X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from [201.225.225.168] (HELO cwpanama.net) by logan.com (CommuniGate Pro SMTP 5.0.8) with ESMTP id 1033114 for flyrotary@lancaironline.net; Mon, 13 Mar 2006 20:55:26 -0500 Received-SPF: none receiver=logan.com; client-ip=201.225.225.168; envelope-from=rijakits@cwpanama.net Received: from [201.224.93.110] (HELO usuarioq3efog0) by frontend2.cwpanama.net (CommuniGate Pro SMTP 4.2.10) with SMTP id 61207987 for flyrotary@lancaironline.net; Mon, 13 Mar 2006 21:15:08 -0500 Message-ID: <004a01c6470a$3f518530$6e5de0c9@usuarioq3efog0> From: "rijakits" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] heat output Date: Mon, 13 Mar 2006 20:54:36 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0046_01C646E0.563D89D0" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1437 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1441 This is a multi-part message in MIME format. ------=_NextPart_000_0046_01C646E0.563D89D0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit ----- Original Message ----- From: M Roberts To: Rotary motors in aircraft Sent: Monday, March 13, 2006 4:44 PM Subject: [FlyRotary] heat output Here's an interesting question. Considering the exhaust heat of the rotary is so much higher than a Lycoming, if doing a side-by-side comparison of the two with equal fuel burn rates, wouldn't the Lycoming have more engine heat to remove from under the cowl than the rotary? I think this one is a no-brainer, but my mother often said the same about me... Ernest, Not necessarily. The conventional wisdom: The Wankel has a higher exhaust temp because of uncombusted hydrocarbons (due to the flat combustion chamber) and possibly a lower expansion ratio (depending on which engine you may be comparing it to). So the Lycoming may make more power for the same fuel flow with less heat rejection. The Wankel also has a lot more surface area for the combustion chamber and rotors so the heat rejected to the coolant will be more. You never get something for nothing and giving up all those valves, push-rods, lifters, ad nauseum, comes with a price. The price is slightly higher cooling load and egts. Just to confuse the issue and tickle some nuerons: Now that is the conventional wisdom, and if you were to compare the wankel to 4 cyl engine of 1.3 L displacement you would conclude that the surface area is greater and the bearing area is greater etc. If you were to compare it to a 3.9 L 6 cyl engine at 2/3 the rpm (which is a much more accurate comparison IMNSHO) you might find the surface areas and bearing areas are not quite so different after all. This is like saying that a single cylinder 302 in^3 engine has less surface area than a V8. DUH!!!. I don't recall anybody at the drag races with a 302 briggs in their muscle car. So even if you say the frictional losses are actually fictional losses, the lack of complete combustion and lower expansion still makes for higher egt and less efficient operation. From a cooling drag standpoint this is not good. You have to ingest more air and you have a lower temperature gradient to work with than with a Lycoming. This is all very academic, but in practice, I'm not sure it makes a hill of beans. Most aircraft cooling systems are so far from optimum that you will never get an apples to apples comparison, plus props, airframes etc are all different. The other issue is the rotary (normally aspirated fixed pitch) can be run LOP at most practical power settings without damage. This is not true of the Lycoming. So this makes up for some of the difference. Now if you have identical airframes with ideal cooling set ups for both types of engines running LOP at the same flight condition I think you would find the Lycoming may have a very slight advantage in BSFC. How much fuel can you buy for the price of top end overhaul on a 180hp Lycoming? Or for that matter the difference in the purchase price of the rotary vs. the Lycoming? Monty You also might want to think really good about Exhaust Augmentation, a good place to recover a lot of heat engery.... Thomas J. ------=_NextPart_000_0046_01C646E0.563D89D0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
 
----- Original Message -----
From:=20 M=20 Roberts
Sent: Monday, March 13, 2006 = 4:44=20 PM
Subject: [FlyRotary] heat = output

Here's an=20 interesting question. Considering the exhaust heat of the rotary is so = much=20 higher than a Lycoming, if doing a side-by-side comparison of the two = with=20 equal fuel burn rates, wouldn't the Lycoming have more engine heat to = remove=20 from under the cowl than the rotary?

I think this one is a = no-brainer,=20 but my mother often said the same about me...
 
Ernest,
 
Not necessarily.
 
The conventional wisdom:
 
The Wankel has a higher exhaust = temp=20 because of uncombusted hydrocarbons (due to the flat = combustion=20 chamber) and possibly a lower expansion ratio (depending on which = engine you=20 may be comparing it to). So the Lycoming may make more power = for the=20 same fuel flow with less heat rejection. The Wankel also has a lot = more=20 surface area for the combustion chamber and rotors so the = heat=20 rejected to the coolant will be more. You never get something for = nothing=20 and giving up all those valves, push-rods, lifters, ad = nauseum, comes=20 with a price. The price is slightly higher cooling load and=20 egts.
 
Just to confuse the issue and tickle = some=20 nuerons:
 
Now that is the conventional wisdom, = and if you=20 were to compare the wankel to 4 cyl engine of 1.3 L displacement you = would=20 conclude that the surface area is greater and the bearing area is = greater etc.=20 If you were to compare it to a 3.9 L 6 cyl engine at 2/3 the = rpm (which=20 is a much more accurate comparison IMNSHO) you might find the surface = areas=20 and bearing areas are not quite so different after all. This is = like=20 saying that a single cylinder 302 in^3 engine has less surface area = than a V8.=20 DUH!!!. I don't recall anybody at the drag races with a 302 briggs in = their=20 muscle car.
 
So even if you say the frictional = losses are=20 actually fictional losses, the lack of complete combustion and = lower=20 expansion still makes for higher egt and less efficient=20 operation.  
 
From a cooling drag standpoint this = is not good.=20 You have to ingest more air and you have a lower temperature gradient = to work=20 with than with a Lycoming. This is all very academic, but in practice, = I'm not=20 sure it makes a hill of beans. Most aircraft cooling systems are so = far from=20 optimum that you will never get an apples to apples comparison, plus = props,=20 airframes etc are all different. The other issue is the rotary = (normally=20 aspirated fixed pitch) can be run LOP at most practical power settings = without=20 damage. This is not true of the Lycoming. So this makes up for some of = the=20 difference. Now if you have identical airframes with ideal cooling set = ups for=20 both types of engines running LOP at the same flight condition I think = you=20 would find the Lycoming may have a very slight advantage in BSFC.=20
 
How much fuel can you buy for the = price of top=20 end overhaul on a 180hp Lycoming? Or for that matter the difference in = the=20 purchase price of the rotary vs. the Lycoming?
 
Monty
 

You also might want to think really good about = Exhaust=20 Augmentation, a good place to recover a lot of heat = engery....
 
Thomas = J.
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