Return-Path: Received: from fed1rmmtao03.cox.net ([68.230.241.36] verified) by logan.com (CommuniGate Pro SMTP 4.3c3) with ESMTP id 855176 for flyrotary@lancaironline.net; Tue, 05 Apr 2005 01:02:39 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.36; envelope-from=ALVentures@cox.net Received: from BigAl ([68.7.14.39]) by fed1rmmtao03.cox.net (InterMail vM.6.01.04.00 201-2131-118-20041027) with ESMTP id <20050405050153.UZHN1282.fed1rmmtao03.cox.net@BigAl> for ; Tue, 5 Apr 2005 01:01:53 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: Cooling Inlet Areas/Bernie's RV9 Date: Mon, 4 Apr 2005 22:02:03 -0700 Message-ID: <000001c5399c$9b69a2c0$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C53961.EF0ACAC0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C53961.EF0ACAC0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable 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. =20 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. =20 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. =20 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. =20 I expect he may agree with a. and b. but never c. :-); right Ed?=20 =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. =20 Al =20 > 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)." > =20 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. =20 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. =20 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 {:>). =20 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). =20 Ed A =20 =20 =20 =20 >> Homepage: http://www.flyrotary.com/ >> Archive: http://lancaironline.net/lists/flyrotary/List.html ------=_NextPart_000_0001_01C53961.EF0ACAC0 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

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.

 <= /font>

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.

 <= /font>

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

 <= /font>

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.

 <= /font>

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

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