Mechanical Vario

At 03:06 30 September 2007, Eric Greenwell wrote:
Dan G wrote:

BTW, on the gust issue, there is another solution
(though not nearly
as elegant as the rotating TE probe) - accelerometers.


I think I understand how accelerometers could distinguish
between a
horizontal gust and the vertically moving air in a
thermal, but I don't
understand how aligning the probe with the horizontal
gust will reduce
it's effect on the vario. Wouldn't that accentuate,
rather than
attenuate, the gust effect?

--
Eric Greenwell - Washington State, USA

Not at all, at least not if it is the 2 or 3 way probe
and this is why. It is first and foremost the static
system that is particularly sensitive to gusting. When
a horizontal gust hits the side of a plane, it creates
positive pressure on one side of the static inputs
(whether fuse or probe mounted), throwing the reading
way out of whack. With the static on a rotating probe,
it can align itself to always face directly into the
wind and alleviate the big errors in static reading
that horizontal gusts ( or other disturbances in yaw)
create. It does not hurt to have the TE also rotate
with it, and does not hurt to have the dynamic rotate
as well (with rotating dynamic, a cup shaped Kiel tip
is not required to maintain accuracy-less drag) but
dynamic and TE are not as sensitive to misalignments
in airflow as the static system is. This probe system
will provide accurate readings during both slipping
maneuvers (like if you mildly slip while thermalling
ala Holighaus) as well as gusting incidents. BTW, the
'fancy' 2 way probe Dr Smolik sells is only 80 Euros,
and the 3 way probe only 99. This video is the 3 way
probe:
http://youtube.com/watch?v=OpN9sYHF_yc , and this link
shows drawings and prices for the whole line:
http://www.eaglebrandproducts.com/TE...rices_2006.pdf
I am only assuming here, but I would imagine these
probes to be much cheaper than an accelerometer compensated
computerized vario system (not to mention compatible
with most anyone's current setup) but perhaps maybe
not as effective in all situations. It is a simple
and elegant aerodynamic solution to an old problem,
that I'm sure will be seen on many more gliders in
the near future. Again, I will share the data tables
Ludek provides, once he sends them to me.

Paul Hanson

PS. I have no financial involvement with these probes,
I just think they are very cool.
PPS. there is a reason that NASA and most other flight
test groups use static/dynamic (they don't mess with
TE) probes that rotate (in 2 axis) to keep readings
accurate while evaluating aircraft.

I think that if the airspeed is reduced by 40 knots or so in, say, 20
seconds, that's a zoom. I often see a quicker speed reduction than that. I
would agree than smooth control inputs are better. Timing of the airspeed
changes is more important than the amount.

The key as to whether it worked or not is the barogram trace. If the
downward trend of the glide is displaced upward at the zoom so a new trend
starts at the top of the zoom, there was a net gain. If the thermal was too
narrow or was followed by heavy sink, the barogram trace will just show a
spike with no change in the trend - just a loss in average speed due to the
slowing.

A couple of pilots who seem to be the masters of the "Long Glide" are Kevin
Wyatt and Gary Ittner. You will notice that their airspeed trace is almost
an exact inverse of the vario trace. i.e. vario up, arispeed down and vario
down airspeed up.

On the other hand you will see pilots where there is only a weak correlation
between airspeed and vario. These folks seldom get more than the published
L/D.

Bill Daniels


wrote in message
oups.com...
Bill, are you seeing the effect of "dolphin" flying, or just following
the lines of energy (or, avoiding sink). I try real hard to avoid the
classic "pull hard in lif" type of dolphin flying, since in my
experience it slows me down (from comparison flying); OTOH, I try real
hard to look for and exploit lift lines, and gently vary speeds to
match the trend of the airmass. Doing this, I consistently better my
polar's L/D for the speed being flown.

Of course, this is semantics - whatever technique being used, it is a
skill that takes knowledge, practice, and good instruments.

And the fast pilots usually have all three!

Kirk
66

Paul Hanson wrote:
At 03:06 30 September 2007, Eric Greenwell wrote:
Dan G wrote:

BTW, on the gust issue, there is another solution
(though not nearly
as elegant as the rotating TE probe) - accelerometers.

I think I understand how accelerometers could distinguish
between a horizontal gust and the vertically moving air in a
thermal, but I don't understand how aligning the probe with the horizontal
gust will reduce it's effect on the vario. Wouldn't that accentuate,
rather than attenuate, the gust effect?

--
Eric Greenwell - Washington State, USA

Not at all, at least not if it is the 2 or 3 way probe
and this is why. It is first and foremost the static
system that is particularly sensitive to gusting. When
a horizontal gust hits the side of a plane, it creates
positive pressure on one side of the static inputs
(whether fuse or probe mounted), throwing the reading
way out of whack. With the static on a rotating probe,
it can align itself to always face directly into the
wind and alleviate the big errors in static reading
that horizontal gusts ( or other disturbances in yaw)
create.

The gusting that cause false readings on my varios seems small enough
that it doesn't move the yaw string very much. I can use the rudder to
slip/skid the same amount, and the vario hardly notices it. So it seems
like the gust itself is the problem, not the direction it comes from. If
that's true, an aligning probe won't help any.

Also, suppose the gust comes directly from the front or the back. This
will cause a change in the airspeed and "fool" a TE vario. A probe that
aligns with the airflow won't help in this case, as the airflow
direction doesn't change at all.

It does not hurt to have the TE also rotate
with it, and does not hurt to have the dynamic rotate
as well (with rotating dynamic, a cup shaped Kiel tip
is not required to maintain accuracy-less drag) but
dynamic and TE are not as sensitive to misalignments
in airflow as the static system is.

If that's the case, why don't we just use a TE probe and forget about
using a pitot/static system to run the vario?

This probe system
will provide accurate readings during both slipping
maneuvers (like if you mildly slip while thermalling
ala Holighaus) as well as gusting incidents.

It seems like the aligning probe ensures that a gust will add it's
entire velocity to the glider's speed through the air, making it even
more sensitive to gusts than a probe that doesn't align.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

Paul Hanson wrote:
When
a horizontal gust hits the side of a plane, it creates
positive pressure on one side of the static inputs
(whether fuse or probe mounted), throwing the reading
way out of whack.

I can see that this would make the ASI twitch (and the altimeter if it
wasn't on cockpit pressure) but I don't see the relevance to my varios
because:

- my B.40 only has one line that connects to the TE probe, so the static
isn't affected and you say that a TE probe is relatively little
affected by gusts.

- my SDI C4 which has static and pitot as well as TE connections.
My guess is that it only uses TE for its vario function and the
static+pitot for airspeed and pressure altitude.

BTW, what the heck is a "dynamic pressure" probe? Is it a pitot tube?


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

At 12:06 08 October 2007, Martin Gregorie wrote:
Paul Hanson wrote:
When
a horizontal gust hits the side of a plane, it creates
positive pressure on one side of the static inputs
(whether fuse or probe mounted), throwing the reading
way out of whack.

I can see that this would make the ASI twitch (and
the altimeter if it
wasn't on cockpit pressure) but I don't see the relevance
to my varios
because:

- my B.40 only has one line that connects to the TE
probe, so the static
isn't affected and you say that a TE probe is relatively
little
affected by gusts.

Relative being a relative term, this is somewhat true.
In comparison it is not AS affected as the static,
but it is indeed affected. There are many plumbing
combos for different types of system, so while something
that works well with one system does not mean it will
work for another. Although in this case, I do believe
you would get better readings from your B-40 with the
Yaw-free TEK probe. Read the stats on the charts for
yourself that I am posting links to in a new post,
that compare a standard TE and a yawing unit under
the same conditions.

- my SDI C4 which has static and pitot as well as TE
connections.
My guess is that it only uses TE for its vario function
and the
static+pitot for airspeed and pressure altitude.

Without actually studying your system your guess is
only that-a guess. Just because the B-40 runs only
on TE does not mean that this one does, although it
may. Rather than guess though, I would do my homework
to figure that out if it were mine before deciding
how to improve anything.

BTW, what the heck is a 'dynamic pressure' probe? Is
it a pitot tube?

Dynamic pressure is what a Pitot tube is measuring,
and what a TE is attempting to create a perfectly matched
inverse of.

Paul Hanson
"Do the usual, unusually well"--Len Niemi

Paul Hanson wrote:

Dynamic pressure is what a Pitot tube is measuring,
and what a TE is attempting to create a perfectly matched
inverse of.

Clear and concise. Thanks!


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |