Can you make a sensor that detects wind direction?
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Can you make a sensor that detects wind direction?
For a Physics A-level project (another one) I have been tasked with building and testing my own sensor.
My idea was to make a sensor that digitally detects wind direction and or speed and display it on an LCD or something, you think I could do this?
If you have any tips or ideas could you let me know as im kinda stumped on this one!
Thanks,
Rusty
My idea was to make a sensor that digitally detects wind direction and or speed and display it on an LCD or something, you think I could do this?
If you have any tips or ideas could you let me know as im kinda stumped on this one!
Thanks,
Rusty
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To: Rusty Cessna
It has been done and is in use on at least two helicopters. One system is used on the AH 64 Apache and it sits on top of the rotorhead. It measures the wind direction in relation to the direction of flight. When in operation, I believe it spins at a speed higher than the rotor system. It looks something like an anemometer, which measures wind speed, but instead of cups on the end of the arms it has pressure sensors that measure air impact pressure. It knows which way the helicopter is flying and it measure the pressure differential between itself and the pitot air pressure as it rotates in a circular path. The internal computer derives the direction of the wind and its speed in relation to the helicopter.
The final calculation is fed into the weapons control system and is used to calculate trajectory and deflection.
The other system is used on the Bell AH1 J and possibly others including the Agusta 129. It is usually mounted to the fuselage on the right hand side near the pilots’ position. This unit is free to pick up its’ own position relative to the direction of flight and it has sensors to detect airspeed and position relative to the direction of flight. The position can also be influenced by the downwash of the rotor if the helicopter is stationary when firing its' weapons. The output is also used in weapons calculations.
There is also a third type that was made by a company called J Tech, which was located in the State of Iowa in the USA. This unit looked like a double-ended venturi. In the center of the venturi was a thin metal rod. On opposite sides of the venturi but not quite in line with the rod were two ultrasonic detectors. The operation of this unit is based on a phenomenon called vortex shedding. When air or water passed over the rod the flow would be disrupted and the air or water would form vortices as it passed the rod. The ultrasonic detectors sensed these vortices and recorded the frequency of vortex shedding. This went into a microcomputer and the output was the airspeed or water speed. It could not sense direction but it could record the speed if you knew which direction it was coming from. I believe they developed a multiple unit that was sensitive in several directions and the microcomputer could figure out the direction.
Good luck on your project.
------------------
The Cat
It has been done and is in use on at least two helicopters. One system is used on the AH 64 Apache and it sits on top of the rotorhead. It measures the wind direction in relation to the direction of flight. When in operation, I believe it spins at a speed higher than the rotor system. It looks something like an anemometer, which measures wind speed, but instead of cups on the end of the arms it has pressure sensors that measure air impact pressure. It knows which way the helicopter is flying and it measure the pressure differential between itself and the pitot air pressure as it rotates in a circular path. The internal computer derives the direction of the wind and its speed in relation to the helicopter.
The final calculation is fed into the weapons control system and is used to calculate trajectory and deflection.
The other system is used on the Bell AH1 J and possibly others including the Agusta 129. It is usually mounted to the fuselage on the right hand side near the pilots’ position. This unit is free to pick up its’ own position relative to the direction of flight and it has sensors to detect airspeed and position relative to the direction of flight. The position can also be influenced by the downwash of the rotor if the helicopter is stationary when firing its' weapons. The output is also used in weapons calculations.
There is also a third type that was made by a company called J Tech, which was located in the State of Iowa in the USA. This unit looked like a double-ended venturi. In the center of the venturi was a thin metal rod. On opposite sides of the venturi but not quite in line with the rod were two ultrasonic detectors. The operation of this unit is based on a phenomenon called vortex shedding. When air or water passed over the rod the flow would be disrupted and the air or water would form vortices as it passed the rod. The ultrasonic detectors sensed these vortices and recorded the frequency of vortex shedding. This went into a microcomputer and the output was the airspeed or water speed. It could not sense direction but it could record the speed if you knew which direction it was coming from. I believe they developed a multiple unit that was sensitive in several directions and the microcomputer could figure out the direction.
Good luck on your project.
------------------
The Cat
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Personally, I liked the wind direction indicator used on the Mk1 harrier. It was similar to a weather vane and had a luminessent strip on it for when the weather was poor. The best thing about it? No electronics and very simple to understand how it worked!
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A good project me thinks,
It might be an idea to consult some Honeywell manuals for their air data inertial reference unit's and see what base units they compute it from (it's too much to go in to here!!). These manuals if you can get them, provide some easy to digest info.
Good luck.
It might be an idea to consult some Honeywell manuals for their air data inertial reference unit's and see what base units they compute it from (it's too much to go in to here!!). These manuals if you can get them, provide some easy to digest info.
Good luck.
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Speed.
You want to spin a shaft, then measure the rate of rotation. To spin it, you could
1. Attach an axial flow fan blade (propellor like) which you will have to maintain pointed into the wind. OR
2. Make a cup anemometer - four small light, rigid cups (bottoms of coke bottles ?) attached to the shaft by four identical arms. Less sensitive to orientation. Axis of rotation at right angles to airflow, which on the ground generally means vertical.
In each case you will need to minimise friction.
To measure its rate of rotation, either
1. Connect a small model maker's DC motor to the shaft. Motor will output DC current. Will have some AC ripple which may need to be filtered out with a capacitor. Output is DC. If you want to digitise it, get an Analog/digital converter device from your local electronics store. Match up the output of the motor (now generator) to the ADC if necessary, and display the digital output. OR
2. Attach a disk to the rotating shaft, with a hole on it near the edge. Build an optical sensor around that hole so that in conjunction with a timer circuit, you can count the rate at which the hole appears at the sensor.
Calibrate against a car speedo on a no wind, no police day by holding the device clear of flow distubances from the car.
Direction
You need a digital shaft encoder. Instrument suppliers like Honeywell make them to allow remote sensing of the position of things like valves, crane boom angles etc.
You could make a very rudimentary one to at least show you understand the principle as follows
Imagine a disk with a radial reference line drawn on it, which we will call zero.
On the outside, inscribe it with an arc, starting a 180 degrees, which goes exactly half way around the circle back to zero. Suppose we call that circle "3", with the bit of the circle which is black called "1", and the other bit "0"
Come in a bit and get ready for another circle called "2". Start inscribing more alternating arcs on the disk, starting at 90, but this time each arc subtends only half the angle of the previous arcs. So you draw an arc 90 to 180 degrees, then skip to 270 where you draw another from 270 to 0. Black bits are "1", others are "0".
Come in again for another circle called "1". Start at 45, and draw alternating arcs, but only half the angle subtended by the last set of arcs. That is, the black bits go 45 to 90, 135 to 180, 225 to 270 and so on.
Come in again for another circle called "0" which has black bits going 22.5 to 45, 67.5 to 90, 112.5 to 135 etc.
Each new circle doubles the number of alternating arcs.
Now if you can make up a detector which can read through a radial window what bits of drawn arcs (the 1s) are displayed in what circles, you can now establish the position of the disk to within 360/16 or 22.5 degrees.
More circles - higher resolution.
So 0 to 22.5 reads 0000 binary = 0
22.5 to 45 reads 0001 binary = 1
247.5 to 270 reads 1011 binary = 11 and so on
And the angular position is in the range (22.5 x output) to (22.5 x (output + 1))
All you have to do now is attach such a disk to a wind vane.
If you don't want to do the mechanicals and electronics, you could dummy up a pretty good cardboard replica with neat little windows displaying the binary output, a mock wind vane attached to it and so on.
Lots of other analog and digital alternatives if you think about it.
Hope that prompts some ideas for you.
You want to spin a shaft, then measure the rate of rotation. To spin it, you could
1. Attach an axial flow fan blade (propellor like) which you will have to maintain pointed into the wind. OR
2. Make a cup anemometer - four small light, rigid cups (bottoms of coke bottles ?) attached to the shaft by four identical arms. Less sensitive to orientation. Axis of rotation at right angles to airflow, which on the ground generally means vertical.
In each case you will need to minimise friction.
To measure its rate of rotation, either
1. Connect a small model maker's DC motor to the shaft. Motor will output DC current. Will have some AC ripple which may need to be filtered out with a capacitor. Output is DC. If you want to digitise it, get an Analog/digital converter device from your local electronics store. Match up the output of the motor (now generator) to the ADC if necessary, and display the digital output. OR
2. Attach a disk to the rotating shaft, with a hole on it near the edge. Build an optical sensor around that hole so that in conjunction with a timer circuit, you can count the rate at which the hole appears at the sensor.
Calibrate against a car speedo on a no wind, no police day by holding the device clear of flow distubances from the car.
Direction
You need a digital shaft encoder. Instrument suppliers like Honeywell make them to allow remote sensing of the position of things like valves, crane boom angles etc.
You could make a very rudimentary one to at least show you understand the principle as follows
Imagine a disk with a radial reference line drawn on it, which we will call zero.
On the outside, inscribe it with an arc, starting a 180 degrees, which goes exactly half way around the circle back to zero. Suppose we call that circle "3", with the bit of the circle which is black called "1", and the other bit "0"
Come in a bit and get ready for another circle called "2". Start inscribing more alternating arcs on the disk, starting at 90, but this time each arc subtends only half the angle of the previous arcs. So you draw an arc 90 to 180 degrees, then skip to 270 where you draw another from 270 to 0. Black bits are "1", others are "0".
Come in again for another circle called "1". Start at 45, and draw alternating arcs, but only half the angle subtended by the last set of arcs. That is, the black bits go 45 to 90, 135 to 180, 225 to 270 and so on.
Come in again for another circle called "0" which has black bits going 22.5 to 45, 67.5 to 90, 112.5 to 135 etc.
Each new circle doubles the number of alternating arcs.
Now if you can make up a detector which can read through a radial window what bits of drawn arcs (the 1s) are displayed in what circles, you can now establish the position of the disk to within 360/16 or 22.5 degrees.
More circles - higher resolution.
So 0 to 22.5 reads 0000 binary = 0
22.5 to 45 reads 0001 binary = 1
247.5 to 270 reads 1011 binary = 11 and so on
And the angular position is in the range (22.5 x output) to (22.5 x (output + 1))
All you have to do now is attach such a disk to a wind vane.
If you don't want to do the mechanicals and electronics, you could dummy up a pretty good cardboard replica with neat little windows displaying the binary output, a mock wind vane attached to it and so on.
Lots of other analog and digital alternatives if you think about it.
Hope that prompts some ideas for you.
