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.

Philip Plane wrote in message ...
In article , Tom Seim wrote:
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.

Ah, the happy sound of a 'safe' pilot.

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

You're probably right.

Low pass flyers love the rush. They like a little excitement.
They probably also have a better safety record than the rule
followers who think rules will keep them safe when the
reality is that the only thing that will keep you safe is your
own judgement.


Philip,

You should avoid debating as an occupation. 'Probably' is the choice
of word for those who haven't done their homework. We know that pilots
have died attempting these low passes; are you seriously arguing that
their safety records are better than the norm?

I agree with you that good judgment enhances your safety. I just don't
think that you (and the low passers) have good judgment. You are free
to partake in your high-risk sport, just don't argue that it is safe.
Newbies do look to veterans when formulating the rules that,
eventually, become what we call *judgment*. Bad judgment, for this
reason, must be clearly labled as such because the newbies are reading
these posts.

Tom

In article , Tom Seim wrote:

Low pass flyers love the rush. They like a little excitement.
They probably also have a better safety record than the rule
followers who think rules will keep them safe when the
reality is that the only thing that will keep you safe is your
own judgement.


Philip,

You should avoid debating as an occupation. 'Probably' is the choice
of word for those who haven't done their homework. We know that pilots
have died attempting these low passes; are you seriously arguing that
their safety records are better than the norm?

You're right, I probably should.

I wouldn't shy away from the safety record of people who do low passes
though. A well executed low pass is nothing to be worried about.

I certainly know that the pilots I am familiar with who do a low
pass whenever they see the opportunity all have good safety records.
Probably because they (mostly) use good judgement about where and when
to perform the low pass.

I have seen a few badly executed low passes though, and they
are the sort of thing that people should worry about. But the
same can be said of any part of gliding. Do it right, or you're
in trouble. I expect base jumpers also have to do it right.

I agree with you that good judgment enhances your safety. I just don't
think that you (and the low passers) have good judgment. You are free
to partake in your high-risk sport, just don't argue that it is safe.

Newbies do look to veterans when formulating the rules that,
eventually, become what we call *judgment*. Bad judgment, for this
reason, must be clearly labled as such because the newbies are reading
these posts.

Whoops. You just pushed another of my buttons.

Rules aren't judgement. Rules are used to define the normal, expected
way to do things. There are, for instance, rules to be followed
when doing a low pass. Judgement is knowing when to follow the rules.

And 'newbies' can use their own judgement to stay within their own
capabilities. Because an activity is beyond the skill level of some
pilots doesn't mean that those who can do it should not. If the
newbies don't see people doing advanced stuff, how will they know
what more there is on offer?

Aviation is a risky business. We can manage that risk to make it 'safe'.
We manage the risk by building our skills up so we can reduce the
risk. We manage the risk by building our judgement up to recognise
what is within our skill level. And we all have a personal level of
risk we are willing to accept.

--
Philip Plane _____
|
---------------( )---------------
Glider pilots have no visible means of support

in article , Kirk Stant at
wrote on 2003/09/08 15:32:

...post-[low]pass stall-spins from pattern altitude [are] a pattern
problem, not a low pass problem.

Bad judgement is attempting something you are not trained for or
experienced enough for. Good judgement is acquiring the skills
necessary prior to performing any demanding task. Otherwise, anything
can be dangerous.

...the ex-fighter pilot senior airline captain does a gentle,
tail first, low energy landing in his glass ship.



Low passes, in themselves, are no more dangerous than the aero tow.

Lots of low passes are safely done all over the world, at much higher speeds
and in more hostile environments than your local glider port will ever be --
with live ordnance yet!

The busy-body self-appointed safety minders will squeeze every drop of fun
from life if we let them. Don't be one of them -- but don't ever give them
more ammunition by trying maneuvers for which you are not thoroughly trained
and prepared.



Jack

(ex-fighter pilot, retired airline captain, new glider pilot -- not yet
ready to do low glider passes -- and too cheap to buy "glass")

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

(Kirk Stant) wrote in message . com...
(Tom Seim) wrote in message

We know that pilots have died attempting these low passes; are you
seriously arguing that their safety records are better than the norm?

Name a pilot who has died during a low pass.

I agree with you that good judgment enhances your safety. I just don't
think that you (and the low passers) have good judgment. You are free
to partake in your high-risk sport, just don't argue that it is safe.
Newbies do look to veterans when formulating the rules that,
eventually, become what we call *judgment*. Bad judgment, for this
reason, must be clearly labled as such because the newbies are reading
these posts.

Tom

You are so full of it! Show me an accident directly caused by a low
pass, while in the low and fast part of it. Don't cheat by using
post-pass stall-spins from pattern altitude - that is a pattern
problem, not a low pass problem.

You, also, should avoid employment as a debater. Character assignation
is a definte debate loser. Present your supporting evidence and let it
speak for itself.

I searched the records and found 4 such accidents. And, no, I will not
exclude pull up stall-spins following the low pass. This is 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. The accidents a

N117JB 11/3/01
N4458 8/26/00
N597R 10/4/96
N48032 5/26/84

When one considers the fatal accident rate by usual measures, namely
accidents per 100,000 flight hours, this maneuver goes off the Richter
scale. You, and others like you, can consider it perfectly safe, but
you are in a huge state of denial.

BTW: To estimate the accident rate you need to.
1. Estimate the duration of the manouvour in hours.
2. Estimate the number operations per year.
3. Multiply (1) by (2) and by the number of years.
4. Divide the number of accidents, 4, by the result of (3).
5. Multiple (4) by 100,000.

Rate = 4 *100000 / (.0333 * 1000 *9)
= 1333
Assumes 2 min per operation and 1000 operations per year.

Compare this to all other accident rates and you will find there is
not comparison whatsoever. Changing the assumptions, even by an order
of magnitude, doesn't change this.


Bad judgement is attempting something you are not trained for or
experienced enough for.

Good judgement is acquiring the skills
necessary prior to performing any demanding task. Otherwise, anything
can be dangerous.

What training did you get for high speed low passes? It isn't part of
the practical test standards and it certainly wasn't a part of my
training.



I do low passes because they are fun. I do them safely (no overflying
people, structures, lots of speed, no strangers in the pattern, proper
radio calls, etc. Done correctly, they are safe. Just as skydiving,
done correctly, is safe. Just as SCUBA divingm, done correctly, is
safe.

We just had a SCUBA diving fatality over the weekend that involved a
certified instructor.


I can just picture you and a "newbie", standing next to your ancient
2-33, watching somebody doing a nice high-energy low pass in a state
of the art glass ship, water still streaming from it. The newbie says
"Wow, that's cool, someday I want to do that!" And you respond with a
sneer "That guy is just showing off, he's dangerous, has no judgement,
a safe pilot would never do that, blah blah blah - stick to the local
area and 1000ft patterns in the 2-33 like real glider pilots!

And the newbie wanders off, never to be seen again....while the
ex-fighter pilot senior airline captain does a gentle, tail first, low
energy landing in his glass ship.

Well, the guy IS showing off, that's why they do the low passes.

I am not saying that there aren't pilots qualified to do this
maneuver, because there are. The guy that gets into trouble is the one
with 200 hours or is a high time power pilot recently transitioned
into gliders.

I see that I touched a nerve here, but that isn't my concern. Judgment
is the integration of training and experience. Let the record speak
for itself; this maneuver is, deservedly, a high risk one.

(Tom Seim) wrote in message

You, also, should avoid employment as a debater. Character assignation
is a definte debate loser. Present your supporting evidence and let it
speak for itself.

Confusing sarcastic disagreement with character assignation (sic) is
probably not a debate winner either.

(lots of stats snipped)

Andy does an excellent rebuttal, I won't bother. I prefer first hand
observations, anyway - I've seen CFIGs crash a lot of planes on simple
training flights; the only racers I've seen hurt planes is on
outlandings (which is another issue altogether!)

What training did you get for high speed low passes? It isn't part of
the practical test standards and it certainly wasn't a part of my
training.

What does the PTS have to do with it? Some things in life you have to
figure out for yourself, find out who to talk to, watch carefully, and
ease yourself into. Acro training help (is there any PTS for that?).
Self-preservation instinct helps a lot. Prior military training helps
a lot - but can be a bit expensive in time and effort. If you want
dual, go to a field with any 2 seat glass and I'm sure any competent
CFIG would be happy to show you.

We just had a SCUBA diving fatality over the weekend that involved a
certified instructor.

So? Anybody can screw up.

Well, the guy IS showing off, that's why they do the low passes.

And what is wrong with showing off? We all do it - the cars we buy,
the clothes we wear, the sports we play. Just because someone is
showing off doesn't mean they lack judgement and are dangerous! What
about airshows - everybody is showing off there - thats what they are
all about!

I am not saying that there aren't pilots qualified to do this
maneuver, because there are. The guy that gets into trouble is the one
with 200 hours or is a high time power pilot recently transitioned
into gliders.

No that is exactly what you said. You were hammering the originator
of this thread for his choice of activity and "lack of judgement".

I see that I touched a nerve here, but that isn't my concern. Judgment
is the integration of training and experience. Let the record speak
for itself; this maneuver is, deservedly, a high risk one.

Again, risk is not the same as danger. Arguably, landings are a much
more dangerous maneuver than low passes - you get much closer to the
ground, at speeds close to the stall, and can't get away from it.

You are right about touching a nerve - We wonder why this sport is
shrinking. It's not the cost (time x money probably hasn't changed
much). But while the sport is advancing, our attitudes (in the US)
seem to stand still. Very few places seem to emphasize the excitement
of soaring; all I hear is how "peaceful and relaxing" it is. That's
fine for retirees who have had all the excitement they need, but
younger newcomers to the sport need to see something more exciting to
motivate them to stay in. And yes, that means that some "risky"
behavior is part of the attraction - XC, Acro, racing. But while the
racing crowd isn't much concerned with the training/local crowd (as
long as they stay out of the way), the training/local crowd seems to
get more vocal about their dislike of the racing crowd - the
Glassholes, showing off, etc..

No stats, just personal observation.

Kirk
66