Return-Path: Sender: "Marvin Kaye" To: lml@lancaironline.net Date: Wed, 29 Dec 2004 23:30:32 -0500 Message-ID: X-Original-Return-Path: Received: from imo-d23.mx.aol.com ([205.188.139.137] verified) by logan.com (CommuniGate Pro SMTP 4.2.5) with ESMTP id 583787 for lml@lancaironline.net; Wed, 29 Dec 2004 22:59:32 -0500 Received-SPF: pass receiver=logan.com; client-ip=205.188.139.137; envelope-from=Sky2high@aol.com Received: from Sky2high@aol.com by imo-d23.mx.aol.com (mail_out_v37_r3.8.) id q.96.1d92343b (4410) for ; Wed, 29 Dec 2004 22:58:59 -0500 (EST) From: Sky2high@aol.com X-Original-Message-ID: <96.1d92343b.2f04d703@aol.com> X-Original-Date: Wed, 29 Dec 2004 22:58:59 EST Subject: Re: [LML] Re: RAM, SLAM, BAM - MAP, WHAP, ZAP - HUH? X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1104379139" X-Mailer: 9.0 Security Edition for Windows sub 5000 -------------------------------1104379139 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en In a message dated 12/29/2004 8:39:42 P.M. Central Standard Time, =20 Walter@advancedpilot.com writes: **MAP (displayed in inches of Hg) is not actually =E2=80=9Cabsolute=E2=80= =9D since it=20 is ambient pressure (AP) plus gauge sensed pressure (GP). That is =20 indicated MAP =3D AP + GP. At wide open throttle (WOT), GP can be =20 positive from pressure created via a ram air induction system and =20 limited by KIAS. GP can be negative (vacuum) at reduced throttle=20 (reducing air in the induction system). Ram air may overcome the=20 slight closing of the throttle to where the MAP =3D AP.** I can see how the GP could be higher than ambient in a non-running=20 induction system undergoing ram air effect. Are you saying that in a=20 RUNNING engine's intake that the GP can be higher than ambient? If=20 so, can you explain the physics of this to me. I must be missing=20 something. Are you measuring that the RAM air effect can be so high as=20 to overcome the air sucked in by the engine? Walter, =20 I am only talking about running engines in flight, not on a laboratory =20 stand. At WOT and 200 KIAS utilizing a ram air induction system, the GP co= mponent=20 of indicated MAP is positive, perhaps even by as much as 2" Hg. Thus, the=20 MAP =3D AP + GP. Lets say at an altitude where the AP is 20" and the GP is= +2",=20 the MAP is 22". At the same altitude, suppose the throttle is reduced,=20 yielding a GP of -2" (vacuum). thus the MAP would be 18" (momentarily, as t= he ram=20 would be reduced when the air speed bled off), a 4" Hg swing. If the=20 throttle was closed only slightly, enough to reduce the total stream pressu= re 1"=20 (to 21"), some ram air would still keep the MAP higher than AP alone. =20 ** This gives rise to the question: Should I connect the AP port to the=20 same static air used by the altimeter?** It sure looks that way, doesn't it? Yes, and I wonder if pressurized aircraft do just that. =20 **Side Note: If an electronic ignition is used and one of the=20 controlling parameters is MAP, the ambient pressure is obtained from=20 the position of the sensor, generally located in the =E2=80=9Cbrain=E2=80= =9D box that=20 is often placed under the cowling and is sensing the cooling air output=20 pressure. This is generally slightly above =E2=80=9Cstatic=E2=80=9D ambient= pressure. =20 I misplaced the measurement I once made of this but I remember it was=20 maybe about .25=E2=80=9D Hg greater. At cruise, this is a true difference=20= of=20 about .5=E2=80=9D in what the MAP indicator is showing and what the electro= nic=20 ignition is using for timing adjustments.** In answer to your side note, there are some pitfalls in using MAP as a =20 determining factor in setting timing. The only factor which trumps all=20 others is thetaPP. The optimal thetaPP is about 16. The major factor=20 after that is peak pressure being maintained below the detonation=20 margin. The use of multiple factors in attempting to calculate those=20 answers is, at best, iffy. It's much better to measure thetaPP than to=20 try to calculate it.. It's the only way I've seen that has the=20 capability to maximize output and be certain that the detonation margin=20 is maintained. Regardless of the ideal, my commentary was only to point out that what you =20 see ain't necessarily what you got. The fact is that extant electronic =20 ignitions have an option that allows combinations of RPM and MAP (or a facsi= mile =20 thereof) to alter timing - usually by advancing the timing. An option with=20= the=20 Lightspeed system is a display that shows the MAP used for making such =20 adjustments - it may not match the MAP display on on engine monitoring syst= em. =20 **Side note: Consider that ram air can raise the induction air=20 pressure higher than that utilized by the fuel injectors (obtained, for=20 example, from the upper cooling plenum) to help atomize the fuel. This=20 may suppress the best atomization and shrouded injectors utilizing the=20 higher ram air, available before the throttle body, may improve=20 atomization. Such a system is similar to the way super/turbo charged=20 engines operate.** Yes, it appears that the optimal upper deck pressure on injectors may=20 be in the area of a 3 psi differential. That's interesting, 3 psi is 6.1" Hg. - not possible for me no matter how=20 fast I go. The best I can hope for is 0 psi at WOT or by flying with a=20 greatly reduced throttle setting. But, at least it is not negative psi. Do= es this=20 mean that turbo/super charged systems maintain such a differential? If onl= y=20 I could use the 12-port electronic injectors supplied with my motorcycle an= d,=20 they don't need no stink'nr to help with atomization. =20 Scott Krueger AKA Grayhawk Lancair N92EX IO320 Aurora, IL (KARR) -------------------------------1104379139 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en
In a message dated 12/29/2004 8:39:42 P.M. Central Standard Time,=20 Walter@advancedpilot.com writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>**MAP=20 (displayed in inches of Hg) is not actually =E2=80=9Cabsolute=E2=80=9D sin= ce it
is ambient=20 pressure (AP) plus gauge sensed pressure (GP).   That is=20
indicated MAP =3D AP + GP.  At wide open throttle (WOT), GP can b= e=20
positive from pressure created via a ram air induction system and=20
limited by KIAS.   GP can be negative (vacuum) at reduced=20 throttle
(reducing air in the induction system).  Ram air may=20 overcome the
slight closing of the throttle to where the MAP =3D=20 AP.**

I can see how the GP could be higher than ambient in a=20 non-running
induction system undergoing ram air effect.  Are you=20 saying that in a
RUNNING engine's intake that the GP can be higher tha= n=20 ambient?   If
so, can you explain the physics of this to=20 me.  I must be missing
something.  Are you measuring that th= e=20 RAM air effect can be so high as
to overcome the air sucked in by the=20 engine?
Walter,
 
I am only talking about running engines in flight, not on a laboratory=20 stand.  At WOT and 200 KIAS utilizing a ram air induction system, the G= P=20 component of indicated MAP is positive, perhaps even by as much as 2" Hg.&nb= sp;=20 Thus, the MAP =3D AP + GP.  Lets say at an altitude where the AP is 20"= and=20 the GP is +2", the MAP is 22".  At the same altitude, suppose the throt= tle=20 is reduced, yielding a GP of -2" (vacuum). thus the MAP would be 18"=20 (momentarily, as the ram would be reduced when the air speed bled off), a 4"= Hg=20 swing.  If the throttle was closed only slightly, enough to reduce the=20 total stream pressure 1" (to 21"), some ram air would still keep the MAP hig= her=20 than AP alone.
 
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size= =3D2>
**=20 This gives rise to the question: Should I connect the AP port to the
s= ame=20 static air used by the altimeter?**

  It sure looks that way,=20 doesn't it?
Yes, and I wonder if pressurized aircraft do just that.
 
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20 size=3D2>

   **Side Note:  If an electronic ignition= is=20 used and one of the
controlling parameters is MAP, the ambient pressur= e is=20 obtained from
the position of the sensor, generally located in the=20= =E2=80=9Cbrain=E2=80=9D=20 box that
is often placed under the cowling and is sensing the cooling=20= air=20 output
pressure.  This is generally slightly above =E2=80=9Cstati= c=E2=80=9D ambient=20 pressure. 
I misplaced the measurement I once made of this but I=20 remember it was
maybe about .25=E2=80=9D Hg greater.  At cruise,=20= this is a=20 true difference of
about .5=E2=80=9D in what the MAP indicator is show= ing and what=20 the electronic
ignition is using for timing adjustments.**

In=20 answer to your side note, there are some pitfalls in using MAP as a=20
determining factor in setting timing.  The only factor which trum= ps=20 all
others is thetaPP.  The optimal thetaPP is about 16.  Th= e=20 major factor
after that is peak pressure being maintained below the=20 detonation
margin.  The use of multiple factors in attempting to=20 calculate those
answers is, at best, iffy.  It's much better to=20 measure thetaPP than to
try to calculate it..  It's the only way=20= I've=20 seen that has the
capability to maximize output and be certain that th= e=20 detonation margin
is maintained.
Regardless of the ideal, my commentary was only to point out that what=20= you=20 see ain't necessarily what you got.  The fact is that extant electronic= =20 ignitions have an option that allows combinations of RPM and MAP (or a facsi= mile=20 thereof) to alter timing - usually by advancing the timing.  An option=20= with=20 the Lightspeed system is a display that shows the MAP used for making such=20 adjustments - it may not match the MAP display on on engine monitoring=20 system.
 
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000=20 size=3D2>
**Side note:  Consider that ram air can raise the induct= ion=20 air
pressure higher than that utilized by the fuel injectors (obtained= ,=20 for
example, from the upper cooling plenum) to help atomize the=20 fuel.  This
may suppress the best atomization and shrouded inject= ors=20 utilizing the
higher ram air, available before the throttle body, may=20 improve
atomization.  Such a system is similar to the way super/t= urbo=20 charged
engines operate.**

Yes, it appears that the optimal upp= er=20 deck pressure on injectors may
be in the area of a 3 psi=20 differential.
 
That's interesting,  3 psi is 6.1" Hg. - not possible for me no ma= tter=20 how fast I go.  The best I can hope for is 0 psi at WOT or by=20 flying with a greatly reduced throttle setting. But, at least it i= s=20 not negative psi.  Does this mean that turbo/super charged systems= =20 maintain such a differential?  If only I could use the 12-port=20 electronic injectors supplied with my motorcycle and, they don't need no=20 stink'nr to help with atomization.  
 
 
Scott Krueger=20 AKA Grayhawk
Lancair N92EX IO320 Aurora, IL=20 (KARR)

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