X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 30 [X] Return-Path: Received: from fed1rmmtao107.cox.net ([68.230.241.39] verified) by logan.com (CommuniGate Pro SMTP 5.1.7) with ESMTP id 1931346 for flyrotary@lancaironline.net; Mon, 19 Mar 2007 20:00:35 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.39; envelope-from=alventures@cox.net Received: from fed1rmimpo01.cox.net ([70.169.32.71]) by fed1rmmtao107.cox.net (InterMail vM.7.05.02.00 201-2174-114-20060621) with ESMTP id <20070319235948.JQRZ321.fed1rmmtao107.cox.net@fed1rmimpo01.cox.net> for ; Mon, 19 Mar 2007 19:59:48 -0400 Received: from BigAl ([72.192.132.90]) by fed1rmimpo01.cox.net with bizsmtp id cnzn1W00W1xAn3c0000000; Mon, 19 Mar 2007 19:59:48 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: water boiling point Date: Mon, 19 Mar 2007 15:59:47 -0800 Message-ID: <000001c76a82$acdbfee0$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C76A3F.9EBB2FE0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C76A3F.9EBB2FE0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Al W; =20 I don=92t disagree with your concept, but I think there are other considerations. =20 The air volume number of 2 cups only applies to your system. The 7 psig = you mention implies that you only get a bit over =BD cup expansion of = coolant. In my system I know I get at least 6 times that much. =20 In addition to the boiling point protection, there is the consideration = of pump cavitation. When I was designing my system, I recall some pretty = awful photos (on the ACRE list) of what cavitation can do a pump impellor. = Since we generally run at high rpm, it=92s likely an issue. =20 =20 And =93ideal=94 pressure depends on where you measure it, and where the = cap pressure is. There is likely at least a few psi difference between the = pump inlet and the outlet. If the 7 psig (gauge pressure) you mention is on = the outlet side, then it may be close to 0 psig at the inlet, and = considerably lower behind the vane in the pump. At 180F water flashes to steam = bubbles at about -7 psig (8 psia), so there could be a have high probability of cavitation. And that=92s at sea level. If the 7 psig is at the pump = inlet, you=92d be a bit better off. =20 That=92s why I designed my system to have a =91cap pressure=92 of 23 = psig on the pump inlet side, why I have no air under that cap, and why I have a = pressure cap on the expansion bottle; so even when the coolant temp is = decreasing, and the cap pressure is 0 psig, there is still some positive pressure at = the pump inlet. Of course designing for this consideration takes care of = the boiling protection as well, and provides some margin for altitude, since = we generally fly considerably above sea level. It has worked fine for me so far. Concerning masking a compression leak, I think whether the = pressure is 7 or 27 it is negligible compared to combustion pressures. =20 =20 I don=92t know that this is necessary, right, wrong, or ideal; but it = made sense to me. =20 Al G =20 There's one coolant design that's substantially better than the others. = I discovered it when doing severe ground testing...deliberately = overheating my engine.=20 =20 Three basic requirements: =20 1) Place your radiator cap and reservoir above engine. The higher the better. This allows trapped air in system to rise out of the flow and = stay there.=20 2) Put a 24 psi cap on the system. You can throw away your overflow = stuff. Not needed. 3) Always keep around 2 cups of air under the cap. This is the key item. = It brings a big safety advantage. It allows you to use coolant pressure to predict well in advance how good your system is doing. It minimizes pressure. Mine never exceeds 7 psi. But if something goes wrong, then my pressure rises and I gain boilover protection due to the increase in = system pressure. -al wick Cozy IV =20 =20 ------=_NextPart_000_0001_01C76A3F.9EBB2FE0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Re: [FlyRotary] water boiling point

Al W;

 

I don’t disagree with your concept, but I think there are other considerations.

 

The air volume number of 2 cups = only applies to your system.=A0 The 7 psig you mention implies that you only = get a bit over =BD cup expansion of coolant.=A0 In my system I know I get at least = 6 times that much.

 

In addition to the boiling point = protection, there is the consideration of pump cavitation. =A0When I was designing = my system, I recall some pretty awful photos (on the ACRE list) of what = cavitation can do a pump impellor.=A0 Since we generally run at high rpm, = it’s likely an issue. =A0

 

And “ideal” pressure = depends on where you measure it, and where the cap pressure is.=A0 There is = likely at least a few psi difference between the pump inlet and the outlet.=A0 If = the 7 psig (gauge pressure) you mention is on the outlet side, then it may be close = to 0 psig at the inlet, and considerably lower behind the vane in the pump. At = 180F water flashes to steam bubbles at about -7 psig (8 psia), so there could be a = have high probability of cavitation.=A0 And that’s at sea level. If the = 7 psig is at the pump inlet, you’d be a bit better off.

 

That’s why I designed my = system to have a ‘cap pressure’ of 23 psig on the pump inlet side, why = I have no air under that cap, and why I have a pressure cap on the expansion = bottle; so even when the coolant temp is decreasing, and the cap pressure is 0 = psig, there is still some positive pressure at the pump inlet. =A0Of course = designing for this consideration takes care of the boiling protection as well, and provides some margin for altitude, since we generally fly considerably = above sea level. It has worked fine for me so far. =A0Concerning masking a = compression leak, I think whether the pressure is 7 or 27 it is negligible compared = to combustion pressures. =A0

 

I don’t know that this is necessary, right, wrong, or ideal; but it made sense to = me.

 

Al G

 

There's one coolant design that's substantially better than the others. I = discovered it when doing severe ground testing...deliberately overheating my engine. =

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Three basic requirements:

 <= /font>

1) Place your radiator cap and reservoir above engine. The higher the = better. This allows trapped air in system to rise out of the flow and stay there. =

2) Put a 24 psi cap on the system. You can throw away your overflow stuff. = Not needed.

3) Always keep around 2 cups of air under the cap. This is the key item. It = brings a big safety advantage. It allows you to use coolant pressure to predict = well in advance how good your system is doing. It minimizes pressure. Mine = never exceeds 7 psi. But if something goes wrong, then my pressure rises and I = gain boilover protection due to the increase in system = pressure.

=A0-al wick
Cozy IV

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 <= /font>

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