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" 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 -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body