Glide Ratio

[+SecretSpy]

Any Vista guys out there having problems with the Glide Ratio. Mine doesn't work all the time. Most of the time it just displays [ __:1 ] even if I'm going down a steep grade. If it does display it will show [ 468:1 ] or something and then go blank. Garmin tech support gave me the default respose. Not much help. It seems to work a bit better if I select "Glide Ratio to Destination".

Anders had his timezone bug the "Anders Bug" boy I hope this isn't the "SecretSpy Bug". Curious to know what Anders and Hawk-Eye think.

 

LowlyWorm Says Gig 'em Aggies

[+apersson850]

That it works better if you select glide ratio to destination isn't to peculiar. That value is calculated as the distance from where you are to you next waypoint, divided by the difference in altitude between these two points. That's not measured, that's just a calculation.

 

The current glide ratio, however, is supposed to be calculated by measuring the difference in air pressure, thus calculating the height difference and then put that in relation to the travelled distance. Must be rather difficult to get a stable reading for that, I assume. Maybe that's because they don't get any really stable reading.

 

On my unit, I noticed that if I held it with one finger below the sensor hole (not blocking it, just below), the elevation wasn't steady. At that time, I was moving into a rather powerful headwind. I assume that turbulence around my finger caused a somewhat erratic air pressure outside the sensor. When I moved my finger a little, it became somewhat better.

 

The glide ratio is a little difficult to test without any kind of aircraft, which I don't have. I suggested throwing one of the daughters over a cliff, having her shouting the readings to me via mobile phone, while falling, but she just looked at me...

 

European customer support, read Tony Broad (very good service from there, I must say!), recommended the CTRL+ALT+DEL (total reset) cure for the Anders Bug. Has so far worked for 19 hours. I'll keep you posted.

 

Anders

 

[This message was edited by Anders on August 15, 2002 at 01:19 AM.]

[+apersson850]

That it works better if you select glide ratio to destination isn't to peculiar. That value is calculated as the distance from where you are to you next waypoint, divided by the difference in altitude between these two points. That's not measured, that's just a calculation.

 

The current glide ratio, however, is supposed to be calculated by measuring the difference in air pressure, thus calculating the height difference and then put that in relation to the travelled distance. Must be rather difficult to get a stable reading for that, I assume. Maybe that's because they don't get any really stable reading.

 

On my unit, I noticed that if I held it with one finger below the sensor hole (not blocking it, just below), the elevation wasn't steady. At that time, I was moving into a rather powerful headwind. I assume that turbulence around my finger caused a somewhat erratic air pressure outside the sensor. When I moved my finger a little, it became somewhat better.

 

The glide ratio is a little difficult to test without any kind of aircraft, which I don't have. I suggested throwing one of the daughters over a cliff, having her shouting the readings to me via mobile phone, while falling, but she just looked at me...

 

European customer support, read Tony Broad (very good service from there, I must say!), recommended the CTRL+ALT+DEL (total reset) cure for the Anders Bug. Has so far worked for 19 hours. I'll keep you posted.

 

Anders

 

[This message was edited by Anders on August 15, 2002 at 01:19 AM.]

[Chaplain]

Anders, recommend throwing wife in lieu of daughters off cliff.

[Chaplain]

Anders, recommend throwing wife in lieu of daughters off cliff.

[fig]

I say, just go it yourself. It will save you the cell phone minutes too...

 

 

(Note: This is intended to be a joke, not a derogatory remark toward Anders, or anyone else. Just pretend it's me going off the cliff.)

[fig]

I say, just go it yourself. It will save you the cell phone minutes too...

 

 

(Note: This is intended to be a joke, not a derogatory remark toward Anders, or anyone else. Just pretend it's me going off the cliff.)

[+Gliderguy]

Another thing about glide ratio if it is getting its info for altitude from the barometric sensor, and you are trying to get a glide ratio in a car going over a hill:

 

Some automobiles develop a slight suction in the passenger compartment that increases with speed. This is intentional as it uses the pressure change to move fresh air through the passenger compartment. If you accelerate down a hill you may negate the pressure rate change from decending. The opposite is also true, if you lose speed going uphill you may negate the pressure change from ascending.

 

I discovered this one day when I had a variometer (a sensitive rate of climb insturment) inside a vehicle testing it out over some hills. Acceleration could peg the thing in climb mode, and hard braking would peg it to more than 1000fpm down.

 

Using a GPS in the mountains, the steepest hill I could climb and maintain highway speeds only showed about 350 fpm up. This in a pickup truck with a large V-8 engine.

 

Constant speed over the hills will possibly make a difference.

[+apersson850]

I've also noticed that a hot day, when the ECC (Electronic Climate Control) tries to cool down the inside of the car, the elevation decreses several meters. That's when the fan revs up to top speed, which it maintains for a while. When the worst heat has been blown out of the car, fan speed decreases, and things go back to "normal" again.

 

Anders

[+SecretSpy]

Ok thanks for the replys. I understand how the glide ratio works etc. I also know about A/C fans and cars and all that but I'm getting constant readings on my vertical fpm and nothing on the glide ratio display. My vertical fpm readings are changing correctly according to the ambient conditions whether I've got the windows down in the car or I'm in my Cessna 172 it's not making the fpm convert to glide ratio. I need to know if you guys are getting real info on your G/R displays that corresponds with what your vertical fpm says.

 

LowlyWorm Says Gig 'em Aggies

[+apersson850]

In lack of an aeroplane, I'll have to come back to the daughter/wife concept again...

 

Anders

[+SecretSpy]

Fellow Vista guru's please try this experiment. Go to your altimeter page and in one of the bottom rectangles change the display to glide ratio. In the other rectangle choose to display vertical speed. Then get in your vehicle and drive up some hills or get on your bike and ride around, whatever. When I do this I get plenty of readings in my vert speed both positive and negative rate of climb no problems. But my glide ratio is always blank. If my vertical fpm is constant and I'm traversing the countryside I should be getting GR readings but I'm not. GR to Dest gives the same results.

 

LowlyWorm Says Gig 'em Aggies

[HangGlider]

I never see a value for glide ratio either, even when I took the unit with me for a sailplane ride a couple of weeks ago.

 

-HangGlider

[+apersson850]

I agree that the glide ratio isn't very consistent, although I have seen values there, even when travelling along the ground. I still have to try a nice downhill some 50 km from here, where the warning signs says 10%, which should then be displayed as 10:1.

 

But to see a consistent value for glide ratio to destination, do like this:

 

Hold the click stick (assuming the Vista) so that a waypoint can be marked where you are right now.

 

Search for nearby waypoints, and call up the one you just marked.

 

Project a new waypoint, that's 1.00 km away, but at an altitude that's 100 m below where you are now (just change the value that's suggested, which is the elevation of the first waypoint you marked).

 

Search for the most recent waypoint, and select GoTo when the waypoint page is shown.

 

Now inspect the glide ratio to destination, and you'll find that it's 10:1, which is what to expect, since it's 1000 meters away and 100 meters below.

 

If you are using the obsolete units (miles or what they are called), you either have to change your setting or do some mathematics, to find out that 1/10th of a mile is 528 feet. Sigh.

 

Anders

 

[This message was edited by Anders on August 28, 2002 at 07:09 AM.]

[+apersson850]

This morning, while driving to my work, I had the elevation display visible, with both the Glide Ratio and the Vertical speed visible.

 

Now, this area isn't that hilly, to be modest. The max difference in altitude along the road isn't even 15 meters, but there are a few small downhill slopes. The glide ratio isn't displayed when you go uphill (it doesn't assume that you glide then, I presume).

 

The Glide ratio did show some figures on several occasions, though. But in these not to distinct downhills, it often varied between 150:1 to 300:1, and changed a lot when I (experimentally) opened the sunroof. Not unexpected, I admit.

 

However, in one of the "steepest" downhills, just before I arrive, I got a reasonably steady reading.

 

Glide ratio 50:1

Vertical speed 14 m/min

Vehicle speed 50 km/h.

 

Both the glide ratio and the vertical speed weren't too stable, but the values above are estimated as being somewhat average-like.

 

50 km/h = 833 m/min, which implies a glide ratio of 833/14 = 60. OK, it's not 50, but on the other hand these values weren't very steady, as I said above. At least it gives values that are in the same neighborhood, not in the other state.

 

Any other experimenters?

 

Anders

[+apersson850]

This morning, while driving to my work, I had the elevation display visible, with both the Glide Ratio and the Vertical speed visible.

 

Now, this area isn't that hilly, to be modest. The max difference in altitude along the road isn't even 15 meters, but there are a few small downhill slopes. The glide ratio isn't displayed when you go uphill (it doesn't assume that you glide then, I presume).

 

The Glide ratio did show some figures on several occasions, though. But in these not to distinct downhills, it often varied between 150:1 to 300:1, and changed a lot when I (experimentally) opened the sunroof. Not unexpected, I admit.

 

However, in one of the "steepest" downhills, just before I arrive, I got a reasonably steady reading.

 

Glide ratio 50:1

Vertical speed 14 m/min

Vehicle speed 50 km/h.

 

Both the glide ratio and the vertical speed weren't too stable, but the values above are estimated as being somewhat average-like.

 

50 km/h = 833 m/min, which implies a glide ratio of 833/14 = 60. OK, it's not 50, but on the other hand these values weren't very steady, as I said above. At least it gives values that are in the same neighborhood, not in the other state.

 

Any other experimenters?

 

Anders

[+apersson850]

A little further testing (lunch time) reveals that this doesn't work, unless you are navigating to something. That the Glide ratio to the destination can't be shown, unless the destination is known, isn't too peculiar. But the current Glide ratio isn't calculated either, unless you have a destination.

 

You can navigate to whatever place, that doesn't matter, but it must be active. When I turned navigation off, while driving downhill (Glide ratio 58:1), the Glide ratio display frooze at 58:1. Didn't matter if I was going down- or uphill, or stood still. Had to start navigating to any waypoint to reset it to ____:1 again.

 

Perhaps the same goes for the GPSMAP 76S, which didn't work either, according to a post above? More experiments to the people!

 

Anders

 

[This message was edited by Anders on August 29, 2002 at 05:20 AM.]

[+apersson850]

While testing the Glide ratio values, I also checked on the "Vertical speed to destination", which was introduced at the same time.

 

It turns out that that value is calculated as the difference in elevation between the destination and your current position, divided by the ETE.

 

An example: If you target is 30 meters above you, and the GPS estimates that it will take you five minutes to go there, it will show up that a climb rate of 6 m/min is necessary for you to hit the correct elevation when you reach the correct (2D) position.

 

It came to my mind that this whole thing could be more useful if the Glide ratio could work in both ways. As it is now, it's useful for flying only (more or less), since "gliding" upwards is out of the question. When you go up, it's always shown as ____:1. But if it could show 15:1/ as well as 15:1/ (well, an arrow like the one that goes with the vertical speed, which indeed does work in both directions), it would be much more useful on the ground too.

 

When on the ground, the rate of a downhill is ususally not that important, unless it's very steep. It's not that much work anyway. Going up, on the other hand, requires a substantially larger effort, and there it could be interesting to see if the Glide ratio (Height ratio?) to destination is 234:1^ (i.e. Illinois) or 12:1^ (i.e. Colorado) or whatever. The up-arrow (^) is my addition.

 

Since I've sent the poor Vista Beta team so many mails already, I can just as well give them another.

 

Anders

[+SecretSpy]

Thanks for your experiments Anders. I navigated to a waypoint and only got a few readings. All downhill only, and they were very brief maybe one second or two. It also seemed to give me more frequent readings when I was actually heading towards my destination. ( ie Heading=Bearing )

It will not work without navigation which explains why it didn't work while I was on a very steady decending glide slope during a recent final approach to land. Is the computer to slow to do the math? It seems fast enough to calculate everything else! I e-mailed Garmin about a week ago still no reply. Anders has more luck with their tech guys than I do. Still need to check the Jumpmaster stuff out. Guess I better learn how to skydive. The lengths we go to to test the limits of our toys. Maybe we should be getting paid for all of this field research we provide for Garmin! Ha Ha

 

LowlyWorm Says Gig 'em Aggies

[+SecretSpy]

Thanks for your experiments Anders. I navigated to a waypoint and only got a few readings. All downhill only, and they were very brief maybe one second or two. It also seemed to give me more frequent readings when I was actually heading towards my destination. ( ie Heading=Bearing )

It will not work without navigation which explains why it didn't work while I was on a very steady decending glide slope during a recent final approach to land. Is the computer to slow to do the math? It seems fast enough to calculate everything else! I e-mailed Garmin about a week ago still no reply. Anders has more luck with their tech guys than I do. Still need to check the Jumpmaster stuff out. Guess I better learn how to skydive. The lengths we go to to test the limits of our toys. Maybe we should be getting paid for all of this field research we provide for Garmin! Ha Ha

 

LowlyWorm Says Gig 'em Aggies

[+apersson850]

I'm not that hungry for money, that they have to pay me. It's fully enough if they send me some new GPS models, when they are available, so I have more toys to play with...

 

Anders

[+apersson850]

I'm not that hungry for money, that they have to pay me. It's fully enough if they send me some new GPS models, when they are available, so I have more toys to play with...

 

Anders

[+SecretSpy]

Got this back from Tech support today. It didn't work when I was flying.

 

"Thank you for contacting GARMIN.

The glide ratio will not display when you are traveling in a car. It is designed to work for an aircraft when you are descending. As soon as the glider flies straight and level or climbs the value goes blank. The glide ratio to target will only display when you are flying and you have the unit navigating to a waypoint. If you are still having trouble please give customer service a call and they can trouble shoot the problem with you. Have a nice day! "

Larry Keegan

Product Support Specialist

GARMIN International

1200

Oh well

 

LowlyWorm Says Gig 'em Aggies

[+apersson850]

And just how the hrm would the Vista know that your vehicle is a car, going downhill, rather than something that flies? Does it have eyes now, too??

 

Anders