Return-Path: Received: from [24.25.9.100] (HELO ms-smtp-01-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.1.8) with ESMTP id 2970081 for flyrotary@lancaironline.net; Sun, 01 Feb 2004 23:30:56 -0500 Received: from edward (clt78-020.carolina.rr.com [24.93.78.20]) by ms-smtp-01-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id i124UraM009077 for ; Sun, 1 Feb 2004 23:30:54 -0500 (EST) Message-ID: <002801c3e945$58f45a50$2402a8c0@edward> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] air flow, induction air scoop Date: Sun, 1 Feb 2004 23:30:54 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0025_01C3E91B.6FC62030" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1158 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0025_01C3E91B.6FC62030 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable ----- Original Message -----=20 From: Al Gietzen=20 To: Rotary motors in aircraft=20 Sent: Sunday, February 01, 2004 3:23 PM Subject: [FlyRotary] air flow, induction air scoop Subject: [FlyRotary] Re: air flow Here is a formula 80 CID * RPM/1728. Example for 6000 rpm, = 80*6000 rpm/1728 =3D 277.77 Cubic Feet of air per minute. A cubic foot of = air (at sea level standard day) is approx 0.076 lbm/cubic foot so 277.77*0.076 = =3D 21.11 lbm/min air mass at 6000 rpm . Just change the rpm to what ever = value you want. Also note the weight of air of course decreases with altitude = so 277.77 CFM provides 21.11 lbm/minute at sea level but less at = altitude. Note this assumes 100 % Volumetric efficiency. Ed Anderson Oh; boy, now you've done it. My beautiful intake scoop is already = installed, and I apparently designed it based on the wrong number. You're numbers look right to me. I'll have see if I can figure out = what I did. Thanks. Al Your Welcome, Al Perhaps you used the correct number for the design and just had = a brain fade when you quoted the number for CFM - Hopefully? Ed Anderson Ed: Well, it seems that I did use my number (275 cfm) and then computed = a scoop inlet area of 3.9 sq. in. based on an airspeed of 100 mph (steep = climb). When I fabricated it, I made a little larger so it would be = less restrictive for low speed. Yesterday I made a more accurate = measurement of the opening, and found it to be 5 =BC sq in. Assuming = everything is ideal, this would be about right for zero ram pressure at = about 130 mph, which is close to my typical climb speed. At typical = cruise of 200 mph at say 8000 ft, I should have same ram pressure for a = little better cruise efficiency. So all that is fine. There is always the trade off of a scoop that is not restrictive on = the takeoff roll, and one that gives you some ram air advantage without = much drag at high speed. I am considering a small, weighted trapdoor in = the bottom of the intake duct inside the cowl that will open and allow = more air in when the pressure in the duct is less than ambient, and = closes when the pressure is more than ambient. Al Glad to hear that it all turned out OK. I would say that 5 1/4 sq = inch should do the job, 3.9 might have been a bit on the restrictive = side for a WOT 3 rotor. I agree - every decision seems to involve a = compromise of some type. Reducing any pressure loss in the duct should = certainly help more air flow into the engine. Good looking installation = - coming along well. Cruise at 200 MPH should give you some where between 0.5 and 0.75 = psi additional inlet pressure depending on the density altitude. Any = estimate of when first engine run on the airframe? Ed -------------------------------------------------------------------------= --- >> Homepage: http://www.flyrotary.com/ >> Archive: http://lancaironline.net/lists/flyrotary/List.html ------=_NextPart_000_0025_01C3E91B.6FC62030 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
----- Original Message -----
From:=20 Al = Gietzen=20
Sent: Sunday, February 01, 2004 = 3:23=20 PM
Subject: [FlyRotary] air flow, = induction=20 air scoop

 

Subject:=20 [FlyRotary] Re: air flow

 

 

 Here is a = formula   80=20 CID * RPM/1728.  Example for 6000 rpm,  = 80*6000

rpm/1728 =3D 277.77 Cubic = Feet of air per=20 minute.  A cubic foot of air (at sea

level standard day) is = approx 0.076=20 lbm/cubic foot   so 277.77*0.076 =3D = 21.11

lbm/min air mass at 6000 = rpm . =20 Just change the rpm to what ever value you

want.  Also note the = weight of air=20 of course decreases with altitude so

277.77 CFM provides 21.11 = lbm/minute at=20 sea level but less at altitude.

 

Note this assumes 100 % = Volumetric=20 efficiency.

 

Ed = Anderson

 

Oh; = boy, now=20 you=92ve done it.  My beautiful intake scoop is already = installed, and I=20 apparently designed it based on the wrong number.

 

You=92re numbers=20 look right to me.  I=92ll have see if I can figure out what I=20 did.

 

Thanks.

 

Al

 

Your = Welcome,=20 Al

 

   =20 Perhaps you used the correct number for the design and just had a = brain fade=20 when you quoted the number for CFM - Hopefully?

 

Ed=20 Anderson

 

Ed:

Well, = it seems=20 that I did use my number (275 cfm) and then computed a scoop inlet = area of=20 3.9 sq. in. based on an airspeed of 100 mph (steep climb).  = When I=20 fabricated it, I made a little larger so it would be less = restrictive for=20 low speed.  Yesterday I made a more accurate measurement of the = opening, and found it to be 5 =BC sq in.  Assuming everything = is ideal,=20 this would be about right for zero ram pressure at about 130 mph, = which is=20 close to my typical climb speed.  At typical cruise of 200 mph = at say=20 8000 ft, I should have same ram pressure for a little better cruise=20 efficiency.  So all that is fine.

 

There = is always=20 the trade off of a scoop that is not restrictive on the takeoff = roll, and=20 one that gives you some ram air advantage without much drag at high=20 speed.  I am considering a small, weighted trapdoor in the = bottom of=20 the intake duct inside the cowl that will open and allow more air in = when=20 the pressure in the duct is less than ambient, and closes when the = pressure=20 is more than ambient.

 

Al

 

 

Glad to = hear that=20 it all turned out OK.  I would say that 5 1/4 sq inch should do = the=20 job, 3.9 might have been a bit on the restrictive side for a WOT 3=20 rotor.  I agree - every decision seems to involve a compromise = of some=20 type.  Reducing any pressure loss in the duct should certainly = help=20 more air flow into the engine.  Good looking installation - = coming=20 along well.

Cruise = at 200=20 MPH  should give you some where between 0.5 and 0.75 psi = additional=20 inlet pressure depending on the density altitude.   Any = estimate=20 of when first engine run on the airframe?

 

Ed

>>  Homepage: =20 http://www.flyrotary.com/
>>  Archive:  =20 = http://lancaironline.net/lists/flyrotary/List.html
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