Return-Path: Received: from [203.37.234.168] (HELO venus3.veridas.net) by logan.com (CommuniGate Pro SMTP 4.3c3) with ESMTP id 855339 for flyrotary@lancaironline.net; Tue, 05 Apr 2005 05:47:34 -0400 Received-SPF: none receiver=logan.com; client-ip=203.37.234.168; envelope-from=mburke@southernphone.com.au Received: (qmail 14202 invoked from network); 5 Apr 2005 19:46:46 +1000 Received: from mburke@southernphone.com.au by venus3 by uid 1001 with qmail-scanner-1.15 (clamscan: 0.74. Clear:. Processed in 5.533587 secs); 05 Apr 2005 09:46:46 -0000 Received: from dsl-202-52-51-019.nsw.veridas.net (HELO veridas) (202.52.51.19) by southernphone.com.au with SMTP; 5 Apr 2005 19:46:41 +1000 Message-ID: <002d01c539c4$3981ac60$0601010a@veridas> From: "Michael Burke" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Cooling Inlet Areas/Bernie's RV9 Date: Tue, 5 Apr 2005 19:45:37 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_002A_01C53A18.0A8F0B60" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1409 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1409 This is a multi-part message in MIME format. ------=_NextPart_000_002A_01C53A18.0A8F0B60 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Michael Burke wrote, new list member Gentlemen, I have no expertise whatsoever in this area, but I do remember reading = about liquid cooled W.W. II aircraft, like the Heinkel that had major = cooling problems when the heat exchangers were placed in the front of = the cowl. To solve the problem the engineers moved them back in the = fuselage, with redesigned ducting and the problem was solved. The problem as I understood it, was that the air in front of the cowl is = very turbulent, and very chopped up as a result of the prop. The = advancing blade pushes the air in the duct, and then as it retreats it = pulls it back out again. so you have this constant pull / push of the = air which is detrimental to good air flow in the duct, not to mention = the turbulence of the air in general. The Germans solved the problem by = moving the heat exchangers to where they could get a clean air supply. I'm just wondering whether this might be a factor affecting some of your = installations where you are getting less than satisfactory results. ----- Original Message -----=20 From: Al Gietzen=20 To: Rotary motors in aircraft=20 Sent: Tuesday, April 05, 2005 3:02 PM Subject: [FlyRotary] Re: Cooling Inlet Areas/Bernie's RV9 Before we get too carried away by Ed running with a lot less intake = area than the 'rule-of-thumb' suggests; keep in mind that there are = other variables, and there are some simple laws of physics. The 'rules = of thumb' assume ability for sustained high power with outside air temps = of 90 - 100F. It also assumes an air temp increase through the rad of 40-50F. If = you can achieve higher temp increase, then you can adjust down the flow. = The law of physics is that the air has a known specific heat; i.e., the = amount of heat it will absorb per degree of heat up. Knowing how much = heat you have to dissipate, it tells you directly how much flow you = need, and knowing how fast you are going tells you directly how big an = opening you need to get that much air. When the intakes are up front = behind the prop you get some benefit from 'external diffusion' in front = of the cowl, and perhaps some improved flow from the prop wash. Having more outlet area then the 1.4 factor may also reduce require = inlet area a bit, but at the expense of drag. Ideally you would like to = use some remaining pressure to accelerate the exit air to near free = stream velocity, the larger the outlet the slower the exit air, the more = drag. I would suggest that with 28 sq. in. of intake a.) Ed could not do = sustained full power climb from low altitude on a 95F day, b.) he is = getting greater than 50F air temp increase through the rads, and c.) he = is actually generating less than 180 hp because fuel flow estimate will = give you a max, which is not actually achieved in a rotary because of = unburned fuel burning/going out the exhaust port. I expect he may agree with a. and b. but never c. J; right Ed?=20 Clearly the 'rules-of-thumb' give you more inlet area than needed at = cruise on an average day. That's why cowl flaps are good. Al > Al Gietzen wrote: > > > Doug; > > > > I agree with your 'rule-of-thumb' numbers. My analysis came up = with > > coolant inlet area in sq. in. of 1/3 the HP (.33) for climb out on = a > > 90F day. It assumes a 120kt climb speed for my Velocity. I used = 45% of > > that additional for the oil cooler. Assumes scoop efficiencies of = 85% > > or better. > > > > Al > > > > > Second, even if cooling can get out, if it can't get in, it can't = be > > there to cool the heat exchangers. Rule of thumb: 0.3 sq. in. of > > cowling inlet air opening per HP. 200 HP x .3 =3D 60 sq. in. Note: = This > > assumes a reasonably shaped inlet cowl which has been discussed = online > > often. IMHO: Berni's plane inlet shape and inlet cowl is fine, but = I > > question his inlet opening _area_. > > > snip > > > Don't mean to start another stream of threads on an old subject, = but > > we sweated over this one for 3 months and 3 systems and one might = save > > a lot of time by comparing ones system to these simple "works = great" > > rules of thumb which are the result of LOTS of technical and > > experimental work. > > > > Doug Dempsey > > > > N6415Q and RV7 in process > > > > Colorado, USA > > > > Don't won't do demean or dismiss your experimental work in any way, = but > Ed is running with half the inlet area, and unless something has = changed > with his new found power, he'd doing just fine. Just to be sure that > we're all talking apples, I can confidently quote him at 28 in^2 = inlet > for coolant, which I believe is half of what you recommend above. > Reality isn't meeting theory at eye level here, and everyone will be > much better off if we know why. > > -- > This is by far the hardest lesson about freedom. It goes against > instinct, and morality, to just sit back and watch people make > mistakes. We want to help them, which means control them and their > decisions, but in doing so we actually hurt them (and ourselves)." > I am running with 28 sq inches of total inlet area, much more outlet = area than Doug mentions and not producing 200HP continuos. My best = estimate based on fuel flow is I produce around 180HP perhaps a bit more on a = cooler morning. I agree apples and oranges get compared frequently. But, rules of = thumb are just that - generally a place to get started. I don't think = anyone would say that a rule of thumb means the "optimum" for a specific installation. Just good enough. I have a rule of thumb that says = given enough surface area and airflow you WILL cool. Not too helpful though = and certainly does not address the cooling drag you may impose. I mean if = your rule of thumb says you have to have sufficient area to let the hot air = out and sufficient inlet to let the cold air in - well, OK, I can buy that = - but not too useful. If you put numbers to it like Doug has done that = becomes more useful but is not the final answer. For some of us, rules of thumb are simply a gore to understand what's = behind them. How did they come about, what do they mean? To others they are = a heaven - sent- answer that does not require listening to or reading = this sort of stuff {:>). So I am not certain we need to necessarily even attempt to explain = Rules of Thumb, they are simply a starting point that experience has shown = will work (most of the time). Ed A >> Homepage: http://www.flyrotary.com/ >> Archive: http://lancaironline.net/lists/flyrotary/List.html ------=_NextPart_000_002A_01C53A18.0A8F0B60 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Michael Burke wrote,
new list member
 
Gentlemen,
I have no expertise whatsoever in this area, but = I do=20 remember reading about liquid cooled W.W. II aircraft, like the Heinkel = that had=20 major cooling problems when the heat exchangers were placed in the front = of the=20 cowl. To solve the problem the engineers moved them back in the = fuselage, with=20 redesigned ducting and the problem was solved.
 
The problem as I understood it, was that = the air in=20 front of the cowl is very turbulent, and very chopped up as a result of = the=20 prop. The advancing blade pushes the air in the duct, and then as it = retreats it=20 pulls it back out again. so you have this constant pull / push of the = air which=20 is detrimental to good air flow in the duct, not to mention the = turbulence of=20 the air in general. The Germans solved the problem by moving the heat = exchangers=20 to where they could get a clean air supply.
I'm just wondering whether this might be a = factor=20 affecting some of your installations where you are getting less than=20 satisfactory results.
----- Original Message -----
From:=20 Al = Gietzen=20
Sent: Tuesday, April 05, 2005 = 3:02=20 PM
Subject: [FlyRotary] Re: = Cooling Inlet=20 Areas/Bernie's RV9

Before we get too = carried away=20 by Ed running with a lot less intake area than the =91rule-of-thumb=92 = suggests;=20 keep in mind that there are other variables, and there are some simple = laws of=20 physics.  The =91rules of thumb=92 assume ability for sustained = high power=20 with outside air temps of 90 =96 100F.

 

It also assumes an air = temp=20 increase through the rad of 40-50F.  If you can achieve higher = temp=20 increase, then you can adjust down the flow.  The law of physics = is that=20 the air has a known specific heat; i.e., the amount of heat it will = absorb per=20 degree of heat up.  Knowing how much heat you have to dissipate, = it tells=20 you directly how much flow you need, and knowing how fast you are = going tells=20 you directly how big an opening you need to get that much air.  = When the=20 intakes are up front behind the prop you get some benefit from = =91external=20 diffusion=92 in front of the cowl, and perhaps some improved flow from = the prop=20 wash.

 

Having more outlet = area then the=20 1.4 factor may also reduce require inlet area a bit, but at the = expense of=20 drag.  Ideally you would like to use some remaining pressure to=20 accelerate the exit  air to near free stream velocity, the larger = the=20 outlet the slower the exit air, the more drag.

 

I would = suggest=20 that with 28 sq. in. of intake a.) Ed could not do sustained full = power climb=20 from low altitude on a 95F day, b.) he is getting greater than 50F air = temp=20 increase through the rads, and c.) he is actually generating less than = 180 hp=20 because fuel flow estimate will give you a max, which is not actually = achieved=20 in a rotary because of unburned fuel burning/going out the exhaust=20 port.

 

I expect = he may=20 agree with a. and b. but never c. J; = right Ed?=20

 

Clearly = the=20 =91rules-of-thumb=92 give you more inlet area than needed at cruise on = an average=20 day.  That=92s why cowl flaps are good.

 

Al

 

> Al Gietzen wrote:

>

> > Doug;

> >

> > I agree with your = =91rule-of-thumb=92 numbers.=20 My analysis came up with

> > coolant inlet area in sq. in. of = 1/3 the HP=20 (.33) for climb out on a

> > 90F day. It assumes a 120kt climb = speed for=20 my Velocity. I used 45% of

> > that additional for the oil = cooler. Assumes=20 scoop efficiencies of 85%

> > or better.

> >

> > Al

> >

>

> > Second, even if cooling can get = out, if it=20 can't get in, it can't be

> > there to cool the heat exchangers. = Rule of=20 thumb: 0.3 sq. in. of

> > cowling inlet air opening per HP. = 200 HP x=20 .3 =3D 60 sq. in. Note: This

> > assumes a reasonably shaped inlet = cowl which=20 has been discussed online

> > often. IMHO: Berni's plane inlet = shape and=20 inlet cowl is fine, but I

> > question his inlet opening=20 _area_.

> >

> snip

>

> > Don't mean to start another stream = of=20 threads on an old subject, but

> > we sweated over this one for 3 = months and 3=20 systems and one might save

> > a lot of time by comparing ones = system to=20 these simple "works great"

> > rules of thumb which are the = result of LOTS=20 of technical and

> > experimental = work.

> >

> > Doug Dempsey

> >

> > N6415Q and RV7 in = process

> >

> > Colorado, USA

> >

>

> Don't won't do demean or dismiss your=20 experimental work in any way, but

> Ed is running with half the inlet area, = and=20 unless something has changed

> with his new found power, he'd doing = just fine.=20 Just to be sure that

> we're all talking apples, I can = confidently quote=20 him at 28 in^2 inlet

> for coolant, which I believe is half of = what you=20 recommend above.

> Reality isn't meeting theory at eye = level here,=20 and everyone will be

> much better off if we know = why.

>

> --

> This is by far the hardest lesson about = freedom.=20 It goes against

> instinct, and morality, to just sit = back and=20 watch people make

> mistakes. We want to help them, which = means=20 control them and their

> decisions, but in doing so we actually = hurt them=20 (and ourselves)."

>

 

I=20 am running with 28 sq inches of total inlet area, much more outlet=20 area

than Doug mentions and  not producing = 200HP=20 continuos.  My best estimate

based on fuel flow is I produce around 180HP = perhaps a=20 bit more on a cooler

morning.

 

 I agree apples and oranges get = compared=20 frequently.  But, rules of thumb

are just that - generally a place to get=20 started.  I don't think anyone

would say that a rule of thumb means the = "optimum" for=20 a specific

installation.  Just good enough.  = I have a=20 rule of thumb that says given

enough surface area and airflow you WILL = cool. =20 Not too helpful though and

certainly does not address the cooling drag = you may=20 impose.  I mean if your

rule of thumb says you have to have = sufficient area to=20 let the hot air out

and sufficient inlet to let the cold air in = - well,=20 OK, I can buy that - but

not too useful.  If you put numbers to = it like=20 Doug has done that becomes

more useful but is not the final=20 answer.

 

For some of us, rules of thumb are simply a = gore to=20 understand what's behind

them. How did they come about, what do they=20 mean?  To others they are a

heaven - sent- answer that does not require = listening=20 to or reading this

sort of stuff {:>).

 

So I am not certain we need to  = necessarily even=20 attempt to explain  Rules

of Thumb, they are simply a starting point = that=20 experience has shown will

work (most of the time).

 

Ed A

 

 

 

 

>>  Homepage: =20 http://www.flyrotary.com/

>>  Archive:  =20 = http://lancaironline.net/lists/flyrotary/List.html

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