Our heavyweight helicopter equal in the world does not have
In Rostov started production of the most load-lifting rotary-wing car The Russian holding «Helicopt[...]
Parasitic Power
The parasitic power, Pp, is a power loss as a result of viscous shear effects and flow separation (pressure drag) on the airframe, rotor hub, and so on. Because helicopter airframes are much less aerodynamic than their fixed-wing counterparts (for the same weights), this source of drag can be very significant. We can write the parasitic power as
/ л
Pp = (дрО«г Є„Л Voo, (5.47)
where SVef is some reference area and Cof is the drag coefficient based on this reference area. In nondimensional form, this becomes
с”4(т)^ = :К£И (548)
where A is the rotor disk area and / (= CDfSTef) is known as the equivalent wetted area or equivalent flat-plate area. This parameter accounts for the drag of the hub, fuselage, landing gear, and so on, in aggregate. The concept of equivalent wetted area comes from noting that while the drag coefficient can be written in the conventional way as
Df
‘f ipV&Srt’
 |
 |
where Sref is a reference area, the definition of SKf may not be unique. Thus an equivalent wetted area is used, which is defined as
This avoids any confusion that may arise through the definition of ST&f. It is found that values of / range from about 10 ft2 (0.93 m2) on smaller helicopters to as much as 50 ft2 (4.65 m2) on large utility helicopter designs. The concept of equivalent flat-plate area is discussed further in Section 6.6.1.
Another approach represents the parasitic drag of the helicopter relative to a value measured at a reference speed of 100 units (ft/s, kts, etc.) at sea level conditions. The drag at any airspeed and altitude is then calculated using
( V 2
D = Dm{m)a’ (5-51)
where о — p/po as given by Eq. 5.11 or Eq. 5.12.
5.4.3 Climb Power
The climb power is equal to the time rate of increase of potential energy. If the potential energy is denoted as E, then E = Wh. The rate of increase of potential energy is Wh = TVC = WVC, where W is~the aircraft weight and Vc is the climb velocity. The climb power coefficient can be written as Cpc = kcCw- The effect of the fuselage vertical drag is normally taken into account when estimating the climb power, and this is discussed further in Section 6.6.2.
