Certain things to consider when flying and more importantly making an autogyro are the physics of the environment that it will be run in. Numerous forces play an integral role in the movement, and must be taken into account when deciding which parts will be used where. Weight, drag, thrust, rotor drag, airspeed, and rotor lift are all part of the vector forces.

Free-body diagram showing all forces.

Picture courtesy of huizen.dds.nl/~w-p/bookaut

Weight is essentially the force that keeps us on the ground. More specifically, it is our actual mass multiplied by the acceleration of the earth. This is known as a Newton, or a measure of weight. Keep in mind that this is not how massive something is, it is the force being applied on the object. This force keeping us on the ground consequently is the reason that we build flying contraptions in the first place. In the aerospace field, weight is generally a word that is frowned upon. This isn't so much that it keeps us on the ground, but for the fact that added weight usually causes more added weight. For example, if you want to put more of a load, you might need stronger supports, and a more powerful engine, both which cause more weight. Sometimes, you can even more your aircraft stronger and more resistant to stress by removing everything you don't need.

Because weight is such a drag (pun intended), we need something to counteract it and create a force to keep the aircraft in the air. This force is called lift. Lift is caused by the downward deflection of air and is always perpendicular to the flow of the air stream. As discussed earlier, lift in the case of an autogyro is caused by a rotating wing deflecting the air downward.

Drag forces due to blade movement.

Picture courtesy of huizen.dds.nl/~w-p/bookaut

Alas, we have reached drag. In anything moving, whether in the x or y-axis where there is a medium involved, there will be drag. Drag isn't necessarily bad if you look at it in the right perspective, it is just something that we all must live with. Think of drag more as a limiter than an overall negative thing. Because the rotor is tilted back, in order for air to pass through the blades and create lift, it has two components of lift, a lift in the y direction, and a lift in the x direction. This x directional lift is known as induced drag. Induced drag has nothing to do with the viscosity, or "stickiness" of the air and purely to do with the vector forces involved.

The drag that is caused by viscosity is caused profile drag. I put quotation marks around stickiness to show that the air isn't really sticky; it just holds a profile around the object passing through it. Take an object dipped in water for example. The water itself isn't sticky, but it holds a very thin layer around the object that is dipped in it. It works similarly for profile drag.

Another form of drag is called aesthetic drag. This drag was named such because it has been found that ugly looking parts generally aren't aerodynamic and therefore create a blunt drag force on the object. There is a joke theory that physicists use pertaining to aesthetic drag. The theory is that if someone were to make the front end of an object so incredibly ugly and un-aerodynamic, no air molecule with fashion sense would want to touch it, creating a vacuum which actually pulls the machine forward. Negative drag! Experiments have shown conclusively however, that this negative aestheticism extends throughout the machine, not remaining just in the front, thereby eliminating anyone to want to fly it.

Thrust is the final and perhaps one of the most important forces in the system. Enough thrust allows you to overcome drag and therefore produce a net motion of forward, and therefore climb. The thrust in an autogyro system is different than that of a fixed-wing aircraft in that it is not always wise to give more or full power to correct an emergency situation. Often decreasing your thrust will produce a higher rotor speed. This has to do with the angle that the rotor hits the air. When you decrease thrust, the tail end of the gyro tends to dip down, making the rotor tilt back giving more air to hit the blades, and thereby increasing the rotor speed. In contrast, it would be wise to pull the stick back a bit when increasing thrust.