Air Density

[Frank Lee]

I reduce speed in head/strong xwinds, and have delayed trips when the winds were too unfavorable. I like driving at night and oftentimes strong daytime/evening winds really diminish after sunset.

[mluckham]

I'm a glider pilot - yaw strings assist us to operate the rudder properly for best coordinated flight and minimizing drag. But they don't provide a number readable by an Arduino!

Test aircraft which might be flying in a yawed condition use a swivelling probe with a fin, but I think the important data for a ground vehicle will be obtained by readings straight ahead.

I have a dual-port pressure transducer from Freescale MPXV5010DP which measures 0-1.45 PSI and provides a differential measurement (dynamic and static ports) in a suitable mounting arrangement. I read that 1 PSI = 235 mph, so it may have too wide a range such that the noise figure or ADC conversions make it hard to measure lower airspeed very accurately. Here's another reference Airspeed

Doviat's comment

I guess you could use it to help justify your bad run or tank in all headwinds driving. ;-)

is about at my level. But if you could use the data to correct for air resistance and get a corrected mileage figure, it should then be possible to make small improvements on the car and see the difference. As it is now, one needs to drive quite a distance to do so - or wait for times of no wind.

Interesting about measuring the vacuum behind the vehicle as well.

[dcb]

an arduino can read a spring loaded plate on a potentiometer, on a stick out in front. Calibrate w/speedo on a calm day.

[dcb]

these thingies would probably be easy to fabricate for cheap too and stick out front if you didn't want to spend $70
SparkFun Electronics - Weather Meters

[mluckham]

ha-ha, that's good - the car will start to look like a storm-chaser

I got the pressure transducers as free samples from Freescale - can't beat that price. I've mounted two in a plastic "test tube". One of the transducers is connected for dynamic+static pressure for airspeed. The other, I blocked one of the ports so as to read static pressure only. Haven't tested these in a vehicle yet. I may have damaged one during soldering/handling - it gives odd readings

I have a GPS Shield with SD memory card - haven't worked on it in a few months due to work commitments, there was an issue running out of stack space while creating files on the card - it needs to be solved, or change the platform ... I have Atmega 328's but that won't solve the stack issue I think. Probably the Arduino Mega is what I should be using for this project.

[mluckham]

I have a working Arduino sketch (not MPGuino) that is outputting airspeed in knots, using the pitot-static tube. It hasn't been testing a lot, but speed agrees quite well with GPS-calculated ground speed - a GPS modem is also part of the project.

So far I've been testing by holding the pitot-static tube out the window - getting kind of cold for that up here! Thinking about it more though, the pressure transducer should be relocated inside the vehicle and just run plastic tubing outside - with a method to collect/drain moisture from the lines as in an aircraft. I'd hate to get water into the actual sensor.

[basjoos]

If you search back through the older Gassavers threads, Crousdb installed an ultralight aircraft airspeed indicator on his Civic VX. In addition to detecting head/tailwinds, it also was good for finding the best position when drafting.