Return-Path: Sender: (Marvin Kaye) To: flyrotary Date: Fri, 23 May 2003 17:42:52 -0400 Message-ID: X-Original-Return-Path: Received: from ms-smtp-03.southeast.rr.com ([24.93.67.84] verified) by logan.com (CommuniGate Pro SMTP 4.1b6) with ESMTP id 2360538 for flyrotary@lancaironline.net; Fri, 23 May 2003 09:58:56 -0400 Received: from o7y6b5 (clt78-198.carolina.rr.com [24.93.78.198]) by ms-smtp-03.southeast.rr.com (8.12.5/8.12.2) with SMTP id h4NDvLZp003351 for ; Fri, 23 May 2003 09:57:22 -0400 (EDT) X-Original-Message-ID: <002401c32134$8e3415e0$1702a8c0@WorkGroup> From: "Ed Anderson" X-Original-To: "Rotary motors in aircraft" References: Subject: Re: [FlyRotary] Tuned Induction X-Original-Date: Fri, 23 May 2003 10:06:50 -0400 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0021_01C32113.06F01B40" X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1106 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 This is a multi-part message in MIME format. ------=_NextPart_000_0021_01C32113.06F01B40 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable ----- Original Message -----=20 From: Al Gietzen=20 To: Rotary motors in aircraft=20 Sent: Thursday, May 22, 2003 5:10 PM Subject: [FlyRotary] Tuned Induction Al, I don't know much about induction systems and they appear to be as = much "Magic" as science. Obviously, I don't either. But I'd like to be able to get it out of the = realm of magic. My own personal story is that when I had a Weber throttle body with = two 2" dia throats with a relative short length induction (about 1/2 my = current length), my static rpm was 5000 rpm, my top speed was 182 MPH = TAS and rate of climb was around 900 fpm. When I created an intake = using smaller (1 5/8 and 1 3/8" dia tubes) of the length that = theoretically are tuned to provide the "dynamic charging effect" at 5900 = rpm, my static went up to 5300 rpm, my ROC went up to 1200 fpm and my = top speed to 196 MPH TAS. So while I can't prove that my current = induction system is better "tuned" to my operating regime and rpm - I = sure like the improved results much better.=20 Given that speed goes by the cube root of HP; the speed change suggests = that your power increased by 25%; so maybe something suspect there, or = there was something really wrong with your original setup. What else = changed besides your runner length? Al,=20 The changes were runner length (longer by approx 20%) and diameter of = tubes (smaller by 25%). =20 After reading Paul Yaw's tech stuff about the importance of the velocity = of the air/fuel mixture in an intake. I calculated that on my original = manifold (two 2" dia throats) that my intake velocity (assuming I was = producing 180 HP which I defintely was NOT!) would have been approx 71 = MPH. According to what I read, you want much higer air velocity. The = theory (If I understood it) was that the interia of a faster moving slug = of air/fule would stuff more air/fuel mixture into the chamber than = slower moving air/fuel mixture. My change in tube diameter and length = more than double my air velocity (calculated not measured) through the = tubes and into the chamber Below is an extract of Paul Yaws very understandable and excellent = series on airflow for the rotary: "....Velocity alone determines at what rpm peak torque and horsepower = will occur for a given intake and exhaust duration. (Duration is the = amount of time that the ports are open.) As most readers know, the = intake port on a rotary engine closes well after bottom dead = center.(BDC) What this means, is that the rotor is starting to compress = the mixture while the port is still open. When velocity is low, some of = the mixture will be squeezed back into the intake manifold. If velocity = is high, the inertia of the incoming mixture will overcome the rising = pressure of the chamber, and continue to pack mixture into the engine = well after bdc. This effect is called inertial supercharging, and you = can feel this while you are driving. At low speed, the engine does not = make much torque, but as rpm increases, the engine really starts to put = you back in your seat. The power increase that you are feeling is the = result of the extra mixture being packed into the chamber as a result of = higher intake velocity.=20 Now that you know how important velocity is, you must also understand = that there is such a thing as excessive intake velocity. It has been = determined that once the velocity in the induction system reaches = approximately .6 mach, (60% of the speed of sound) the engine will "top = out". Beyond this speed the additional airflow into the motor does not = create enough extra power to overcome the pumping losses, and the result = is a decrease in horsepower. It should be obvious now that velocity is = critical, and must be carefully balanced with airflow. " So while my air velocity falls quite short of Mach 0.6, I think the = smaller diameter/longer runners did help quite a bit. FWIW=20 Ed Anderson ------=_NextPart_000_0021_01C32113.06F01B40 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

----- Original Message ----- =
From: Al=20 Gietzen
To: Rotary motors in aircraft
Sent: Thursday, May 22, = 2003 5:10=20 PM
Subject: [FlyRotary] Tuned Induction



Al, I don't = know much=20 about induction systems and they appear to be as much "Magic" as=20 science.

Obviously, I don=92t either.  = But I=92d=20 like to be able to get it out of the realm of magic.
 My own=20 personal  story is that when I had a Weber throttle body with two = 2" dia=20 throats with a relative short length induction (about 1/2 my current = length), my=20 static rpm was 5000 rpm, my top speed was 182 MPH TAS and rate of climb = was=20 around 900 fpm.  When I created an intake using smaller (1 5/8 and = 1 3/8"=20 dia tubes) of the length that theoretically are tuned to provide the = "dynamic=20 charging effect" at 5900 rpm, my static went up to 5300 rpm, my ROC went = up to=20 1200 fpm and my top speed to 196 MPH TAS.   So while I can't = prove=20 that my current induction system is better "tuned" to my operating = regime and=20 rpm - I sure like the improved results much better.

Given that = speed=20 goes by the cube root of HP; the speed change suggests that your power = increased=20 by 25%; so maybe something suspect there, or there was something really = wrong=20 with your original setup.  What else changed besides your runner=20 length?


Al,
The changes were runner length (longer = by=20 approx 20%) and diameter of tubes (smaller by 25%).
 
After = reading=20 Paul Yaw's tech stuff about the importance of the velocity of the = air/fuel=20 mixture in an intake.  I calculated that on my original manifold = (two 2"=20 dia throats) that my intake velocity (assuming I was producing 180 HP = which I=20 defintely was NOT!) would have been approx 71 MPH.  According to = what I=20 read, you want much higer air velocity.  The theory (If I = understood it)=20 was that the interia of a faster moving slug of air/fule   = would stuff=20 more air/fuel mixture into the chamber than slower moving air/fuel=20 mixture.  My change in tube diameter and length more than double my = air=20 velocity (calculated not measured) through the tubes and into the=20 chamber

Below is an extract of Paul Yaws very understandable and=20 excellent series on airflow for the rotary:

"....Velocity alone=20 determines at what rpm peak torque and horsepower will occur for a given = intake=20 and exhaust duration. (Duration is the amount of time that the ports are = open.)=20 As most readers know, the intake port on a rotary engine closes well = after=20 bottom dead center.(BDC) What this means, is that the rotor is starting = to=20 compress the mixture while the port is still open. When=20 velocity is low, some of the mixture will be squeezed back into the = intake=20 manifold. If velocity is high, the inertia of the incoming mixture will = overcome=20 the rising pressure of the chamber, and continue to pack mixture into = the engine=20 well after bdc. This effect is called inertial supercharging, and = you can=20 feel this while you are driving. At low speed, the engine does not make = much=20 torque, but as rpm increases, the engine really starts to put you back = in your=20 seat. The power increase that you are feeling is = the result=20 of the extra mixture being packed into the chamber as a result of higher = intake=20 velocity.

Now that you know how important velocity is, = you must=20 also understand that there is such a thing as excessive intake velocity. = It has=20 been determined that once the velocity in the induction system reaches=20 approximately .6 mach, (60% of the speed of sound) the engine will "top = out".=20 Beyond this speed the additional airflow into the motor does not create = enough=20 extra power to overcome the pumping losses, and the result is a decrease = in=20 horsepower. It should be obvious now that velocity is critical, and must = be=20 carefully balanced with airflow. "
 
 

So while my air velocity falls quite short of Mach 0.6, I think = the=20 smaller diameter/longer runners did help quite a bit.
FWIW

Ed = Anderson
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