Prop performance in clouds question

[[email protected]]

Only flying after today for the next month will be as a passenger as
November 1943 lima has been delivered to Batesville for the extreme
interior makeover. I asked the interior guy if he could email me some
progress pics and he said he would.

Another pilot followed me up in his piper seen here at
http://picasaweb.google.com/allenlieberman/AirplanePics/photo#5173324852142956722

I **thought** air is less dense in a cloud, but when you watch the
prop strobing at http://www.youtube.com/watch?v=QniPjy0gkBI you can
see the regression of the prop strobing, and in my experiences when
the prop starts turning counter clockwise, the prop RPM is slowing
down.

We were in level flight, 6000 feet. Engine is 180 hp. I don't
remember what settings he had for the prop or engine.

Would the moisture in the cloud cause a change in the prop speed even
though we couldn't detect it via gauge or sound? Or is air inside a
cloud more dense?

What I found most fascinating is that we both left the same time, and
he only got there 2.5 minutes faster. I was 45 to a downwind when his
wheels touched down. He planned 130 knots, I planned 110 knots and
the trip was 116 NM.

This for sure verfied I don't need a high performance plane for my
kind of flying :D as even on my trips to Bessemer, who would really
notice 7 to 10 minutes longer flight time difference **in the full
scheme of things**.

Allen

[Kyle Boatright]

I suspect the moisture in the air made your engine deliver less power,
therefore fewer RPM...

More water per cubic foot of air = less of everything else, including
oxygen.

> wrote in message
...
> Only flying after today for the next month will be as a passenger as
> November 1943 lima has been delivered to Batesville for the extreme
> interior makeover. I asked the interior guy if he could email me some
> progress pics and he said he would.
>
> Another pilot followed me up in his piper seen here at
> http://picasaweb.google.com/allenlieberman/AirplanePics/photo#5173324852142956722
>
> I **thought** air is less dense in a cloud, but when you watch the
> prop strobing at http://www.youtube.com/watch?v=QniPjy0gkBI you can
> see the regression of the prop strobing, and in my experiences when
> the prop starts turning counter clockwise, the prop RPM is slowing
> down.
>
> We were in level flight, 6000 feet. Engine is 180 hp. I don't
> remember what settings he had for the prop or engine.
>
> Would the moisture in the cloud cause a change in the prop speed even
> though we couldn't detect it via gauge or sound? Or is air inside a
> cloud more dense?
>
> What I found most fascinating is that we both left the same time, and
> he only got there 2.5 minutes faster. I was 45 to a downwind when his
> wheels touched down. He planned 130 knots, I planned 110 knots and
> the trip was 116 NM.
>
> This for sure verfied I don't need a high performance plane for my
> kind of flying :D as even on my trips to Bessemer, who would really
> notice 7 to 10 minutes longer flight time difference **in the full
> scheme of things**.
>
> Allen

[Doug Palmer]

I would look at how the video camera compensates for the lower light
level in the cloud. If it changes its scan/shutter rate it would
cause the apparent change in relative movement of
the propeller. Also these apparent flicker/stroboscopic patterns are
not always directly related, that is the prop could be going faster
not slower as it appears. That is why car hubcaps seemed to turn
backwards in the old flicks, in spite of the vehicle obviously going
forward. What you are witnessing is the sync of the prop with the
shutter and any variation in either can cause the illusion of
movement.

D

[Bob Gardner]

I think what you are seeing is an optical illusion. The prop speed doesn't
change because of the air it is penetrating.

Bob Gardner

> wrote in message
...
> Only flying after today for the next month will be as a passenger as
> November 1943 lima has been delivered to Batesville for the extreme
> interior makeover. I asked the interior guy if he could email me some
> progress pics and he said he would.
>
> Another pilot followed me up in his piper seen here at
> http://picasaweb.google.com/allenlieberman/AirplanePics/photo#5173324852142956722
>
> I **thought** air is less dense in a cloud, but when you watch the
> prop strobing at http://www.youtube.com/watch?v=QniPjy0gkBI you can
> see the regression of the prop strobing, and in my experiences when
> the prop starts turning counter clockwise, the prop RPM is slowing
> down.
>
> We were in level flight, 6000 feet. Engine is 180 hp. I don't
> remember what settings he had for the prop or engine.
>
> Would the moisture in the cloud cause a change in the prop speed even
> though we couldn't detect it via gauge or sound? Or is air inside a
> cloud more dense?
>
> What I found most fascinating is that we both left the same time, and
> he only got there 2.5 minutes faster. I was 45 to a downwind when his
> wheels touched down. He planned 130 knots, I planned 110 knots and
> the trip was 116 NM.
>
> This for sure verfied I don't need a high performance plane for my
> kind of flying :D as even on my trips to Bessemer, who would really
> notice 7 to 10 minutes longer flight time difference **in the full
> scheme of things**.
>
> Allen

[[email protected]]

Bob Gardner > wrote:
> I think what you are seeing is an optical illusion. The prop speed doesn't
> change because of the air it is penetrating.

It may be an optical illusion, but engine RPM for a fixed throttle/mixture
setting will most definitely change because of the air, otherwise there
would be no reason to have a mixture control.


--
Jim Pennino

Remove .spam.sux to reply.

[John T]

"Doug Palmer" > wrote in message

>
> I would look at how the video camera compensates for the lower light
> level in the cloud. If it changes its scan/shutter rate it would
> cause the apparent change in relative movement of
> the propeller. ... What you are witnessing is the sync of the prop
> with the shutter and any variation in either can cause the illusion of
> movement.

That's my guess, as well.

--
John T
http://sage1solutions.com/blogs/TknoFlyer
http://sage1solutions.com/products
NEW! FlyteBalance v2.0 (W&B); FlyteLog v2.0 (Logbook)
____________________

[John T]

> wrote in message

>
> It may be an optical illusion, but engine RPM for a fixed
> throttle/mixture setting will most definitely change because of the
> air, otherwise there would be no reason to have a mixture control.

Would the use of a constant speed prop change your equation? :)

--
John T
http://sage1solutions.com/blogs/TknoFlyer
http://sage1solutions.com/products
NEW! FlyteBalance v2.0 (W&B); FlyteLog v2.0 (Logbook)
____________________

[Bob Gardner]

Good point, but I still think that the OP is seeing an optical illusion.

Bob

> wrote in message
...
> Bob Gardner > wrote:
>> I think what you are seeing is an optical illusion. The prop speed
>> doesn't
>> change because of the air it is penetrating.
>
> It may be an optical illusion, but engine RPM for a fixed throttle/mixture
> setting will most definitely change because of the air, otherwise there
> would be no reason to have a mixture control.
>
>
> --
> Jim Pennino
>
> Remove .spam.sux to reply.

[[email protected]]

On Mar 3, 9:56*am, "John T" > wrote:
> "Doug Palmer" > wrote in message
>
>
>
>
>
> > I would look at how the video camera compensates for the lower light
> > level in the cloud. *If it changes its scan/shutter rate it would
> > cause the apparent change in relative movement of
> > the propeller. *... What you are witnessing is the sync of the prop
> > with the shutter and any variation in either can cause the illusion of
> > movement.
>
> That's my guess, as well.
>
> --
> John Thttp://sage1solutions.com/blogs/TknoFlyerhttp://sage1solutions.com/products
> NEW! *FlyteBalance v2.0 (W&B); FlyteLog v2.0 (Logbook)
> ____________________

I am using a Kodak Easy Share camera. Does that adjust based on what
it "sees"?

I just put it on Movie and point and shoot, thus me being intrigued
figuring it was the airplane and and not the camera end.

Unless of course if the frame rate can change based on what the camera
sees being "so automatic"?

I sure don't know myself, but pretty coincidental seeing the strobe
change in VMC vs IMC.

Allen

[[email protected]]

On Mar 2, 8:37*pm, "Kyle Boatright" > wrote:
> I suspect the moisture in the air made your engine deliver less power,
> therefore fewer RPM...
>
> More water per cubic foot of air = less of everything else, including
> oxygen.
>

So, on that volkswagon / SUV parcel size chunk of air, would the air
be less dense? I am not quite sure I understand what you mean above,
but what you describe above, I perceive you saying more dense as the
prop would have to work harder to slice through moisture laden air.

Everything I have read so thus so far, deals with the air in general
going up, is less dense, but nothing within a "benign" fair weather
cumulus cloud. Air below a stratus cloud is more dense then the
stratus cloud itself, and above the cloud is even less dense.

I think I will post to a weather forum and see if they can answer the
meteorological portion of that question.

Allen

[buttman]

On Mar 2, 7:08 pm, " > wrote:
> Only flying after today for the next month will be as a passenger as
> November 1943 lima has been delivered to Batesville for the extreme
> interior makeover. I asked the interior guy if he could email me some
> progress pics and he said he would.
>
> Another pilot followed me up in his piper seen here athttp://picasaweb.google.com/allenlieberman/AirplanePics/photo#5173324...
>
> I **thought** air is less dense in a cloud, but when you watch the
> prop strobing athttp://www.youtube.com/watch?v=QniPjy0gkBIyou can
> see the regression of the prop strobing, and in my experiences when
> the prop starts turning counter clockwise, the prop RPM is slowing
> down.
>
> We were in level flight, 6000 feet. Engine is 180 hp. I don't
> remember what settings he had for the prop or engine.
>
> Would the moisture in the cloud cause a change in the prop speed even
> though we couldn't detect it via gauge or sound? Or is air inside a
> cloud more dense?
>
> What I found most fascinating is that we both left the same time, and
> he only got there 2.5 minutes faster. I was 45 to a downwind when his
> wheels touched down. He planned 130 knots, I planned 110 knots and
> the trip was 116 NM.
>
> This for sure verfied I don't need a high performance plane for my
> kind of flying :D as even on my trips to Bessemer, who would really
> notice 7 to 10 minutes longer flight time difference **in the full
> scheme of things**.
>
> Allen

The prop strobing clockwise does not necessarily mean the prop is
slowing down. If you've ever seen a turboprop shut down under the
artificial 60hz strobing lights of an airport apron, you'll see the
prob strobe back and forth as it gradually slows down.

[[email protected]]

On Mar 3, 11:02*am, buttman > wrote:

> The prop strobing clockwise does not necessarily mean the prop is
> slowing down. If you've ever seen a turboprop shut down under the
> artificial 60hz strobing lights of an airport apron, you'll see the
> prob strobe back and forth as it gradually slows down.- Hide quoted text -
>
> - Show quoted text -

Yeah, I figured the clockwise motion wasn't indication of it slowing
down, it was when I was IMC, that it "stopped" or started going
counter clockwise, and then when I popped out, it resumed it's
clockwise motion.

It was "hands off flying" before entering the cloud, smooth inside and
same outside and NO changes in airplane configuration insofar as prop,
mixture or throttle.

Something I can try to experiment in my Sundowner a month down the
road when it gets back in service since I only have a fixed pitch
prop.

Allen

[Bob F.]

"John T" > wrote in message
m...
> > wrote in message
>
>>
>> It may be an optical illusion, but engine RPM for a fixed
>> throttle/mixture setting will most definitely change because of the
>> air, otherwise there would be no reason to have a mixture control.
>
> Would the use of a constant speed prop change your equation? :)
>
> --
> John T
> http://sage1solutions.com/blogs/TknoFlyer
> http://sage1solutions.com/products
> NEW! FlyteBalance v2.0 (W&B); FlyteLog v2.0 (Logbook)
> ____________________
>
>

No, since there is a concept of a "dead zone" where there needs to be a more
than a minimum change for a the servo to react. Otherwise a concept of
"hunting" kicks in and the RPM constantly change and "hunts" for a center of
the constant RPM speed.

--
BobF.

[John T]

"Bob F." > wrote in message

>
> No, since there is a concept of a "dead zone" where there needs to be
> a more than a minimum change for a the servo to react. Otherwise a
> concept of "hunting" kicks in and the RPM constantly change and
> "hunts" for a center of the constant RPM speed.

True, but as you allude, only to a limited extent. It wasn't clear to me
from Jim's post that he was accounting for CS props.

--
John T
http://sage1solutions.com/blogs/TknoFlyer
http://sage1solutions.com/products
NEW! FlyteBalance v2.0 (W&B); FlyteLog v2.0 (Logbook)
____________________

[John T]

> wrote in message

>
> I am using a Kodak Easy Share camera. Does that adjust based on what
> it "sees"?

Cameras typically use a combination of shutter speed, aperture and exposure
to maintain the "best" picture (as defined by the software). I haven't
researched your camera, though I suspect it manipulates all three based on
the video I've seen on your channel. I know for certain your shutter speeds
are way different from mine based on the prop filtering.

> Unless of course if the frame rate can change based on what the camera
> sees being "so automatic"?

Possible, though I doubt actual frame rate is changing (different from
shutter speed).

> I sure don't know myself, but pretty coincidental seeing the strobe
> change in VMC vs IMC.

I don't doubt a small change in prop speed as I've seen similar changes in
my own prop "strobe," but I'd put it more to general atmospheric (or, more
likely, attitude changes) rather than specific to clouds as I've seen
similar changes well outside clouds on "severe clear" days.

Try this: Take video during a flight on a clear VMC day. Maintain level
flight as absolutely as you can, then enter climbs and descents. See what
that does to your prop strobe. I suspect even slight attitude changes will
show different strobe patterns without touching engine or prop controls.

--
John T
http://sage1solutions.com/blogs/TknoFlyer
http://sage1solutions.com/products
NEW! FlyteBalance v2.0 (W&B); FlyteLog v2.0 (Logbook)
____________________

[Andrew Sarangan]

On Mar 2, 9:08 pm, " > wrote:
> Only flying after today for the next month will be as a passenger as
> November 1943 lima has been delivered to Batesville for the extreme
> interior makeover. I asked the interior guy if he could email me some
> progress pics and he said he would.
>
> Another pilot followed me up in his piper seen here athttp://picasaweb.google.com/allenlieberman/AirplanePics/photo#5173324...
>
> I **thought** air is less dense in a cloud, but when you watch the
> prop strobing athttp://www.youtube.com/watch?v=QniPjy0gkBIyou can
> see the regression of the prop strobing, and in my experiences when
> the prop starts turning counter clockwise, the prop RPM is slowing
> down.
>
> We were in level flight, 6000 feet. Engine is 180 hp. I don't
> remember what settings he had for the prop or engine.
>
> Would the moisture in the cloud cause a change in the prop speed even
> though we couldn't detect it via gauge or sound? Or is air inside a
> cloud more dense?
>
> What I found most fascinating is that we both left the same time, and
> he only got there 2.5 minutes faster. I was 45 to a downwind when his
> wheels touched down. He planned 130 knots, I planned 110 knots and
> the trip was 116 NM.
>
> This for sure verfied I don't need a high performance plane for my
> kind of flying :D as even on my trips to Bessemer, who would really
> notice 7 to 10 minutes longer flight time difference **in the full
> scheme of things**.
>
> Allen

I am not sure how you came to the conclusion that air is less dense in
the cloud than the surrounding air. Density decreases with increasing
moisture for unsaturated air, but once the air is saturated (clouds),
any excess moisture is suspended as tiny droplets, and the average
density will start to increase. Darker the cloud, the higher the
density. This is why you need an updraft to hold these clouds up. When
the density gets too large to overcome the updrafts, you get rain, and
the density returns to normal.

[WingFlaps]

On Mar 4, 8:27*am, Andrew Sarangan > wrote:
> On Mar 2, 9:08 pm, " > wrote:
>
>
>
>
>
> > Only flying after today for the next month will be as a passenger as
> > November 1943 lima has been delivered to Batesville for the extreme
> > interior makeover. *I asked the interior guy if he could email me some
> > progress pics and he said he would.
>
> > Another pilot followed me up in his piper seen here athttp://picasaweb.google.com/allenlieberman/AirplanePics/photo#5173324...
>
> > I **thought** air is less dense in a cloud, but when you watch the
> > prop strobing athttp://www.youtube.com/watch?v=QniPjy0gkBIyoucan
> > see the regression of the prop strobing, and in my experiences when
> > the prop starts turning counter clockwise, the prop RPM is slowing
> > down.
>
> > We were in level flight, 6000 feet. *Engine is 180 hp. *I don't
> > remember what settings he had for the prop or engine.
>
> > Would the moisture in the cloud cause a change in the prop speed even
> > though we couldn't detect it via gauge or sound? *Or is air inside a
> > cloud more dense?
>
> > What I found most fascinating is that we both left the same time, and
> > he only got there 2.5 minutes faster. *I was 45 to a downwind when his
> > wheels touched down. *He planned 130 knots, I planned 110 knots and
> > the trip was 116 NM.
>
> > This for sure verfied I don't need a high performance plane for my
> > kind of flying *:D as even on my trips to Bessemer, who would really
> > notice 7 to 10 minutes longer flight time difference **in the full
> > scheme of things**.
>
> > Allen
>
> I am not sure how you came to the conclusion that air is less dense in
> the cloud than the surrounding air. Density decreases with increasing
> moisture for unsaturated air, but once the air is saturated (clouds),
> any excess moisture is suspended as tiny droplets, and the average
> density will start to increase. Darker the cloud, the higher the
> density. This is why you need an updraft to hold these clouds up. When
> the density gets too large to overcome the updrafts, you get rain, and
> the density returns to normal.- Hide quoted text -
>
> - Show quoted text -

BINGO!

Cheers

[[email protected]]

On Mar 3, 1:27*pm, Andrew Sarangan > wrote:

> I am not sure how you came to the conclusion that air is less dense in
> the cloud than the surrounding air. Density decreases with increasing
> moisture for unsaturated air, but once the air is saturated (clouds),
> any excess moisture is suspended as tiny droplets, and the average
> density will start to increase. Darker the cloud, the higher the
> density. This is why you need an updraft to hold these clouds up. When
> the density gets too large to overcome the updrafts, you get rain, and
> the density returns to normal.- Hide quoted text -

While I plan to ask on a meteorological forum when I get home, play
with me a sec...

I am not talking about small clouds vs big rain making clouds. What I
am talking about is the density of the air comparing VMC to IMC at an
established level of flight.

If that cloud was "denser" then the surrounding air (as you can see in
the video, it was a sparse cloud cover), then why doesn't the cloud
sink if that parcel of air is heavier (denser) then the surrounding
air?

Winds aloft were 35 knots so surely, the updraft time was extremely
minimal and I would say none, since I didn't get any lifting feeling
in the seat of my pants in penetrating that volkswagon size puffy.

When I googled the topic, it talked mainly of stratiform clouds, and
that layer being less dense below the cloud deck, which I already
understand the higher you go, the less dense the air. This is
probably where I got my initial impressions that the air in clouds is
less dense.

Allen

[[email protected]]

On Mar 3, 1:19*pm, "John T" > wrote:

> Try this: Take video during a flight on a clear VMC day. Maintain level
> flight as absolutely as you can, then enter climbs and descents. See what
> that does to your prop strobe. I suspect even slight attitude changes will
> show different strobe patterns without touching engine or prop controls.

Actually, with my Sundowner, prop controls will be one less variable
in the equation. (one month down time will feel like eternity!)

The trick will be to maintain the "exact" flight "attitude" throughout
the cloud as YOU ARE RIGHT, any pitch up or pitch down will affect the
RPM as I noticed this on my ILS approaches in my Sundowner. (Video
was in a Piper).

I like to listen to the engine noise as well as watch the strobing to
associate the quality of the approach, I.E the less power changes I
hear, the more stable the approach, and strobing remains "constant"
whether it be clockwise, or counter clockwise or even standing still.

It may be that there was a pitch change in the plane that I couldn't
feel in the video that just may have existed even though I didn't feel
it in the seat of my pants (I was passenger holding the camera). Of
course in IMC, we will really never know but gauges were steady as
they can be.

Allen

[[email protected]]

On Mar 3, 2:20*pm, " > wrote:

> When I googled the topic, it talked mainly of stratiform clouds, and
> that layer being less dense below the cloud deck, which I already
> understand the higher you go, the less dense the air. *This is
> probably where I got my initial impressions that the air in clouds is
> less dense.
>
> Allen

To clarify, the above should say MORE dense below the stratiform cloud
deck!

Allen

[Andrew Sarangan]

On Mar 3, 3:20 pm, " > wrote:
> On Mar 3, 1:27 pm, Andrew Sarangan > wrote:
>
> > I am not sure how you came to the conclusion that air is less dense in
> > the cloud than the surrounding air. Density decreases with increasing
> > moisture for unsaturated air, but once the air is saturated (clouds),
> > any excess moisture is suspended as tiny droplets, and the average
> > density will start to increase. Darker the cloud, the higher the
> > density. This is why you need an updraft to hold these clouds up. When
> > the density gets too large to overcome the updrafts, you get rain, and
> > the density returns to normal.- Hide quoted text -
>
> While I plan to ask on a meteorological forum when I get home, play
> with me a sec...
>
> I am not talking about small clouds vs big rain making clouds. What I
> am talking about is the density of the air comparing VMC to IMC at an
> established level of flight.
>
> If that cloud was "denser" then the surrounding air (as you can see in
> the video, it was a sparse cloud cover), then why doesn't the cloud
> sink if that parcel of air is heavier (denser) then the surrounding
> air?

Good question. Let us know what the meteorologists say about this. My
thinking is that the cloud will eventually sink to the ground if left
undisturbed (think fog). But it may float for quite some time,
especially if the droplets are small. From your photo, the clouds look
white, which implies very small droplets. Think of those parachute-
like flowers that float in the spring. All they need is a tiny gust of
air, and they stay afloat for ever.




>
> Allen

[Kyle Boatright]

> wrote in message
...
>On Mar 2, 8:37 pm, "Kyle Boatright" > wrote:
>> I suspect the moisture in the air made your engine deliver less power,
>> therefore fewer RPM...
>>
>> More water per cubic foot of air = less of everything else, including
>> oxygen.
>>

>So, on that volkswagon / SUV parcel size chunk of air, would the air
>be less dense? I am not quite sure I understand what you mean above,
>but what you describe above, I perceive you saying more dense as the
>prop would have to work harder to slice through moisture laden air.
>
>Everything I have read so thus so far, deals with the air in general
>going up, is less dense, but nothing within a "benign" fair weather
>cumulus cloud. Air below a stratus cloud is more dense then the
>stratus cloud itself, and above the cloud is even less dense.
>
>I think I will post to a weather forum and see if they can answer the
>meteorological portion of that question.
>
>Allen

The air density doesn't change, but the amount of oxygen per cubic foot
does. Imagine a one cubic foot in size. It is full of red balls
(nitrogen), white balls(oxygen), and green balls (CO2). It won't hold
another ball without removing something. Now, you have to add a bunch of
black balls (H2O). Which means you have to take out some red, white, and
green ones to make space. Now your 1 cubic foot box holds less nitrogen,
oxygen, and CO2. This is essentially what happens when the humidity rises.
What it means to a combustion engine is that the engine won't produce as
much power, because there is less oxygen per cubic foot (or whatever) of
air.

KB

[[email protected]]

On Mar 3, 6:15*pm, "Kyle Boatright" > wrote:

> The air density doesn't change, but the amount of oxygen per cubic foot
> does. *Imagine a one cubic foot in size. *It is full of red balls
> (nitrogen), white balls(oxygen), and green balls (CO2). *It won't hold
> another ball without removing something. *Now, you have to add a bunch of
> black balls (H2O). *Which means you have to take out some red, white, and
> green ones to make space. *Now your 1 cubic foot box holds less nitrogen,
> oxygen, and CO2. *This is essentially what happens when the humidity rises.
> What it means to a combustion engine is that the engine won't produce as
> much power, because there is less oxygen per cubic foot (or whatever) of
> air.

Actually the above just **may** help support what I am thinking but in
an opposite sense..

The balls you describe above are not the same size, therefore if you
remove some of the bigger balls and replace them with smaller balls,
wouldn't that make the air "denser"

Conversly, if you take out the little balls and replace them with
bigger balls, there is more space between the balls making it less
denser.

I figure if the visible was the "bigger balls" in that parcel of air,
as compared to the surrounding air outside the IMC, then the air
inside that cloud would be less dense verifying what I have been
reading?

Does this make any sense?

It does make sense that there would be less air, thus reducing ening
power, which would change the strobing of the prop once entering IMC,
and after leaving it, that power would resume since the visible
moisture now is replaced with air.

Allen

[[email protected]]

On Mar 3, 3:32*pm, Andrew Sarangan > wrote:

> Good question. Let us know what the meteorologists say about this. My
> thinking is that the cloud will eventually sink to the ground if left
> undisturbed (think fog). But it may float for quite some time,
> especially if the droplets are small. From your photo, the clouds look
> white, which implies very small droplets. *Think of those parachute-
> like flowers that float in the spring. All they need is a tiny gust of
> air, and they stay afloat for ever.

Okee dokee, this was response I received on the meteorological aspect
between the dashed lines.
--------------
All other things being equal (temperature, pressure,etc), air with
more water vapor in it is less dense than air with less water vapor in
it. Air is mostly Nitrogen (N2, roughly 78%, molecular weight 14) and
Oxygen (O2, roughly 21%, molecular weight 16), while water vapor is
H2O (molecular weight 10).

The problem is, I don't think all other things are equal when you go
from non-cloud to in-cloud. It may be within the degree of accuracy of
your instruments, but there are still some very small differences in
temperature and/or pressure.
----------------

Meteorologist also said, though not with any conviction since he is
not a mechanic by any stretch of the imagination becuase there is less
air in a cloud, that **could** reduce engine performance (he said it's
plausible, no necessarilyt the answer) which in turn could reduce the
RPM of a prop.

Allen

[Bertie the Bunyip[_24_]]

"Kyle Boatright" > wrote in
:

>
> wrote in message
>>news:99678464-7bae-4911-931b-4b5bd798fc75
@n58g2000hsf.googlegroups.com.
>>.. On Mar 2, 8:37 pm, "Kyle Boatright" >
>>wrote:
>>> I suspect the moisture in the air made your engine deliver less
>>> power, therefore fewer RPM...
>>>
>>> More water per cubic foot of air = less of everything else,
>>> including oxygen.
>>>
>
>>So, on that volkswagon / SUV parcel size chunk of air, would the air
>>be less dense? I am not quite sure I understand what you mean above,
>>but what you describe above, I perceive you saying more dense as the
>>prop would have to work harder to slice through moisture laden air.
>>
>>Everything I have read so thus so far, deals with the air in general
>>going up, is less dense, but nothing within a "benign" fair weather
>>cumulus cloud. Air below a stratus cloud is more dense then the
>>stratus cloud itself, and above the cloud is even less dense.
>>
>>I think I will post to a weather forum and see if they can answer the
>>meteorological portion of that question.
>>
>>Allen
>
> The air density doesn't change, but the amount of oxygen per cubic
> foot does. Imagine a one cubic foot in size. It is full of red balls
> (nitrogen), white balls(oxygen), and green balls (CO2). It won't hold
> another ball without removing something. Now, you have to add a bunch
> of black balls (H2O). Which means you have to take out some red,
> white, and green ones to make space. Now your 1 cubic foot box holds
> less nitrogen, oxygen, and CO2. This is essentially what happens when
> the humidity rises. What it means to a combustion engine is that the
> engine won't produce as much power, because there is less oxygen per
> cubic foot (or whatever) of air.

http://www.csgnetwork.com/relhumhpcalc.html



Bertie

[[email protected]]

On Mar 4, 2:12*am, Bertie the Bunyip > wrote:

> http://www.csgnetwork.com/relhumhpcalc.html
>
> Bertie- Hide quoted text -

Very interesting link. Thanks

That appears to confirm the reaction of the prop in the video in that
the video is picking up the approximately 1 percent degradation of
engine performance inside the cloud through the strobing of the prop
using the values of 70F (OAT of flight in video) 29.92 70 percent or
100 percent humidity and 6000 ft altitude.

Allen

[[email protected]]

On Mar 4, 8:10 am, " > wrote:
> On Mar 4, 2:12 am, Bertie the Bunyip > wrote:
>
> >http://www.csgnetwork.com/relhumhpcalc.html
>
> > Bertie- Hide quoted text -
>
> Very interesting link. Thanks
>
> That appears to confirm the reaction of the prop in the video in that
> the video is picking up the approximately 1 percent degradation of
> engine performance inside the cloud through the strobing of the prop
> using the values of 70F (OAT of flight in video) 29.92 70 percent or
> 100 percent humidity and 6000 ft altitude.
>
> Allen

The marginal reduction in BHP performance is offset by the marginal
increased TAS, n'est pas?

Dan

[[email protected]]

On Mar 4, 8:58*am, " > wrote:

> The marginal reduction in BHP performance is offset by the marginal
> increased TAS, n'est pas?
>
> Dan

Do I understand you to be saying TAS would increase after entering
IMC???

Allen

[[email protected]]

On Mar 4, 10:03 am, " > wrote:
> On Mar 4, 8:58 am, " > wrote:
>
> > The marginal reduction in BHP performance is offset by the marginal
> > increased TAS, n'est pas?
>
> > Dan
>
> Do I understand you to be saying TAS would increase after entering
> IMC???
>
> Allen

If the air density has decreased due to increased humidity (clouds),
there will be offset between to reduction in BHP efficiency and the
increased TAS (due to reduced profile drag)....


Dan

[Bertie the Bunyip[_24_]]

" > wrote in news:77bb7a2a-6285-4bb2-
:

> On Mar 4, 10:03 am, " > wrote:
>> On Mar 4, 8:58 am, " > wrote:
>>
>> > The marginal reduction in BHP performance is offset by the marginal
>> > increased TAS, n'est pas?
>>
>> > Dan
>>
>> Do I understand you to be saying TAS would increase after entering
>> IMC???
>>
>> Allen
>
> If the air density has decreased due to increased humidity (clouds),
> there will be offset between to reduction in BHP efficiency and the
> increased TAS (due to reduced profile drag)....
>


Maybe, but the water on your wings is going to cost you quite a lot.


Bertie

[[email protected]]

On Mar 4, 10:33 am, Bertie the Bunyip > wrote:
> " > wrote in news:77bb7a2a-6285-4bb2-
> :
>
>
>
> > On Mar 4, 10:03 am, " > wrote:
> >> On Mar 4, 8:58 am, " > wrote:
>
> >> > The marginal reduction in BHP performance is offset by the marginal
> >> > increased TAS, n'est pas?
>
> >> > Dan
>
> >> Do I understand you to be saying TAS would increase after entering
> >> IMC???
>
> >> Allen
>
> > If the air density has decreased due to increased humidity (clouds),
> > there will be offset between to reduction in BHP efficiency and the
> > increased TAS (due to reduced profile drag)....
>
> Maybe, but the water on your wings is going to cost you quite a lot.
>
> Bertie

Not every cloud will produce water on the wings, though?

If it does, that's right -- there's an additional drag due to liquid
water coursing over the airframe.

If not, then ...?

[Bertie the Bunyip[_24_]]

" > wrote in
:

> On Mar 4, 10:33 am, Bertie the Bunyip > wrote:
>> " > wrote in
>> news:77bb7a2a-6285-4bb2-
>> :
>>
>>
>>
>> > On Mar 4, 10:03 am, " > wrote:
>> >> On Mar 4, 8:58 am, " > wrote:
>>
>> >> > The marginal reduction in BHP performance is offset by the
>> >> > marginal increased TAS, n'est pas?
>>
>> >> > Dan
>>
>> >> Do I understand you to be saying TAS would increase after entering
>> >> IMC???
>>
>> >> Allen
>>
>> > If the air density has decreased due to increased humidity
>> > (clouds), there will be offset between to reduction in BHP
>> > efficiency and the increased TAS (due to reduced profile drag)....
>>
>> Maybe, but the water on your wings is going to cost you quite a lot.
>>
>> Bertie
>
> Not every cloud will produce water on the wings, though?

True.
>
> If it does, that's right -- there's an additional drag due to liquid
> water coursing over the airframe.
>
> If not, then ...?

Dunno. I remember flying in actual rain and losing quite a lot of
performance in things like Navajos. Most noticable difference is the
fuel consumption. I don't think any performance loss will be significant
unless there's water running over the airframe, though. Just thought i'd
interject that bit about the water


Bertie
>

[[email protected]]

On Mar 4, 11:36 am, Bertie the Bunyip > wrote:
>
> > If it does, that's right -- there's an additional drag due to liquid
> > water coursing over the airframe.
>
> > If not, then ...?
>
> Dunno. I remember flying in actual rain and losing quite a lot of
> performance in things like Navajos. Most noticable difference is the
> fuel consumption. I don't think any performance loss will be significant
> unless there's water running over the airframe, though. Just thought i'd
> interject that bit about the water
>
> Bertie
>

I suppose the reduction in BHP performance would be due to water
ingestion, reducing the combustible mixture?

IIRC, some high performance engines used water injection to boost HP.

Dan

[Bertie the Bunyip[_24_]]

" > wrote in news:2069ba74-10bc-4280-
:

> On Mar 4, 11:36 am, Bertie the Bunyip > wrote:
>>
>> > If it does, that's right -- there's an additional drag due to liquid
>> > water coursing over the airframe.
>>
>> > If not, then ...?
>>
>> Dunno. I remember flying in actual rain and losing quite a lot of
>> performance in things like Navajos. Most noticable difference is the
>> fuel consumption. I don't think any performance loss will be significant
>> unless there's water running over the airframe, though. Just thought i'd
>> interject that bit about the water
>>
>> Bertie
>>
>
> I suppose the reduction in BHP performance would be due to water
> ingestion, reducing the combustible mixture?
>
> IIRC, some high performance engines used water injection to boost HP.

I've flown one jet that does tht, but I was talking about reducion in
performance overall. It's to do with drag from the water on the aiframe.

Bertie

[[email protected]]

On Mar 4, 12:27 pm, Bertie the Bunyip > wrote:
>
> > I suppose the reduction in BHP performance would be due to water
> > ingestion, reducing the combustible mixture?
>
> > IIRC, some high performance engines used water injection to boost HP.
>
> I've flown one jet that does tht, but I was talking about reducion in
> performance overall. It's to do with drag from the water on the aiframe.
>
> Bertie

So I suppose we can assume a marginal decrease in BHP due to reduced
engine efficiency and a marginal increase in TAS due to decreased air
density in clouds that don't cause water to stream along the airframe.

Ok..whew.

[Robert M. Gary]

On Mar 2, 6:37*pm, "Kyle Boatright" > wrote:
> I suspect the moisture in the air made your engine deliver less power,
> therefore fewer RPM...

I have a very hard time believing the RPM changed. That would be
pretty dramatic. I would guess that the difference is the camera
opening to allow more light in in the reduced light environment of the
inner cloud.

-Robert, CFII (who knows little about photography)

[[email protected]]

On Mar 4, 2:31 pm, "Robert M. Gary" > wrote:
> On Mar 2, 6:37 pm, "Kyle Boatright" > wrote:
>
> > I suspect the moisture in the air made your engine deliver less power,
> > therefore fewer RPM...
>
> I have a very hard time believing the RPM changed. That would be
> pretty dramatic. I would guess that the difference is the camera
> opening to allow more light in in the reduced light environment of the
> inner cloud.
>
> -Robert, CFII (who knows little about photography)

If there were actually an RPM change that was visible every time we
passed through clouds, we'd certainly have to address that in
instrument training.

I've never seen such an indication in either a constant speed, fixed
pitch, or controllable pitch (ie, electric prop).

Your theory sounds like the most plausible explanation for the OPs
observation.



Dan

[[email protected]]

On Mar 4, 3:49*pm, " > wrote:

> If there were actually an RPM change that was visible every time we
> passed through clouds, we'd certainly have to address that in
> instrument training.
>
> I've never seen such an indication in either a constant speed, fixed
> pitch, or controllable pitch (ie, electric prop).

I think that's the problem, it's not visible on the analogue gauges,
nor in sound level, only digitally.

It does make more sense to me, now that I have posted the density
content of a cloud, showing less O2, that it is possible (I don't know
for sure) that the engine output **could be** reduced from less oxygen
being available.

The meteorologist figured based on the strobing, and 30 frames per
second on the camera, and 2300 prop rpm, that while in the cloud, the
rpms dropped by about 24 rpms in the cloud.

So, just maybe we do need to lean **a touch** more while IMC????

24 RPM isn't much and like I have been saying, while in flight, never
saw any changes in the gauges, no change in sound, air was smooth so
no change in pitch, but is our antiquated equipment sensitive enough
to detect a 24 rpm change?

I'm not so sure we would notice it without digital equipment.

When I get my plane out of the shop in about a month, I plan to
explore this more.

Allen

[Dan[_10_]]

On Mar 6, 11:01 am, " > wrote:
> On Mar 4, 3:49 pm, " > wrote:
>
> > If there were actually an RPM change that was visible every time we
> > passed through clouds, we'd certainly have to address that in
> > instrument training.
>
> > I've never seen such an indication in either a constant speed, fixed
> > pitch, or controllable pitch (ie, electric prop).
>
> I think that's the problem, it's not visible on the analogue gauges,
> nor in sound level, only digitally.
>
> It does make more sense to me, now that I have posted the density
> content of a cloud, showing less O2, that it is possible (I don't know
> for sure) that the engine output **could be** reduced from less oxygen
> being available.
>
> The meteorologist figured based on the strobing, and 30 frames per
> second on the camera, and 2300 prop rpm, that while in the cloud, the
> rpms dropped by about 24 rpms in the cloud.
>
> So, just maybe we do need to lean **a touch** more while IMC????
>
> 24 RPM isn't much and like I have been saying, while in flight, never
> saw any changes in the gauges, no change in sound, air was smooth so
> no change in pitch, but is our antiquated equipment sensitive enough
> to detect a 24 rpm change?
>
> I'm not so sure we would notice it without digital equipment.
>
> When I get my plane out of the shop in about a month, I plan to
> explore this more.
>
> Allen

The A36 has a digital RPM readout --in and out of the clouds today --
no change in MP or RPM.

Dan