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I was obsessing with the issue I had with my AOA yesterday all day. I needed to head back to the hangar tonight to fix my AOA detection box to work with the new data I found from yesterdays run.  I was quickly able to re-plumb the AOA sensor box. The biggest change is what the AOA differential pressure sensor was using. Before, I was comparing the pressure between the AOA port on the pitot tube to the static pressure. This didn't work out so well, because the AOA port would sometimes be less than the static port. I replumbed the AOA pressure sensor to detect the difference between the AOA port and the pitot port.  The details of my change. The AOA pressure is on the low pressure side of the sensor, and the Pitot Pressure is on the high pressure side of the sensor.  Another look at the Pitot Tube. I still am baffled as to why the AOA sensing port pulls a vacuum compared to the static pressure during some phases of flight. The only thing I can think of is a Venturi effect happens as high airspeed passes over the AOA sensing port.  It was a great night to be at the airport. A few scattered thunderstorms in the distance. I was lucky and I was able to get my AOA sensor fixed and reinstalled with plenty of daylight left in the day.  I went on a quick ~20 minute flight to get more data. Here is the airspeed plot of my flight.  The pressure Altitude for the flight.  The raw AOA data - it tracks pretty close to airspeed.  Now here's the data I've been looking for - when you divide the AOA pressure (Differential Pressure) by the Pitot pressure (Dynamic or Impact Pressure)- you get the AOA! The two extremes of the AOA are indicated in this chart. The two zero-G maneuvers give me data where there wing is producing no lift. The other end of the spectrum is when the wing is at a high angle of attack during a stall. Notice that the AOA for a no-flap stall is lower than the AOA for a full-flap stall - as to be expected. Flaps add lift to the wing, causing it to be able to survive a higher AOA before stalling.  There was a mystery spot in my hangar tonight. Looks like oil dripping?  Hmm, something from this shelf.  Under closer inspection, it looks like my crappy Harbor Freight grease gun was haphazardly returned after being borrowed, with little regard taken for the proper orientation it should be stored in. I think I need to re-evaluate who has access to my hangar keys! 
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Last Modified: August 13, 2023 |