X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Fri, 13 Jul 2012 11:41:47 -0400 Message-ID: X-Original-Return-Path: Received: from pacmmta53-web.windstream.net ([162.39.147.134] verified) by logan.com (CommuniGate Pro SMTP 5.4.6) with ESMTP id 5650169 for lml@lancaironline.net; Fri, 13 Jul 2012 08:00:12 -0400 Received-SPF: pass receiver=logan.com; client-ip=162.39.147.134; envelope-from=cassutt@windstream.net X-Original-Return-Path: X-WS-COS: WSOB806 X-Cloudmark-Category: Undefined:Undefined X-Cloudmark-Analysis: v=1.1 cv=ItSgKUvEgpuArvFeGcEX9ho8h0+4pTt73K5WgrMP114= c=1 sm=0 a=0XymMpopf0QA:10 a=UT_QgiwtmQIA:10 a=CjxXgO3LAAAA:8 a=y1BBXd_fAAAA:8 a=0U9VY7gieyTIKnmqpyMA:9 a=QEXdDO2ut3YA:10 a=rC2wZJ5BpNYA:10 a=o2QoyYduAAAA:8 a=RkNg253L_RwiXMkQg5MA:9 a=tXsnliwV7b4A:10 a=KP/U7WliE+sSBYd5aIavkw==:117 X-Cloudmark-Score: 0 Received: from [10.135.134.182] ([10.135.134.182:54266] helo=pamxwww06-z02) by pacmmta53 (envelope-from ) (ecelerity 2.2.3.47 r(39824M)) with ESMTP id 59/01-21063-7AD00005; Fri, 13 Jul 2012 07:59:35 -0400 X-Original-Message-ID: <20120713075935.45XX0.150213.root@pamxwww06-z02> X-Original-Date: Fri, 13 Jul 2012 06:59:35 -0500 From: X-Original-To: Lancair Mailing List Subject: Re: [LML] TAS for Red Line MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_661490_1908576877.1342180775808" X-Priority: 3 (Normal) Sensitivity: Normal X-Originating-IP: 75.89.232.254 X-Auth-IP: 75.89.232.254 ------=_Part_661490_1908576877.1342180775808 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Not being an aeronautical engineer I only post this as a layman's understan= ding of the Vne question. I know there are a lot of factors in play here b= ut my basic understanding of this was IAS was structural performance (ie, w= hite arc, green arc, red arc) and TAS was used for flight planning to acoun= t for temp and altitude. =20 This is a quoted statement, but followed my train of thought on this questi= on: =20 "IAS: Indicated Airspeed. This is what you see on the airspeed indicator wh= en flying, obtained by measuring pressure acting on the aircraft by having = a little tube pointing into the wind. But here is the trick: What if you ar= e flying in thin air because it is a hot day, or you are high in the air? T= he air is thinner, so there is less pressure. Well, there will clearly be l= ess pressure on the little tube (the pitot tube) so there will be a lower i= ndication on the airspeed indicator. Aeii! ERROR! But, really, we LIKE this= error. Why? Because if there is less pressure pushing on the airspeed indi= cator, then there is less pressure PUSHING ON THE WINGS AS WELL! So, if we = really want to measure the air pressure available for the props and wings (= which is what we really care about since more pressure gives more lift and = drag) then what we really want is a measure of the pressure acting on the a= irplane: which is what the airspeed indicator really is, BECAUSE of this er= ror that varies with the pressure! So think of it this way: If you are goin= g 120 mph in thin air, but the pressure is only strong enough to measure 10= 0 mph on the airspeed indicator, then that means the aerodynamic pressure o= n the WINGS is only 100 mph worth of pressure! And it is this pressure that= determines how much lift and drag the wings can put out. So we pilots LIKE= this error in the system because it means that if the airplane likes to ap= proach the runway at 100 mph, then we should fly the plane at 100 mph on th= e airspeed indicator. Maybe one day we are at high altitude or high tempera= ture, and that thin air means we actually need to go 120 mph to get the sam= e pressure on the pitot tube to indicate 100 mph on the airspeed indicator,= but that also means we must go 120 mph to get 100 mph worth of pressure on= the wings! So the error in the airspeed indicator exactly counter-acts the= speed change we need to make the plane fly properly. This is not a coincid= ence, because the pitot tube and the wings both need the same thing: dynami= c pressure, or inertia of air smacking into them to function." =20 Eric D N58JJ =20 =20 On Thursday, July 12, 2012 9:26 PM, Steve Colwell wr= ote:=20 >=20 Having coffee with some high time pilots this morning, the subject of Never= Exceed Speed came up. Before I read the original Van=E2=80=99s article ye= ars ago, I thought Indicated Airspeed was the indicator=E2=80=A6 WRONG, it= is True Airspeed. Does your EFIS display TAS or do you have a table for r= eference?? =20 =20 http://www.vansaircraft.com/pdf/hp_limts.pdf =20 =20 Steve Colwell Legacy ------=_Part_661490_1908576877.1342180775808 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable

Not being an aeronautical engineer I only post this as a layman's u= nderstanding of  the Vne question. I know there are a lot of fact= ors in play here but my basic understanding of this was IAS was structural = performance (ie, white arc, green arc, red arc) and TAS was used for flight= planning to acount for temp and altitude.

 

This is a quoted statement, but followed my train of thought on this que= stion:

 
"IAS: Indicated Airspeed. This is what = you see on the airspeed indicator when flying, obtained by measuring pressu= re acting on the aircraft by having a little tube pointing into the wind. B= ut here is the trick: What if you are flying in thin air because it is a ho= t day, or you are high in the air? The air is thinner, so there is less pre= ssure. Well, there will clearly be less pressure on the little tube (the pi= tot tube) so there will be a lower indication on the airspeed indicator. Ae= ii! ERROR! But, really, we LIKE this error. Why? Because if there is less p= ressure pushing on the airspeed indicator, then there is less pressure PUSH= ING ON THE WINGS AS WELL! So, if we really want to measure the air pressure= available for the props and wings (which is what we really care about sinc= e more pressure gives more lift and drag) then what we really want is a mea= sure of the pressure acting on the airplane: which is what the airspeed ind= icator really is, BECAUSE of this error that varies with the pressure! So t= hink of it this way: If you are going 120 mph in thin air, but the pressure= is only strong enough to measure 100 mph on the airspeed indicator, then t= hat means the aerodynamic pressure on the WINGS is only 100 mph worth of pr= essure! And it is this pressure that determines how much lift and drag the = wings can put out. So we pilots LIKE this error in the system because it me= ans that if the airplane likes to approach the runway at 100 mph, then we s= hould fly the plane at 100 mph on the airspeed indicator. Maybe one day we = are at high altitude or high temperature, and that thin air means we actual= ly need to go 120 mph to get the same pressure on the pitot tube to indicat= e 100 mph on the airspeed indicator, but that also means we must go 120 mph= to get 100 mph worth of pressure on the wings! So the error in the airspee= d indicator exactly counter-acts the speed change we need to make the plane= fly properly. This is not a coincidence, because the pitot tube and the wi= ngs both need the same thing: dynamic pressure, or inertia of air smacking = into them to function."
 
Eric D
N58JJ
 
 


On Thursday, July 12, 2012 9:26 PM, Steve Colwell <mcmess1919@yah= oo.com> wrote:
>

Having coffee with some= high time pilots this morning, the subject of Never Exceed Speed came up.&= nbsp; Before I read the original Van=E2=80=99s article years ago, I thought= Indicated Airspeed was the indicator=E2=80=A6  WRONG, it is True Airs= peed.  Does your EFIS display TAS or do you have a table for reference= ?? 

 

http://www.vansairc= raft.com/pdf/hp_limts.pdf 

 

Steve Colwell  Leg= acy


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