Why small radius collects ice faster?

Is there an explanation for why small radii objects collect ice
faster? The NASA icing video simply states this fact without giving an
explanation. I have found the same with most other sources as well.

In article ,
(Andrew Sarangan) wrote:

Is there an explanation for why small radii objects collect ice
faster? The NASA icing video simply states this fact without giving an
explanation. I have found the same with most other sources as well.

Here's a somewhat fuzzy/unscientific answer which may help at an
intuitive level...

A larger radius object disturbs the air a further distance out in front
of it than a smaller object does. So, if a water droplet is sitting
there suspended in the air, with the smaller object, it has less of a
chance to get deflected up or down before the object slams into it.

I don't know if that explanation will stand up to critical examination
by somebody who really understands the subtleties of aerodynamics, but
that's the way I've always understood it.

Your description matches everything that I have read. It is discussed in
"Severe Weather Flying".
Mike
MU-2


"Roy Smith" wrote in message
...
In article ,
(Andrew Sarangan) wrote:

Is there an explanation for why small radii objects collect ice
faster? The NASA icing video simply states this fact without giving an
explanation. I have found the same with most other sources as well.

Here's a somewhat fuzzy/unscientific answer which may help at an
intuitive level...

A larger radius object disturbs the air a further distance out in front
of it than a smaller object does. So, if a water droplet is sitting
there suspended in the air, with the smaller object, it has less of a
chance to get deflected up or down before the object slams into it.

I don't know if that explanation will stand up to critical examination
by somebody who really understands the subtleties of aerodynamics, but
that's the way I've always understood it.

In article ,
(Andrew Sarangan) wrote:

Is there an explanation for why small radii objects collect ice
faster? The NASA icing video simply states this fact without giving an
explanation. I have found the same with most other sources as well.

"Roy Smith" wrote in message
...

Here's a somewhat fuzzy/unscientific answer which may help at an
intuitive level...

A larger radius object disturbs the air a further distance out in front
of it than a smaller object does. So, if a water droplet is sitting
there suspended in the air, with the smaller object, it has less of a
chance to get deflected up or down before the object slams into it.

I don't think it's unscientific. It seems like a rather good scaling
argument. The critical parameter is the ratio of the radius of the droplet
to the radius of curvature of the object. For a very large ratio (e.g. 1,
think baseball-sized droplet vs wing), you wouldn't expect the object to be
much affected by the airflow around the object, and it will simply slam into
the object. For a very small ratio (e.g. 10^-6), the droplet will simply
follow the streamlines around the object. Thus it's clear that there is a
dependence there.

Julian Scarfe

In article Wgb8c.23$Rn4.14@newsfe1-win,
"Julian Scarfe" wrote:

In article ,
(Andrew Sarangan) wrote:

Is there an explanation for why small radii objects collect ice
faster? The NASA icing video simply states this fact without giving an
explanation. I have found the same with most other sources as well.

"Roy Smith" wrote in message
...

Here's a somewhat fuzzy/unscientific answer which may help at an
intuitive level...

A larger radius object disturbs the air a further distance out in front
of it than a smaller object does. So, if a water droplet is sitting
there suspended in the air, with the smaller object, it has less of a
chance to get deflected up or down before the object slams into it.

I don't think it's unscientific. It seems like a rather good scaling
argument. The critical parameter is the ratio of the radius of the droplet
to the radius of curvature of the object. For a very large ratio (e.g. 1,
think baseball-sized droplet vs wing), you wouldn't expect the object to be
much affected by the airflow around the object, and it will simply slam into
the object. For a very small ratio (e.g. 10^-6), the droplet will simply
follow the streamlines around the object. Thus it's clear that there is a
dependence there.

Well, assuming it's not bad usenet form to argue both side of the issue,
here's the problem...

With a smaller object, yes, the droplet has less of a chance to be
deflected, but it also has to be deflected less to miss the leading edge
entirely. The wing on a typical spam can is maybe 8 inches thick, so a
droplet has to move up or down 4 inches to avoid hitting the wing. The
temperature probe is maybe 1/4 inch thick, so the droplet only has to
move 1/8 of an inch.

So, you've got two basic effects working in opposite directions. A
larger object creates a larger disturbance in the airflow, but it also
requires a larger droplet displacement. It's not immediately clear
which wins.

Roy Smith wrote
Is there an explanation for why small radii objects collect ice
faster? The NASA icing video simply states this fact without giving an
explanation. I have found the same with most other sources as well.

Here's a somewhat fuzzy/unscientific answer which may help at an
intuitive level...

A larger radius object disturbs the air a further distance out in front
of it than a smaller object does. So, if a water droplet is sitting
there suspended in the air, with the smaller object, it has less of a
chance to get deflected up or down before the object slams into it.

I don't know if that explanation will stand up to critical examination
by somebody who really understands the subtleties of aerodynamics, but
that's the way I've always understood it.

Actually, it's not unscientific at all, and no fuzzier than any other
'explanation' of fluid mechanics that leaves the math out. Having
suffered through many semesters of fluid mechanics I can't do any
better without math either.

What you're basically describing is the reason it's much easier to
catch a fish with a net than with a bucket.

Michael

"Michael" wrote in message
om...
Roy Smith wrote
Is there an explanation for why small radii objects collect ice
faster? The NASA icing video simply states this fact without giving an
explanation. I have found the same with most other sources as well.

Here's a somewhat fuzzy/unscientific answer which may help at an
intuitive level...

A larger radius object disturbs the air a further distance out in front
of it than a smaller object does. So, if a water droplet is sitting
there suspended in the air, with the smaller object, it has less of a
chance to get deflected up or down before the object slams into it.

I don't know if that explanation will stand up to critical examination
by somebody who really understands the subtleties of aerodynamics, but
that's the way I've always understood it.

Actually, it's not unscientific at all, and no fuzzier than any other
'explanation' of fluid mechanics that leaves the math out. Having
suffered through many semesters of fluid mechanics I can't do any
better without math either.

What you're basically describing is the reason it's much easier to
catch a fish with a net than with a bucket.

We can throw out all of the wind tunnel testing, based solely on the fact
that it is not representative of nature. NASA does well to demonstrate wind
tunnel icing without comment.

"Andrew Sarangan" wrote in message
om...
Is there an explanation for why small radii objects collect ice
faster? The NASA icing video simply states this fact without giving an
explanation. I have found the same with most other sources as well.

The acretion of ice is statistical in nature and that is why small objects
gather ice.

Tarver Engineering wrote:
"Andrew Sarangan" wrote in message
om...

Is there an explanation for why small radii objects collect ice
faster? The NASA icing video simply states this fact without giving an
explanation. I have found the same with most other sources as well.


The acretion of ice is statistical in nature and that is why small objects
gather ice.



What??

Matt

"Matthew S. Whiting" wrote in message
...
Tarver Engineering wrote:
"Andrew Sarangan" wrote in message
om...

Is there an explanation for why small radii objects collect ice
faster? The NASA icing video simply states this fact without giving an
explanation. I have found the same with most other sources as well.

The acretion of ice is statistical in nature and that is why small
objects
gather ice.

What??

That is how icing works in real life.