Brodhead Pietenpol Association

Original Posted By: "Richard Navratil"
Hey all,I have been having a problem with airspeed readings, the readings are way low.The main question is that I located my pitot tube thru the leading edge of thewing. I have been trying to adjust the angle of the tube but so far no improvement.I know the guage works because readings go up in decent. I have alingedthe tube and bent it to be level at normal flight.My question is, could it be that that location of the tube is the cause? The tubeextends out about 6" from the LE. I have a GPS and now also installed asecondary ASI from a ultralite till this is resolved. I have a spare guage andwill also try changing it out.Dick N.________________________________________________________________________________

Original Posted By: Don Morris

Original Posted By: Ed Smith

Original Posted By: Michael D Cuy

Original Posted By: "John Ford"
Subject: Re: Pietenpol-List: airspeedIn a message dated 8/25/04 10:30:17 PM Central Daylight Time, horzpool(at)goldengate.net writes:>Richard,My first hunch is that your static port is in a positive pressure area - once you are airborne. As you decend, the positive pressure area becomes neutral. Where is your static port ? Is your altimeter and airspeed static port plumbed together ? Is your altimeter reading accurately, or does it read lowerthan you actually are - once you are airborne at several thousand feet ? Doesthe altimeter needle bounce, or move rapidly ?Chuck G.________________________________________________________________________________Date: Wed, 25 Aug 2004 16:24:24 -0500

Original Posted By: Les Schubert
Thanks to Mike Del and ChuckMy static port is directly on the ASI, there is a headrest in front of it to blockwind. The altimiter is fine doesnt bounce around and seems accurate. I drilleda hole in the plug as Mike described, I will try enlarging it a bit. I will order a spare pitot tube and install a temp secondary guage as Del suggested.I have a spare guage.The reason I brought this point up is, I chatted with P.F. Beck offline on thispoint. He has pitot in the same location and had the same problem, which clearedup with a new pitot tube.Del, I was out flying last night and if conditions permit will go again on Sat.Dick N.________________________________________________________________________________Date: Thu, 26 Aug 2004 09:46:11 -0600

Original Posted By:
is this why the pitot/static tube I bought from Aircraft spruce has 2 1/4"tubes brazed together in the shape of an "L". One benig open for pitot andone sealed shut with a small hole for static?? This way they are in thesame air huh?DJ----- Original Message -----

Original Posted By: BARNSTMR(at)aol.com

Original Posted By: BARNSTMR(at)aol.com

Original Posted By: Richard Navratil
One thing I haven't heard anybody address is that the air coming into the leadingedge of a wing DOES NOT approach from straight ahead. There is a strong upwashahead of the wing and strong downwash behind it. As the angle of attackincreases the stagnation point on the leading edge (the point where the air ishitting the airfoil straight on and splits with some going over and the restgoing under) moves down. That is one very good reason you don't see so many planeswith the air speed probe mounted on the front of the wing. You have toget the end of the tube well out in front of the leading edge to get straightin flow. If the flow is hitting the end of the probe at an angle you get a lowerair speed indication. If you look at production test aircraft you will seereally long booms sticking out in front with a gadget on the front that weathervanesinto the air flow. This keeps the air going straight into the pitottube so they can adjust the production pitot to have minimum error. With a boomit is pretty easy to optimize the pitot tube but the static port is still prettymuch black magic. You have to get the pressure at the port to be the sameas the free stream pressure in all attitudes. For us, that is a real pain.Using an open static port in the back of the instrument is probably a reallyBAD way to do it but if it's consistent it works. You may be stalling at 10MPH different than what's indicated, but who cares if it always stalls at thesame indicated speed? In this case you optimize for cruise accuracy and let thestall be off (but consistent). One BIG problem is with a passenger in frontyou should expect the airspeed to be different and each new shape passengerwill change the ASI. In my Taylorcraft I can fly faster with the passenger windowopen and slower with the pilots window open. With both open I can't readthe ASI so I'm not sure what is happening. ;-)Hank (At least the ASI says I'm faster and slower) J ----- Original Message -----

Original Posted By: hjarrett
My tube extends at least 6" out from LE. I made some modfications this morningbut was grounded in the morning by rain and heavy traffic from a head bangin rockconcert in the area this aftrenoon.Will try again on Mon.Dick ----- Original Message -----

Original Posted By: Gary W Meadows
Please, lets not get started on Replicraft again. We just did 4-5 days on copyrights.Dick ----- Original Message -----