AEROLAB MODULE 7

Question 1

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.

Answer 1

high lift devices

Question 2

Relationship of CLmax and Vstall

Answer 2

Indirectly proportional

Question 3

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.

Answer 3

healthy gap ; high

Question 4

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.

Answer 4

camber

Question 5

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.

Answer 5

high drag at cruising speeds

Question 6

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 _______.

Answer 6

flaps ; flapsed

Question 7

Types of Trailing Edge Flaps

Answer 7

Plain, Split, Slotted and multiple slotted, fowler

Question 8

• 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.

Answer 8

Plain Flap

Question 9

• 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.

Answer 9

Split Flap

Question 10

• 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.

Answer 10

split flap

Question 11

• 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.

Answer 11

slot ; slotted

Question 12

• 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.

Answer 12

Fowler

Question 13

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.

Answer 13

greatest increase in lift

Question 14

• ________ 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.

Answer 14

drag

Question 15

• 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.

Answer 15

lift / drag ratio

Question 16

• Flap motion, up or down, typically can cause a pitching moment to change. This is due to the _________ at the tailplane of the ___________.

Answer 16

displacement and downwash ; Pressure Center (CP)

Question 17

• 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,

Answer 17

flap area ; Pressure Center

Question 18

• 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.

Answer 18

effective angle of attack

Question 19

• 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.

Answer 19

resulting pitching moment

Question 20

• 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.

Answer 20

steady flight

Question 21

Types of leading edge flaps

Answer 21

Krueger, Variable camber

Question 22

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.

Answer 22

flow separation

Question 23

• 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.

Answer 23

Krueger flaps

Question 24

• 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.

Answer 24

leading edge profile

Question 25

* 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.

Answer 25

delay separation

Question 26

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).

Answer 26

leading edge slot

Question 27

* 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.

Answer 27

slat

Question 28

* 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.

Answer 28

prolonging the lift curve

Question 29

* 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.

Answer 29

Automatic slots

Question 30

* 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.

Answer 30

Disadvantages of the slot

Question 31

* 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.

Answer 31

trailing edge and leading edge

Question 32

* 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.

Answer 32

leading edge ; trailing edge flap

Question 33

* 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.

Answer 33

asymmetrical situation

Question 34

* 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.

Answer 34

Flap load relief system

Question 35

* __________: 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.

Answer 35

Take-Off

Question 36

* _______: 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.

Answer 36

Climb

Question 37

* _________: 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.

Answer 37

Landing

Question 38

* 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.

Answer 38

Boundary Layer Control

Question 39

* ____________ 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.

Answer 39

Blowing

Question 40

* Methods of Preventing the separation of Boundary layer are:

Answer 40

1. Suction of the slow moving fluid by suction slot 2. Supplying additional energy from a blower 3. Providing a bypass in the slotted wing. 4. Rotating boundary in the direction of flow. 5. Providing small divergence in a diffuser. 6. Providing guide-blades in a bend. 7. Streamlining of body shapes.

Question 41

* 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.

Answer 41

nose-up pitching moment

Question 42

* 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.

Answer 42

75% ; 25 deg