Constant Speed Prop vs Variable Engine Timing

[Jay]

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.

[Bill Daniels]

"Jay" > wrote in message
om...
> 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.

Prop blades are just rotating wings. The goal is to run the blades at their
most efficient angle of attack for the RPM and aircraft airspeed. The
performance of the prop is best at low RPM but the piston engine driving it
is likely to be most efficient at a higher RPM. That is the reason that
high performance piston aircraft have both PRSU's and constant speed props.

Some experimental powerplant/prop systems included a two speed gearbox in
addition to the CS prop to run the engine at high RPM at takeoff and low RPM
for cruise. These experimental engines also shifted the cam and ignition
timing for the two PRSU ratios. This helped the prop blades stay at the
best AOA to maximize thrust and optimized the engine at two set points, high
RPM for takeoff and low RPM for long range cruise. This was at the very end
of large piston engine development and an attempt to wring the last bit of
performance out of these monsters.

Having an engine with a wide "dynamic range" is nice for a car but less
useful for an airplane where it is best to optimize the engine for one RPM
and let the CS prop and PRSU operate the prop in the most efficient way.

Bill Daniels

[Jay]

Thanks for your insight, which raise a few questions:

Apart from the geared Cessna (which isn't all that hi performance)
which aircraft have a PSRU AND a CS prop?

Which experimental aircraft has 2 speed gear boxes? I heard of a guy
flying a WW1 replical biplane on a Honda motocycle engine. He just
kept the original gear box and said he actually shifts gears depending
on if he's climbing or cruising.

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.


"Bill Daniels" > wrote in message >...
> "Jay" > wrote in message
> om...
> > 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.
>
> Prop blades are just rotating wings. The goal is to run the blades at their
> most efficient angle of attack for the RPM and aircraft airspeed. The
> performance of the prop is best at low RPM but the piston engine driving it
> is likely to be most efficient at a higher RPM. That is the reason that
> high performance piston aircraft have both PRSU's and constant speed props.
>
> Some experimental powerplant/prop systems included a two speed gearbox in
> addition to the CS prop to run the engine at high RPM at takeoff and low RPM
> for cruise. These experimental engines also shifted the cam and ignition
> timing for the two PRSU ratios. This helped the prop blades stay at the
> best AOA to maximize thrust and optimized the engine at two set points, high
> RPM for takeoff and low RPM for long range cruise. This was at the very end
> of large piston engine development and an attempt to wring the last bit of
> performance out of these monsters.
>
> Having an engine with a wide "dynamic range" is nice for a car but less
> useful for an airplane where it is best to optimize the engine for one RPM
> and let the CS prop and PRSU operate the prop in the most efficient way.
>
> Bill Daniels

[Ron Natalie]

"Jay" > wrote in message om...

> Apart from the geared Cessna (which isn't all that hi performance)
> which aircraft have a PSRU AND a CS prop?
>
Navions, Helio Couriers, Twin Commanders, Beech Twin Bonanzas,
Republic SeaBee, Beech Queen Air all have models that use variants
of the Geared Lycomings (435 and 480). They almost always drive
a variable pitch (some cases not constant speed ) prop.

[Mike Rapoport]

All moderate to high power geared piston engines and all turboprops have
gear reduction and CS props. It is not just about engine efficiency, it is
about prop efficiency over a range of airspeeds and altitudes. As airspeed
increases, AOA of the prop decreases so you can not have a prop which works
efficiently for takeoff and cruise unless the airplane is very slow. My
airplane advances 19 feet for each revolution of the prop at cruise vs. 0
feet at the beginning of the takeoff roll. Similiarly, the prop needs more
pitch when the air is less dense to be efficient..

Mike
MU-2

"Jay" > wrote in message
om...
> Thanks for your insight, which raise a few questions:
>
> Apart from the geared Cessna (which isn't all that hi performance)
> which aircraft have a PSRU AND a CS prop?
>
> Which experimental aircraft has 2 speed gear boxes? I heard of a guy
> flying a WW1 replical biplane on a Honda motocycle engine. He just
> kept the original gear box and said he actually shifts gears depending
> on if he's climbing or cruising.
>
> 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.
>
>
> "Bill Daniels" > wrote in message
>...
> > "Jay" > wrote in message
> > om...
> > > 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.
> >
> > Prop blades are just rotating wings. The goal is to run the blades at
their
> > most efficient angle of attack for the RPM and aircraft airspeed. The
> > performance of the prop is best at low RPM but the piston engine driving
it
> > is likely to be most efficient at a higher RPM. That is the reason that
> > high performance piston aircraft have both PRSU's and constant speed
props.
> >
> > Some experimental powerplant/prop systems included a two speed gearbox
in
> > addition to the CS prop to run the engine at high RPM at takeoff and low
RPM
> > for cruise. These experimental engines also shifted the cam and
ignition
> > timing for the two PRSU ratios. This helped the prop blades stay at the
> > best AOA to maximize thrust and optimized the engine at two set points,
high
> > RPM for takeoff and low RPM for long range cruise. This was at the very
end
> > of large piston engine development and an attempt to wring the last bit
of
> > performance out of these monsters.
> >
> > Having an engine with a wide "dynamic range" is nice for a car but less
> > useful for an airplane where it is best to optimize the engine for one
RPM
> > and let the CS prop and PRSU operate the prop in the most efficient way.
> >
> > Bill Daniels

[Corky Scott]

On 27 Feb 2004 09:28:04 -0800, (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.

Aircraft engines, even the direct drive ones, don't take as much a hit
on efficiency as you might think. They're designed to run at
relatively slow steady speed from the outset, unlike auto engines
which are designed for many rpm ranges. Just because aircraft engines
don't run like auto engines doesn't mean it's bad, or inefficient.

When you get to cruise power, and lean it way back, the aircraft
engine generally gets a better brake specific fuel consumption (BSFC)
than does the auto engine when configured to run as an aircraft
engine.

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

[Dan Thomas]

(Jay) wrote in message >...
> 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

[Dale Alexander]

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
>...
> > 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

[UltraJohn]

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


Dan Thomas wrote:

> (Jay) wrote in message
> >...
>> 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
>

[Morgans]

"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


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.594 / Virus Database: 377 - Release Date: 2/24/2004

[David O]

(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

[RU ok]

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 -

[RU ok]

>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 -

[David O]

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

[Dan Thomas]

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

[pacplyer]

(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

[Veeduber]

>the test pilot was
>interviewed in the hospital. He stated that nothing happened when he
>called for max power.

--------------------------------------------------------------

I hate it when that happens :-)

-R.S.Hoover

[AnyBody43]

(Dan Thomas) wrote in message >...
> (Jay) wrote in message >...
> > 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.
>
.. . . snip . . .
> 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.

It seems to me that the gear analogy is spot on. A variable pitch
prop has EXACTLY the same function as the gearbox on a car.

[BllFs6]

>It seems to me that the gear analogy is spot on. A variable pitch
>prop has EXACTLY the same function as the gearbox on a car.
>
>

Dumb newbie question here...

If you have a prop that is best for cruise....am I right in assuming it has
"too much of a bite" on the air when the aircraft is sitting still...therefore
the engine doesnt have enough torque...and therefore the prop cant spin quite
as fast as it would otherwise...and both these lead to less low speed thrust
than you would like?

And if that is the case...could you not use something like water mist injection
or nitrous oxide to temporarily increase the torque the motor produces?

Probably wount make much sense if you really wanted it for many minutes of
climbing....but it might make sense if all your trying to do is shorten your
takeoff distance.....

take care

Blll

[Kevin Horton]

On Sun, 29 Feb 2004 18:52:16 -0800, pacplyer wrote:

> (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

Two comments:

You've mixed up two different accidents here. The 330 at Toulouse was a
loss of control due to the aircraft (on autopilot) going way below VMCA
with one engine at idle and the other at full take-off thrust. The sat
and watched until it was too late to recover.

The accident you are referring to was the A320 at Mulhouse-Habsheim. The
pilot did a very low (30 ft AGL) pass with the thrust at idle. The speed
decreased til he was at full aft stick, riding on the AOA limiter just
above the stall. Then he realized that what he had thought were just low
bushes when he was looking down on them as he descended, were actually
trees that were higher than he was. He couldn't raise the nose, as
the fly-by-wire (FBW) was already on the AOA limiter, so the only way to
climb was to get more airspeed. He slammed the thrust levers forward, and
the FADEC accelerated the engine on its normal acceleration schedule.

Turbine engines run more efficiently if they are running close to the
surge line (i.e almost ready to compressor stall). But the engine has to
come closer to the surge line to accelerate. So the closer you run to the
surge line the slower acceleration you'll have.

FAR 25.119(a) requires go-around performance to be calculated using the
thrust that is available 8 seconds after a throttle slam from idle.
Manufacturers want the engine to run as efficiently as possible, but they
don't want to take a hit on the AFM go-around performance. So, they
typically design the fuel controls to allow full go-around thrust to be
reached in just less than 8 seconds from a throttle slam from idle. I've
done tests to check the acceleration on many transport category aircraft,
and the result is usually somewhere between 7 and 8 seconds, and this is
the same no matter whether the engine has a FADEC or an "old fashioned"
hydro-mechanical fuel control unit.

So don't blame the FADEC for the A320 accident at Mulhouse-Habsheim. It
was caused by a pilot who had way too much confidence in the low-speed
protections of the FBW. Fortunately the FBW prevented him from raising
the nose, as then the aircraft would have stalled, any many people would
probably have died. As it was "only" three live were lost.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

[Bill Daniels]

"AnyBody43" > wrote in message
om...
> (Dan Thomas) wrote in message
>...
> > (Jay) wrote in message
>...
> > > 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.
> >
> . . . snip . . .
> > 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.
>
> It seems to me that the gear analogy is spot on. A variable pitch
> prop has EXACTLY the same function as the gearbox on a car.

Not quite. Gears don't have preferred operating conditions, props do.

The engine has its preferred RPM and torque for optimum efficiency and the
prop blades have their optimum angle of attack. If the engine/prop
combination results in the prop operating at a higher (or lower) angle of
attack than optimum to absorb the torque of the engine (Prop governor
increases pitch to hold RPM setting.) then the combination operates below
optimum conditions.

Under some conditions, it would make sense to introduce a third variable
i.e. a gearbox between the engine and prop, to allow both the engine and
prop to operate at peak efficiency. This was the reason that two-speed
grearsets were installed in the nose case of some large radials. This, in
turn, allowed the propeller designer to optimize his prop blades for a
single AOA, thus gaining still more efficiency.

The problem, simply stated was this: How does a heavily loaded, long-range
bomber haul itself off a short runway and climb to cruise altitude and then
shift to highly efficient, long-range cruise. The answer was just emerging
from the labs as the world shifted to turbines. The flight engineer would
shift his engines into a "hole gear" by selecting a cam profile and engine
timing optimized for the low gear that would let the engines scream at high
RPM and pump massive HP into props set for maximum acceleration and climb.
Once in cruise, the engineer would shift his engines back to low RPM, high
efficiency settings.

A propeller is not a gear box analog. It is more like the torque converter
in an automatic transmission. A torque converter still needs a gearbox
behind it for efficiency.

Bill Daniels

[Jay]

Either that or a WEP setting (break a wire at full throttle) that
basically says to the microcontroller "Its now or never." Something
that indicates that there is a real possibility of loss of vehicle and
also disconnects the field current for the alternator.

(pacplyer) wrote in message >...
> If I had FADEC in a single-engine GA aircraft I
> would want a non-software override.
>
> pacplyer

[Corky Scott]

On 01 Mar 2004 14:03:35 GMT, (BllFs6) wrote:

>>It seems to me that the gear analogy is spot on. A variable pitch
>>prop has EXACTLY the same function as the gearbox on a car.
>>
>>
>
>Dumb newbie question here...
>
>If you have a prop that is best for cruise....am I right in assuming it has
>"too much of a bite" on the air when the aircraft is sitting still...therefore
>the engine doesnt have enough torque...and therefore the prop cant spin quite
>as fast as it would otherwise...and both these lead to less low speed thrust
>than you would like?
>
>And if that is the case...could you not use something like water mist injection
>or nitrous oxide to temporarily increase the torque the motor produces?
>
>Probably wount make much sense if you really wanted it for many minutes of
>climbing....but it might make sense if all your trying to do is shorten your
>takeoff distance.....
>
>take care
>
>Blll

Anything that causes the engine to produce more power also causes it
to produce more heat. If the cooling system cannot efficiently rid
itself of that extra heat, you could be looking at detonation, or even
pre-ignition. You don't have to worry about pre-ignition for very
long because just a little of that and the engine is history.

The thing that to me makes the most sense to me would be to have an
engine/prop combination that works well for your application, and pay
attention to gross weight/high density altitude situations.

Corky Scott

[Dan Thomas]

"Bill Daniels" > wrote in message news:<5_-> > It seems to me that the gear analogy is spot on. A variable pitch
> > prop has EXACTLY the same function as the gearbox on a car.
>
> Not quite. Gears don't have preferred operating conditions, props do.
>
> The engine has its preferred RPM and torque for optimum efficiency and the
> prop blades have their optimum angle of attack. If the engine/prop
> combination results in the prop operating at a higher (or lower) angle of
> attack than optimum to absorb the torque of the engine (Prop governor
> increases pitch to hold RPM setting.) then the combination operates below
> optimum conditions.
>
> Under some conditions, it would make sense to introduce a third variable
> i.e. a gearbox between the engine and prop, to allow both the engine and
> prop to operate at peak efficiency. This was the reason that two-speed
> grearsets were installed in the nose case of some large radials. This, in
> turn, allowed the propeller designer to optimize his prop blades for a
> single AOA, thus gaining still more efficiency.
>
> The problem, simply stated was this: How does a heavily loaded, long-range
> bomber haul itself off a short runway and climb to cruise altitude and then
> shift to highly efficient, long-range cruise. The answer was just emerging
> from the labs as the world shifted to turbines. The flight engineer would
> shift his engines into a "hole gear" by selecting a cam profile and engine
> timing optimized for the low gear that would let the engines scream at high
> RPM and pump massive HP into props set for maximum acceleration and climb.
> Once in cruise, the engineer would shift his engines back to low RPM, high
> efficiency settings.

First time I've ever heard of gear-shifted props in certified
engines. Which engines were these? I know that many radials (and other
engine layouts) used reduction gearing in the case nose to allow the
engine to run faster and produce more HP while keeping the prop within
safe limits, and that there were two-speed geared superchargers on
many of these engines, but two-speed props?
Jim Bede used a snowmobile-type propshaft drive in the early
BD-5s but abandoned it as unworkable. It still required a relatively
tiny prop to keep the tip speeds subsonic.
As far as the propeller pitch angles go, the constant speed prop
improves takeoff performance by more than just letting engine RPM
reach redline to produce max HP. It reduces the angle of attack so
that more of the prop is unstalled and producing thrust in the static
condition, improving acceleration and shortening takeoff distance. The
inboard sections of a fixed-pitch prop blade have a large angle so
that they still produce thrust in faster forward flight even though
they don't travel the circumferential distance that blade areas near
the tips do, but the large angle means a stalled blade, or at least a
really turbulent flow, at low forward speeds. A gear-shifted
fixed-pitch prop will still have those problems.

Dan

[Kevin Horton]

On Mon, 01 Mar 2004 12:38:15 -0800, Dan Thomas wrote:

> "Bill Daniels" > wrote in message news:<5_-> > It
> seems to me that the gear analogy is spot on. A variable pitch
>> > prop has EXACTLY the same function as the gearbox on a car.
>>
>> Not quite. Gears don't have preferred operating conditions, props do.
>>
>> The engine has its preferred RPM and torque for optimum efficiency and
>> the prop blades have their optimum angle of attack. If the engine/prop
>> combination results in the prop operating at a higher (or lower) angle
>> of attack than optimum to absorb the torque of the engine (Prop
>> governor increases pitch to hold RPM setting.) then the combination
>> operates below optimum conditions.
>>
>> Under some conditions, it would make sense to introduce a third
>> variable i.e. a gearbox between the engine and prop, to allow both the
>> engine and prop to operate at peak efficiency. This was the reason
>> that two-speed grearsets were installed in the nose case of some large
>> radials. This, in turn, allowed the propeller designer to optimize his
>> prop blades for a single AOA, thus gaining still more efficiency.
>>
>> The problem, simply stated was this: How does a heavily loaded,
>> long-range bomber haul itself off a short runway and climb to cruise
>> altitude and then shift to highly efficient, long-range cruise. The
>> answer was just emerging from the labs as the world shifted to
>> turbines.
>> The flight engineer would shift his engines into a "hole gear" by
>> selecting a cam profile and engine timing optimized for the low gear
>> that would let the engines scream at high RPM and pump massive HP into
>> props set for maximum acceleration and climb. Once in cruise, the
>> engineer would shift his engines back to low RPM, high efficiency
>> settings.
>
> First time I've ever heard of gear-shifted props in certified
> engines. Which engines were these? I know that many radials (and other
> engine layouts) used reduction gearing in the case nose to allow the
> engine to run faster and produce more HP while keeping the prop within
> safe limits, and that there were two-speed geared superchargers on many
> of these engines, but two-speed props?
> Jim Bede used a snowmobile-type propshaft drive in the early
> BD-5s but abandoned it as unworkable. It still required a relatively
> tiny prop to keep the tip speeds subsonic.
> As far as the propeller pitch angles go, the constant speed prop
> improves takeoff performance by more than just letting engine RPM reach
> redline to produce max HP. It reduces the angle of attack so that more
> of the prop is unstalled and producing thrust in the static condition,
> improving acceleration and shortening takeoff distance. The inboard
> sections of a fixed-pitch prop blade have a large angle so that they
> still produce thrust in faster forward flight even though they don't
> travel the circumferential distance that blade areas near the tips do,
> but the large angle means a stalled blade, or at least a really
> turbulent flow, at low forward speeds. A gear-shifted fixed-pitch prop
> will still have those problems.
>
> Dan

Some of the supercharged recips had a gear box with two different gear
ratios to drive the supercharger. They needed to spin the supercharger at
high rpm at high altitude in order to get enough manifold pressure. But
if they used the same supercharger gear ratio at low altitude it would
produce more manifold pressure than the engine could handle at full
throttle. The engine would then have to be run very throttled, and there
would be a lot of wasted power used to spin that supercharger at a
needlessly high rpm. So, they used a different gear ratio to spin the
supercharger at a lower rpm for take-off and low altitude flight.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

[pacplyer]

Great Stuff Kevin, thanks for your insight. I have a couple of points
I slightly disagree with however further down in your post. :-)

Kevin Horton > wrote:

> You've mixed up two different accidents here. The 330 at Toulouse was a
> loss of control due to the aircraft (on autopilot) going way below VMCA
> with one engine at idle and the other at full take-off thrust. The sat
> and watched until it was too late to recover.

Yeah I mixed those up. Thanks for keeping me honest. Those were both
IMHO over-reliance in airbus automation accidents IIRC. I saw this
frequently with new-to-airbus co-pilots who would stare at the PFD
trying too figure out why the last button push on the FCP didn't do
anything. Instead of disconnecting everything and regaining control.

After you got yourself behind the power curve, however, for whatever
reason, I'm essentially talking about old-school guys like me who were
used to flying non-FADEC machines capable of "overboost." If you got
into trouble, because you were stupid, in say the previous generation
of Boeing products: You could always push up and call for power far
in excess of limiting max GA epr or N1, N2, EGT limits. (but maybe
that's because like you say: old eng's didn't operate so close to the
surge/stall margin.) It's unlikely the engines were going to fail
like a piston or super/turbo charged engine might. Those old buckets
would warp. The blades might creep and stretch and the engines might
have to be scrapped (at say 5 mill a copy.) But you had a better
chance of clearing the trees by going all way the to the mechanical
stops (physical wire to the FCU Hydr/Mech linkage) than you do now
with a Throttle resolver / PFM/MEC/ FADEC arrangement. The airbus
test pilot may think he's called for Jesus power, but FADEC will not
let him have it.
This may have saved me a couple of times in my career flying 60's gen
aircraft overseas. You smash everything to the wall and only slightly
pull back on the engines that are "barking." (compressor stalling.)
ATC would steer you into mountains in those days in some places.
(more war stories.)

>
> The accident you are referring to was the A320 at Mulhouse-Habsheim. The
> pilot did a very low (30 ft AGL) pass with the thrust at idle. The speed
> decreased til he was at full aft stick, riding on the AOA limiter just
> above the stall.

I haven't flown any FBW. But we had the predecessor AOA system on
the A310 which had a A/T "alpha floor" mode (Vls) which would not
allow you to command (not select) a speed slower than 1.2 Vso. Check
pilots would scare the **** out of themselves relying on this system,
and come back and rewrite the manual! This also lead to a bunch of
documented (AWST) vertical tailslides at third world airlines where a
little turbulence knocked the A/S below alpha floor for a second.
Throttles (sometimes asymmetrically) would in about six seconds from
(flight) idle reach G/A thrust: locked into what the french call
Thrust Latch mode: meaning if you disconnected A/T's and manually
retarded them, and let go, they would re-engauge themselves (without
your permission) and smoothly place you back up to full pwr again.
(New guys never noticed the uncommanded re-power up. They would
fixate on the airplane departing altitude and start ****ing around
with the pickle switch trim: which was active!) The auto pilot would
respect redline on flaps at all costs. It would pull the airframe up
into a 90 degree body angle and then stall the machine into an airshow
tailslide just like Art Shoal used to. Even if you disc the A/P on
the pull up it's too late. The machine has insuficient down elevator
authority now to arrest the pull up(cuz nugget ran the tailplane down
and "Auhhto" overshot it the back the other direction to get even;
there was no aural stabilizer-in-motion sound in a/p trim so nobody
noticed the comming set-up!) Great French design! Hang on Grandma!
We called these man vs. machine incidents/accidents.

> bushes when he was looking down on them as he descended, were actually
> trees that were higher than he was. He couldn't raise the nose, as
> the fly-by-wire (FBW) was already on the AOA limiter, so the only way to
> climb was to get more airspeed. He slammed the thrust levers forward, and
> the FADEC accelerated the engine on its normal acceleration schedule.
>
> Turbine engines run more efficiently if they are running close to the
> surge line (i.e almost ready to compressor stall). But the engine has to
> come closer to the surge line to accelerate. So the closer you run to the
> surge line the slower acceleration you'll have.
>
> FAR 25.119(a) requires go-around performance to be calculated using the
> thrust that is available 8 seconds after a throttle slam from idle.
> Manufacturers want the engine to run as efficiently as possible, but they
> don't want to take a hit on the AFM go-around performance. So, they
> typically design the fuel controls to allow full go-around thrust to be
> reached in just less than 8 seconds from a throttle slam from idle. I've
> done tests to check the acceleration on many transport category aircraft,
> and the result is usually somewhere between 7 and 8 seconds, and this is
> the same no matter whether the engine has a FADEC or an "old fashioned"
> hydro-mechanical fuel control unit.

Were the engines in flight idle? Were you guys pulling the ground
sensor breaker? Ground idle takes longer. Older High Bypass designs
eg: the GE CF6-80 series only take about six seconds from flight idle
to reach GA thrust IIRC, but still cannot over boost. But it's more
like twelve seconds in profile mode (slow spool up looking at FMS
parameters.) So I remembered it wrong. I think he tried to change alt
with Level Change and Profile mode engaged first, and when nothing
much happened (norm) he smashed the thrust levers to the wall and ate
wood. But Kevin, I'll concede the acceleration argument to you.
(Older designs were even slower (something like fifteen seconds to
spool up (e.g. GE CF700's aft-fans.) You could bust altitudes
descending, if you didn't lead with the throttles a couple thousand
feet before level off.

>
> So don't blame the FADEC for the A320 accident at Mulhouse-Habsheim. It
> was caused by a pilot who had way too much confidence in the low-speed
> protections of the FBW.

Yep, you're right. FADEC by itself didn't put him in the trees. But
most accidents have "a chain" of factors that cause the accident. If
you can break any one of the factorial links the accident would not
happen. I submit the inability to get over-boost power was just one
of those links. Another was a FBW AOA limit that cannot be
temporarily sacrificed to clear obstacles.

> Fortunately the FBW prevented him from raising
> the nose, as then the aircraft would have stalled, any many people would
> probably have died. As it was "only" three live were lost.

Well I have to disagree with this. We train annually now to fly below
stick shaker to escape microburst wind shear ground contact on t/o.
We will go below stall speed (bugged) momentarily in ground effect
will full power to avoid contact. We don't care about airspeed. We
only look at V/S. If we didn't do this, some dry microbusts would
kill us. Risking a stall is always better than contact with hard
objects. (remember impact g-force energy goes up exponentially with
speed) (besides: most jets don't break fast, they burble and
pre-buffet a bit first. After a positive rate is obtained and we're
still alive, then we fly on intermittent stick shaker (way higher deck
angles than FD/AP AOA limits) until about 1000 ft AGL. AOA FBW
autopilots never fly at speeds this low to escape terrain to my
knowledge. But I'd have to ask an A320 driver to be sure. The other
thing that bugs me about that machine is not being able to bust into a
45 degree bank. (Another thread for that one.)

But keep in mind that if you'd advocated these advanced techniques
twenty years ago, they would've pulled your ticket. :-(

(but you'd still be alive.) :-) Now's its req FAA training. Note:
These techniques vary widely from airline to airline and change from
Chief Kahuna to Chief Kahuna. YMMV. For the record I think FADEC is
great. Do you want it in your GA airplane?

Cheers,

pacplyer

[pacplyer]

(Veeduber) wrote in message >...
> >the test pilot was
> >interviewed in the hospital. He stated that nothing happened when he
> >called for max power.
>
> --------------------------------------------------------------
>
> I hate it when that happens :-)
>
> -R.S.Hoover

It can ruin your whole day. ;-) Enjoyed your sheetmetal "air
drill" stuff last night. Thanks

pac

[Kevin Horton]

On Mon, 01 Mar 2004 17:52:00 -0800, pacplyer wrote:

> Great Stuff Kevin, thanks for your insight. I have a couple of points I
> slightly disagree with however further down in your post. :-)
>
> Kevin Horton > wrote:
>
> After you got yourself behind the power curve, however, for whatever
> reason, I'm essentially talking about old-school guys like me who were
> used to flying non-FADEC machines capable of "overboost." If you got into
> trouble, because you were stupid, in say the previous generation of Boeing
> products: You could always push up and call for power far in excess of
> limiting max GA epr or N1, N2, EGT limits. (but maybe that's because like
> you say: old eng's didn't operate so close to the surge/stall margin.)
> It's unlikely the engines were going to fail like a piston or super/turbo
> charged engine might. Those old buckets would warp. The blades might
> creep and stretch and the engines might have to be scrapped (at say 5 mill
> a copy.) But you had a better chance of clearing the trees by going all
> way the to the mechanical stops (physical wire to the FCU Hydr/Mech
> linkage) than you do now with a Throttle resolver / PFM/MEC/ FADEC
> arrangement. The airbus test pilot may think he's called for Jesus power,
> but FADEC will not let him have it.
> This may have saved me a couple of times in my career flying 60's gen
> aircraft overseas. You smash everything to the wall and only slightly
> pull back on the engines that are "barking." (compressor stalling.) ATC
> would steer you into mountains in those days in some places. (more war
> stories.)
>
OK. I misunderstood your gripe against FADECs in the first message. I
too am not happy to have a FADEC limit how much thrust I get out of the
engine. I would much rather have some way to override it if the s*** hits
the fan. But, I don't think this would have made any difference in the
Habsheim accident. All published reports have said either that the
engines didn't respond at all, or that they were still spooling up when he
hit the trees. The only report I can find that actually quotes an N1 says
the engines were at 83% N1, which must be well below TOGA, so the engines
would have still been accelerating, and it wouldn't have mattered what rpm
was commanded.

There was a bit on an internal bun fight at Bombardier when the CRJ-700
was being designed. It has a FADEC engine, and the flight test folks were
not happy about the inability to get more thrust if needed. The engine
does have an Automatic Power Reserve (APR) that commands a thrust bump if
you have an engine failure. The powerplants engineers were persuaded to
add a heavy detent that you can push the thrust levers through to allow
you to get APR thrust with both engines running if you really need it.

The Bombardier Global Express also has a FADEC engine, but there are two
little switches behind the thrust levers that allow the crew to manually
select a back up N1 control mode. If the engine is in N1 control mode,
you are no longer limited except by the overspeed limiter, which allows
you to get much more thrust if needed.


>
>>
>> Turbine engines run more efficiently if they are running close to the
>> surge line (i.e almost ready to compressor stall). But the engine has
>> to come closer to the surge line to accelerate. So the closer you run
>> to the surge line the slower acceleration you'll have.
>>
>> FAR 25.119(a) requires go-around performance to be calculated using the
>> thrust that is available 8 seconds after a throttle slam from idle.
>> Manufacturers want the engine to run as efficiently as possible, but
>> they don't want to take a hit on the AFM go-around performance. So,
>> they typically design the fuel controls to allow full go-around thrust
>> to be reached in just less than 8 seconds from a throttle slam from
>> idle. I've done tests to check the acceleration on many transport
>> category aircraft, and the result is usually somewhere between 7 and 8
>> seconds, and this is the same no matter whether the engine has a FADEC
>> or an "old fashioned" hydro-mechanical fuel control unit.
>
> Were the engines in flight idle? Were you guys pulling the ground sensor
> breaker? Ground idle takes longer. Older High Bypass designs eg: the GE
> CF6-80 series only take about six seconds from flight idle to reach GA
> thrust IIRC, but still cannot over boost. But it's more like twelve
> seconds in profile mode (slow spool up looking at FMS parameters.) So I
> remembered it wrong. I think he tried to change alt with Level Change and
> Profile mode engaged first, and when nothing much happened (norm) he
> smashed the thrust levers to the wall and ate wood. But Kevin, I'll
> concede the acceleration argument to you. (Older designs were even slower
> (something like fifteen seconds to spool up (e.g. GE CF700's aft-fans.)
> You could bust altitudes descending, if you didn't lead with the throttles
> a couple thousand feet before level off.

The 8 second requirement is for an acceleration from flight idle. There
is typically some worst case condition (specific bleed configuration,
altitude and temperature) where the engine will be close to 8 seconds, and
it will be a bit better at other conditions. So I am not surprised if you
saw about 6 seconds in many cases.

>
>
>> So don't blame the FADEC for the A320 accident at Mulhouse-Habsheim. It
>> was caused by a pilot who had way too much confidence in the low-speed
>> protections of the FBW.
>
> Yep, you're right. FADEC by itself didn't put him in the trees. But most
> accidents have "a chain" of factors that cause the accident. If you can
> break any one of the factorial links the accident would not happen. I
> submit the inability to get over-boost power was just one of those links.
> Another was a FBW AOA limit that cannot be temporarily sacrificed to clear
> obstacles.
>
>> Fortunately the FBW prevented him from raising the nose, as then the
>> aircraft would have stalled, any many people would probably have died.
>> As it was "only" three live were lost.
>
> Well I have to disagree with this. We train annually now to fly below
> stick shaker to escape microburst wind shear ground contact on t/o. We
> will go below stall speed (bugged) momentarily in ground effect will full
> power to avoid contact. We don't care about airspeed. We only look at
> V/S. If we didn't do this, some dry microbusts would kill us. Risking a
> stall is always better than contact with hard objects. (remember impact
> g-force energy goes up exponentially with speed) (besides: most jets
> don't break fast, they burble and pre-buffet a bit first. After a
> positive rate is obtained and we're still alive, then we fly on
> intermittent stick shaker (way higher deck angles than FD/AP AOA limits)
> until about 1000 ft AGL. AOA FBW autopilots never fly at speeds this low
> to escape terrain to my knowledge. But I'd have to ask an A320 driver to
> be sure. The other thing that bugs me about that machine is not being
> able to bust into a 45 degree bank. (Another thread for that one.)
>
Well, the AOA limiter an the Airbus's is set very close to the stall. It
is well beyond where a stick shaker would be. The curve of lift vs AOA
tends to have a fairly flat top with modern swept wing jets, so once you
get up on top of that curve there isn't any benefit to pulling more AOA,
as you don't get any more lift. I wish there was some way to get in a FBW
Airbus sim with you. We could do two windshear recoveries - one using
full aft stick riding on the AOA limiter, and one in Direct Law, with no
AOA limiter. I'm convinced you would do better just using the AOA limiter.

>For the record I think FADEC is great. Do you want it in your GA airplane?

Well, I'm a suspicious type, and I want to see some more service history
first to assure myself that they've sorted all the bugs out. So not on
my RV-8 project, but maybe on the next one.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

[Bill Daniels]

"Dan Thomas" > wrote in message
om...
> "Bill Daniels" > wrote in message news:<5_-> > It seems
to me that the gear analogy is spot on. A variable pitch
> > > prop has EXACTLY the same function as the gearbox on a car.
> >
> > Not quite. Gears don't have preferred operating conditions, props do.
> >
> > The engine has its preferred RPM and torque for optimum efficiency and
the
> > prop blades have their optimum angle of attack. If the engine/prop
> > combination results in the prop operating at a higher (or lower) angle
of
> > attack than optimum to absorb the torque of the engine (Prop governor
> > increases pitch to hold RPM setting.) then the combination operates
below
> > optimum conditions.
> >
> > Under some conditions, it would make sense to introduce a third variable
> > i.e. a gearbox between the engine and prop, to allow both the engine and
> > prop to operate at peak efficiency. This was the reason that two-speed
> > grearsets were installed in the nose case of some large radials. This,
in
> > turn, allowed the propeller designer to optimize his prop blades for a
> > single AOA, thus gaining still more efficiency.
> >
> > The problem, simply stated was this: How does a heavily loaded,
long-range
> > bomber haul itself off a short runway and climb to cruise altitude and
then
> > shift to highly efficient, long-range cruise. The answer was just
emerging
> > from the labs as the world shifted to turbines. The flight engineer
would
> > shift his engines into a "hole gear" by selecting a cam profile and
engine
> > timing optimized for the low gear that would let the engines scream at
high
> > RPM and pump massive HP into props set for maximum acceleration and
climb.
> > Once in cruise, the engineer would shift his engines back to low RPM,
high
> > efficiency settings.
>
> First time I've ever heard of gear-shifted props in certified
> engines. Which engines were these? I know that many radials (and other
> engine layouts) used reduction gearing in the case nose to allow the
> engine to run faster and produce more HP while keeping the prop within
> safe limits, and that there were two-speed geared superchargers on
> many of these engines, but two-speed props?
> Jim Bede used a snowmobile-type propshaft drive in the early
> BD-5s but abandoned it as unworkable. It still required a relatively
> tiny prop to keep the tip speeds subsonic.
> As far as the propeller pitch angles go, the constant speed prop
> improves takeoff performance by more than just letting engine RPM
> reach redline to produce max HP. It reduces the angle of attack so
> that more of the prop is unstalled and producing thrust in the static
> condition, improving acceleration and shortening takeoff distance. The
> inboard sections of a fixed-pitch prop blade have a large angle so
> that they still produce thrust in faster forward flight even though
> they don't travel the circumferential distance that blade areas near
> the tips do, but the large angle means a stalled blade, or at least a
> really turbulent flow, at low forward speeds. A gear-shifted
> fixed-pitch prop will still have those problems.
>
> Dan

The gear shifted prop was the last gasp of piston engine development before
the turbine age. Look at the Lycoming XR7755, Napier Nomad or the Rolls
Royce Crecy. These were 5000 HP+ monsters that needed every trick in the
engineers bag. Piston engines produce more HP at high RPM at the cost of
fuel consumption but deliver low fuel consumption at low RPMS. Props
produce more thrust at low RPM and most efficiency with the blades at a
single best AOA. That AOA must be maintained over a wide range of
airspeeds. Just too many variables for a CS prop to deal with alone.

The two speed gearbox isn't perfect but it does buy the engineer a bigger
range of options.

Bill Daniels

[Dan Thomas]

Kevin Horton > wrote in message >...
> Some of the supercharged recips had a gear box with two different gear
> ratios to drive the supercharger. They needed to spin the supercharger at
> high rpm at high altitude in order to get enough manifold pressure. But
> if they used the same supercharger gear ratio at low altitude it would
> produce more manifold pressure than the engine could handle at full
> throttle. The engine would then have to be run very throttled, and there
> would be a lot of wasted power used to spin that supercharger at a
> needlessly high rpm. So, they used a different gear ratio to spin the
> supercharger at a lower rpm for take-off and low altitude flight.


Yes, I knew that about the supercharger gearing to allow different
settings at altitude, but the poster I was questioning had discussed
(or seemed to hint at) a two-speed propeller drive; in other words, a
transmission. I had never heard of it, outside of Jim Bede's
belt-driven variable-ratio system in the early BD-5.
The only propeller gearing I've ever seen is a fixed reduction as
used in many larger radials, all the V-12s except very early ones, and
many opposed engines such as the Continental GO-300 (Cessna 175),
Lyc's GO-480 (Helio), and GTSIO-540 (Cessna 414 or 421?), and
Continental's Tiara engine that never reached significant production.
And, of course, all turboprop, turbofan and turboshaft engines. All
with a fixed ratio, single reduction. And all to allow the engine to
develop high RPM and therefore higher HP, while allowing a larger,
slower prop to operate in an efficient range.
It seems to me that turning a prop faster in cruise flight is
self-defeating, since drag rises as tip speeds rise with forward speed
factored into the operation. It's why airplanes with big props like
the Dash 8 turn at around 1300 for takeoff and 850 or so in cruise,
and why variable pitch of the blade is absolutely necessary.
Dan

[Corky Scott]

On Tue, 2 Mar 2004 07:32:33 -0700, "Bill Daniels" >
wrote:

>The gear shifted prop was the last gasp of piston engine development before
>the turbine age. Look at the Lycoming XR7755, Napier Nomad or the Rolls
>Royce Crecy. These were 5000 HP+ monsters that needed every trick in the
>engineers bag. Piston engines produce more HP at high RPM at the cost of
>fuel consumption but deliver low fuel consumption at low RPMS. Props
>produce more thrust at low RPM and most efficiency with the blades at a
>single best AOA. That AOA must be maintained over a wide range of
>airspeeds. Just too many variables for a CS prop to deal with alone.
>
>The two speed gearbox isn't perfect but it does buy the engineer a bigger
>range of options.
>
>Bill Daniels
>
Bill, are you talking about a two position propeller, as opposed to a
two position reduction drive transmission for the engine?

Early in WWII, some props used a variable pitch mechanism that allowed
the pilot to adjust the pitch, and therefore the engine rpm to any
setting withing the design limits of the prop's pitch. Normally
they'd select fine pitch for takeoff and coarse pitch for cruise. I
suppose some of the props had just those two settings, but most of
them allowed any setting inbetween.

This wasn't a constant speed prop, just an adjustable prop.

Is this what you are referring to?

Thanks, Corky Scott

PS, it isn't a bygone design, there are some adjustable props on the
market for the homebuilt industry today that allow variable pitch, but
are not constant speed props.

[Big John]

This is kind of a mish mash for a number of posts to this thread.

1. The Merlin (In P-51) had a 2/1 reduction gear. At full throttle
engine turned 3000 rpm and the big prop only turned 1500 rpm.

2. Merlin had a two stage blower. Low blower was set so at 'gate' you
could pull 61 inches at sea level. There was a spring loaded switch
that you could check high blower prior to T/O. The high blower was
controlled by a aneroid and it automatically shifted to high blower
between 12-14K (not a precise altitude). If you were in formation and
the lead bird shifted to high blower and your bird hadn't yet, we had
a fix for that problem. The mech would take a length of safety wire
and loop it under the spring loaded switch and thread it up behind the
safety guard over switch. Then to manually switch to high blower to
stay in formation you would grab the ends of the safety wire and
manually lift the switch to shift to high blower and at the same time
just wrap the safety wire around the safety cover over switch. Of
course after your engine had shifted to high blower automatically, you
could unwind the wire and let switch go back to the automatic position
so you wouldn't inadvertently over boost the engine during descent.

3. I also on a number of missions, flew with the prop pitch pulled
full back (high pitch) and full throttle. (all within the allowable
BMEP). Airspeed was about 140-150 mph under 500 feet where we were
flying. About every 30 minutes Merlin would get rough with that power
setting and we would have to clean the engine out. First pull the
throttle back and then start the prop lever forward (toward flat
pitch). That 'old' Merlin would buck and spit and shake and blow
black balls of smoke out of stacks and cut out and you would have to
stop and let if clean itself out a little at which time you could push
the prop some more forward again. If would take a minute or two to get
the engine to take full throttle at max rpm and you then ran full
throttle for 2-3 minutes to clean things out and then you pulled back
to the low rpm again. At the low rpm the MP was self limiting and full
throttle only gave you 15 or so inches. In this mode the prop was
turning so slow that you could see the blades and count them as they
went by.

All this is just an aside on engine operation with the Merlin in a
time and land far away (sure beats a 65 Cont <G>).

Big John


On 26 Feb 2004 13:04:46 -0800, (Jay) wrote:

>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.

[Bill Daniels]

"Corky Scott" > wrote in message
...
> On Tue, 2 Mar 2004 07:32:33 -0700, "Bill Daniels" >
> wrote:
>
> >The gear shifted prop was the last gasp of piston engine development
before
> >the turbine age. Look at the Lycoming XR7755, Napier Nomad or the Rolls
> >Royce Crecy. These were 5000 HP+ monsters that needed every trick in the
> >engineers bag. Piston engines produce more HP at high RPM at the cost of
> >fuel consumption but deliver low fuel consumption at low RPMS. Props
> >produce more thrust at low RPM and most efficiency with the blades at a
> >single best AOA. That AOA must be maintained over a wide range of
> >airspeeds. Just too many variables for a CS prop to deal with alone.
> >
> >The two speed gearbox isn't perfect but it does buy the engineer a
bigger
> >range of options.
> >
> >Bill Daniels
> >
> Bill, are you talking about a two position propeller, as opposed to a
> two position reduction drive transmission for the engine?
>
> Early in WWII, some props used a variable pitch mechanism that allowed
> the pilot to adjust the pitch, and therefore the engine rpm to any
> setting withing the design limits of the prop's pitch. Normally
> they'd select fine pitch for takeoff and coarse pitch for cruise. I
> suppose some of the props had just those two settings, but most of
> them allowed any setting inbetween.
>
> This wasn't a constant speed prop, just an adjustable prop.
>
> Is this what you are referring to?
>
> Thanks, Corky Scott
>
> PS, it isn't a bygone design, there are some adjustable props on the
> market for the homebuilt industry today that allow variable pitch, but
> are not constant speed props.
>
>
No, I'm really talking about a two-speed gearbox that lets the engine rev
higher for a given prop rpm during takeoff and initial climb. The system,
as I understand it was as follows:

|-----------------|
| Engine |>>>>|Two speed planetary gear box|>>>>>|Constant Speed
Prop|
|-----------------|

The engine had cams that could move axially to use two different cam
profiles. One for high-RPM power and another for low-RPM cruise. The
ignition timing was adjustable at the same time.

The gearbox was a planetary not unlike the old Chevy two speed automatics
but without the torque converter. The gear change was accomplished by bands
that braked one part or another of the planetary set. To continue the
analogy of the old Chevy, the prop takes the place of the torque converter.

The prop was designed to absorb the extra torque at takeoff with the engine
screaming in low gear and to turn slowly, about 800 RPM, at cruise. It is
just an attempt to address the issue of the prop being off its design point
in certain flight regimes. Basically you want the prop at its maximum
Thrust/Power at TO and its best Thrust/Drag at cruise.

If the prop is used alone to control engine RPM, then it will not always be
at those best design points. You may know that a Mooney or Bonanza has
"sweet spots" where the range is noticeably better. In the old Mooney, 1900
RPM and 22-25 inches MP gave much better range than running it "square". It
would have been better if the engine turned a bit faster but that would have
put the prop at a lower pitch (think wing AOA) than optimum for the blade
geometry and airfoils.

Bill Daniels
|

[Steve Smith]

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 >...
> (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

[Ernest Christley]

BllFs6 wrote:
>>It seems to me that the gear analogy is spot on. A variable pitch
>>prop has EXACTLY the same function as the gearbox on a car.
>>
>>
>
>
> Dumb newbie question here...
>
> If you have a prop that is best for cruise....am I right in assuming it has
> "too much of a bite" on the air when the aircraft is sitting still...therefore
> the engine doesnt have enough torque...and therefore the prop cant spin quite
> as fast as it would otherwise...and both these lead to less low speed thrust
> than you would like?
>
> And if that is the case...could you not use something like water mist injection
> or nitrous oxide to temporarily increase the torque the motor produces?
>
> Probably wount make much sense if you really wanted it for many minutes of
> climbing....but it might make sense if all your trying to do is shorten your
> takeoff distance.....
>
> take care
>
> Blll

Only up to a point. If you put in too much pitch, the prop will start
the takeoff roll in a stalled situation. The prop will be pushing air
around in a circle instead of back. The extreme case is flat paddles
that will push no air backwards at all.

Many people actually do this on purpose as a way to exchange more top
speed when they have enough power to accelerate quickly after wasting
half the runway with a stall prop.

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

[Dillon Pyron]

On Mon, 1 Mar 2004 08:25:38 -0700, "Bill Daniels" >
wrote:


>A propeller is not a gear box analog. It is more like the torque converter
>in an automatic transmission. A torque converter still needs a gearbox
>behind it for efficiency.
>
>Bill Daniels

Sounds like a CVT to me. Of course, I don't know nothing about props.
--
dillon

Life is always short, but only you can make it sweet

[Kevin Horton]

On Tue, 02 Mar 2004 07:32:33 -0700, Bill Daniels wrote:

>
> The gear shifted prop was the last gasp of piston engine development
> before the turbine age. Look at the Lycoming XR7755, Napier Nomad or the
> Rolls Royce Crecy. These were 5000 HP+ monsters that needed every trick
> in the engineers bag. Piston engines produce more HP at high RPM at the
> cost of fuel consumption but deliver low fuel consumption at low RPMS.
> Props produce more thrust at low RPM and most efficiency with the blades
> at a single best AOA. That AOA must be maintained over a wide range of
> airspeeds. Just too many variables for a CS prop to deal with alone.
>
> The two speed gearbox isn't perfect but it does buy the engineer a bigger
> range of options.
>
> Bill Daniels


Bill,

Thanks for pointing out these fascinating engines. I had heard of all of
them, but had never really looked into the details before.

The Lycoming XR-7755 certainly was a huge, complicated monster.

http://www.aviation-history.com/engines/xr-7755.html
http://www.people.virginia.edu/~rjr/engines/

The Napier Nomad was a bizarre combination of two-stroke diesel and gas
turbine. It managed a very impressive specific fuel consumption of 0.345
lb/ehp/hr. The only reference I can find to a gear box was a variable
ratio gearbox between the gas turbine and the piston crankshaft of the
Nomad 2. Not exactly what the original poster was referring too, but
interesting non-the-less.

http://www.home.aone.net.au/shack_one/nomad.htm
http://www.yourencyclopedia.net/Napier_Nomad

The Rolls-Royce Crecy was a highly supercharged diesel, that supposedly
produced about 5,000 on the test stand. I can't find any reference to a
two-speed gear box between the engine and the prop either on-line, or in
Aero Engines, Bill Gunston, but neither have I found a detailed technical
description of the engine. So perhaps that detail was left out.

<http://www.stobbe.dk/technical_literature/combustion_engines/rolls-royce/Rolls-aircraft.html>

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

[Richard Lamb]

Bill Daniels wrote:
>
> "Corky Scott" > wrote in message
> ...
> > On Tue, 2 Mar 2004 07:32:33 -0700, "Bill Daniels" >
> > wrote:
> >
> > >The gear shifted prop was the last gasp of piston engine development
> before
> > >the turbine age. Look at the Lycoming XR7755, Napier Nomad or the Rolls
> > >Royce Crecy. These were 5000 HP+ monsters that needed every trick in the
> > >engineers bag. Piston engines produce more HP at high RPM at the cost of
> > >fuel consumption but deliver low fuel consumption at low RPMS. Props
> > >produce more thrust at low RPM and most efficiency with the blades at a
> > >single best AOA. That AOA must be maintained over a wide range of
> > >airspeeds. Just too many variables for a CS prop to deal with alone.
> > >
> > >The two speed gearbox isn't perfect but it does buy the engineer a
> bigger
> > >range of options.
> > >
> > >Bill Daniels
> > >
> > Bill, are you talking about a two position propeller, as opposed to a
> > two position reduction drive transmission for the engine?
> >
> > Early in WWII, some props used a variable pitch mechanism that allowed
> > the pilot to adjust the pitch, and therefore the engine rpm to any
> > setting withing the design limits of the prop's pitch. Normally
> > they'd select fine pitch for takeoff and coarse pitch for cruise. I
> > suppose some of the props had just those two settings, but most of
> > them allowed any setting inbetween.
> >
> > This wasn't a constant speed prop, just an adjustable prop.
> >
> > Is this what you are referring to?
> >
> > Thanks, Corky Scott
> >
> > PS, it isn't a bygone design, there are some adjustable props on the
> > market for the homebuilt industry today that allow variable pitch, but
> > are not constant speed props.
> >
> >
> No, I'm really talking about a two-speed gearbox that lets the engine rev
> higher for a given prop rpm during takeoff and initial climb. The system,
> as I understand it was as follows:
>
> |-----------------|
> | Engine |>>>>|Two speed planetary gear box|>>>>>|Constant Speed
> Prop|
> |-----------------|
>
> The engine had cams that could move axially to use two different cam
> profiles. One for high-RPM power and another for low-RPM cruise. The
> ignition timing was adjustable at the same time.
>
> The gearbox was a planetary not unlike the old Chevy two speed automatics
> but without the torque converter. The gear change was accomplished by bands
> that braked one part or another of the planetary set. To continue the
> analogy of the old Chevy, the prop takes the place of the torque converter.
>
> The prop was designed to absorb the extra torque at takeoff with the engine
> screaming in low gear and to turn slowly, about 800 RPM, at cruise. It is
> just an attempt to address the issue of the prop being off its design point
> in certain flight regimes. Basically you want the prop at its maximum
> Thrust/Power at TO and its best Thrust/Drag at cruise.
>
> If the prop is used alone to control engine RPM, then it will not always be
> at those best design points. You may know that a Mooney or Bonanza has
> "sweet spots" where the range is noticeably better. In the old Mooney, 1900
> RPM and 22-25 inches MP gave much better range than running it "square". It
> would have been better if the engine turned a bit faster but that would have
> put the prop at a lower pitch (think wing AOA) than optimum for the blade
> geometry and airfoils.
>
> Bill Daniels
> |

I vaguely misremember some thing like that cam shifting and stuff.

But I don't think anything ever came of it.

I'm holding out for software controlled valves.

Look Ma, No Cams!

[Blueskies]

So what did you do if your plane shifted to high blower but the lead didn't? Pull it back real quick I suppose...

I like that 15" and (maybe) 500 rpm - really lugging it...

--
Dan D.



..
"Big John" > wrote in message ...
> This is kind of a mish mash for a number of posts to this thread.
>
> 1. The Merlin (In P-51) had a 2/1 reduction gear. At full throttle
> engine turned 3000 rpm and the big prop only turned 1500 rpm.
>
> 2. Merlin had a two stage blower. Low blower was set so at 'gate' you
> could pull 61 inches at sea level. There was a spring loaded switch
> that you could check high blower prior to T/O. The high blower was
> controlled by a aneroid and it automatically shifted to high blower
> between 12-14K (not a precise altitude). If you were in formation and
> the lead bird shifted to high blower and your bird hadn't yet, we had
> a fix for that problem. The mech would take a length of safety wire
> and loop it under the spring loaded switch and thread it up behind the
> safety guard over switch. Then to manually switch to high blower to
> stay in formation you would grab the ends of the safety wire and
> manually lift the switch to shift to high blower and at the same time
> just wrap the safety wire around the safety cover over switch. Of
> course after your engine had shifted to high blower automatically, you
> could unwind the wire and let switch go back to the automatic position
> so you wouldn't inadvertently over boost the engine during descent.
>
> 3. I also on a number of missions, flew with the prop pitch pulled
> full back (high pitch) and full throttle. (all within the allowable
> BMEP). Airspeed was about 140-150 mph under 500 feet where we were
> flying. About every 30 minutes Merlin would get rough with that power
> setting and we would have to clean the engine out. First pull the
> throttle back and then start the prop lever forward (toward flat
> pitch). That 'old' Merlin would buck and spit and shake and blow
> black balls of smoke out of stacks and cut out and you would have to
> stop and let if clean itself out a little at which time you could push
> the prop some more forward again. If would take a minute or two to get
> the engine to take full throttle at max rpm and you then ran full
> throttle for 2-3 minutes to clean things out and then you pulled back
> to the low rpm again. At the low rpm the MP was self limiting and full
> throttle only gave you 15 or so inches. In this mode the prop was
> turning so slow that you could see the blades and count them as they
> went by.
>
> All this is just an aside on engine operation with the Merlin in a
> time and land far away (sure beats a 65 Cont <G>).
>
> Big John
>
>
> On 26 Feb 2004 13:04:46 -0800, (Jay) wrote:
>
> >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.
>

[Big John]

Dan

Yep. Not a problem it you shifted first to high blower. You just
adjusted your power to stay in formation. You had more power than lead
and so just tucked it in and went on with mission.

Engine did not lug. We ran the figures on the BMEP and well within
acceptable range. Was not stressing the engine at all.

Big John

On Wed, 03 Mar 2004 01:17:54 GMT, "Blueskies" > wrote:

>So what did you do if your plane shifted to high blower but the lead didn't? Pull it back real quick I suppose...
>
>I like that 15" and (maybe) 500 rpm - really lugging it...

[Blueskies]

I didn't mean stressing, it was really just ticking over, and still you were going 140-150 mph - what was the power
output at that setting?

--
Dan D.



..
"Big John" > wrote in message ...
> Dan
>
> Yep. Not a problem it you shifted first to high blower. You just
> adjusted your power to stay in formation. You had more power than lead
> and so just tucked it in and went on with mission.
>
> Engine did not lug. We ran the figures on the BMEP and well within
> acceptable range. Was not stressing the engine at all.
>
> Big John
>
> On Wed, 03 Mar 2004 01:17:54 GMT, "Blueskies" > wrote:
>
> >So what did you do if your plane shifted to high blower but the lead didn't? Pull it back real quick I suppose...
> >
> >I like that 15" and (maybe) 500 rpm - really lugging it...
>

[Bill Daniels]

"Kevin Horton" > wrote in message
...
> On Tue, 02 Mar 2004 07:32:33 -0700, Bill Daniels wrote:
>
> >
> > The gear shifted prop was the last gasp of piston engine development
> > before the turbine age. Look at the Lycoming XR7755, Napier Nomad or
the
> > Rolls Royce Crecy. These were 5000 HP+ monsters that needed every trick
> > in the engineers bag. Piston engines produce more HP at high RPM at the
> > cost of fuel consumption but deliver low fuel consumption at low RPMS.
> > Props produce more thrust at low RPM and most efficiency with the blades
> > at a single best AOA. That AOA must be maintained over a wide range of
> > airspeeds. Just too many variables for a CS prop to deal with alone.
> >
> > The two speed gearbox isn't perfect but it does buy the engineer a
bigger
> > range of options.
> >
> > Bill Daniels
>
>
> Bill,
>
> Thanks for pointing out these fascinating engines. I had heard of all of
> them, but had never really looked into the details before.
>
> The Lycoming XR-7755 certainly was a huge, complicated monster.
>
> http://www.aviation-history.com/engines/xr-7755.html
> http://www.people.virginia.edu/~rjr/engines/
>
> The Napier Nomad was a bizarre combination of two-stroke diesel and gas
> turbine. It managed a very impressive specific fuel consumption of 0.345
> lb/ehp/hr. The only reference I can find to a gear box was a variable
> ratio gearbox between the gas turbine and the piston crankshaft of the
> Nomad 2. Not exactly what the original poster was referring too, but
> interesting non-the-less.
>
> http://www.home.aone.net.au/shack_one/nomad.htm
> http://www.yourencyclopedia.net/Napier_Nomad
>
> The Rolls-Royce Crecy was a highly supercharged diesel, that supposedly
> produced about 5,000 on the test stand. I can't find any reference to a
> two-speed gear box between the engine and the prop either on-line, or in
> Aero Engines, Bill Gunston, but neither have I found a detailed technical
> description of the engine. So perhaps that detail was left out.
>
>
<http://www.stobbe.dk/technical_literature/combustion_engines/rolls-royce/Ro
lls-aircraft.html>
>
> --
> Kevin Horton RV-8 (finishing kit)
> Ottawa, Canada
> http://go.phpwebhosting.com/~khorton/rv8/
> e-mail: khorton02(_at_)rogers(_dot_)com
>

I keep dreaming that someone sifted through all the old engineering test
reports to find the gems of wisdom developed by the slide-rule engineers who
built these fantastic engines. I'd bet there are ideas that might not have
worked then that could be used today given the advances in materials and
fabrication techniques.

Imagine a Nomad or Crecy with ceramic bearings and piston crowns and thermal
barrier coatings - or with a FADEC system. I've read that all three
companies were certain that their engines could have been developed to
10,000 HP. Imagine a C-130 with one third the fuel consumption.

Bill Daniels

[pacplyer]

Kevin Horton > wrote <snip>

> Well, the AOA limiter an the Airbus's is set very close to the stall. It
> is well beyond where a stick shaker would be. The curve of lift vs AOA
> tends to have a fairly flat top with modern swept wing jets, so once you
> get up on top of that curve there isn't any benefit to pulling more AOA,
> as you don't get any more lift. I wish there was some way to get in a FBW
> Airbus sim with you. We could do two windshear recoveries - one using
> full aft stick riding on the AOA limiter, and one in Direct Law, with no
> AOA limiter. I'm convinced you would do better just using the AOA limiter.
>

I would enjoy that. You could be right.

> >For the record I think FADEC is great. Do you want it in your GA airplane?
>
> Well, I'm a suspicious type, and I want to see some more service history
> first to assure myself that they've sorted all the bugs out. So not on
> my RV-8 project, but maybe on the next one.

Sounds very wise indeed. Great shots of your RV-8 by the way.

pac

[Kevin Horton]

On Tue, 02 Mar 2004 20:25:48 -0700, Bill Daniels wrote:


> "Kevin Horton" > wrote in message
> ...
>> On Tue, 02 Mar 2004 07:32:33 -0700, Bill Daniels wrote:
>>
>>
>> > The gear shifted prop was the last gasp of piston engine development
>> > before the turbine age. Look at the Lycoming XR7755, Napier Nomad or
> the
>> > Rolls Royce Crecy. These were 5000 HP+ monsters that needed every
>> > trick in the engineers bag. Piston engines produce more HP at high
>> > RPM at the cost of fuel consumption but deliver low fuel consumption
>> > at low RPMS. Props produce more thrust at low RPM and most efficiency
>> > with the blades at a single best AOA. That AOA must be maintained
>> > over a wide range of airspeeds. Just too many variables for a CS
>> > prop to deal with alone.
>> >
>> > The two speed gearbox isn't perfect but it does buy the engineer a
> bigger
>> > range of options.
>> >
>> > Bill Daniels
>>
>>
>> Bill,
>>
>> Thanks for pointing out these fascinating engines. I had heard of all
>> of them, but had never really looked into the details before.
>>
>> The Lycoming XR-7755 certainly was a huge, complicated monster.
>>
>> http://www.aviation-history.com/engines/xr-7755.html
>> http://www.people.virginia.edu/~rjr/engines/
>>
>> The Napier Nomad was a bizarre combination of two-stroke diesel and gas
>> turbine. It managed a very impressive specific fuel consumption of
>> 0.345 lb/ehp/hr. The only reference I can find to a gear box was a
>> variable ratio gearbox between the gas turbine and the piston
>> crankshaft of the Nomad 2. Not exactly what the original poster was
>> referring too, but interesting non-the-less.
>>
>> http://www.home.aone.net.au/shack_one/nomad.htm
>> http://www.yourencyclopedia.net/Napier_Nomad
>>
>> The Rolls-Royce Crecy was a highly supercharged diesel, that supposedly
>> produced about 5,000 on the test stand. I can't find any reference to
>> a two-speed gear box between the engine and the prop either on-line, or
>> in Aero Engines, Bill Gunston, but neither have I found a detailed
>> technical description of the engine. So perhaps that detail was left
>> out.
>>
>>
> <http://www.stobbe.dk/technical_literature/combustion_engines/rolls-royce/Ro
> lls-aircraft.html>
>>
>> --
>> Kevin Horton RV-8 (finishing kit) Ottawa, Canada
>> http://go.phpwebhosting.com/~khorton/rv8/ e-mail:
>> khorton02(_at_)rogers(_dot_)com
>>
>>
> I keep dreaming that someone sifted through all the old engineering test
> reports to find the gems of wisdom developed by the slide-rule engineers
> who built these fantastic engines. I'd bet there are ideas that might
> not have worked then that could be used today given the advances in
> materials and fabrication techniques.
>
> Imagine a Nomad or Crecy with ceramic bearings and piston crowns and
> thermal barrier coatings - or with a FADEC system. I've read that all
> three companies were certain that their engines could have been
> developed to 10,000 HP. Imagine a C-130 with one third the fuel
> consumption.
>
> Bill Daniels

They were very complicated engines though, with a lot of moving parts. It
is hard to imagine that their reliability could have approached that of a
modern turbine engine.

The SFC of modern turbo props isn't all that bad. I couldn't find specs
quickly for the engine in the C-130J, but the 5,000 hp PW-150 supposedly
has an SFC of 0.433 at take-off power. I imagine the cruise SFC should be
slightly better, as that would be the design point. The engine supposedly
weighs 1521 lb. So I don't see how a development of those last great
piston engines would have one third the fuel consumption.

http://roger.ecn.purdue.edu/~propulsi/propulsion/jets/tprops/pw100.html

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

[Big John]

Dan

We normally cruised about 240 mph IAS under 10K in low blower. When
escorting bombers we would cut back to 190-225 or such for duration
and range. Still had to 'S'.

As I remember:

3000 rpm and 61 in. HG for T/O. Only time I pulled 67 In. HG (War
Emergency) got detonation even with the 'purple' (115-145
octane) gas.
2700 rpm and 45 in. HG for climb.
2200-2400 and 30-35 in. HG for cruise.
100 mph landing speed.
Final was 115 mph +/- depending on weight and reducing over over run
to stick on end of R/W.

Been a long time ago and could have been 125-130 cruise?? but seem to
remember it was a little higher than that.

Remember it was not close to stall speed and comfortable to fly.

Dash one shows that 1400 rpm/24 in. = 140 CAS at sea level where we
were flying but am sure the power setting was lower than that.

The '51 was a pretty slick bird and both oil and coolant doors were
probably stream lined due to low power output so no extra drag there
and still got the heat boost/thrust.

Weren't many rules back then and you could do a lot of things
especially during the war.

One story about a P-47 jock in Italy after VE day. One of the things
they did was capsize sail boats by flying over at full throttle and
low altitude and pulling the nose up as they went over and the prop
blast in the sails would turn the boat over.

So, one day this guy was out screwing around and there was a big fancy
sail boat and he made the pass and capsized it. Next day the word came
down asking who was flying that day and was turning boats over? The CO
asked around and sent the jocks name up the line thinking it was some
Italian big wig complaining.

Seems that all the Generals were out for a Sunday sail and partying
and they got turned over. Next day this guy was on a boat for the
Pacific and stayed well after VJ day <G> They wouldn't let him come
home even though he had the points.

With nothing but time on his hands, he used to fly (P-51) up to the
British (BCOF) base at Bofu (Honshu) that had a hill in the center of
the field with the tower on it. He wouldn't call in but dive down to
deck off the field and as he got to field roll over inverted and fly
across the field going up and over and then down the hill at 20 FT
altitude or so. BCOF troops thought that was wonderful and asked our
base who was doing it so they could invite him up to meet the troops
and have a party. When the Base CO found out he sent the guy home to
be kicked out so guess he finally broke the chain and got his
discharge <G>

Big John

On Wed, 03 Mar 2004 02:03:45 GMT, "Blueskies" > wrote:

>I didn't mean stressing, it was really just ticking over, and still you were going 140-150 mph - what was the power
>output at that setting?