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Propeller thrust measurement is particularly critical in the design and operation of Vertical Takeoff and Landing (VTOL) aircraft. These aircraft rely on the thrust generated by their propellers for lifting and control their vertical and horizontal movement.
In a VTOL or eVTOL (electrical VTOL) aircraft, the propellers must produce enough thrust to overcome the weight and generate lift for takeoff and landing. This requires accurate measurements of the propeller's thrust output to ensure that the aircraft is capable of safe and stable operation.
Furthermore, differently from regular helicopters, VTOL or e-VTOL aircraft often utilize multiple propellers, with each propeller contributing to the overall thrust produced by the aircraft but also interfering in the overall performance and stability of the aircraft. As such, measuring the thrust output of each propeller individually is key in maintaining the balance and stability of the aircraft during flight.
In addition to thrust, the ability to precisely measure the propeller shaft torque in a VTOL is also crucial for maintaining control of the aircraft. Torque measurement allows engineers to optimize the performance of the propellers when operating in conjunction and ensure that they are operating within safe and efficient parameters.
How to measure the thrust of a propeller
Thrust is a fundamental principle in the aerospace industry. This force is produced by the rotation of a VTOL propeller's blades, creating a flow of air that propels the aircraft forward.
To measure thrust, a load cell is mounted axially to the motor stand base to measure upward lift load over the range of propeller speeds. The load cell is then used to measure the force in Newtons (N) produced by the propeller in the axial direction, which is the direction of the propeller's axis of rotation.
How Multi-Axis Load Cells are Utilized for Propeller Thrust and Torque Measurement:
Bi-axis load cells are a valuable tool in measuring simultaneously the thrust and torque produced by a VTOL aircraft propeller. FUTEK MBA500 Thrust and Torque Sensor is capable of measuring axial load and torque, allowing for the capture of all axial forces and torques produced by the propeller.
The axial force, measured in Newtons (N), is the thrust produced by the propeller, while the torque, measured in Newton-meters (Nm), are the torque acting perpendicular to the axis of rotation.
Contact us to discuss your requirements of propeller thrust stand. Our experienced sales team can help you identify the options that best suit your needs.
This is a very tricky subject. It is both easy to learn the basics but can take years to master, like chess...or women. (sorry Epi)
There are three main determining factors in prop/motor selection.
1. The motors KV rating. This will tell you what the motor wants to spin at with no load/per volt. Easy example: KV motor on 3v will spin...drumroll please... rpm. The math: (the kv) times 3 (volts) = revolutions per minute (revolutions in this case is turns the shaft makes, not a forcible overthrow of a government or social order in favor of a new system.) The higher the KV rating, the faster that motor is going to spin the prop. The faster the prop moves, the more lift the airfoils on the blade can create. More lift = more drag and therefore will have a huge impact on number 3. But before that, we move to number...
2. The prop. Prop size will ultimately determine what the amp draw will be by putting a load on the motor. Just how much load is determined by the diameter of the prop and it's pitch. The larger the diameter, the larger the column of air it will affect. Think of this as the torque or pulling power of the prop. This is why everyone says a larger prop is like a lower gear in your car, it will get you up to speed faster. But a prop also has pitch. Pitch is what determines your top speed. A high pitch prop will fly faster than a low pitch prop.
3. Amp draw. The maximum amp rating on your motor is very important. This will tell you what you can and can't run on your motor. Why? That is a fantastic question and I'm so happy you asked it!
Let's say you want to go flying. You know that a large prop will get you up to speed fast and a high pitch will make it go fast. So, you grab a 14x9 prop and run for the door. Bad idea! Why? Again a fantasti...ok right. Back to props.
The real balancing act in prop selection is just that, balance. You want a large enough prop to get you up to speed quickly and one that will make you go fast. The trouble is, a large diameter prop will create a larger load on the motor. A larger load on the motor will cause the motor to do what, class?
Yes! Very good! A larger prop will cause the motor to draw more amperage. A high pitch will do the same thing, cause the motor to draw more amps. Why does this matter? Well, at a certain point, you will make that poor little motor work harder than it can handle and it will release the magic smoke. A too large prop can very quickly burn up a motor. So, where does the balance part come in? Amp draw! If you go with a lower pitch, you can get away with a larger diameter. If you go with a smaller diameter, you can get away with a larger pitch.
So, by starting at the manufacturers recommended prop size, you can play around and fine tune what you need the plane to do and still stay within the maximum capability of the motor.
There are many other factors involved which is why most people have a hard time learning how to choose a prop, but this should give you a good basic knowledge of prop selection and hopefully should show you why the guys suggest a larger diameter/smaller pitch on 2S.
Now, I am assuming the 9x4.7 is on a 2 cell only because I don't think the motor would survive that prop on a 3 cell for very long. I could be wrong and it might survive, but I'm thinking it would be at very moderate throttle settings...
Disclaimer:This post is meant to be informative and entertaining so I really hope it doesn't come across as condescending...it certainly wasn't meant that way.
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