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X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from ms-smtp-02.southeast.rr.com ([24.25.9.101] verified) by logan.com (CommuniGate Pro SMTP 5.1.11) with ESMTP id 2250091 for flyrotary@lancaironline.net; Wed, 08 Aug 2007 10:02:54 -0400 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.101; envelope-from=eanderson@carolina.rr.com Received: from edward2 (cpe-024-074-103-061.carolina.res.rr.com [24.74.103.61]) by ms-smtp-02.southeast.rr.com (8.13.6/8.13.6) with SMTP id l78E25Bw010365 for ; Wed, 8 Aug 2007 10:02:06 -0400 (EDT) Message-ID: <002201c7d9c4$d68eab00$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] electric fans Date: Wed, 8 Aug 2007 10:03:03 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_001F_01C7D9A3.4F2993D0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.3138 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_001F_01C7D9A3.4F2993D0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MessageHumm, Rusty, I think a fan might be useful for ground operations, but once = airborne, my calculations indicate it would likely hinder airflow more = than help it. Here's the rationale. Normally, duct design calls for slowing duct air velocity down to 0.1 = cruise speed or 0.3 Climb speed (Horner). So if your cruise climb is = 120 MPH IAS then the air flow in the duct should (ideally) be around 0.3 = * 120 =3D 36 MPH. That is 36 MPH or 52.8 feet/sec. =20 With a core with a face area of say 200 sq inch. That would give 52.8 * = 200/144 =3D 73 cubic feet/sec or 73*60 =3D 4400 CFM of air flow = through the core. I personally doubt a fan would do anything more than = hinder that much air flow. If you are not getting that much air flow, = then I believe attention to the ducting would be more productive than = adding a fan. But, that is just my opinion based on back of envelope = calculations.=20 Again, for ground and taxi operations, I agree, a Fan would undoubtedly = help, but I don't believe it would help once airborne. FWIW Ed . =20 ----- Original Message -----=20 From: Russell Duffy=20 To: Rotary motors in aircraft=20 Sent: Wednesday, August 08, 2007 9:16 AM Subject: [FlyRotary] electric fans Greetings, I've only been skimming through the cooling posts, but I haven't seen = much talk of electric fans. I was thinking about this during my drive = time yesterday, and it seems to me that we have exactly the same need = for an electric fan as a car does. =20 - Packaging limits size and location of radiators. - Ducting optimized for normal cruise speed, fan compensates at low = speeds. =20 It would seem to me that the best situation would be to optimized your = inlet and ducting for normal cruise flight, then use a fan during climb. = The drawbacks would be weight, drag, and perhaps bearing life on the = fan, but the positives could make up for these I think. =20 From what I've read, it's common to use a switch to tie the motor = leads together, which keeps the motor from completely freewheeling when = unpowered in cruise. It would seem that you can reduce the drag and = bearing problems that way. I would also think a clever guy could = provide a switch mode that allows you to generate alternate electricity = from the freewheeling fan. =20 Just something old to think about again.=20 Rusty ------=_NextPart_000_001F_01C7D9A3.4F2993D0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Message

Humm,

Rusty, I think a fan might be useful for ground=20 operations, but once airborne, my calculations indicate it would = likely=20 hinder airflow more than help it.

Here's the rationale.

Normally, duct design calls for slowing = duct air=20 velocity down to 0.1 cruise speed or 0.3 Climb speed = (Horner). So if=20 your cruise climb is 120 MPH IAS then the air flow in the duct should = (ideally)=20 be around 0.3 * 120 =3D 36 MPH. That is 36 MPH or 52.8 = feet/sec. =20

With a core with a face area of say 200 sq = inch. =20 That would give 52.8 * 200/144 =3D 73 cubic feet/sec or = 73*60 =3D=20 4400 CFM of air flow through the core. I personally doubt a fan = would do=20 anything more than hinder that much air flow. If you are not = getting=20 that much air flow, then I believe attention to the ducting would be = more=20 productive than adding a fan. But, that is just my = opinion=20 based on back of envelope calculations.

Again, for ground and taxi operations, I agree, = a Fan=20 would undoubtedly help, but I don't believe it would help once=20 airborne.

FWIW

----- Original Message -----
From:=20 Russell=20 Duffy
To: Rotary motors in = aircraft

Sent: Wednesday, August 08, = 2007 9:16=20 AM

Subject: [FlyRotary] electric = fans

Greetings,

I've only = been skimming=20 through the cooling posts, but I haven't seen much talk of electric=20 fans. I was thinking about this during my drive time yesterday, = and it=20 seems to me that we have exactly the same need for an electric fan as = a car=20 does.

- Packaging = limits size=20 and location of radiators.

- Ducting optimized=20 for normal cruise speed, fan compensates at low=20 speeds.

It = would seem to me=20 that the best situation would be to optimized your inlet and = ducting for normal cruise flight, then use a = fan during=20 climb. The=20 drawbacks would be weight, drag, and perhaps bearing life on the fan, = but the=20 positives could make up for these I=20 think.

From what = I've read, it's=20 common to use a switch to tie the motor leads together, which = keeps the=20 motor from completely freewheeling when unpowered=20 in cruise.   It would seem that you can reduce the drag = and=20 bearing problems that way. I would also think a clever guy could = provide=20 a switch mode that allows you to generate alternate electricity = from the=20 freewheeling fan.

Just = something old=20 to think about again.

Rusty

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