X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from ispmxmta05-srv.alltel.net ([166.102.165.166] verified) by logan.com (CommuniGate Pro SMTP 5.0.8) with ESMTP id 1032675 for flyrotary@lancaironline.net; Mon, 13 Mar 2006 16:44:59 -0500 Received-SPF: pass receiver=logan.com; client-ip=166.102.165.166; envelope-from=montyr2157@alltel.net Received: from Thorstwin ([166.102.185.184]) by ispmxmta05-srv.alltel.net with SMTP id <20060313214410.BWWE18974.ispmxmta05-srv.alltel.net@Thorstwin> for ; Mon, 13 Mar 2006 15:44:10 -0600 Message-ID: <000501c646e7$4761cfa0$01fea8c0@Thorstwin> From: "M Roberts" To: Subject: heat output Date: Mon, 13 Mar 2006 15:44:17 -0600 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0002_01C646B4.FC92E220" 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_0002_01C646B4.FC92E220 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable 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. =20 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.=20 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 ------=_NextPart_000_0002_01C646B4.FC92E220 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
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 equal=20 fuel burn rates, wouldn't the Lycoming have more engine heat to remove = from=20 under the cowl than the rotary?

I think this one is a no-brainer, = but my=20 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 may=20 be comparing it to). So the Lycoming may make more power for = the same=20 fuel flow with less heat rejection. The Wankel also has a lot more = surface area=20 for the combustion chamber and rotors so the heat rejected to = the=20 coolant will be more. You never get something for nothing and = giving up all=20 those valves, push-rods, lifters, ad nauseum, comes with a price. = The=20 price is slightly higher cooling load and 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 is=20 a much more accurate comparison IMNSHO) you might find the surface areas = and=20 bearing areas are not quite so different after all. This is like = saying=20 that a single cylinder 302 in^3 engine has less surface area than a V8. = DUH!!!.=20 I don't recall anybody at the drag races with a 302 briggs in their = muscle=20 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 = 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 would=20 find the Lycoming may have a very slight advantage in BSFC. =
 
How much fuel can you buy for the price = of top end=20 overhaul on a 180hp Lycoming? Or for that matter the difference in the = purchase=20 price of the rotary vs. the Lycoming?
 
Monty
 

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