X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 2 [X] Return-Path: Received: from imo-m26.mx.aol.com ([64.12.137.7] verified) by logan.com (CommuniGate Pro SMTP 5.1.8) with ESMTP id 2021379 for flyrotary@lancaironline.net; Wed, 02 May 2007 10:11:27 -0400 Received-SPF: pass receiver=logan.com; client-ip=64.12.137.7; envelope-from=Lehanover@aol.com Received: from Lehanover@aol.com by imo-m26.mx.aol.com (mail_out_v38_r9.2.) id q.c9c.edd1966 (60432) for ; Wed, 2 May 2007 10:10:18 -0400 (EDT) Received: from MBLK-M10 (mblk-m10.mblk.aol.com [64.12.136.43]) by ciaaol-d01.mail.aol.com (v115.11) with ESMTP id MAILCIAAOLD011-ec1046389bca242; Wed, 02 May 2007 10:10:18 -0400 References: To: flyrotary@lancaironline.net Subject: Re: [FlyRotary] Re: Throttle body size/ other "Paul" issues Date: Wed, 02 May 2007 10:10:18 -0400 In-Reply-To: X-MB-Message-Source: WebUI MIME-Version: 1.0 From: lehanover@aol.com X-MB-Message-Type: User Content-Type: multipart/alternative; boundary="--------MB_8C95ADABF71D88B_1388_7709_MBLK-M10.sysops.aol.com" X-Mailer: AOL WebMail 25698 Received: from 67.101.110.221 by MBLK-M10.sysops.aol.com (64.12.136.43) with HTTP (WebMailUI); Wed, 02 May 2007 10:10:18 -0400 Message-Id: <8C95ADABF71D88B-1388-4175@MBLK-M10.sysops.aol.com> X-AOL-IP: 64.12.136.43 X-Spam-Flag: NO ----------MB_8C95ADABF71D88B_1388_7709_MBLK-M10.sysops.aol.com Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii" When the TB is opened suddenly from idle or near idle, the the very low pressure inside the manifold is replaced by a sudden inrush of local air pressure. So should the local air moving through the manifold not contain enough fuel to provide a viable fuel/air mixture, the engine starts to die. But, as you have noticed, the situation seems worse than that. Not just a stumble. At very low throttle openings, the available air for cylinder filling is far below the actual displacement of the engine. So, the amount of air available to compress before combustion is also very low, so, the effective compression ratio at idle is likewise very low. Just fine for running smoothly at 700 RPM and little to no load. So now we slam the throttle open, the inrush of air roars down the runners and into the chambers with far less than an ideal mixture, and what is the effect on cylinder filling for the next revolution? Why it is outstanding. Maybe over 100%. And it is too lean to light. So when you see that old guy in the Champ, who always kills the mags and goes to full throttle at the same time, as he was told to do back in 42, what is he doing? He is going from a very low cylinder filling idle with low effective compression ratio, with a carb that has no accellerator pump, or, very little accellerator pump, to great cylinder filling and a high effective compression ratio and poor to well over lean mixture, and pop pop. The engine stops in two blades with little to no fuel in the cylinders. And its the original engine, and it has good compression, and its no use telling him otherwise, because he learned it that way, and that way it will stay. Same thing for the rotary. You come in a bit hot, with the power (throttle all the way closed) off and in a beautifull forward slip, and it is going well but a bit too well as it looks like touchdown will be just a hair short of the numbers, with your moron friends watching who will settle for nothing short of a great landing, you snap out of the slip right on the centerline, and after waiting a bit too long you pop open the throttle to extend just a bit, and you get nothing at all. So then a bunch more throttle and nothing, and just as the mains touch a bit too hard, the damn power comes on like a top fuel dragster, and you fly down the centerline a hundred yards, to the same landing you commited at the end of your first solo, 43 years ago. The carburretors cure this with the accelerator pump and jet system, in the same way a big hammer can kill a gnat. It cures it a bunch, with enough fuel to go around the patch once shot into the hole in a long hard stream. Mixture be damned, its way over rich and lasts longer than is ever required for the lean low rev situation. The carbs with no accelerator pump systems have other bleed air gags to do some of the same thing. If you screw with the idle jet too much you can make them act the same as the overlean carb. At low revs an over rich mixture is a happy mixture. It lights easy and burns slow. It reduces the possible detonation of the low RPM big throttle setting (looks like over advanced timing to the engine). Power comes on as the throttle moves, not after it is at the stop and about to go into burner. Lynn E. Hanover Subject: [FlyRotary] Re: Throttle body size/ other "Paul" issues Humm, that very interesting, Lynn. The primary reason I removed the 75 mm TB and reinstalled the 65mm TB was that the engine would "bog" upon rapid opening of the throttle with the larger dia TB. If this was not caused by the large TB then I guess I'm wondering what was causing it as the rest of the induction system was the same. My thinking (apparently in error) was that the sudden change in "effective" area by opening the large TB had a momentary impact on the air velocity in the runners thereby causing the hesitation.. Ed ----- Original Message ----- From: lehanover@aol.com To: Rotary motors in aircraft Sent: Wednesday, May 02, 2007 1:58 AM Subject: [FlyRotary] Re: Throttle body size/ other "Paul" issues On further review, TB size should have no affect on throttle response at all in an injected system. ________________________________________________________________________ AOL now offers free email to everyone. Find out more about what's free from AOL at AOL.com. ----------MB_8C95ADABF71D88B_1388_7709_MBLK-M10.sysops.aol.com Content-Transfer-Encoding: 7bit Content-Type: text/html; charset="us-ascii"
When the TB is opened suddenly from idle or near idle, the the very low pressure inside the manifold is replaced by a sudden inrush of local air pressure. So should the local air moving through the manifold not contain enough fuel to provide a viable fuel/air mixture,  the engine starts to die.

But, as you have noticed, the situation seems worse than that. Not just a stumble.

At very low throttle openings, the available air for cylinder filling is far below the actual displacement of the engine. So, the amount of air available to compress before combustion is also very low, so, the effective compression ratio at idle is likewise very  low.  Just fine for running  smoothly at 700 RPM and little to no load.

So now we slam the throttle open, the inrush of air roars down the runners and into the chambers with far less than an ideal mixture, and what is the effect on cylinder filling for the next revolution?

Why it is outstanding. Maybe over 100%. And it is too lean to light.

 So when you see that old guy in the Champ, who always kills the mags and goes to full throttle at the same time, as he was told to do back in 42,
what is he doing? He is going from a very low cylinder filling idle with low effective compression ratio, with a carb that has no accellerator pump,
or, very little accellerator pump, to great cylinder filling and a high effective compression ratio and poor to well over lean mixture, and pop pop. The engine stops in two blades with little to no fuel in the cylinders.

And its the original engine, and it has good compression, and its no use telling him otherwise, because he learned it that way, and that way it will stay.

Same thing for the rotary. You come in a bit hot, with the power (throttle all the way closed) off and in a beautifull forward slip, and it is going well but a bit too well as it looks like touchdown will be just a hair short of the numbers, with your moron friends watching who will settle for nothing short of a great landing, you snap out of the slip right on the centerline, and after waiting a bit too long you pop open the throttle to extend just a bit, and you get nothing at all. So then a bunch more throttle and nothing, and just as the mains touch a bit too hard, the damn power comes on like a top fuel dragster, and you fly down the centerline a hundred yards, to the same landing you commited at the end of your first solo, 43 years ago.

The carburretors cure this with the accelerator pump and jet system, in the same way a big hammer can kill a gnat. It cures it a bunch, with enough fuel to go around the patch once shot into the hole in a long hard stream. Mixture be damned, its way over rich and lasts longer than is ever required for the lean low rev situation. The carbs with no accelerator pump systems have other bleed air gags to do some of the same thing. If you screw with the idle jet too much you can make them act the same as the overlean carb.

At low revs an over rich mixture is a happy mixture. It lights easy and burns slow. It reduces the possible detonation of the low RPM big throttle setting (looks like over advanced timing to the engine). Power comes on as the throttle moves, not after it is at the stop and about to go into burner.

Lynn E. Hanover


 
 

Subject: [FlyRotary] Re: Throttle body size/ other "Paul" issues

Humm, that very interesting, Lynn.   The primary reason I removed the 75 mm TB and reinstalled the 65mm TB was that the engine would "bog" upon rapid opening of the throttle with the larger dia TB.
 
  If this was not caused by the large TB then I guess I'm wondering what was causing it as the rest of the induction system was the same.  My thinking (apparently in error) was that the sudden change in "effective" area by opening the large TB had a momentary impact on the air velocity in the runners thereby causing the hesitation..  
 
Ed 
----- Original Message -----
Sent: Wednesday, May 02, 2007 1:58 AM
Subject: [FlyRotary] Re: Throttle body size/ other "Paul" issues

On further review,

TB size should have no affect on throttle response at all in an injected system.


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