On Tuesday 04 May 2004 20:24, Jim Wilson wrote:

> In any case it'd be interesting to know if this method is anything like how
> a real AP works,  both in the AN-225 and others, like the c172.  My guess
> is that it isn't even close, and the whole heading intercept espeicially
> and nav1-heading-error method we're using is wrong.  Maybe we can treat
> interception and ils hold as two seprate functions.

I _guess_ autopilots separate the interception and tracking modes.

Check out the KAP140 autopilot in the default C172. The nav/localizer hold 
mode is implemented with 3 controllers. One controls the ailerons to reach a 
specified turn rate. This turn rate is output by a controller that gets the 
desired intercept angle as input. The third controller outputs this desired 
intercept angle from the nav/localizer needle deflection. The second 
mentioned controller uses the heading bug as reference so the desired 
intercept angle is to the left or right of the current heading bug heading. 
Heading bug has to be set roughly to the radial or the desired course for 
this to work right. This works in crosswinds too. Try it!

If this explanation was less than understandable (my fault entirely) then take 
a look at the KAP140.xml file under /Aircraft/c172p/Systems.

Roy Vegard Ovesen

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