X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from poplet2.per.eftel.com ([203.24.100.45] verified) by logan.com (CommuniGate Pro SMTP 5.2.16) with ESMTP id 3884950 for flyrotary@lancaironline.net; Tue, 13 Oct 2009 16:49:42 -0400 Received-SPF: none receiver=logan.com; client-ip=203.24.100.45; envelope-from=lendich@aanet.com.au Received: from sv1-1.aanet.com.au (sv1-1.per.aanet.com.au [203.24.100.68]) by poplet2.per.eftel.com (Postfix) with ESMTP id 9EA55173848 for ; Wed, 14 Oct 2009 04:49:04 +0800 (WST) Received: from ownerf1fc517b8 (203.171.92.134.static.rev.aanet.com.au [203.171.92.134]) by sv1-1.aanet.com.au (Postfix) with SMTP id 81443BEC00F for ; Wed, 14 Oct 2009 04:48:59 +0800 (WST) Message-ID: From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: intake manifold 13b 86 Date: Wed, 14 Oct 2009 06:48:58 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_003C_01CA4C9A.67D0EB60" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5843 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 X-Antivirus: avast! (VPS 091013-0, 10/13/2009), Outbound message X-Antivirus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_003C_01CA4C9A.67D0EB60 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Lynn,=20 About what RPM does the secondaries come in, if I go by memory, which = isn't always the best thing for mew to do, It's about 3500 rpm - does = that sound right? George (down under) That would be like disabling one of the intake valves in a 4 valve per = cylinder piston engine. Yes it will still run but the power would be = down somewhat. Just not a good idea. Tracy On Mon, Oct 12, 2009 at 4:24 PM, jrhopkins = wrote: has anyone used blocked off the center two apertures and used the = front and rear intake manifolds only? i do not understand the need for = the center split intake for aircraft use. =20 thanks Richard The center ports are smaller (the primary ports in the center iron) = are part of a system designed to use a carburetter. That means that high = velocity was needed to keep the energy high and the fuel air mixture = from forming droplets and adding to HC.=20 So the smaller barrels of the 4 barrel carb open first to operate the = engine on the high velocity runners to those ports. Most of the time = the engine ran only on those ports. So the effect is that the carb looks = small and the fuel mileage is fair, and HC (unburned Hydrocarbons) are = within requirements.=20 The key is velocity. The smaller the tube per cubic foot of mixture = per second, the higher the velocity. So the center ports and runners are = small. Since only about 20 HP is needed to go 60 MPH, most of the = engines life is run out on the small ports.=20 When more power is demanded, low manifold pressure opens the = secondaries in the carb via a vacuum diaphragm and the big ports in the = front and rear irons are called into use. The fuel economy idea is out = the window and in a properly tuned car the engine RPM will be high = enough to provide fair velocity in the big runners and ports. So the = engine will accelerate to the best power RPM (red line) to deliver the = engines rated HP. =20 In the fuel injected engine this feature is still in use so you see = the throttle bodies multiple inlets. Same idea.=20 In aircraft use, there is little use for 20 HP beyond a slow taxi. = Take off power would be everything you can come up with HP wise. So all = 4 ports and runners are needed. Once in flight, close to 50 HP would be = needed just to maintain level slow flight, so there is just no = application where the plane would fly on just the center ports. As the = plane climbs the available HP goes down based on air density changes,=20 so in most cases, the throttle is left at wide open or very close to = that. Further power reduction is by leaning to maintain the ideal fuel = air mixture, or even leaning further to well over lean, or Lean Of Peak. That is Lean Of Peak EGT (the rotary does that very well), So power = goes down as well as fuel consumption and EGT. The throttle will be left = wide open.=20 Closing off the center ports would be the same as not opening the = throttle by some amount. If you want to build in more power, the 84-85 12A has the biggest = runners and ports in the center iron. Lynn E. Hanover ------=_NextPart_000_003C_01CA4C9A.67D0EB60 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Lynn,
About what RPM does the secondaries = come in, if I=20 go by memory, which isn't always the best thing for mew to do, It's = about 3500=20 rpm - does that sound right?
George (down under)
That would be like disabling one of the intake valves in a 4 = valve per=20 cylinder piston engine. Yes it will still run but the power would be = down=20 somewhat.  Just not a good idea.
 
Tracy

On Mon, Oct 12, 2009 at 4:24 PM, jrhopkins = <jrhopkins@windstream.net>= =20 wrote:
has anyone used blocked off the = center two=20 apertures and used the front and rear intake manifolds only?  i = do not=20 understand the need for the center split intake for aircraft=20 use.  
 
thanks  =20 Richard
 
 
The center ports are smaller (the primary ports in the center = iron) are=20 part of a system designed to use a carburetter. That means that high = velocity=20 was needed to keep the energy high and the fuel air mixture from = forming=20 droplets and adding to HC. 
 
So the smaller barrels of the 4 barrel carb open first to operate = the=20 engine on the high velocity runners to those ports. Most of the = time  the=20 engine ran only on those ports. So the effect is that the carb looks = small and=20 the fuel mileage is fair, and HC (unburned Hydrocarbons) are within=20 requirements. 
 
The key is velocity. The smaller the tube per cubic foot of = mixture per=20 second, the higher the velocity. So the center ports and runners are = small.=20 Since only about 20 HP is needed to go 60 MPH, most of the engines = life is run=20 out on the small ports. 
 
When more power is demanded, low manifold pressure opens the = secondaries=20 in the carb via a vacuum diaphragm and the big ports in the front and = rear=20 irons are called into use. The fuel economy idea is out the window and = in a=20 properly tuned car the engine RPM will be high enough to provide fair = velocity=20 in the big runners and ports. So the engine will accelerate to the = best power=20 RPM (red line) to deliver the engines rated HP.  
 
In the fuel injected engine this feature is still in use so you = see the=20 throttle bodies  multiple inlets.
Same idea.
 
In aircraft use, there is little use for 20 HP beyond a slow = taxi. Take=20 off power would be everything you can come up with HP wise. So all 4 = ports and=20 runners are needed. Once in flight, close to 50 HP would be needed = just to=20 maintain level slow flight, so there is just no application where the = plane=20 would fly on just the center ports. As the plane climbs the available = HP goes=20 down based on air density changes,
so in most cases, the throttle is left at wide open or very close = to=20 that. Further power reduction is by leaning to maintain the ideal fuel = air=20 mixture, or even leaning further to well over lean, or Lean Of = Peak.
That is Lean Of Peak EGT (the rotary does that very well), So = power goes=20 down as well as fuel consumption and EGT. The throttle will be left = wide open.=20
 
Closing off the center ports would be the same as not opening the = throttle by some amount.
 
If you want to build in more power, the 84-85 12A has the biggest = runners=20 and ports in the center iron.
 
Lynn E. Hanover

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