Part 2

Aerodynamics Glossary

We will not get into any discussions of model kit building, or radio systems at this time. Together they could have their own entire manual.

A general understanding of basic aerodynamics will help to understand why an aircraft does what it does. Our objective here is to provide you with the concept of aerodynamics, not the technicalities. For those who wish to go into aerodynamics at greater depth, student or private pilot flight manuals are a good place to start.

Note: Referring to aircraft as to right or left, is as a pilot would view it from the cockpit.

Wings:

There are three basic wing profiles.

Flat Bottom:

Creates the most lift and is the most stable. Most trainers are flat bottom.

Semi-Symmetrical:

Still stable, yet allows more maneuverability and extends aerobatic capability. Great for "second" planes.

Fully Symmetrical:

Least stable and most aerobatic. For more experienced flyers only. There are three basic wing locations.

High-Wing, Mid-Wing, Low-Wing:

Stability diminishes as the wing comes down; the high wing being the most stable. Here too, most trainers are high wing. A fully symmetrical, mid-wing with no dihedral is the most aerobatic.

Dihedral:

Dihedral is the angle in the wing when looking at it from front or rear. The more dihedral, the more stable and self recovering. The straighter, the more aerobatic but less stable. A low-wing aircraft requires more dihedral to be as stable as a high-wing, all other factors being equal.

Washout:

Washout is a twisting of the wing when viewed from the wing tip. The trailing edge is higher at the wing tip than at the fuselage. This increases stability and self recovery. It allows the outer wing area to still "fly" (maintain control) even if the inner wing area is in a stall condition. Refer to "stalls" later. Washin is reverse, and has no practical application.

Ailerons:

Ailerons control the bank of the aircraft which turns the aircraft. Refer to "lift" later. The up aileron decreases "lift", while the down aileron creates more "lift", thereby banking the aircraft. The aircraft always banks or turns toward the up aileron.

Vertical Stabilizer:

The stationary part of the rudder assembly.

Rudder:

The movable control surface of the assembly. Its primary function is to coordinate the bank and turn. However, in the case of model aircraft, it can be used to steer or turn the craft.

Horizontal Stabilizer:

The stationary part of the elevator assembly.

Elevator:

The movable control surface of the assembly. Its primary function is to control the angle (nose up, etc) of the aircraft. However, in the case of model aircraft, it is basically used to control altitude. Technically, power controls altitude and elevator controls angle, which in turn controls airspeed. Refer to more advanced flight manuals.

Flaps:

Flaps create more "lift". There are several basic types of flaps, none of which are used on trainer planes. Refer to more technical manuals.

Lift:

Lift is created when the air moving over the top of the wing moves faster that the air underneath. Air over the top must travel a greater distance, therefore it must move faster to get to the rear at the same time. The faster the air moves past a surface, the less pressure it exerts on that surface. The pressure underneath is greater pushing the wing up. This is lift. Lift is always 90 degrees to the relative wind. Lift is always 90 degrees to the span of the wing.

Relative Wind:

RW is the air coming at the aircraft; it is always exactly opposite the direction of travel. Do not confuse this with the wind conditions you are flying in. The angle of the wing as it hits the RW is called the angle of attack. Too high of an angle of attack, without enough airspeed, will cause the wing to stall. Refer to "stalls "later.

Components of lift:

When the aircraft is banked, the "lift" is banked too. The "vertical component of lift" is no longer as great. This is why you have to add up elevator to maintain altitude. The "horizontal component of lift' causes the aircraft to turn. If you bank too steep, the "vertical component" will lessen even more and the wing will stall and fall. Refer to "stalls" later.

Propellers:

A propeller is nothing more than a rotating airfoil in the horizontal direction. Applying more power creates more horizontal lift (better known as thrust) which pulls the aircraft through the air. Do not think of a propeller as blowing air rearward.

P-Factor:

For the sake of simplicity we will only say that P-factor is the unequal thrust or torque of the propeller. During power on, or climbing conditions, the right side of the propeller produces more thrust. This causes the aircraft to drift left. This is why an aircraft that rolls straight, will run off to the left of the runway on take-off. Correct with a slight right rudder.

Stalls:

A stall is the loss of "lift". This condition occurs when the angle of attack becomes too great for the air to flow smoothly over the top surface. The air then becomes turbulent (much like the spoiler on a race car) and no longer produces lift. When this happen, the nose of the aircraft will drop abruptly resulting in the loss of altitude. Stalls can occur with power on, or power off, at low speed or high speed, depending on various other conditions. The most common are while climbing too steeply and turning after take-off, or when banking too steeply while turning final to land. All stalls have one thing in common. They all require lowering the nose to recover. Point of interest: A spin is nothing more than a sustained stall with rotation.