In the last Mothcast I promised that I would write a blog post on how I measure the AOA on my boat, … well here is how I do it.
Firstly I flip the boat upside down, and get it flat so it won’t move. I don’t need it to be level, so I don’t bother with that.
I insert my iPhone in to the patented angle-o-meter that I have built, using very bush mechanic skills …
The critical thing is that the bottom of the gauge is exactly parallel to the chord line of the foil section.
With the phone on my known measurement datum (right behind the centreboard I reset the reading on the iPhone application (I use iHandy Level or the one I wrote myself), so it reads 0.0.
I then slide the bracket over the end of the foil, and then read the AOA off the gauge.
If you don’t have an iPhone you can buy an Angle Pro from hangar 9, and use the same method.
I just posted how I measured my angle of attack. I used a laser level which only shoots a horizontal beam so I had to level out the boat which was a bit of a pain. I think I’m gonna get an electronic level which you can zero out.
I wouldn’t trust that as far as I could throw it, and based on my desire to throw my iPhone a very long way… I tried hanging a picture with it the other week and could get it straighter by eye than using Handy Level! It’s a shame as it would make life so much easier!
are the measurements repeatable?
ive had sucess with one of these
http://www.sydneytools.com.au/shopexd.asp?id=11890&bc=no
@Cookie it depends largely on calibration and sensitivity, i.e. how the noise from the accelerometers in the phone is removed.
I have written my own version as well, so as I wrote the code (and tested it) I have a lot more confidence that it is doing what it is supposed to.
I read your post on the Angle Pro, looks nice. I am doing a bit of carbon stuff at the moment for a Dubai race team, and we talked about it. They showed me a good unit they use for setting up the GT cars. Will borrow it when the Mach 2′s and Assassin arrive, always interesting to see how things compare.
PS: You could write something on the iPhone to work out the height of a tall building, just get it to beep every second, and count the beeps after you drop it …
we swear by these
http://www.testntools.co.nz/digital-protractor-angle-finder-level-v-groove-p30192.html
i phone level is a gadget Big Fella, I have it also and they are not accurate.
Water level is old school and a great deal slower to set up but it is always true.
Hope you are well,
Grant
I can tell you guys don’t write software for a living …I have written and adjusted the code myself. the problem is that they are TOO accurate, and you need to remove the noise. It is the algorithm on removing the noise from the waveform that is produced by the three axis accelerometer that leads to the “inaccuracy”.
The correct term would be they are not precise, not that they are not accurate.
A bubble level by contrast is accurate but not precise.