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182 flap position detection

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achimha View Drop Down

Joined: 24 Mar 2013
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    Posted: 24 Oct 2013 at 7:23am
I am happy that my DFC90 install is now 100% working. Apart from the problem with the display dimming (missing connection), I had the issue that the autopilot would not detect the flap position and give me "CAUTION, UNDERSPEED" on each touchdown.

Well, the problem was because the setup doesn't work the way Avidyne spells it out in the installation manual. It uses the mechanical flap position indicator of the Cessna and brings in two microswitches which are actuated by an arm glued to the Cessna mechanism (who came up with this???). Each microswitch has a different resistor which causes a different voltage drop on the 10V on pin 30 of P2. The resistor for the full flap position is indicated as 60kOhm and the target voltage on pin 31 is supposed to be 7.5V+-2V if I remember correctly. Well, that is not the voltage you get with 60kOhm, the drop is much higher (to ca. 4.5V). We ended up installing a 15kOhm resistor and getting ca 6V which worked.

Is the resistor value given in the installation manual incorrect? Also why did you design such a crude and complex flap position detection mechanism? Why didn't you just keep the S-TEC setup which consists of a potentiometer installed next to the flap motor? Compared to the rest of the system, this detail really is substandard...
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