Study on the lift and propulsive force shares to improve the flight performance of a compound helicopter

To investigate the effects of lift and propulsive force shares on flight performance,a compound helicopter model is derived.The model consists of a helicopter model,a wing model and a propeller model.At a low speed of 100 km/h,the Lift-to-Drag ratio(L/D)of the compound helicopter is improved when the wing provides 20.2%of the take-off weight.At high speeds,the L/D can be improved when the propeller provides the total propulsive force.Lowering the main rotor speed increases the wing lift share,however,the maximum L/D increases first and then decreases.The maximum L/D increases with decreasing the blade twist of the main rotor.Decreasing the blade twist from-16°to-8°increases the maximum L/D by 2.3%,and the wing lift share is increased from 65.0%to 74.7%.When the main rotor torque is balanced by the rudder,the maximum L/D is increased by 2.2%without changing the wing lift share.The wing should provide more lift as increasing the take-off weight,which reduces the induced power of the main rotor and increases the L/D.When increasing the take-off weight from 9500 kg to 11000 kg,the maximum L/D is increased by 6.5%,and the wing lift share is increased from 74.7%to 80.2%.

Effect of the structure of backward orifices on thejet performance of self-propelled nozzles

Self-propelled nozzle is a critical component of the radial jet drilling technology.Its backward orifice structure has a crucial influence on the propulsive force and the drilling performance.To improve the working performance of the nozzle,the numerical simulation model is built and verified by the experimental results of propulsive force.Then the theoretical model of the energy efficiency and energy coefficient of the nozzle is built to reveal the influence of the structural parameters on the jet performance of the nozzle.The results show that the energy efficiency and energy coefficient of the backward orifice increase first and then decrease with the angle increases.The energy coefficient of forward orifice is almost constant with the angle increases.With the increase in the number and diameter,energy efficiency and energy coefficient of the forward orifice gradually decrease,but the backward orifice energy coefficient first increases and then decreases.Finally,it is obtained that the nozzle has better jet performance when the angle of backward orifice is 30°,the number of backward orifice is 6,and the value range of diameter is 2-2.2 mm.This study provides a reference for the design of efficiently self-propelled nozzle for radial jet drilling technology.

HYDRODYNAMIC ANALYSIS AND SIMULATION OF A SWIMMING BIONIC ROBOT TUNA

A dynamic model for undulatory locomotion was proposed to study the swimming mechanism of a developed bionic robot tuna. On the basis of inviscid hydrodynamics and rigid-body dynamics, the momentum and propulsive force required for propelling the swimming robot tuna＇s flexible body was calculated. By solving the established dynamic equations and efficiency formula, the swimming velocity and propulsive efficiency of the bionic robot tuna were obtained. The relationship between the kinematic parameters of the robot tuna＇s body curve and the hydrodynamic performances was established and discussed after hydrodynamic simulations. The results presented in this article can be used to increase the swimming speed, propulsive thrust, and the efficiency of underwater vehicles effectively.