X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 01 Jun 2010 13:30:58 -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 4332822 for lml@lancaironline.net; Tue, 01 Jun 2010 12:57:24 -0400 Received-SPF: pass receiver=logan.com; client-ip=216.33.127.82; envelope-from=troneill@charter.net Received: from imp09 ([10.20.200.9]) by mta31.charter.net (InterMail vM.7.09.02.04 201-2219-117-106-20090629) with ESMTP id <20100601165647.BVLU22217.mta31.charter.net@imp09> for ; Tue, 1 Jun 2010 12:56:47 -0400 Received: from [192.168.1.100] ([75.132.241.174]) by imp09 with smtp.charter.net id Qgwi1e0063mUFT705gwlgo; Tue, 01 Jun 2010 12:56:46 -0400 X-Authority-Analysis: v=1.0 c=1 a=Iti9qD_iJ6gA:10 a=hO-oPbc3tlwA:10 a=YSD6EIYw9IC2RNj-zxEA:9 a=b8fwv3-RzSUuhpqnP4cA:7 a=jB5z2CnMWwWLWJnsa23H4IoFue8A:4 a=CjuIK1q_8ugA:10 a=Jiw2_SG_MKBFI9MHHJkA:7 a=3PHS5HmXOfboS6d6Z6GUfCDP3JoA:4 From: Terrence O'Neill Mime-Version: 1.0 (Apple Message framework v1078) Content-Type: multipart/alternative; boundary=Apple-Mail-4-751457820 Subject: Re: [LML] FW: [LML] Re: cowl flap cooling drag reduction X-Original-Date: Tue, 1 Jun 2010 11:56:41 -0500 In-Reply-To: X-Original-To: "Lancair Mailing List" References: X-Original-Message-Id: <4A86829B-27D5-4287-BEAB-91E9F0821C38@charter.net> X-Mailer: Apple Mail (2.1078) --Apple-Mail-4-751457820 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii Looks like you are perfect or hot weather ops, and as you said, could = close down the exit flow more for low temp or low power cruise. I'd like to do the same by reducing the base drag at the open aft side = of the cowl bottom ... thinking about a pair of longer bottom cowl = controllable ramps, so the external flow can go gently back to and along = the fuselage bottom. I haven't pulled the bottom cowl off yet to make = measurements... would have to add some side walls to the inner cowl to = keep the seal alongside the ramps. There's a lot of stuff in there. On my last design, the Magnum Pickup, I used an auto power window w/ = rack and pinion to actuate the big flaps, and that worked great... a = ramp on each side, not the bottom. I tried to reduce the Lancair's inlet airflow with inch-thick short = airfoils just inside each inlet, but the air just slips right past = them... little change and CHTs still running around 300F at 24/24, so = I'll probably pull them back out, and work on the cowl flap idea. Yours = did the job. Thanks, Terrence O'Neill On Jun 1, 2010, at 10:33 AM, Frederick Moreno wrote: > Update on cowl flaps. I closed off the exit area about 20% by = changing the cowl flap exhaust ramp shape (added some curved sheet = metal). Temperatures at 65% cruise 50F LOP rose modestly to above 300F = during flight conditions that were 9F above standard at 8500F. Speed up = about four knots. Looks like I can reduce exit area even further! This = would be consistent with the observations of big radials with closed = cowl flaps operating in economy cruise. > =20 > Full power climb with best power mixture (worst heating conditions), = cowl flaps open at Vy produced maximum temperatures of about 340F = starting with 65F ambient at sea level take off. I would expect about = 380-390F maximum with a 100F sea level departure. Further cooling can = be obtained by accelerating from Vy (135 knots) to 160-170 IAS. Cooling = with cowl flaps open is thus more than adequate even with abusive = conditions. > =20 > Larger inlets are GOOD (assuming you use cowl flaps) because they = permit pressure recovery in front of the inlet as the flow slows and = then spreads around the inlet. Small inlets require flow deceleration = inside the inlet which is much harder to do without flow separations. = The rule of thumb that seems to work and is fairly widely used is to = figure your cruise air flow requirements (actual cubic feet per minute) = and size the inlets so that the velocity at the throat of the inlet is = about 50% of the free stream velocity. This gets about 75% of the = available pressure recovery in front of the inlet, and with some good = internal design should get up to 90+% total pressure recovery. This = gives plenty of surplus pressure to accelerate the hot flow out the cowl = flap nozzles and recover most of the lost momentum thus reducing = cooling drag. > =20 > Fred Moreno --Apple-Mail-4-751457820 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=us-ascii Looks like you are perfect or hot weather ops, and = as you said, could close down the exit flow more for low temp or low = power cruise.
I'd like to do the same by reducing the base drag at = the open aft side of the cowl bottom ... thinking about a pair of longer = bottom cowl controllable ramps, so the external flow can go gently back = to and along the fuselage bottom.  I haven't pulled the bottom cowl = off yet to make measurements... would have to add some side walls to the = inner cowl to keep the seal alongside the ramps.  There's a lot of = stuff in there.
On my last design, the Magnum Pickup, I used = an auto power window w/ rack and pinion  to actuate the big flaps, = and that worked great... a ramp on each side, not the = bottom.

I tried to reduce the Lancair's inlet = airflow with inch-thick short airfoils just inside each inlet, but the = air just slips right past them... little change and CHTs still running = around 300F at 24/24, so I'll probably pull them back out, and work on = the cowl flap idea.  Yours did the = job.

Thanks,
Terrence = O'Neill


On Jun 1, 2010, at 10:33 = AM, Frederick Moreno wrote:

Update on cowl flaps.  I closed off the = exit area about 20% by changing the cowl flap exhaust ramp shape (added = some curved sheet metal).  Temperatures at 65% cruise 50F LOP rose = modestly to above 300F during flight conditions that were 9F above = standard at 8500F.  Speed up about four knots.  Looks like I = can reduce exit area even further!  This would be consistent with = the observations of big radials with closed cowl flaps operating in = economy cruise.
 
Full = power climb with best power mixture (worst heating conditions), cowl = flaps open at Vy  produced maximum temperatures of about 340F = starting with 65F ambient at sea level take off.  I would expect = about 380-390F maximum with a 100F sea level departure.  Further = cooling can be obtained by accelerating from Vy (135 knots) to 160-170 = IAS.  Cooling with cowl flaps open is thus more than adequate even = with abusive conditions.
Larger inlets are GOOD (assuming you = use cowl flaps) because they permit pressure recovery in front of the = inlet as the flow slows and then spreads around the inlet.  Small = inlets require flow deceleration inside the inlet which is much harder = to do without flow separations.  The rule of thumb that seems to = work and is fairly widely used is to figure your cruise air flow = requirements (actual cubic feet per minute) and size the inlets so that = the velocity at the throat of the inlet is about 50% of the free stream = velocity.   This gets about 75%  of the available = pressure recovery in front of the inlet, and with some good internal = design should get up to 90+% total pressure recovery.  This gives = plenty of surplus pressure to accelerate the hot flow out the cowl flap = nozzles and recover  most of the lost momentum thus reducing = cooling drag.
 
Fred = Moreno
=
= --Apple-Mail-4-751457820--