GPS glide ratio calculations

(Kirk Stant) wrote in message om...
James,

Interesting hobby!

You could use a GPS logger (like a Volkslogger or Colibri), set to
minimum logging interval (1 or 2 seconds). You would have to download
the trace afterwards and use a program to view it. I would recommend
SeeYou, but some other more terrain-oriented programs might have
better terrain resolution (which would be important for you, I
assume).

This setup would require a small battery hooked up to the logger, but
with the short flight duration it shouldn't be too big.

Some of the newer Garmin handhelds also log altitude, they may be a
lot cheaper and just as useful. The key is probably going to be the
software you use to look at the trace.

Let us know how it works out.

Kirk
LS6-b "66"

Given the relatively short flight time, and the inherent inaccuracy of
GPS (even with Selective Availability switched off by the US
Government), you might find that the error in the GPS fix is
insufficient for accurate speed measurements.

Try setting up your GPS in a fixed location, and then leave it there
logging data for a few minutes. You will see that the position fix
moves around slightly due to the inherent inaccuracy of the system.

For a discussion of Selective Availability and accurace of GPS, see
the following site:

http://www.ngs.noaa.gov/FGCS/info/sans_SA/

and the linked-to Accuracy Comparison pages, especially the most
recent one

http://www.ngs.noaa.gov/FGCS/info/sa...mpare/ERLA.htm

which suggests 6.3 metre accuracy with SA off and 45 metres with SA
on.

Small, perhaps, but maybe important when you're taking short-period
differentials (1st derivative of position give speed). If you're
moving 60 km/h (approx 16.6 m/sec) then an error of 1m in your
position fix (well within the error limits of GPS) will give you a
derived speed now of between 15.6 m/sec (56 km/h) and 17.6 m/sec (63.3
km/h). Try repeating those calculations with a worst-case inaccuracy
of 6.3 metres and you get speeds between 37 km/h and 82.4 km/h !

I would perhaps consider going to a Differntial GPS (DGPS) system,
where a known fixed local station broadcasts supplemental position
correction information that improves the accuracy of the satellite
location fix.

For a good discussion of accuracy between GPS and DGPS systems, see

http://www.gpscontrol.com/php/suppor...l/accuracy.php

In summary, my take on all this is that GPS is good for averaged
velocity based on samples over a period of several seconds (our
minutes, like gliding !), rather than instantaneous velocity based on
sample-to-sample differentiation where GPS accuracy can cloud the
results (like your free-falling bird man attempts).

Good luck and watch those landings !


Cheers

Jason

On 4 Sep 2003 21:11:38 -0700, (Jason Armistead)
wrote:

(Kirk Stant) wrote in message om...
James,

Interesting hobby!

You could use a GPS logger (like a Volkslogger or Colibri), set to
minimum logging interval (1 or 2 seconds). You would have to download
the trace afterwards and use a program to view it. I would recommend
SeeYou, but some other more terrain-oriented programs might have
better terrain resolution (which would be important for you, I
assume).

This setup would require a small battery hooked up to the logger, but
with the short flight duration it shouldn't be too big.

Some of the newer Garmin handhelds also log altitude, they may be a
lot cheaper and just as useful. The key is probably going to be the
software you use to look at the trace.

Let us know how it works out.

Kirk
LS6-b "66"

Given the relatively short flight time, and the inherent inaccuracy of
GPS (even with Selective Availability switched off by the US
Government), you might find that the error in the GPS fix is
insufficient for accurate speed measurements.

Try setting up your GPS in a fixed location, and then leave it there
logging data for a few minutes. You will see that the position fix
moves around slightly due to the inherent inaccuracy of the system.

For a discussion of Selective Availability and accurace of GPS, see
the following site:

http://www.ngs.noaa.gov/FGCS/info/sans_SA/

and the linked-to Accuracy Comparison pages, especially the most
recent one

http://www.ngs.noaa.gov/FGCS/info/sa...mpare/ERLA.htm

which suggests 6.3 metre accuracy with SA off and 45 metres with SA
on.

Small, perhaps, but maybe important when you're taking short-period
differentials (1st derivative of position give speed). If you're
moving 60 km/h (approx 16.6 m/sec) then an error of 1m in your
position fix (well within the error limits of GPS) will give you a
derived speed now of between 15.6 m/sec (56 km/h) and 17.6 m/sec (63.3
km/h). Try repeating those calculations with a worst-case inaccuracy
of 6.3 metres and you get speeds between 37 km/h and 82.4 km/h !

I would perhaps consider going to a Differntial GPS (DGPS) system,
where a known fixed local station broadcasts supplemental position
correction information that improves the accuracy of the satellite
location fix.

For a good discussion of accuracy between GPS and DGPS systems, see

http://www.gpscontrol.com/php/suppor...l/accuracy.php

In summary, my take on all this is that GPS is good for averaged
velocity based on samples over a period of several seconds (our
minutes, like gliding !), rather than instantaneous velocity based on
sample-to-sample differentiation where GPS accuracy can cloud the
results (like your free-falling bird man attempts).

Good luck and watch those landings !


Cheers

Jason


Jason,

GPS does not use the sample to sample differences to give you
velocities. The 3 D velocities are done from Doppler shifts.

Mike Borgelt

Not much use to Jason, when his Garmin or IGC logger won't record that
velocity information. Or are you suggesting he look at the velocity
screen and take notes while falling (I mean flying).

Jonathan Gere


Mike Borgelt wrote in message . ..

Jason,

GPS does not use the sample to sample differences to give you
velocities. The 3 D velocities are done from Doppler shifts.

Mike Borgelt

Why don't you try a safer sport, like standing in front of a Mach
truck and seeing how close it can get before jumping out of the way.

Base jumpers are in the same class as low pass flyers, in my opinion.
This is a contest you don't want to win.

I suggest that you go to a group more alligned to your thinking, like
the alt.sport.russion.roulette people.

On 8 Sep 2003 22:58:50 GMT, Andy Blackburn
wrote:

Over the past 30 years I have known more than a few
people who've died while flying a sailplane - and I've
been witness to a couple. I can think of a few speed
related accidents and they all invloved loss of control
and/or structural failure at several thousand feet
altitude. I've never heard of a fatality, or even
an accident during a 'contest finish' - either during
a contest or at any other time, though I cannot say
definitively that it's never happend. My personal experience
(and statistics on the subject) suggests that we should
be more concerned with too little speed (stall/spin)
than too much speed.

I reject the notion that contest finishes are inherently
unsafe any more than gaggle flying, landing or tow.
Pilots making contest finishes have as high or higher
situational awareness than in any other phase of flight
- they tend to be more focused and less likely to be
multi-tasking. Like all other phases of flight, the
maneuver can be performed well or poorly, but that
is not the basis for making generalizations.

The contest finish is an exuberant and graceful way
to put an exclamation point on the end of a cross-country
or racing flight (or even a local flight, for that
matter). They are perhaps the one phase of glider flight
that generates positive excitement with spectators
on the ground.

Goodness knows the sport could use ways to get visitors
to the glider field excited.


Well said, Andy.
During the 1970's in Western Australia I flew at several clubs where
contest type finishes were the norm and the only guy ever to screw up
was the Chief Flying Instructor of one club in his own glider who spun
in from the top of the pullup. We used to go down to about 20 - 30
feet. I think that is reasonable as you won't hit the ground if you
encounter a gust.(that has happened in WA at another club and at Alice
Springs it was I think an IS 28 got flown through the club bar on a
low finish. Fortunately nobody was in there and the building wasn't
all that substantial and no fatalities. The 28 and the bar were write
off though.)

I then had the misfortune to spend 15 years at another club in another
state who banned contest type finishes.(amonst other things) They sure
managed to make a nice thing like gliding boring and unpleasant. They
also can't figure out why they lose members.

Mike Borgelt

Hi the

I think the Vista and will log altitude, but you have no control over
the timing of the recording unless it is a higher end version - it is
always automatic. The Garmin76 has long tracks and has better timing
control (more expensive though) - The GPS12X does not record altitudes.
Magellans have much worse support for logging tracks. They are always on
and you have almost no control over the track. I don't know about the
Flyer - it may be better. Occasionally the altitudes on GPS can be be
off and sometimes will jump around or plummet to the ground (goes to
zero suddenly because of loss of signal). I think you must keep the
antenna on the GPS clear of obstructions and then everything is fine. I
would say that the Garmin76 would be the best for your purposes.

On software - I have 3DTracer myself. It will calculate glide ratios as
you can select any section of the flight track and then perform
calculations on it. You can also load 3d maps from terrain DEM files.
(The animations are just amazing - but off topic I suppose). It is
cheaper than SeeYou and the animations are better - but less support for
OLC. I also looked at CompeGPS, too - it is geared to hanggliders - But
it had a few crashes on my machine and the 3D part was difficult to move
around in. The hard part in 3DTrace is getting the files properly set up
- the data is on the web you just must find it and calibrate the map
properly. Oh yes it also has a cool flight deck that shows you
everything thats occurring.

The other option is to hook up a PDA to the GPS and this can be your
logger - this has the difficulty that it is and extra cable, an extra
set of batteries and getting the software on the PDA. But it works - I
have the GPS12 with PDA software on an old Palm, with spliced together
cabling. It was around $500 altogether - $200 for GPS, $200 for the PDA,
$100 for the software - and you can use the PDA for its originally
intended use.

Any how my 2 cents


Kirk Stant wrote:
James,

Interesting hobby!

You could use a GPS logger (like a Volkslogger or Colibri), set to
minimum logging interval (1 or 2 seconds). You would have to download
the trace afterwards and use a program to view it. I would recommend
SeeYou, but some other more terrain-oriented programs might have
better terrain resolution (which would be important for you, I
assume).

This setup would require a small battery hooked up to the logger, but
with the short flight duration it shouldn't be too big.

Some of the newer Garmin handhelds also log altitude, they may be a
lot cheaper and just as useful. The key is probably going to be the
software you use to look at the trace.

Let us know how it works out.

Kirk
LS6-b "66"

Sorry, but I still don't see it. Two accidents in 20
years doesn't strike me as a top ten safety issue.
Certainly finding better ways to train for more advanced
forms of soaring (cross country, racing, acro, etc.)
and exercising good judgement generally are motherhood
issues for the sport.

I think it is possible to construct worst case scenarios
for any phase of flight and thinking about these scenarios
may prove instructive for the development of flying
judgement -- after all judgement is generally born
out of learning from experience. If you construct a
low pass scenario of gliders converging from different
directions on a busy, mixed-use airport without proper
radio procedures or situational awareness, crossing
active runways without looking, squeezing between buildings
and frightening the children it starts to sound reckless.
But in my view that is a debating canard. I can make
a simple pattern tow sound dangerous with similar 'scenario-buildi
ng' just by adding in high crosswinds, local thunderstorms,
poor preflight procedures... you get the picture.

If there are facts about actual accidents (Tom's search
turned up two that were of questionable applicability
since I don't think we're talking about attempting
loops at low altitude as a standard procedure), or
facts about near misses where another aircraft was
forced to take emergency evasive action, then maybe
there can be a productive discussion about what to
do to improve safety. But the facts don't seem to bear
this out.

Tom, I don't dispute your general points about judgement
and training, I just think we need to be careful about
characterizing certain types of flying as inherently
risky if the real point is reckless or thoughtless
flying in any phase of flight is potentially dangerous.
The first thought tends to lead to rules and regulations
about specific flight procedures (e.g. no low-passes,
no more than one glider in a thermal, no ridge soaring,
no landings [okay that might be a tough one to implement]),
but if the real issue is poor judgement generally,
than all the rules do is take the fun out of flying
and give some people a false sense of security. Some
of the clubs I've belonged to that have been the most
'rule happy' actually have poorer safety records (no
I don't have statistics). I'd hate to distract people
away from the real safety issues, which (according
to the statistics) have to do with maintaining proper
control of the aircraft and adequate flying speed/coordination.

Hope these thoughts are viewed as constructive - it's
how they are intended.

9B

At 01:54 10 September 2003, Tom Seim wrote:
Jack wrote in message news:...
in article ,
Tom Seim at
wrote on 2003/09/08 23:52:

Character assignation is a definte debate loser.

Perhaps you meant '...assassination', rather than
'...assignation'?

Yes, my fingers were a couple words behind my brain.
Shows the problem
with spell check.



...pull up stall-spins following the low pass [are]
an
essential part of the maneuver which would not have
been
attempted had it not been for the low pass. Thus
the low
pass was directly contributory to the accident.

I think you may have to go further and tell us how
you define
'low pass'. Are pull ups from three feet more dangerous
than pullups from
ten feet, or one hundred feet, or three hundred? And
by how much,
statistically speaking?

Now you are in the 'bring me a rock' mode. You are
no more interested
in additional stats than you are in changing your mind
on the matter.
The maneuver is an inherently high-risk one with little
margin for
error. Blasting thru a busy GA airport such as the
one where I fly out
of with piston A/C, turbine A/C, ultra-lights and helicopters
is using
questionable judgment. Not all pilots are on the correct
frequency or
have their squelch set properly. Some don't have radios
at all. None
will be expecting this maneuver.

Some maneuvers are inherently more dangerous than others
(i.e. ridge
soaring and landings). Their accident rate per flight
hour WILL be
higher, but you don't see it referenced. It gets lumped
into the
overall rate. All of us will be doing one landing for
each flight; few
will be doing a low pass.



...training...for high speed low passes...isn't part
of
the practical test standards and it certainly wasn't
a
part of my training.

Then please don't do them. Nor should you presume
to decide who is qualified
to do them and who is not, nor how much risk exposure
is involved.


Judgment is the integration of training and experience.
Let the record speak for itself; this maneuver is,
deservedly, a high risk one.

The record merely tells us that some glider pilots
have performed the low
pass maneuver poorly. You have no idea how many do
it every day with success
and even aplomb.

Not many. I seldom see it performed. Most of them were
done at
contests until the rules were changed over concern
about safety. I
personally have done them at contests. And I admit
it; they were fun!
With the new tasks which had gliders coming in to the
finish line from
any direction, even though we all crossed the finish
line in the same
direction, heightened the risk substantially.


It is a failing of our government-approved so-called
system of training
which refuses to even acknowledge, let alone prepare
pilots for, any number
of maneuvers which a competent pilot should have in
his repertoire. No
wonder they occasionally do them poorly.


The current program doesn't even address cross country
soaring. It
basically teaches gliding, not soaring. Yet much of
the glider hours
flown are cross country. The Feds will change training
requirements
when they see unusually high accident rates, which
is probably just as
well because we would have a real problem getting instructors.

Let me be clear about one thing: the low pass maneuver
is legal except
where prohibited by local A/P rules (assuming you don't
violate some
other rule in the process). I have no intention of
petitioning the FAA
otherwise (have you read the posts by the club that
is having major
difficulties with the A/P management?). I was expressing
my opinion to
which I am entitled, and just think that low time pilots
should not be
attempting it. Now, the bird man thing is another story.

In article ,
says...
I've never heard of a fatality, or even
an accident during a 'contest finish' - either during
a contest or at any other time, though I cannot say
definitively that it's never happend.

Here are two I can definitively remember:

A fatality occurred after a low pass at California City contest a few
years ago.

There was a famous accident at our local regional many years ago,
where a pilot finished too slowly, pulled up, and flew through the
aerials on the Flight Service Station. No injury, limited damage, very
lucky.

My personal experience
(and statistics on the subject) suggests that we should
be more concerned with too little speed (stall/spin)
than too much speed.

The scary low passes I've seen were almost all done with too little
speed, which means when the pilot pulls up, he is still low, making a
pattern (any kind of pattern) to the landing more difficult.

--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)

"Eric Greenwell" wrote in message
.. .
In article ,
says...
The scary low passes I've seen were almost all done with too little
speed, which means when the pilot pulls up, he is still low, making a
pattern (any kind of pattern) to the landing more difficult.

--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)


A "rule of thumb" I've used is 1 knot = about 9 feet. So if I start the
pull-up at 110 knots and push over to level for the pattern at about 60
knots, I'll be around 450 feet plus whatever altitude the low pass was flown
at.

I've done a few low passes at Napa, CA, a towered airport. I never ask when
there's other pattern traffic and so far the tower has always cleared me for
the low pass.

Disclaimer: the "formula" above isn't mine, don't know where I read it, it's
probably inaccurate, and don't try it at home . . . or in a glider for that
matter and try it at altitude first.
--
bumper
"Dare to be different . . . circle in sink."
to reply, the last half is right to left




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The rule I use is simple
At ground level!
70knots to 90 knots I have enough energy for a 180degree turn
90 knots + I have energy for 360 degree turn.
THESE ARE ABSOLUTE MINIMUMS.
I add 10-20knots to avoid a case of "brown adrenalin"
These figures are calculated on Cirrus,Libelle,Asw19 type aircraft
so later generation gliders gain on on these figures
I REPEAT I ADD 10-20 KNOTS FOR SAFETY
These figures were calculated about by a well known pilot
15-20 years whose name I cannot recall.
gary
"John Morgan" wrote in message
...

"Eric Greenwell" wrote in message
.. .
In article ,
says...
The scary low passes I've seen were almost all done with too little
speed, which means when the pilot pulls up, he is still low, making a
pattern (any kind of pattern) to the landing more difficult.

--
!Replace DECIMAL.POINT in my e-mail address with just a . to reply
directly

Eric Greenwell
Richland, WA (USA)


A "rule of thumb" I've used is 1 knot = about 9 feet. So if I start the
pull-up at 110 knots and push over to level for the pattern at about 60
knots, I'll be around 450 feet plus whatever altitude the low pass was
flown
at.

I've done a few low passes at Napa, CA, a towered airport. I never ask
when
there's other pattern traffic and so far the tower has always cleared me
for
the low pass.

Disclaimer: the "formula" above isn't mine, don't know where I read it,
it's
probably inaccurate, and don't try it at home . . . or in a glider for
that
matter and try it at altitude first.
--
bumper
"Dare to be different . . . circle in sink."
to reply, the last half is right to left




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