X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Thu, 24 Oct 2013 12:47:57 -0400 Message-ID: X-Original-Return-Path: Received: from mail.carneal.com ([174.129.224.69] verified) by logan.com (CommuniGate Pro SMTP 6.0.7) with ESMTPS id 6563019 for lml@lancaironline.net; Thu, 24 Oct 2013 12:04:02 -0400 Received-SPF: none receiver=logan.com; client-ip=174.129.224.69; envelope-from=walter@advancedpilot.com Received: (qmail 16810 invoked from network); 24 Oct 2013 16:03:40 -0000 Received: from c-75-70-32-170.hsd1.co.comcast.net (HELO ?10.0.0.3?) (walter@advancedpilot.com@75.70.32.170) by mail.carneal.com with ESMTPA; 24 Oct 2013 16:03:40 -0000 From: Walter Atkinson Mime-Version: 1.0 (Apple Message framework v1283) Content-Type: multipart/alternative; boundary="Apple-Mail=_EB485EB9-5205-47BF-867A-0FD46B07D4A5" Subject: Re: [LML] Hot TITs on X country leg. LIVP X-Original-Date: Thu, 24 Oct 2013 10:03:27 -0600 In-Reply-To: X-Original-To: "Lancair Mailing List" References: X-Original-Message-Id: <4C23D298-825E-482F-B51A-758C8195264B@advancedpilot.com> X-Mailer: Apple Mail (2.1283) --Apple-Mail=_EB485EB9-5205-47BF-867A-0FD46B07D4A5 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=iso-8859-1 Gary: To further the educational exchange: *** I made the assumption that the timing was originally "correct" with = the peak pressure occurring at the right time - not always a valid = assumption. If the burn rate is slowed, the peak cylinder pressure will = occur at a later point in the cycle, reducing the power, but only if it = was originally correct. ** With the thing correct, at takeoff power the thetaPP is closer to TDC = than desirable. So, moving the thetaPP away from TDC increases power. = IN some applications, it would produce MORE power to takeoff on one mag = when the thetaPP would be 16dATDC rather than about 10dATDC. I am NOT = recommending this, just pointing out that the physics is what it is. *** I'd challenge Walter to do a quick dyno test at maybe 15 inches MAP = with only one plug firing. What does the EGT vs fuel flow curve look = like?*** It looks the same. What I think you are referring to is the situation = where the EGT begins to rise when VERY LOP and leaning continues. This = is a normal phenomenon in the AT THAT POINT the exhaust valve beings to = open while a minimal amount f burning is still taking place. This is = normal but MUCH leaner than any mixture that would be useful on the lean = side of peak. This occurs significantly past the BSFC(min) mixture. The problem with doing the mag check after the flight at low power is = that is is poorly diagnostic compared to the in-flight, high power LOP = mag check. Thousands of pilots are currently doing them routinely. The = piston airlines did them routinely in flight with paying passengers on = board. If one is not comfortable with anything, I suggest either not = doing it or getting comfortable. That is a personal choice. It is = helpful to know that there is no scientific reason not to do the = in-flight mag check. Walter Atkinson (225) 939-7508 On Oct 24, 2013, at 7:07 AM, Gary Casey wrote: It is with great reluctance that I would contradict - or even question - = anything said by Walter, but here goes... I said: The slower burn rate on one plug means that a significant portion of the = =3D burn happens during the expansion stroke and less heat is converted to =3D= power. =3D20 Walter replied: Uh, not really. You can actually end up with MORE power, depending on =3D= where the thetaPP started. My reply to his reply: I made the assumption that the timing was = originally "correct" with the peak pressure occurring at the right time = - not always a valid assumption. If the burn rate is slowed, the peak = cylinder pressure will occur at a later point in the cycle, reducing the = power, but only if it was originally correct.=20 I said: Further, when the mixture is leaned past the best power (or maybe peak =3D= EGT) the flame travel is even slower and consequently the exhaust =3D temperature will likely just continue to go up when leaning, not peak =3D and go down. Walter replied: NO! EGT will always rise to peak, then fall when LOP. ALWAYS. Unless, = =3D of course, Sir Isaac Newton was wrong. My reply to his reply: I'm not sure Walter conclusion is always = correct, especially when running on one plug(which was how the = conversation started) and at low BMEP (naturally aspirated at high = altitude. I have tested my Lycoming at 15,000 feet (both plugs firing) = and found that, while there was a noticeable change in slope of the EGT = when going LOP, with the slope leveled off and then continued to go up, = not down. In another case I was completing a flight with the Lightspeed = not firing on all cylinders. The only way I could keep the EGT down to = a reasonable value was to run ROP - when going lean the EGT of that = cylinder would seem to just keep rising as I leaned. My conclusion is = that the EGT doesn't ALWAYS decrease LOP. If the flame travel is = already slow with the thetaPP occurring after the optimum, the opposite = can happen. I'd challenge Walter to do a quick dyno test at maybe 15 = inches MAP with only one plug firing. What does the EGT vs fuel flow = curve look like? Gary ps: There was another post that concerned itself about doing a mag test = in flight. It suggested it be done at only certain conditions. = Actually a single mag should fire the mixture reliably under ALL = conditions. Otherwise there is something wrong. I agree with the idea = of doing inflight mag checks, but I'll admit I have a fundamental = problem shutting things off in flight, so I rarely do them. It makes = all the sense in the world to do a quick mag check after flight. What = better time to find out if maintenance is required?=20 --Apple-Mail=_EB485EB9-5205-47BF-867A-0FD46B07D4A5 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=iso-8859-1  I made the = assumption that the timing was originally "correct" with the peak = pressure occurring at the right time - not always a valid assumption. =  If the burn rate is slowed, the peak cylinder pressure will occur = at a later point in the cycle, reducing the power, but only if it was = originally correct. **
With the thing correct, = at takeoff power the thetaPP is closer to TDC than desirable. So, moving = the thetaPP away from TDC increases power.  IN some applications, = it would produce MORE power to takeoff on one mag when the thetaPP would = be 16dATDC rather than about 10dATDC.  I am NOT recommending this, = just pointing out that the physics is what it = is.


*** I'd challenge Walter to = do a quick dyno test at maybe 15 inches MAP with only one plug firing. =  What does the EGT vs fuel flow curve look = like?***
It looks the same. =  What I think you are referring to  is the situation where the = EGT begins to rise when VERY LOP and leaning continues.  This is a = normal phenomenon in the AT THAT POINT the exhaust valve beings to open = while a minimal amount f burning is still taking place.  This is = normal but MUCH leaner than any mixture that would be useful on the lean = side of peak.  This occurs significantly past the BSFC(min) = mixture.
The problem with doing = the mag check after the flight at low power is that is is poorly = diagnostic compared to the in-flight, high power LOP mag check. =  Thousands of pilots are currently doing them routinely.  The = piston airlines did them routinely in flight with paying passengers on = board.  If one is not comfortable with anything, I suggest either = not doing it or getting comfortable.  That is a personal choice. =  It is helpful to know that there is no scientific reason not to do = the in-flight mag check.

Walter Atkinson
<walter@advancedpilot.com><= /div>
(225) 939-7508





On Oct 24, 2013, at 7:07 = AM, Gary Casey wrote:

It is with = great reluctance that I would contradict - or even question - anything = said by Walter, but here goes...


I = said:

The = slower burn rate on one plug means that a significant portion of the = =3D
burn happens during the = expansion stroke and less heat is converted to =3D
power. =3D20

Walter replied:
Uh, not = really.  You can actually end up with MORE power, depending on = =3D
where the thetaPP = started.

My reply to = his reply:  I made the assumption that the timing was originally = "correct" with the peak pressure occurring at the right time - not = always a valid assumption.  If the burn rate is slowed, the peak = cylinder pressure will occur at a later point in the cycle, reducing the = power, but only if it was originally correct. 

I said:
Further, when the mixture is leaned past the best = power (or maybe peak =3D
EGT) the flame travel is = even slower and consequently the exhaust =3D
temperature will likely just continue to = go up when leaning, not peak =3D
and go down.

Walter = replied:
NO!  EGT will always = rise to peak, then fall when LOP.  ALWAYS.  Unless, = =3D
of course, Sir Isaac = Newton was wrong.

My reply to his reply: =  I'm not sure Walter conclusion is always correct, especially when = running on one plug(which was how the conversation started) and at low = BMEP (naturally aspirated at high altitude.  I have tested my = Lycoming at 15,000 feet (both plugs firing) and found that, while there = was a noticeable change in slope of the EGT when going LOP, with the = slope leveled off and then continued to go up, not down.  In = another case I was completing a flight with the Lightspeed not firing on all cylinders. =  The only way I could keep the EGT down to a reasonable value was = to run ROP - when going lean the EGT of that cylinder would seem to just = keep rising as I leaned.  My conclusion is that the EGT doesn't = ALWAYS decrease LOP.  If the flame travel is already slow with the = thetaPP occurring after the optimum, the opposite can happen.   I'd = challenge Walter to do a quick dyno test at maybe 15 inches MAP with = only one plug firing.  What does the EGT vs fuel flow curve look = like?

Gary

ps:  There was another post that concerned itself about doing a mag test in flight.  It suggested = it be done at only certain conditions.  Actually a single mag = should fire the mixture reliably under ALL conditions.  Otherwise = there is something wrong.  I agree with the idea of doing inflight = mag checks, but I'll admit I have a fundamental problem shutting things = off in flight, so I rarely do them.  It makes all the sense in the = world to do a quick mag check after flight.  What better time to = find out if maintenance is = required? 

= --Apple-Mail=_EB485EB9-5205-47BF-867A-0FD46B07D4A5--