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Airplanes designed to be trainers have a high wing for one simple reason - stability
When choosing between model rc airplanes, wing shape (aerofoil) is another factor to consider. There are basically 3 types - flat bottomed, semi-symmetrical and symmetrical.
An airplane with a flat wing section will have the most lift at the slowest airspeed - obviously good for the beginner.
A symmetrical aerofoil provides equal amounts of lift regardless of whether the plane is right-side up or upside down - perfect for aerobatics.
An airplane with a semi-symmetrical aerofoil holds advantages of both flat and symmetrical, so is ideal for the 'sport' flyer.
Rarely will a trainer be of a symmetrical aerofoil; the most common will be flat bottomed.
Dihedral is the upward 'V' angle of the wings from the fuselage, looking at the plane from the front.
Greater dihedral increases the airplane's stability, as it will naturally want to center itself to its lowest point.
Model airplanes that are designed for aerobatics will have very little or no dihedral, so maneuvers can be executed without the tendency for the model to keep righting itself.
Ones that are designed to be trainers will always have noticeable dihedral.
While some models will have no undercarriage, there are two choices otherwise; tricycle or taildragger.
Airplanes with a tricycle undercarriage have two main wheels beneath the wing and a (sometimes steerable) nosewheel. On the ground, the plane is held level and is easier to steer, making it better suited to beginners.
A taildragger has the same two main wheels but instead of a nosewheel, has a much smaller wheel located beneath the fin. Taildraggers are generally harder to steer on the ground.
The primary flight controls on any aeroplane are:
Pitch : Roll : Yaw : Throttle
The following descriptions give an explanation of the effect of each control in isolation, for a theoretical aircraft. Obviously in flight, control are operated together, and there are also secondary effects of controls to consider.
Pitch
Pitch changes raise or lower the nose of the aircraft. This effect is caused by the operation of the elevator. As the elevator is raised, the force of the airflow pushes the tail down, rotating the aircraft about the balance point and raising the nose.
Roll
Roll is a rotation around the long axis of the fuselage. This effect is caused by the operation of the ailerons. To roll left, the left aileron is raised and the right aileron lowered. The combined effects of the airflow on the controls lifts the right wing and lowers the left wing. The operation is reversed to roll right.
Yaw
Yaw is a horizontal rotation around the vertical axis of the aircraft, and is initiated by the rudder. If the rudder is deflected left, the pressure from the airflow pushes the back around and the aircraft rotates around the vertical axis. Right rudder makes it rotate in the opposite direction. In the absence of any other control inputs, the aircraft will carry on the original direction of flight but with a sideways motion; it will only turn as a consequence of the secondary effects of controls.
Throttle
Controls the amount of power the engine produces. Contrary to what you may see at the flying field, most models are not required to be flown around at full throttle all the time!
Opening the throttle will cause the aircraft to speed up, thus creating more lift, resulting in a climb. Closing it will cause the aircraft to slow down, reducing the lift and hence making the aircraft descend.
Now you have seen how the control surfaces affect the flight path of the model, you can read about how the radio operates the control surfaces.
Secondary effects of controls
None of these controls actually work in isolation, whenever a control is applied, there are always secondary effects which influence the reaction of the aircraft.
Pitch - elevator:
If the elevator is used to pitch the nose of the aircraft up, this has the secondary effect of increasing the angle of attack of the wing and so more lift is generated which will make the aircraft climb, however at the same time the change of attitude will increase the drag of the aircraft which will tend to slow it down and cause it to descend. So, provided the engine output remains the same, the secondary effects of the elevator are to control the speed of the aircraft.
Roll - aileron:
If the stick is moved to the left the aircraft will bank to the left. As the lift always acts at 90º to the wing, and weight always acts straight down, the resultant imbalance of forces causes the aircraft to sideslip to the left. This sideslip causes a flow of air towards the fuselage sides. As there will be more area behind the Centre of Gravity than in front of it, the resultant force will tend to rotate the aircraft causing it to yaw.
Yaw - rudder:
Lift, thrust, weight and drag aerodynamic forces
Flight is the result of four basic forces: lift, weight, thrust and drag.
Lift lifts you up. Weight pulls you down. Drag slows you down. Thrust thrusts you forward.
If you're flying straight and level at a constant speed, thrust equals drag and lift equals weight.
If thrust is bigger than drag, you speed up. If thrust is smaller, you slow down. If lift exceeds weight, you climb. If lift is less, down you go.
The four forces: An aircraft's motion is the net result of its lift, weight, drag and thrust
How wings work: This diagram of a wing in cross-section shows how the different speeds of the air passing above and below the wing cause a pressure difference, resulting in lift
Thrust
The thrust moving the plane comes from the propeller. It is like a special, spinning wing which pulls air past its blades.
Drag
Hold a sheet of paper vertically in front of an electric fan (at a safe distance). Drag is the force pushing the paper backwards. Skateboarders speed up by crouching, to reduce drag. Modern planes retract landing gear to reduce drag.
On a modern jet at full speed, there is enough drag to tear off the undercarriage if it is not retracted. Early Q.A.N.T.A.S. planes flew too slowly for this to matter. Drag only occurs in a moving fluid. Stop the fan and the force on the paper vanishes.
Weight
You experience your own weight all day every day. Unless you're an astronaut in space.
Lift
Lift is the force keeping a plane in the air. Most lift is created by the wings. Like drag, lift only exists in a moving fluid, such as air.
How lift and drag are created
When air moves over curved surfaces, some speeds up. Some slows down. Some crowds together. Some spreads out thinly.
This causes changes in pressure all over the surface. Lift or drag comes from adding together all of these small changes.
Air approaching the top surface of a wing is compressed upwards. As the wing curves down and away from the airstream, a low-pressure area develops. Air above is pulled down toward the back of the wing.
Air approaching the bottom surface is slowed, compressed and directed downward.
Wing shape helps determine how much pressure change occurs and thus the amount of lift or drag.
Roll, pitch and yaw aircraft control
The tail controls a planes direction by two small wings horizontal and vertical stabilisers.
The horizontal tail wing controls whether the plane goes up or down.
The vertical tail wing controls turning left or right.
On the outer ends, ailerons turn the plane and keep it level. And that takes us into roll, pitch and yaw.
The three axes: Roll, pitch and yaw describe an aircraft's motion about three axes which intersect at its centre of gravity
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