**2.3.5 Results**

Presented method for blade air-loads calculation has been implemented in a computer code. Forward flight application is presented for SA 341 "Gazelle" helicopter at moderate forward speed condition (advance ratio is 0.35).

Fig. 18. Calculated free wake geometry; = 0.35 (3D view)

method of least squares. After that, it can be solved by some of the usual approaches, by

After unknown circulations *i* are obtained, velocity at every point of the flow field is known, and we can use them for the determination of aerodynamic forces that act on the blade. The calculation aerodynamic force is necessary for the defining of the blade position at the next moment of time. The total aerodynamic force is calculated as the sum of forces

> *<sup>i</sup> i ef* . *F V BC*

1 1 4 .

*dl Vt Vt* 

*i ef i ik*

 

is bound circulation vector and effective circulation can be defined by using:

*Mi i*

*LE k*

 

After determination of aerodynamic forces, moment of aerodynamic forces *MA* , necessary for blade flapping equation, can be calculated as sum of moments acting flapping hinge.

Presented method for blade air-loads calculation has been implemented in a computer code. Forward flight application is presented for SA 341 "Gazelle" helicopter at moderate forward

1

*i*

1

acting on all panels. Aerodynamic force acting on a single panel can be defined by:

which the unknown values of circulations *i* at the time *t* are obtained.

**2.3.4.4 Determination of the aerodynamic force** 

where *Mi* denote point at quarter-chord position on the *i*-th panel.

Fig. 18. Calculated free wake geometry; = 0.35 (3D view)

is 0.35).

where *BC* 

**2.3.5 Results** 

speed condition (advance ratio

By analyzing the drawing of the blade wakes, it can be concluded that model applied in this paper gives reasonable simulation of actual wake behavior, specially in the domain of wake boundaries, where wake roll-up occurs (although it is slightly underestimated compared with existing experimental data). In addition, larger wake distortion in the domains of the forerunning blades or their wakes is noticeable.

Fig. 19. Circulation distribution on the rotor disk; =0.35 (different points of view)

The program results (Figure. 19), show the difference in circulation distributions at different azimuths, as well as the disturbances caused when blades are passing the wakes of other blades, and the characteristic reversal flow domains.
