Return-Path: Received: from [24.25.9.103] (HELO ms-smtp-04-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.2) with ESMTP id 373718 for flyrotary@lancaironline.net; Sat, 21 Aug 2004 16:35:37 -0400 Received-SPF: none receiver=logan.com; client-ip=24.25.9.103; envelope-from=eanderson@carolina.rr.com Received: from EDWARD (cpe-069-132-183-211.carolina.rr.com [69.132.183.211]) by ms-smtp-04-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id i7LKYWSH025768 for ; Sat, 21 Aug 2004 16:34:33 -0400 (EDT) Message-ID: <000a01c487be$466ef7b0$2402a8c0@EDWARD> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: EM-2 MAP readings Date: Sat, 21 Aug 2004 16:34:36 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0007_01C4879C.BF1F6450" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1409 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1409 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0007_01C4879C.BF1F6450 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message=20 ----- Original Message -----=20 From: Russell Duffy=20 To: Rotary motors in aircraft=20 Sent: Saturday, August 21, 2004 3:39 PM Subject: [FlyRotary] Re: EM-2 MAP readings Hmm, Weber was pretty much upfront with the fact that their TB ports were only for balancing idle and shouldn't be relied upon for accurate readings at any sort of power setting. Perhaps the TWM port is placed differently than the Weber TB. I'm still skeptical, but I can't think of any way to prove whether = they're correct or not. =20 IMHO, I think your 42s should do just fine at the revs you're turning. In fact, I think the intake charge velocity created by the 42mm tract may help you. I have info here (not in the attic!) reference intake VNE as well as a link to a calculator for gas velocity in a pipe. The link is http://not2fast.com/gasflow/velocity.shtml - you'll have to do the metric/English conversion thing but the math is sound. I'll post the = gas velocity thing later when I can get to the info. I want to say 600 = f/s but will confirm. Neat calculator, but let's see if I'm using this correctly. =20 I'm looking at one rotor, since each TB bore and intake runner feeds = only one rotor. The displacement of a 13B is 1.3 liters, so one rotor = is .65 liters. My handy converter turns this into .023 cubic feet per = rotor, per revolution. Multiply this by 7000 rpm, and I get 161 cubic = feet per minute. I enter this into the gas flow program, leave the temp = at 100F, and put in the runner ID of 1.625". That gives me a mean = velocity of 186 ft/sec. =20 From the notes at the bottom of the program screen, and your = recollection of 600 fps, my 186 fps figure doesn't appear to be = stressing my intake size at all. The real question is- did I screw = something up in the way I figured this?=20 Feeling better about my intake all the time. Pity the area is covered = with thunderstorms today. I really don't want to test my new XM weather = that bad :-) Thanks, Rusty (replacing home security system destroyed by lightning) Rusty, for airflow/ displacement purposes, expecially when using = calculators for reciprociating engines, you can simply treat it as a = 160 CID 4 cyclinder, 4 stroke engine, each cylinder of 40 CID. =20 But for a sanity check, taking your inputs we have 160*7000/(1728*2) = =3D 324 CFM or since you are only taking 1 runner (1/2 the intake) we = divided that by 2 =3D 162 CFM divide by area of runner with ID 1.625" A = =3D 2.07 sq inches converting to feet =3D 0.014402 ft^2 and (162ft^3/min)/.0144 ft^2 =3D 11248 ft/min / 60 =3D = 187.4691 ft/sec which I say is close to your figure. Now this is your = average intake velocity over a revolution. The 600 fps velocity figure is frequently mentioned in lituerature on = intake tuning. However, it turns out that is the MAXMIUM allowable = (recommended?) velocity in the tubes. Above this velocity, air flow = losses start to become prohibitive. Your average velocity is = considerably lower as you have to taken into consideration the pulsating = nature of the flow which could mean the lowest velocity you will see is = considerably lower than your average. But, none of those conditions = exists but for a fleeting moment. =20 So the fact that your average velocity is 187 fps really tells you = little about your peak velocity. To put it into perspective your little = 1.625 ID tube has air flow an average of 127MPH! The peak goes above = this but can't say how much So the air is not exactly sitting still. = I would say considerably stronger than your average vacuum cleaner {:>). = =20 But, again it does not tell you whether you are exceeding the peak = recommended velocity of 600 fps and possibly incurring substantial = losses. I personally doubt that you are. Your intake size is not = significantly different from the Rotary stock intake (if you add area = of a primary and secondary) perhpas a bit larger so, I believe that they = would have paid carefully attention to high rpm airflow and avoided = tubes that would have caused serious airflow problems. But, thats not a = fact, just my opinion. You would need a fairly sophisticated simulation to arrive at anything = close to an accurate peak velocity. There's a good one on the market = for about $600 if you are interested {:>) No, have not got to the airport yet, tomorrow if it goes better than = the rest of the week {>) FWIW Ed =20 ------=_NextPart_000_0007_01C4879C.BF1F6450 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message
 
----- Original Message -----
From:=20 Russell=20 Duffy
Sent: Saturday, August 21, 2004 = 3:39=20 PM
Subject: [FlyRotary] Re: EM-2 = MAP=20 readings

Hmm, Weber was pretty much upfront with the fact = that their TB=20 ports
were only for balancing idle and shouldn't be relied upon for = accurate
readings at any sort of power setting. Perhaps the TWM = port =20 is placed
differently than the Weber TB.

I'm = still skeptical,=20 but I can't think of any way to prove whether = they're correct or=20 not. 

 IMHO, I think your 42s should do = just
fine=20 at the revs you're turning. In fact, I think the intake = charge
velocity=20 created by the 42mm tract may help you. I have info here (not
in = the=20 attic!) reference intake VNE as well as a link to a calculator
for = gas=20 velocity in a pipe. The link is
http://not2fast.com/g= asflow/velocity.shtml=20 - you'll have to do the
metric/English conversion thing but the = math is=20 sound. I'll post the gas
velocity  thing later when I can get = to the=20 info. I want to say 600 f/s
but will confirm.
 
Neat = calculator, but=20 let's see if I'm using this correctly. 
 
I'm = looking at one=20 rotor, since each TB bore and intake runner feeds only=20 one rotor.  The displacement of a 13B is 1.3 liters, so = one=20 rotor is .65 liters.  My handy converter turns this into = .023 cubic=20 feet per rotor, per revolution.  Multiply this by 7000 rpm,=20 and I get 161 cubic feet per minute.  I enter this into = the gas=20 flow program, leave the temp at 100F, and put in the runner ID of = 1.625".   That gives me a mean velocity of 186 ft/sec.  =   
 
From the notes at the bottom = of=20 the program screen, and your recollection of 600 fps, my 186 fps = figure=20 doesn't appear to be stressing my intake size at all.  = The real=20 question is- did I screw something up in the way I = figured=20 this? 
 
Feeling better about my intake = all the=20 time.  Pity the area is covered with thunderstorms today.  I = really=20 don't want to test my new XM weather that bad :-)
 
Thanks,
Rusty (replacing home security = system=20 destroyed by lightning)
 
Rusty, for airflow/ displacement = purposes,=20 expecially when using calculators for reciprociating engines, you can = simply=20  treat it as a 160 CID 4 cyclinder, 4 stroke engine, each = cylinder=20 of 40 CID. 
 
But for a=20 sanity check,  taking your inputs we have 160*7000/(1728*2) =3D = 324 CFM or=20 since you are only taking 1 runner (1/2 the intake) we divided that by = 2 =3D 162=20 CFM  divide by area of runner with ID 1.625" A =3D 2.07 sq inches = converting to feet =3D

0.014402 ft^2  and = (162ft^3/min)/.0144 ft^2 =3D 11248 ft/min / 60 =3D  187.4691 = ft/sec which I=20 say is close to your figure.  Now this is your average intake = velocity=20 over a revolution.

The 600 fps = velocity  figure is=20 frequently mentioned in lituerature on intake tuning.  However, = it turns=20 out that is the MAXMIUM allowable (recommended?) velocity in the=20 tubes.   Above this velocity, air flow losses start to = become=20 prohibitive.  Your average velocity is considerably lower as you = have to=20 taken into consideration the pulsating nature of the flow which = could=20 mean the lowest velocity you will see is considerably lower than your=20 average.    But, none of those conditions exists but = for a=20 fleeting moment.  

So the fact that your = average=20 velocity is 187 fps really tells you little about your peak=20 velocity.  To put it into perspective your little 1.625 ID = tube has=20 air flow an average of  127MPH!  The peak = goes above this=20 but can't say how much   So the air is not exactly sitting = still.  I would=20 say considerably stronger than your average vacuum cleaner = {:>). =20

But, again it does not = tell you=20 whether you are exceeding the peak recommended velocity of 600 fps and = possibly incurring substantial losses.  I personally doubt that = you=20 are.  Your intake size is not significantly different from = the =20 Rotary stock intake (if you add area of a primary and secondary) = perhpas a bit=20 larger so, I believe that they would have paid carefully attention to = high rpm=20 airflow and avoided tubes that would have caused serious airflow=20 problems.  But, thats not a fact, just my opinion.

You would need a fairly = sophisticated=20 simulation to arrive at anything close to an accurate peak = velocity. =20 There's a good one on the market for about $600 if you are interested=20 {:>)

No, have not got to the = airport yet,=20 tomorrow if it goes better than the rest of the week {>)

 

FWIW

Ed

 

 

 

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