[المنتصر]

Straight and Level Flight

If an airplane maintains a given altitude, airspeed, and heading, it is said to be in "straight and level flight." This condition is achieved and maintained by equalizing all opposing forces. Lift must equal weight so the airplane does not climb or descend. Thrust must equal drag so the airplane does not speed up or slow down. The wings are kept level so the airplane does not turn. Any imbalance will result in a change in altitude or airspeed. It is the pilot's responsibility to prevent or correct for such an imbalance.

Proper trim is essential for maintaining this balance. If the pilot, by being "out of trim," is forced to maintain a given amount of stick pressure, the arm holding the stick will eventually tire. But in the short term the pilot must very precisely hold that pressure -- any change will result in a change in attitude. If the airplane is properly trimmed, the correct stick position is held automatically, and no pressure need be exerted.

Obviously, an airplane cannot remain indefinitely in this ideal condition. Due to mission, airspace, and fuel requirements, the pilot must change the airspeed, altitude, and heading from time to time.

Speed

Speeding up and slowing down is not simply a matter of changing the throttle setting (changing the force produced by the engines). Airspeed can also be changed by changing the drag. Many aircraft are equipped with a "speedbrake" for this purpose -- a large ****l plate that can be extended out into the windstream, increasing parasite drag and slowing the airplane.

As an airplane speeds up or slows down, the amount of air passing over the wing follows suit. For instance, to maintain a constant altitude as the airspeed is decreasing, the pilot must compensate for this decreased airflow by changing the AOA (pulling back on the stick) to equalize the amount of lift to the weight of the airplane. All this works nicely until stall speed is reached, when an increase in AOA is met with a decrease in lift, and the airplane, its weight not completely countered by lift, begins to dramatically lose altitude. Conversely, an increase in airspeed must be met with a decrease in the AOA (moving the stick forward) to maintain a constant altitude. As airspeed increases or decreases, trim must be changed as well.

Mach number is the most influential parameter in the determination of range for most jet-powered aircraft. The most efficient cruise conditions occur at a high altitude and at a speed which is just below the start of the transonic drag rise. The drag (and thus the thrust required to maintain constant Mach number) will change as the weight of the airplane changes. The angle of attack (and thus the drag) of an airplane will become slightly lower as fuel is used since the airplane is becoming lighter and less lift is required to hold it up.

Climb

Climbs and descents are accomplished by using power setting respectively higher or lower than that required for level flight. When an airplane is in level flight, just reducing the power begins descent. Instead of pulling back on the stick to maintain altitude as the airspeed slows, the pilot keeps the stick neutral or pushes it forward slightly to establish a descent. Gravity will provide the force lost by the reduction in power. Likewise, increased power results in a climb.

Airspeed can be controlled in a climb or descent without changing the throttle setting. By pulling back on the stick and increasing the climb rate or by decreasing the descent rate, the airspeed can be decreased. Likewise, lowering the nose by pushing forward on the stick will effectively increase the airspeed. In most climbs and descents, this is the way airspeed is maintained. A constant throttle setting is used and the pilot changes pitch in small increments to control airspeed.

If the pilot were to fly a climb such that the airplane was at the best-climb speed as it passed through each altitude, it would be achieving the best possible rate of climb for the entire climb. This is known as the "best-climb schedule" and is identified by the dotted line.

Flying the best-climb schedule will allow the airplane to reach any desired altitude in the minimum amount of time. This is a very important parameter for an interceptor attempting to engage an incoming enemy aircraft. For an aircraft that is equipped with an afterburner, two best climb schedules are determined; one for a Maximum Power climb (afterburner operating) and one for a Military Power climb (engine at maximum RPM but afterburner not operating). The Max Power climb will result in the shortest time but will use a lot of fuel and thus will be more useful if the enemy aircraft is quite close. The Mil. Power climb will take longer but will allow the interceptor to cruise some distance away from home base to make the intercept.

For cargo or passenger aircraft the power setting for best climb is usually the maximum continuous power allowed for the engines. By flying the best-climb schedule the airplane will reach it's cruise altitude in the most efficient manner, that is, with the largest quantity of fuel remaining for cruise.

Range

One of the most critical characteristics of an airplane is its range capability, that is, the distance that it can fly before running out of fuel. Range is also one of the most difficult features to predict before flight since it is affected by many aspects of the airplane/engine combination. Some of the things that influence range are very subtle, such as poor seals on cooling doors or small pockets of disturbed air around the engine inlets.

Turns

The aerodynamics of a turn widely misunderstood, since many people think that the airplane is "steered" by the stick or the rudder pedals (probably the result of thinking of the airplane as a sort of "flying car.") A turn is actually the result of a change in the direction of the lift vector produced by the wings.

A pilot turns an airplane by using the ailerons and coordinated rudder to roll to a desired bank angle. As soon as there is bank, the force produced by the wings (lift) is no longer straight up, opposing the weight. It is now "tilted" from vertical so that part of it is pulling the airplane in the direction of the bank. It is this part of the lift vector that causes the turn. Once the pilot has established the desired bank angle, the rudder and the aileron are neutralized so that the bank remains constant.

When part of the lift vector is used for turning the airplane, there is less lift in the vertical opposing weight. If the pilot were to establish a bank angle without increasing the total amount of lift being produced, the lift opposing the weight would decrease, and the resulting imbalance would cause in a descent. The pilot compensates by pulling back on the stick (increasing the AOA and therefore lift). By increasing the total lift, the lift opposing the weight can balance out the weight and control level flight. This increase in total lift also increases lift in the turn direction and results in a faster turn.