outlined by the manufacturer. Every flight imposes loads and stresses on the aircraft. How carefully it is flown, therefore, will have an effect on the service life of its assemblies.

It is the UFO’s ability to withstand or defy the normal loads and stresses of our conventional aircraft that allows them to fly in such erratic modes as zigzag flight, instantaneous decelerations, and instantaneous accelerations.  The type of flight pattern makes a UFO stand out from the aerobatic performances of conventional aircraft. This is only a small part of a subject that could fill a textbook.  It is by capturing these details of UFO flight dynamics for the record that adds weight to the evidence that unconventional flying objects have been cavorting around the earth for decades.

Please feel free to add to this discussion.


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