Return-Path: Received: from [24.25.9.101] (HELO ms-smtp-02-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 4.1.8) with ESMTP id 2881619 for flyrotary@lancaironline.net; Mon, 08 Dec 2003 09:10:55 -0500 Received: from o7y6b5 (clt78-020.carolina.rr.com [24.93.78.20]) by ms-smtp-02-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id hB8EAod3029926 for ; Mon, 8 Dec 2003 09:10:53 -0500 (EST) Message-ID: <000e01c3bd94$a2ef3120$1702a8c0@WorkGroup> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: K&M and Thick Radiators Date: Mon, 8 Dec 2003 09:07:37 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_000B_01C3BD6A.B9BD9BA0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1106 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_000B_01C3BD6A.B9BD9BA0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable =20 > <... How do the Mass Air requirements change with altitude ...> > They don't, except as the heat rejection requirements change. > You get the same mass airflow at 180 kias at sea level or 15 k ft. Of = course > your TRUE airspeed at 15k is a lot higher and that's what pumps more = of the > thinner air through the system. Also, to the extent that fuel flow is = less at > 15 k ft, so you have less heat rejection requirements and therefore = less mass > flow requirements. >=20 > <... if the fuel burn was 8.5gph and altitude was 25K ...> > .... you'd be making about 300 kts TAS and would no doubt have the = same mass > airflow as at SL 8.5 gph. >=20 > Mass airflow is a function of indicated airspeed which is dynamic = pressure which > is how many molecules are going past a point in a unit of time. >=20 > Just a theory ... Jim S. >=20 One common formula for air mass flow is as follows: W =3D p*V*A Where W is air mass flow either in Slugs/Unit time or pounds mass (lbm) = or kilograms/unit time, etc. p is the density of the air mass, V the = velocity of the air stream and A the area of the duct (or what ever) you = have the air flowing through. A formula for Dynamic pressure on the other hand is=20 Pd =3D 1/2pV^2 which results in units of pressure (lbf - pound force per square foot, = square inch, square CM or other such area units. So Dynamic pressure = and air mass flow are two separate things. However, density and = velocity of the air are a factor in both.=20 You can have high dynamic pressure and low mass flow or vise versa. = Velocity (V^2) is the dominate factor in dynamic pressure whereas volume = (V*A) is the dominate factor in dynamic pressure. =20 FWIW Ed Anderson ------=_NextPart_000_000B_01C3BD6A.B9BD9BA0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

> <... How do the Mass Air = requirements=20 change with altitude ...>
> They don't, except as the heat = rejection=20 requirements change.
> You get the same mass airflow at 180 kias = at sea=20 level or 15 k ft. Of course
> your TRUE airspeed at 15k is a lot = higher=20 and that's what pumps more of the
> thinner air through the = system. =20 Also, to the extent that fuel flow is less at
> 15 k ft, so you = have less=20 heat rejection requirements and therefore less mass
> flow=20 requirements.
>
> <... if the fuel burn was 8.5gph and = altitude=20 was 25K ...>
> .... you'd be making about 300 kts TAS and would = no=20 doubt have the same mass
> airflow as at SL 8.5 gph.
> =
> Mass=20 airflow is a function of indicated airspeed which is dynamic pressure=20 which
> is how many molecules are going past a point in a unit of=20 time.
>
> Just a theory ... Jim S.
> =

One common formula for air mass flow is = as=20 follows:

W =3D = p*V*A

Where W is air mass flow either in = Slugs/Unit time=20 or pounds mass (lbm) or kilograms/unit time, etc. p is the density = of the=20 air mass, V the velocity of the air stream and A the area of the duct = (or what=20 ever) you have the air flowing through.

A formula for Dynamic pressure on the = other hand is=20

Pd =3D = 1/2pV^2

which results in = units of=20 pressure (lbf - pound force per square foot, square inch, square CM or = other=20 such area units. So Dynamic pressure and air mass flow are two = separate=20 things. However, density and velocity of the air are a factor in=20 both.

You can have high dynamic pressure and = low mass=20 flow or vise versa. Velocity (V^2) is the dominate factor in = dynamic=20 pressure whereas volume (V*A) is the dominate factor in dynamic = pressure. =20

FWIW

Ed Anderson

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