X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from [65.54.250.91] (HELO hotmail.com) by logan.com (CommuniGate Pro SMTP 5.0.8) with ESMTP id 1030594 for flyrotary@lancaironline.net; Sat, 11 Mar 2006 10:28:06 -0500 Received-SPF: pass receiver=logan.com; client-ip=65.54.250.91; envelope-from=lors01@msn.com Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Sat, 11 Mar 2006 07:27:22 -0800 Message-ID: Received: from 4.171.150.140 by BAY115-DAV19.phx.gbl with DAV; Sat, 11 Mar 2006 15:27:19 +0000 X-Originating-IP: [4.171.150.140] X-Originating-Email: [lors01@msn.com] X-Sender: lors01@msn.com From: "Tracy Crook" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: NACA's, Cooling and Sport Aviation Mag.. Date: Sat, 11 Mar 2006 10:27:12 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_023F_01C644F6.5C66EA90" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: MSN 9 X-MimeOLE: Produced By MSN MimeOLE V9.10.0011.1703 Seal-Send-Time: Sat, 11 Mar 2006 10:27:12 -0500 X-OriginalArrivalTime: 11 Mar 2006 15:27:22.0009 (UTC) FILETIME=[4AA2C890:01C64520] This is a multi-part message in MIME format. ------=_NextPart_000_023F_01C644F6.5C66EA90 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Measuring differential pressure IS a super tool in diagnosing cooling = system performance but be sure to evaluate the whole picture when = grabbing figures from tests like I ran. The 5" H2O was a reasonable = pressure at the flight condition tested but that was only at 120 MPH. = If that's all you had at 200 MPH the engine would be fried pretty quick. = The full available dynamic pressure at 120 mph is only something like = 7.2" H2O but it goes up as a square function of airspeed. Tracy BTW, Great comments on the NACA scoop Monty. ----- Original Message -----=20 From: Ernest Christley=20 To: Rotary motors in aircraft=20 Sent: Friday, March 10, 2006 10:00 AM 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, =20 > the cabin pressure will build up and the NACA scoops will be =20 > ineffective. > Buly 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=20 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=20 pressure DIFFERENTIAL across it. Differential implies that there are=20 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=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 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=20 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=20 exit could possibly give you -2". There you go. Your done. You'll = get=20 more than enough airflow to cool the engine. 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=20 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=20 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=20 scoop in, but before it is even halfway in you hit the 3" mark.=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 = 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 = 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=20 scoop. Mabybe you have 2.5" instead of the 2", and you can sink the=20 scoop just a little more. 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 = sticking out in the wind as far for less profile drag. What if you = gave=20 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=20 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=20 naca.larc.gov to pull up old studies where 50 years ago they derived=20 actual equations to predict what will happen. I guess my point is to not think of the NACA scoop as anything more = than=20 one end of the spectrum that starts with a pot-belly stove flue = sticking=20 out the belly. I will be using a scoop that will be eerily similar to = a=20 NACA, except that it isn't. Due to it's location just below the = leading=20 edge on the thick airfoil of the delta wing, it will work much more = like=20 a traditional scoop at high AOA. During cruise, it will flatten out = and=20 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. =20 I have high hopes, but the water manometer will tell the true story. = 8*) --=20 ,|"|"|, Ernest Christley | ----=3D=3D=3D<{{(oQo)}}>=3D=3D=3D---- 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/ ------=_NextPart_000_023F_01C644F6.5C66EA90 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Measuring differential pressure IS a super tool in = diagnosing cooling system performance but be sure to evaluate the whole = picture=20 when grabbing figures from tests like I ran.  The 5"  H2O was = a=20 reasonable pressure at the flight condition tested but that was only at = 120=20 MPH.  If that's all you had at 200 MPH the engine would be fried = pretty=20 quick.  The full available dynamic pressure at 120 mph is only = something like 7.2" H2O but it goes up as a square function of = airspeed.
 
Tracy
 
BTW, Great comments on the NACA scoop Monty.
 
 
----- Original Message -----
From: Ernest=20 Christley
To: Rotary motors in = aircraft
Sent: Friday, March 10, 2006 = 10:00=20 AM
Subject: [FlyRotary] Re: = NACA's, Cooling=20 and Sport Aviation Mag..

Bulent Aliev wrote:

> Bob, if the cabin does = not have=20 exhaust path for the incoming air, 
> the cabin pressure = will=20 build up and the NACA scoops will be 
> = ineffective.
>=20 Buly

That is correct.  But it is also correct for any = other type=20 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=20 around NACA inlets, but
without a system approach it all signifies = nothing.

The radiator doesn't care what sort of scoop is out=20 front.  And it has
no idea what sort of exhaust is behind = it. =20 All that matters is the
pressure DIFFERENTIAL across it. =20 Differential implies that there are
TWO values to consider.  = You=20 could have a working system with negative
pressure compared to = ambient in=20 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=20 like talking about voltage without a
reference ground.

The = Honorable Mr. Crook has done us all the favor of showing how to =
create a=20 water manometer for less than the cost of a Coke at the =
movies.  The=20 only number for pressure differential that I've seen for a
working = system=20 is Tracy's. I recall that to be 5" H20, so let's go with
that and = make up=20 a few more numbers.  You need 5" of pressure across the =
radiator to=20 get adequate cooling.  A P-51 style scoop stuck out in the =
wind could=20 probably give you 4" of ram pressure.  A properly designed =
exit could=20 possibly give you -2".  There you go. Your done.   = You'll get=20
more than enough airflow to cool the engine.

But you want = to cut=20 the drag down, so you consider an submerged inlet. 
Use John = Slade's=20 approach, the partially submerged inlet.  Don't just go =
straight for=20 the fully flush inlet, but start slowly sinking the scoop
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"=20 on
the front you won't have adequate cooling.  You start to = slowly=20 pull the
scoop in, but before it is even halfway in you hit the 3" = mark.=20

Hmm?  Maybe work on the exit.  Change the shape a = little,=20 clean it up
and maybe it will push the exhaust pressure down to = -3". =20 Now you only
need 2" on the front, and you can get the scoop down = to only=20 half the
original obstruction.  What else?  Maybe you = can fit a=20 K&W streamlined
duct in before the radiator.  Now that = your duct=20 is using the air it
does have more efficiently, the frontal = pressure is=20 higher with the same
scoop.  Mabybe you have 2.5" instead of = the 2",=20 and you can sink the
scoop just a little more.

Hmm?  = But what=20 happens if you scoop out a little bit of the air frame
and put the = scoop=20 in the rut that is formed?  Would that let you sink
the scoop = even=20 further?  You have the same sized opening, but it isn't =
sticking out=20 in the wind as far for less profile drag.  What if you gave =
the rut a=20 carefully designed shape so that air will get a little extra
pull = into the=20 rut instead of just flowing right over the top?  Could you =
sink it=20 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.

I guess my = point is=20 to not think of the NACA scoop as anything more than
one end of = the=20 spectrum that starts with a pot-belly stove flue sticking
out the=20 belly.  I will be using a scoop that will be eerily similar to a=20
NACA, except that it isn't.  Due to it's location just below = the=20 leading
edge on the thick airfoil of the delta wing, it will work = much=20 more like
a traditional scoop at high AOA.  During cruise, it = will=20 flatten out and
begin to work more closely but not exactly like = the=20 submerged inlet. 
The exit will be on the top of the wing, = just=20 behind the max thickness. 
I have high hopes, but the water = manometer=20 will tell the true story.  8*)

--=20
        =20 = ,|"|"|,           =    =20 Ernest Christley    =20 = |
----=3D=3D=3D<{{(oQo)}}>=3D=3D=3D----     = Dyke Delta=20 Builder    = |
       =20 o|  d  = |o          www.ernest.isa-geek.org = =20 |

--
Homepage:  http://www.flyrotary.com/
Archi= ve and=20 UnSub:   http://mail.lanca= ironline.net/lists/flyrotary/
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