SAS or TAS on your ProTrack ?

[Cornholio 0]

So, I was out at the dz on Sunday and I was comparing protracks with another person whom I had just completed a two way sit with. We both had different speed readings and when we looked at the TAS or SAS setting, I was at SAS and he was at TAS.

I know the techincal differences between the two, from reading past posts and RTFM !! What I want to know is what do you have yours set to and why do you use that setting rather than the other.

so what happens when you are computing your freefall time for your awards ?? The two settings change the total time elapsed too, right ??

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Beavis: Yeah! Yeah! Cool!
bellyflier on the dz.com hybrid record jump

[sundevil777 102]

SAS

Because comparisons are more valid.

Where did you get the idea that the freefall time would be affected?

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[SkydiveMonkey 0]

SAS cos I do different things at different areas of the dive and want a good comparison.

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Say no to subliminal messages

[skycat 0]

SAS cause I live in CO and it gives a better comparison to someone who jumps at sea level

Fly it like you stole it!

[quade 4]

I have mine set to TAS because I'm an old pilot and instructor type a guy and I like the idea of True Airspeed. While SAS is a nice idea, I don't think the calculations ever took into account the mounting of audible with respect to the temperature sensor and whether it would be outside the helmet or inside the helmet. Compare two different ProTracks mounted these two ways at SAS and you'll see what I mean. Especially in the summer.

Oh, and the time doesn't (shoudn't) change when you switch between the two. BTW, you -did- know you can have the ProTrack set for SAS and then change it back to read TAS and vise versa -- right?

Oh, and for any speed skydiving -- it's ALWAYS TAS.

quade -
The World's Most Boring Skydiver

[fundgh 0]

I haven't bought a pro track yet but would like to know what you guys are talking about. True Air speed vs. ????? How does it messure differently and why would you have the two different modes?

...FUN FOR ALL!

[Cornholio 0]

Quote

Oh, and the time doesn't (shoudn't) change when you switch between the two. BTW, you -did- know you can have the ProTrack set for SAS and then change it back to read TAS and vise versa -- right?

I knew about the first one, but didn't know about the second. That's why I was unsure. I thought that if you changed from mode to mode, it also affected the Time Elapsed, but I see now I was mistaken.

Thanks!

Butthead: Whoa! Burritos for breakfast!
Beavis: Yeah! Yeah! Cool!
bellyflier on the dz.com hybrid record jump

[quade 4]

The ProTrack knows three things;
Pressure
Time
Temperature

By a fairly simple calculation it can use the change in pressure over time to figure out "about" how fast you're traveling through the air -- corrrected just slightly for temperature, this is True Airspeed (TAS) or how fast you're moving past the air molecules.

Because temperature varies so dang much across the planet and because drop zones are at different elevations all across the planet, a TAS reading at 4,000 ft above ground level at one drop zone doesn't really mean jack squat compared to a TAS reading at 4,000 ft AGL another. So, L&B, the makers of the ProTrack came up with a solution. They take the TAS and apply a further calculation to it that changes it to be what it would have been at 4,000 above mean sea level on a "standard" day. This is called Skydiver's Airspeed or SAS.

In theory, you can jump at a drop zone located at sea level, get a speed reading and it will then be a good indicator and valid as a comparison with how fast other skydivers are falling at another drop zone located at say 5,000 ft MSL. A pretty cool idea, but a little flawed in that skydivers just don't always mount these things in the same exact way, so the calculation gets a little inaccurate sometimes.

quade -
The World's Most Boring Skydiver

[cpoxon 0]

Sorry to disagree with you Paul, but you're slightly wrong. The ProTrack doesn't know about Temperature, it assumes it. From Chapter 43 of the manual, ICAO Exit Temperature, it states,

Quote

The Pro-Track’s altitude calculations are also based on the ICAO standard atmosphere and will reflect the correct altitude only when conditions match those of the ICAO standard.

The "Exit temperature selector" shows the temperature at exit altitude as if the ICAO conditions were in effect. Generally, temperature conditions are different.

For that reason, you may manually change "exit temperature" to the actual temperature value at exit altitude if that information is available. Jump-Track will then calculate the true altitude based on the selected exit temperature.

So TAS is adjusted for standard conditions and SAS is an adjustment on that, as you correctly stated! If you want to be accurate you need to look at and remember the external temperature before exit and adjust it in JumpTrack accordingly.

[Genn 0]

True Airspeed

[quade 4]

Actually, I've written to Mads about this and according to the last email I got from him the ProTrack does have a temperature sensor in it for the reasons I've stated.

I assume you're actually talking about the JumpTrack software which can be "tweeked" to be slightly more accurate.

quade -
The World's Most Boring Skydiver

[riddler 0]

So if a ProTrac can measure temperature and pressure, why don't they make a density altitude function? The only other factor in DA is humidity, which is much less of a factor, and could probably be ignored for the rough estimate that a skydiver needs (+- 500 feet).

It would be nice to have a convenient DA measurement on these hot summer days. I've asked pilots, and most of the time, they don't know the number - they just guess.

Trapped on the surface of a sphere. XKCD

[SkydiveMonkey 0]

The temperature isn't going to be right anyway - my pro track is inside my helmet between the shell and the (quite thick) liner. It's also right next to your head which gives out the most amount of heat out of any of your body parts.

____________________
Say no to subliminal messages

[riddler 0]

It's not for the Protrac, it's for me. I wouldn't be looking at it if it was on my head. I would look at it before the jump and before it got near my head. Once my helmet is on my head, I'm getting ready to skydive and I don't care anymore.

Of course, you have to take into account that the temperature sensor isn't going to change instantly. So don't look at it as your standing in the hot blast from the engines getting ready to get on the plane, or right after your jump when you're all sweaty.

My mount is on the outside of my helmet. I would probably be looking at it after I pack, and before I get on the next load. Assuming I don't let my helmet sit in the sun while I pack, I can probably get a good temperature measurement at that time.

Trapped on the surface of a sphere. XKCD

[quade 4]

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It would be nice to have a convenient DA measurement on these hot summer days. I've asked pilots, and most of the time, they don't know the number - they just guess.

I wouldn't be so sure. There's a fairly simple rule of thumb calculation you can do in your head for Density-Altitude.

Check out THIS.

quade -
The World's Most Boring Skydiver

[skycat 0]

You can also find out if that airport has an AWOS. Cannon City does and they play it over the intercom during jump run. Although I still shiver a little when the little mecanical voice says.....Density...Altitude..9.5.0.0

Fly it like you stole it!

[riddler 0]

Quote

You can also find out if that airport has an AWOS.

Mile-Hi has an AWOS, but every time I ask anyone, noone knows So it's what - a useless piece of equipment??

Sorry - done venting.

I like your write-up Quade - as an example, it's supposed to be 82 degrees this Saturday at Mile-Hi (field elevation 5050 feet), which is nominal at 41 degrees, so I subtract and get 41 degrees, divide by 15 and get about 3, which corresponds to 3,000 above 5,000 or about 8,000 feet DA. Seems easy enough.

Trapped on the surface of a sphere. XKCD

[quade 4]

Yep, pretty easy if you know how to do it -- and now you do.

quade -
The World's Most Boring Skydiver

[skycat 0]

http://www.colorado-aeronautics.org/awosphonefreq.htm

Ok, longmont doesn't have phone number for thier AWOS, but Derek said for DA Jeffco's (303-466-8744) should work fine. Boulder (303-541-9540) also has one, so if you are bored you can call all over the state. (try one of the passes like Monarch or something on a really hot day)

Fly it like you stole it!

[riddler 0]

Thanks Skycat - I plugged those phone numbers into my cell phone so I can call between jumps.

You guys are so useful! And I'm not just saying that because Hook has my other rig in pieces right now while we wait for my Cypres to get back from it's four-year.

I also did a quicky Internet search and found phone numbers for all 600 AWOS systems in the US. Gentlemen, start your cellphones!

AWOS Locations and phone numbers

[riddler 0]

Quote

The temperature isn't going to be right anyway - my pro track is inside my helmet between the shell and the (quite thick) liner. It's also right next to your head which gives out the most amount of heat out of any of your body parts.

Mads sent me a nice email and said almost the same thing you said:

Quote

When mounting the Pro-Track inside or even on the outside of the helmet the built-in temperature sensor will never read the exact ambient
temperature, because it takes some time before the case and circuit board have the same temperature as the surroundings.

[QuickDraw 0]

TAS and i wear mine on my wrist (clipped over my alti strap) as i just use it for data atm until i get checked out for ff.

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[Amazon 7]

Mine is set to TAS and is mounted in the pocket on my left ear in my Z-1 Openface helmet.

Its all good and I get good reading with similar data output to others I am jumping with.

Amazon

[leroydb 0]

what is AWOS?

.

Leroy


..I knew I was an unwanted baby when I saw my bath toys were a toaster and a radio...

[quade 4]

Automated Weather Observing System

quade -
The World's Most Boring Skydiver