X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from qw-out-2122.google.com ([74.125.92.27] verified) by logan.com (CommuniGate Pro SMTP 5.3.3) with ESMTP id 4154459 for flyrotary@lancaironline.net; Sat, 06 Mar 2010 10:07:08 -0500 Received-SPF: pass receiver=logan.com; client-ip=74.125.92.27; envelope-from=rwstracy@gmail.com Received: by qw-out-2122.google.com with SMTP id 8so1171083qwh.25 for ; Sat, 06 Mar 2010 07:06:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:sender:received:in-reply-to :references:date:x-google-sender-auth:message-id:subject:from:to :content-type; bh=BKjL87sScQa+YOUuE0zS2C/9maQ2Wumnr+0zBv/OTmI=; b=SAL31MiD1T9dkELQOvQu2nzIw9D0gJwgWXN/oBA49NWHowzlyuHaAbltehUNzkHqiW qCZMuKsLlgIEPzowwkwVA08bOr1mVOHxr+lYbzxTlCnHclBS6LYoAOZUoWeTHcN0hPpc vsLcIPaRk6blMiIerhpprl+tchOmQk2c55jCc= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:content-type; b=i1foDjsD3vrIA2oU5td4I93IQ6d2PG0ZGIuH8UoK342gcuhqVQmftJ+qr7k+wbiHxX dAOr1Xl4qwArPBJM9Kn0d/6UTXOwYTV61dPzZkAi7ZkivO0gK+E9AVGOypa0uxtkyVBx AzoFSGpG65x7tn/+4TEENhzyMuJwd5G06bbdY= MIME-Version: 1.0 Sender: rwstracy@gmail.com Received: by 10.224.35.163 with SMTP id p35mr1228741qad.6.1267887991392; Sat, 06 Mar 2010 07:06:31 -0800 (PST) In-Reply-To: References: Date: Sat, 6 Mar 2010 07:06:31 -0800 X-Google-Sender-Auth: 50a940fa5a21cfe5 Message-ID: <1b4b137c1003060706u5722b895ya37a1ef56dc2884c@mail.gmail.com> Subject: Re: [FlyRotary] Re: TB size, Travel and Power From: Tracy Crook To: Rotary motors in aircraft Content-Type: multipart/alternative; boundary=00c09f9db0ec578c750481232de9 --00c09f9db0ec578c750481232de9 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Mike, you are measuring the MP exactly where you should, You can't do it properly anywhere else, at least not with a simple instrument. But are you at last confirming that you DO have full ambient MP at 2/3 throttle setting? That IS an important question if you want to know the right answer to your question. BTW, ditch the vacuum gauge (if that's what you are using) and get a proper MP gauge. Tracy On Fri, Mar 5, 2010 at 9:30 PM, Mike Wills wrote: > Ed, > > I hear what your saying (and I get it). Here's the thing, and I admit I > may have a misunderstanding here. Your explanation applies if you are > measuring manifold pressure essentially at the rotor face. If you measure= MP > closer to the TB as I do unfortunately, it is possible to see ambient at > full throttle but have restrictions in the intake tract that would result= in > less than ambient at the rotor face. Conversely (and again theory - I'm o= pen > to being shown wrong here), a properly designed DIE manifold would show > ambient MP measured at the TB and greater than ambient measured at the ro= tor > face. > > I accept that by trimming the prop I can lighten the load and gain some H= P > (though some here seem to think that HP will increase linearly with RPM t= o > infinity and I don=92t buy that either). But as you alluded to in > your previous, there's some potential for mistake in trimming any prop un= til > you are quite sure that you are not HP limited by something other than lo= ad. > And I'm not sure yet. Just a feeling based on the fact that I'm using a c= ut > down RX-7 TB that=92s maxed out about 1/3 short of fully open. And honest= ly I > still havent dug any deeper because the airplane is flying well and has g= ood > performance. But sooner or later I'm going to want to get more than the > 5700RPM I'm currently getting - I want all the performance that=92s there= . > > Mike Wills > > *From:* Ed Anderson > *Sent:* Friday, March 05, 2010 6:36 PM > *To:* Rotary motors in aircraft > *Subject:* [FlyRotary] TB size, Travel and Power > > 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). > > > > IF you put a =BD =94 dia TB on you engine. You could have it wide open a= nd > 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 sufficient= ly - > that the manifold air density never approaches the ambient air density. > Since we know that the engine power is directly proportional to the densi= ty > 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. > > > > 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 th= e > 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 yo= ur > 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 openin= g > the TB fully. Its simply large enough that all the air the engine can us= e > (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. > > > > 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 a= ll > that throttle travel remaining which does nothing to produce more power > {:>). > > > > 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 po= int > where the equilibrium point between ambient air density in the manifold a= nd > rpm is again reached. Lighten the load further and you can again increas= e > engine power by opening your TB more. Etc, etc. > > > > > > Ah, ain=92t 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.rotaryaviation.com/Rotorhead%20Truth.htm > > > --00c09f9db0ec578c750481232de9 Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: quoted-printable
Mike,
=A0=A0 you are measuring the MP exactly where you should,=A0=A0 You ca= n't do it properly anywhere else, at least not with a simple instrument= .
=A0
But are you at last confirming that you DO have full ambient MP at 2/3= throttle setting?=A0=A0 That IS an important question if you want to know = the right answer to your question.=A0=A0=A0 BTW, ditch the vacuum gauge (if= that's what you are using) and get a proper MP gauge.
=A0
Tracy

On Fri, Mar 5, 2010 at 9:30 PM, Mike Wills <rv-4mike@cox.net&g= t; wrote:
Ed,
=A0
=A0I hear what your saying (and I get it).=A0He= re's the thing, and I admit I may have a misunderstanding here.=A0Your = explanation=A0applies if you are measuring manifold pressure essentially at= the rotor face.=A0If you measure MP closer to the TB as I do unfortunately= , it is possible to see ambient at full throttle but have restrictions in t= he intake tract that would result in less than ambient at the rotor face. C= onversely (and again theory - I'm open to being shown wrong here), a pr= operly designed DIE manifold would show ambient MP measured at the TB and g= reater than ambient measured at the rotor face.
=A0
I accept that by trimming the prop I can lighte= n the load and gain some HP (though some here seem to think that HP will in= crease linearly with RPM to infinity and I don=92t buy that either). But as= you alluded to in your=A0previous, there's some potential for mistake = in trimming any prop until you are quite sure that you are not HP limited b= y something other than load. And I'm not sure yet. Just a feeling based= on the fact that I'm using a cut down RX-7 TB that=92s maxed out about= 1/3 short of fully open. And honestly I still havent dug any deeper becaus= e the airplane is flying well and has=A0good performance. But sooner or lat= er I'm going to want to get more than the 5700RPM I'm currently get= ting - I want all the performance that=92s there.
=A0
Mike Wills

Sent: Friday, March 05, 2010 6:36 PM
Subject: [FlyRotary] TB size, Travel and Power

I am apparently not doing a very good job m= aking the point about the relationship between throttle body size, throttle= travel and engine power clear.=A0 So here is another try at it - using ext= reme examples and no math.=A0 Let=92s assume your volumetric efficiency is = 100% (no losses).

=A0

IF you put a =BD =94 dia TB on you engine.= =A0 You could have it wide open and your engine (under normal prop load) pr= obably wouldn=92t turn 4000 rpm.=A0 That is because even wide open, the =BD= =94 dia TB restricts airflow sufficiently - that the manifold air density n= ever approaches the ambient air density.=A0 Since we know that the engine p= ower is directly proportional to the density of air in the combustion chamb= er =96 and this density is limited in this case to less than ambient, you e= ngine is not going to produce much power, certainly not full power.=A0 So t= his bit of information tells us =93Bigger Lithium Crystals, Scotty!!=94 =96= i.e =A0try a larger throttle body.

=A0

Now if you keep enlarging the diameter of t= he TB you would find that at fully open -your engine would be producing mor= e 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 th= e better, but still restrictive effect of the TB size on the air flow.=A0 N= ow if you continued enlarging the TB size, you would reach a point where wi= th the TB just reaching fully open - your manifold air density is exactly a= mbient and your engine is producing all the power it is going to.

=A0

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 tha= t all the air the engine can use (ambient air density point) =A0is met at p= artial throttle opening.=A0 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 wi= ll not produce any additional power for that additional throttle travel.

=A0

Bigger Throttle body=92s result in more pow= er 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 =96 by having all that throttle travel remaining which does not= hing to produce more power {:>).

=A0

Now if you can somehow =A0lighten 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 yo= ur =93oversize=94 TB a bit more will produce more power because you are inc= reasing the airflow again to the point where the equilibrium point between = ambient air density in the manifold and rpm is again reached.=A0 Lighten th= e load further and you can again increase engine power by opening your TB m= ore. Etc, etc.

=A0

=A0

Ah, ain=92t this hobby wonderful {:>)

=A0

=A0

Ed

=A0

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<= a href=3D"http://www.dmack.net/mazda/index.html" target=3D"_blank">

=A0


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