Increasing the prop diameter by a factor of 2 will increase the power needed to rotate the prop at the same RPM by a factor of 16. As you can see in your equation, the prop diameter has a very large affect on power. The variable of interest (the D in your equation above) is the length from one blade tip to the other blade tip on a two bladed propeller. That part of the propeller should have very little to do with thrust and power calculations because it introduces very little rotational inertia and contributes nothing to thrust. I can only assume that the propeller center hub refers to the center of the propeller where the two blades meet in the middle. Hi Duc, I’m really glad you’re enjoying my blog. The importance of hovering will be addressed in the following section (DC Motors). In particular, a thrust (mass) that equals the mass of the aircraft is needed for hovering. Solving for mass is useful for quadrotor helicopters because it can be directly related to the mass of the aircraft. Newton’s Law, F=ma, is used to obtain equation 6. In doing so, Δv is eliminated and torque can be calculated.įinally, it is advantageous to express the results of equation 5 in terms of mass. Equation 5 shows the result of solving equation 4 for Δv and substituting it into equation 3. Equation 2 gives thrust based on the Momentum Theory.Ī commonly used rule is that velocity of the air at the propeller is v=½Δv of the total change in air velocity: Therefore, and equation 3 is derived.Įquation 4 gives the power that is absorbed by the propeller from the motor. The next step is to determine the thrust produced by a propeller. Given a rotational speed of 10,000 rpm, the calculation goes as follows: Power=0.015X10 3.2=24 W. For example, a 6X4 APC propeller has a propeller constant of 0.015 and a power factor of 3.2. Where power is in watts and rpm is in thousands. has compiled empirical data used to calculate power, and the formula used for their datasheet is given in Equation 1. The first step in calculating static thrust is determining the power transmitted by the motors to the propellers in terms of rpm. Also, it is important to note that the final calculations of static thrust are estimates and not actual values. This low-speed performance ensures that the calculations of static thrust can be applied to a wide range of flight conditions. This calculation is particularly important for this project because quadrotor helicopters are more likely to perform at low speeds relative to the earth. Static thrust is defined as the amount of thrust produced by a propeller which is located stationary to the earth. Calculations of static thrust are needed in order to ensure that the proper propellers and motors have been selected.
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