Return-Path: <lancair.list-request@olsusa.com>
Received: from pop3.olsusa.com ([63.150.212.2] verified)
  by logan.com (CommuniGate Pro SMTP 3.5.1)
  with ESMTP id 1010174 for rob@logan.com; Sat, 05 Jan 2002 10:27:53 -0500
Received: from qbert.gami.com ([65.66.11.38]) by pop3.olsusa.com
          (Post.Office MTA v3.5.3 release 223 ID# 0-71866U8000L800S0V35)
          with ESMTP id com for <lancair.list@olsusa.com>;
          Thu, 3 Jan 2002 01:11:15 -0500
Received: by QBERT with Internet Mail Service (5.5.2650.21)
	id <Z66LX1NA>; Thu, 3 Jan 2002 00:22:18 -0600
Message-ID: <52548863F8A5D411B530005004759A93013008@QBERT>
From: George Braly <gwbraly@gami.com>
To: "'lancair.list@olsusa.com'" <lancair.list@olsusa.com>
Subject: RE: V-8 engines for IV's 
Date: Thu, 3 Jan 2002 00:22:17 -0600 
MIME-Version: 1.0
Content-Type: text/plain;
	charset="iso-8859-1"
X-Mailing-List: lancair.list@olsusa.com
Reply-To: lancair.list@olsusa.com

          <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
          <<  Lancair Builders' Mail List  >>
          <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> 
>>


Jack,

In a another message,  you state:

>>I meant no offense to George, who is a noted authority in his field.
However, 
when I see misleading stuff coming from a source having significant 
credibility, sometimes my keyboard just gets excited.<<

I did go back and re-read your message.  I am fairly certain that I
responded to it in a fair manner and that I responded to what you said and
the implications that are rationally derived from what you said.

I certainly hope nothing I said was either 1) inaccurate, or  2) misleading.
If I did, it is my fault, and I apologize to the rest of the folks on the
mail list.

I don't disagree and have never said that I disagree that BMEP is just a
short hand way of describing torque as a function of displacement.

The issue that I was trying to raise in my message to you, and to alert
other readers on the mail list to,  is that the term BMEP is often used in a
misleading way.

Thus, your stating that,  a TSIO-550, for example, which is making 325Hp at
2700 RPM and only needs 176PSI BMEP, and then suggesting that it won't last
very long under those conditions  (or at a lower 65% power) is a statement
that tends to perpetuate the misunderstanding about the significance or lack
of significance  of BMEP.

[Which is why I pointed out that there are about 400 million (my estimate,
based on the fleet size and average utilization over the active life of the
fleet) very successful engine operating hours  at a cruise BMEP of 175 BMEP.
The engine I had in mind is the C-W 3350, also known as the TC-18.  This was
the first (and maybe the only) aircraft piston engine to accumulate a
systematic set of statistical data used for maintaining optimal engine
performance.   Even today, if you look for it, you will see some of those
engines installed with more than 2500 to 3000 hours since the last overhaul
and still in service.]

Whether the TCM  TSIO-550 engine  lives or dies at the typical   262.5 Hp
number (and the corresponding 157.5BMEP at 2400 RPM) that a lot of Lancair
IV/ IV-P owners would like to be able to fly with (that, itself, being based
on another hoary artifact involved in the "industry standard" 75% of 350 Hp
= 262.5 nonsense)  depends almost entirely on the kinds of parameters that I
described in my message to you.  

Based on the known long term operating experience with aircraft piston
engines,  there is no reason why a TSIO-550 engine should not have good
service history durability when operated at a cruise 157 BMEP or higher.
The experience with the TC-18 engines suggests that 176 BMEP IS obtainable
from a durability issue... but, if you run the TC-18 engines like Lancair
would recommend you run the TSIO-550, then neither the TC-18 or the TSIO-550
will last very long at 176BMEP or 157 BMEP, respectively.

The key parameters that determine whether or not a given level of BMEP is
"good" for the engine or "bad" for the engine are:

1) The magnitude of the peak combustion pressure; 

2) How many crank shaft rotational degrees  that peak combustion pressure
event occurs after top dead center (Theta_p-p); and,
  
3) How hot are the CHTs (which, itself, is substantially affected by 1 and
2, above.)


One can make that same 157.5 BMEP with some really bad values for peak
combustion pressure and Theta P-P (similar to the way the Lancair factory's
recent recommendations would have one do that) or you can make that same
BMEP with some rather benign values for the peak combustion pressure and
Theta_p-p, similar to the manner in which C-W  required the TC-18 engines to
be operated in order for C-W to honor their warranty agreement with American
Airlines, Pan Am, Eastern, etc.     On this subject, you might consider
consulting with Capt. John Miller, somewhere around Poughkeepsie, N.Y. (age
around 95, mind sharp as a nail, medical current).   As he put it in a
letter to me,  "I ran those engines about 20,000 hours,  four at a time...
had a crankshaft break, once, only trouble I ever had..."

It is true, that a routine statistical analysis would show that the
durability of the engine in actual service is dependant (inversely) upon the
value of the BMEP.

However, if the study were done properly, and  also controlled for two
further variables,  max cylinder pressure and Theta_p-p,  the results would
end up showing a much stronger correlation with high peak pressures and too
early Theta_p-p values than would be the correlation with BMEP. 

Because of the expense, neither such study will ever be done, again.  But,
fortunately, it already was done.  By C-W. They proved rather conclusively
that if you ignore the three issues I described above, and ran those engines
as Lancair's most recent recommendations would have one run them, at those
same high BMEP values, you would, routinely, destroy the engine in a single
trip to Paris or back.

Bottom line,  the issue of evaluating  engine durability verses power output
is much more accurately done if one takes note of HOW one achieves the power
in terms of the first two of the parameters I mentioned, rather than just
jotting down the BMEP values.

I am of the opinion, and believe that there is fairly convincing evidence to
support the concept that the old and traditional practice in general
aviation of just throwing out a BMEP value as part of the discussion about
how an engine should be run is  1) antiquated; 2) misleading in its
implications, 3)a continuing disservice to the pilot and mechanic community;
and 4) potentially dangerous as it will, eventually, lead to somebody having
an unnecessary engine crisis that gets somebody hurt. 

This issue is not something I just pulled out of thin air.  I brought this
subject up to one of the former V.P.s in charge of engineering at TCM about
3 and 1/2 years ago (Carl Goulet, John Barton's predecessor).  He and I had
a long discussion on the subject.  He shared the same general view of the
matter, expressed regret at not having had the time and resources and
technology during his working life to pursue the issues years before, and
encouraged me to pursue the subject matter and refine and develop these
issues into a usable form.   He only worked in engineering at TCM for 40
years.  


>>Thank you for your erudite response....  While your explanation of the
original derivation of BMEP is correct, it is 
clear from other comments in your letter that you (and many others) don't
have a full grasp of the true significance of BMEP. <<

Jack, you may be right.  I may not know squat about any of this.

However,  consider, that several times a week, I walk over to the engine
test stand, and fire up a 350 Hp turbocharged engine.  The test stand
(actually, there are two of them) is fully calibrated to the satisfaction of
the FAA for certification work.  Every time I walk over there and fire up
one of those engines,  I only measure (directly) IMEP and calculate BMEP
from the IMEP and the measured friction MEP curves, on a cylinder by
cylinder basis, about 22 times per second, for each of six cylinders.  I
then get to compare that combustion pressure derived BMEP calculation with
the dyno measured BMEP calculation.  Pretty darn good correlation.  Every
time.  I don't know anybody anywhere working on general aviation piston
engines that has ever done that before.  

So, yup, you may be right, surely I lack some "... grasp of the true
significance..." of the subject.



>>In fact, if I have correctly interpreted the scrambled chart in your
response 
(which, coupled with its subsequent weak conclusions, I take to be a 
transparent promotion of your PRISM system), the data given to define the 
"Condition A" and "Condition B" are deficient of critical specifics, as is 
often typical of anecdotal argument. <<

[If the people on this mail list believe I spend the kind of time these
email exchanges require to prepare, just in order to  promote  some product
that is still in certification,  then I have badly underestimated the folks
who read this mail list, and I will be glad to drop offline and go back to
much more productive work.  Just say the word, somebody, anybody, and I'm
gone.]

Now, I do apologize for the inadequate software that MicroSoft sells to all
of us, and its inability to adequately re-format on your computer that which
I typed on my computer.  So, here it is again:

       * * * * * * *

Example (these numbers are approximations, from memory, from recent
experience on the test stand):

		Peak 				Peak Torsional
		Combustion			Crankshaft Stress 
    BMEP	Pressure	Theta(p-p)	Reversals

A)  	175	1100 psi	 5-8deg	~5  x mean 

B)	175	 850 psi	17-19deg	~3.5 x mean 

Where "Theta(p-p)" is the rotational angle between TDC and the peak of the
combustion pressure event.

I hope it formats, better, this time. 

BTW, the data above is not "anecdotal", as it is not "... based on or
consisting of reports or observations of usually unscientific observers."
It is hard data, collected from a fully calibrated engine test stand that is
routinely used for the collection of data that the Administrator of the FAA
then deems to be "approved" data. 

Come by and visit us and you can run the engine on the test stand and see
that data in real time.  

>>For example, you claim that both engines (Condition A and Condition B) are

making the same power, but you conveniently omit the remainder of the 
defining parameters, including: (a) whether or not they have the same 
displacement, (b) whether or not both have identical power-section geometry,

and (c) whether or not they are being evaluated at the same RPM. <<

I apologize for not having made it more clear. That data applies to the SAME
engine  on the SAME day, in the SAME five minute interval of time, operating
at the SAME RPM.  It is an absolutely classic example of why BMEP numbers
are so easily misconstrued when offered up to non-engine head pilots and
mechanics, without an understanding that all BMEPs are NOT the same in terms
of engine durability issues.

>>Also, in view of the simplicity of making a dyno say pretty much anything 
you want, I am highly suspect of power claims based on any dyno other than
my 
own.<<

That is a statement that we agree upon.  There is a lot of very bad dyno
data floating around.  

However, in our case,  we calibrate our dyno to the satisfaction of the
friendlies at the FAA, and, more importantly, to my satisfaction, and have
directly checked it against engines transported from other FAA approved
dynos, and then, every once in a while, throw a Lebow torque meter on the
prop flange to make sure. So far, we have been pretty darn close, and our
consistency has been better than that.


>>If, however, I assume that all three of those factors (displacement, 
geometry, RPM) are the same in both A and B engines, then clearly both are 
operating at the same BMEP, even though the pressure distribution for 
Condition B is clearly different from the (more peaky) distribution in A. <<


Your assumption is correct and your conclusion is correct to this point.

>>What that revelation shows is that brake torque (the difference between
the 
indicated torque and the friction torque) is, as has been known for over a 
century, a function of the integral of the "combustion pressure v. rotation"

curve, and that many different curves can produce the same integral.<< 

You almost have that right.  

>>While you do state a few disjoint facts, your argument against the
usefulness 
of the BMEP yardstick is based upon small and infrequent exceptions in an 
attempt to invalidate a basic engineering procedure of comparative analysis.

(To label that an epistemological exercise is, I think, a bit of a 
self-important hyperbole.)<<

I don't agree that the differences in critical operating parameters set
forth in the example are either "small" or that they are infrequent.  

In fact, those differences are usually critical to the issue,  not something
that should properly be considered as an  exception.



>>I think it's unfortunate that you might not have had the opportunity to
study 
statistical methodology in order to appreciate the usefulness of not only 
simple concepts such as "mean", but even more useful concepts such as "rms" 
(root-mean-square), "standard deviation", "poisson distributions", "surface 
modelling", and lots of others.<<

That is an excellent tactic Jack.  Attack the messenger, not the message.
And attack the messenger with innuendo and false accusations for which you
have no basis in fact.  

So, yeah... Jack.  Of course!  You are undoubtedly correct in your
understanding and view of my background and training. 
Surely I never ran into any of that stuff during four years in the physics
and engineering departments at Brown.

They must have made a terrible mistake in having me in their classrooms.
Worse, I surely never was exposed to any of that while I worked for Ted
Smith during the R&D phase of the development of the Aerostar.

Very unfortunate.  Just terrible my lack of formal training on any aspect of
this subject.  So glad you were so careful to get your facts straight when
you pointed out my educational deficiencies  to me.  

For mercy sake, Jack,  don't you realize that most of the folks on this mail
list are each capable of better sarcasm then either you or I ? 

>> In fact, if you are interested, I can provide you with specifics on
engines which operate for 
VERY long lives at peak cylinder pressures in excess of what you have quoted

for Condition A.<<

Yes, we would all, I am sure, be very interested if you can provide several
examples of Lycoming or TCM aircraft piston engines that operate  for "VERY"
long lives  with continuous peak cylinder pressures in excess of 1100 PSI.  

Let's stay focused on aircraft spark ignition piston engines, please.

Regards,  George 
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
LML website:   http://members.olsusa.com/mkaye/maillist.html
LML Builders' Bookstore:   http://www.buildersbooks.com/lancair
Please remember that purchases from the Builders' Bookstore
assist with the management of the LML.

Please send your photos and drawings to marvkaye@olsusa.com.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>