From: Bes1612@aol.com Date: Mon, 8 Feb 1999 05:39:56 EST Subject: COZY: pitot tube extention Greetings all; Does the pitot have to extend past the surface? Mine is slightly off center, and was thinking that just a hole there would be better looking. If so how far must it extend? How big must the hole be? Can the end of the tube be reduced? Bob Smith. (Looking forward to spending my refund on material!) Date: Mon, 08 Feb 1999 16:47:29 -0500 From: Bulent Aliev Subject: Re: COZY: pitot tube extention Jeff Russel has his pitot tube flush with the skin and works the same From: cdenk@ix.netcom.com Date: Mon, 8 Feb 1999 16:14:58 -0600 (CST) Subject: Re: COZY: pitot tube extention The pitot tube should extend to the point of being in relatively undistrurbed air flow. What the drawings show is a minimum probably. WHen you see test aircraft like CAFE tests, its much longer. I have seen them on booms a foot or 2 long. Therefore flush is not acceptable. Date: Mon, 08 Feb 1999 21:06:31 -0500 From: Bulent Aliev Subject: Re: COZY: pitot tube extention I had discussion with Jeff and had the same argument. He told me that with or without the extension of the PITOT tube, NOT the static source the readings were the same. So he removed it permanently. I did not make this up. Just the facts . cdenk@ix.netcom.com wrote: > On 02/08/99 16:47:29 you wrote: > > > >Jeff Russel has his pitot tube flush with the skin and works the same > > > Unless properly calibrated, I wouldn't think so. Put another airspeed with > the pitot on a long boom. and compare. We are talking pitot tubes (ram air > to the airspeed indicator), NOT the static source ??? From: Bes1612@aol.com Date: Tue, 9 Feb 1999 02:30:13 EST Subject: COZY: pitot extension Looks like aesthetics wins out for now. I can always put an extention on later if there is any problems. I like the idea of a small, slightly elongated hole just off the nose. Thanks to all the response. Bob (Original question- Should the pitot tube have an extension or can it be flush with the surface?) From: ernie de goveia Subject: COZY: Pitot extension Date: Tue, 9 Feb 1999 13:51:19 +0200 Bob wrote "looks like aesthetics wins" Aesthetics dont work, physics do. A pitot must be in a position to measure air pressure and not be affected by the slip stream. This is the reason most aircraft have the pitot supported away from the structure on a mast. the hole in the pitot faces directly at the airflow to measure all it's pressure. A slightly elongated hole will be affected by the slip stream and will not feel the airflow directly ,it will only measure part of the air flowing past this hole and will give low reading on the airspeed indicator. Go with what works. Ernie in Cape Town Date: Tue, 09 Feb 1999 09:11:53 -0500 From: bil kleb Subject: Re: COZY: pitot tube extention cdenk@ix.netcom.com wrote: > > The pitot tube should extend to the point of being in > relatively undistrurbed air flow. true, but the nose _is_ in relatively undisturbed flow. > when you see test aircraft like CAFE tests, its much longer. this is because the pitot is typically mounted on the wing which creates all sorts of disturbances ahead of it in subsonic flow (upwash--see the latest sport aviation article about how lift works). > Therefore flush is not acceptable. not true. since we're putting the pitot port on the nose of the bird and this location is a few chord-lengths away from the canard, we can get away with quite a bit: a flush pitot port will give _exactly_ the same reading as and extended one IF the location of the port on the nose coincides with the stagnation point on the nose. note: the location of the stagnation point varies with angle of attack. to put it another way, for the readings to be the same between a flush and extended pitot inlet, your flush-mounted inlet must be located at the stagnation point on the nose whereas the extended pitot is not so location critical. the extended (maybe only 2" or so) pitot probe inlet has it's own stagnation point on its tip which remains useful up to angle of attack deviations of about +/-15 degrees. however, the flush mounted inlet will start to experience errors as soon as the stagnation point on the nose moves due to angle of attack. note: the sharper the nose, the less the stagnation point moves with angle of attack. so, if you manage to get your flush inlet located pretty close to the stagnation point of the nose during cruise flight, then it will read the same as an extended probe. however, at different angles of attack, it will be in error depending on how blunt the nose is, but that is what cas is all about, right? (cas is ias corrected for position and installation error--see the poh of your favorite spam can for a sample chart comparing the two.) as mentioned earlier, those wing-mounted pitot probe people have the same sort of angle-of-attack errors creeping in but this time it is due to the upwash of the wing `disturbing' the incoming flow to the probe inlet. IAS is what you fly by, so as long as you know when stall (er, minimum airspeed) is and the IAS is pretty close in cruise, then it's the same situation that the little-wing-in-the-back people have dealt with all along. -- bil Date: Tue, 09 Feb 1999 09:06:24 -0600 From: vaatk@flash.net Subject: COZY: pitot tube I noticed a lot of talk about pitot tube location on the EZ types. In 1980 when I built my first VariEZ.  I talked to Mike Melville about location of the tube, (they were getting squashed and tromped on when parked) and  about a different location.

Mike said " the best and most accurate location is where the plans show, with the tube protruding into relative undisturbed air.  Most other arrangements will not be as accurate, (he didn't say how much the value would be off) and the key would be a good static location and the pitot located in undisturbed air.  I took that to mean, at least get the tube out there.

In my COZY, I have flown with several other aircraft comparing airspeeds (factory and home built) and most all are within 1 to 10 percent accurate.  If you change your tube location be aware, if you flush it in, the relative angle of attack will have an effect on the readout, sometimes drastically, like high angle of attacks when coming into land, or crosswinds, just when you need accurate airspeed the most.......who needs it at cruise ?

In the Jets (yes the factory makes experimental ones with EXPERIMENTAL slapped on the side)  the factory installs a huge 6 inch dia. airspeed gauge marked in knots  and a very long pitot tube, (on the order of 4 to 6 feet) just to get the truth.

                Vance Atkinson N43CZ  1300TT
 
 
  From ???@??? Wed Feb 10 16:49:05 1999 Return-Path: owner-cozy_builders@betaweb.com Received: from twc2.betaweb.com (majordomo@betaweb.com [206.43.209.18]) by acestes-fe0.ultra.net (8.8.8/ult/n20340/mtc.v2) with ESMTP id CAA28199 for ; Wed, 10 Feb 1999 02:51:01 -0500 (EST) Received: (from majordomo@localhost) by twc2.betaweb.com (8.8.5/8.8.5) id CAA13136 for cozy_builders-list; Wed, 10 Feb 1999 02:21:36 -0500 X-Authentication-Warning: twc2.betaweb.com: majordomo set sender to owner-cozy_builders@betaweb.com using -f Received: from daimler-benz.com (firewall-user@pluto1.str.daimler-benz.com [53.122.2.31]) by twc2.betaweb.com (8.8.5/8.8.5) with ESMTP id CAA13128 for ; Wed, 10 Feb 1999 02:21:31 -0500 Received: by daimler-benz.com; id IAA26010; Wed, 10 Feb 1999 08:08:18 +0100 (MET) Received: from unknown(53.113.192.12) by pluto.daimler-benz.com via smap (3.2) id xma025976; Wed, 10 Feb 99 08:08:12 +0100 Received: by S97H1H02 with Internet Mail Service (5.5.1960.3) id <14M72NNB>; Wed, 10 Feb 1999 08:17:18 +0100 Message-ID: From: "Melchinger, Klaus" To: "'Bulent Aliev'" Cc: cozy_builders Subject: AW: COZY: pitot tube extention Date: Wed, 10 Feb 1999 08:13:38 +0100 MIME-Version: 1.0 X-Mailer: Internet Mail Service (5.5.1960.3) Content-Type: text/plain Sender: owner-cozy_builders@betaweb.com Precedence: bulk Reply-To: "Melchinger, Klaus" X-UIDL: 6d6e3e8a5154d711681361b657554693 Why not have a look at todays high performance gliders ? They all have the pitot tube inside the fuselage nose !? Best Klaus > ... Jeff ... told me that with or without the extension of the PITOT tube, > cdenk@ix.netcom.com wrote: > > Unless properly calibrated, I wouldn't think so.