AEROLAB MODULE 7 Flashcards
Aircraft are equipped with
________________
to reduce the distances from take-off and
landing. This allows operation at greater
weights from the provided runway lengths
and allows carrying higher payloads.
high lift devices
Relationship of CLmax and Vstall
Indirectly proportional
The distances of take-off and landing depend on the velocities required and these are
set out in the performance regulations.
One of the criteria for both take-off and
landing is for a __________ over the stoppage speed (1.2 VS1 for take-off and 1.3 VSO
for landing).
The stalling speed is determined by the wing’s CLMAX and the CLMAX, therefore, must be as ______ as possible to achieve the lowest possible distances.
healthy gap ; high
One of the main factors that defines an aerofoil section’s CLMAX is the ________. Increasing an
aerofoil section’s _______ increases the CL at a given angle of attack and increases CLMAX.
camber
A cambered section is suitable for take-off and landing but this would give ______________ and require a very nose-down attitude. To maximize the cruise and adjust the section for take-off and landing by using flaps, it is normal to choose a less cambered aerofoil section.
high drag at cruising speeds
A ______ is a hinged portion of the trailing
or leading edge that can be deflected
downwards and thus create a camber
increase. The _____ will only be on the
trailing edge for low-speed aerofoils,
but on high-speed aerofoils where the
leading edge might be symmetrical or
have a negative camber, both the
leading edge and the trailing edge will
generally be _______.
flaps ; flapsed
Types of Trailing Edge Flaps
Plain, Split, Slotted and multiple slotted, fowler
- Has a simple construction
and provides a reasonable
increase in CLMAX, but with
a reasonably high drag. - It is 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
- The _________ 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. - However, because of the wake’s increased depth the drag is higher than for the simple flap.
split flap
- The aim of the ______ is to guide
higher pressure air over the flap
from the lower surface, and to
re-energize the boundary layer. - This retards the airflow
separation on the flap’s upper
surface. - The ________ flap gives CLMAX a
greater increase than the plain
or split flap, and much less drag,
but has a more complicated
design.
slot ; slotted
- The ________ flap travels
backwards and downwards,
giving initially an increase in
wing area, and then an increase
in camber. It can be slotted to
the ________ flap.
Fowler
Because of the combined effects
of increased area and camber,
the Fowler flap gives the flaps
considered the_____________, and also gives the least
drag because of the slot and
decreased thickness (chord
ratio). However the pitching
moment adjustment is bigger
because of the chord’s rearward
extension.
greatest increase in lift
- ________ decreases the acceleration during take-off, and so the flap should
offer as little ______ as possible.
______ therefore contributes to the braking
force for landing and therefore the drag of the flap is advantageous.
- Adding _____ during approach also increases velocity stability. As in the
case of lift increments, the ______ increments with increasing flap angle
are not constant, as the flap angle changes, the changes in ______ get
larger.
drag
- The_________ is a measure of
aerodynamic efficiency, which
affects the performance of the
aircraft in areas such as range,
angle of climb which angle of glide. - The range would decrease with the
flaps lowered, the climb angle
decreased and the glide angle
increased.
lift / drag ratio
- Flap motion, up or down, typically can cause a pitching moment to change. This is due to the _________ at the tailplane of the ___________.
displacement and downwash ; Pressure Center (CP)
- Moving a trailing edge flap will alter the
distribution of pressure over the entire
aerofoil chord, but the greatest
changes will occur in the________. - The __________ will shift rearward
when the flap is lowered, providing a
nose-down pitching moment,
flap area ; Pressure Center
- The ____________ to the
tailplane is determined by the wing
downwash. If the flaps are lowered the
downwash will increase and the angle
of attack on the tailplane will decrease,
creating a moment of nose-up pitching.
effective angle of attack
- The _________________ for an aircraft would depend on which of
the two effects is dominant. The pitching moment will be affected by flap
form, wing position and tail plane relative position, and may be nose-up,
nose-down, or near zero.
resulting pitching moment
- The lift must be equal to the weight when the aircraft is in __________.
If the flaps are lowered but the velocity is kept constant, the lift will increase and
the angle of attack must be decreased to maintain it at its original value. Thus,
if the flaps are down the aircraft can fly in a more nose-down attitude. This is
an advantage on landing approach as it provides greater visibility of the
landing field.
steady flight
Types of leading edge flaps
Krueger, Variable camber
The leading edge can have very little
camber on high speed aerofoil parts and
have a tiny radius.
This can offer ___________ at reasonably low angles of
attack just aft of the leading edge. Using a
leading edge flap which increases the
leading edge camber can be remedied for
this.
flow separation
- The _____________ is part of the
lower surface of the leading
edge which can be rotated
around its forward edge.
__________ are used on the
inboard section to facilitate root
stall on a swept wing, because
they are less effective than the
opposite variable camber.
Krueger flaps
- As it is deployed, the camber of
a leading edge flap can be
increased to improve efficiency
by offering a better ___________.
The leading edge devices
are either fully extended
(deployed) or retracted (stowed)
unlike trailing edge flaps that
can be selected to intermediate
positions.
leading edge profile
- The leading edge flap’s main effect is
to ____________, thus increasing
the angle of stalling and the resulting
CLMAX. However due to the
increased camber of the aerofoil
section, there will be some increase
in lift at lower angles of attack.
delay separation
A ___________ is 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
(the slat).
leading edge slot
- A _____ is a small auxiliary aerofoil
fixed to the wing ‘s leading edge. - It 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
_______________ by delaying
the separation of the boundary layer
until a higher angle of attack. Due to
its marked camber, when working at
high angles of attack the slat itself
produces a high lift coefficient.
prolonging the lift curve
- The slots are not operated by the pilot on certain aircraft but they operate
automatically. - Their motion is caused by pressure shifts that occur along the leading edge
as the angle of attack increases. The high stresses around the stagnation
point hold the slat in the closed position at low angles of attack. The
stagnation point underneath the leading edge has shifted at high angles of
attack, and pressure ‘suction’ occurs on the upper surface of the slat.
These stresses carry forward the slat and build the slot.
Automatic slots
- The slot can give CLMAX increases of the same magnitude as the trailing
edge flap, but while the trailing edge flap gives its CLMAX at a slightly
lower angle than the usual stalling angle, to give its CLMAX, the slot needs
a much greater angle of attack. In flight, this implies that the aircraft would
have a very nose-up attitude at low speeds, and visibility of the landing
area may be restricted when approaching ground.
Disadvantages of the slot
- The differences in drag and pitching time
resulting from the activity of leading edge
devices are minimal compared to trailing
edge flaps. - Both________________
systems are used for most large transport
planes.
trailing edge and leading edge
- The ___________ system
must be deployed before the
flap to the trailing edge is
lowered. - The ____________must be
withdrawn until the leading
edge unit is lifted when the
flaps are withdrawn.
leading edge ; trailing edge flap
- 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. - However, 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 prevent damage to the flaps.
A _____________ will sense the flap load
and prevent flaps deployment. If the flaps
selection is made but the speed is too high,
the flaps would extend as soon as the
speed drops below Vfe (Vertical Flap
Extension.
Flap load relief system
- __________: 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.
Take-Off
- _______: 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.
Climb
- _________: Landing distance will depend on touchdown speed and
deceleration. The lowest touchdown speed will depend on the Clmax
obtained which helps in deceleration. Leading edge devices are also used
to obtain high Clmax.
Landing
- In the process of suction, air is drawn from the boundary layer which has formed through minute holes into a plenum chamber formed by providing an inner skin over the upper surface of the wing. This decreases the thickness of the boundary layer and
ensures that longer laminar airflow stays over the wing. At the trailing edge of the wing, the air that has been pulled into the plenum chamber is ducted overboard.
Boundary Layer Control
- ____________ is accomplished by jetting high-velocity air from vents
through the upper surface of the wing just below the leading edge.
This speeds up the airflow near the skin of the wing and makes
sure the boundary layer stays thin. The blown method is easier,
but either a dedicated pump or motor extracts air.
Blowing
- Methods of Preventing the separation of Boundary layer are:
- 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 nose-down pitching moment of the trailing edge flaps is countered by the _________________ of the leading edge systems, where flaps and slats are deployed
together.
nose-up pitching moment
- Using a combination of a slotted flap and slat increases the aerofoil’s lift by _______ and its
stalling angle to ______.. Using a double-slotted fowler flap and slat combination raises
the lift of the aerofoil by 120% and the angle of stagnation by 28 deg. This combination
is also used on air haulage aircraft.
75% ; 25 deg
