Module 7 - Wing and High Lift Devices Testing Flashcards
Why are aircraft equipped with high lift devices?
- to reduce the distances from take-off and landing
- allows operations at greater weights from the provided runway lengths
- allows carrying higher payloads
The distances of _______ and _______ depend on the velocities required and these are set out in the performance regulations.
take-off, landing
One of the criteria for both take-off and landing is for a healthy gap over the _____________.
stoppage speed
Stoppage speed for take-off
1.2 VS1
Stoppage speed for landing
1.3 VSO
What determines the stalling speed?
wing’s CLMAX
CLMAX must be as ____ as possible to achieve the ______ possible distances
high, lowest
formula for stalling speed
VSTALL = √(2W)/(ρACLMAX)
What is the relationship between CLMAX and VSTALL
inverse relationship
One of the main factors that defines an aerofoil section’s CLMAX is the _______.
camber
Increasing an aerofoil section’s camber increases the ________ at a given angle of attack and increases ________.
lift coefficient (CL), CLMAX
A cambered section is suitable for take-off and landing but this would give ______ at cruising speeds and require a very _____________.
high drag, nose-down attitude
To maximize the cruise and adjust the section for take-off and landing by using _____, it is normal to choose a __________ aerofoil section.
flaps, less cambered
a hinged portion of the trailing or leading edge that can be deflected downwards and thus create a camber increase
flap
The flaps will only be on the
trailing edge for ___________.
low-speed aerofoils
On _______________ where the leading edge might be symmetrical or have a negative camber, both the leading edge and the trailing edge will generally be flapped.
high-speed aerofoils
Types of trailing edge flaps
- plain flap
- split flap
- slotted flap
- fowler flap
- slotted fowler flap
has a simple construction and provides a reasonable increase in CLMAX, but with a reasonably high drag
plain flap
primarily used on low-speed aircraft and where very fast take-off and landing are not necessary
plain flap
The flap forms part of the lower surface of the trailing edge of the wing, with the upper surface contour not affected when the flap is lowered.
split flap
gives about the same increase in lift as the plain flap at low angles of attack, but gives slightly more at higher angles as there is no increase in the upper surface camber and so separation is delayed
split flap
split flap: because of the wake’s increased depth the drag is ______ than for the simple flap
higher
The aim of the slot is to guide __________ over the flap from the lower surface, and to ___________ the boundary layer.
higher pressure air, re-energize
This retards the airflow separation on the flap’s upper surface.
slots
The slotted flap gives CLMAX a _________ than the plain or split flap, and much ____ drag, but has a more ________ design.
greater increase, less, complicated
The ___________ travels backwards and downwards, giving initially an increase in __________, and then an increase in _________.
fowler flap, wing area, camber
Can fowler flaps be slotted?
Yes
the _________ gives the flaps considered the greatest increase in lift, and also gives the least drag because of the slot and decreased thickness (chord ratio).
fowler flap
Why is the pitching moment adjustment bigger for fowler flaps?
because of the chord’s rearward extension
For lowered flaps, the CLMAX is ________ but the angle of stalling is ________.
increased, decreased
the lowering of the flap ________ the effective attack angle
raises
What decreases the acceleration during take-off?
drag
Flaps should offer as _________ drag as possible.
little
When and why is drag of the flap advantageous?
during landing because it contributes to the braking force
Adding drag during approach also increases ____________.
velocity stability
as the flap angle changes, the changes in drag get ________
larger
the lift/drag ratio is a measure of _____________
aerodynamic efficiency
affects the performance of the aircraft in areas such as range, angle of climb which angle of glide
lift/drag ratio
Flap motion, up or down, typically can cause a _______________ to change.
pitching moment
caused due to the displacement and downwash at the tailplane of the Pressure Center (CP)
pitching moment
Moving a trailing edge flap will alter the ____________ over the entire aerofoil chord, but the greatest changes will occur in the __________.
distribution of pressure, flap area
the ____________ will shift rearward when the flap is lowered, providing a nose-down pitching moment
Pressure Center
The effective angle of attack to the tailplane is determined by the _____________.
wing downwash
If the flaps are lowered, the downwash will ________ and the angle of attack on the tailplane will __________, creating a moment of nose-up pitching.
increase, decrease
the pitching moment will be affected by ________________
flap form, wing position, and tail plane relative position
the pitching moment may be ______________
nose-up, nose-down, or near zero
The lift must be equal to the weight when the aircraft is in ____________.
steady flight
If the flaps are lowered but the velocity is kept constant, the lift will _________ and the angle of attack must be ___________ to maintain it at its original value.
increase, decreased
if the flaps are down the aircraft can fly in a more ______________
nose-down attitude
What provides greater visibility of the landing field?
nose-down attitude
can have very little camber on high speed aerofoil parts and have a tiny radius
leading edge
What can remedy flow separation at reasonably low angles of attack just aft of the leading edge? Why?
leading edge flap because it increase leading edge camber
part of the lower surface of the leading edge which can be rotated around its forward edge
Krueger flap
used on the inboard section to facilitate root stall on a swept wing, because they are less effective than the opposite variable camber
Krueger flap
as it is deployed, the camber of a leading edge flap can be increased to improve efficiency by offering a better leading edge profile
variable camber leading edge flap
unlike trailing edge flaps, leading edge devices can be _________
fully extended (deployed) or retracted (stowed)
The leading edge flap’s main effect is to _____________, thus increasing the angle of stalling and the resulting CLMAX.
delay separation
a gap between the lower surface and the upper edge of the leading edge, and can be fixed or formed by pushing forward part of the leading edge
leading edge slot
a small auxiliary aerofoil fixed to the wing ‘s leading edge
slat
forms a slot when deployed which allows air passage from the high pressure region below the wing to the low pressure region above it
slat
The slat has the benefit of prolonging the lift curve by _______________ of the boundary layer until a higher angle of attack.
delaying the separation
Due to its marked camber, when working at high angles of attack the slat itself produces a _____________.
high lift coefficient
Automatic slot’s motion is caused by ____________ that occur along the leading edge as the angle of attack increases.
pressure shifts
The high stresses around the stagnation point hold the slat in the ____________ at low angles of attack.
closed position
What stresses carry forward the slat and build the slot at high angles of attack?
pressure ‘suction’ caused by the shift of the stagnation point
disadvantages of the slot
- very nose-up attitude at low speeds
- visibility of the landing area may be restricted when approaching ground
The differences in drag and pitching time resulting from the activity of leading edge devices are ________ compared to trailing edge flaps.
minimal
_______________ are used for most large transport planes.
both trailing edge and leading edge systems
The leading edge system must be deployed _______ the flap to the trailing edge is lowered.
before
The trailing edge flap must be _______ until the leading edge unit is lifted when the flaps are withdrawn.
withdrawn
The deflection on the two sides is contrasted on many flap control systems when the flaps are moving, and if one side fails, the movement on the other side is _________________.
automatically halted
a failure of the operating mechanism may lead to an _______________ in less sophisticated systems
asymmetrical situation
On a large aircraft, flaps are prevented to be deployed beyond certain high speed (Vfe) to ___________ to the flaps.
prevent damage
A ____________ will sense the flap load and prevent flaps deployment.
flap load relief system
If the flaps selection is made but the speed is too high, the flaps would extend as soon as the _______________.
speed drops below Vfe
What is Vfe?
Vertical Flap Extension
flap setting for take-off
Lowest take-off speed will be possible at large flap deflection but this gives large increase in drag as well which will make acceleration
to take off speed difficult. So a compromise is made and a lower flap setting is selected.
flap setting for climb
Climb gradient is reduced by flaps. So if climb gradient is limited, a lesser flap angle could be used to compensate but the take-off distance required will increased.
flap setting for landing
Landing distance will depend on touchdown speed and deceleration. The lowest touchdown speed will depend on the CLMAX obtained which helps in deceleration.
In the process of suction, air is drawn from the _________ which has formed through minute holes into a __________ formed by providing an inner skin over the upper surface of the wing.
boundary layer, plenum chamber
decreases the thickness of the boundary layer and ensures that longer laminar airflow stays over the wing
boundary layer control via suction
At the trailing edge of the wing, the air that has been pulled into the plenum chamber is _____________.
ducted overboard
accomplished by jetting high-velocity air from vents through the upper surface of the wing just below the leading edge
blowing
speeds up the airflow near the skin of the wing and makes sure the boundary layer stays thin
boundary layer control via blowing
methods of preventing the separation of boundary layer
- suction of the slow moving fluid by suction slot
- supplying additional energy from a blower
- providing a bypass in the slotted wing
- rotating boundary in the direction of flow
- providing small divergence in a diffuser
- providing guide-blades in a bend
- streamlining of body shapes
The _________ pitching moment of the trailing edge flaps is countered by the _______ pitching moment of the leading edge systems, where flaps and slats are deployed together.
nose-down, nose-up
Using a combination of a slotted flap and slat increases the aerofoil’s lift by ____ and its stalling angle to _______.
75%, 25 deg
Using a double-slotted fowler flap and slat combination raises the lift of the aerofoil by ______ and the angle of stagnation by _____.
120%, 28 deg
combination used on air haulage aircraft
double-slotted fowler flap and slat combination
