X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from mail15.syd.optusnet.com.au ([211.29.132.196] verified) by logan.com (CommuniGate Pro SMTP 5.1.11) with ESMTPS id 2269757 for flyrotary@lancaironline.net; Fri, 17 Aug 2007 20:43:29 -0400 Received-SPF: none receiver=logan.com; client-ip=211.29.132.196; envelope-from=lendich@optusnet.com.au Received: from george (d58-104-136-84.dsl.nsw.optusnet.com.au [58.104.136.84]) by mail15.syd.optusnet.com.au (8.13.1/8.13.1) with SMTP id l7I0ghGl024530 for ; Sat, 18 Aug 2007 10:42:45 +1000 Message-ID: <009d01c7e130$b1ef5380$5488683a@george> From: "George Lendich" To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Re: Fw: [FlyRotary] Air/fuel flow Date: Sat, 18 Aug 2007 10:42:44 +1000 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_009A_01C7E184.82A829E0" 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 X-Antivirus: avast! (VPS 0657-0, 12/12/2006), Outbound message X-Antivirus-Status: Clean This is a multi-part message in MIME format. ------=_NextPart_000_009A_01C7E184.82A829E0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Ed, I would like to clarify another point and that is your velocity = figure of 120 mph. I will explain:- I have studied carb sites for snippets of information ( they don't = give much away), however one did say that carb choke speeds are usually = 450' per second and racing cars 125' per second. I assume the racing car inlet speeds are lower because the = throttle is wide open with massive sized inlets, therefore lower vacuum = signal. Your calculations use 176' per second. Can you clarify where you = acquired that figure from as a higher figure would reduce the inlet area = calculations. The carb I am looking at is the Revmaster, they currently only = have 40mm carbs available due to slow demand of the 42/44mm. One good = thing is that the carb operates without a need of venturi, however the = vacuum signal must be weaker ( because of this)coupled with a weaker = signal because of the shape of the rotor face.=20 At the very least the lack of venturi also eliminates the choke = potential. Some carbs have a 44mm inlet but are choked to 36mm which = would increase inlet speed (good), but as you say, may move into the = choke restriction area (bad). A weaker signal would also effect the idle mixture as this is = driven by vacuum rather than air flow, however I guess this can be = adjusted manually. Should be plenty of vacuum at idle with the slide = closed. I have asked Revmaster for air flow and velocity figures, but = these may be derived from piston engine type figures. If you or Lynn could comment on this it would be greatly = appreciated.=20 Also my research indicates that flow air/ fuel mix richens at = higher RPM and altitude. I can't remember why at higher RPM - mind = block, however for altitude it is because fuel flow is driven by air = flow and even though the density of the air is lower ( at altitude) the = flow remains the same - therefore richer mixture. Revmaster says their = needle design is self leaning ( to a degree) because of design. I assume = because the air density directly affects the suction to the rear side of = the flat ground needle, ( this provides the low pressure area rather = than the venturi) therefore with reduced density you have reduced = suction and reduced fuel and leaner mixture. However I will clarify that = when next we talk. I find this all very interesting! George ( down under) Well I'll be Ed, 2.4137sq" =3D (.877x.877xPi =3D 2.416), therefore .877 Radius or = 1.754 Dia or 44.55 mm for the carb opening. I'm working on the rest! George ( down under) For inlet, you take the CFM and you need one other factor - what = velocity do you want through your inlet? Lets say you want a higher = velocity of around 176 feet/sec (120 MPH) then we know that Volume =3D = Area * length. If were want 176 feet/sec velocity from 176 CFM air flow = then coverting CFM to cubic feet per second were have 176Ft^3/min / 60 = Second/Minute =3D 29.333 Ft^3/ Second ------=_NextPart_000_009A_01C7E184.82A829E0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
 
Ed,
 I would like to clarify = another point=20 and that is your velocity figure of 120 mph.
 
I will explain:-
 
I have studied carb sites = for snippets=20 of information ( they don't give much away), however one did say=20 that carb choke speeds  are usually 450' per second and = racing=20 cars 125' per second.
 
I assume the racing car inlet = speeds are=20 lower because the throttle is wide open with massive sized inlets, = therefore lower vacuum signal.
 
Your calculations use 176' per = second. Can=20 you clarify where you acquired that figure from as a higher figure = would=20 reduce the inlet area calculations.
 
The carb I am looking at is the = Revmaster,=20 they currently only have 40mm carbs available due to slow demand = of the=20 42/44mm. One good thing is that the carb operates without a = need=20 of venturi, however the vacuum signal must be weaker ( = because of=20 this)coupled with a weaker signal because of the shape of the = rotor face.=20
 
At the very least the lack of = venturi also=20 eliminates the choke potential. Some carbs have a 44mm inlet but = are=20 choked to 36mm which would increase inlet speed (good), but as you = say,=20 may move into the choke restriction area (bad).
 
A weaker signal would also effect = the idle=20 mixture as this is driven by vacuum rather than air flow, however = I guess=20 this can be adjusted manually. Should be plenty of vacuum at idle = with the=20 slide closed.
 
I have asked Revmaster for air = flow and=20 velocity figures, but these may be derived from piston engine type = figures.
 
If you or Lynn could comment on = this it would=20 be greatly appreciated.
 
Also my research indicates that = flow air/=20 fuel mix richens at higher RPM and altitude. I can't remember = why at=20 higher RPM - mind block, however for altitude it is because = fuel flow=20 is driven by air flow and even though the density of the air = is lower=20 ( at altitude) the flow remains the same - therefore richer = mixture.=20 Revmaster says their needle design is self leaning ( to a degree) = because=20 of design. I assume because the air density directly affects = the=20 suction to the rear side of the flat ground needle, ( this = provides the=20 low pressure area rather than the venturi) therefore with = reduced=20 density you have reduced suction and reduced fuel and leaner = mixture.=20 However I will clarify that when next we talk.
I find this all very=20 interesting!
George ( down under)
 
 
 
Well I'll be Ed,
2.4137sq" =3D (.877x.877xPi =3D = 2.416), therefore=20 .877 Radius or 1.754 Dia or 44.55 mm for the carb = opening.
I'm working on the = rest!
George ( down under)
 
For inlet, you take the CFM and you need = one other=20 factor - what velocity do you want through your inlet?  Lets = say you=20 want a higher velocity of around 176 feet/sec (120 MPH)  then = we know=20 that Volume =3D Area * length.  If were want 176 feet/sec = velocity from=20 176 CFM air flow then coverting CFM to cubic feet per second were = have=20 176Ft^3/min / 60 Second/Minute =3D 29.333 Ft^3/=20 = Second
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