X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from omc2-s12.bay6.hotmail.com ([65.54.249.22] verified) by logan.com (CommuniGate Pro SMTP 5.0.8) with ESMTP id 1032718 for flyrotary@lancaironline.net; Mon, 13 Mar 2006 17:23:39 -0500 Received-SPF: pass receiver=logan.com; client-ip=65.54.249.22; envelope-from=thomphy@msn.com Received: from hotmail.com ([65.54.172.119]) by omc2-s12.bay6.hotmail.com with Microsoft SMTPSVC(6.0.3790.211); Mon, 13 Mar 2006 14:22:55 -0800 Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC; Mon, 13 Mar 2006 14:22:55 -0800 Message-ID: Received: from 67.42.209.162 by BAY5-DAV15.phx.gbl with DAV; Mon, 13 Mar 2006 22:22:53 +0000 X-Originating-IP: [67.42.209.162] X-Originating-Email: [thomphy@msn.com] X-Sender: thomphy@msn.com From: "Thomas Phy" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] heat output Date: Mon, 13 Mar 2006 14:35:33 -0800 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0018_01C646AB.62CD2000" 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 X-OriginalArrivalTime: 13 Mar 2006 22:22:55.0842 (UTC) FILETIME=[AD2F4420:01C646EC] Return-Path: thomphy@msn.com This is a multi-part message in MIME format. ------=_NextPart_000_0018_01C646AB.62CD2000 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hi guys, I've been kind of following this thread, and with my not so = engineering background, I was thinking (and that's dangerous). Just how = much unburned fuel are we pumping overboard? Is there enough to say, = shape the exhaust pipe into a nozzle, add an igniter, and have a home = boy's jato, on all the time? If so, how much thrust might it produce? = Just thinking out loud. TP =20 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_0018_01C646AB.62CD2000 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Hi guys, I've been kind of following = this thread,=20 and with my not so engineering background, I was thinking (and = that's=20 dangerous). Just how much unburned fuel are we pumping overboard? Is = there=20 enough to say, shape the exhaust pipe into a nozzle, add an = igniter, and=20 have a home boy's jato, on all the time? If so, how much thrust might it = produce? Just thinking out loud. TP
 
I think this one = is a=20 no-brainer, 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
 

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