wind meter

"Ron Hardin" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Philip Holman said:

Quoted message said:

Alternatively put, the forward component of the vector drag
increases.
v^2 isn't linear.

If I'm traveling north at 8mph and there is a 6mph straight crosswind
from the east, my pathway through the air is at10mph but in a
direction
that is N 36.87 E. Drag force will be proportional to 10^2 = 100 in
this
direction. The forward component of this will be proportional
to100cos36.87 = 80. This is greater than when travelling at 8mph with
no
croswind i.e 8^2 = 64. Is this what you mean?

Yes. that's the effect. So you're riding along at 8mph, and your
airspeed is
8mph, and a sudden gust hits from the east. Both your actual speed
and your
forward airspeed fall together. That's a little unexpected, is all.

If the wind meter were mounted to swivel into the wind, the airspeed
would
go up, which is what you expected.

Well, if it points at N36.87E through weather vaning, it will show
10mph. The equivalent windspeed is Sqrt 80 = ~9mph which would be a
little harder to determine.

Phil H

Sheldon Brown said:

Frankly I don't see why this is of such interest, since it is of no
practical import, the wind being outside of human control.

It's of interest to people interested in physics, a large segment of
males. There you are, pedalling along happily measuring your ground
speed with your GPS and your forward airspeed with the wind meter
at the top of this thread, knowing that since you're a top experienced
cyclist you're running at exactly constant power, when whoa! along
comes a gust of wind, and BOTH your ground speed and your air speed
drop. What is a physicist to make of that? That the wind meter is
broken? It may be of no practical import, but it's an urgent problem.

It comes from the nonlinearity of air drag, and all the meters are
working fine.
--
Ron Hardin
[email hidden]

On the internet, nobody knows you're a jerk.

Ron Hardin said:

Quoted message said:

In liquids, which are enormously denser, you get a bow wave
at even low speeds. (The spoon is an example of a
displacement hull.)

But in gases, as far as I know, you don't get a bow wave of
any consquence at similar speeds.

I don't know if you're thinking of the surface wave (a gravity wave)
as in the wake of a boat, or not. I'm not talking about a propagating
wave but just motion in getting around the obstacle.

What the fluid decides to do about the obstacle as it approaches depends
on the reynolds number of the flow. Water speed has to be about 1/20
of air speed to duplicate the flow. So think of water at 1 mph.

At low speeds, the fluid moves out of the way well in advance of
the object. Viscous forces give it ample warning and have time to act.

Or think of a wind meter, and you put your hand a foot downstream
of it, blocking the flow somewhat. How far downstream would you
expect to see an effect from?

Dear Ron,

No, I don't think that either of us is talking about a
propagating wave.

I like your idea about the hand behind the wind meter, but
I'm not sure that the effect (which is noticeable about six
inches or so behind the meter at 20 mph) is quite what
you're thinking of.

The problem is that the wind meter works by constraining a
column of already moving air through a four-inch long tunnel
less than half an inch square, which is right next to the
comparatively enormous mass of the rest of the wind meter.

This creates a surprisingly long low-pressure plume of
turbulence behind the meter. If we start filling that zone
in with our hand, the pressure rises. This is not so much a
bow wave of air as a complicated interference.

What we really need is to separate the sensor tunnel from
the interfering (but convenient) body of the meter with some
thin wires and then mount the tunnel on some sliding stick
stick arrangement that lets us extend it forward.

If you're right about the bow wave effect being significant,
then the meter should show the wind speed increasing as the
meter gets further from the rider.

But most of what I see in wind tunnel testing is a slight
sideways deflection, usually greatly exaggerated in diagrams
and not actually large enough to be even visible in
low-speed tests. Again, try a hand test. The hairs on your
forearm are quite sensitive. Stick one arm out and move your
other palm toward it briskly. You'll feel the trailing plume
of turbulence washing over your forearm, but not a
preliminary pressure wave.

Cockroaches have far more delicate hairs, so they can sense
the extremely faint increase in air pressure of a rapidly
approaching object and evade your palm, but I don't think
that this is anywhere near the kind of bow wave effect that
you have in mind.

So far, I can't think of an easy way to mount the meter on a
stick to let it slide back and forth, much less how to
separate the meter from the display body, but I'll ponder it
some more.

Carl Fogel

Boyle M. Owl said:

RonSonic said:

I am appalled by your speciist bigotry which has produced a staggeringly
incurious and ascientific outlook. Your refusal to test the windspeed of a
basset hound has denied the world of science a brilliant opportunity for
research. Nevermind the chew testing that will remain undone.

The measurement of basset hound windspeed would entail several scenarios.

1. Attach the wind meter to the basset hound's back. Play "fetch" with
an old slipper. That is, if the hound is so inclined.

[snip]

Dear Boyle,

Bah! Typically impractical theory! Obviously ivory-tower
thinking!

As has been discussed, basset hounds lose interest in
"fetch" by the age of one when the objects are tennis balls,
puppy toys, slippers, and so forth. Even squirrels and cats
are ignored. The only objects pursued are liver treats,
porcupines, and rabbits.

Facing into a steady 15 mph wind, the ears of a basset will
begin to spread and rise. Since the Windscribe is portable,
I expect to confirm this within a week or two.

Carl Fogel

On Sat, 12 Feb 2005 13:09:32 -0500, Sheldon Brown
<[email hidden]> wrote:

[snip]

Quoted message said:

Frankly I don't see why this is of such interest, since it is of no
practical import, the wind being outside of human control.

Sheldon "Graphs" Brown

Dear Sheldon,

I hear that the slope of the road is also outside human
control, but many riders seem to be interested in that, too.

Possibly much of what we do with bicycles is only faintly
related to practicality?

Carl Fogel

On Thu, 10 Feb 2005 19:51:05 -0700, [email hidden]
wrote:

[snip greatest story ever told]

Ron Hardin and I have been wondering elsewhere in this
thread about bow waves from the rider confusing the wind
meter's reading.

Ron foolishly believes in such bow waves in the face of my
disbelief, presumably relying on such weak reeds as theory
and experiment.

While I'm not yet convinced that this will be a tough spot
to lie my way out of, I'm beginning to wonder if Ron might
be right.

After three rides with the Windscribe, I think that I'm
noticing a pattern of the wind speed being noticeably lower
than the road speed on a long downhill.

That is, I'm seeing the Windscribe that was within a mile or
two per hour of my road speed at about 20 mph on an
unusually calm series of days lagging 6 mph behind road
speeds of 34-39 mph.

It's hard to be sure about the wind on the downhill (it's
open and has a fifty-mile view), but my experience suggests
that 39 mph is my normal maximum speed on a calm day at the
very bottom--which consists of a well-sheltered curve
dropping to the river bottom. I think that a 6 mph tailwind
would push me into the low 40 mph range.

A possible explanation is that a bow wave from the rider
expands as speed rises, which leads to the Windscribe
showing less and less of the true wind speed.

(Not that I believe in the bow wave yet.)

A scheme involving a broom stick clamped to the top tube and
protruding past the handlebars like the needle on the nose
of supersonic jet is taking shape.

Carl Fogel

Quoted message said:

Dear Boyle,

Bah! Typically impractical theory! Obviously ivory-tower
thinking!

Hey, you forgot the CYA disclaimer at the end!

Quoted message said:

Facing into a steady 15 mph wind, the ears of a basset will
begin to spread and rise.

Obviously since the ears rise, they have enough aerodynamic lift for
themselves...which leads to: What are the lift capabilities of a
basset's ears and can the hounds be bred to be heavy lift aircraft?

--
BMO

Boyle M. Owl said:

Quoted message said:

Dear Boyle,

Bah! Typically impractical theory! Obviously ivory-tower
thinking!

Hey, you forgot the CYA disclaimer at the end!

Quoted message said:

Facing into a steady 15 mph wind, the ears of a basset will
begin to spread and rise.

Obviously since the ears rise, they have enough aerodynamic lift for
themselves...which leads to: What are the lift capabilities of a
basset's ears and can the hounds be bred to be heavy lift aircraft?

Dear Boyle,

Unfortunately, legal considerations prevent me from pursuing
this matter.

Let's just say that copies of Disney's "Dumbo the Flying
Elephant" will soon be recalled and replaced with more
accurate information if there is any justice.

Carl "Class Action" Fogel

Quoted message said:

A possible explanation is that a bow wave from the rider
expands as speed rises, which leads to the Windscribe
showing less and less of the true wind speed.

As far as I can see, such a bow wave would get smaller at
higher speed rather than bigger. However, it might be mostly
unchanged, which means the same percentage of speed drop, which
of course would get bigger in absolute terms.

Putting it off to the side is better than ahead, if you want to
try to figure out what's going on. I was going to do two experiments
when the weather got nicer, with my three of them, an broomstick
across the bars (and compare the average speeds of all 3) on
a calm day, swapping the devices halfway to cancel any differences
among them (and not letting them recalibrate).

And on some day with a good headwind, do the same with a vertical
broomstick, to see how much the wind depends on height. After all,
the wind way down by the handlebars may be childs' play compared to
what's working against your chest.
--
Ron Hardin
[email hidden]

On the internet, nobody knows you're a jerk.

Ron Hardin said:

Quoted message said:

A possible explanation is that a bow wave from the rider
expands as speed rises, which leads to the Windscribe
showing less and less of the true wind speed.

As far as I can see, such a bow wave would get smaller at
higher speed rather than bigger. However, it might be mostly
unchanged, which means the same percentage of speed drop, which
of course would get bigger in absolute terms.

Putting it off to the side is better than ahead, if you want to
try to figure out what's going on. I was going to do two experiments
when the weather got nicer, with my three of them, an broomstick
across the bars (and compare the average speeds of all 3) on
a calm day, swapping the devices halfway to cancel any differences
among them (and not letting them recalibrate).

And on some day with a good headwind, do the same with a vertical
broomstick, to see how much the wind depends on height. After all,
the wind way down by the handlebars may be childs' play compared to
what's working against your chest.

Dear Ron,

Curse you for such a sensible idea!

Out to the side sounds good, as long as I can find a place
where my outrigger won't hit anything. Either way, there's
the problem of seeing the damned display.

Your idea about the bow wave decreasing with speed is
possible, but I'm not sure whether it will increase or
decrease in the smooth manner of the generally simple
objects used in theory.

The trouble with a bicyclist is that two arms out to the
side channel turbulence into the forwar-slanted torso above
two alternately flailing thighs.

So if there is a bow wave as large as you suspect, it's
probably changing shape as we pedal and may behave strangely
with increased speed. The flaring turublence from the arms
and thighs as speed rises might constrain and increase a
pressure wave from the torso--or bleed it off instead.

Carl Fogel

Dear Carl:

Perhaps you might adapt one of these hats to suit your experimental needs.

http://www.geekculture.com/geekculturestore/webstore/caps.html#Anchor-11481

Quoted message said:

On Thu, 10 Feb 2005 19:51:05 -0700, [email hidden]
wrote:

[yeah, sure, right]

Today I braved the icy winter hell of Colorado to continue
experimenting with my wind meter toy.

...

catzz66 said:

Dear Carl:

Perhaps you might adapt one of these hats to suit your experimental needs.

http://www.geekculture.com/geekculturestore/webstore/caps.html#Anchor-11481

Quoted message said:

On Thu, 10 Feb 2005 19:51:05 -0700, [email hidden]
wrote:

[yeah, sure, right]

Today I braved the icy winter hell of Colorado to continue
experimenting with my wind meter toy.

...

Dear Catzz,

I do like the dual propeller model higher up on that page.

However, on Valentine's Day I favor the elegant, understated
look associated with this sort of headgear:

http://www.villagehatshop.com/viking_horns_helmet_hat.html

Carl Fogel

On Thu, 10 Feb 2005 19:51:05 -0700, [email hidden]
wrote:

[interminably]

Woe is me! I begin to suspect that Ron Hardin is right about
a time limit.

A brisk Chinook was blowing this afternoon, so I took pains
to clear the bejesus out of the wind meter's display and set
off.

The running average began to climb in a gratifying fashion,
reaching a bit over 23 mph in the first six miles into the
wind, while the road speed often dipped down to 12 mph in
lower gears on the flats as I dodged the rare winter
tumbleweeds, which were frisking about here and there.

Then the running average began to drop as I reached the foot
of the dam and turned ninety degrees. By the top of the
ridge west of town, it was down to 15.3 mph after half an
hour.

And it stubbornly stayed there at 15.3 mph while I glared at
it for over two miles downhill with the current windspeed
wavering between 25 and 35 mph. There was no blinking "hold"
display, just a dim-witted average unaffected by anything.

Half-way down, I said something very bad, very loudly,
because the 15.3 running average abruptly dropped to 15.1,
climbed to 15.2 for a moment, and then steadied again at
15.3 for the next five miles, no matter what the current
wind speed showed.

I'll look at the web site to see if there's any mention of
this insect-like feature.

Carl Fogel

I haven't timed it exactly, but put it out on a pole in a good breeze
and it will go negative at about 45 minutes, which represents the
point where some integer overflows to two's complement negative, I
think.

The blurb says 45 hours, is the reason I suspect it's 45 minutes,
assuming a mistranscribing.

So compare with your favorite alternate device before 45 minutes
and reset.
--
Ron Hardin
[email hidden]

On the internet, nobody knows you're a jerk.

Ron Hardin said:

I haven't timed it exactly, but put it out on a pole in a good breeze
and it will go negative at about 45 minutes, which represents the
point where some integer overflows to two's complement negative, I
think.

The blurb says 45 hours, is the reason I suspect it's 45 minutes,
assuming a mistranscribing.

So compare with your favorite alternate device before 45 minutes
and reset.

Dear Ron,

I watched today with a suspicious eye.

Sure enough, the wind meter's running average sank to 15.3
mph and stayed there after about 25 minutes.

At this point on my ride, I expect speed averages to sink,
since I'm toiling up a 400 foot hill at about 10 mph after
about 6 miles of 20 mph level riding.

Today, there was a nice tailwind, but the running average
just sat at 15.3 mph, while the current wind speed hovered
around 1 to 4 mph.

After I turned around at the top of the ridge, the wind
meter began reporting 25-35 mph for the next three miles,
but the running average sat at 15.3.

Eventually, I noticed that it was either -15.3 mph, or else
a minus sign meant to show that the current speed was below
a 15.3 mph average. It didn't change when some turns and
trees dropped the current speed to nearly zero.

Once again, I noticed the odd momentary change after a few
minutes from 15.3 to 15.2 to 15.1 and back up to 15.3 in
about five seconds, with no apparent reason--current wind
speed was about 25 mph at the time.

I'm baffled as to why your wind meter takes 45 minutes to go
stupid on the running average, while mine loses its IQ in
less than 30 minutes. (Possibly they end up resembling their
owners?)

Maybe I have a later version with a different bug?

Maybe the overflow varies according to what the average is,
or whether the meter is calculating in kilometers or miles?

Maybe your wind pole experiment included more periods of
calm than you thought?

That reminds me, the wind meter is supposed to shut itself
down into the equivalent of a cyclocomputer's sleep mode
after five minutes of no recorded wind, so it doesn't eat
batteries if you forget to turn it off overnight in the
garage. Outside in the wind, batteries wouldn't last as
long.

A minor triumph--I flip my bike upside-down in the garage,
so I was twisting the wind meter under the handlebar to
avoid using it as a bike stand. However, I also put the far
handlebar on a piece of 2x4 to tip the bike slightly so that
any oil drops to the side instead of onto the seat and
spares bag. This turns out to be enough to keep the meter
off the floor, so I don't bother twisting it under the
handlebar any more.

Carl Fogel

Quoted message said:

Maybe the overflow varies according to what the average is,
or whether the meter is calculating in kilometers or miles?

I wouldn't be surprised that they're just adding up the wind displays
and divide by the number of additions, and the former overflows,
which means the time depends on the wind speed.

Why it goes to -15.3 I don't know, unless it's that they cease the
attempted division on overflow, and -15.3 is a typical result on
quitting for some reason. The average wind itself could well be
-15.3, so they're probably getting it as a result of a software
artifact on error.

I didn't try flipping to km knots or f/s to see if the displayed
amount changed. Perhaps in whatever the internal units are, it's
some nice power of 2, and only -15.3 in mph.
--
Ron Hardin
[email hidden]

On the internet, nobody knows you're a jerk.

On Thu, 10 Feb 2005 19:51:05 -0700, [email hidden]
wrote:

[yada-yada-yada]

Sheldon Brown goes sledding:

http://www.ucomics.com/calvinandhobbes/1994/02/18/

Carl Fogel

Ron Hardin said:

Quoted message said:

Maybe the overflow varies according to what the average is,
or whether the meter is calculating in kilometers or miles?

I wouldn't be surprised that they're just adding up the wind displays
and divide by the number of additions, and the former overflows,
which means the time depends on the wind speed.

Why it goes to -15.3 I don't know, unless it's that they cease the
attempted division on overflow, and -15.3 is a typical result on
quitting for some reason. The average wind itself could well be
-15.3, so they're probably getting it as a result of a software
artifact on error.

I didn't try flipping to km knots or f/s to see if the displayed
amount changed. Perhaps in whatever the internal units are, it's
some nice power of 2, and only -15.3 in mph.

Dear Ron,

Aha! I think I've got the bug figured out after a few days.

No ride, too cold. Gave up thoughts of borrowing a small fan
and experimenting. I have my dignity, after all.

Next day, warm enough to ride, but wind meter fuss
interrupted by goathead thorn.

Yesterday, got a normal ride in, but the running average
never crashed--it lasted just under 50 minutes and worked
fine. I kept watching it all the way up the dam road and
then to the top of the ridge, but with a slight tail wind
the running average never dropped below 15.9 mph.

I thought that this was the bug--don't dip down to 15.3 mph,
and it will work.

I was wrong.

Today, a balmy Chinook was blowing into my face (I saw the
first tandem of spring out early), so I had a running
average over 20 mph on the wind meter up to the dam, where I
make a 90 degree turn, start to climb, and slow down--and
the wind goes silly anyway in the lee of the dam.

About 25 minutes out, with the running average still over 17
mph, I happened to be looking at the wind meter showing
about +10 mph when a mild gust reversed the wind direction,
the wind speed went to -3 mph for a moment--and the running
average instantly changed over thirty miles per hour to
-15.3 mph and stayed there until I cleared it.

The manufacturer mentions that a rapid shift from +60 to -60
mph will goof things up, but I expect that they aren't
mentioning this bug at a much smaller shift. Your 45 minute
loss on a pole might well correspond to how long it took
before your local wind managed to reverse quickly enough for
even a free-mounted wind meter to see a negative wind speed.

It's annoying, but at least the current wind speed seems
unaffected when the running average crashes to -15.3 mph.

Carl Fogel