Ultrasonic airspeed measurement

[Hauntme13]

Has anyone tried this in rc aircraft? Look at kit 168 at www.kitsrus.com This kit is very good at measuring low airspeeds like 1 mph on up.

[Marion]

What is the MAX speed it can measure ?? Any idea ??

[Hauntme13]

It's already measuring the speed of sound. It shouldn't have a problem with 100+mph winds. If the resolution gets too low, the transducers could be placed further apart. I would use one of these rangefinder modules modified with the transducers facing each other along with a pic to read it. would keep the weight way down. Plus a simple lightweight telemetry system can be made from these twx434 modules.

[Marion]

Most interesting !! Keep us posted on this...

[treehog]

I looked for the cost of this Kit 168 the Ultrasonic Wind Speed Meter
non of the importers listed had it or any price
how much did you pay and and where did you purchase it
also would it measure speeds acuratly at any altidude
I have a high altitude requirement
ralf

[jeffs555]

Ralf,
Since the kit measures the time in both directions, that should take the speed of sound with its altitude variation out of the equation. You should update your profile with your location especially when you are asking where to buy something. Here is one Canadian source for the kit. http://www.qkits.com/serv/qkits/diy/pages/QK168.asp

Jeff

[Hauntme13]

Actually, the module pictured to the left of the radio modules above is a sonar rangefinder. It could be used for airspeed if one of the transducers were relocated so it faced the other. It should work like this: in calm air, the speed of sound could be calculated since we know the distance between the sensors, and the length of time the 'ping' took to travel from the sender to the reciever. Let's call the calm air measurement 'X'. Now in moving air (air is moving from the sender to the rx sensor) the time measured would be 'Y'. Airspeed = Y-X. Since only the speed of the air affects the measurement, not the air density, altitude should have little or no effect. BTW, the sonic rangefinder module and the 433mHz data link modules can be found at www.rentron.com. (I have these and they work great, data rate of 5kbps.)

[jeffs555]

The problem with measuring in one direction only, is that the speed of sound varies with temperature, so you would have to recalibrate it often in calm air. A temperature change of 1 degree celsius will change the speed of sound about 1.3 mph. Not too significant at 100mph, but for a slow flying model it might be.

Jeff

[treehog]

My location is europe southern france mostly but sometimes south germany

The device could be of some use so I will pursue these links

Ralf

[Hauntme13]

Yes temp may have an effect on the measurement, but if we know the amount i.e. 1.3mph per degree celsius, it wouldn't be too difficult to add a thermistor or digital temp gauge to the microcontroller to compensate. Dallas Semiconductor makes a neat 1 wire digital temp sensor that would be ideal-DS18B20. Very small, light, low cost, digital accuracy, and only uses 1 microcontroller pin.