11.01 Theory of Flight Flashcards
What are the three axes of motion?
Lateral, longitudinal and vertical
Which flying controls control movement around the lateral axis?
Elevators
What is meant by aileron lockout?
Outboard ailerons become inactive
What are the advantages and disadvantages of a V tail?
A: - Weight saving D: - More complicated adjustment - Needs larger surface area - Less stable - Cant get full elevator and full rudder simultaneously
What are the secondary flying controls?
Lift devices and trim systems
What lift device gives the maximum increase in lift?
Triple slotted fowler flap
What are trim systems used for?
To compensate for aircraft imbalance
How do vortex generators reduce wave drag?
By producing an oblique shockwave inside the suspersonic airflow
Name the three types of balance used on flying controls
- Balance tab
- Anti balance tab
- Balance panel
Does the balance tab aid the pilot?
Yes
What is an anti balance tab?
A tab that moves in the same direction as the control surface increasing the effectiveness of the control surface
What property of air changes with the onset of transonic flight?
It becomes compressible (large pressure and density changes)
What is mach number?
Aircraft speed divided by speed of sound
What is the critical mach number?
the fastest speed the aircraft can achieve without being subjected to supersonic airflow
What wing design feature delays the onset of Mcrit?
Wing sweep
Where does supersonic airflow first occur on an aerofoil?
On the upper surface
How are oblique shockwaves employed in intakes?
To gradually slow the supersonic airflow before the normal shock occurs
What happens to air velocity in an expansion wave?
It increases
Why does flow separation occur behind a shockwave?
Boundary layer does not have enough kinetic energy to withstand the large increase in static pressure
When does a bow wave form in front of the leading edge?
When flight speed exceeds the speed of sound
What drag increases due to the use of vortex generators?
Parasitic drag
Which wing profile is also known as rear loaded?
Transonic
What are the possible advantages of a rear loaded wing profile?
- Lighter
- greater fuel capacity
- less drag
- less sweepback
- smaller wing
- better low speed characteristics
How is tuck under avoided on modern aircraft?
Mach trim system
Where on the wing does a shockwave first form?
Wing root
What are the two types of shockwave that can form on supersonic aerofoils?
Normal and oblique
Which type of shock wave causes an increase in the velocity of airflow?
Neither, an expansion wave causes an increase in velocity
How does the vortex generator re-energise the boundary layer flow?
By transferring energy from the free air flow to the boundary layer
What would be the effect on the AOA if the slats were extended?
Decreases the relative AOA of the wing
When would the boundary layer separate from the aerofoil section?
When the normal shockwave forms
What are the advantages and disadvantage of the anti-balance tab?
A:
- Increases the efficiency of the control surface
D:
- Requires more effort to deflect the control surface
What detrimental effect does aerodynamic heating have on metals?
They lose their strength
What is the point at which airflow over a wing is at its maximum but below the speed of sound?
Critical mach number
What is the normal sweep wing angle on modern aircraft?
30 degrees
What is formed at a supersonic intake to ensure good airflow to the engine?
Oblique shockwaves
What level of flight control surface correct for imbalance in flight?
Secondary
What causes the deflection of the tab in the balance panel trim system?
The difference in static pressure between the two chambers
There is a large increase in what, behind the shock wave on an aerofoil section?
A large increase in static pressure
What are the differences between a normal wing profile and a transonic profile?
Transonic wing has:
- Flatter upper surface
- More curved leading edge
- Thinner trailing edge
What happens when a shock stall occurs in the transonic region and how is it corrected?
- Centre of lift moves outboard on the wing and aft on the aircraft
- Nose tucks under
- Corrected with horizontal stabilizer (mach trim)
Where is the centre of gravity located on a balanced control surface?
On the hinge line
Extending flaps and slats will do what to the profile of a wing?
Increase camber and area
How is a high speed turn controlled by flying control surfaces?
Aileron and roll spoilers with rudder input
How does a horn balance surface assist control deflection?
Air loading assists control deflection
The automatic trim system of the horizontal stabiliser which corrects for tuck under is called what?
Mach trim
How many ailerons are fitted to large aircraft and how do they operate?
- four (two inboard and two outboard)
- outboard are locked out at high speed
Aluminium can lose approximately what percentage of its strength at 250 celcius?
80%
