"positive"???  You mean positive relative to ambient,
rather than positive absolute, right?

If so, then why?  I would expect that it should just be
ambient, unless the gaps are in such a location that it
has a ram-air effect.  In either case, should it be
easy to calibrate/compensate for this in code?




-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Bob Japundza
Sent: Wednesday, June 19, 2002 12:30 PM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [PIC]: Autopilot landing system for model aircraft


Because pressure is usually positive inside the fuselage.

The best place for a static port is about 1/3 the way between the trailing
edge of the wing and the horizontal stabilizer.

Bob


> -----Original Message-----
> From: Pic Dude [mailto:picdude@AVN-TECH.COM]
> Sent: Wednesday, June 19, 2002 12:23 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]: Autopilot landing system for model aircraft
>
>
> Missed a bunch of this thread, but just looking at this...
> Why can't you just use the pressure *inside* the aircraft
> for the static pressure (assuming it's not airtight)?  If
> so, then it would be really easy to do using any of the
> low-cost gauge or diff pressure sensors out there.
>
> Cheers,
> -Neil.
>
>
>
> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Jeremy Furtek
> Sent: Wednesday, June 19, 2002 12:14 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]: Autopilot landing system for model aircraft
>
>
> ----- Original Message -----
> From: "Walter Banks" <walter@BYTECRAFT.COM>
> Sent: Wednesday, June 19, 2002 4:41 AM
> Subject: Re: [PIC]: Autopilot landing system for model aircraft
>
>
> > "Andrei B." wrote:
> > >
> > >  Such a small scale air speed sensor is a challenge
> itself (I think).
> > >
> > This may be one of the easier parts to build. Airspeed
> measurement is
> > a function of ratio between ram air pressure and static pressure.
> > There are lots of pressure sensors these days.
> >
> > w..
>
> I think that the subtle and challenging part of doing this
> (accurately) is
> measuring static pressure. The presence of the aircraft
> influences the flow
> field. For full size aircraft I think that they expend some
> effort to find a
> position on the aircraft that will give an accurate reading for static
> pressure under a representative set of operating conditions.
>
> A wind tunnel test ($$$) of an aircraft may include placing
> pressure taps
> along the model along the centerline. If you plot the
> pressure coefficient
> (comparing measured pressure to the static pressure measured
> well upstream
> or far away from the aircraft) along the axis of the aircraft, good
> locations for the static pressure tap would be places where
> this value is
> zero.
>
> For a flying model, to determine the static pressure, I think
> that they may
> sometimes drag an instrumented object far behind the
> aircraft, and compare
> that to the taps on the aircraft.
>
> For an R/C, you could do something similar. Another
> alternative would be to
> determine the best location computationally, a la CFD.
>
> Just my $.02.
>
> Jeremy Furtek
> mailto:jfurtek@agames.com
>
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