Mixture--science vs witchcraft?

Michael wrote:
: On Aug 23, 9:24 pm, (Frank Ch. Eigler) wrote:
: It may be interesting that the vulnerable time between the spark and
: TDC is also to some extent under one's control, with the blue knob.

: Good point, and you are of course correct. This takes us into a whole
: 'nother discussion - not can you run oversquare safely (because of
: course you can, and virtually every flat-four, six, and eight out
: there does) but how much oversquare you can run and under what
: circumstances. This is precisely the factor that limits how much
: oversquare you can run in most circumstances.

: I left that part of it out mainly because I've never heard anyone
: advocating making high density altitude takeoffs at reduced RPM, and
: the post was already longer than most people will read.

: Michael

...but it does bring up an interesting point. One that I have yet to see adequately explained anywhere. I've seen a
few engine operating curves that limit max manifold pressure as a function of RPM, there are many that don't. My fixed-pitch
Cherokee doesn't have the option, but I'd be interested to know any source that explains it adequately.

-Cory

--

************************************************** ***********************
* Cory Papenfuss, Ph.D., PPSEL-IA *
* Electrical Engineering *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

On Thu, 23 Aug 2007 08:44:27 -0700, wrote:

On Aug 18, 3:43 pm, "Douglas Paterson"
wrote:
Still getting to know my new baby (1990 TB-20, normally aspirated 250hp
Lycoming IO-540). I imagine my question here must apply to most non-turbo,
non-FADEC pistons (though I gather there's some sort of altitude compensator
on some airplanes' engines?). I live in Colorado, which means routine
high-elevation airport ops.

The people who manufacture that engine, and who have lots to
lose if it quits on you, have a procedure he

http://www.lycoming.textron.com/supp...fs/SI1094D.pdf

Dan


That Lycoming document describes leaning for takeoff at high DA for
these cases:

- fixed pitch - lean for max rpm
- constant speed but no engine instrumentation - lean with smooth
operation of the engine as a deciding factor

What if I have a CS prop plus EGT, MP and fuel flow instrumentation?






randall g =%^) PPASEL+Night 1974 Cardinal RG
http://www.telemark.net/randallg
Lots of aerial photographs of British Columbia at:
http://www.telemark.net/randallg/photos.htm
Vancouver's famous Kat Kam: http://www.katkam.ca

wrote:



...but it does bring up an interesting point. One that I have yet to see adequately explained anywhere. I've seen a
few engine operating curves that limit max manifold pressure as a function of RPM, there are many that don't. My fixed-pitch
Cherokee doesn't have the option, but I'd be interested to know any source that explains it adequately.


One of the absolute worst sources of information on how to properly run
an engine is the engine manufacturer. They are utterly uninterested in
proper engine management, only reducing liability and costs. For proper
engine operation you need to talk to the GAMI guys in Ada, OK. For
example Continental or Lyc will never tell you that the absolute worst
place to run your engine is 40 degrees rich of peak at any power
setting. Or that Continental flat out refuses to even discuss LOP
operations on any engine other than the 550. But install their
electronic engine controls and where do you think your engine is
running? Yep, LOP. We've all been taught that detonation is bad.
Turns out detonation is a trivial concern for our engines. GAMI has set
up an engine to detonate for days at a time of constant running. End
result? No damage whatsoever. Now preignition is a completely
different animal.


http://www.gami.com/frames.htm

"Newps" wrote in message
. ..


wrote:



...but it does bring up an interesting point. One that I have yet to see
adequately explained anywhere. I've seen a few engine operating curves
that limit max manifold pressure as a function of RPM, there are many
that don't. My fixed-pitch Cherokee doesn't have the option, but I'd be
interested to know any source that explains it adequately.


One of the absolute worst sources of information on how to properly run an
engine is the engine manufacturer. They are utterly uninterested in
proper engine management, only reducing liability and costs. For proper
engine operation you need to talk to the GAMI guys in Ada, OK.

Completely agree!

Quite frankly, from what Deakin points, manufacturers recommend operating in
the worst possible ranges as far as mixture goes, both for ICP and for
fouling. Then they try to claim you didn't follow their directions.

At least TCM is (slowly) getting its act together in the Columbia's 550
series.
--
Matt Barrow
Performance Homes, LLC.
Cheyenne, WY

On Aug 26, 6:53 pm, wrote:
...but it does bring up an interesting point. One that I have yet to see adequately explained anywhere. I've seen a
few engine operating curves that limit max manifold pressure as a function of RPM, there are many that don't. My fixed-pitch
Cherokee doesn't have the option, but I'd be interested to know any source that explains it adequately.

The main reason such a chart is not universal is because there is no
requirement to publish such a chart, not because it's not relevant. I
suppose there might be a (horizontally opposed) engine installation
out there that will comfortably run at sea level with the throttle
control all the way forward and the prop control all the way back, but
I doubt this is the norm.

While few manufacturers provide a limit chart, most provide
recommended power settings (generally with quite a few 'oversquare'
options) and other guidelines (for example: Do not exceed 25" MP at
2000 RPM or less).

Michael