X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from cdptpa-omtalb.mail.rr.com ([75.180.132.121] verified) by logan.com (CommuniGate Pro SMTP 5.3.3) with ESMTP id 4154026 for flyrotary@lancaironline.net; Fri, 05 Mar 2010 21:37:22 -0500 Received-SPF: pass receiver=logan.com; client-ip=75.180.132.121; envelope-from=eanderson@carolina.rr.com Return-Path: X-Authority-Analysis: v=1.0 c=1 a=ayC55rCoAAAA:8 a=arxwEM4EAAAA:8 a=QdXCYpuVAAAA:8 a=7g1VtSJxAAAA:8 a=ekHE3smAAAAA:20 a=UretUmmEAAAA:8 a=B2njKpslnhgLXp57N5cA:9 a=o5K2QCZeuEA5u7zqHMUA:7 a=hqwGoU0APnjihYmYD3JHe-DYzqkA:4 a=wPNLvfGTeEIA:10 a=1vhyWl4Y8LcA:10 a=SSmOFEACAAAA:8 a=R7ESLSo7hzNZd332zfkA:9 a=GlUu7mntE2TC-N4t7OcA:7 a=rI-CvUt4VRwL4qWgtsZdwX5HScsA:4 X-Cloudmark-Score: 0 X-Originating-IP: 75.191.186.236 Received: from [75.191.186.236] ([75.191.186.236:2763] helo=computername) by cdptpa-oedge03.mail.rr.com (envelope-from ) (ecelerity 2.2.2.39 r()) with ESMTP id 8A/E9-21054-FBFB19B4; Sat, 06 Mar 2010 02:36:47 +0000 From: "Ed Anderson" Message-ID: <8A.E9.21054.FBFB19B4@cdptpa-omtalb.mail.rr.com> To: "'Rotary motors in aircraft'" Subject: TB size, Travel and Power Date: Fri, 5 Mar 2010 21:36:55 -0500 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_000E_01CABCAB.FA0017A0" X-Mailer: Microsoft Office Outlook, Build 11.0.5510 Thread-Index: Acq81eKYByjGNrosTVC0NddSGlA9LA== X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5579 This is a multi-part message in MIME format. ------=_NextPart_000_000E_01CABCAB.FA0017A0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable I am apparently not doing a very good job making the point about the relationship between throttle body size, throttle travel and engine = power clear. So here is another try at it - using extreme examples and no = math. Let=92s assume your volumetric efficiency is 100% (no losses). =20 IF you put a =BD =94 dia TB on you engine. You could have it wide open = and your engine (under normal prop load) probably wouldn=92t turn 4000 rpm. That = is because even wide open, the =BD=94 dia TB restricts airflow sufficiently = - that the manifold air density never approaches the ambient air density. = Since we know that the engine power is directly proportional to the density of = air in the combustion chamber =96 and this density is limited in this case to = less than ambient, you engine is not going to produce much power, certainly = not full power. So this bit of information tells us =93Bigger Lithium = Crystals, Scotty!!=94 =96 i.e try a larger throttle body.=20 =20 Now if you keep enlarging the diameter of the TB you would find that at fully open -your engine would be producing more power than it was, but perhaps still not the maximum power it is capable of. This is because = the air density in the manifold has increase due to the less restrictive = flow, but is still below ambient. This is due to the better, but still restrictive effect of the TB size on the air flow. Now if you continued enlarging the TB size, you would reach a point where with the TB just reaching fully open - your manifold air density is exactly ambient and = your engine is producing all the power it is going to. =20 Now if you enlarge the TB even further, you will simply find that you = can cause the manifold pressure (air density) to reach ambient without = opening the TB fully. Its simply large enough that all the air the engine can = use (ambient air density point) is met at partial throttle opening. In = fact , you can certainly continue to advance the throttle thereby opening the throttle plate even more =96 but, you are not going to increase the air density in the manifold and therefore you will not produce any = additional power for that additional throttle travel. =20 Bigger Throttle body=92s result in more power only up to the point the = airflow they permit causes manifold air density to reach ambient. Beyond that point, the only thing they do is provide frustration =96 by having all = that throttle travel remaining which does nothing to produce more power {:>). =20 Now if you can somehow lighten the load on your engine, then engine can turn faster providing more =93suction=94 on the manifold volume reducing = the air density below ambient, now opening your =93oversize=94 TB a bit more = will produce more power because you are increasing the airflow again to the = point where the equilibrium point between ambient air density in the manifold = and rpm is again reached. Lighten the load further and you can again = increase engine power by opening your TB more. Etc, etc. =20 =20 Ah, ain=92t this hobby wonderful {:>)=20 =20 =20 Ed =20 Ed Anderson Rv-6A N494BW Rotary Powered Matthews, NC eanderson@carolina.rr.com http://www.andersonee.com http://www.dmack.net/mazda/index.html http://www.flyrotary.com/ http://members.cox.net/rogersda/rotary/configs.htm#N494BW http://www.rotaryaviation.com/Rotorhead%20Truth.htm =20 =20 ------=_NextPart_000_000E_01CABCAB.FA0017A0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

I am apparently not doing a very good job making the = point about the relationship between throttle body size, throttle travel and = engine power clear.=A0 So here is another try at it - using extreme examples = and no math.=A0 Let’s assume your volumetric efficiency is 100% (no = losses).

 

IF you put a =BD ” dia TB on you engine.=A0 You = could have it wide open and your engine (under normal prop load) probably = wouldn’t turn 4000 rpm.=A0 That is because even wide open, the =BD” dia TB = restricts airflow sufficiently - that the manifold air density never approaches = the ambient air density.=A0 Since we know that the engine power is directly proportional to the density of air in the combustion chamber – and = this density is limited in this case to less than ambient, you engine is not = going to produce much power, certainly not full power.=A0 So this bit of = information tells us “Bigger Lithium Crystals, Scotty!!” – i.e = =A0try a larger throttle body.

 

Now if you keep enlarging the diameter of the TB you = would find that at fully open -your engine would be producing more power than = it was, but perhaps still not the maximum power it is capable of.=A0 This is = because the air density in the manifold has increase due to the less restrictive flow, = but is still below ambient.=A0 This is due to the better, but still restrictive = effect of the TB size on the air flow.=A0 Now if you continued enlarging the TB = size, you would reach a point where with the TB just reaching fully open - = your manifold air density is exactly ambient and your engine is producing all = the power it is going to.

 

Now if you enlarge the TB even further, you will = simply find that you can cause the manifold pressure (air density) to reach ambient = without opening the TB fully.=A0 Its simply large enough that all the air the = engine can use (ambient air density point) =A0is met at partial throttle = opening.=A0 In fact , you can certainly continue to advance the throttle thereby opening the = throttle plate even more – but, you are not going to increase the air = density in the manifold and therefore you will not produce any additional power for = that additional throttle travel.

 

Bigger Throttle body’s result in more power = only up to the point the airflow they permit causes manifold air density to reach = ambient.=A0 Beyond that point, the only thing they do is provide frustration – = by having all that throttle travel remaining which does nothing to produce more = power {:>).

 

Now if you can somehow =A0lighten the load on your = engine, then engine can turn faster providing more “suction” on the = manifold volume reducing the air density below ambient, now opening your = “oversize” TB a bit more will produce more power because you are increasing the = airflow again to the point where the equilibrium point between ambient air = density in the manifold and rpm is again reached.=A0 Lighten the load further and = you can again increase engine power by opening your TB more. Etc, = etc.

 

 

Ah, ain’t this hobby wonderful {:>) =

 

 

Ed

 

Ed Anderson

Rv-6A N494BW Rotary Powered

Matthews, NC

eanderson@carolina.rr.com

http://www.andersonee.com

http://www.dmack.net/mazda/index.html

http://www.flyrotary.com/

http://members.cox.net/rogersda/rotary/configs.htm#N494BW

http://www.r= otaryaviation.com/Rotorhead%20Truth.htm

 

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