Aero 1 Flashcards
Standard Lapse Rate
2°C per 1000 feet.
Static Pressure
Result of the weight of the column of air supported above that elevation. (S=p/p0)
Density
Mass of air per unit volume
Sigma = p/p0
What affects density?
Pressure and Temperature
Humidity Corrections
10% Rule: For every 10% of relative humidity add 100 feet to your density altitude.
40% Rule Same as 10% rule, but subtract 40% RH to apply. (don’t go negative)
Name three varying components of the atmosphere
*Pressure
*Density
*Temperature
What components of the atmosphere are constant
*78% N2
*21%O2
*1% Other
Ideal Gas Law
P = pRT
Continuity Principle
A1V1 = A2V2
As area is decreased, velocity will increase
Bernoulli Equation
PTotal = Ps + ½ p V
T = PE + KE
Stagnation Point
Point on an airfoil when velocity of an air particle reaches zero
Front of leading edge and end of tip (vortices come together)
Airspeed Conversion
Indicated –> Calibrated –> Equivalent –> True
Indicated –> Calibrated via NATOPS
Calibrated –> Equivalent via compression correction (N/A)
Calibrated –> True via Rule of thumb (add 2% for every 1000’ PA)
Error Sources for Airspeed
*Calibrated A/S - Position/Location; Installation; Downwash
*Equivalent A/S - Compressibility
*True A/S - DA/Air density
Lift
Lift is the force perpendicular to the Relative Wind
Drag
Drag is the force parallel to the Relative Wind.
Generation of Lift
Lift results from a change in STATIC PRESSURE relative to the airfoil
Lower pressure on top leads to higher velocity, higher static pressure on the bottom causes force to lift airfoil
3 types of Drag
*Induced - air swirling over the airfoil
*Parasitic - air curling around itself on back of airfoil
*Profile - other things on aircraft (stores, gear, etc)
Chordline
Imaginary line moving through the middle of the airfoil
Camber
Measure of the chord from the chordline to top of airfoil
AOA
Angle between chordline and realitve wind
Blade Pitch
Angle between chordline and horizon
Induced Velocity
Vertical component of relative wind
Rotational velocity
Horizontal component of relative wind
Induced drag
Force pushing Lift vector away from perpendicular to the horizon; equal to induced velocity
Profile drag
Parallel to horizon
Total Aero Forces
Summation of Lift Vector and Profile Drag
Relationship of Induced Velocity to AOA and Lift
Inversely related
IV increases… AOA decreases, Lift decreases,
IV decreases, AOA increases, Lift increases
Types of Airfoils
Symmetry - no lift at 0 AOA
Non-symmetric - some lift at 0 AOA (cambered); creates a pitching moment
Factors that affect Lift and Drag
Degrees of freedom for a helicopter blade
*Feathering - physically changing the pitch of the blade (either via design or control inputs)
*Flapping - as velocity increases at the blade tip, lift is increased causing blade to flap up
*Lead-Lag - allows blade to move horizontally within plane as a flapping blade wants to spin faster due to centrifugal force
Blowback
Blowback is the separation of the Virtual Axis (Tip Path Plane) from the Control Axis (Swashplate). (Shaft axis is aligned with rotor shaft)
As airspeed is increased, the lead blade wants to flap up, causing the blade to blow back even though the controls are still pushing forward. The Virtual Axis blows back and requires more forward cyclic to overcome.
How to obtain more ideal lift distribution over the rotor blades
*Geometric Twist - Change angle of twist (Rotor blade is twisted to maximize performance in all flight regimes)
*Aerodynamic Twist
-1. Change Shape of Airfoil - Blade root is thicker than blade tip
2. Taper
*Dynamic Twist
-1. Swept tip blades - Change angles of incidence
-2. Alters dynamic stall characteristics
-3. Higher AVERAGE lift around rotor disk
Precession
Maximum displacement occurs 90 degrees after force introduction
Fastest speed at 3 o’clock position flaps up at 12 o’clock position
Rotor Head types
*Teetering - Has feathering and teetering hinge for flapping (no lead-lag)
*Articulated - has hinges for all 3 axis of travel
*Bearingless - no hinges; requires more flexible materials
LTA vs LTE
- Loss of TR Authority (LTA) - Power Issue
-Pr > Pa
-TR thrust required > TR thrust available - Loss of TR Effectiveness (LTE) - Wind Issue
Aerodynamics of LTA
POWER = TORQUE X RPM
Tail Rotor Thrust balances Main Rotor Torque, so as RPM decreases,
-TR must produce more thrust
-(must increase tail rotor pitch).
Aircraft reaction to loss of TR thrust
Loss of TR Anti-Torque
*Fuselage Rotates toward Advancing Blade Side
* Right Rotation – (CCW U.S. Helo’s)
* Accelerated rotation response
- Pilot Response - Lower Collective to reduce Torque on MR
- Less Anti-Torque requirement since less Q on MR
Aircraft reaction to loss of engine power
- Initial tendency is to yaw LEFT (CCW rotor)
-This is an instantaneous response
*The sudden removal of power cancels the need for anti-torque
-Therefore, the left pedal applied must be removed
TR Design types
*Pusher - A few Percentages (1-5%) More efficient than puller
- Puller - Design accepts the reduced efficiency (Canted provides 2.5% of total lift)
- Fenestron (within tail pylon) - Even more efficient (minimizes tip loss)
