Basic modes of flight
Steady level flight: Steady flight or equilibrium flight is a special case in flight dynamics where the aircraft's linear and angular velocity are constant in a body-fixed reference frame.Basic aircraft maneuvers such as level flight, climbs and descents, and coordinated turns can be modeled as steady flight maneuvers. Typical aircraft flight consists of a series of steady flight maneuvers connected by brief, accelerated transitions. Because of this, primary applications of steady flight models include aircraft design, assessment of aircraft performance, flight planning, and using steady flight states as the equilibrium conditions around which flight dynamics equations are expanded.
Steady balanced turn including bank angle: When a fixed-wing aircraft is making a turn (changing its direction) the aircraft must roll to a banked position so that its wings are angled towards the desired direction of the turn. When the turn has been completed the aircraft must roll back to the wings-level position in order to resume straight flight. When any moving vehicle is making a turn, it is necessary for the forces acting on the vehicle to add up to a net inward force, to cause centripetal acceleration. In the case of an aircraft making a turn, the force causing centripetal acceleration is the horizontal component of the lift acting on the aircraft.In straight, level flight, the lift acting on the aircraft acts vertically upwards to counteract the weight of the aircraft which acts downwards. During a balanced turn where the angle of bank is θ the lift acts at an angle θ away from the vertical.It is useful to resolve the lift into a vertical component and a horizontal component. If the aircraft is to continue in level flight (i.e. at constant altitude), the vertical component must continue to equal the weight of the aircraft and so the pilot must pull back on the stick a little more. The total (now angled) lift is greater than the weight of the aircraft so the vertical component can equal the weight. The horizontal component is unbalanced, and is thus the net force causing the aircraft to accelerate inward and execute the turn.
Load factor: Load factor is the ratio of the total load supported by the airplane’s wing to the total weight of the airplane. In still air flight, the load on the wing equals the lift it generates. The load factor is expressed in G units. In an unaccelerated level flight the load on the wings is equal to lift and to the weight. Consequently, the load factor equals 1G. If Lift = Weight then Lift /Weight = 1G. The load factor may be Positive or Negative.
Positive Load Factor - During normal flight, the load factor is 1 G or greater than 1 G. Whenever the load factor is one or greater the load factor is defined as positive.
Negative Load Factor - Under certain conditions, an abrupt deviation from the airplane's equilibrium can cause an inertial acceleration that in turn will cause the weight to become greater than the lift. For example, during a stall, the load factor may be reduced towards zero. This will cause the pilot to feel "weightless". A sudden and forceful elevator control movement forward can cause the load factor to move into a negative region.
Flight Envelope: In aerodynamics, the flight envelope, service envelope, or performance envelope of an aircraft refers to the capabilities of a design in terms of airspeed and load factor or altitude.When an aeroplane is pushed, for instance by diving it at high speeds, to the point it exceeds a published limitation, it is said to be flown "outside the envelope", something considered rather dangerous.
