AEROLAB DRAG Flashcards
As an aircraft moves/travel through air, every part of it that is exposed to the airflow produces a different type of resistance to the forward motion which constitute to the ____________.
Total Drag
2 forms of drag
Parasite and Induced
is comprised of all the forces
that work to slow an aircraft’s
movement which includes
resistance of air moving over
aircraft’s surface.
Parasite drag
is an inevitable
consequence of lift and is
produced by the passage
of an airfoil through the air.
Induced drag
types of parasite drag
Skin friction, Form drag, interference drag
skin friction and form drag are also called?
profile drag
Type of drag is the aerodynamic resistance due to the contact of moving air
with the surface of an object, and in this particular case that object would be an
aircraft. Every surface, no matter how apparently smooth, has a rough, ragged
surface when observed under a microscope.
Skin Friction Drag
Factors that affect the flow in the boundary layer
Flow Quality
Shape
Texture
Pressure Gradient
Reynolds Number
Heating of the fluid
A laminar layer cannot exist when pressure is rising in the direction of the flow. On a curved surface, such as an airfoil, the transition point is usually at, or near to the point of maximum thickness. Because of the _________________ existing on a curved surface the transition point will be further forward than if the surface was flat.
Adverse Pressure Gradient
This is generated due to the aircraft’s shape and the airflow around
it. When the air has to separate to move around a moving aircraft
and its components, it eventually rejoins after passing the body.
How quickly and smoothly it rejoins is representative of the
resistance it creates, which creates additional force to overcome.
Form Drag
To reduce form drag, it is necessary to delay the separation as close to the trailing edge as possible.
___________ increases the ratio between the length and depth of the body, reducing the curvature
of the surfaces and thus the adverse pressure gradient.
Streamlining
___________ is the measure of streamlining.
Fitness ratio
Formula of Fitness Ratio
f = length / depth
An example of this would be the intersection created by the connection of the wing and the fuselage at the wing root. The most _____________ is observed when two surfaces meet at perpendicular angles. Fairings are used to reduce this tendency.
interference drag
Factors affecting Parasite Drag
IAS
Configuration
Airframe Contamination
Once again, ________ is an inherent component, a rather undesirable by-product
of lift. Wing tip vortices modify upwash and downwash in the vicinity of the wing
which produces a rearward component to the lift vector known as the “__________________”.
Induced drag
Factors Affecting Induced Drag
Size of the lift force, speed of the aircraft, aspect ratio of the wing
Lift must be equal to weight in flight so induced drag will depend on the weight of the aircraft. Induced drag will be greater at higher aircraft weights. Certain maneuvers require the lift force to be ___________. This relationship of lift to weight ratio is also known as the
Load Factor.
greater than the aircraft weight
Induced drag decreased with increasing speed. This is because as speed __________ the downwash caused by the tip vortices becomes less significant, the rearward inclination of the lift is less, and therefore induced drag is less.
increases
The tip vortices of a high
aspect ratio wing affect a
smaller proportion of the span
so the overall change in
downwash will be _____, giving a
smaller rearward tilt to the lift
force. Induced drag therefore
decreases as aspect ratio
increases (for a given lift
force).
less
Factors to consider if one decides to continue the increase of AR
Excessive wing bending moments
Reduced rate of roll
Reduced ground clearance in roll during TO and L
Methods of Reducing Induced Drag
Wing end plates
Tip Tanks
Winglets
Wing tip shape
- A flat plate placed at the wing tip will
restrict the tip vortices and have a
similar effect to an increased aspect
ratio, but without the extra bending
loads. - However, the plate itself will cause
parasite drag, and at a higher speeds
there may be no overall
Wing end-plates
- Fuel tanks placed at the wing
tips will have a similar
beneficial effect to an end
plate, will reduce the induced
drag.
Tip tanks
- Small vertical aerofoils which
form part of the wing tip. Shaped
and angled to the induced flow,
they generate a small forward
force. - Winglets partly block the air
flowing from the bottom to the
top surface of the wing, reducing
the strength of the tip vortex.
Winglets
- The shape of the wing
tip can affect the
strength of the tip
vortices, and designs
such as turned down or
turned up wing tips
have been used to
reduce induced drag.
Wing tip shape
