I'm planning to have an airspeed as well as altitude sensor in a PIC-based R/C plane project. My current thoughts are to have a combined static and stagnation pressure pitot tube and mount that in the nose cone. The pitot would be made of two tubes, where the inner tube is open to provide stagnation pressure while the inner would be closed at the end but have drilled holes in the sides for static pressure. The static pressure would be fed both to an absolute pressure sensor for altitude and to one input of a differential sensor for airspeed. Regarding the current discussion, isn't the nose cone, pointing forward the optial place to have the pitot at providing you don't have a propeller disturbing the measurement? Where do an aircraft with a pusher prop have its pitot tube? My model is a ducted fan, ie similar construction as a jet. --Thomas > -----Original Message----- > From: pic microcontroller discussion list > [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Jeremy Furtek > Sent: Wednesday, June 19, 2002 11:39 PM > To: PICLIST@MITVMA.MIT.EDU > Subject: Re: [OT] Autopilot landing system for model aircraft > (air speed) > > > ----- Original Message ----- > From: "Walter Banks" > To: > Sent: Wednesday, June 19, 2002 1:51 PM > Subject: Re: [PIC]: Autopilot landing system for model > aircraft (air speed) > > (snip) > > A simple way to > > get static pressure is the way many full size light A/C do. > > > > Ram air pressure is a tube pointing straight forward outside > > of the propeller wash. From a wing for example) Static is > > a tube in parallel to the RAM air tube with the end capped > > and 3 or 4 small holes drilled in its sides. Both the tubes > > and the hole sizes are non critical. > > > > w.. > > There is an interesting study about pitot-static tube > location relative to > the flow around a wing here: > http://naca.larc.nasa.gov/reports/1936/naca-tn-561/ It would seem, from the diagrams in the report, that naive placement of the tube could result in sizable errors. >From the abstract: "The most satisfactory location on the airfoils without flaps that were investigated was 10 percent of the chord aft and 25 percent of the chord above the trailing edge of a section approximately 40 percent of the semispan inboard of the wing tip. No satisfactory location was found near the wing when the flaps were deflected." Note that this report considered only a single configuration, and didn't consider prop wash. (I'm not disagreeing with you. As a matter of fact, next time I am strolling around amongst my fleet of light A/C ;-), I think that I'll pay more attention to where they are located.) 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 hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu