X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from mtiwmhc13.worldnet.att.net ([204.127.131.117] verified) by logan.com (CommuniGate Pro SMTP 5.0.8) with ESMTP id 1029478 for flyrotary@lancaironline.net; Fri, 10 Mar 2006 10:31:42 -0500 Received-SPF: none receiver=logan.com; client-ip=204.127.131.117; envelope-from=keltro@att.net Received: from mwebmail19.att.net ([204.127.135.58]) by worldnet.att.net (mtiwmhc13) with SMTP id <2006031015305711300753gbe>; Fri, 10 Mar 2006 15:30:57 +0000 Received: from [4.245.36.98] by mwebmail19.att.net; Fri, 10 Mar 2006 15:30:56 +0000 From: keltro@att.net (Kelly Troyer) To: "Rotary motors in aircraft" Subject: Re: NACA's, Cooling and Sport Aviation Mag.. Date: Fri, 10 Mar 2006 15:30:56 +0000 Message-Id: <031020061530.576.44119BAE0003E71A000002402160281060019D9B040A05@att.net> X-Mailer: AT&T Message Center Version 1 (Feb 28 2006) X-Authenticated-Sender: a2VsdHJvQGF0dC5uZXQ= MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="NextPart_Webmail_9m3u9jl4l_576_1142004656_0" --NextPart_Webmail_9m3u9jl4l_576_1142004656_0 Content-Type: text/plain Content-Transfer-Encoding: 8bit Ernest, Great minds think alike !! :O) -- Kelly Troyer Dyke Delta/13B/RD1C/EC2 -------------- Original message from Ernest Christley : -------------- > 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*) > > -- > ,|"|"|, Ernest Christley | > ----===<{{(oQo)}}>===---- Dyke Delta Builder | --NextPart_Webmail_9m3u9jl4l_576_1142004656_0 Content-Type: text/html Content-Transfer-Encoding: 8bit
 Ernest,
     Great minds think alike !!  :O)
--
Kelly Troyer
Dyke Delta/13B/RD1C/EC2




-------------- Original message from Ernest Christley <echristley@nc.rr.com>: --------------


> 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 airflo w 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
> doe s 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 t o 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*)
>
> --
> ,|"|"|, Ernest Christley |
> ----===<{{(oQo)}}>===---- Dyke Delta Builder |
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