Constant Speed Prop vs Variable Engine Timing

The Aerosance FADEC system is currently available for both TCM and
Lycoming engines. It DOES NOT require a "spool-up". In fact the piston
engine deserves more credit than the FADEC with respect to this
characteristic. It has virtually no lag in response to power commands.
The way FADEC is implemented also helps. It responds to throttle valve
movement by sensing air pressure changes. For more info see
www.fadec.com.

Steve

(pacplyer) wrote in message . com...
(Corky Scott snip

That will likely change when auto engines, complete with the
computerized ignition and fuel injection, and all the sensors to make
it work properly get into the air. But then again, the Lycomings and
Continentals would also benefit from such treatment.

Variable timing and fuel injection is coming, it's already running on
several models, it's called FADEC for Fully Automated Digital
Electronic Control.

Corky Scott

I think you are right Corky. FADEC (Full Authority Digital Engine
Control) has been around on jets since the 70's. It is
unquestionably the best way to reach TBO and optimum burn performance
for an individual engine. It however has resulted in unforeseen
accidents (e.g: Airbus 330 in Toulouse, France, where test pilot got
behind power curve, then pushed throttles to the wall, and FADEC
refused due to thermal spool up considerations. Its programming
decided that full power would be available to the crew in something
like five seconds. This saves millions for the fleet every fiscal
year. Problem was: The prototype hit the stand of trees in something
like six seconds? This was caught on video, and the test pilot was
interviewed in the hospital. He stated that nothing happened when he
called for max power. If I had FADEC in a single-engine GA aircraft I
would want a non-software override.

pacplyer

"Jay" wrote

My point about using an engine that can operate efficiently over a
large range of RPMs (like a modern automobile engine) is that the CS
prop is NOT as necessary although it certainly does help, no doubt
about it. Certainly you will get you peak horsepower at high revs,
but the moderm engine has a fatter torque curve due to being able to
change valve AND ignition timing in a manner optimum for the
particular revs it is at. The Lyco/Conti design takes a double hit
for operating at low revs, its off the peak HP point, and its timing
was peaked for a specific RPM.


IMHO, to take advantage of the auto engine's characteristics, you need a CS
prop, even more. Flat pitch for takeoff, then really get the course pitch
at high speed and high altitude, so the engine can loaf along at really slow
and low HP output, to keep the thrust up, while at the low engine RPM'S.

Most of the successful auto conversions tend to keep it simple, and variable
valve timeing is not in that spirit. YMMV.
--
Jim in NC


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On Fri, 27 Feb 2004 23:43:47 -0500, "Morgans"
wrote:


IMHO, to take advantage of the auto engine's characteristics, you need a CS
prop, even more. Flat pitch for takeoff, then really get the course pitch.......
++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++

COURSE?

Sorry, 'Teach'.
It's your turn in the barrel. g

One need not be gifted or an English major to be educated in the
basics of our native tongue. Just being a teacher should induce one to
become somewhat less of an embarrassment to this noble vocation....
by osmosis or a remedial 'course', if nothing else.


COARSE adj. - Consisting of large particles; not fine in texture


COURSE n.

1. a. Onward movement in a particular direction;
progress: the course of events.

2. a. A complete body of prescribed studies constituting a
curriculum: a four-year course in engineering.

b. A unit of such a curriculum: took an introductory course
in chemistry; passed her calculus course.


Barnyard BOb -

(Jay) wrote in message . com...
Seems to me that some of the benefits of the constant speed prop were
based on the limitiations of timing (ignition and valve) of the
Lyco/Conti engines. If your engine was designed to have a large
dynamic range of efficient operation, you won't need the articulated
prop as much.


Horsepower is a function of torque multiplied by RPM. A Lycoming
engine in an older Cessna 172, for example, produces 150 HP at 2700
RPM under standard conditions (sea level atmospheric pressure and
59°F). In the takeoff roll with the fixed-pitch prop, RPM will be
around 2300 RPM, which, according to the POH, would indicate a
horsepower output of about 61% of 150, or about 92 horses. Not very
good, is it?
So, we only have about 60 percent of the engine's power in the
takeoff. Worse yet, this diminished power is going into a propeller
that is largely in a stalled condition at the beginning of the takeoff
roll (because of high blade pitch angle and low forward speed) and is
producing much less than its max thrust as a result, and acceleration
is pretty dismal.
What can we gain by fooling with valve or ignition timing in a
situation like this? Not much. We add weight and failure points,
neither of which are welcome here, and gain very little in
performance.
So the constant-speed prop was invented. It is controlled by a
governor so that the engine is allowed to reach full rated RPM, which
produces full rated HP (if at sea level and standard temp), and
because the propeller's pitch is much lower in this mode, much more of
it is producing thrust instead of useless stall turbulence. In
cruising flight, the pitch increases to keep the engine RPM within
limits while still producing more thrust and a higher cruise speed
than a fixed-pitch prop can.
A fixed-pitch prop is a compromise and is like having only second
gear in your car: lousy acceleration, lousy highway speed. Could this
be fixed with fancy engine doodads? Nope. More gears are needed, and
the constant-speed prop is the airplane's transmission.

Dan

This is directed more at the original poster,

Latest Kitplanes, March 2004 top of page 25 under heading of "Performance".
Comparisons of 6 constant speed props and one fixed pitch prop on a RV-8.
Speeds within 4% fastest to slowest, Constant speed props are very useful
for take-off and speed reduction to pattern, but counter-intuitively, not
much difference in top speed. Given that the piece that takes the bite out
of the air would be difficult to optimize more than it is, it's hard to
figure how current engine tweaking could do any better and I see all the
bells and whistles in New Model Training all the time for cars. There are
practical limits with what you can do with add-on doo-dads.

Dale Alexander
Velocity Stealth RG Gullwing
Toyota Master Tech
Mazda Master Tech
Been working on cars WAY too long...

"Dan Thomas" wrote in message
om...
(Jay) wrote in message
. com...
Seems to me that some of the benefits of the constant speed prop were
based on the limitiations of timing (ignition and valve) of the
Lyco/Conti engines. If your engine was designed to have a large
dynamic range of efficient operation, you won't need the articulated
prop as much.


Horsepower is a function of torque multiplied by RPM. A Lycoming
engine in an older Cessna 172, for example, produces 150 HP at 2700
RPM under standard conditions (sea level atmospheric pressure and
59°F). In the takeoff roll with the fixed-pitch prop, RPM will be
around 2300 RPM, which, according to the POH, would indicate a
horsepower output of about 61% of 150, or about 92 horses. Not very
good, is it?
So, we only have about 60 percent of the engine's power in the
takeoff. Worse yet, this diminished power is going into a propeller
that is largely in a stalled condition at the beginning of the takeoff
roll (because of high blade pitch angle and low forward speed) and is
producing much less than its max thrust as a result, and acceleration
is pretty dismal.
What can we gain by fooling with valve or ignition timing in a
situation like this? Not much. We add weight and failure points,
neither of which are welcome here, and gain very little in
performance.
So the constant-speed prop was invented. It is controlled by a
governor so that the engine is allowed to reach full rated RPM, which
produces full rated HP (if at sea level and standard temp), and
because the propeller's pitch is much lower in this mode, much more of
it is producing thrust instead of useless stall turbulence. In
cruising flight, the pitch increases to keep the engine RPM within
limits while still producing more thrust and a higher cruise speed
than a fixed-pitch prop can.
A fixed-pitch prop is a compromise and is like having only second
gear in your car: lousy acceleration, lousy highway speed. Could this
be fixed with fancy engine doodads? Nope. More gears are needed, and
the constant-speed prop is the airplane's transmission.

Dan

Great expanation Thanks
John
PS my first post to a newsgroup (I'm a Virgin no more;-) )


Dan Thomas wrote:

(Jay) wrote in message
. com...
Seems to me that some of the benefits of the constant speed prop were
based on the limitiations of timing (ignition and valve) of the
Lyco/Conti engines. If your engine was designed to have a large
dynamic range of efficient operation, you won't need the articulated
prop as much.


Horsepower is a function of torque multiplied by RPM. A Lycoming
engine in an older Cessna 172, for example, produces 150 HP at 2700
RPM under standard conditions (sea level atmospheric pressure and
59°F). In the takeoff roll with the fixed-pitch prop, RPM will be
around 2300 RPM, which, according to the POH, would indicate a
horsepower output of about 61% of 150, or about 92 horses. Not very
good, is it?
So, we only have about 60 percent of the engine's power in the
takeoff. Worse yet, this diminished power is going into a propeller
that is largely in a stalled condition at the beginning of the takeoff
roll (because of high blade pitch angle and low forward speed) and is
producing much less than its max thrust as a result, and acceleration
is pretty dismal.
What can we gain by fooling with valve or ignition timing in a
situation like this? Not much. We add weight and failure points,
neither of which are welcome here, and gain very little in
performance.
So the constant-speed prop was invented. It is controlled by a
governor so that the engine is allowed to reach full rated RPM, which
produces full rated HP (if at sea level and standard temp), and
because the propeller's pitch is much lower in this mode, much more of
it is producing thrust instead of useless stall turbulence. In
cruising flight, the pitch increases to keep the engine RPM within
limits while still producing more thrust and a higher cruise speed
than a fixed-pitch prop can.
A fixed-pitch prop is a compromise and is like having only second
gear in your car: lousy acceleration, lousy highway speed. Could this
be fixed with fancy engine doodads? Nope. More gears are needed, and
the constant-speed prop is the airplane's transmission.

Dan

(Dan Thomas) wrote:

Horsepower is a function of torque multiplied by RPM. A Lycoming
engine in an older Cessna 172, for example, produces 150 HP at 2700
RPM under standard conditions (sea level atmospheric pressure and
59°F). In the takeoff roll with the fixed-pitch prop, RPM will be
around 2300 RPM, which, according to the POH, would indicate a
horsepower output of about 61% of 150, or about 92 horses. Not very
good, is it?

snip

Dan,

Those numbers can not be correct. The power curves in the Lycoming
operator's manual show that in standard sea level conditions at 2,300
RPM full throttle, a 150 hp Lyc (O-320 A, E) will produce 132 hp or
88% of full rated power. Interestingly, your 92 hp figure closely
matches the propeller load curve at 2,300 RPM. The propeller load
curve, however, is not a full throttle curve. Rather, it is a
variable throttle static run-up curve using a fixed pitch test prop
(or club) chosen to achieve max rated engine RPM at full throttle. If
your C-172 POH says that the 150 hp Lyc produces only 92 hp at 2,300
RPM full throttle in standard sea level conditions, then it is wrong
by a wide margin.

While I'm here, I'd like commend you on your typically spot-on
explanations and your generosity in frequently answering questions
here. Unfortunately, business and other matters keep me from
participating here as much as I'd like. It is folks like you who make
the difference here, not the... (well, I'll let that go). I Hope you
stick around for a long time.

David O -- http://www.AirplaneZone.com

Those numbers can not be correct. The power curves in the Lycoming
operator's manual show that in standard sea level conditions at 2,300
RPM full throttle, a 150 hp Lyc (O-320 A, E) will produce 132 hp or
88% of full rated power. Interestingly, your 92 hp figure closely
matches the propeller load curve at 2,300 RPM. The propeller load
curve, however, is not a full throttle curve. Rather, it is a
variable throttle static run-up curve using a fixed pitch test prop
(or club) chosen to achieve max rated engine RPM at full throttle. If
your C-172 POH says that the 150 hp Lyc produces only 92 hp at 2,300
RPM full throttle in standard sea level conditions, then it is wrong
by a wide margin.

Same thing in my manual.

While I'm here, I'd like commend you on your typically spot-on
explanations and your generosity in frequently answering questions
here. Unfortunately, business and other matters keep me from
participating here as much as I'd like. It is folks like you who make
the difference here, not the... (well, I'll let that go).......

David O -- http://www.AirplaneZone.com
+++++++++++++++++++++++++++++++++++++++++++++++

Bring it up.....and then let it go? g

What the hell....
Is this an attempt to get in touch with your 'feminine side' or what?


Barnyard BOb -

RU ok wrote:

Bring it up.....and then let it go? g

What the hell....
Is this an attempt to get in touch with your 'feminine side' or what?

Just seeking some balance.

David O -- http://www.AirplaneZone.com

David O wrote in message . ..
(Dan Thomas) wrote:

Horsepower is a function of torque multiplied by RPM. A Lycoming
engine in an older Cessna 172, for example, produces 150 HP at 2700
RPM under standard conditions (sea level atmospheric pressure and
59°F). In the takeoff roll with the fixed-pitch prop, RPM will be
around 2300 RPM, which, according to the POH, would indicate a
horsepower output of about 61% of 150, or about 92 horses. Not very
good, is it?

snip

Dan,

Those numbers can not be correct. The power curves in the Lycoming
operator's manual show that in standard sea level conditions at 2,300
RPM full throttle, a 150 hp Lyc (O-320 A, E) will produce 132 hp or
88% of full rated power. Interestingly, your 92 hp figure closely
matches the propeller load curve at 2,300 RPM. The propeller load
curve, however, is not a full throttle curve. Rather, it is a
variable throttle static run-up curve using a fixed pitch test prop
(or club) chosen to achieve max rated engine RPM at full throttle. If
your C-172 POH says that the 150 hp Lyc produces only 92 hp at 2,300
RPM full throttle in standard sea level conditions, then it is wrong
by a wide margin.

Right you are. The 92 HP figure is taken from cruising charts, less
than full throttle. My mistake in assuming that the 2300 RPM would
have a consistent HP.
We once did some physics calcs regarding the acceleration to
takeoff speed for the 172. We found that the energy to accelerate that
mass to that speed came to 24 HP, demonstrating the enormous losses to
prop and airframe drag and wheel rolling friction. Wouldn't it be
great if we could reduce those to a fraction of what they are and make
truly efficient flying machines?

Dan