Definition: The process of launching an aircraft from the surface into the air for the purpose of controlled flight.
Significance: Takeoffs are necessary because all aircraft must become airborne safely. Their challenge lies in how quickly takeoffs occur under widely varied conditions.
Early History
Every flight begins with a takeoff. Takeoffs come in a variety of styles, and to the untrained, they seem simpler than they truly are. The takeoff presented the greatest challenge to early aviators in their design of controllable airplanes. Unsuccessful takeoffs held little evidence of their causes, because any one of numerous details, from poor planning to faulty design, could ruin a takeoff. Aviators had not amassed a database of accident reports from which they could glean knowledge, and they did not have the experience or insight to pinpoint the problem or sequence of problems causing each failed takeoff. Successful takeoffs require the right combination of aircraft design, favorable conditions, and skillful piloting. Takeoffs also require power. Early aviators such as Otto Lilienthal and Orville and Wilbur Wright first built hand- or foot-launched gliders that required only sufficient wind and downward-sloping terrain. Later, when the Wrights made a gasoline engine for their Flyer, they faced the same challenges that had kept Samuel Pierpont Langley from success. Because early engines were underpowered, takeoffs demanded much room and planning.
The Wright brothers, for example, launched their Flyer not from a field or a runway, but from a monorail track laid in a slight depression. They depended entirely on the engine to provide power for takeoff. The Wrights later supplemented their engine’s meager takeoff power with a weighted catapult that required several men to raise and set. Within a decade, engine power began to grow, and by 1910, the Wrights had abandoned their monorail-takeoff system, allowing wheels to reduce the drag and absorb the stresses of railless launches. The Wrights also sought greater engine power to accelerate the Flyer’s mass and drag to the point that aerodynamic lift overcame gravity.
Takeoff Techniques
Although engine power for takeoff has increased dramatically since the time of the Wright brothers, takeoffs still need planning. The fixed wings of airplanes use airflow to produce lift, and power builds forward momentum to achieve flying speed. After the plane reaches flying speed, the pilot uses training and skill to leave the runway and enter the sky at the correct speeds, pitch attitudes, and recommended power settings. Simple airplanes have simple procedures: The pilot must point the nose skyward and maintain full power. More complex airplanes have different considerations. Complex airplanes require a specific time or height above the surface to make the first power change. Some engines have limits on the amount of time full power may be maintained, as pressures within the engine become very high. In the United States, the Federal Aviation Administration (FAA) certifies airplane engines with slight tolerance to over-boost. Necessary for takeoff, over boost allows pilots to run the engine at very high power settings for a specified amount of time, after which the pilot must reduce the power to the recommended setting, usually called maximum except takeoff (METO), and maintain a prudent airspeed. Pilots may choose between three basic takeoff techniques, normal, short-field, and soft-field takeoffs. Their use depends on both the circumstances and the pilot’s decision.
Takeoffs and Noise Pollution
In response to complaints by those who live near airports about the noise that takeoffs can generate, many airports in the late twentieth century adopted noise-abatement procedures to reduce noise pollution. Most airport noise is a by-product of takeoffs, and noise pollution remains one of the public’s strongest objections to airports. Since the 1980′s, this issue has been an expensive one for airports, as airports across the United States have been forced to buy nearby homes or to pay for expensive soundproofing to minimize the intrusion of noisy airplanes taking off.
After a taxiing plane has reached flight speed, the pilot must judge speed, pitch attitude, and power settings for a successful takeoff. (NASA)
Normal Takeoffs
Pilots use a normal takeoff when there is no need to employ either of the other two types of takeoff. For a normal takeoff, the runway length must pose no challenge, its surface must be firm and dry, and no appreciable obstructions should interfere with the airplane’s climb path. Although normal takeoffs may seem routine to the observer, they require much skill on the part of the pilot. All takeoffs must be carefully planned. Normal takeoffs call for pilots to make certain there is no conflicting airplane traffic, to taxi onto the runway with the wing flaps properly set, and to apply takeoff power. At the right airspeed, the pilot raises the nose and allows the airplane to fly smoothly off the runway while making small adjustments to the pitch attitude to maintain the best rate-of-climb airspeed.
Short-Field Takeoffs
When pilots have a less-than-normal amount of runway available, they use a short-field takeoff technique. Details vary with airplane type, but pilots have basic techniques upon which they rely. The first involves using the aircraft’s short-field takeoff charts to determine the minimum runway distance required by current conditions. These include wind direction and speed, air temperature, the airplane’s weight, and the condition of the runway surface. Some takeoff tables or graphs include mention of the runway’s slope or of the presence of tall grass, if the runway is not paved. In any case, aircraft manuals assume that the airplane is properly maintained, that its engine is producing full power as it did when new, and that its exterior is clean and free of drag-producing dents. The charts also assume that the pilot performs the takeoff procedure smoothly and skillfully, exactly as outlined by the manufacturer.
A pilot must use the runway’s full length by taxiing to the very edge of the runway’s end and then carefully aligning the airplane’s nose with the runway’s centerline. As with all takeoffs, the pilot must quickly ensure that engine oil pressure and oil temperature are proper. Holding the airplane stationary by applying and holding the brakes, the pilot adds power until reaching the manufacturer-specified power setting. When the engine sustains that power, the pilot releases the brakes so the airplane accelerates to the airspeed that the pilot determined when planning the takeoff. At that airspeed, the pilot notes how far down the runway the airplane has traveled, analyzes the airplane’s acceleration, how much runway remains, and the airplane’s ability to fly. Once airborne, the pilot raises the nose to a climb angle that results in the exact airspeed that the aircraft manual demands. The pilot maintains that climb angle and airspeed until no obstacles, such as trees, power lines, or buildings, threaten the airplane’s climb path. When safely above any obstacles, the pilot then lowers the airplane’s nose, increasing the airspeed to one that provides a more efficient climb. This efficiency considers engine cooling, flight visibility, and other safety considerations.
Soft-Field Takeoffs
A third takeoff technique, the soft-field takeoff, involves runways that are poorly maintained, strewn with small debris, or are covered with snow or grass, muddy, or otherwise not hard, clean, and dry. Pilots use soft-field takeoffs to reduce the chance of damage to the nose wheel and to allow the airplane to leave the surface at an airspeed lower than that of either normal or short-field takeoffs. Soft-field takeoffs require a well-developed judgment, because soft fields often pose several challenges, some severe, usually at the same time. Unimproved airstrips are common in rural and remote areas, as are livestock and wildlife. Numerous accidents occur yearly in North America when airplanes collide with deer, coyotes, and even cattle, to name just a few wildlife hazards. Information as basic as the runway’s dimensions are easily found for hard-surfaced runways, but these are often mere guesswork for grass and dirt strips. Compared to concrete runways, which are reasonably consistent in firmness along their entire length, soft fields can vary tremendously in a short distance. Grass causes drag, and long grass at unkempt, idle airstrips can retard an airplane enough to prevent takeoff. Grass that is wet from dew or rain is even more of a hindrance. Pilots sometimes cannot define the runway edges at soft fields, because there are no painted markings, nor any contrast between the runway and its surroundings, as there is on concrete or asphalt runways. Even those airstrips that have well-maintained grass and defined edges and are free of wildlife may still have drainage problems that are invisible to pilots. Some or all of an airstrip may have a very porous soil, which quickly drains away water. Another part of the strip might consist of soil that retains water below the surface, into which an airplane’s wheels may sink. The nose wheel-equipped airplane has no advantage over tail wheel-type aircraft in this environment.
A pilot making a soft-field takeoff must handle the flight controls smoothly, because at the low speed and high nose angle demanded by a soft-field takeoff, roughly handled flight controls could force the airplane back onto the runway. Accidents involving the mishandling of the flight controls in such situations have resulted in damage to property and injury to persons. In the United States, applicants for pilot certificates must not only demonstrate as much skill as is practicable during the flight test, but also demonstrate knowledge relating to the various elements of soft-field takeoffs under various conditions. Safe and efficient takeoffs demand good planning and skill.
Takeoff Testing Standards
Because events during takeoffs happen so quickly as to seem automatic, flight instructors must carefully ensure that their students consider takeoffs an extreme low-altitude maneuver requiring good planning. Accident statistics consistently show mishaps occurring during takeoffs and landings. The aviation industry has worked to improve takeoff planning in different ways. In the United States, the Federal Aviation Administration (FAA) took steps in the mid-1990′s to help flight instructors in their teaching by changing their Practical Test Standards requirements for all takeoffs. Applicants for U.S. pilot certificates must, before takeoff, verbally review the available runway assigned for takeoff, stating its length, the distance required for the takeoff, the airspeeds required for the technique to be used, and the departure procedure.
Seaplane Takeoffs
Seaplane takeoffs have their own considerations. Although seaplane operations are statistically less common than landplane operations, they are a vital part of aviation and require specialized knowledge. A landplane’s pitch attitude, or the relationship of the nose to the horizon, is governed by the landing gear and remains constant until the moment a pilot rotates for takeoff. On the water, a seaplane or amphibian will change its pitch attitude with the rising and falling of the water, or of the taxiing speed, or with a shift in airplane loading. Aileron control is more critical in a flying-boat takeoff, because the craft’s fuselage is a single-keel hull, and it rolls left and right just as in flight. Landplanes’ wheels, as do twin floats on some seaplanes, prevent such rolling. Seaplane takeoffs promise excitement as water pounds the hull while the pilot gives full attention to getting the airplane “on the step.” This means that the bottom of the hull or the floats are mostly out of the water as the wings increase their lift, and water pressure on the V-shaped hull or float bottoms releases its suction and allows the seaplane to fly.
Seaplane pilots must watch for boats, buoys, and such, but give extra care to partially or near-fully submerged logs or other obstacles. Even the water itself may become an obstacle, as seaplanes may strike a large wave that sends the craft airborne too soon for it to fly. As the craft settles onto the water again, a second wave may strike the aircraft in such a manner as to engulf the craft’s nose. Over the decades, pilots have shared their experience to amass a pool of knowledge from which pilots may draw.
