X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from ms-smtp-05.southeast.rr.com ([24.25.9.104] verified) by logan.com (CommuniGate Pro SMTP 5.1.9) with ESMTP id 2078429 for flyrotary@lancaironline.net; Fri, 01 Jun 2007 08:41:18 -0400 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.104; envelope-from=eanderson@carolina.rr.com Received: from edward2 (cpe-024-074-103-061.carolina.res.rr.com [24.74.103.61]) by ms-smtp-05.southeast.rr.com (8.13.6/8.13.6) with SMTP id l51CeOW8002855 for ; Fri, 1 Jun 2007 08:40:24 -0400 (EDT) Message-ID: <001a01c7a44a$0ea07380$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] RV-7a cooling - continued! Date: Fri, 1 Jun 2007 08:40:37 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0017_01C7A428.87343060" 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 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_0017_01C7A428.87343060 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Glad to hear you were able to bring the temps down, Dennis. Controlling = the airflow so your large radiator (which is more than adequate) gets = the maximum benefit is clearly the need. The photos of your turning = vanes looks to me to have a nice curve to them and are clearly helping = the air flow. =20 If I were going to suggest any change it would be to make the lowest = vane a bit shorter than the middle vane and the upper vane a bit longer = than the middle vane. The rationale for this suggestion is that the = bottom portion of your radiator is likely to be getting the major = portion of the air flow as it is from the straight-in approach from the = inlet. It just needs a bit of a vane to get it turned into the core at = a better angle. The upper segment of your duct likely has less = favorable air flow - so having its vane a bit longer poking out into the = inlet air will capture more of the high velocity air and direct it to = the upper portion. But you don't want it so long that it shadows your = two lower vanes. But, this is just a SWAG on my part if you are intent on making any = changes. On the other hand, if you got a 16 deg drop in oil and = cooling temps with your current vane set up -then unless that still is = inadequate for your cooling needs - why mess with success? Regarding interpretation of air pressure in a duct - it can get counter = intuitive. Pressure tends to increase in two circumstances 1. where = there is a sudden change (enlargement) in cross section area (like a = diffuser) and 2. where airflow is restricted (like a core its = encountering or having blockage at the rear of the core). It generally = means that the air arriving in that region of lower pressure has a lower = velocity such that the conversion of its low amount of kinetic energy = (dynamic pressure) does not produce much of an increase in static = pressure.=20 The maximum pressure drop is across a solid core - which has no airflow = - the minimum pressure drop occurs with no core - which has unrestricted = airflow. Neither approach is optimum in removing much heat - but one is = much lighter and has less cooling drag So since the bottom of you radiator is pretty much seeing a straight = shot from the inlet the velocity of that air flow is probably = considerably higher than the air forced to make the turn to the upper = end of your radiator. Therefore you get higher pressure at the bottom = due to the large amount of kinetic energy being converted to static = pressure. Ideally, you would like you pressure distribution across the core to = be equal - but the idea is rarely achieved.=20 Sounds like you are on the right track to me based on the improvement = you got. You may have found the "magic" formula for successfully using = the "James Cowl". =20 Keep going! Ed ----- Original Message -----=20 From: "Dennis Haverlah" To: "Rotary motors in aircraft" Sent: Thursday, May 31, 2007 11:38 PM Subject: [FlyRotary] RV-7a cooling - continued! >I took out the first splitter/duct that was shown in my 5/27 posting=20 > photo 1678. Cooling was than back to slightly marginal not critical! >=20 > I than built a rig with 3 turning vanes to direct air into the = radiator=20 > near the front of the wedge. (See attached photos) I achieved about a = > 16 deg. F drop in oil and water! This told me that most of the inlet=20 > air was going through the radiator at the small end of the wedge. = Bobby=20 > Hughes said he had seen data indicating a wedge duct had the highest=20 > pressure near the end of the wedge and lower pressure near the = opening. =20 > I now am considering modifying the lower cowl - inlet duct bottom -to=20 > include a curved ramp to direct air upward over the first 30 - 40 % of = > the radiator and than transition into a wedge the rest of the way back = > to the trailing edge of the radiator. >=20 > I have not found any information I feel comfortable to use to design=20 > the curved ramp and may try to build a wind tunnel in the cowl on the=20 > plane. I should be able to insert several ramps and wedge shapes in = the=20 > test area and measure air pressure on the back side of the radiator=20 > using a sensitive manometer. I have two electric leaf blowers that = may=20 > provide enough air to run it. I'm planning on a 3 in wide x 4 in high = > inlet size. Any comments or suggestions? >=20 > Radiator to Duct Sealing: > My radiators are sealed to the duct with silicone baffle rubber strips = > used on cowl-to-baffles on spam cans. I believe my seals are very=20 > good. But - after several E mails concerning sealing the duct I = looked=20 > more closely at the total air flow sealing package. On the Griffin=20 > radiator the fins between the tubes do not extend to the water tanks. = > There is gap of 1/4 to 1/2 inch!! This is on both ends of the = radiator.=20 > The area of the holes is 0.375 in X 12.5 in X 2 ends =3D 9.375 sq in = of=20 > holes just in the one radiator! The Mazda oil cooler also has gaps = but=20 > they are only about 1/8 inch wide. I also found about 2 more sq. in of = > other potential leaks I can fill using Leons light testl Thanks for=20 > the info. to make me look harder at this area! If I get the wind=20 > tunnel working I will first test with the holes and no ramp/wedge - = fill=20 > the holes and retest to determine how much the holes decrease the = outlet=20 > air pressure. >=20 > Air Speed in Duct at Radiator: > The inlet duct is 51 sq. in. (per James Cowls) and expands to about=20 > 17.25 X 8.5 inchs or 146 sq . in. at the start or forward end of the=20 > radiator wedge. This gives a velocity of about 42 mph for the cooling = > air at the front entrance of the wedge at the radiator at a climb = speed=20 > of 120 mph. The duct is a wedge from that point on the the rear of = the=20 > radiators. > -------------------------------------------------------------------------= ------- > -- > Homepage: http://www.flyrotary.com/ > Archive and UnSub: = http://mail.lancaironline.net:81/lists/flyrotary/List.html > ------=_NextPart_000_0017_01C7A428.87343060 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Glad to hear you were able to bring the temps = down,=20 Dennis.  Controlling the airflow so your large radiator (which is = more than=20 adequate) gets the maximum benefit is clearly the need. The = photos of=20 your turning vanes looks to me to have a nice curve to them and are=20 clearly  helping the air flow. 
 
If I were going to suggest any change it would = be to make=20 the lowest vane a bit shorter than the middle vane and = the upper=20 vane a bit longer than the middle vane. The rationale for this = suggestion is that the bottom portion of your radiator is likely to be = getting=20 the major portion of the air flow as it is from the straight-in approach = from=20 the inlet.  It just needs a bit of a vane to get it = turned into the=20 core at a better angle.  The upper segment of your duct likely = has=20 less favorable air flow - so having its vane a bit longer poking out = into the=20 inlet air will capture more of the high velocity air and direct it to = the upper=20 portion.  But you don't want it so long that it shadows your two = lower=20 vanes.
 
But, this is just a SWAG on my part if you are = intent on=20 making any changes.   On the other hand, if you got a 16 deg = drop in=20 oil and cooling temps with your current vane set up -then unless that = still is=20 inadequate for your cooling needs - why mess with success?
 
Regarding interpretation of air pressure in a = duct - it=20 can get counter intuitive.  Pressure tends to increase in two=20 circumstances 1.  where there is a sudden = change (enlargement) in=20 cross section area (like a diffuser) and 2.  where airflow is=20 restricted (like a core its encountering or  having = blockage at the=20 rear of the core). It generally means that the air arriving in that = region=20 of lower pressure has a lower velocity such that the conversion of = its low=20 amount of kinetic energy (dynamic pressure) does not produce much = of an=20 increase in static pressure.
 

The maximum pressure drop is across a solid = core - which=20 has no airflow =96 the minimum pressure drop occurs with no core - which = has=20 unrestricted airflow. Neither approach is optimum in removing much heat = =96 but=20 one is much lighter and has less cooling drag

 
So since the bottom of you radiator is pretty = much seeing=20 a straight shot from the inlet the velocity of that air flow is probably = considerably higher than the air forced to make the turn to the upper = end of=20 your radiator.  Therefore you get higher pressure at the bottom due = to the=20 large amount of kinetic energy being converted to static = pressure.
 
  Ideally, you would like you pressure = distribution=20 across the core to be equal - but the idea is rarely=20 achieved. 
 
Sounds like you are on the right track to me = based on the=20 improvement you got.  You may have found the "magic" formula for=20 successfully using the "James Cowl". 
 
Keep going!
 
Ed
 
 
 
 
 
 
----- Original Message -----
From: "Dennis Haverlah" <clouduster@austin.rr.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Thursday, May 31, 2007 11:38 = PM
Subject: [FlyRotary] RV-7a cooling -=20 continued!

>I took = out the first=20 splitter/duct that was shown in my 5/27 posting
> photo = 1678. =20 Cooling was than back to slightly marginal not = critical!
> 
> I=20 than built a rig with 3 turning vanes to direct air into the radiator =
>=20 near the front of the wedge. (See attached photos)  I achieved = about a=20
> 16 deg. F drop in oil and water!  This told me that most = of the=20 inlet
> air was going through the radiator at the small end of = the=20 wedge.  Bobby
> Hughes said he had seen data indicating a = wedge duct=20 had the highest
> pressure near the end of the wedge and lower = pressure=20 near the opening. 
> I now am considering modifying the = lower cowl -=20 inlet duct bottom -to
> include a curved ramp to direct air = upward over=20 the first 30 - 40 % of
> the radiator and than transition into a = wedge=20 the rest of the way back
> to the trailing edge of the = radiator.
>=20
> I have not found any information I feel comfortable to use = to=20 design
> the curved ramp and may try to build a wind tunnel in = the cowl=20 on the
> plane. I should be able to insert several ramps and = wedge shapes=20 in the
> test area and measure air pressure on the back side of = the=20 radiator
> using a sensitive manometer.  I have two electric = leaf=20 blowers that may
> provide enough air to run it.  I'm = planning on a=20 3 in wide x 4 in high
> inlet size.   Any comments or=20 suggestions?
>
> Radiator to Duct Sealing:
> My = radiators are=20 sealed to the duct with silicone baffle rubber strips
> used on=20 cowl-to-baffles on spam cans.  I believe my seals are very
> = good.   But - after several E mails concerning sealing the = duct I=20 looked
> more closely at the total air flow sealing = package.  On the=20 Griffin
> radiator the fins between the tubes do not extend to = the water=20 tanks. 
> There is gap of 1/4 to 1/2 inch!!  This is on = both=20 ends of the radiator.
> The area of the holes is  0.375 in X = 12.5 in=20 X 2 ends =3D 9.375 sq in of
> holes just in the one = radiator!  The=20 Mazda oil cooler also has gaps but
> they are only about 1/8 inch = wide. I=20 also found about 2 more sq. in of
> other potential leaks I can = fill=20 using Leons light testl   Thanks for
> the info. to = make me=20 look harder at this area!   If I get the wind
> tunnel = working=20 I will first test with the holes and no ramp/wedge - fill
> the = holes and=20 retest to determine how much the holes decrease the outlet
> air=20 pressure.
>
> Air Speed in Duct at Radiator:
> The = inlet duct=20 is 51 sq. in. (per James Cowls) and expands to about
> 17.25 X = 8.5 inchs=20 or 146 sq . in. at the start or forward end of  the
> = radiator=20 wedge.  This gives a velocity of about 42 mph for the cooling =
> air=20 at the front entrance of the wedge at the radiator at a climb speed =
> of=20 120 mph.   The duct is a wedge from that point on the the rear = of the=20
> radiators.
>

> --
> Homepage:  http://www.flyrotary.com/
> Archive=20 and UnSub:   http://mail.lancaironline.net:81/lists/flyrotary/List.html
> ------=_NextPart_000_0017_01C7A428.87343060--