X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from mtiwmhc12.worldnet.att.net ([204.127.131.116] verified) by logan.com (CommuniGate Pro SMTP 5.1.11) with ESMTP id 2269779 for flyrotary@lancaironline.net; Fri, 17 Aug 2007 21:04:58 -0400 Received-SPF: none receiver=logan.com; client-ip=204.127.131.116; envelope-from=keltro@att.net Received: from mwebmail18.att.net ([204.127.135.57]) by worldnet.att.net (mtiwmhc12) with SMTP id <2007081801041111200ogn57e>; Sat, 18 Aug 2007 01:04:21 +0000 Received: from [4.245.37.20] by mwebmail18.att.net; Sat, 18 Aug 2007 01:04:11 +0000 From: keltro@att.net (Kelly Troyer) To: "Rotary motors in aircraft" Subject: [FlyRotary] Air/fuel flow Date: Sat, 18 Aug 2007 01:04:11 +0000 Message-Id: <081820070104.21224.46C6458900094942000052E82160376316019D9B040A05@att.net> X-Mailer: AT&T Message Center Version 1 (Mar 24 2007) X-Authenticated-Sender: a2VsdHJvQGF0dC5uZXQ= MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="NextPart_Webmail_9m3u9jl4l_21224_1187399051_0" --NextPart_Webmail_9m3u9jl4l_21224_1187399051_0 Content-Type: text/plain Content-Transfer-Encoding: 8bit George, Not Ed and not great at math but from my skydiving days the figure of 176 feet per sec (approx 120 mph) is called terminal velocity for the average human body in a flat stable freefall position........Just a bit of trivia......... -- Kelly Troyer "Dyke Delta"_13B ROTARY Engine "RWS"_RD1C/EC2/EM2 "Mistral"_Backplate/Oil Manifold -------------- Original message from "George Lendich" : -------------- 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. 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. 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" = (.877x.877xPi = 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 = 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 = 29.333 Ft^3/ Second --NextPart_Webmail_9m3u9jl4l_21224_1187399051_0 Content-Type: text/html Content-Transfer-Encoding: 8bit
George,
    Not Ed and not great at math but from my skydiving days the figure
of 176 feet per sec (approx 120 mph) is called terminal velocity for the
average human body in a flat stable freefall position........Just a bit of
trivia.........
--
Kelly Troyer
"Dyke Delta"_13B ROTARY Engine
"RWS"_RD1C/EC2/EM2
"Mistral"_Backplate/Oil Manifold




-------------- Original message from "George Lendich" <lendich@optusnet.com.au>: --------------

 
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.
 
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.
 
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" = (.877x.877xPi = 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 = 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 = 29.333 Ft^3/ Second
--NextPart_Webmail_9m3u9jl4l_21224_1187399051_0--