X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from ispmxmta05-srv.windstream.net ([166.102.165.166] verified) by logan.com (CommuniGate Pro SMTP 5.2c1) with ESMTP id 2491545 for flyrotary@lancaironline.net; Fri, 16 Nov 2007 10:41:17 -0500 Received-SPF: pass receiver=logan.com; client-ip=166.102.165.166; envelope-from=montyr2157@alltel.net Received: from ispmxaamta05-gx.windstream.net ([75.88.21.93]) by ispmxmta05-srv.windstream.net with ESMTP id <20071116154032.EUVR19750.ispmxmta05-srv.windstream.net@ispmxaamta05-gx.windstream.net> for ; Fri, 16 Nov 2007 09:40:32 -0600 Received: from Thorstwin ([75.88.21.93]) by ispmxaamta05-gx.windstream.net with SMTP id <20071116154031.BKAT9878.ispmxaamta05-gx.windstream.net@Thorstwin> for ; Fri, 16 Nov 2007 09:40:31 -0600 Message-ID: <000d01c82867$07fea2d0$6501a8c0@Thorstwin> From: "M Roberts" To: "Rotary motors in aircraft" Subject: Cowling Airflow Date: Fri, 16 Nov 2007 09:40:35 -0600 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_000A_01C82834.BD3BC340" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3138 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3198 This is a multi-part message in MIME format. ------=_NextPart_000_000A_01C82834.BD3BC340 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Doug, There are basically three types of drag that you wind up dealing with = when planning a cooling installation.=20 1.) Pressure drag, due to the local pressure acting on the surface of a = the aircraft or duct 2.) Viscous drag, due to the scrubbing and mixing of the air 3.) Momentum drag, due to any mass of air taken on board (think of = trying to scoop water out of lake from a speeding boat with a bucket) Your bleed air idea will more than likely cause all of these types of = drag, and it is dubious that it will help with cooling any. If you want = to achieve this the best way is to use the high energy present in the = exhaust gas jet to accomplish the same thing.=20 The bleed air ducts found on aircraft are to accomplish the exact = opposite of what you are trying to do. They ingest and remove the low = energy boundary layer, so that the main duct only sees high energy = airflow. You are ingesting the valuable stuff and then trying to use it = to accelerate the low energy stuff. What you really need to do is figure = out how to accelerate the low energy stuff without disturbing all that = nice high energy flow. I would copy Dennis' installation as much as = possible. He seems to be cooling well with the Renesis and the same = cowl. He did mention to me that he saw a large improvement when he = separated the combustion air inlet from the radiator inlet. He placed = the combustion air inlet in the space between the spinner and the = radiator inlet. That is a really good place for it. It will help keep = the boundary layer from spilling around the radiator inlet, and it = should have really good pressure recovery due to external diffusion. I would also not recommend the location for cooling outlet on top of the = cowl where you have it drawn. Melmoth II has the outlet near the front = of cowl on top, just behind the prop. This is a low pressure area, as = you move aft, the pressure rises and at the base of the canopy it is = quite high. I can think of a lot of reasons not to use a top outlet in = our case. What if you have an oil/coolant leak? Wouldn't you prefer it = splatter the bottom of the airplane rather than the canopy? What if you = have an exhaust leak and the fumes spill up over the top and get sucked = into the cockpit? I would stick with the bottom exit and a cowl flap, or = go for the side of the fuselage with cowl flaps. A weighted door that is = closed in flight on top of the cowl is not a bad idea to let heat out = when parked. Planning a cooling installation is a big bunch of compromises. I have my = radiator behind my seat, the inlet under the wing, and the outlets just = aft of the thickest point on the side of the fuselage. That is about as = optimum as it gets. However, I have made several compromises to reach = that point. There are long runs of coolant that go through the center = console. Not something that makes me very happy. There has been at least = one fatal crash of a P51 due to coolant lines rupturing and filling the = cockpit with steam. It is also heavy. Coolant weighs a lot. I still have = to have cooling air in the cowl for the engine, exhaust etc so there is = still going to be some drag due to that. Then there is the fact that the = inlet is placed farther back on the fuselage and the boundary layer is = thicker. A good deal of what could be baggage area is eaten up with = radiator and duct work. There is no perfect solution. The winner has the = best combination of compromises for a given mission. Monty ------=_NextPart_000_000A_01C82834.BD3BC340 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Doug,
 
There are basically three types of drag = that you=20 wind up dealing with when planning a cooling installation.
 
1.) Pressure drag, due to the local = pressure acting=20 on the surface of a the aircraft or duct
 
2.) Viscous drag, due to the scrubbing = and mixing=20 of the air
 
3.) Momentum drag, due to any mass of = air taken on=20 board (think of trying to scoop water out of lake from a speeding boat = with a=20 bucket)
 
Your bleed air idea will more than = likely cause all=20 of these types of drag, and it is dubious that it will help with cooling = any. If=20 you want to achieve this the best way is to use the high energy present = in the=20 exhaust gas jet to accomplish the same thing.
 
The bleed air ducts found on aircraft = are to=20 accomplish the exact opposite of what you are trying to do. They ingest = and=20 remove the low energy boundary layer, so that the main duct only sees = high=20 energy airflow. You are ingesting the valuable stuff and then trying to = use it=20 to accelerate the low energy stuff. What you really need to do is figure = out how=20 to accelerate the low energy stuff without disturbing all that nice high = energy=20 flow. I would copy Dennis' installation as much as possible. He seems to = be=20 cooling well with the Renesis and the same cowl. He did mention to me = that he=20 saw a large improvement when he separated the combustion air inlet = from the=20 radiator inlet. He placed the combustion air inlet in the space = between the=20 spinner and the radiator inlet. That is a really good place = for=20 it. It will help keep the boundary layer from spilling around=20 the radiator inlet, and it should have really good pressure = recovery due to=20 external diffusion.
 
I would also not recommend the location = for cooling=20 outlet on top of the cowl where you have it drawn. Melmoth II = has the=20 outlet near the front of cowl on top, just behind the prop. This is a = low=20 pressure area, as you move aft, the pressure rises and at the base of = the canopy=20 it is quite high. I can think of a lot of reasons not to use a top = outlet in our=20 case. What if you have an oil/coolant leak? Wouldn't you prefer it = splatter the=20 bottom of the airplane rather than the canopy? What if you have an = exhaust leak=20 and the fumes spill up over the top and get sucked into the cockpit? I = would=20 stick with the bottom exit and a cowl flap, or go for the side of the = fuselage=20 with cowl flaps. A weighted door that is closed in flight on top of the = cowl is=20 not a bad idea to let heat out when parked.
 
Planning a cooling installation is a = big bunch of=20 compromises. I have my radiator behind my seat, the inlet under the = wing, and=20 the outlets just aft of the thickest point on the side of the fuselage. = That is=20 about as optimum as it gets. However, I have made several compromises to = reach=20 that point. There are long runs of coolant that go through the center = console.=20 Not something that makes me very happy. There has been at least one = fatal crash=20 of a P51 due to coolant lines rupturing and filling the cockpit with = steam. It=20 is also heavy. Coolant weighs a lot. I still have to have cooling air in = the=20 cowl for the engine, exhaust etc so there is still going to be some drag = due to=20 that. Then there is the fact that the inlet is placed farther back on = the=20 fuselage and the boundary layer is thicker. A good deal of what could be = baggage=20 area is eaten up with radiator and duct work. There is no perfect = solution.=20 The winner has the best combination of compromises for a given=20 mission.
 
 
Monty 
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