DQ-147

Question 1

Q1. Define total aerodynamic force (TAF).

Answer 1

As air flows around an airfoil, a pressure differential develops between the upper and lower surfaces. The differential combined with air resistance to passage of the airfoil, creates a force on the airfoil. This is known as TAF.

Question 2

Identify the following

Answer 2

A. Chord line

B. Rotational relative wind

C. AoI

D. Resultant relative wind

E. AoA

F. TAF

G. Drag

H. Center of Pressure, C_P

Question 3

Q3. Increased rotor efficiency IGE is caused by what two factors?

Answer 3

• Less Induced Flow. Velocity of induced flow IGE is reduced. AoA up, induced drag down -> more vertical lift vector.
• Reduced Vortex Generation. In ground effect, downward and outward flow of air tends to restrict vortex generation. Outboard portion of each blade becoming more efficient.

Question 4

Q4. Effective translational lift begins between 16-24knots, this increased efficiency continues until what airspeed?

Answer 4

Until the best climb airspeed is reached, when total drag is at it’s lowest point.

(FM 3-04.203 para. 1-116 pg. 1-45)

Question 5

Q5. Explain transverse flow effect and when it is most recognizable in a UH-60?

Answer 5

• In forward flight, air passing through the rear portion of the rotor disk has a greater downwash angle than the air passing through the forward portion.
• Less AOA and lift in the aft portion
• Higher AOA and lift in the front portion
• Results in vibrations
• Occurs between 10 and 20 knots
• Due to gyroscopic precession, right rolling motion.
• UH 60: Shudder?

Question 6

Q6. What is “blowback” and what pilot action is required to compensate for it?

Answer 6

When blade flapping has compensated for dissymmetry of lift, the rotor disc is tilted to the rear.

The pilot compensates by cyclic feathering.

(From ATM, page 4-50: As the transverse flow shudder develops, increase forward cyclic. As the aircraft enters ETL, make a significant forward cyclic input to prevent blowback.)