**4. Conclusion**

such separation zone. Forward wings are high-wings, so there is no negative interference

**Figure 12.** Vortex over forward left wing (rotation angle 15°, angle of attack 24°).

As for tandem-scheme, distance between center of mass and vertical tail is relatively lower than for traditional aerodynamic scheme, so two fins are often necessary to provide yaw stability. As fins also rotate after launch, there are small separation areas after them (**Figure 15**). These aerodynamic defects also may be healed with some flexible fairings as

**Figure 13.** Vortices from rear wings go on forward wings (rotation angle 15°, angle of attack 24°).

with the fuselage.

82 Flight Physics - Models, Techniques and Technologies

for wing rotation units.

Quantitative results prove that UAV is unstable with wings' rotation angles up to 60° because rear wings produce lift ahead of center of gravity.

For high angles of wings, rotation (low sweep angles) UAV model is stable in a wide range of angles of attack because separation occurs mainly from forward wing and from root sections, so despite UAV asymmetry, it does not have tendencies to roll or spin.

Local aerodynamic defects were found in the area of the rotation units of both wings. A longitudinal vortex along the left side of fuselage was observed. It is generated due to model asymmetry so that the right wings are higher than the left ones. It was shown that this vortex does not result in significant roll moment.

Due to UAV longitudinal instability for small wings rotation angles, low time of wings unfolding is required.

Further research might include UAV dynamics modelling based on calculated aerodynamics characteristics or flight tests.
