X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao107.cox.net ([68.230.241.39] verified) by logan.com (CommuniGate Pro SMTP 5.1.10) with ESMTP id 2201640 for flyrotary@lancaironline.net; Fri, 27 Jul 2007 00:47:43 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.39; envelope-from=alventures@cox.net Received: from fed1rmimpo02.cox.net ([70.169.32.72]) by fed1rmmtao107.cox.net (InterMail vM.7.08.02.01 201-2186-121-102-20070209) with ESMTP id <20070727044701.YRZP1358.fed1rmmtao107.cox.net@fed1rmimpo02.cox.net> for ; Fri, 27 Jul 2007 00:47:01 -0400 Received: from BigAl ([72.192.132.90]) by fed1rmimpo02.cox.net with bizsmtp id UUn21X00S1xAn3c0000000; Fri, 27 Jul 2007 00:47:03 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: Oil cooler inlet - what next? Date: Thu, 26 Jul 2007 21:48:55 -0800 Message-ID: <001701c7d011$d2017200$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0018_01C7CFCE.C3E0A300" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3138 In-Reply-To: Importance: Normal This is a multi-part message in MIME format. ------=_NextPart_000_0018_01C7CFCE.C3E0A300 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable =20 =20 I do have a question - what is the core volume of your oil cooler?=20 =20 Cooler core is 375 cu. in.; should be quite capable of handling the job. =20 A stock 2 rotor color has a core area of approx 19x4/12x2 =3D 171 Cubic Inches. That will cool a two rotor at 160 mph producing 160 Hp with an = oil BTU heat factor of 2688 BTU/min. A 3 rotor producing 1/3 more HP (213 = HP) rpm would create a corresponding rise in BTU/min to 3360. =20 Something wrong with the numbers there I think, ED; or else I=92m way = off. My calcs say 160hp out results in about 1700 Btu/min to the oil. 160 hp is 6770 Btu/min (2538 Btu/hr/hp), and is about 28% of the fuel energy of = 24,175 Btu/min. About 7% of the total goes to the oil. The percentages will = vary a bit depending on operating point =96 I picked these off the graph at = 6000 rpm. 215 hp out should result in somewhere close to 2300 Btu/min to the oil. =20 The reason I ask, is that if forcing more air through the core does not decrease the oil temp - could there exist the possibility that the core = is saturated and can is simply not capable of transferring more oil heat to = the air? If that were the case, then, as you know, no amount of additional = air through the core would make any significant difference. =20 I don=92t know what you mean by =93saturated=94. More air through = removes more heat =96 the limit is driving force (pressure) available to push it = through =96 until you get to the point that tube and fin surface temps are the same = as the average air temp. I think it=92s a long way from that. But = apparently it=92s close to the limit of the available pressure, and the pressure = drop of the core is a bit higher than expected. =20 You=92d think that if the scoop was even reasonable effective, it should recover about 6=94 out of the 9.5=94 pressure available. I=92m still = wondering if there could be enough air leakage around the cooler to lose a = significant amount of that pressure. =20 =20 Kelly wrote: Uneducated guess but I will vote for a boundry layer problem......How = about extending the baffle below the bottom of the wing an inch or two and = retest.......It will be dirty and draggy but if that helps delta T it can be cleaned up with a proper installation......IMHO =20 That=92s an educated guess, or better yet, a fact =96 that it is A = problem. But I=92m still thinking it is not THE problem since there is 9.5=94 H2O = dynamic pressure 12 =96 5/8=94 off the surface, which is in the BL, and should = represent something like the average velocity into the 1 =BC=94 opening of the = scoop. Not sure what you mean extending the baffle below the bottom of the wing an = inch or two? Do you mean opening the scoop up wider? I think making a = larger radius on the entry edge of the scoop could help, and would give an indication whether opening the scoop more would help. =20 Thanks, guys. =20 Let=92s see; was it Steve who suggested the solution is moving to a = cooler climate?? Or I guess I could just fly between Nov. and March:-). =20 Al =20 =20 =20 =20 =20 --- Original Message -----=20 From: Al Gietzen =20 To: Rotary motors in aircraft=20 Sent: Thursday, July 26, 2007 7:06 PM Subject: [FlyRotary] Re: Oil cooler inlet - what next? =20 Installed sheet metal =91baffle=92 to form new upper wall of the = diffuser as shown in the photo. The idea was to assist in maintaining attached = flow, and to block leakage through the gap at the top. The baffle was done in = 3 pieces in order to insert past the divider/supports in the scoop; each = piece is about 7 =BD=94 wide. There are gaps between pieces of about 3/8 =96 = =BD=94 inch. The inlet pressure probe was placed at point =93D=94. =20 Test flight showed no noticeable difference in delta T on the oil. The pressure measured at =93D=94 was 3=94 H2O. Pressure behind the exit = fairing was again -3/4=94. The pressures at C and D (measured at different times) = are at about 6=94 from the inboard end of the 22=94 long cooler. There may be = some variation axially. Because of the gaps in the baffle, and fitting = around the end tanks, there is still some air bypassing the cooler; but I = don=92t know how significant. Given the 9+=94 H2O dynamic pressure out in front = of the scoop still indicates not good pressure recovery. =20 Nonetheless; it is certainly disappointing that there was no change = (within the accuracy of the temp measurements) in the effective cooling. This suggests that the wall shape and the air leakage are not the problem. =20 Calculating back from the temp changes in oil and air suggest there is = only about 1000 cfm going through the cooler core. The extrapolation of my measured data on air flow vs pressure drop across the core suggests that = at 3=94 H2O there should be about 2000 cfm through the core. Because of = the centrifugal blower I was using for flow tests I was only able to get = data up to about 0.6=94 H2O and 700 cfm. I fit the data to Y=3Dax+bx2 using = regression analysis, which gave a very good fit up to that point; but extrapolating = out to 3=94 may be stretching it. If I assume the pressure drop goes as the = cube of the flow velocity, the extrapolation is considerable different =96 = about 1330 cfm at 3=94 H2O. =20 Al =20 =20 -----Original Message----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen Sent: Friday, July 20, 2007 10:42 AM To: Rotary motors in aircraft Subject: [FlyRotary] Re: Oil cooler inlet =20 Well; I may end up with VGs and change in upper duct wall shape. My intention yesterday was to install VGs as a first step, test fly, = measure pressure and temps; then proceed with installing sheet metal upper duct = wall change. =20 In deciding where to put the VGs, I looked at things with the gear up = (Photo 1). The gear door has a bump, and there is some gap around the door. = Don=92t know what all this does to BL. Ended up putting VG toward the left side about 26=94 in font of scoop, and toward the right side right on the = gear door bump. =20 I then spent a bunch of time trying to get the pressure measuring tube situated. The only access is through the scoop opening, and I can=92t = get my hands in there; so it is very tough. Plus the tube going in there, or = along the surface in front will affect the flow behavior, so what affect are = we going to measure. Having multiple measurements would be great; but very difficult to achieve. =20 While doing that, I spent some time looking in there with a small = mirror. What I noted was that initial gaps above and below the cooler (required = to slide the unit in and out) had changed a bit. The cooler is supported = on pads of =91Cool-Mat=92 insulation. Those have compressed just a little, = so now there is very little gap at the bottom, and 1/8=94+ along the top. That = is a fairly substantial leak, and the loss of pressure at the top likely exacerbates the flow separation. I decided it wasn=92t worth going to = test the VGs as long as that leakage gap was there. =20 Taking the wing off (mostly getting it back on because of next to = impossible access to nuts), and removing the cooler looks a bit much right now. I realized then; that by putting in a sheet metal =91false=92 upper duct = wall, I could extend it up into the gap at the top (photo 2), thereby changing = the shape, and (mostly) closing the gap at the top. =20 The false wall has to be in three parts for the three openings, and = there will be gaps between because of the supporting dividers; but it could = make a substantial difference. I made the piece for the center, and considered testing just that; but the upper gap concerns me enough that I think = I=92ll try to get all three fit in. =20 Then go take a flight test. Unfortunately this combines three changes, = VGs, closing gap, and changing duct wall. I had hoped to test these one at a time. If there is a substantial change; it will be easy to remove the = VGs to see what that effect was. =20 Of course I=92ll let you know when I get some results. =20 Oh, the price of innovation:-). =20 Al =20 =20 -----Original Message----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Thomas Jakits Sent: Thursday, July 19, 2007 10:31 AM To: Rotary motors in aircraft Subject: [FlyRotary] Re: Oil cooler inlet =20 Okay, =20 Monty thinks the emphasis is on the BL. I believe (don't know), the main-problem is the upper ductwall shape. = Even if you have perfect BL flow, the upper wall shape is still not good and = will stall the flow.=20 At the end of the game you want good flow at all speeds and be able to = close any ducts to limit excess cooling (when you hopefully get there). Obviously BL will play a role in your installation as the intake is = rather narrow. However BL or not - BL does not mean there is no flow, just slower and = more turbulent, but still generally going towards the cooler. Aerodynamics in the duct should be much the same for laminar, turbulent, = any flow, as long as there is flow. When things stall is when flow pretty much ceases (in the stalled area ....), no matter how well things where at the entrance. The stall in this case is rather "easy" to get, as the speed seems = rather low already. Still may be good enough if you can do away with the stall. So I suggest to work on the duct wall first and optimize it. =20 As suggested, with some kind of sheet, alu, fiberglass, etc. You can = curve it more and more until you peak. Maybe pinched ducts (copyright Ed!!) are not working here, but it may as well - if they work a Ed's theory explains (energizes the flow...) =20 If this works, modify according to the best shape found. Then try to improve with VGs or sanding or turbolator tape. Then go for the exit - after all it is a differential pressure game.... =20 TJ =20 On 7/18/07, M Roberts wrote:=20 Al, =20 I think you need to do something to energize the boundary layer. If you can't divert it you need to put some energy into it. It is probably = getting slow and separating from the face of the duct. That is what your data = seems to indicate to me.=20 =20 I like the shape that Thomas proposes better than what you have now, however, I still think you will need some VG's in front of the inlet.=20 =20 I know it may seem counter intuitive, but turbulence may actually help = in this case. You will not get very efficient internal diffusion, but it = will be a lot better than what you have now. I don't think that putting a = turning vane will help too much without doing something to energize the boundary layer first. You'll just have a slow thick low energy layer, and a high energy layer separated by a turning vane.=20 =20 It is really easy to duct tape some aluminum VG's in front of the inlet = and see what it does.=20 =20 You may need a combination of Thomas' contour, VG's and a turning vane. = Go with the easy fix and work your way up in complexity. =20 Monty =20 _____ =20 -- Homepage: http://www.flyrotary.com/ Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html ------=_NextPart_000_0018_01C7CFCE.C3E0A300 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

 

 

I do have a question - what is the core volume of = your oil cooler? 

 

Cooler core is 375 cu. in.; = should be quite capable of handling the job.

 

=A0A stock 2 rotor color = has a core area of approx 19x4/12x2 =3D 171 Cubic Inches.  That will cool a = two rotor at 160 mph producing 160 Hp with an oil BTU heat factor of 2688 = BTU/min.  A 3 rotor producing 1/3 more HP (213 HP) rpm would create a = corresponding rise in BTU/min to 3360.

 

Something wrong with the numbers = there I think, ED; or else I’m way off.=A0 My calcs say 160hp out results = in about 1700 Btu/min to the oil. =A0160 hp is 6770 Btu/min (2538 Btu/hr/hp), and = is about 28% of the fuel energy of 24,175 Btu/min. =A0About 7% of the total goes = to the oil.=A0 The percentages will vary a bit depending on operating point = – I picked these off the graph at 6000 rpm. =A0215 hp out should result in = somewhere close to 2300 Btu/min to the oil.

 

The reason I ask, is that = if forcing more air through the core does not decrease the oil temp - could there  exist the possibility that the core is saturated and can is simply not capable of transferring more oil heat to the = air?  If that were the case, then, as you know,  no amount of additional = air through the core would make any significant = difference.

 

I don’t know what you mean = by “saturated”.=A0 More air through removes more heat – the limit is driving force (pressure) available to push it through – until you get to the = point that tube and fin surface temps are the same as the average air temp.=A0 I think it’s a long way = from that.=A0 But apparently it’s close to the limit of the available = pressure, and the pressure drop of the core is a bit higher than = expected.

 

You’d think that if the = scoop was even reasonable effective, it should recover about 6” out of the = 9.5” pressure available.=A0 I’m still wondering if there could be = enough air leakage around the cooler to lose a significant amount of that pressure. = =A0

 

Kelly wrote:

Uneducated guess but I will vote for a boundry layer = problem......How about extending

the baffle below the bottom of the wing an inch or two and retest.......It will be dirty and

draggy but if that helps delta T it can be cleaned up with a proper installation......IMHO

 

That’s an educated guess, = or better yet, a fact – that it is A problem.=A0 But I’m still = thinking it is not THE problem since there is 9.5” H2O dynamic pressure 12 = – 5/8” off the surface, which is in the BL, and should represent = something like the average velocity into the 1 =BC” opening of the scoop.=A0 = Not sure what you mean extending the baffle below the bottom of the = wing an inch or two?=A0 Do you mean opening the scoop up = wider?=A0 I think making a larger radius on the entry edge of the scoop could = help, and would give an indication whether opening the scoop more would = help.

 

Thanks, guys.

 

Let’s see; was it Steve who suggested the solution is moving to a cooler climate??=A0 Or I guess I = could just fly between Nov. and MarchJ.

 

Al

 

 

 

 

 

--- Original Message -----

=

From: Al = Gietzen

Sent: Thursday, July 26, 2007 7:06 PM

Subject: [FlyRotary] Re: Oil cooler inlet - what next?

 

 Installed sheet metal ‘baffle’ to form new upper wall of the diffuser = as shown in the photo.  The idea was to assist in maintaining attached = flow, and to block leakage through the gap at the top.  The baffle was = done in 3 pieces in order to insert past the divider/supports in the scoop; each = piece is about 7 =BD” wide.  There are gaps between pieces of about = 3/8 – =BD” inch.  The inlet pressure probe was placed at point “D”.

 

Test flight showed no noticeable difference in delta T on the oil.  The pressure measured at “D” was 3” H2O.  Pressure = behind the exit fairing was again -3/4”.  The pressures at C and D (measured at different times) are at about 6” from the inboard end = of the 22” long cooler.  There may be some variation axially.  = Because of the gaps in the baffle, and fitting around the end tanks, there is = still some air bypassing the cooler; but I don’t know how = significant.  Given the 9+” H2O dynamic pressure out in front of the scoop still indicates not good pressure recovery.

 

Nonetheless; it is certainly disappointing that there was no change (within the = accuracy of the temp measurements) in the effective cooling.  This suggests = that the wall shape and the air leakage are not the problem.

 

Calculating back from the temp changes in oil and air suggest there is only about = 1000 cfm going through the cooler core. The extrapolation of my measured data on = air flow vs pressure drop across the core suggests that at 3” H2O = there should be about 2000 cfm through the core.  Because of the = centrifugal blower I was using for flow tests I was only able to get data up to = about 0.6” H2O and 700 cfm.  I fit the data to = Y=3Dax+bx2 using regression analysis, which gave a very good fit up to that point; but extrapolating out to 3” may be stretching it.  If I assume = the pressure drop goes as the cube of the flow velocity, the extrapolation is = considerable different – about 1330 cfm at 3” H2O.

 

Al

 

 

-----Original = Message-----
From: Rotary motors in = aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen
Sent: Friday, July 20, = 2007 10:42 AM
To: Rotary motors in = aircraft
Subject: [FlyRotary] Re: = Oil cooler inlet

 

Well; I may end up with VGs and change in upper duct wall shape. My intention = yesterday was to install VGs as a first step, test fly, measure pressure and = temps; then proceed with installing sheet metal upper duct wall = change.

 

In deciding where to put the VGs, I looked at things with the gear up = (Photo 1).  The gear door has a bump, and there is some gap around the = door.  Don’t know what all this does to BL.  Ended up putting VG = toward the left side about 26” in font of scoop, and toward the right side = right on the gear door bump.

 

I then spent a bunch of time trying to get the pressure measuring tube = situated.  The only access is through the scoop opening, and I can’t = get my hands in there; so it is very tough.  Plus the tube going in there, = or along the surface in front will affect the flow behavior, so what affect = are we going to measure.  Having multiple measurements would be great; but = very difficult to achieve.

 

While doing that, I spent some time looking in there with a small mirror. =  What I noted was that initial gaps above and below the cooler (required to = slide the unit in and out) had changed a bit.  The cooler is supported on = pads of ‘Cool-Mat’ insulation.  Those have compressed just a = little, so now there is very little gap at the bottom, and 1/8”+ along the top.  That is a fairly substantial leak, and the loss of pressure = at the top likely exacerbates the flow separation.  I decided it = wasn’t worth going to test the VGs as long as that leakage gap was = there.

 

Taking the wing off (mostly getting it back on because of next to impossible = access to nuts), and removing the cooler looks a bit much right now.  I = realized then; that by putting in a sheet metal ‘false’ upper duct = wall, I could extend it up into the gap at the top (photo 2), thereby changing = the shape, and (mostly) closing the gap at the top.

 

The false wall has to be in three parts for the three openings, and there = will be gaps between because of the supporting dividers; but it could make a substantial difference.  I made the piece for the center, and = considered testing just that; but the upper gap concerns me enough that I think = I’ll try to get all three fit in.

 

Then go take a flight test. Unfortunately this combines three changes, VGs, = closing gap, and changing duct wall.  I had hoped to test these one at a time.  If there is a substantial change; it will be easy to remove = the VGs to see what that effect was.

 

Of course I’ll let you know when I get some = results.

 

Oh, the price of innovationJ.

 

Al

 

 

-----Original = Message-----
From: Rotary motors in = aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Thomas Jakits
Sent: Thursday, July 19, = 2007 10:31 AM
To: Rotary motors in = aircraft
Subject: [FlyRotary] Re: = Oil cooler inlet

 

Okay,

 

Monty thinks the emphasis is on the = BL.

I believe (don't = know), the main-problem is the upper ductwall shape. Even if you have perfect BL flow, the upper = wall shape is still not good and will stall the flow.

At the end of the game you want good flow at = all speeds and be able to close any ducts to limit excess cooling (when you hopefully get there).

Obviously BL will play a role in your = installation as the intake is rather narrow.

However BL or not - BL does not mean there is = no flow, just slower and more turbulent, but still generally going towards the = cooler.

Aerodynamics in the duct should be much the = same for laminar, turbulent, any flow, as long as there is = flow.

When things stall is when flow pretty much = ceases (in the stalled area ....), no matter how well things where at the = entrance.

The stall in this case is rather = "easy" to get, as the speed seems rather low already. Still may be good enough if = you can do away with the stall.

So I suggest to work on the duct wall first = and optimize it.

 

As suggested, with some kind of sheet, alu, fiberglass, etc. You can curve it more and more until you = peak.

Maybe pinched ducts (copyright Ed!!) are not = working here, but it may as well - if they work a Ed's theory explains = (energizes the flow...)

 

If this works, modify according to the best = shape found.

Then try to improve with VGs or sanding or = turbolator tape.

Then go for the exit - after all it is a = differential pressure game....

 

TJ

 

On = 7/18/07, M Roberts <montyr2157@alltel.net> = wrote:

Al,

 

I think you need to do = something to energize the boundary layer. If you can't divert it you need to put some = energy into it. It is probably getting slow and separating from the face of the = duct. That is what your data seems to indicate to me.

 

I like the shape that = Thomas proposes better than what you have now, however, I still think you will = need some VG's in front of the inlet.

 

I know it may seem counter intuitive, but turbulence may actually help in this case. You will not = get very efficient internal diffusion, but it will be a lot better than what you = have now. I don't think that putting a turning vane will help too much = without doing something to energize the boundary layer first. You'll just have a slow = thick low energy layer, and a high energy layer separated by a turning vane. =

 

It is really easy to duct = tape some aluminum VG's in front of the inlet and see what it does. =

 

You may need a combination = of Thomas' contour, VG's and a turning vane. Go with the easy fix and work = your way up in complexity.

 

Monty

 

--
Homepage:  http://www.flyrotary.com/
Archive and UnSub:   http://mail.lancaironline.net:81/lists/flyrotary/List.html<= /p>

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