11.1 Theory Of Flight Flashcards
What aircraft axes are there and what motions do each take? (3)
Lateral = pitch
longitudinal = roll,
vertical = yaw
What primary flight controls are there? [3]
- Ailerons
- elevators
- rudder
What is the definition of primary flight controls?
Required to safely control the aircraft during flight
What is the purpose of secondary flight controls?
Intended to improve aircraft performance characteristics or to relieve excessive control loading
What devices can be used as secondary flight controls?[4]
- Slats
- Flaps
- flight spoilers
- trims systems
What motion do ailerons control and around what axis?
Roll about the longitudinal axis
What supplement the ailerons?
Roll spoilers
On which wing will the aileron deflect downwards?
The up-going wing
When will the outboard ailerons be locked out during flight? Why?
During high speed flight, less deflection required to provide motion
What motion do elevators control and around what axis?
Pitch, lateral axis
Which way will the aircraft point if the elevators are deflected downwards?
Downward
What is a stabilator?
Sometimes referred to as an all moving tail, fully moveable horizontal stabiliser
What 2 types of canards are there?
Lifting canard and control canard
Which canard generates an upload or positive lift that opposite to a conventional Horizontal stabiliser?
Lifting canard
Which canard is primarily used for pitch control during manoeuvring?
Control canard
At what angle of attack is a control canard usually at?
Zero
What motion does the rudder provide and on what axis?
Yaw and vertical axis
At what speed does the rudder have minimum travel?
Above 200 knots
What prevents rudder/stabiliser overload during high speed?
Rudder limiter system
What angle of deflection in the rudder is permitted at speeds up to 150 knots?
30 degrees
What angle of deflection is permitted in the rudder at speeds of 150-200 knots?
15 degrees
What angle of deflection in the rudder is permitted at 200 knots?
5.7 degrees
What are ruddervators also known as?
V-tails
How is a yaw motion made in v-tail aircraft ?
When one surface moves up and the other down
On a v-tail, when both control surfaces are moved up at the same time, what happens to the orientation of the aircraft?
Nose up
What advantage is there for v-tail aircraft?
Saves weight as no Vertical stabiliser required
What are the disadvantages of v-tail aircraft? [3]
- Large Control surfaces,
- Both motions can’t be achieved at the same time,
- Complicated adjustments
What are elevons?
Elevator and aileron combination
What 2 lift devices are there?
- Flaps
- Slats
With flap and slat extension, what changes on the wing?
Increased camber
What are flaps and slats used for?
Increase lift at low speed flight
What drag devices are there? [2]
- speed brakes
- Spoilers
Where are flaps usually located?
Trailing edge
What percentage of lift is created by the several types of flaps? [4]
- Plain flap = 55%
- Split edge flap = 65%
- Slotted flap = 70%
- fowler flap = 95%
Which flap is most effective at generating lift?
Fowler flap
What percentage of lift is generated by slats?
35%
Where are spoilers located?
On the upper surface of the wing
What is the function of spoilers?
Increase drag and reduce lift
What effect does spanwise flow have on the boundary layer?
Thickens the boundary layer towards the wingtips
What devices could be used to prevent spanwise flow? [3]
-Wing fences-
sawtooth leading edge
-stall strips
What do wing fences do to airflow?
Keep the air going in a straight line
What does a vortex generator produce?
Lift
What does a vortex generator do?
Takes high energy air from outside the boundary layer and mixes it with the low energy air.
Reenergise air flow within the boundary layer
Where are stall strips fixed?
On the leading edge near wing root
What does the stall strip do?
At high angles of attack, Creates turbulent flow, creating a progressive outward stall starting from the root to minimise the risk of going out of control
What do trim systems do?
Compensate for the imbalance of the aircraft
What can flight control systems be divided into? [3]
- Control inputs
- Control transmissions
- Control surface output
What is required for combined control inputs to control rudder/elevator motions on v-tails?
Mixer unit
What rotates within the mixer unit?
Gimbal
Where are the control inputs located for the secondary flight controls?
Centre pedestal
What is used to control pitch trim?
Pitch trim wheel
what 3 types of control runs are there?
- mechanical
- hydraulic
- electric
what is aerodynamic horn balance?
part of the surface forward of the hinge line, moves into the wind aiding deflection
what is a balance tab?
deflects the control surface in the opposite direction,
reduces efficiency of control surface but assists deflection
what two parts make up the balance panel?
- upper chamber
- lower chamber
how do balance panels work?
a difference in pressure produces a force on the balance panel and assists deflection.
how is the static pressure from outside the balance panels allowed into the chambers?
via slots
In a balance panel, why is the upper chamber smaller?
as the airflow assists in returning the control surface into a streamlined profile
what is an anti-balance tab?
deflects in the same direction as the control surface, increasing efficiency of the control surface, but more effort is required
Where do you operate control tabs from?
from the flight deck, directly by the pilot
how do control tabs work?
the pilot operates the tab and lift is produced by the tab which operates the control surface
how does a trim tab operate?
operated in the flight deck, with a cable system, a screw jack and trim rod
what does the trim tab do when it’s deflected?
respositioned to a new neutral position, the ‘trim position’
how fast is the speed of sound in m/s at 20 degrees C
343.2m/s
which speed region is where the air is incompressable?
subsonic
what are the 3 speed regions? and what are the mach regions for each?
- subsonic <0.8
- transonic 0.8-1.2
- supersonic 1.2-1.5
which speed region is where the air density can change?
supersonic
what is critical mach number?
the highest speed before any part of the aircraft travels at the speed of sound
what is MACH?
aircraft speed divided by the speed of sound
what is a build up of pressure concentration also called?
shockwaves
at what mach does a normal shockwave occur?
mach 1.2
what occurs behind the normal shockwave?
a large increase in static pressure
when the airspeed exceeds the speed of sound, what shockwave forms?
oblique shockwave
what are the characteristics of an oblique shockwave?[2]
- slight change of direction
- small decrease in speed
what forms directly behind the oblique shockwave?
normal shockwave
what is wave drag?
portion of total drag which is due to shockwaves
what 2 ways reduce wave drag?
vortex generators, area rule
what does a vortex generator create inside supersonic airflow?
oblique shockwave
what is area rule?
cross section areas plotted against body length to show smooth curve on area diagram
what structural design could aide the area rule?
waisted fuselage
which thickness profile is used for aircraft designed for super sonic speeds? why?
- thin
- because shockwaves form smaller when approaching transonic and super sonic speeds
what 2 things do designers of wings have to take into account?
- strong enough to take the weight
- house the fuel tanks
swept wings have a longer chord length and?
a reduced thickness for aerodynamic purposes
what is the sweep angle of modern jets?
30 degrees
what does a higher sweep angle do? [2]
- reduces thickness
- increase critical mach number
what advantage does a moveable sweptwing have? [2]
- improve performance at low speeds (thicker chord to length ratio)
- high speeds, has a greater critical speed
what design features do transonic profiles have? [3]
- flatter upper surface
- more curved leading edge
- thinner trailing edge
what does a transonic profile do to air flow?
airflow immediately accelerates because of rounded leading edge,
then decellerates because of the flat upper surface giving off a smaller shockwave and no flow seperation behind the shockwave so it can be used for lift
on a transonic profile, what helps with generating lift?
negative chamber at the trailing edge on the lower side recduces velocity of airflow and increases static pressure (higher static pressure, greater lift)
what is a transonic profile also known as?
rear loaded wings
what advantages do transonic profiles have over conventional wings? [5]
- made out of thinner and lighter material allowing for greater wingspan without huge weight increase
- reduction in drag,
- bigger wing bigger fuel tanks
- greater lift means wings can be smaller
- higher mach numbers means sweep angle can be reduced (improves low speed characteristics)
what is the disadvantage of transonic profiles?
from below critical mach number to just above, greater drag than conventional
where does the shockwaves appear first in the transonic region?
wing root, at its thickest
what is the name given to the flow seperation on the control surfaces in the transonic region?
shock stall or high speed stall
what is the reaction known as when the aircraft has a nose down reaction after passing critical mach number?
tuck under effect
what system can automatically prevent tuck under?
mach trim system
what must the horizontal stabiliser do to compensate for the tuck under effect?
increase the downward acting force
what effect does transonic flight have on the elevator
has a different effect, operates opposite to usual operation
what are some aircraft installed with to prevent the elevator from operation in transonic flight?
elevator lock
what 4 things change when airflow passes through a shockwave?
- density
- pressure
- temperature
- velocity
how are temperature, pressure, density and velocity effected when air flow passes through a shock wave?
- density increases
- pressure increases
- temperature increases
- velocity decreases
what angle does a normal shock sit at in relation to airflow?
right angle
what happens to the airflow after a normal shockwave?
slows suddenly and generates heat and keeps going in the same direction
what does an expansion wave do to airflow?
increases speed an turns away from the preceding air flow, follows the surface
how is stability increased?
the distance between centre of gravity and centre of lift is increased
what must be slowed when entering an engine intake? and how?
airflow the use of shockwaves with the least possible waste of energy
how can shockwaves be used in engine intakes?
creating oblique shockwaves to slow air gradually minimising energy loss, and then a normal shock wave
at what temperature does aluminium lose 80% of its strength?
250 degrees c
