X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from [24.25.9.103] (HELO ms-smtp-04-eri0.southeast.rr.com) by logan.com (CommuniGate Pro SMTP 5.0.4) with ESMTP id 891390 for flyrotary@lancaironline.net; Wed, 21 Dec 2005 13:01:03 -0500 Received-SPF: pass receiver=logan.com; client-ip=24.25.9.103; envelope-from=eanderson@carolina.rr.com Received: from edward2 (cpe-024-074-025-165.carolina.res.rr.com [24.74.25.165]) by ms-smtp-04-eri0.southeast.rr.com (8.12.10/8.12.7) with SMTP id jBLI0H1u007781 for ; Wed, 21 Dec 2005 13:00:17 -0500 (EST) Message-ID: <001d01c60658$6979b370$2402a8c0@edward2> From: "Ed Anderson" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Tracy, Ed, delta T Date: Wed, 21 Dec 2005 13:00:21 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_001A_01C6062E.806F2DF0" 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 X-Virus-Scanned: Symantec AntiVirus Scan Engine This is a multi-part message in MIME format. ------=_NextPart_000_001A_01C6062E.806F2DF0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Interesting, Monty. My read was since IAS is a reflection of "q" or dynamic pressure which = is the pressure factor responsible for shoving air molecules through the = cores - that you would want to compare cooling at the same IAS.=20 From our own Al Gietzen http://www.tvbf.org/archives/velocity/msg02818.html The pressure we have to work with is limited to the dynamic head. And = if air isn't treated right in the ducting it will form back eddies and = pressure waves, and find lots of ways to give you less flow than you calculate = from your intake area. Core thickness can be traded for x-sectional area = only if the ducting is designed to get the air slowed and through it. =20 http://www.vansaircraft.com/pdf/hp_limts.pdf Because the airspeed indicator is The Gauge That Lies. Despite its name, an airspeed indicator does not measure speed. It measures "q" - dynamic pressure caused by packing air molecules into a tube. =20 http://duxford.iwm.org.uk/upload/pdf/Instrumentation.pdf=20 Airspeed The airspeed is directly related to dynamic pressure. To find out what = the Dynamic Pressure is, Static Pressure (the pressure of the air surrounding the = aircraft) is subtracted from the Total Pressure, which is the force of the air = impacting with the aircraft (this is measured using a pitot tube which protrudes from the = aircraft to meet the oncoming airflow directly). So it would seem to me for apples and apples you would want to compare = your cooling at different altitudes at the same dynamic pressure (or = IAS) in order to isolate the effects of ambient temperature on cooling. = But, then I've been wrong before {:>) Ed A ----- Original Message -----=20 From: Monty Roberts=20 To: Rotary motors in aircraft=20 Sent: Wednesday, December 21, 2005 12:18 PM Subject: [FlyRotary] Tracy, Ed, delta T 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_001A_01C6062E.806F2DF0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Interesting, Monty.
 
My read was since IAS is a reflection of "q" or = dynamic=20 pressure which is the pressure factor responsible for shoving air = molecules=20 through the cores - that you would want to compare cooling at the same = IAS.=20
 
From our own  Al=20 Gietzen

http://www.t= vbf.org/archives/velocity/msg02818.html

The pressure we have to work with is = limited to the=20 dynamic head.  And if
air isn't treated right in the ducting it = will=20 form back eddies and pressure
waves, and find lots of ways to give = you less=20 flow than you calculate from
your intake area.  Core thickness = can be=20 traded for x-sectional area only if
the ducting is designed to get = the air=20 slowed and through it.

 

http://www.vansairc= raft.com/pdf/hp_limts.pdf

Because the airspeed indicator is The Gauge That

Lies. Despite its name, an airspeed indicator does = not

measure speed. It measures "q" =96 dynamic pressure

caused by packing air molecules into a tube.

 

http://= duxford.iwm.org.uk/upload/pdf/Instrumentation.pdf 

Airspeed

The airspeed is directly related to dynamic pressure. To = find out=20 what the Dynamic

Pressure is, Static Pressure (the pressure of the air = surrounding=20 the aircraft) is

subtracted from the Total Pressure, which is the force = of the air=20 impacting with the

aircraft (this is measured using a pitot tube which = protrudes from=20 the aircraft to meet

the oncoming airflow directly).

So it would seem to me for = apples and=20 apples you would want to compare your cooling at different altitudes at = the same=20 dynamic pressure (or IAS) in order to isolate the effects of ambient = temperature=20 on cooling.  But, then I've been wrong before {:>)

 

Ed A

 

----- Original Message -----
From:=20 Monty=20 Roberts
Sent: Wednesday, December 21, = 2005 12:18=20 PM
Subject: [FlyRotary] Tracy, Ed, = delta=20 T

Good question Monty = but I don't=20 know.  Only looked at it down low on hot days.  I'l try the=20 following 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=20 of 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.=20 I 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=20 pressure as we have there should be a higher delta T. My guess is the = outlets=20 are so big that there is way too much air moving through these = coolers.=20 Closing the outlet down should reduce the flow and up the deltaT. This = of=20 course assumes the core volume and diffuser is up to the task. My = low=20 hanging fruit meter is going 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=20 to get close we are going to have to stop ingesting so much air. Take = a look=20 at a competitive F1 racer's cooling inlets (TINY). They might make = 130-150 hp.=20 Why are we flying around with garbage can size openings for not too = much more=20 power? Of course if you are up against the drag of the airframe, this = is less=20 of an 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=20 about that too much. ;-). My initial inlet size is 3.5inX10.5in = variable to=20 7X10.5. with a spray bar to take care of any oops I may have = made in=20 calculating this. I'll probably compromise and make it a little = bigger, plus=20 it just seems scary small. But then again if you look at a P51 = and=20 realize how much HP it was making and then look at the inlet, = maybe 35=20 in^2 is not so small 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=20 have looked at as well and it gives some really enticing numbers! 50 = gal of=20 fuel goes a long way at that flight level. My main cruise = design point is=20 in the 200 mph range at 10-12Kft.
 
Monty
 
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