Gageteers, we need a digital heading sensor

The GPS gives TRACK, not HEADING. It can't tell what direction the glider is
pointing in, only the direction its motion is taking it across the ground.

David Starer

"f.blair" wrote in message
news:E5aAc.44219$2i5.30680@attbi_s52...
Why can't the GPS create the 'heading data' my $90 Etrex gives a heading
reading.

"Bill Daniels" wrote in message
news:_y8Ac.53766$0y.15362@attbi_s03...
Dave, can it give highly accurate, real-time wind data, second by second
on
a straight one hour glide?

My last flight showed this problem during a long glide. For 30 miles
the
wind data showed SW winds at 20 knots but then I noticed the glider
drifting
to the west. Two 360 turns and the computer showed wind at 090 at 10
knots.
When I crossed the wind shift line I had a chance to change strategy.
30
miles later when the wind error became obvious it was too late.

More and more I think we need very accurate real-time wind data with no
requirement to be constantly changing heading. A cheap, reliable
heading
sensor would make this possible.

Bill Daniels

"Dave Nadler YO" wrote in message
m...
Bill - The heading is not required. In the ILEC SN10 we do this
without heading, and it normally has the wind by the time you're
off tow. Pilot feedback and measurements indicate that we do
it quite accurately. We just use TAS and GPS ground track over
multiple observations (TAS requiring accurate IAS, press, temp).
Best Regards, Dave "YO"

"Bill Daniels" wrote in message
news:gw%zc.59643$HG.25574@attbi_s53...
I've been analyzing the IGC files from my flights and comparing them
to
others.

Generally, in good conditions, I'm circling less than 25% of the
time.
Other, far better pilots than I, are circling less than 15% of the
time.
This means that wind data that depends on the glider flying circles
gets
way
out of date during the long glides. OK, "S" turns can give the
computer
a
chance to compute wind if you remember to fly them but there are
still
a
lot
of long, straight glides.

To compute real-time wind data we need Groundspeed, Ground Track
(any
GPS
gives these)True Airspeed (Some computers do this if they have OAT,
Pressure
Altitude and IAS) and accurate heading data. Heading data it the
tough
nut
to crack.

So, how do we get Heading? One way might be to put a GPS antenna in
each
wing and look at the carrier phase difference. If the computer saw
a
constant track, it could assume the wings are level and determine a
heading
value. This heading value might update an aerospace quality MEMS
heading
gyro that would maintain a flow of heading data to the glide
computer
during
times when the wings were banked.

With good heading data we could get uninterrupted high quality wind
data
regardless of the gliders' maneuvering or lack of it.

OK, RAS gageteers, how about it?

Bill Daniels

"David Starer" wrote in message ...
The GPS gives TRACK, not HEADING. It can't tell what direction the glider is
pointing in, only the direction its motion is taking it across the ground.

David Starer


True, but the issue is confused because some Etrex models incude a
magnetic heading sensor.


Andy

Subject: Gageteers, we need a digital heading sensor
From: "Bill Daniels"

My last flight showed this problem during a long glide. For 30 miles the
wind data showed SW winds at 20 knots but then I noticed the glider drifting
to the west. Two 360 turns and the computer showed wind at 090 at 10 knots.
When I crossed the wind shift line I had a chance to change strategy. 30
miles later when the wind error became obvious it was too late.

More and more I think we need very accurate real-time wind data with no
requirement to be constantly changing heading. A cheap, reliable heading
sensor would make this possible.

I very strongly agree, because I too am "cursed" with long glides between
thermals when flying long cross country flights. Air masses may change
dramatically in 10's of miles, but you won't know if you don't stop for a few
turns, also late in the day shear lines come through and cannot be easily
spotted on blue days without real-time wind info. This info WILL make the
difference between getting there faster or slower (or getting there at all!).
If you don't understand this, then you either haven't flown 50-60+ mile glides,
or are just not observant enough of the situation to care.
Our climb instruments have evolved to the point that we really know what the
air is doing in the vertical direction, it would sure be nice to have as much
info about the horizontal direction.

-
Mark Navarre
2/5 black ace
LoCal, USA
remove brain to reply
-

Bill, you're absolutely right, during a dead straight glide
with constant airspeed their isn't enough information to
compute the result. With an SN10 you need to make an S-turn
at least to get an update.

The heading sensor issue is a bit difficult. Certainly it can
be done with GPS using multiple antennas (I can't remember the
commercial products that do this off-hand). Google and you'll
find a few research projects using GPS for attitude as well
as heading. Cost is not on for gliders real soon. Compasses
are very cranky beasts, especially if they need to be glider-
pilot-proof (about which I could tell stories for hours).
Making something that is low-cost, self-calibrating, immune
to stupid installations - that's the hard bit.

Hope that all makes sense,
Best Regards, Dave

PS: Haven't seen anyone suggest a sun-tracker yet ?
Or vision-system with terrain matching ?

"Bill Daniels" wrote in message news:_y8Ac.53766$0y.15362@attbi_s03...
Dave, can it give highly accurate, real-time wind data, second by second on
a straight one hour glide?

My last flight showed this problem during a long glide. For 30 miles the
wind data showed SW winds at 20 knots but then I noticed the glider drifting
to the west. Two 360 turns and the computer showed wind at 090 at 10 knots.
When I crossed the wind shift line I had a chance to change strategy. 30
miles later when the wind error became obvious it was too late.

More and more I think we need very accurate real-time wind data with no
requirement to be constantly changing heading. A cheap, reliable heading
sensor would make this possible.

Bill Daniels

"Dave Nadler YO" wrote in message
m...
Bill - The heading is not required. In the ILEC SN10 we do this
without heading, and it normally has the wind by the time you're
off tow. Pilot feedback and measurements indicate that we do
it quite accurately. We just use TAS and GPS ground track over
multiple observations (TAS requiring accurate IAS, press, temp).
Best Regards, Dave "YO"

"Bill Daniels" wrote in message
news:gw%zc.59643$HG.25574@attbi_s53...
I've been analyzing the IGC files from my flights and comparing them to
others.

Generally, in good conditions, I'm circling less than 25% of the time.
Other, far better pilots than I, are circling less than 15% of the time.
This means that wind data that depends on the glider flying circles gets
way
out of date during the long glides. OK, "S" turns can give the computer
a
chance to compute wind if you remember to fly them but there are still a
lot
of long, straight glides.

To compute real-time wind data we need Groundspeed, Ground Track (any
GPS
gives these)True Airspeed (Some computers do this if they have OAT,
Pressure
Altitude and IAS) and accurate heading data. Heading data it the tough
nut
to crack.

So, how do we get Heading? One way might be to put a GPS antenna in
each
wing and look at the carrier phase difference. If the computer saw a
constant track, it could assume the wings are level and determine a
heading
value. This heading value might update an aerospace quality MEMS
heading
gyro that would maintain a flow of heading data to the glide computer
during
times when the wings were banked.

With good heading data we could get uninterrupted high quality wind data
regardless of the gliders' maneuvering or lack of it.

OK, RAS gageteers, how about it?

Bill Daniels

"Dave Nadler YO" wrote in message
om...
Bill, you're absolutely right, during a dead straight glide
with constant airspeed their isn't enough information to
compute the result. With an SN10 you need to make an S-turn
at least to get an update.

The heading sensor issue is a bit difficult. Certainly it can
be done with GPS using multiple antennas (I can't remember the
commercial products that do this off-hand). Google and you'll
find a few research projects using GPS for attitude as well
as heading. Cost is not on for gliders real soon. Compasses
are very cranky beasts, especially if they need to be glider-
pilot-proof (about which I could tell stories for hours).
Making something that is low-cost, self-calibrating, immune
to stupid installations - that's the hard bit.

Hope that all makes sense,
Best Regards, Dave

PS: Haven't seen anyone suggest a sun-tracker yet ?
Or vision-system with terrain matching ?


Bob Lepp e-mailed me info on a company called Aventech that makes wind
direction detection equipment for crop dusters. These folks need very
accurate winds aloft data to predict the drift of chemicals sprayed on
crops.

Their gadget works just like a glider computer with the addition of a
two-antenna GPS array that provides heading data accurate to .5 degree. To
cover any gaps in the GPS signal, they use a solid state inertial unit.

Sensors that detect the earth's magnetic field will always be tricky. GPS
heading sensing looks like a winner since we need the GPS receiver anyway.
Maybe a couple of self-contained Bluetooth GPS receivers attached to the
wingtips would work. An inertial measurement unit would be very useful for
applications other than wind data. These could determine true vertical
regardless of the glider's attitude and very accurately measure Z-axis
acceleration. What vario maker wouldn't love to have that data.

No doubt this will be expensive at first but then we couldn't afford GPS 20
years ago. Twenty years before that glider pilots couldn't afford radios.
Electronics always seems to follow a learning curve that exponentially
reduces cost.

Bill Daniels

This is what we need but smaller, cheaper, lighter and all other good things
engineering-wise.
http://www.xbow.com/Products/product...s.aspx?sid=104

Bill Daniels

"Dave Nadler YO" wrote in message
om...
Bill, you're absolutely right, during a dead straight glide
with constant airspeed their isn't enough information to
compute the result. With an SN10 you need to make an S-turn
at least to get an update.

The heading sensor issue is a bit difficult. Certainly it can
be done with GPS using multiple antennas (I can't remember the
commercial products that do this off-hand). Google and you'll
find a few research projects using GPS for attitude as well
as heading. Cost is not on for gliders real soon. Compasses
are very cranky beasts, especially if they need to be glider-
pilot-proof (about which I could tell stories for hours).
Making something that is low-cost, self-calibrating, immune
to stupid installations - that's the hard bit.

Hope that all makes sense,
Best Regards, Dave

PS: Haven't seen anyone suggest a sun-tracker yet ?
Or vision-system with terrain matching ?

"Bill Daniels" wrote in message
news:_y8Ac.53766$0y.15362@attbi_s03...
Dave, can it give highly accurate, real-time wind data, second by second
on
a straight one hour glide?

My last flight showed this problem during a long glide. For 30 miles
the
wind data showed SW winds at 20 knots but then I noticed the glider
drifting
to the west. Two 360 turns and the computer showed wind at 090 at 10
knots.
When I crossed the wind shift line I had a chance to change strategy.
30
miles later when the wind error became obvious it was too late.

More and more I think we need very accurate real-time wind data with no
requirement to be constantly changing heading. A cheap, reliable
heading
sensor would make this possible.

Bill Daniels

"Dave Nadler YO" wrote in message
m...
Bill - The heading is not required. In the ILEC SN10 we do this
without heading, and it normally has the wind by the time you're
off tow. Pilot feedback and measurements indicate that we do
it quite accurately. We just use TAS and GPS ground track over
multiple observations (TAS requiring accurate IAS, press, temp).
Best Regards, Dave "YO"

"Bill Daniels" wrote in message
news:gw%zc.59643$HG.25574@attbi_s53...
I've been analyzing the IGC files from my flights and comparing them
to
others.

Generally, in good conditions, I'm circling less than 25% of the
time.
Other, far better pilots than I, are circling less than 15% of the
time.
This means that wind data that depends on the glider flying circles
gets
way
out of date during the long glides. OK, "S" turns can give the
computer
a
chance to compute wind if you remember to fly them but there are
still a
lot
of long, straight glides.

To compute real-time wind data we need Groundspeed, Ground Track
(any
GPS
gives these)True Airspeed (Some computers do this if they have OAT,
Pressure
Altitude and IAS) and accurate heading data. Heading data it the
tough
nut
to crack.

So, how do we get Heading? One way might be to put a GPS antenna in
each
wing and look at the carrier phase difference. If the computer saw
a
constant track, it could assume the wings are level and determine a
heading
value. This heading value might update an aerospace quality MEMS
heading
gyro that would maintain a flow of heading data to the glide
computer
during
times when the wings were banked.

With good heading data we could get uninterrupted high quality wind
data
regardless of the gliders' maneuvering or lack of it.

OK, RAS gageteers, how about it?

Bill Daniels

(Dave Nadler YO) writes:

The heading sensor issue is a bit difficult. Certainly it can be
done with GPS using multiple antennas (I can't remember the
commercial products that do this off-hand). Google and you'll find a
few research projects using GPS for attitude as well as
heading. Cost is not on for gliders real soon. Compasses are very
cranky beasts, especially if they need to be glider- pilot-proof
(about which I could tell stories for hours). Making something that
is low-cost, self-calibrating, immune to stupid installations -
that's the hard bit.

Many of the Marine GPS units have a `compass' option to add a second
antena and give a heading.

But if you are going to add a second set of electronics, then it is
almost a done deal to add TWO sets and have the full 6D position and
orientation data.

--
Paul Repacholi 1 Crescent Rd.,
+61 (08) 9257-1001 Kalamunda.
West Australia 6076
comp.os.vms,- The Older, Grumpier Slashdot
Raw, Cooked or Well-done, it's all half baked.
EPIC, The Architecture of the future, always has been, always will be.

One thing that a lot of the UAV guys are doing, is to use a magnetic
heading sensor coupled with a MEMS gyro, or if more money is available,
a FOG. The magnetic sensor can be used to periodically determine heading
and to correct for signal drift from the gyro. For instance, the gyro
can be used as the primary source for heading info, while the magnetic
sensor is used during long, stable glides. Very similar to how the DG
and compass are used in power planes. Of course, the gyro would have to
be either mechanically gimbaled to remain parallel to the horizon, or,
alternatively, several gyros on different axes can be used together to
determine actual heading change, rather than yaw rate.

Using some basic Kalman filtering, it should be possible to get fairly
accurate (5-8 degree) heading info. This will, of course, be magnetic
heading, and subject to the usual accuracy issues. However, it might be
possible to correct the data to true heading by loading a map of lines
of deviation and magnetic anomalies (which can also be fed into the
Kalman filter). Simply feed the wind component data from the GPS, the
raw heading info from the magnetic sensor, and the stabilized data from
the gyro into a Kalman filter, and pretty stable and accurate heading
data should be available.

Definitely do-able. Let's do it! :O)

BTW, check out www.rotomotion.com. These guys have several fairly cheap
AHRS', as well as several cheap IMU's. They've also published a bunch of
open source code on Sourceforge under the Autopilot project
http://autopilot.sourceforge.net/ with an effective Kalman filter to
integrate GPS, IMU, and magnetic sensor data.

- Robert

Marine users have been using electronic compasses for some time. These are
fluxgate compasses and most have NEMA output so what you want is not
impossible. The marine ones are expensive circa $400 but there are a new
bread of digital compasses some of which are included in GPS handhelds but I
cannot see if any have NEMA outputs. In addition there ae some aviation
sensors coming n the market (MEMS) (see
http://www.willow.co.uk/html/heading.html) You will need a NEMA sentance
output of HDM or better HDG from such a device and a NEMA concatenator to
meld the NEMA output into the IPAQ datastream.

On the Plus side
You would have a compass that had little lag - easier to roll out of
thermals onto heading
You would get your wind data

On the downside
Expensive as one-off
Yet more battery drain
Device would need A solid state memory for an electronic version of
deviation card
Device would have to be installed in tail as they are V sensitive
You only get Magnetic heading from device - GPS is essentially True and if
flying in areas of local magnetic anomalies you will get strange results.

Given most gliders fly Track as opposed to bearing it would be easier simply
to note magnetic heading & speed once on track and make sure that the two
remain constant if they diverge then your wind direction has changed and you
can either do the mental maths (or use a flight computer) or put in a 360.

What we are all really waiting for is a Touch Single panel display system
that would include something like this along with a Head-Up display. But the
market is just too small to make something like this a real economic
proposition at this time along with the associated battery drain. You would
be lucky to sell more than 500 units.

rgds
stephen


"Bill Daniels" wrote in message
news:_y8Ac.53766$0y.15362@attbi_s03...
Dave, can it give highly accurate, real-time wind data, second by second
on
a straight one hour glide?

My last flight showed this problem during a long glide. For 30 miles the
wind data showed SW winds at 20 knots but then I noticed the glider
drifting
to the west. Two 360 turns and the computer showed wind at 090 at 10
knots.
When I crossed the wind shift line I had a chance to change strategy. 30
miles later when the wind error became obvious it was too late.

More and more I think we need very accurate real-time wind data with no
requirement to be constantly changing heading. A cheap, reliable heading
sensor would make this possible.

Bill Daniels

"Dave Nadler YO" wrote in message
m...
Bill - The heading is not required. In the ILEC SN10 we do this
without heading, and it normally has the wind by the time you're
off tow. Pilot feedback and measurements indicate that we do
it quite accurately. We just use TAS and GPS ground track over
multiple observations (TAS requiring accurate IAS, press, temp).
Best Regards, Dave "YO"

"Bill Daniels" wrote in message
news:gw%zc.59643$HG.25574@attbi_s53...
I've been analyzing the IGC files from my flights and comparing them
to
others.

Generally, in good conditions, I'm circling less than 25% of the time.
Other, far better pilots than I, are circling less than 15% of the
time.
This means that wind data that depends on the glider flying circles
gets
way
out of date during the long glides. OK, "S" turns can give the
computer
a
chance to compute wind if you remember to fly them but there are still
a
lot
of long, straight glides.

To compute real-time wind data we need Groundspeed, Ground Track (any
GPS
gives these)True Airspeed (Some computers do this if they have OAT,
Pressure
Altitude and IAS) and accurate heading data. Heading data it the
tough
nut
to crack.

So, how do we get Heading? One way might be to put a GPS antenna in
each
wing and look at the carrier phase difference. If the computer saw a
constant track, it could assume the wings are level and determine a
heading
value. This heading value might update an aerospace quality MEMS
heading
gyro that would maintain a flow of heading data to the glide computer
during
times when the wings were banked.

With good heading data we could get uninterrupted high quality wind
data
regardless of the gliders' maneuvering or lack of it.

OK, RAS gageteers, how about it?

Bill Daniels

Dave,

Posting to the group in hopes you answer might serve others...

My SN-10B serves me well. However, I am having a small problem based
on airspeed error. I have noted on ridge flights that after prolonged
high-speed flight without turns, the instrument starts counting up the
wind speed. On one leg, I saw a 25 knot increase. Clearly I need to
fix the asi error table, but if the SN-10 is counting up, which way do
I need to go in the table?

OC