X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 1 [X] Return-Path: Sender: To: lml Date: Tue, 06 Feb 2007 08:25:08 -0500 Message-ID: X-Original-Return-Path: Received: from smtp106.sbc.mail.re2.yahoo.com ([68.142.229.99] verified) by logan.com (CommuniGate Pro SMTP 5.1.5) with SMTP id 1814567 for lml@lancaironline.net; Tue, 06 Feb 2007 04:06:43 -0500 Received-SPF: none receiver=logan.com; client-ip=68.142.229.99; envelope-from=elippse@sbcglobal.net Received: (qmail 16718 invoked from network); 6 Feb 2007 09:05:44 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=sbcglobal.net; h=Received:X-YMail-OSG:Message-ID:From:To:Subject:Date:MIME-Version:Content-Type:X-Priority:X-MSMail-Priority:X-Mailer:X-MIMEOLE; b=r/nokWUuv1i8/BbhH4vA7FIiWi7jZhLDdi8ed8pRVt4UHa2eDYl46UOmfIMBuxgRpGly54u/MVPsruMblO5hX5IgvpCvULQqmY0O9ZYRJUkkUX9Hu+QdJ0Vit8G2bPSmOaOsvceEeZNiS2ntwY8EYoTmUWCpcxmpYsVp1t4VN/k= ; Received: from unknown (HELO Computerroom) (elippse@sbcglobal.net@75.15.117.168 with login) by smtp106.sbc.mail.re2.yahoo.com with SMTP; 6 Feb 2007 09:05:43 -0000 X-YMail-OSG: p96roX8VM1nhHvO3qpadTMzMui1AkpIOH21UFTm08LluAU8KpuvS8u1ItZ9Ey3qglAurDm_EP7BcTbTNEvJCREHYnsiz6LGFSoxGNAmvguAhzkczv3Z.k9I5qNqWKCywj.rO0C6TArqvxoE- X-Original-Message-ID: <000901c749cd$fbb2f080$a8750f4b@Computerroom> From: "Paul Lipps" X-Original-To: "Marv Kaye" Subject: Coanda, et al X-Original-Date: Tue, 6 Feb 2007 01:05:42 -0800 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0006_01C7498A.EC468EB0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.3028 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.3028 This is a multi-part message in MIME format. ------=_NextPart_000_0006_01C7498A.EC468EB0 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable On a flight in a DC-9 landing in sleet at Syracuse, NY, I was seated = just ahead of the wing's LE. It was night, and the landing light was on. = I saw the most incredible thing; the sleet in the air ahead, being = illuminated by the landing light, was rising up toward the LE. "How was = that happening?", I mused. When I returned to California, I looked up an = acquaintance who was a Cal Poly Aero grad and told him of my observation = and inquired if he knew why that was happening. With a straight face, in = all seriousness, he said the air at the LE was broadcasting its = pressure. I then, with a straight face, asked him if the medium was AM, = FM, or some more complex modulation scheme. When I asked him to further = illuminate me on the cause of this phenomenon, he told me that that's = what his professor said, and he really had no idea what the mechanism = was. After much rumination, I came to the conclusion that the only way = that could take place is that if the molecules of air that were = traveling in the direction of the LE were not replaced from the air in = the vicinity of the LE, a net flow would occur. Now keep in mind, the mean free velocity of air is about M 1.4 in = all directions. Molecules are constantly moving from any given parcel of = air into all directions toward other parcels. Those parcels in turn are = also radiating molecules out in all directions, so that at any one = instant in time, some parcels have more molecules, and some have less, = but over time, the average density is the same if the air is not being = disturbed. On a micro level, there is a continual flow going on in all = directions, but on a macro scale the air is still. Another tidbit: air = does not have pressure as an intrinsic part of itself. Air has density = and velocity, the latter is what we call heat, which is why the velocity = of sound is proportional to the absolute temperature. Pressure is a = force that acts on a membrane that gets in the way of those fast moving = molecules. If we were able to view the pressure being generated, we = would see all these little molecules banging into the membrane like a = ball-peen hammer beating on it. If the membrane is surrounded by air on = both sides, it will absorb blows to it on both sides, which will = average-out, and so it will tend to remain where it is. So what was taking place on that wing's LE is that the passage of = the wing through the air divided it into jets of air over the upper and = lower surfaces. That wing, just as in Brent's venturi tube, organized = the air flow in a particular direction. I doing that, more of the little = devils were flowing in a direction parallel to the surface, and fewer = were normal or perpendicular. When Bernoulli says that the pressure goes = down when the velocity goes up, what that really means is that the = pressure normal to the flow direction is lower, but it is higher in the = direction of the flow, so that the total pressure remains the same. I = once told someone that he should place an inlet facing forward at the = point of maximum thickness of a wing where the velocity is highest to = get the highest pressure, and he argued that no, the pressure would be = lower there. I said that if he put a probe facing forward, a pitot, into = the airstream, the pressure would be higher. No! he affirmed, Bernoulli = says that when the velocity is highest, the pressure is the lowest, and = that was good enough for him! But what Henri saw in his attempt in 1911 to make a jet-propelled = airplane was that when he dumped fuel into the cowling behind an = engine-driven compressor, and provided curved plates from the cowling = onto the sides of the fuselage for its exit, that instead of the burning = gases being ejected at an angle from the cowling, they instead followed = the curve right around onto the side of the fuselage, which, of course, = they set on fire! He was so fascinated looking at this that he almost = flew into a wall in his path. It wasn't until the 20's that he finally = formulated the "Coanda effect". There's a logic element for a fluidic = computer that is a bistable element, a flip-flop. It is a small jet that = emerges between two outward curving walls. Each wall is provided with a = small hole through which controlled air may enter. When the jet first = emerges, it will attach itself to one of the walls and stay there. There = is less pressure acting outward from the wall into the jet since the air = in the jet is organized in one direction, so that the air ouside of the = jet holds it against the wall. If the hole in that wall is opened so = that air may enter on the wall side of the jet, the pressure unbalance = is removed, and the jet immediately detaches from that wall and attaches = to the other one where its hole is closed. That is how it becomes a = bistable element, under control of some other element which controls the = holes. That jet of air flowing up and around the LE has centrifugal force = since it has mass. It is held against the curve by the molecules in = parcels of air above and forward of the jet which are flowing toward the = LE. That and the fact that there is no air between the jet and the LE = which would push it away and counter the force from the molecules on the = other side of the jet. Remember the hole in the fluidic element's walls? = So what is then obtained is this flow upward toward the LE, which is = really what the prof meant when he said the pressure was broadcast! You can use this Coanda effect in several places on your plane to = reduce its drag. Right behind the spinner on the front of the cowling we = usually make the edges of the cowling follow immediately behind the = spinner's curvature to provide a seemingly smooth flow. But there's a = fly in the ointment! Pressurized air from the cooling plenum will flow = forward along the crankshaft and enter the space between the back of the = spinner and the cowling. From there it will flow outward and disturb the = airflow from the spinner, making the flow turbulent. If you made the = cowling immediately behind the spinner about 1.5" larger in diameter and = shaped it into a quarter-round shape with a 0.75" radius, the Coanda = effect would take that jet emerging from behind the spinner and turn it = around to flow smoothly back. That's also the drag-lessening effect that = can be done by doing the same to the LE of the ailerons and elevator. By = thickening their LEs by 15% on each side with a smooth radius, gap flow = can be turned into the flow direction. Enough! ------=_NextPart_000_0006_01C7498A.EC468EB0 Content-Type: text/html; charset="Windows-1252" Content-Transfer-Encoding: quoted-printable
    On a flight in a DC-9 landing = in sleet=20 at Syracuse, NY, I was seated just ahead of the wing's LE. It was night, = and the=20 landing light was on. I saw the most incredible thing; the sleet in = the air=20 ahead, being illuminated by the landing light, was rising up toward = the LE.=20 "How was that happening?", I mused. When I returned to California, I = looked up=20 an acquaintance who was a Cal Poly Aero grad and told him of my = observation and=20 inquired if he knew why that was happening. With a straight face, in all = seriousness, he said the air at the LE was broadcasting its pressure. I = then,=20 with a straight face, asked him if the medium was AM, FM, or some = more=20 complex modulation scheme. When I asked him to further illuminate me on = the=20 cause of this phenomenon, he told me that that's what his professor = said, and he=20 really had no idea what the mechanism was. After much rumination, I came = to the=20 conclusion that the only way that could take place is that if the = molecules of=20 air that were traveling in the direction of the LE were not replaced = from the=20 air in the vicinity of the LE, a net flow would occur.
    Now keep in mind, the mean = free=20 velocity of air is about M 1.4 in all directions. Molecules are = constantly=20 moving from any given parcel of air into all directions toward other = parcels.=20 Those parcels in turn are also radiating molecules out in all = directions, so=20 that at any one instant in time, some parcels have more molecules, and = some have=20 less, but over time, the average density is the same if the air is not = being=20 disturbed. On a micro level, there is a continual flow going on in all=20 directions, but on a macro scale the air is still. Another tidbit: = air does=20 not have pressure as an intrinsic part of itself. Air has density and = velocity,=20 the latter is what we call heat, which is why the velocity of sound is=20 proportional to the absolute temperature. Pressure is a force that acts = on a=20 membrane that gets in the way of those fast moving molecules. If we were = able to=20 view the pressure being generated, we would see all these little = molecules=20 banging into the membrane like a ball-peen hammer beating on it. If = the=20 membrane is surrounded by air on both sides, it will absorb blows to it = on both=20 sides, which will average-out, and so it will tend to remain where = it=20 is.
    So what was taking place on = that wing's=20 LE is that the passage of the wing through the air divided it into jets = of air=20 over the upper and lower surfaces. That wing, just as in Brent's venturi = tube,=20 organized the air flow in a particular direction. I doing that, more of = the=20 little devils were flowing in a direction parallel to the surface, and = fewer=20 were normal or perpendicular. When Bernoulli says that the pressure goes = down=20 when the velocity goes up, what that really means is that the pressure = normal to=20 the flow direction is lower, but it is higher in the direction of = the flow,=20 so that the total pressure remains the same. I once told someone that he = should=20 place an inlet facing forward at the point of maximum thickness of a = wing where=20 the velocity is highest to get the highest pressure, and he argued = that no,=20 the pressure would be lower there. I said that if he put a probe facing = forward,=20 a pitot, into the airstream, the pressure would be higher. No! he = affirmed,=20 Bernoulli says that when the velocity is highest, the pressure is = the=20 lowest, and that was good enough for him!
    But what Henri saw in his = attempt in=20 1911 to make a jet-propelled airplane was that when he dumped fuel into = the=20 cowling behind an engine-driven compressor, and provided curved plates = from the=20 cowling onto the sides of the fuselage for its exit, that instead of the = burning=20 gases being ejected at an angle from the cowling, they instead followed = the=20 curve right around onto the side of the fuselage, which, of course, they = set on=20 fire! He was so fascinated looking at this that he almost flew into a = wall in=20 his path. It wasn't until the 20's that he finally formulated the = "Coanda=20 effect". There's a logic element for a fluidic computer that is a = bistable=20 element, a flip-flop. It is a small jet that emerges between two outward = curving=20 walls. Each wall is provided with a small hole through which = controlled air=20 may enter. When the jet first emerges, it will attach itself to one of = the walls=20 and stay there. There is less pressure acting outward from the wall into = the=20 jet since the air in the jet is organized in one direction, so that = the air=20 ouside of the jet holds it against the wall. If the hole in that = wall is=20 opened so that air may enter on the wall side of the jet, the pressure = unbalance=20 is removed, and the jet immediately detaches from that wall and = attaches to=20 the other one where its hole is closed. That is how it becomes a=20 bistable element, under control of some other element which = controls the=20 holes.
    That jet of air flowing up = and around=20 the LE has centrifugal force since it has mass. It is held against = the=20 curve by the molecules in parcels of air above and forward of = the jet which=20 are flowing toward the LE. That and the fact that there is no air = between the=20 jet and the LE which would push it away and counter the force from the = molecules=20 on the other side of the jet. Remember the hole in the fluidic element's = walls?=20 So what is then obtained is this flow upward toward the LE, which is = really what=20 the prof meant when he said the pressure was broadcast!
     You can use this Coanda = effect in=20 several places on your plane to reduce its drag. Right behind the = spinner on the=20 front of the cowling we usually make the edges of the cowling follow = immediately=20 behind the spinner's curvature to provide a seemingly smooth flow. But = there's a=20 fly in the ointment! Pressurized air from the cooling plenum will flow = forward=20 along the crankshaft and enter the space between the back of the spinner = and the=20 cowling. From there it will flow outward and disturb the airflow from = the=20 spinner, making the flow turbulent. If you made the cowling immediately = behind=20 the spinner about 1.5" larger in diameter and shaped it into a = quarter-round=20 shape with a 0.75" radius, the Coanda effect would take that jet = emerging=20 from behind the spinner and turn it around to flow smoothly back. That's = also=20 the drag-lessening effect that can be done by doing the same to the = LE of=20 the ailerons and elevator. By thickening their LEs by 15% on each = side with=20 a smooth radius, gap flow can be turned into the flow=20 direction.   =20  Enough!  
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