During the development of the
AOA instruments, Jim accumulated reams of L/D data over a wide range of flight
parameters which he ultimately used to write the code that makes them work.
The original R&D work was done with his LA4 and then refined when he
started using his LNC2 for further testing. In the process he discovered
that, in general, as you lowered the flaps that the lift increased more than
the drag up until you reached about 1/3 flaps down. At that point, the
lift curve flattened out and the drag curve steepened. Consequently,
the critical AOA remained fairly constant from about 1/3 flaps down to full
flaps, so switching the instrument to the flaps database at that point
resulted in the most conservative indications throughout the entire AOA range
of the wing. Another way of looking at it (considering there are only 2
airfoil databases) is that the critical AOA is similar from flaps up to just
about 1/3 flaps down, and the critical AOA from 1/3 to full flaps is also very
similar... yes, there will be some minor inaccuracies in both databases at
that 1/3 flaps position, but it's the most convenient and reasonable place to
switch from one to the other and reflect as closely as possible to the actual
L/D curve throughout the full range of flap travel. I hope this makes
sense.
<marv>
Colyn Case <colyncase@earthlink.net>
wrote:
> Marv,
>
> I asked that question to current
owners of aoa pro and couldn't get a
>straight answer. What
I would really like to understand is what does the AOA
>"see" as the
flaps change position, ignoring the effect of the flap switch
>for a
minute.
>
> Colyn
>
> On Jan 6, 2014, at 10:13 AM,
<marv@lancair.net> <marv@lancair.net> wrote:
>
> I
don't know if it was mentioned in the installation instructions but the
>AOA flap switch should be setup to signal flaps down at about 1/3 of
their
>down travel. While there are an infinite number of
flap positions the AOA
>only tracks 2 of them, flaps up and flaps
down. The logic of setting the
>switch to trigger flaps down
when they're only 1/3 of the way down is that's
>the approximate
location when the flaps' position impact drag more than lift.
> The
critical AOA from 1/3 to full flaps is very similar and is the reason
>that Jim Frantz always suggested that switch position as the most
appropriate
>compromise to not having multiple flap position data
available for the
>instrument. I hope this helps.
>
> <Marv>
>
>
> John Cooper <snopercod@comporium.net>
wrote:
>
>> On my L-235 I couldn't figure out a good way to
mount a microswitch for the
>>AoA system which would engage in the
"flaps down" position, so I used a
>>U-shaped magnetic reed switch
instead. The NO contacts close when a ferrous
>>object passes
between the two arms of the switch and my flap actuator arm
>>serves
that function. I glued a couple phenolic "guides" onto the switch in
>>case the flap actuator and switch became mis-aligned for any
reason. This
>>scheme seems to work, but I'm fiddling with the
adjustment at the moment.
>>This photo (looking aft) shows the flaps
in the "UP" position and the
>>microswitch not engaged.
>>
>
>
>
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