Control harmonisation

For an aircraft to be comfortable and easy to fly, all of the primary control actions should require roughly the same amount of effort to operate them. The correct harmonisation of controls is often difficult to achieve with manual controls, but with the powered systems they can normally be tuned with precision.

Engine control

The power output of an aircraft piston engine is controlled in much the same way as a road vehicle engine, by means of a throttle, which varies the amount of air/fuel mixture admitted to the engine. A mixture control lever is used to give a rich fuel/air mixture for an extra, but inefficient boost of power for take­off and to adjust for air density changes.

In addition, most propeller-driven aircraft are fitted with an rpm control lever, which is used to set the propeller, and hence, engine speed.

On turbocharged engines, a means of varying the boost pressure may be provided, although in some installations, the process is automatically controlled.

The correct setting of the various controls depends on the chosen flight plan, and a good pilot will work out the best settings for each stage before take-off.

It is important to note that on a reciprocating engine, the rate of fuel con­sumption depends mainly on the power output. The pilot’s primary control of the power is by means of the throttle lever.

In gas-turbine systems, the primary engine control operated by the pilot is the fuel flow control. This serves a similar purpose to the throttle on a piston engine, except that in the gas turbine, it controls the thrust produced. The thrust and engine speed of a gas-turbine system cannot be separately varied to any significant extent, and any movable vanes, nozzles or surfaces are primarily used to fine-tune the operation of various components.

On more complex gas-turbine systems, with adjustable nozzles and multiple spools, there are many variables to control and monitor, and some form of automatic engine management control system is necessary. The pilot’s primary input is still via a single lever (or set of levers in a multi-engined installation). Further controls are required for reversed thrust, and reheat, where fitted. A host of minor controls can also be found, depending on the particular aircraft type. In the turbo-prop, there is also a means of selecting the propeller rpm.

For the pilot, the most obvious difference between a piston engine and a turbo-jet installation is the lack of torque reaction, and the relatively slow throttle response of the turbine. Changes in thrust and speed have to be anticipated much more carefully in the latter case. The lack of propeller drag braking effect can also make jet-propelled aircraft more difficult to handle.

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