Aerodynamics Flashcards
Define airfoil
A surface body or structure producing lift
“If you increase the velocity of air over the top of an airfoil surface what will happen to dynamic pressure
what will happen to static pressure
Dynamic pressure increases
static pressure decreases
Define chord line
The chord line is an imaginary line protruding through the leading edge on which all angles and winds are measured
Blade span
The length of a single blade from its tip to its root
Why is center of pressure important?
because it is a point along the chord line through which all aerodynamic forces are considered to act
Rotational wind
Parallel and in the same direction as the blades
Induced flow/angle of attack standard rule
Increase induced flow, decreased AOA, decreased lift
Can only diminish effects of induced flow with forward airspeed
Define angle of attack
Angle between the chord of an airfoil and the resultant relative wind
An aerodynamic angle
What are the two components of total aerodynamic force
Lift
Drag
What is the relationship of lift to resultant relative wind
perpendicular
What is the relationship of drag to resultant relative wind
Parallel to and in the same direction of the resultant relative wind
Induced drag
By-product of lift, most important in helo operations. Caused by vortices and induced flow
Profile drag - caused by
Main rotor ONLY
Parasite drag -
Tail rotor, fuselage, skids etc
Dissymmetry of lift
Unequal lift between advancing and retreating halves of the rotor disk
No lift area
Where reverse flow is the greatest, you get no lift assist (0 velocity)
The 9 O clock position near the root of the rotor blades
Differences in lift due to airspeed (advancing/retreating) are
significant
Differences in lift due to flap up/flap down are
insignificant
“How does the helicopter compensate for dissymmetry of lift
Blade flapping
Four causes of excessive coning
Low rotor RPM
High gross weight
High G manuvers
Turbulent air
why is blade twisting necessary
to distribute the lifting force more evenly along the blade
Three ways to compensate for translating tendency
At the factory, they rig the cyclic left
Tilt the mast slightly left
Left cyclic input by pilot
What are the three conditions for settling with power
-A vertical or near vertical descent rate of at least 300 FPM
-The engine must be using 20 to 100% of available power
-airspeed less than ETL (dont need numbers here)
Settling with power recovery procedures
Increase airspeed with cyclic
Reduce collective pitch as altitude permits
Autorotation - two key descriptions
no engine power supplied
rotors driven by relative wind only
Dynamic rollover onset conditions
Pivot point
Rolling motion
Exceed critical angle
What is the primary cause of retreating blade stall
Excessive airspeed
Two symptoms of retreating blade stall
Pitch up of the nose
Followed by a roll to the left
What are the two initial recovery procedures for blade stall
Reduce collective pitch
Regain control of aircraft
How does induced drag change with increased airspeed
drops off sharply, stays low as airspeed increases
How does profile drag change with increased airspeed
Steady climb up
How does parasitic drag change with increase with airspeed
Rapid climb up
Get paper and draw an airfoil
bitch
