Power questions

I've been looking at the performance charts for the Lycoming O-320-B and D series
engines. There's a line that is labeled "Limiting manifold pressure for continuous
operation". This line starts at sea level and 2400 rpm, runs through 2300 rpm at
about 2,000' ASL, and continues to 2000 rpm at about 6,500' ASL. Does this mean that
I am not supposed to operate this engine at 2000 rpm below 6,500' ASL? I have a fixed
pitch prop.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.

On Sun, 17 Oct 2004 03:43:47 GMT, "G.R. Patterson III"
wrote:

"Limiting manifold pressure for continuous
operation".

This sounds like a Constant Speed prop chart to me. As you know MP
isn't relavant for fixed pitch props. The manual may be for an engine
that can have both CS and fixed mated to it.

HTH.
z

On Sun, 17 Oct 2004 04:21:17 GMT, zatatime
wrote:

On Sun, 17 Oct 2004 03:43:47 GMT, "G.R. Patterson III"
wrote:

"Limiting manifold pressure for continuous
operation".

This sounds like a Constant Speed prop chart to me. As you know MP
isn't relavant for fixed pitch props. The manual may be for an engine
that can have both CS and fixed mated to it.

HTH.
z

Patterson's note of the chart referenced from altitude, as opposed to
manifold pressure, causes me to scratch my head, too.

May I ask why there is a limitation? I'm sure its not good to lug the
engine, and its impossible to lug an engine having a fixed-pitch prop.
But wouldn't the damage come from extra heat generated? So the temps
would change, but they could also be monitored. Yes, Lycoming knows
when their engine will overheat, but environment is not isolated from
it. Are rpm and manifold pressure so isolated to itself?

--Mike

zatatime wrote:

The manual may be for an engine
that can have both CS and fixed mated to it.

The engine has a hollow crank, so a manufacturer *could* use a CS prop. The note
*may* apply to only CS prop applications, but I don't know -- it doesn't say.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.

Mike Rhodes wrote:

Patterson's note of the chart referenced from altitude, as opposed to
manifold pressure, causes me to scratch my head, too.

There's another chart in the manual that relates combinations of manifold pressure
and rpm to horsepower (but not to altitude). It has a similar limit band, but this
one makes sense to me. It basically says that you should never exceed a manifold
pressure of 25.3 HG at 2200 rpm (for example). I don't know why that limit band is on
the altitude/hp chart. I'm hoping that it's something that only applies to CS props.
In that case, perhaps the chart simply means that it is impossible to exceed a
manifold pressure of 25.3 HG at 2200 rpm above 6,000' ASL but below that the pilot
needs to be careful?

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.

"G.R. Patterson III" wrote in message
...
I've been looking at the performance charts for the Lycoming O-320-B
and D series
engines. There's a line that is labeled "Limiting manifold pressure
for continuous
operation". This line starts at sea level and 2400 rpm, runs through
2300 rpm at
about 2,000' ASL, and continues to 2000 rpm at about 6,500' ASL. Does
this mean that
I am not supposed to operate this engine at 2000 rpm below 6,500' ASL?
I have a fixed
pitch prop.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to
have
been looking for it.

Since you don't have a constant-speed prop, don't worry about it. That
curve's just to keep you from over-boosting. With your fixed-pitch prop,
your rpm won't get too low.

John Lowry
Flight Physics

John T Lowry wrote:

Since you don't have a constant-speed prop, don't worry about it. That
curve's just to keep you from over-boosting. With your fixed-pitch prop,
your rpm won't get too low.

Thanks. I'd hoped that was the case.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.

Patterson's note of the chart referenced from altitude, as opposed to
manifold pressure, causes me to scratch my head, too.

May I ask why there is a limitation? I'm sure its not good to lug the
engine, and its impossible to lug an engine having a fixed-pitch prop.
But wouldn't the damage come from extra heat generated? So the temps
would change, but they could also be monitored. Yes, Lycoming knows
when their engine will overheat, but environment is not isolated from
it. Are rpm and manifold pressure so isolated to itself?

--Mike

Of course you can lug an engine with a fixed pitch prop. However, if you're
flying a certified airplane with the correct prop, you shouldn't have that
problem. In the experimental world, fast aircraft with cruise props (i.e.
RV's and the like) have real concerns with this, particularly during takeoff
and initial climb.

KB

If you dont have a manifold pressure gauge then you cant properly use
the chart. However, I have only seen ONE aircraft with a fixed pitch
prop and a MP gauge (on a C-152, no less.. talk about a "feature"). In a
factory/certified/STC install one would THINK that the prop is pitched
such that the limit isnt exceeded... but we all know what happens when
one assumes.

I have only seen POH's... not engine manuals...

Dave

G.R. Patterson III wrote:
I've been looking at the performance charts for the Lycoming O-320-B and D series
engines. There's a line that is labeled "Limiting manifold pressure for continuous
operation". This line starts at sea level and 2400 rpm, runs through 2300 rpm at
about 2,000' ASL, and continues to 2000 rpm at about 6,500' ASL. Does this mean that
I am not supposed to operate this engine at 2000 rpm below 6,500' ASL? I have a fixed
pitch prop.

George Patterson
If a man gets into a fight 3,000 miles away from home, he *had* to have
been looking for it.

"G.R. Patterson III" wrote in message
...

There's another chart in the manual that relates combinations of manifold
pressure
and rpm to horsepower (but not to altitude). It has a similar limit band,
but this
one makes sense to me. It basically says that you should never exceed a
manifold
pressure of 25.3 HG at 2200 rpm (for example). I don't know why that limit
band is on
the altitude/hp chart.

I think you're looking at Figure 3-6, right?

The chart on the left is a sea level power chart. The chart on the right is
a full-throttle power chart. Both show manifold pressure (MP) vs RPM as
coordinates. The difference is that the chart on the left has MP lines
vertical, the chart on the right has the MP lines sloping a little, because
at full throttle you get slightly more MP at lower RPMs. In either case,
there is a maximum MP that you can apply for a given RPM. Why the maximum
RPM at altitude is less than at sea level is left as an exercise for the
reader. ;-)

I'm hoping that it's something that only applies to CS props.
In that case, perhaps the chart simply means that it is impossible to
exceed a
manifold pressure of 25.3 HG at 2200 rpm above 6,000' ASL but below that
the pilot
needs to be careful?

It applies to the engine. But fixed pitch props are normally chosen so that
it is impossible to exceed the maximum (full throttle) manifold pressure for
the RPM achieved at any altitude. Part of the role of the line is to guide
the selection of prop. So if 29" of MP at sea level doesn't give you at
least 2400 RPM at all (flying) speeds, the prop pitch is too coarse.

Julian Scarfe