June Daily Questions

June Daily Questions

Week 1

Aerodynamics: Reference TC 3-04.4

1. Rotational relative wind modified by induced flow (at a hover, as well as airspeed during directional flight) is known as: Resultant Relative Wind

Figure 1-8

2. You pick up the aircraft to conduct a hover power check. Your predicted hover power torque is 60%. You have a 23kt headwind. Your actual hover power torque is 53%. If all other factors remain the same, what aerodynamic factor is causing the decrease in power required?

Effective Translational Lift. ETL is an increase in efficiency of the rotor system as the helicopter begins to work in relatively undisturbed air (usually by "out-running" it's vortexes). It occurs at about 16-24 knots. Even though we usually think about ETL occurring because we gain airspeed until 16-24 knots, aerodynamically a wind of the same amount has the same effect on the helicopter.

3. I am in a single rotor helicopter traveling at a high rate of speed. I apply rapid left cyclic to avoid a bird. What should I be concerned with in regards to torque? Rotor? What is the name of this aerodynamic factor?

Torque will increase. NR will decrease (Transient Droop Improvement and the additional NR sensor will prevent a considerable decrease in NR; however, if the amount of transient TQ exceeds power available, you will droop the rotor.)

Transient torque is a phenomenon occurring in single-rotor helicopters when lateral cyclic is applied and is caused by aerodynamic forces. For conventional American helicopters where the main rotor turns counterclockwise, a left cyclic input causes a temporary rise in torque and a right cyclic input causes a temporary drop in torque. This is due to the increased AoA over the rear half of the aircraft leading to an increase in induced drag.

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