X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao102.cox.net ([68.230.241.44] verified) by logan.com (CommuniGate Pro SMTP 5.2.0) with ESMTP id 2782495 for flyrotary@lancaironline.net; Fri, 07 Mar 2008 22:31:44 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.44; envelope-from=rv-4mike@cox.net Received: from fed1rmimpo01.cox.net ([70.169.32.71]) by fed1rmmtao102.cox.net (InterMail vM.7.08.02.01 201-2186-121-102-20070209) with ESMTP id <20080308033105.TVIV17893.fed1rmmtao102.cox.net@fed1rmimpo01.cox.net> for ; Fri, 7 Mar 2008 22:31:05 -0500 Received: from wills ([68.105.86.251]) by fed1rmimpo01.cox.net with bizsmtp id yTWq1Y0055RMxr00000000; Fri, 07 Mar 2008 22:30:52 -0500 Message-ID: <004901c880cc$d70b12d0$fb566944@wills> From: "Mike Wills" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] FW: Oil Cooler re-visit Date: Fri, 7 Mar 2008 19:31:04 -0800 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0046_01C88089.C896CCA0" 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_0046_01C88089.C896CCA0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Maybe the reason the Lyc oil cooler install worked so well was that the = Lyc didnt need much cooling in the first place? I dont know what Lyc we = are talking about and dont know how hot (or cool) the oil runs in a = Velocity airframe. The O-320 (160HP) in my RV-6A runs so cool that I = have to completely block off the oil cooler inlet in the winter time and = oil temps are still borderline too cool. Had the cable for the oil = cooler door break last summer and flew on a hot day with no airflow = through the cooler and the oil still ran around 190 - 200. Not convinced that its a useful reference point unless he did what you = did and actually measured pressure differential across the cooler. Mike Wills RV-4 N144MW=20 ----- Original Message -----=20 From: Al Gietzen=20 To: Rotary motors in aircraft=20 Sent: Friday, March 07, 2008 5:17 PM Subject: [FlyRotary] FW: Oil Cooler re-visit My first attempt at sending this was too large; so I eliminated = attach. 3. Re-number accordingly. Subject: FW: Oil Cooler re-visit Some of you may recall that I brought up the issue of marginal oil = cooling in my Velocity 20B last fall after finding that I was limited in = climb rate in the warmer summer weather. I continued to enjoy flying = during the cooler winter months, and it hasn't been much of an issue. = Now as we approach summer again, I intend to institute some changes. = Before doing so I wanted some further data on the air flow. The cooler is in the wing root; behind the strake, behind the spar. = Inlet is under the wing behind the main gear door cover. The cross = section of the inlet is shown in the Attachmt 1. The sketch shows the = original shape when pressures A (ram, in front of scoop), B and C = (static) were made. I then modified the upper profile as shown, and = sealed all the gaps around the cooler, and measured the pressure at D. = Cooling improved very slightly. The exit above the wing is shown in attachmt 2. A pressure = measurement at the mid point of the outlet was about -1" of water - = somewhat disappointing since the theory was that there would be lower = pressure there. I had concluded that the airflow in front of the scoop was being = somewhat disrupted by the gear door, which does have a bump on it for = the wheel toward the out-board portion of the entry scoop. Paul Lamar was kind enough to ship his multi-manometer setup (attach = 3) to me so I could get some more data. One challenge was to find ways = to get many tubes from the measuring point to the manometers. Some = 4-wide color coded clear 1/8" ribbon tube from McMaster-Carr helped = facilitate that. I then fabricated a couple of velocity rakes (attach 4, = also one from 1/8" copper tubes), and we measured 8 points at one time. = The tubes are at 5/16" spacing. The wide inlet scoop (23") is divided into three sections. We placed = one rake at the middle of the in-board 1/3, and one at the mid point of = the outer 1/3 (this one behind the bump in the gear door). We then took = measurements at 120 KIAS climb (138 mph), and at 150 (173 mph) level. = The results for 150 KIAS are shown on the upper chart in attach 5. I = penciled in the curve to the 5 points including 0 at the surface. (I = should point out that the measurements were made on the opposite wing = which has a matching radiator installation, and still has the original = non scoop inlet, in order to facilitate running the tubes. The location = behind the gear door is the same.) The result shows a fairly normal boundary layer profile; at both = positions. The low velocity portion is less than =BD" thick which is = consistent with that computed by a little BL program that I have. The = scoop extends into the airstream about 1 =BC", at which point ther is = essentially free stream velocity. What does it tell me? 1. My assumption that the BL was somewhat mixed and turbulent was not = correct. 2. Segmenting the profile and determining an average velocity (about = 135 mph) would give me very close to the desired air flow rate IF the = scoop were operating at 90% efficiency. It was also interesting to find the profile shape changed little with = the planes airspeed, however; the profile at the lower speed was more = like 20 mph less, when the planes speed was 35 mph less - indicating a = slightly higher pressure under the wing at the higher AOA. OK, that was fun. Next we set up to measure the air velocity profile = at the exit of the core. This was done by positioning 1/8" copper tubes = as 'pitot' tubes close to the surface at different positions across the = core, near the center of it's 22" length. That result is shown in the = lower chart in Attach 5. Clearly the flow is not very uniform, being quite highly peaked toward = the center. This of course indicates the 'diffuser' is not being = effective. Again, by segmenting the profile, and adjusting to the = actual flow area (minus the tube area, but not accounting for the fins), = I could compute the approximate total flow rate through the core. It is = about 68% of the potential inflow for an effective scoop- telling me = that some amount of air is flowing around (under) the scoop. Two other relavent pieces of info: we measured the static pressure on = the upper surface outboard of the outlet fairing, about 1/2" off the = surface. It was consistent with the earlier measurement behind the exit = fairing (about -1"). We also tufted the back edge of the exit fairing = with some 4" strings, and noted that they went straight back - = indicating the air cleanly detaching at the edge, and no swirling down = into the exit stream. These things suggest that the exit fairing is not = inhibiting the flow. It is also not enhancing it, but does provide = protection for the core - and looks pretty coolJ. We did not tuft the = surface of the wing behind the fairing because that is not visible from = the cabin. We also did not use longer tufts because these were the = longest we could scavenge from the dust mop, since the tufting was an = afterthought and we did not come equippedJ. So-o-o-o; before going into these measurements, I had pretty much = decided to install an oil/coolant heat exchanger since my coolant temps = run 20 - 40F lower than the oil, and have some margin. That is a fairly = major mod to the plumbing. Trying to modify the air inlet to get more = effective diffusion is also major, as it requires removal of the wing = and the oil cooler. This would require some reshaping, and a baffle(s) = the width of the scoop to confine the slow BL to the upper portion of = the inlet. And 'how' effective it could be made within the confines of = the wing root, and ingesting the BL, and without adding drag - is = uncertain. Therein lies the dilemma.=20 BTW; the placement of these coolers in the wing root in this manner = was based on the testimony of another Velocity builder you had placed = his Lyc oil cooler there, and said it worked great - even without a = scoop - because of the pressure differential above and below the wing. = I don't know why his experience was so different, but it does not = surprise me that there isn't much differential since the stake area on a = canard airplane is basically neutral in level flight. Anybody read this without falling asleep? Al -------------------------------------------------------------------------= ----- -- Homepage: http://www.flyrotary.com/ Archive and UnSub: = http://mail.lancaironline.net:81/lists/flyrotary/List.html ------=_NextPart_000_0046_01C88089.C896CCA0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Maybe the reason the Lyc oil cooler = install worked=20 so well was that the Lyc didnt need much cooling in the first place? I = dont know=20 what Lyc we are talking about and dont know how hot (or cool) the oil = runs in a=20 Velocity airframe. The O-320 (160HP) in my RV-6A runs so cool that I = have to=20 completely block off the oil cooler inlet in the winter time and oil = temps are=20 still borderline too cool. Had the cable for the oil cooler door break = last=20 summer and flew on a hot day with no airflow through the cooler and the = oil=20 still ran around 190 - 200.
 
 Not convinced that its a useful = reference=20 point unless he did what you did and actually measured pressure = differential=20 across the cooler.
 
Mike Wills
RV-4 N144MW 
----- Original Message -----
From:=20 Al = Gietzen=20
Sent: Friday, March 07, 2008 = 5:17=20 PM
Subject: [FlyRotary] FW: Oil = Cooler=20 re-visit

My first attempt at = sending this=20 was too large; so I eliminated attach. 3. Re-number=20 accordingly.

 

Subject: FW: Oil=20 Cooler re-visit

 

 

Some of you may recall = that I=20 brought up the issue of marginal oil cooling in my Velocity 20B last = fall=20 after finding that I was limited in climb rate in the warmer summer=20 weather.  I continued to enjoy flying during the cooler winter = months,=20 and it hasn=92t been much of an issue.  Now as we approach summer = again, I=20 intend to institute some changes.  Before doing so I wanted some = further=20 data on the air flow.

 

The cooler is in the = wing root;=20 behind the strake, behind the spar. Inlet is under the wing behind the = main=20 gear door cover. The cross section of the inlet is shown in the = Attachmt=20 1.  The sketch shows the original shape when pressures A (ram, in = front=20 of scoop), B and C (static) were made.  I then modified the upper = profile=20 as shown, and sealed all the gaps around the cooler, and measured the = pressure=20 at D. Cooling improved very slightly.

 

The exit above the = wing is shown=20 in attachmt 2.  A pressure measurement at the mid point of the = outlet was=20 about -1=94 of water =96 somewhat disappointing since the theory was = that there=20 would be lower pressure there.

 

I had concluded that = the airflow=20 in front of the scoop was being somewhat disrupted by the gear door, = which=20 does have a bump on it for the wheel toward the out-board portion of = the entry=20 scoop.

 

Paul Lamar was kind = enough to=20 ship his multi-manometer setup (attach 3) to me so I could get some = more=20 data.  One challenge was to find ways to get many tubes from the=20 measuring point to the manometers. Some 4-wide color coded clear = 1/8=94 ribbon=20 tube from McMaster-Carr helped facilitate that. I then fabricated a = couple of=20 velocity rakes (attach 4, also one from 1/8=94 copper tubes), and we = measured 8=20 points at one time. The tubes are at 5/16=94 = spacing.

 

The wide inlet scoop = (23=94) is=20 divided into three sections. We placed one rake at the middle of the = in-board=20 1/3, and one at the mid point of the outer 1/3 (this one behind the = bump in=20 the gear door). We then took measurements at 120 KIAS climb (138 mph), = and at=20 150 (173 mph) level. The results for 150 KIAS are shown on the upper = chart in=20 attach 5. I penciled in the curve to the 5 points including 0 at the = surface.=20 (I should point out that the measurements were made on the opposite = wing which=20 has a matching radiator installation, and still has the original non = scoop=20 inlet, in order to facilitate running the tubes.  The location = behind the=20 gear door is the same.)

 

The result shows a = fairly normal=20 boundary layer profile; at both positions.  The low velocity = portion is=20 less than =BD=94 thick which is consistent with that computed by a = little BL=20 program that I have. The scoop extends into the airstream about 1 = =BC=94, at which=20 point ther is essentially free stream velocity. What does it tell=20 me?

1. My assumption that = the BL was=20 somewhat mixed and turbulent was not correct.

2. Segmenting the = profile and=20 determining an average velocity (about 135 mph) would give me very = close to=20 the desired air flow rate IF the scoop were operating at 90%=20 efficiency.

It was also = interesting to find=20 the profile shape changed little with the planes airspeed, however; = the=20 profile at the lower speed was more like 20 mph less, when the planes = speed=20 was 35 mph less =96 indicating a slightly higher pressure under the = wing at the=20 higher AOA.

 

OK, that was fun. Next = we set up=20 to measure the air velocity profile at the exit of the core.  = This was=20 done by positioning 1/8=94 copper tubes as =91pitot=92 tubes close to = the surface at=20 different positions across the core, near the center of it=92s 22=94 = length. =20 That result is shown in the lower chart in Attach 5.

 

Clearly the flow is = not very=20 uniform, being quite highly peaked toward the center. This of course = indicates=20 the =91diffuser=92 is not being effective.  Again, by segmenting = the profile,=20 and adjusting to the actual flow area (minus the tube area, but not = accounting=20 for the fins), I could compute the approximate total flow rate through = the=20 core.  It is about 68% of the potential inflow for an effective = scoop-=20 telling me that some amount of air is flowing around (under) the=20 scoop.

 

Two other relavent = pieces of=20 info: we measured the static pressure on the upper surface outboard of = the=20 outlet fairing, about 1/2=94 off the surface. It was consistent with = the earlier=20 measurement behind the exit fairing (about -1=94).  We also = tufted the back=20 edge of the exit fairing with some 4=94 strings, and noted that they = went=20 straight back =96 indicating the air cleanly detaching at the edge, = and no=20 swirling down into the exit stream. These things suggest that the exit = fairing=20 is not inhibiting the flow. It is also not enhancing it, but does = provide=20 protection for the core =96 and looks pretty coolJ. We did not tuft = the surface=20 of the wing behind the fairing because that is not visible from the=20 cabin.  We also did not use longer tufts because these were the = longest=20 we could scavenge from the dust mop, since the tufting was an = afterthought and=20 we did not come equippedJ.

 

So-o-o-o; before going = into=20 these measurements, I had pretty much decided to install an = oil/coolant heat=20 exchanger since my coolant temps run 20 =96 40F lower than the oil, = and have=20 some margin.  That is a fairly major mod to the plumbing.  = Trying to=20 modify the air inlet to get more effective diffusion is also major, as = it=20 requires removal of the wing and the oil cooler.  This would = require some=20 reshaping, and a baffle(s) the width of the scoop to confine the slow = BL to=20 the upper portion of the inlet.  And =91how=92 effective it could = be made=20 within the confines of the wing root, and ingesting the BL, and = without adding=20 drag - is uncertain.

 

Therein lies the = dilemma.=20

 

BTW; the placement of = these=20 coolers in the wing root in this manner was based on the testimony of = another=20 Velocity builder you had placed his Lyc oil cooler there, and said it = worked=20 great =96 even without a scoop =96 because of the pressure = differential above and=20 below the wing.  I don=92t know why his experience was so = different, but it=20 does not surprise me that there isn=92t much differential since the = stake area=20 on a canard airplane is basically neutral in level = flight.

 

Anybody read this = without=20 falling asleep?

 

Al

 

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Homepage:  http://www.flyrotary.com/
Archive and=20 UnSub:  =20 = http://mail.lancaironline.net:81/lists/flyrotary/List.html
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