Visual flight

See also Visual_Flight_-_airplanes.

Visual flight in any type of aircraft relies on similar principles.

Visual flight or "Visual Attitude Flyng" is a method of controlling an aircraft where the aircraft attitude is determined by observing outside visual references.

The primary visual reference used is usually the appearance of the natural horizon or the ratio of visible sky to ground, when the pilot is looking straight ahead.

The pilot can maintain or change the airspeed, altitude, and direction of flight (heading) as well as the rate of climb or descent and rate of turn (bank angle) through the use of the aircraft flight controls (and aircraft engine controls if a powered aircraft) to adjust the "sight picture". Some reference to flight instruments is usually necessary to determine exact airspeed, altitude, heading, bank angle and rate of climb/descent. When flying unpowered aircraft such as gliders or hang gliders, the pilot does not usually need to know the exact airpseed and altitude, and minimal or no instrumentation may be used. Visual, auditory and kinesthetic cues provide suprisingly accurate feedback to the experienced pilot.

There are 3 components to the aircraft's attitude. They are pitch, roll and yaw.

• Pitch can be seen as the ratio of visible sky to ground. The exact ratio of sky to ground will vary from one aircraft type to another. A typical ratio might be 2/3 ground and 1/3 sky when the aircraft is in the cruise attitude
  • Increasing the pitch attitude (nose up) (more sky than ground visible)
    • Airspeed will decrease
    • Altitude will increase
    • Rate of climb will increase (or rate of descent will decrease)
    • Load factor will increase
  • Decreasing the pitch attitude (nose down) (more ground than sky visible)
    • Airspeed will increase
    • Altitude will decrease
    • Rate of descent will increase (or rate of climb will decrease)
    • Load factor will decrease
• Roll or bank can be seen as how much the pilot perceives a tilt of the aircraft's wings or nose to the horizon. The tilt or bank angle usually ranges from 0 to about 30 degrees. Bank angles up to 80 degrees are used in military fighter jets. Light aircraft and transport category aircraft usually use maximum bank angles of 25-30 degrees. Glider and hang glider pilots will commonly use bank angles of up to 45 to 60 degrees.
  • Changing the bank attitude directly affects :
    • Bank Angle
    • Rate of Turn
    • Load factor
• When the bank angle increases past about 25-30 degrees, secondary effects oocur :
  • Airspeed - will decrease as the bank angle is increased
  • Pitch attitude - will decrease (nose down) as a result of the decreasing airpspeed
  • Altitude - will decrease as a result of the decreased (nose down) pitch attitude
• If a constant altitude / constant airspeed turn is desired, the pilot compensates for the secondary effects by
  • increasing the power setting - to maintain airspeed
    • In an unpowered aircraft it may not be possible to maintain altitude while turning unless the aircraft is in a natural source of lift, such as thermal, ridge or wave. (See also soaring).
  • increasing pitch attitude.
• Yaw refers to the direction in which the nose of the aircraft is pointing. It is seen as a horizontal movement of the nose across the horizon. It is possible for the nose of the aircraft to be pointing in a direction different than which the aircraft is moving ! A pilot can deliberately mis-align the nose of the aircraft with the direction of flight in order to produce a slipping attitude. This is normally used to increase aerodynamic drag and is commonly used when it is desired to increase the rate of descent, without increasing the airspeed. The result of the slipping attitude is that the aircraft "slides" sideways and downwards instead of flying cleanly downwards, and therefore the airspeed does not increase as it normally would when a decrease in pitch attitude (nose down) is applied.

Depending on the aircraft type, the sight picture will vary, but in general the principles are the same regardless of type. For example, if a pilot's sight is completely filled with ground, with no sky visible, this would indicate an extremely nose-down attitude and a corresponding rapid rate of descent. An obvious exception would be in a mountainous region, which in this case could indicate the aircraft is in level cruise flight, but possibly in danger of impacting the terrain ! If the pilot can see only sky, a nose-high attitude is indicated. In either of these cases, the horizon would not be visible, and would be one of the first indications that the aircraft is in an unusual flight attitude.

Cruise attitude

An aircraft is usually designed so that the "horizon/nose sight picture" that the pilot sees in cruising flight is similar to that seen when the aircraft is on the ground. This will also usually coincide with a "level" attitude. In cruise flight, a powered aircraft maintains a constant airspeed and altitude, which is the result of a constant pitch attitude and aircraft power setting. For unpowered aircraft, there will usually be minimum sink and maximum glide speeds, either of which the pilot may choose depending on the flight situation. Soaring and gliding pilots also rely on a principle called speed to fly, when transiting between natural sources of lift, to maximize the overall efficiency and average speed of the flight.

When a pilot is undergoing flight training, the cruise attitude is usually one of the first things that they will learn. The sight picture associated with cruise flight, will include the horizon and a combination of sky and ground. Using this reference attitude makes it easier to recognize the other attitudes of flight.

Climb attitude

To make an aircraft climb, i.e. gain altitude, the pilot will raise the nose higher than it is in the cruise attitude. For many light aircraft, this will correspond to a sight picture where the aircraft nose appears to be on or just slightly above the horizon. The amount of pitch increase will typically not exceed 10-15 degrees.

If the pilot does not increase the engine power (in a powered aircraft), the airspeed will decrease. The amount of decrease will depend how much the pitch atittude was increased, and the amount of excess airspeed (over the stall speed) that the aircarf has. When flying light aircraft, power is usually increased to full for any extended climb.

Even if excess kinetic energy (speed) is available, the airspeed will still decrease if the pitch attitude is increased beyond a certain point. The amount that the airpseed decreases with increasing pitch attitude (nose up) is aircraft type dependent. Usually the pilot will not increase the pitch-attitude beyond appoximately 30 degrees "nose-up", or 10 degrees "nose down", for most normal flight maneouvers.

Descent attitude

To make an aircraft descend, i.e. lose altitude, the pilot will lower the nose lower than it was in the cruise attitude. For many light aircraft, this will correspond to a sight picture where the aircraft nose appears to be slightly below the horizon. The actual amount of down movement usually will not exceed about 10 degrees for most normal descents. Decreasing the pitch-attitude will result in an in increase in airpseed. The amount of increase will depend on how much the nose was lowered compared to the cruise attitude. When flying [light aircraft], power usually is decreased to around 2/3 full for a cruise descent.

Even if power is decreased (in a powered aircraft), the airspeed will still increase if the pitch attitude is decreased (nose down) beyond a certain point. The amount that the airpseed increases with decreasing pitch attitude '(nose down)' is type dependent, and is usually drectly related to how aerodynamically clean the aircraft is. If the airspeed is allowed to increase to or past Vne structural damage can occur.

Takeoff attitude

The takeoff attitude is similar to and for some aircraft, identical to a cruise climb attitude. Takeoff speed is usually around 1.3 times Vso (stall speed). The actual airspeed will vary directly with the aircraft's wing loading. Glider and hang gliders rely either on winch towing or aerotowing to become airborne. Hang gliders also self launch from the sides of ridges or other elevated areas.

Landing attitude

The landing attitude has 3 actual "sub attitudes" :

Descent

The descent during the final leg is typically flown at 1.3 times the stall speed of the aircraft. This speed provides a good compromise between flight at the lowest possible airspeed, while allowing for turbulence and wind shear. "Airline" (transport) type aircraft, are flown on a 3 degree slope or glidepath. Smaller light aircraft, and unpowered aircraft will typically be flown on a 4 to 6 degree glidepath. Typical power settings are 3/4 full power. The rate of descent typically ranges from approximately 300 feet per minute for light aircraft to 700 f.p.m. for transport category.

Roundout

Contacting the runway with a 300 f.p.m. descent rate will be extremely uncomfortable and can cause damage to both the aircraft and the pilot/passengers. For that reason, the aircraft will be put into a roundout attitude shortly before it would otherwise contact the ground. The attitude is similar to the cruise attitude and is accomplished by the pilot increasing the pitch attitude (raising the nose) at approximately ten to fifty feet above the ground, depending on the aircraft type. Larger, heavier aircraft will be put into the roundout attitude at higher heights than smaller lighter aircraft.

Flare

The final attitude is the flare which is basically a continuation of the roundout attitude to a slight climb attitude. The objective is to descend at the minimum descent rate and lowest possible forward speed. When performed correctly the aircraft will gently contact the ground at a descent rate of 100 f.p.m. or less.