X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao02.cox.net ([68.230.241.37] verified) by logan.com (CommuniGate Pro SMTP 5.0.8) with ESMTP id 1029493 for flyrotary@lancaironline.net; Fri, 10 Mar 2006 10:45:49 -0500 Received-SPF: none receiver=logan.com; client-ip=68.230.241.37; envelope-from=ALVentures@cox.net Received: from BigAl ([68.7.14.39]) by fed1rmmtao02.cox.net (InterMail vM.6.01.05.02 201-2131-123-102-20050715) with ESMTP id <20060310154208.PRPW17006.fed1rmmtao02.cox.net@BigAl> for ; Fri, 10 Mar 2006 10:42:08 -0500 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: NACA's, Cooling and Sport Aviation Mag.. Date: Fri, 10 Mar 2006 07:45:15 -0800 Message-ID: <000001c64459$a0b98a10$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C64416.9298BB10" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C64416.9298BB10 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable I agree that the 'automatic' assumption that a NACA will not work for a rad/oil cooler is not always valid. Equally incorrect is the = 'automatic' assumption that the NACA scoop is lower drag. Drag is a measure of the directed energy of the air in vs the directed energy out. It's about = the design of the scoops, the core and the ducting - both in and out. =20 All we know for sure is that a ram scoop has a better chance of = successfully providing the cooling you need because you have a larger pressure head = to work with. =20 Al =20 -----Original Message----- From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ernest Christley Sent: Friday, March 10, 2006 7:01 AM To: Rotary motors in aircraft Subject: [FlyRotary] Re: NACA's, Cooling and Sport Aviation Mag.. =20 Bulent Aliev wrote: =20 > Bob, if the cabin does not have exhaust path for the incoming air, =20 > the cabin pressure will build up and the NACA scoops will be =20 > ineffective. > Buly =20 That is correct. But it is also correct for any other type of inlet=20 you'd care to mention. I'm not trying to be a smarta$$, just trying to = point out that there is so much sound and fury around NACA inlets, but=20 without a system approach it all signifies nothing. =20 The radiator doesn't care what sort of scoop is out front. And it has=20 no idea what sort of exhaust is behind it. All that matters is the=20 pressure DIFFERENTIAL across it. Differential implies that there are=20 TWO values to consider. You could have a working system with negative=20 pressure compared to ambient in front of the radiator, if and only if=20 you had a much more negative pressure behind it. Flatly stating that a=20 NACA will or won't work is like talking about voltage without a=20 reference ground.=20 =20 The Honorable Mr. Crook has done us all the favor of showing how to=20 create a water manometer for less than the cost of a Coke at the=20 movies. The only number for pressure differential that I've seen for a=20 working system is Tracy's. I recall that to be 5" H20, so let's go with=20 that and make up a few more numbers. You need 5" of pressure across the = radiator to get adequate cooling. A P-51 style scoop stuck out in the=20 wind could probably give you 4" of ram pressure. A properly designed=20 exit could possibly give you -2". There you go. Your done. You'll get = more than enough airflow to cool the engine. =20 But you want to cut the drag down, so you consider an submerged inlet. =20 Use John Slade's approach, the partially submerged inlet. Don't just go = straight for the fully flush inlet, but start slowly sinking the scoop=20 into the skin. As it moves in, the positive pressure in front will=20 drop. You still have the -2" on the back, but if you drop below 3" on=20 the front you won't have adequate cooling. You start to slowly pull the = scoop in, but before it is even halfway in you hit the 3" mark.=20 =20 Hmm? Maybe work on the exit. Change the shape a little, clean it up=20 and maybe it will push the exhaust pressure down to -3". Now you only=20 need 2" on the front, and you can get the scoop down to only half the=20 original obstruction. What else? Maybe you can fit a K&W streamlined=20 duct in before the radiator. Now that your duct is using the air it=20 does have more efficiently, the frontal pressure is higher with the same = scoop. Mabybe you have 2.5" instead of the 2", and you can sink the=20 scoop just a little more. =20 Hmm? But what happens if you scoop out a little bit of the air frame=20 and put the scoop in the rut that is formed? Would that let you sink=20 the scoop even further? You have the same sized opening, but it isn't=20 sticking out in the wind as far for less profile drag. What if you gave = the rut a carefully designed shape so that air will get a little extra=20 pull into the rut instead of just flowing right over the top? Could you = sink it still further? Maybe you can even play with negative pressure=20 gradients and vortex sheets. Damn, now we're having to head over to=20 naca.larc.gov to pull up old studies where 50 years ago they derived=20 actual equations to predict what will happen. =20 I guess my point is to not think of the NACA scoop as anything more than = one end of the spectrum that starts with a pot-belly stove flue sticking = out the belly. I will be using a scoop that will be eerily similar to a = NACA, except that it isn't. Due to it's location just below the leading = edge on the thick airfoil of the delta wing, it will work much more like = a traditional scoop at high AOA. During cruise, it will flatten out and = begin to work more closely but not exactly like the submerged inlet. =20 The exit will be on the top of the wing, just behind the max thickness. = I have high hopes, but the water manometer will tell the true story. = 8*) =20 --=20 ,|"|"|, Ernest Christley | ----=3D=3D=3D<{{(oQo)}}>=3D=3D=3D---- Dyke Delta Builder | o| d |o www.ernest.isa-geek.org | =20 -- Homepage: http://www.flyrotary.com/ Archive and UnSub: http://mail.lancaironline.net/lists/flyrotary/ ------=_NextPart_000_0001_01C64416.9298BB10 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

I agree that = the 'automatic' assumption that a NACA will not work for a rad/oil cooler is not always valid.  Equally incorrect is the 'automatic' assumption that the = NACA scoop is lower drag.  Drag is a measure of the directed energy of = the air in vs the directed energy out.  It’s about the design of the = scoops, the core and the ducting – both in and out.

 

All we know = for sure is that a ram scoop has a better chance of successfully providing the = cooling you need because you have a larger pressure head to work = with.

 

Al

 

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On = Behalf Of Ernest Christley
Sent: Friday, March 10, 2006 7:01 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: NACA's, Cooling and Sport Aviation = Mag..

 

Bulent Aliev wrote:

 

> Bob, if the cabin does not have exhaust path for the incoming air,  =

> the cabin pressure will build up and the NACA scoops will be  =

> ineffective.

> Buly

 

That is correct.  But it is also correct for any other type of inlet =

you'd care to mention.   I'm not trying to be a smarta$$, just = trying to

point out that there is so much sound and fury around NACA inlets, but =

without a system approach it all signifies nothing.

 

The radiator doesn't care what sort of scoop is out front.  And it has =

no idea what sort of exhaust is behind it.  All that matters is the =

pressure DIFFERENTIAL across it.  Differential implies that there are =

TWO values to consider.  You could have a working system with negative =

pressure compared to ambient in front of the radiator, if and only if =

you had a much more negative pressure behind it.  Flatly stating that a =

NACA will or won't work is like talking about voltage without a =

reference ground.

 

The Honorable Mr. Crook has done us all the favor of showing how to =

create a water manometer for less than the cost of a Coke at the =

movies.  The only number for pressure differential that I've seen for a =

working system is Tracy's. I recall that to be 5" H20, so let's go with =

that and make up a few more numbers.  You need 5" of pressure = across the

radiator to get adequate cooling.  A P-51 style scoop stuck out in the =

wind could probably give you 4" of ram pressure.  A properly = designed

exit could possibly give you -2".  There you go. Your = done.   You'll get

more than enough airflow to cool the engine.

 

But you want to cut the drag down, so you consider an submerged inlet.  =

Use John Slade's approach, the partially submerged inlet.  Don't just = go

straight for the fully flush inlet, but start slowly sinking the scoop =

into the skin.  As it moves in, the positive pressure in front will =

drop.  You still have the -2" on the back, but if you drop below 3" = on

the front you won't have adequate cooling.  You start to slowly pull = the

scoop in, but before it is even halfway in you hit the 3" mark. =

 

Hmm?  Maybe work on the exit.  Change the shape a little, clean it up =

and maybe it will push the exhaust pressure down to -3".  Now you = only

need 2" on the front, and you can get the scoop down to only half the =

original obstruction.  What else?  Maybe you can fit a K&W = streamlined

duct in before the radiator.  Now that your duct is using the air it =

does have more efficiently, the frontal pressure is higher with the same =

scoop.  Mabybe you have 2.5" instead of the 2", and you can sink the =

scoop just a little more.

 

Hmm?  But what happens if you scoop out a little bit of the air frame =

and put the scoop in the rut that is formed?  Would that let you sink =

the scoop even further?  You have the same sized opening, but it isn't =

sticking out in the wind as far for less profile drag.  What if you gave =

the rut a carefully designed shape so that air will get a little extra =

pull into the rut instead of just flowing right over the top?  Could you =

sink it still further?  Maybe you can even play with negative pressure =

gradients and vortex sheets.  Damn, now we're having to head over to =

naca.larc.gov to pull up old studies where 50 years ago they derived =

actual equations to predict what will happen.

 

I guess my point is to not think of the NACA scoop as anything more than =

one end of the spectrum that starts with a pot-belly stove flue sticking =

out the belly.  I will be using a scoop that will be eerily similar to = a

NACA, except that it isn't.  Due to it's location just below the leading =

edge on the thick airfoil of the delta wing, it will work much more like =

a traditional scoop at high AOA.  During cruise, it will flatten out = and

begin to work more closely but not exactly like the submerged inlet.  =

The exit will be on the top of the wing, just behind the max = thickness. 

I have high hopes, but the water manometer will tell the true story.  = 8*)

 

--

       &nbs= p; ,|"|"|,         &n= bsp;     Ernest Christley     |

----=3D=3D=3D<{{(oQo)}}>=3D=3D=3D----&nb= sp;    Dyke Delta Builder    |

        o|  d  = |o          www.ernest.isa-geek.org  |

 

--

Homepage:  http://www.flyrotary.com/

Archive and UnSub:   = http://mail.lancaironline.net/lists/flyrotary/

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