This paper describes comparison between virtual simulation of quadrotor flying platforms (mini UAV - Unmanned Aerial Vehicle) and real experiments. In quadrotor helicopter (quadrocopter) air flows that are going out from rotors and affecting each other were simulated. Analysis of several helicopters that have different distances between rotors on different angular velocities were compared. During virtual simulation (with CFD Computational Fluid Dynamics software) there were conducted similar to real experiments with the use of scanned rotors (with 3D scanner) and same environment conditions. These experiments were compared with real experiments. Optimal gap distance between rotors is determined, when helicopter mass is minimum and rotors are creating maximum lifting force and consuming minimum energy (minimum impact on air flows to each other).

This article discusses the lift force generated by a mini unmanned aerial vehicle. Shrouded propellers were considered and analyses of shroud influence on lift force and energy saving were done. By help of laboratory experiments and computational fluid dynamics simulations (propeller velocity varied from 1000 rpm to 6000 rpm, shroud height from 20 mm to 60 mm, gap from 3 mm to 28 mm), it was shown that the shroud diameter influenced the rotor energy consumption up to 30% at velocities of more than 4000 rpm. With the increase shroud diameter (increase of distance between shroud and propeller borders), the lifting force increased. A gap of more than 30 mm practically did not influence the lifting force. Shroud height (from 20 mm to 60 mm, gap is 28 mm) also influenced the propeller efficiency (up to 10%) on small shroud heights (up to 30 mm). With the increase of the shroud height, the lift force decreased about 3% and then it increased up to 12%. From a value of about 50 millimetres, this influence will be unchanged but the total lifting force will be about 5% less in comparison with the force produced by propeller without shroud.

The article discusses lift force generated by mini UAVs (Unmanned Aerial Vehicles). CFD (Computational Fluid Dynamics) simulations were made on the base of a 3D scanned propeller model. Influence of some geometrical parameters of propeller (like velocity or pitch) and quadcopter (like gap) on lifting force was considered. Different propeller pitches were used and pitch influence on propeller lift force was analysed. Normally, lifting force will increase with the increasing of propeller pitch but for different rotation velocities, this increasing is different and in all cases, it can be approximated by a linear relationship. To obtain dependency functions, an equation for calculation of lift force given took into account the correction coefficients. This equation gave reliable results at pitch values equal to 0.3 -0.7 of the propeller diameter and at rotation velocities of 2000 min -1 -8000 min -1 .Lift force dependency from distance between rotors was also considered. Simulations and experiments showed that the lifting force of a quadcopter increased about 15% on gap distances from 5 mm to 35 mm. From a distance of 70 mm, the lifting force will decrease about 2% and then will stabilise. At increasing of distance between propellers from 5 mm until 25 mm, the power consumption decreased 8% -10% and after the gap distance equal to 40 mm, it will be stable and minimal. It can be asserted that quadcopters have different optimal distances between the propellers at different rotation speeds to generate the same force. Equations for calculation of optimal gap distances for different multicopters were derived and calculation results are presented in graphs and tables.

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