# Shared Flashcard Set

## Details

V/STOL Final 2
Stuff to remember for NCState MAE452 Final set 2
24
Aerospace Engineering
12/13/2010

Term
 Draw the Power required graph as a function of forward speed, include components of total power.
Definition
 [image]
Term
 What is the first step to put a helicopter in autorotation?
Definition
 Cut power to the rotor.
Term
 What happens if a pilot doesn't adjust the input pitch fast enough to enter autorotation?
Definition
 Profile drag of the blade will slow the rotor beyond the point where autorotation can be achieved and rotor will stall experiencing excessive blade stall.
Term
 How much time does a pilot have to set the input pitch to put the helicopter in autorotation
Definition
 1.5 to 4 seconds depending on helicopter
Term
Definition
 Without taper the lift coefficients at the root of the blade are relatively high and cannot operate at the best Cl/Cd ratio for the airfoil section.
Term
 What are two methods of rotor design that result in uniform inflow?
Definition
 Ideal twist and ideal taper.
Term
 Find on the following Power vs Airspeed graph: a.The Airspeed for max rate of climb and endurance b.The airspeed for max range c.Max level flight speed [image]
Definition
 [image]
Term
 What is the effective distance for ground effect?
Definition
 Within one rotor diameter.
Term
 What is the primary factor in determining autorotative rate of descent?
Definition
Term
 At approximately what forward speed does ground effect become negligible?
Definition
 ~30 knots
Term
 In the equation of motion for a rotating body what does an instability in the C (damping) term represent?
Definition
 Flutter
Term
 In the equation of motion for a rotating body what does an instability in the K (stiffness) term represent?
Definition
 Divergence
Term
 Resonance occurs when?
Definition
 When the external forcing frequency is at or near the natural frequency of the structure.
Term
 Flutter is?
Definition
 a self-excited oscillation with exponentially increasing amplitude caused by an interaction of elastic, aerodynamic and inertial forces and moments.
Term
 The fundamental frequency of the rotor noise is determined by?
Definition
Term
 What are the three main sources of noise?
Definition
 Thickness, Normal Forces (Lift and Drag), and Turbulence (Shear Forces)
Term
 What type of acoustic source is caused by blade thickness
Definition
 Monopole
Term
 What type of acoustic source is caused by blade normal forces (lift and drag)
Definition
 Dipoles
Term
 What type of acoustic source is caused by blade turbulence?
Definition
Term
 Weathercock stability acts in which direction in relation to a helicopter in yaw?
Definition
 Opposite of the yaw
Term
 What causes weathercock stability?
Definition
 The tail rotor goes into a state of climb, without additional power this causes a loss of thrust which in turn decreases the anti-torque.
Term
 Why might the tail rotor be placed higher on the tail fin or canted?
Definition
 To resist the sideways movement produced by the tail rotor, thrust from the main rotor must be tilted to the opposite side, because the tail rotor and main rotor are usually separated by a distance this produces a rolling moment, canting or placing the rotor high on the tail minimize this couple.
Term
 Tail rotors are generally how large compared to the main rotor?
Definition
 1/6th the diameter
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