Return-Path: Received: from pop3.olsusa.com ([63.150.212.2] verified) by logan.com (CommuniGate Pro SMTP 3.4.5) with ESMTP id 777173 for rob@logan.com; Fri, 11 May 2001 12:33:31 -0400 Received: from imo-m01.mx.aol.com ([64.12.136.4]) by pop3.olsusa.com (Post.Office MTA v3.5.3 release 223 ID# 0-71175U5500L550S0V35) with ESMTP id com for ; Fri, 11 May 2001 11:10:43 -0400 Received: from N934td@cs.com by imo-m01.mx.aol.com (mail_out_v30.10.) id k.75.148c44b7 (3847) for ; Fri, 11 May 2001 11:17:26 -0400 (EDT) From: N934td@cs.com Message-ID: <75.148c44b7.282d5c86@cs.com> Date: Fri, 11 May 2001 11:17:26 EDT Subject: Re: Groundspeed as a Flight Reference To: lancair.list@olsusa.com MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-Mailing-List: lancair.list@olsusa.com Reply-To: lancair.list@olsusa.com <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> >> <> Greg: There is a quick and dirty method to check your IAS by using the GPS. As you know, IAS is the sum of Pitot (total) minus Static (total) or Pt - St = V, or put another way, IAS =1/2 V roe X V2. To test your Static system for having the correct port location on the fuselage, just fly two legs at low altitude, holding exactly the same IAS, both directions. Note the GS from the GPS each leg. Total the 2 GS readings and divide by 2, this will give you your exact TAS. Then compute your TAS from your IAS using altitude and temperature. Remember how to do this? The TAS you receive should match the TAS you derived from the average of the two GPS ground speed readings. If your computed TAS is "higher" than the GPS derived TAS, then your error *high*. Your IAS will then have to be corrected for critical speeds, mentally. I.E. when doing slow flight, or at Vx or Vy. There is another test you can do to confirm your Static port position error: Select a quiet airport that will allow you to make low passes at different speeds. Set your altimeter to read the airport elevation. Then takeoff and make a low pass at slow speed, and note the altimeter reading when you are at 50' above the runway. Do this at several speeds, finally at your highest speed, noting the altimeter reading at 50' above the runway. If the altimeter shows "higher" that 50,' then you have an error in the location of the Static port. You can then plot a curve on a chart and see the error at all speeds. This error is related to "Q", or dynamic pressure. The error should confirm what you found on your GPS GS readings for TAS. This static error at "Q" will effect everything in your airplane that uses static inputs, even an air data computer. Both test are fun, and informative. If the error is 6 knots or less in your plane, forget it. If higher, maybe you should try another port location. Regards, Tony Durizzi DAR(F)636157NM >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> LML website: http://www.olsusa.com/Users/Mkaye/maillist.html LML Builders' Bookstore: http://www.buildersbooks.com/lancair Please send your photos and drawings to marvkaye@olsusa.com. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>