?Final glide calculator coupled to GPS?
David Noyes
Who makes a final-glide calculator (with vario) that contains its own
altitude sensor but no GPS receiver? I want one that can be connected to a
hand-held Garmin GPS with moving map display. The end result should be a
final glide calculator which calculates a height above or below final glide to
whatever airport is selected in the Garmin's data base. Or at least gives
some graphical indication of being above or below final glide to the selected
airport. The vario portion should give the usual immediate and average climb
indications.
Any suggestions? Thanks. Dave "NL"
(Remove "NOSPAM_" from return address to reply.)
Basilhome
In article <NOSPAM_dnoyes...@pop.service.ohio-state.edu>,
NOSPAM...@pop.service.ohio-state.edu (David Noyes) writes:
>
> Who makes a final-glide calculator (with vario) that contains its own
>altitude sensor but no GPS receiver?
Almost everyone! The cambridge L and S Navs and the SDI C3 and probably
several others. I use the C3 as it goes in one 80mm hole and needs no
flask. It gives final glide to the next waypoint or the end of a route,
it calculated the wind when circling (speed and direction) and it has a
very good vario, speed director, averager etc. See adverts in Sailplane
and Glider for price in UK.
Ian Lewis
Most flight computers can be used with an external GPS. E.g.
Cambridge L-Nav
Cambridge S-Nav
SDI C4
I installed an SDI C3 (basically the same as a C4 with different
switches) in my ASW-24 this winter, and have been practicing with the
instrument running up to the UK Lasham Regionals last week, where the
computer was a valuable addition to the panel.
Here are some comments. The last about WIND measurement is a new issue.
------------------------------------------------------------------------
(In general I haven't been too complimentary about Cambridge... anyone
with one of these fine instruments should add their comments.)
I use a Garmin 12XL, which works very well with the SDI C3. I use
the built-in antenna in the GPS, without a remote antenna. I made
up the power/data cable myself using the ShareHardWare plug available
from Purple Computing. The GPS is still on its original batteries, as
all the time it's in the glider it's on glider power. 12XLs will
get through a set of AA cells in one flight. The internal logger in
the 12XL works very well, for 5 and 1/2 hours at 20 seconds, or around
8 hours at 30 second logging interval. Ian Molesworth's free utility
directly downloads the track log into an IGC file for viewing with
any soaring analysis software ( I use the shareware 'glidplan.exe').
Any flight computer will take a dozen flights to get used to. You have
to set up a number of parameters on installation, such as polar,
default volume, vario characteristics (Netto or TE). Pre-flight, you
put in at least arrival height for your home airfield, and set the
current height if QNH. In flight you're adjusting the McCready/Bugs/
Ballast settings, and maybe switching the instrument from cruise to
climb, and maybe using it to look at battery voltages or external
temperature.
The computers use a variety of ways to decide whether you are
cruising or climbing. Most will look at an external switch, which
can be triggered by the flap lever in a 15m ship. The C-Nav had
a fixed 60kt threshold, below which you were climbing, above that speed
you were assumed to be cruising. The L-Nav and S-Nav have optional
G-meters to detect the increased G while turning. The SDI C3/C4
allows you to specify (a) a lower speed threshold which you have to go
BELOW to change from cruise to climb, and (b) a higher speed threshold
which you have to go ABOVE to change from climb to cruise (get it?).
Also you can have an external switch, or you can have the instrument
detect circling from the GPS input (that's what I use).
In the old old old days, the switch from cruise to climb was paricularly
important on final glide, as the instrument was integrating speed to
count down your remaining distance-to-go. If you stopped to top up a
final glide (as we all do now and again) you had to make sure the
computer knew you were no longer travelling along the last leg.
Now you have GPS, much of this guess work (including inputting wind) is
no longer needed, and the final glide calculation is MUCH simpler.
The computer really comes into its own when you're on final glide, as
it will take into account the calculated (or input) wind with the
accurate GPS distance-to-go figure, and give you
a NET figure of height above-or-below glide slope. This is the SAME
figure as expected arrival height (think about it...). This means
you can set off on final glide with the instrument saying maybe
+500 feet at 20-30 miles away, and monitor the figure through the
journey to see if the trend is better (flying though good air) or
worse (bad air). Actually in a competition, the net figure you want to
see on the computer before you start the final glide depends very much
on your judgement of the energy available to you in the air between you
and your home airfield. If there looks like lots of lift about, you set
off BELOW final glide with the expectation of making up some height
through pull-ups on the way home. If the day stinks, you make sure you
get in.
The Cambridge S-Nav has a new Total-Energy final glide calculation,
taking into account your speed above (or below) the correct speed-to-fly
in calculating your effective current height. I've met people who
don't use this optional feature, maybe some who does can comment.
The SDI is customisable in that you can pick which numbers you want
displayed when you're climbing or cruising. For example, an odd
choice would be to display battery volts while cruising and external
temperature while climbing. I have:
CLIMBING: 23-second average climb, climb average from start of climb,
height above/below glide-slope
CRUISING: 20-second netto average, distance-to-go,
height above/below glide-slope
The wind calculation is where the available instruments very much
diverge. I understand (CORRECT ME IF I'M WRONG) that the
Cambridge L/S-Nav uses drift in thermals if you use the Cambridge
logger, and calculates head/tail wind from an attached GPS. I believe
the SDI approach to be far superior, in that they read the LAT/LONGS
coming in from the GPS to calculate a groundspeed vector, and have
the airspeed from the pitot, and resolve the two to produce a
wind vector in half-a-turn. If you select 'WIND' on the SDI screen
you normally see a figure such as "180:14" meaning a Southerly 14 kts.
The SDI approach is superior in giving you are more immediate
readout of windspeed and direction, and it copes better if you
divert off track on a final glide. Frankly, I think the Cambridge
design decisions for wind calculations are inadequate. In any
instrument, the glide calculation is very dependent on an accurate
airpeed, and the SDI gives you a calibration screen so you can get
the airspeed to the same accuracy as your ASI. This is important as
the wind speed is calculated from your AIRSPEED (from pitot) MINUS YOUR
GROUNDSPEED (from GPS) so a few percent error in the computers
understanding of airspeed could translate into a big error in the wind
calculation.
The end result is that on a final glide you basically trust the
instrument to get you onto a glide path, and than monitor the
arrival height as you progress and take a climb and maybe divert if it
says you aren't going to make it, or speed up if you're gaining on it.
In the last 10 miles you pay particular attention out the window in case
the instrument is WRONG.
In the UK the SDI C4 is 2,700 US Dollars, the L-Nav is about 3,000 and
the S-Nav 3,500. The Cambridge loggers are around 2,800 US Dollars.
Ian.
Daniel J. Dunkel
> The wind calculation is where the available instruments very much
> diverge. I understand (CORRECT ME IF I'M WRONG) that the
> Cambridge L/S-Nav uses drift in thermals if you use the Cambridge
> logger, and calculates head/tail wind from an attached GPS. I believe
> the SDI approach to be far superior, in that they read the LAT/LONGS
> coming in from the GPS to calculate a groundspeed vector, and have
> the airspeed from the pitot, and resolve the two to produce a
> wind vector in half-a-turn. If you select 'WIND' on the SDI screen
> you normally see a figure such as "180:14" meaning a Southerly 14 kts.
> The SDI approach is superior in giving you are more immediate
> readout of windspeed and direction, and it copes better if you
> divert off track on a final glide. Frankly, I think the Cambridge
> design decisions for wind calculations are inadequate. In any
> instrument, the glide calculation is very dependent on an accurate
> airpeed, and the SDI gives you a calibration screen so you can get
> the airspeed to the same accuracy as your ASI. This is important as
> the wind speed is calculated from your AIRSPEED (from pitot) MINUS YOUR
> GROUNDSPEED (from GPS) so a few percent error in the computers
> understanding of airspeed could translate into a big error in the wind
> calculation.
There is one thing about this that I don't understand. Doesn't the
density-altitude have to be included in the calculation?
One of the things that I expected to see when I started flying with my
Garmin 12xl was to be able to calculate the actual wind conditions. It
seemed that all I had to do was to take the difference between the
GPS-measured ground speed and the reading from the ASI.
On my first flight, I was pleased to see that my ground speed was much
higher than my air speed. At first, I thought that this meant that I had a
tail wind. But to my surprise, when I turned around 180 degrees, it still
showed the same thing. Since it didn't seem logical that I had a tail wind
in both directions, I incorrectly suspected that my ASI was off.
When I mentioned this to a fellow pilot, he gave me a strange look and
said, "Of course, when you are flying at 16,000 feet your ASI will almost
always show less than your ground speed". At some theoretical level, I
knew the effect of density-altitude, but until I flew with a GPS I didn't
really think about it--other than to adjust my VNE.
It seems to me, that the GPS-connected flight computers have the same
problem that I do when I try to determine the wind conditions.
I understand the type that calculate drift while thermaling, but I don't
understand the type you describe above. How do they do it?
Regards,
Dan
Regards,
Dan
Ian Spence
David Noyes wrote:
>
> Who makes a final-glide calculator (with vario) that contains its own
> hand-held Garmin GPS with moving map display. The end result should be a
> final glide calculator which calculates a height above or below final glide to
> whatever airport is selected in the Garmin's data base. Or at least gives
> some graphical indication of being above or below final glide to the selected
> airport. The vario portion should give the usual immediate and average climb
> indications.
> Any suggestions? Thanks. Dave "NL"
Dave:
The Cambridge L-NAV or S-NAV units will do this for you.
IMHO the Cambridge instruments have far better ergonomics
than any of the other flight computers on the market.
Ian
--
Ian Spence spe...@psych.utoronto.ca
Department of Psychology http://psych.toronto.edu/~spence/
University of Toronto
Toronto, Ontario (416) 978-7623 (Voice)
Canada M5S 1A1 (416) 978-4811 (FAX)
ASW24
> I believe
>> the SDI approach to be far superior,..
What is the "SDI"? Who makes it?
Basilhome
In article <01bcacce$999328d0$cfd469cf@dan_dunkel>, "Daniel J. Dunkel"
<ddun...@ondisplay.com> writes:
>
>When I mentioned this to a fellow pilot, he gave me a strange look and
>said, "Of course, when you are flying at 16,000 feet your ASI will almost
>always show less than your ground speed". At some theoretical level, I
>knew the effect of density-altitude, but until I flew with a GPS I didn't
>really think about it--other than to adjust my VNE.
>
>It seems to me, that the GPS-connected flight computers have the same
>problem that I do when I try to determine the wind conditions.
>
>I understand the type that calculate drift while thermaling, but I don't
>understand the type you describe above. How do they do it?
>
The glide computers have altimeters and temperature sensors so they can
calculate the density altitude and correct for true air speed.
Andreas Maurer
On 19 Aug 1997 18:34:50 GMT, "Daniel J. Dunkel"
<ddun...@ondisplay.com> wrote:
>When I mentioned this to a fellow pilot, he gave me a strange look and
>said, "Of course, when you are flying at 16,000 feet your ASI will almost
>always show less than your ground speed". At some theoretical level, I
>knew the effect of density-altitude, but until I flew with a GPS I didn't
>really think about it--other than to adjust my VNE.
Here are the values, measured for the Glasfluegel Salto.
Altitude: max. IAS
0 -3000 m NN 250 km/h
5000 230 km/h
7000 205 km/h
9000 180 km/h
11000 155 km/h
13000 130 km/h
All of these speeds are measured at a True Airspeed of 250 km/h.
BTW:
Here in Europe the top ceiling is at maximum at 8.000 ft, so we don't
bother about the difference between IAS and TAS. Some GPS-coupled
calculators too.
>It seems to me, that the GPS-connected flight computers have the same
>problem that I do when I try to determine the wind conditions.
Nope. It's just the IAS measured by your airspeed indicator. Calculate
it into TAS, and you will get the wind component.
Bye
Andreas
Andreas Maurer
On Tue, 19 Aug 1997 13:04:07 +0100, Ian Lewis <ij...@cl.cam.ac.uk>
wrote:
>In the UK the SDI C4 is 2,700 US Dollars, the L-Nav is about 3,000 and
>the S-Nav 3,500. The Cambridge loggers are around 2,800 US Dollars.
And how much is a used Filser LX-4000, a calculator with integrated
GPS?
Here in Germany about $1700. And you get all in one.
Bye
Andreas
David Noyes
I may have asked the wrong question. It would seem from the many replies
I've received (thanks!) that several final glide calculators have built-in
altitude sensors.
Now the question is: Which of them will recieve the airport
elevation information from the External GPS data base in order to calculate
height above or below the final glide slope and display it?
Will the LX-400e or LX-500e do this? (Not the '4000 or '5000.)
Walt Weaver
NOSPAM...@pop.service.ohio-state.edu (David Noyes) wrote:
> Who makes a final-glide calculator (with vario) that contains its own
>altitude sensor but no GPS receiver? I want one that can be connected to a
>hand-held Garmin GPS with moving map display. The end result should be a
>final glide calculator which calculates a height above or below final glide to
>whatever airport is selected in the Garmin's data base. Or at least gives
>some graphical indication of being above or below final glide to the selected
>airport. The vario portion should give the usual immediate and average climb
>indications.
> Any suggestions? Thanks. Dave "NL"
For what it's worth, Ball Varios makes the Graphics Comp, which does
all that stuff. I've connected it to my 12XL and it works fine. It's
made primarily for hang gliders, but Ball will do custom changes to
the Comp to make it easier to install in sailplanes.
All the replies I've read so far in this thread mention only the
Cambridge, so I thought I'd mention a different product!
Go Buckeyes,
--Walt Weaver
Black Forest Soaring Society
Highlands Ranch, CO
MHR
Could somone that has contributed to this thread provide additional
information on the "SDI" line of flight computers. Does the manufactuer
of this line have a web page or dealer in the US?
Ramsey
Ian Spence <spe...@psych.utoronto.ca> wrote in article
<33FB21...@psych.utoronto.ca>...
> Ian Lewis wrote:
>
> > In the UK the SDI C4 is 2,700 US Dollars, the L-Nav is about 3,000 and
> > the S-Nav 3,500. The Cambridge loggers are around 2,800 US Dollars.
>
> Re-reading this, I noticed the qualifier, 'In the UK'. If the UK
> dealers are really charging such high prices you should get on their
> backs--it doesn't cost more than $1400 to ship a logger across
> the Atlantic ...
Actually, the "real" price in the US (having just bought one) of a model
20 is $2200, the GPS/logger and navigation display are priced separately...
_____________________________
Marc Ramsey, ma...@ranlog.com
http://www.ranlog.com/ramsey/
Ramsey
> I have probably made over 100 final glides with the L-NAV/GPS-NAV
> combination. The wind calculation seems to have been very accurate
> and I have never failed to make the goal when the L-NAV told me I
> was on or above glide-slope. This includes several contests (including
> the recent Canadian Standard Class Championship, which I won--see
> http://www.psych.utoronto.ca/~sosa/)
I've found at least one situation in which the glide slope indicated by
the L-NAV/GPS-NAV combination is misleading. I recently finished a speed
task with a final glide from 45 miles out at 9K ft AGL. The indicated
tailwind was 25 knots at that altitude. The indicator was substantially
above glide slope, so I gradually increased speed to 100+ knots. At
about 10 miles out the indicator rather abruptly went from well above to
well below slope in a few moments. Why? I had lost nearly all of the
tailwind as I entered the valley where the airport was located. By
slowing down to best L/D speed and doing some dolphin flying I was just
able to make the finish.
David Leonard
Ramsey wrote:
> I've found at least one situation in which the glide slope indicated
> by
> the L-NAV/GPS-NAV combination is misleading. I recently finished a
> speed
> task with a final glide from 45 miles out at 9K ft AGL. The indicated
> tailwind was 25 knots at that altitude. The indicator was
> substantially
> above glide slope, so I gradually increased speed to 100+ knots. At
> about 10 miles out the indicator rather abruptly went from well above
> to
> well below slope in a few moments. Why? I had lost nearly all of the
>
> tailwind as I entered the valley where the airport was located. By
> slowing down to best L/D speed and doing some dolphin flying I was
> just
> able to make the finish
Yep, so far, no glide computer can see what the air is doing ahead of
you. They can't see wind shifts, thunderstorms, blue holes, waves, or
even mountain ranges. When they can do all that for you, I think I'll go
find something else to do with my spare time ;-)
-Dave ZL
Larry Goddard
Marc Ramsey wrote:
> I've found at least one situation in which the glide slope indicated by
> the L-NAV/GPS-NAV combination is misleading. I recently finished a speed
> task with a final glide from 45 miles out at 9K ft AGL. The indicated
> tailwind was 25 knots at that altitude. The indicator was substantially
> above glide slope, so I gradually increased speed to 100+ knots. At
> about 10 miles out the indicator rather abruptly went from well above to
> well below slope in a few moments. Why? I had lost nearly all of the
> tailwind as I entered the valley where the airport was located. By
> slowing down to best L/D speed and doing some dolphin flying I was just
>
Hmmm. It sounds like the unit did exactly what it was supposed to do.
It gave you a view of the final glide given the conditions of the
moment-- both when you were in a tailwind situation and when you were
in a no wind situation. It is up to us as pilots to determine what that
information means and how to best use it.
There is not a device that I know of that will be able to conjure up
what you are going to do in the future and give you a readout of speeds
to fly based on those unknown conditions.
Larry Goddard
"01" LS-3a USA
Dave Ellis
Ramsey wrote:
>
> Ian Spence <spe...@psych.utoronto.ca> wrote in article
> <33FB20...@psych.utoronto.ca>...
> > I have probably made over 100 final glides with the L-NAV/GPS-NAV
> > combination. The wind calculation seems to have been very accurate
> > and I have never failed to make the goal when the L-NAV told me I
> > was on or above glide-slope. This includes several contests (including
> > the recent Canadian Standard Class Championship, which I won--see
> > http://www.psych.utoronto.ca/~sosa/)
>
a speed task with a final glide from 45 miles out at 9K ft AGL. The
indicated tailwind was 25 knots at that altitude. The indicator was
substantially above glide slope, so I gradually increased speed to 100+
knots. At about 10 miles out the indicator rather abruptly went from
well above to well below slope in a few moments. Why? I had lost
nearly all of the tailwind as I entered the valley where the airport was
located. By slowing down to best L/D speed and doing some dolphin
flying I was just able to make the finish.
>
One cannot ask a final glide calculator to know the future wind. This is
precisely why I feel it is SOMETIMES very useful for the instantaneous
Headwind/Tailwind component to automatically update the calculated final
glide altitude. The L-NAV and S-NAV work as follows in Automatic mode:
When the Track is within +/- 20 degrees of the bearing, the
instantaneous component wind (displayed on the GPS Wind screen) is sent
to a 30 second moving window (FIR) averager. The output of this
averager is the HW/TW component of the final glide altitude calculator.
This works OK most of the time. On very long (<30 km) final glides in
flat terrain, small variations in the instantaneous GPS derived wind
cause undesirable variations in the computed final glide altitude
required. For this reason we also have a Manual mode. In this case the
pilot observes the instantaneous HW/TW value. This number is then
manually entered into the final glide calculator screen. With stable
assumed wind, the final glide altitude required is also stable.
Dave Ellis
Cambridge Aero Instruments