X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from ispmxmta06-srv.alltel.net ([166.102.165.167] verified) by logan.com (CommuniGate Pro SMTP 5.0.4) with ESMTP id 891340 for flyrotary@lancaironline.net; Wed, 21 Dec 2005 12:19:16 -0500 Received-SPF: pass receiver=logan.com; client-ip=166.102.165.167; envelope-from=montyr2157@alltel.net Received: from Thorstwin ([4.227.106.115]) by ispmxmta06-srv.alltel.net with SMTP id <20051221171829.OVQE3660.ispmxmta06-srv.alltel.net@Thorstwin> for ; Wed, 21 Dec 2005 11:18:29 -0600 Message-ID: <000701c60652$914745d0$736ae304@Thorstwin> From: "Monty Roberts" To: Subject: Tracy, Ed, delta T Date: Wed, 21 Dec 2005 11:18:30 -0600 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0004_01C60620.46012C80" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.2180 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0004_01C60620.46012C80 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Good question Monty but I don't know. Only looked at it down low on hot = days. I'l try the following experiment next time I fly: Set fuel burn at a constant value (for roughly the same BTU rejection in = both cases). Measure delta T at 1000 ft then at 8000 ft. Airspeed = should also be similar. Do you think IAS or TAS should be the target? Tracy=20 TAS is the number you need since that is the real velocity through the = medium that the inlet is seeing. I made the mistake of using indicated = speeds to calculate my inlets at first, they were gargantuan! It would = also be nice to know OAT so I can pin down the density. Cp is fairly = insensitive to altitude and temp. Delta t makes a huge difference in the = size of the inlet. 70-80 deg delta T at low altitude on a hot day is really great! That = means you must have a pretty well optimized set up. I think the lower = delta T numbers indicate way too much flow and not enough diffusion to = get the job done. With rads this thick and as much dynamic pressure as = we have there should be a higher delta T. My guess is the outlets are so = big that there is way too much air moving through these coolers. Closing = the outlet down should reduce the flow and up the deltaT. This of course = assumes the core volume and diffuser is up to the task. My low hanging = fruit meter is going off. I don't think that a liquid cooled engine is ever going to compete with = an air cooled engine on minimum cooling drag, but to get close we are = going to have to stop ingesting so much air. Take a look at a = competitive F1 racer's cooling inlets (TINY). They might make 130-150 = hp. Why are we flying around with garbage can size openings for not too = much more power? Of course if you are up against the drag of the = airframe, this is less of an issue. The numbers I am getting using your delta T of around 70-80 F and = cruise from 10Kft-18Kft give inlet area somewhere around 35-40 in^2. For = climb it is as high as 100 in^2 and even that isn't enough in a full = power slow climb on a really hot day. Since I am not operating a WWII = bomber out of North Africa, I will not worry about that too much. ;-). = My initial inlet size is 3.5inX10.5in variable to 7X10.5. with a spray = bar to take care of any oops I may have made in calculating this. I'll = probably compromise and make it a little bigger, plus it just seems = scary small. But then again if you look at a P51 and realize how much HP = it was making and then look at the inlet, maybe 35 in^2 is not so small = for less than 200 hp. I saw in one of your posts where you said your mission was 18Kft at 100 = hp (LOP I assume). That is one flight condition I have looked at as well = and it gives some really enticing numbers! 50 gal of fuel goes a long = way at that flight level. My main cruise design point is in the 200 mph = range at 10-12Kft. Monty ------=_NextPart_000_0004_01C60620.46012C80 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Good question Monty but = I don't=20 know.  Only looked at it down low on hot days.  I'l try the = following=20 experiment next time I fly:
 
Set fuel burn at a = constant value=20 (for roughly the same BTU rejection in both cases).  Measure delta = T at=20 1000 ft then at 8000 ft.  Airspeed should also be similar.  Do = you=20 think IAS or TAS should be the target?
 
Tracy =
 
TAS is the number you need since that = is the real=20 velocity through the medium that the inlet is seeing. I made the = mistake of=20 using indicated speeds to calculate my inlets at first, they = were=20 gargantuan!  It would also be nice to know OAT so I can pin down = the=20 density. Cp is fairly insensitive to altitude and temp. Delta t makes a = huge=20 difference in the size of the inlet.
 
 70-80 deg delta T at low altitude = on a hot=20 day is really great! That means you must have a pretty well optimized = set up. I=20 think the lower delta T numbers indicate way too much flow and not = enough=20 diffusion to get the job done. With rads this thick and as much dynamic = pressure=20 as we have there should be a higher delta T. My guess is the outlets are = so big=20 that there is way too much air moving through these coolers. Closing the = outlet=20 down should reduce the flow and up the deltaT. This of course assumes = the core=20 volume and diffuser is up to the task. My low hanging fruit meter = is going=20 off.
 
I don't think that a liquid cooled = engine is ever=20 going to compete with an air cooled engine on minimum cooling drag, = but to=20 get close we are going to have to stop ingesting so much air. Take a = look at a=20 competitive F1 racer's cooling inlets (TINY). They might make 130-150 = hp. Why=20 are we flying around with garbage can size openings for not too much = more power?=20 Of course if you are up against the drag of the airframe, this is less = of an=20 issue.
 
The numbers I am getting using your = delta T of=20 around 70-80 F  and cruise from 10Kft-18Kft give = inlet=20 area somewhere around 35-40 in^2. For climb it is as high as 100 = in^2 and=20 even that isn't enough in a full power slow climb on a really hot day. = Since I=20 am not operating a WWII bomber out of North Africa, I will not = worry about=20 that too much. ;-). My initial inlet size is 3.5inX10.5in variable to = 7X10.5.=20 with a spray bar to take care of any oops I may have made in = calculating=20 this. I'll probably compromise and make it a little bigger, plus it just = seems=20 scary small. But then again if you look at a P51 and realize how = much HP it=20 was making and then look at the inlet, maybe 35 in^2 is not so = small=20 for less than 200 hp.
 
I saw in one of your posts where you = said your=20 mission was 18Kft at 100 hp (LOP I assume). That is one flight condition = I have=20 looked at as well and it gives some really enticing numbers! 50 gal of = fuel goes=20 a long way at that flight level. My main cruise design point is in = the 200=20 mph range at 10-12Kft.
 
Monty
 
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