Module 6 - Drag Measurements Flashcards
What are the four forces of flight?
- lift
- drag
- thrust
- weight
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
drag
forms of drag
- total drag
- parasite drag
- induced drag
- skin friction drag
- form drag
- interference drag
- profile drag
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
is the aerodynamic resistance due to the contact of moving air with the surface of an object
skin friction drag
factors that affect the type of flow in the boundary layer
- flow quality
- shape
- texture
- pressure gradient
- Reynold’s number
- heating of the fluid
a pressure gradient where the static pressure increases in the direction of the flow
adverse pressure gradient
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 ___________ the point of maximum thickness.
at, or near
Because of the adverse pressure gradient existing on a curved surface, such as an airfoil, the transition point will be ___________ than if the surface was flat.
further forward
is generated due to the aircraft’s shape and the airflow around it
form drag
When the air has to separate to move around a moving aircraft and its components, it eventually ______ after passing the body. How quickly and smoothly it does is representative of the _________ it creates, which creates additional force to overcome.
rejoins, resistance
How to reduce form drag?
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
measure of streamlining
fitness ratio
formula for fitness ratio
fitness ratio = length/depth
an example of this would be the intersection created by the connection of the wing and the fuselage at the wing root
interference drag
The most interference drag is observed when two surfaces meet at _________________.
perpendicular angles
What is used to reduce interference drag?
fairings
factors affecting parasite drag
- indicated airspeed
- configuration
- airframe contamination
parasite drag varies with the square of the _________
indicated airspeed
parasite drag varies directly in proportion to the frontal area presented to the airflow, also known as the _________________
Parasite Area
contamination by ice, frost, snow, mud or slush will increase the ________________
parasite drag coefficient
is an inherent component, a rather undesirable by-product of lift
induced drag
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 _______ in flight so induced drag will depend on the _______ of the aircraft
weight, weight
induced drag will be _______ at higher aircraft weights
greater
certain maneuvers require the lift force to be ________ than the aircraft weight
greater
the relationship of lift to weight ratio is also known as the _________
load factor
relationship of load factor and induced drag
directly proportional
relationship of induced drag and speed of the aircraft
inversely proportional
as speed increases, the downwash caused by the tip vortices become ________________, the rearward inclination of the lift is _____, and therefore induced drag is less
less significant, less
relationship of induced drag and aspect ratio of the wing
inversely proportional
factors to consider if one decides to continue the increase of the aspect ratio
- excessive wing bending moments
- reduced rate of roll
- reduced ground clearance in roll during take-off and landing
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
wing-end plates
What type of drag do wing-end plates cause?
parasite drag
fuel tanks placed at the wing tips will have a similar beneficial effect to an endplate, 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 _____________ 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
shape of the wingtip
is the sum of an aircraft’s induced drag and parasite drag
total drag
a number that aerodynamicists use to model all of the complex dependencies of shape, inclination, and flow conditions on aircraft drag
drag coefficient
