Post by thread:[PICLIST] [OT] Autopilot landing system for model

----- Original Message ----- From: "Walter Banks" <spam_OUTwalterTakeThisOuTBYTECRAFT.COM> To: <.....PICLISTKILLspam@spam@MITVMA.MIT.EDU> Sent: Wednesday, June 19, 2002 1:51 PM Subject: Re: [PIC]: Autopilot landing system for model aircraft (air speed) (snip) {Quote hidden}> 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 jfurtekKILLspamagames.com -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

Jeremy Furtek wrote: {Quote hidden}> > (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. Airspeed in may A/C is notoriously flawed what is more important is repeatable results. Fundamental science is interesting the reference cited was dated March 1936. w.. -- http://www.piclist.com hint: To leave the PICList EraseMEpiclist-unsubscribe-requestspam_OUTTakeThisOuTmitvma.mit.edu

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 removed}

----- Original Message ----- From: "Thomas Holmström" <thomasspam_OUTholmstrom.net> To: <@spam@PICLISTKILLspamMITVMA.MIT.EDU> Sent: Thursday, June 20, 2002 7:14 AM Subject: Re: [OT] Autopilot landing system for model aircraft (air speed) (snip) > 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 I would think, in the absence of a propeller, that the nose cone would be the best choice, unless it gets in the way of your radar system. ;-) Of course, in subsonic flight, the flow ahead of the aircraft is affected. The impact of the fuselage on the measured values is less than that of the wing, and depends on things like the shape of the nose and how far out in front the pressure port is. From http://naca.larc.nasa.gov/reports/1947/naca-tn-1496/ "The results of the test showed that, at 1 fuselage diameter from the nose, the error in static pressure was only about 1.5% of the impact pressure for the pointed-nose body, about 5% of the impact pressure for the elliptical-nose body, and about 10% of the impact pressure for the circular-nose body for zero angle of attack of the bodies." (In this context, it seems that "impact pressure" refers to the dynamic pressure.) There is also some calibration data for some older military aircraft: http://naca.larc.nasa.gov/reports/1957/naca-rm-h57a02/ Jeremy Furtek KILLspamjfurtekKILLspamagames.com -- http://www.piclist.com hint: To leave the PICList RemoveMEpiclist-unsubscribe-requestTakeThisOuTmitvma.mit.edu

One of the links(Chris Good's) at my page; http://www.elkhart.net/~miked/Ulinks.htm has a drawing of one like this. > > 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. Michiana R/C Choppers http://www.mrcc.info TakeThisOuTmikedEraseMEspam_OUTmrcc.info -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads