X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 04 Aug 2009 08:53:20 -0400 Message-ID: X-Original-Return-Path: Received: from nschwmtas04p.mx.bigpond.com ([61.9.189.146] verified) by logan.com (CommuniGate Pro SMTP 5.2.15) with ESMTP id 3794233 for lml@lancaironline.net; Tue, 04 Aug 2009 08:41:31 -0400 Received-SPF: pass receiver=logan.com; client-ip=61.9.189.146; envelope-from=frederickmoreno@bigpond.com Received: from nschwotgx03p.mx.bigpond.com ([58.170.138.242]) by nschwmtas04p.mx.bigpond.com with ESMTP id <20090804124050.GOWK2030.nschwmtas04p.mx.bigpond.com@nschwotgx03p.mx.bigpond.com> for ; Tue, 4 Aug 2009 12:40:50 +0000 Received: from Razzle ([58.170.138.242]) by nschwotgx03p.mx.bigpond.com with ESMTP id <20090804124049.FJXY21568.nschwotgx03p.mx.bigpond.com@Razzle> for ; Tue, 4 Aug 2009 12:40:49 +0000 From: "Frederick Moreno" X-Original-To: "Lancair Mail" Subject: FW: plenum 4P X-Original-Date: Tue, 4 Aug 2009 20:40:41 +0800 X-Original-Message-ID: <084AAEEDEC8E4FFAACCEFB2B3F8EAB87@Razzle> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_00CE_01CA1543.D58166A0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6838 Thread-Index: AcoRxgeka/ed+T0BSoKtH1bABD4JXgDOLzIA X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 Importance: Normal X-RPD-ScanID: Class unknown; VirusThreatLevel unknown, RefID str=0001.0A150204.4A782C52.00A9,ss=1,fgs=0 This is a multi-part message in MIME format. ------=_NextPart_000_00CE_01CA1543.D58166A0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable I have constructed a full plenum on my Lancair IV around my IO-550 engine with good results. A key to getting the best performance is not only installing the plenum, but also making a strong effort to seal all leaks from the high pressure area under the plenum to the lower pressure area under the engine. I think that attention to sealing of leaks, particularly big leaks such as those under the crankshaft at the nose of the engine, is probably more beneficial to cooling and drag reduction than the plenum itself. But that is conjecture as I have no independent data.=20 =20 As to the questions Ralf raises:=20 =20 Question: can I use the standard baffling? =96 I understand that the idea o= f the plenum is to reduce leaks and losses. Therefore the pressure within the plenum should be higher than before. I was planning to bolt the plenum to the standard baffling (which is pretty flimsy). The force that is created b= y the pressure is now taken away from the upper half of the cowl and has to b= e held down by the baffling. How much pressure do I get in a plenum? With the area of the engine I could get an idea of how much force I can expect on th= e baffling. Is this an area of concern or am I over-thinking everything again= ? =20 I used the standard Lancair baffling, and then cut it a lot and threw much away (particularly up front) fabricating new parts of fiberglass. See photos in the archives under Builders Tips. Look at the cooling drag reduction report I wrote which is in five PDF files with lots of photos including many of the plenum I built and the steps taken to minimize leakage. Expect to spend many hours on this project. It will pay off. =20 =20 To specifics: =20 =20 Not all the ram pressure is carried by the plenum. Maximum inlet ram pressure available at the inlets at 200 KIAS is about 23 inches of water. You get about 18 inches in the plenum (about 90 pounds per square foot). But the loss across the engine is typically 7 inches at lower altitudes, bu= t may be up to 15 or 20 at the high altitudes in the turbo airplanes. Then there is additional loss as the flow exits the cowl. If you estimate that the plenum is perhaps 10 square feet, the load separating the cowl or plenu= m from the top of the engine is perhaps 900 pounds at cruise (turbocharged Lancair IV, 280 knots true, 24,000 feet) and could go to double that at Vne (274 knots) in a descent. So the attach points need to be numerous and strong. All those reports of bulging cowls indicate the scope of the problem. I stiffened my top cowl with ribs, but made them excessively deep in my opinion which made the fabrication af fitting of the plenum more problematical than need be. My cowl does not bulge. At all. Zilch. I made it too rigid and created other problems.=20 =20 Be particularly careful to keep the plenum at least =BC inch or more away f= rom the top and side of the cowl, or you will get a rub due to vibration or while flying through rough air.=20 =20 Fred Moreno ------=_NextPart_000_00CE_01CA1543.D58166A0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

I have constructed a full plenum on my Lancair= IV around my I= O-550 engine with good results.=A0 A key to getting the best performance is not o= nly installing the plenum, but also making a strong effort to seal all leaks from the high= pressure area under the plenum to the lower pressure area under the engine.=A0 I thi= nk that attention to sealing of leaks, particularly big leaks such as those un= der the crankshaft at the nose of the engine, is probably more beneficial to cooling and drag reduction than the plenum itself.=A0 But that is conjectur= e as I have no independent data.

 

As to the questions Ralf raises:

 

Question: can I use the standard baffling? –= ; I understand that the idea of the plenum is to reduce leaks and losses. There= fore the pressure within the plenum should be higher than before. I was planning= to bolt the plenum to the standard baffling (which is pretty flimsy). The forc= e that is created by the pressure is now taken away from the upper half of the cow= l and has to be held down by the baffling. H<= font size=3D2 face=3DArial>ow much pressure do I get in a plenum? With the area of the engine I could get= an idea of how much force I can expect on the baffling. Is this an area of con= cern or am I over-thinking everything again?

 

I used the standard Lancair baffling, and then cut it a lo= t and threw much away (particularly up front) fabricating new parts of fiberglass.=A0 See photos in the archives under Builders Tips.=A0 Look at t= he cooling drag reduction report I wrote which is in five PDF files with lots = of photos including many of the plenum I built and the steps taken to minimize leakage.=A0 Expect to spend many hours on this project.=A0 It will pay off.= =A0

 

To specifics:=A0

 

Not all the ram pressure is carried by the plenum.=A0 Ma= ximum inlet ram pressure available at the inlets at 200 KIAS is about 23 inches o= f water.=A0 You get about 18 inches in the plenum (about 90 pounds per square foot).=A0 But the loss across the engine is typically 7 inches at lower altitudes, but may be up to 15 or 20 at the high altitudes in the turbo airplanes.=A0 Then there is additional loss as the flow exits the cowl.=A0 = If you estimate that the plenum is perhaps 10 square feet, the load separating the cowl or plenum from the top of the engine is perhaps 900 pounds at cruise (turbocharged Lancair IV, 280 knots true, 24,000 feet) and could go to double that at Vne= (274 knots) in a descent.=A0 So the attach points need to be numerous and strong= .=A0 =A0All those=A0 reports of=A0 bulging cowls indicate the scope of the problem.=A0 = I stiffened my top cowl with ribs, but made them excessively deep in my opini= on which made the fabrication af fitting of the plenum more problematical than need be. =A0=A0My cowl does not bulge.=A0 At all.=A0=A0 Zilch.=A0 I made it= too rigid and created other problems.

 

Be particularly careful to keep the plenum at least =BC = inch or more away from the top and side of the cowl, or you will get a rub due t= o vibration or while flying through rough air.

 

Fred Moreno

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