• Take-off considerations

    The take-off sequence in a light aircraft is the most critical of all normal flight procedures. All the engine’s available performance must be employed during the acceleration and initial climb — leaving no power in reserve — and there is no potential energy of excess height or excess momentum available. Thus, during take-off, the pilot’s options are extremely limited.

    Prior to take-off, it is essential to check the aircraft, airfield and atmospheric conditions to determine if take-off can be undertaken safely, how the take-off and climb-out will be conducted and to have a predetermined emergency plan.

    (For pre-take-off communication procedures see ‘Radiotelephony communications and procedures‘) Continue reading  Post ID 364


  • Weight and balance

    There are fixed limits to the payload an individual aircraft may safely carry. The payload is the total weight of pilot and passenger, fuel, baggage and portable equipment; i.e. it is the difference between the empty weight of the aircraft and its gross weight at take-off. That load must always be distributed so that the aircraft’s balance — the position of the aircraft’s centre of gravity — is maintained within defined longitudinal limits otherwise very dangerous instability conditions will exist.

     

    Continue reading  Post ID 364


  • Tail assemby surfaces

    We discussed the control surfaces that form part of the wing structure in the ailerons and flaps sections of the ‘Aerofoil and wings’ module. In this module we will look at the stabilising and control surfaces that form the tail assembly. But we first need to consider the basic structure of the usual three-axis very light aeroplane — we will look at ‘trikes’ and powered parachutes in the weight-shift control module.

    Continue reading  Post ID 364


  • Engine and propeller performance

    Engine power is the product of torque and engine speed. Two-stroke engines favour engine speed to produce the power and are very inefficient at other than high rpm; four-stroke engines use lower rpm and higher torque. The efficiency of normally aspirated engines decreases with altitude — but turbocharging helps considerably.

    The propeller converts engine power into an aerodynamic force. The portion of the force acting forward is the thrust power, and the portion acting in the plane of rotation is the propeller torque. In unaccelerated level flight, the propeller torque balances the engine torque while thrust balances the aircraft’s aerodynamic drag. The thrust conversion efficiency depends on the propeller configuration and aircraft speed. The simple fixed-pitch configuration is inefficient at most speeds. The variable-pitch, constant-speed propeller is reasonably efficient at most speeds. Continue reading  Post ID 364


  • Aerofoils and wings

    The lift force is generated by a small pressure differential between the upper and lower surfaces of the wing, caused by the aerodynamic reaction to the wing motion through the atmosphere. The magnitude of the pressure differential, and the consequent momentum applied to the airflow, is generally dependent on the speed of the aircraft, the angle of attack and the physical characteristics of the wing. The wing centre of pressure moves fore and aft in response to changes in the aerodynamic reaction, thereby introducing pitching moments that affect the aircraft’s trim. Drag induced by the generation of lift is modified by the plan form, the twist and the aspect ratio of the wing. Ailerons, flaps, and other lift and drag changing devices are fitted to the wing for control and performance purposes.

     

    Continue reading  Post ID 364


  • Airspeed and the properties of air

    Air density — a function of atmospheric pressure and temperature — decreases with increasing height. It affects the generation of lift and aircraft performance, as does the angle of attack at which the aircraft is flown. In normal, unaccelerated flight, there is a relationship between airspeed and angle of attack and, in light aircraft, the airspeed indicator instrument — which measures dynamic pressure — acts as a very limited angle of attack indicator. The minimum flight speeds are a function of aircraft weight, angle of attack and flight loads. The flight loads applied by the pilot are chiefly accomplished by varying angle of attack and engine power. From this comes the need to establish a design manoeuvring flight envelope that defines the boundaries of the maximum allowable pilot-induced and turbulence-induced loads that may be applied to the aircraft structure without risk, together with certain critical airspeeds — plus the range of performance airspeeds available to the pilot.

     

    Continue reading  Post ID 364


  • Aircraft manoeuvring forces

    The performance of an aircraft in the hands of a competent pilot — at a given altitude — results from the sum of power, angle of attack, attitude and configuration. Power provides thrust and consequently contributes to acceleration, airspeed, lift, drag and radius of turn. The angle of attack dictates the dimensions of the lift force and the induced drag and contributes to airspeed; also the angle of attack is a significant contributor to the aircraft attitude. Attitude is the angle the aircraft longitudinal axis subtends above or below the horizon (usually called the ‘pitch’ which has another meaning associated with propellers) plus the angle of bank and the degree of slip. Attitude dictates the direction of the lift, thrust and drag vectors and, consequently, converts power into velocities and accelerations in the three planes. Configuration relates to the deployment of lift/drag changing devices.

     

    Airspeed is dependent on power, angle of attack, configuration and attitude — under any given set of conditions — and attitude in flight is readily checked by reference to the horizon. The lift, thrust and drag forces produce manoeuvring loads on the aircraft structure, generally expressed in terms of ‘g’, that must be kept within defined limits. There is a fourth performance factor — energy management — which is an art that supplements attitude plus power plus height to produce maximum aircraft performance. The epitome of such an art is demonstrated by air-show pilots who produce extraordinary performances from otherwise relatively mundane aircraft. Continue reading  Post ID 364