X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 05 Aug 2009 10:34:12 -0400 Message-ID: X-Original-Return-Path: Received: from web62507.mail.re1.yahoo.com ([69.147.75.99] verified) by logan.com (CommuniGate Pro SMTP 5.2.15) with SMTP id 3795589 for lml@lancaironline.net; Wed, 05 Aug 2009 10:19:33 -0400 Received-SPF: none receiver=logan.com; client-ip=69.147.75.99; envelope-from=charliekohler@yahoo.com Received: (qmail 56317 invoked by uid 60001); 5 Aug 2009 14:18:57 -0000 DomainKey-Signature:a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:X-YMail-OSG:Received:X-Mailer:References:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type; b=nt13D6b/wSGHi2mZ81RRKWF3jHAP7Rml43hiwBZ/Z4jhaNyS3nysIt7/fpHcUWkkqMshahTSmpvKJjD5fdcUdkpk6Ra62sHjwKmibIw/YzTRMHuxa93qfk1SRpQdmssGPofhRYiOWL17R0PFRm0POl6CA75jEFlrdFS+u+3heRc=; X-Original-Message-ID: <62218.56265.qm@web62507.mail.re1.yahoo.com> X-YMail-OSG: ihDoMmIVM1nnOkWV47abD8HY3.TYZXa5e3urJTR8LoAslZrhiNwE2BS16fUPuIRiK4NEjfa0jCvdcSP_iV1cmlAWSCYKLEjh3z7BH15HqePf.PkA1yVycgD955_EFlzGEnaIQIY2sEiQ5ghRNWMTwk2SIFLiYfcfqMq0q.07OqiVELqW81fKXZlIxwGXW5Stn0K.Dyuos6hk.8cqhUVi4t92Pho6jdmVfQ6w6cJOlpOShImihSBf16Thtnn_E6bzoj8AVxTokZW4pv52.R99.Vt9wQUoxmajO0y2l4YKVgzVvuaeHrIb_4KWz4.QTq4pri6VA3oB_Kpvz3T39WLaxnh2IXHHP.6RMtiwviwsDA9w6vo2 Received: from [97.104.160.94] by web62507.mail.re1.yahoo.com via HTTP; Wed, 05 Aug 2009 07:18:56 PDT X-Mailer: YahooMailRC/1358.27 YahooMailWebService/0.7.289.15 References: X-Original-Date: Wed, 5 Aug 2009 07:18:56 -0700 (PDT) From: Charlie Kohler Subject: Re: [LML] FW: [LML] Ice with OAT 36*F (LIVP): Ram Recovery on OAT X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-1190724252-1249481936=:56265" --0-1190724252-1249481936=:56265 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable My experience with the temperature probe is that anything on the fuselage/w= heel wells/flap well -- will have a higher than ambient temperature on the = TSIO 550 powered Lancair IV's.=0AI once put=C2=A0my probe in a outer wing f= lap well and found that the heat was migrating out to the outboard edge of = the flap. As a result the probe is now in the aileron bell crank dry bay ar= ea. It is working fine there.=0A=C2=A0=0ACharlie K.=0A=0ASee me on the web = at =0Awww.Lancair-IV.com=0A=0A=0A=0A=0A=0A________________________________= =0AFrom: Frederick Moreno =0ATo: lml@lancairon= line.net=0ASent: Wednesday, August 5, 2009 9:13:53 AM=0ASubject: [LML] FW: = [LML] Ice with OAT 36*F (LIVP): Ram Recovery on OAT=0A=0A=0Ado you think th= at we could construct something like this =0Ato reduce OATerror?=0A=C2=A0= =0AI am not familiar with this probe, but I believe that it attempts to cor= rect for further non-linear effects associated with compressibility as the = Mach numbers rise to levels substantially above where we operate.=C2=A0 Thi= nk jet speeds, Mach 0.7 and above.=C2=A0 I do not think such a probe will h= elp at our more modest probes because the problem they attempt to address i= s negligibly small at our speeds. =0A=C2=A0=0AHowever, I could be wrong.=C2= =A0 I leave it to others to research Rosemont probes. =0A=C2=A0=0AAs I note= d elsewhere, at our lower speeds, compression heating at stagnation points = and frictional heating elsewhere (and mixtures of both near stagnation poin= ts) makes the OATerror occur everywhere on the airframe.=C2=A0 The Piper cu= rves published earlier give you a good estimate of the OATerror.=C2=A0 Goin= g in the wheel wells only adds confusion if there is a fuel tank near by wi= th a big thermal sink in the form of avgas that will be very slowly heating= and cooling. =C2=A0=C2=A0Additionally, the OATresponse for a probe in the = wheel well will be really slooooooooowwwwwwww.=C2=A0 =0A=C2=A0=0AThe thing = to do is accept the error, and remove it.=C2=A0 Use the Piper charts to est= imate the error in OAT.=C2=A0 To get an accurate TAS, you have to also corr= ect for compressibility.=C2=A0 The total airspeed error is about 2/3=E2=80= =99s from the termperature error, and about 1/3 from compressibility (varyi= ng depending on speed, true OAT, phase of the moon, and other secondary eff= ects.)=C2=A0 =0A=C2=A0=0AYou can compute the air speed correction with a fa= ncy Jeppesen whiz wheel developed to compensate for all these effects in je= ts, or you can use the simplified chart attached.=C2=A0 It shows the total = airspeed error (compressibility error in the pitot tube and frictional heat= ing error from boundary layer friction) assuming you have a conventional st= eam gage air speed indicator and are reading an =E2=80=9Cuncorrected=E2=80= =9D OATas indicated by your OATgage.=C2=A0 This assumes you are not using a= ny fancy black boxes that make these corrections for your. =C2=A0=C2=A0=0A= =C2=A0=0AThe procedure is simple.=C2=A0 Calculate an =E2=80=9CE6B=C2=A0 TAS= =E2=80=9D using an E6B or that ring correction on the outside of your steam= gage airspeed indicator.=C2=A0 Then go to the chart on the horizontal axis= with this number.=C2=A0 Go vertical to one of the curves that best approxi= mates your OAT.=C2=A0 Then go horizontally to the left to the vertical axis= to get the correction factor.=C2=A0 Subtract this from your =E2=80=9CE6B a= irspeed=E2=80=9D to get a very good estimate of your =E2=80=9CTrue TAS.=E2= =80=9D=C2=A0 Caution: any static port errors will remain, and they can be c= onsiderable.=C2=A0 But at least you can now accurately compare your compute= d =E2=80=9CTrue TAS=E2=80=9D against a four way GPScalculation of =E2=80=9C= True TAS=E2=80=9D and make an estimate of your static port error.=C2=A0 The= n you can modify your static port, and do it again.=C2=A0=C2=A0 And again.= =C2=A0 And again.=C2=A0 When your static port error is less than 1-2 knots = at cruise, you will at last have a fairly accurate number.=C2=A0 (Whew.)=0A= =C2=A0=0AFred=0A=C2=A0=0A-----Original Message-----=0AFrom: marv@lancair.ne= t [mailto:marv@lancair.net] =0ASent: Wednesday, 5 August 20094:27 AM=0ATo: = lml@lancaironline.net=0ASubject: Re: [LML] Ice with OAT 36*F (LIVP): Ram Re= covery on OAT=0A=C2=A0=0APosted for "Bill" :=0A=0A=C2=A0I= ce with OAT 36*F (LIVP): Ram Recovery on OATHey Fred,=0A=C2=A0=0A=C2=A0Airl= iners have an OAT probe called a "Rosemont probe". The idea is to give a = =0Amore accurate OAT reading. It's an enclosure around the probe with a bun= ch of =0Alittle holes in it. Since only a percentage of the air gets throug= h the holes, =0Athe local velocity inside the "cage" is much less. I guess = that the theory is =0Athat the cage absorbs most of the ram and friction ri= se leaving the air inside =0Athe cage at a low relative velocity and at a t= emp somewhere near true OAT. =0AThere might be much more to this device tha= t I don't know about (I never =0Areally gave them much thought other than t= o make sure that it was "there") but =0Aif this is all it is, do you think = that we could construct something like this =0Ato reduce OAT error? I'd be = interested in your thoughts on this.=0A=C2=A0=0A=C2=A0Bill Harrelson=0A=C2= =A0N5ZQ 320 1,650 hrs=0A=C2=A0N6ZQ=C2=A0=C2=A0IV under construction=0A=C2= =A0=0A=C2=A0=0A[Discussion about this very thing long ago led many folks to= install their OAT probes in the gear wells.... the gear doors aren't air-t= ight and the environment inside the gear well is the same as outside (excep= t for rain & stuff) for all intents and purposes.=C2=A0 Just another data p= oint.=C2=A0 =C2=A0 ] --0-1190724252-1249481936=:56265 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable
=0A
=0A

My experience with the tempera= ture probe is that anything on the fuselage/wheel wells/flap well -- will h= ave a higher than ambient temperature on the TSIO 550 powered Lancair IV's.=

=0A

I once put my probe in a outer wing flap well and found that= the heat was migrating out to the outboard edge of the flap. As a result t= he probe is now in the aileron bell crank dry bay area. It is working fine = there.


 
=0A
Charlie K.
=0A
 =0A
See me on the web at
=0A=0A 
=0A

=0A

=0A
=0A
=0AFrom: Frederick Moreno <frederickmoreno@bigpond.com>
To: lml@lancaironline.net
Sent: Wednesday, August 5, 2009 9:13:53 A= M
Subject: [LML] FW: [LM= L] Ice with OAT 36*F (LIVP): Ram Recovery on OAT

=0A=0A=0A
=0A

do you think that we could co= nstruct something like this
to reduce OAT error?

=0A

 =

=0A

I am not familiar with this probe,= but I believe that it attempts to correct for further non-linear effects a= ssociated with compressibility as the Mach numbers rise to levels substanti= ally above where we operate.  Think jet speeds, Mach 0.7 and above.&nb= sp; I do not think such a probe will help at our more modest probes because= the problem they attempt to address is negligibly small at our speeds.

=0A

 

=0A

However, I could be wrong.  I leave it to others to res= earch Rosemont probes.

=0A

 = ;

=0A

As I noted elsewhere, at ou= r lower speeds, compression heating at stagnation points and frictional hea= ting elsewhere (and mixtures of both near stagnation points) makes the OAT<= /FONT> error occur ev= erywhere on the airframe.  The Piper curves published earlier give you= a good estimate of the OAT error.  Going in the wheel wells only adds confusion if = there is a fuel tank near by with a big thermal sink in the form of avgas t= hat will be very slowly heating and cooling.   Additionally, the = OAT response for a probe in the wheel well will = be really slooooooooowwwwwwww. 

=0A

 

=0A

The thing to = do is accept the error, and remove it.  Use the Piper charts to estima= te the error in OAT.  To get an accurate TAS, you have to also correct for compressi= bility.  The total airspeed error is about 2/3=E2=80=99s from the term= perature error, and about 1/3 from compressibility (varying depending on sp= eed, true OAT,= phase of the moon, and other secondary effects.) 

= =0A

 

=0A

You can compute the air speed correction with a fancy Jeppesen whiz = wheel developed to compensate for all these effects in jets, or you can use= the simplified chart attached.  It shows the total airspeed error (co= mpressibility error in the pitot tube and frictional heating error from bou= ndary layer friction) assuming you have a conventional steam gage air speed= indicator and are reading an =E2=80=9Cuncorrected=E2=80=9D <= FONT face=3DArial>OAT as indicated by your OAT<= /FONT> gage.  Th= is assumes you are not using any fancy black boxes that make these correcti= ons for your.   

=0A

&n= bsp;

=0A

<= SPAN style=3D"FONT-FAMILY: Arial; FONT-SIZE: 12pt">The procedure is simple.=   Calculate an =E2=80=9CE6B  TAS=E2=80=9D using an E6B or that ri= ng correction on the outside of your steam gage airspeed indicator.  T= hen go to the chart on the horizontal axis with this number.  Go verti= cal to one of the curves that best approximates your OAT.  Then go horizontally to= the left to the vertical axis to get the correction factor.  Subtract= this from your =E2=80=9CE6B airspeed=E2=80=9D to get a very good estimate = of your =E2=80=9CTrue TAS.=E2=80=9D  Caution: any static port errors w= ill remain, and they can be considerable.  But at least you can now ac= curately compare your computed =E2=80=9CTrue TAS=E2=80=9D against a four wa= y GPS calculation of =E2=80=9CTrue TAS=E2=80=9D and make an estimate of your= static port error.  Then you can modify your static port, and do it a= gain.   And again.  And again.  When your static port e= rror is less than 1-2 knots at cruise, you will at last have a fairly accur= ate number.  (Whew.)

=0A

&nb= sp;

=0A

Fred

=0A=

 

=0A

<= FONT size=3D2 face=3DTahoma>-----Original Message-----
From: marv@lancair.net [mailto:marv@lancair.net]
= Sent: Wednesday, 5 August 2009 4:27 AMTo: lml@lancaironline.net<= BR>Subject: Re: [LML] Ice w= ith OAT 36*F (LIVP): Ram Recovery on OAT

=0A

 

=0A
=0A

Posted for "Bill" <n5z= q@verizon.net>:

 Ice with OAT 36*F (LIVP): Ram Recovery on O= ATHey Fred,
 
 Airliners have an OAT probe called a "Rosemo= nt probe". The idea is to give a
more accurate OAT reading. It's an enc= losure around the probe with a bunch of
little holes in it. Since only = a percentage of the air gets through the holes,
the local velocity insi= de the "cage" is much less. I guess that the theory is
that the cage ab= sorbs most of the ram and friction rise leaving the air inside
the cage= at a low relative velocity and at a temp somewhere near true OAT.
Ther= e might be much more to this device that I don't know about (I never
re= ally gave them much thought other than to make sure that it was "there") bu= t
if this is all it is, do you think that we could construct something like this
to reduce OAT error? I'd be interested in your tho= ughts on this.
 
 Bill Harrelson
 N5ZQ 320 1,650 hr= s
 N6ZQ  IV under construction
 
 
[Di= scussion about this very thing long ago led many folks to install their OAT= probes in the gear wells.... the gear doors aren't air-tight and the envir= onment inside the gear well is the same as outside (except for rain & s= tuff) for all intents and purposes.  Just another data point.  &l= t;M>  ]

--0-1190724252-1249481936=:56265--