X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Mon, 31 May 2010 10:50:59 -0400 Message-ID: X-Original-Return-Path: Received: from mta31.charter.net ([216.33.127.82] verified) by logan.com (CommuniGate Pro SMTP 5.3.7) with ESMTP id 4331529 for lml@lancaironline.net; Mon, 31 May 2010 10:10:51 -0400 Received-SPF: pass receiver=logan.com; client-ip=216.33.127.82; envelope-from=troneill@charter.net Received: from imp11 ([10.20.200.11]) by mta31.charter.net (InterMail vM.7.09.02.04 201-2219-117-106-20090629) with ESMTP id <20100531141014.DZGA22217.mta31.charter.net@imp11> for ; Mon, 31 May 2010 10:10:14 -0400 Received: from [192.168.1.100] ([75.132.241.174]) by imp11 with smtp.charter.net id QEAD1e0033mUFT705EAECc; Mon, 31 May 2010 10:10:14 -0400 X-Authority-Analysis: v=1.0 c=1 a=Iti9qD_iJ6gA:10 a=hO-oPbc3tlwA:10 a=xL3VKAkTHXvMqBlnEC4A:9 a=eEiwQPmYeD0dcJF7uC0A:7 a=91Z3YhC9UWrpkx-WxtrEKOSg-18A:4 a=pILNOxqGKmIA:10 a=2PXxnH5ysZ5_MafB:21 a=6bv4245pCodWoDR5:21 a=QhhpLXFfSKzt2NhwGGAA:9 a=35bCYGPmUugu_PfBuwAA:7 a=en2Ii-efI993GHX3SUMV4gVuQ4YA:4 From: Terrence O'Neill Mime-Version: 1.0 (Apple Message framework v1078) Content-Type: multipart/alternative; boundary=Apple-Mail-1-655072208 Subject: Re: [LML] FW: [LML] Re: cowl flap cooling drag reduction X-Original-Date: Mon, 31 May 2010 09:10:15 -0500 In-Reply-To: X-Original-To: "Lancair Mailing List" References: X-Original-Message-Id: X-Mailer: Apple Mail (2.1078) --Apple-Mail-1-655072208 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=windows-1252 Many thanks for the info. Another vote for retaining the inlet area, = and modifying the cowl to closeable cowl flaps. Again reminds me of watching the cowl flaps close down to not more than = a crack around the P2V's big CW 3350s when going to cruise... and = marvelling at how such a small amount of exit air could cool those big = engines... Also intend to try to radius the bottom of the firewall in = the cowl exit area... trickey geometry at the nosewheel strut... and = maybe make a sealing fairing around the two exhaust stacks on the left = side of the cowl. Terrence=20 L235/320 N211AL On May 30, 2010, at 8:54 AM, Frederick Moreno wrote: > I put cowl flaps on my Lancair IV along with a top cooling air plenum = and I also went to fairly extreme measures to eliminate cooling leakage = around the engine. Inlet area remained unchanged (6 inch diameter) = although the inlets were raised 1.5 inches for a straight shot in and = moved outboard 1.0 inch so that I could insert a boundary layer dam = between spinner and inlets. This removes the boundary layer coming off = the spinner as well as the slower-moving separated wake flow at the = shank of the propeller where it enters the spinner. I drastically cut = the exit area with cowl flaps closed compared to the stock Lancair = outlets which are meant for turbo engines at 25,000 feet. (I believe = turbo engines would gain no benefit from closable cowl flaps =96 they = need all that air flow at altitude.) > =20 > Net result was that overall flat plate drag area went down (compared = to stock) perhaps 7-10% with the cowl flaps closed, and it runs cold at = 65% lean of peak, CHTs below 300F, lower than 250F at low altitudes. = With cowl flaps open (and lots of exit area) I can climb unrestricted at = Vy (135 knots, best power) starting at near sea level on a 90F day. = Difference between cowl flaps closed and faired and wide open and = deflected outward about three inches is about ten knots. That does NOT = mean a ten knot speed improvement over stock. It means that when the = cowl flaps are open, they are draggy.=20 > =20 > I have measured pressure drop across the engine and even with cowl = flaps closed, it is too high (too much cooling air, confirming = temperature data). So last week I made modifications to reduce the = closed cowl flap exit area another 25%. No testing yet. > =20 > Would I do it again? Maybe. It was a lot of work. Estimate of the = overall speed benefit: perhaps 3.0-3.5%. It sure is nice to climb = unrestricted on a hot day.=20 > =20 > Fred > =20 > =20 > Thanks, Gary. =20 > Okay, so I think I would keep the L235 cowl inlet area as-is, and be = generous with the flappable outlet area. > Actual experience is very reassuring. > Terrence > L235/320 N2111AL > =20 > =20 >=20 > I also reduced the inlet area about 20%, adding a diffuser section. = The outlet area was reduced to about half of the original, depending on = what kind of bulges on the bottom are assumed to be "standard." The = cooling is marginal, but adequate - on hot days climb speeds have to be = increased and cruise is done with the flaps open. This is to keep the = CHT's below 400 and oil below 220. Closing the relatively small cowl = flaps increases the speed by 2 to 4 knots.=20 > ES #157, Lycoming engine > =20 > =20 --Apple-Mail-1-655072208 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=windows-1252 Many thanks for the info.  Another vote for = retaining the inlet area, and modifying the cowl to closeable cowl = flaps.
Again reminds me of watching the cowl flaps close down to not = more than a crack around the P2V's big CW 3350s when going to cruise... = and marvelling at how such a small amount of exit air could cool those = big engines...   Also intend to try to radius the bottom of the = firewall in the cowl exit area... trickey geometry at the nosewheel = strut... and maybe make a sealing fairing around the two exhaust stacks = on the left side of the = cowl.

Terrence 
L235/320 =  N211AL


On May 30, 2010, at = 8:54 AM, Frederick Moreno wrote:

I put cowl flaps on my Lancair  IV along with a = top cooling air plenum and I also went to fairly extreme measures to = eliminate cooling leakage around the engine.  Inlet area remained = unchanged (6 inch diameter) although the inlets were raised 1.5 inches = for a straight shot in and moved outboard 1.0 inch so that I could = insert a boundary layer dam between spinner and inlets.  This = removes the boundary layer coming off the spinner as well as the = slower-moving separated wake flow at the shank of the propeller where it = enters the spinner.  I drastically cut the exit area with cowl = flaps closed compared to the stock Lancair outlets which are meant for = turbo engines at 25,000 feet.  (I believe turbo engines would gain = no benefit from closable cowl flaps =96 they need all that air flow at = altitude.)
 
Net = result was that overall flat plate drag area  went down (compared = to stock) perhaps 7-10% with the cowl flaps closed, and it runs cold at = 65% lean of peak, CHTs below 300F, lower than 250F at low = altitudes.  With cowl flaps open (and lots of exit area) I can = climb unrestricted at Vy (135 knots, best power) starting at near sea = level on a 90F day.  Difference between cowl flaps closed and = faired and wide open and deflected outward about three inches is about = ten knots.  That does NOT mean a ten knot speed improvement over = stock.  It means that when the cowl flaps are open, they are = draggy. 
 
I = have measured pressure drop across the engine and even with cowl flaps = closed, it is too high (too much cooling air, confirming temperature = data).  So last week I made modifications to reduce the closed cowl = flap exit area another 25%.  No testing = yet.
 
 
 
 
Thanks, Gary. =  
Okay, so I think I would keep = the L235 cowl inlet area as-is, and be generous with the flappable = outlet area.
Actual experience is very = reassuring.
L235/320 = N2111AL

 I = also reduced the inlet area about 20%, adding a diffuser section.  = The outlet area was reduced to about half of the original, depending on = what kind of bulges on the bottom are assumed to be "standard."  = The cooling is marginal, but adequate - on hot days climb speeds have to = be increased and cruise is done with the flaps open.  This is to = keep the CHT's below 400 and oil below 220.  Closing the relatively = small cowl flaps increases the speed by 2 to 4 = knots. 
ES #157, Lycoming = engine