Protrack location

[Dean Fournier]

Hello everyone. I'm returning to skydiving this spring after a few year layoff, and have a few questions about the Protrack. My speed dives in the past were recorded using a Skycorder, and I had it located in a small inside pocket on my jumpsuit right over my belly button. I know now that one Protrack on either side of the harness webbing is the way to go, but my question is this:

If a recording device is in a rough air, does it tend to read fast or slow? How bad a location is the belly for a device? I've done about 50 or 60 speed dives, and I was (eventually!) able to get into the 230 mph range fairly reliably, and had a top personal best of 252 mph, but I don't know how accurate that is. I will find out this summer with the Protrack!

Also, I see that L and B mention more accurate speed measuring software on their new Protracks. Since I don't have two at the moment, I have a question for those of you who do.
How much difference do you generally see between the 2 Protracks on a reasonable stable speed dive? 5 mph? 20? 50? And for those of you using 2 new (supposedly more accurate) Protracks, do you see the difference compared to the older software? Is the difference between the speeds of the 2 newer Protracks smaller now than it would be with 2 older Protracks - with the older software?
I'm just trying to determine how innaccurate I can expect to be in my (brand new) Protrack recordings of speed if I only have one on the harness instead of two.
Thanks for any help! Great website!
Dean

[Arnold Hohenegger]

@ ProTrack position: the best position would be 1 meter to the left and right side of the skydiver, but there is no way to do that :-) The actual position of the ProTrack is the best one and result of the development of the past years. Some Skydivers put small pockets on the left an right side of the maincontainer near bottom of container (its according to the rules).

@ Difference ProTracks: the difference during a stable, perfect jump is less than 5 km/h. So much faster you are, so much bigger is the difference if you are unstable. Front/back unstability effects the difference not so much, left/right wobbling effects the difference much more. According to the rules we use the L&B Software Jumptrack 2.00.D, we set the OB difference to 30 km/h avarage speed.

Check also www.speedskydiving.eu

Where are you from Dean?

[Dean]

Hello Arnold,

Thanks for that information. It is exactly the kind of detail I was looking for.

Maybe you could answer another puzzle for me.

From what I can see, it is turbulence from the body that is the enemy when it comes to accurate Protrack speed readings. Now it would seem to me that in a speed dive, the least turbulent air would be at your head, because it is hitting undisturbed air. Why then, is inside the helmet not a good location for a Protrack clocking a speed dive? As far as turbulence goes, I would think one over each ear would be better than one on each main lift web, but I am obviously overlooking something, or else that is how it would be done in competition. Do you know the answer to this?
And I am from Ottawa, Canada. Pleased to meet you Arnold, and thanks again for the info!
Dean

[Arnold Hohenegger]

Why is the Helmet not a good location for the ProTracks? Place two of them to the left and right of your helmet and do two jumps on your belly. At the first jump dont move your head, at the second jump move your head. You will see the difference on the graph.

During a speedjump you controle your body a lot with your head and your shoulders. At high speeds head movements effects big differences on ProTracks. Not so when the ProTracks are mounted on the rig near your hips.

Mark Calland from the UK did a lot of windtunnel research in cooperation with the university of Manchester to find the right body position, best suit and best ProTrack location.

Two of the research results are:
- For the speed it does not matter if you are jumping a big, small or slicksuit rig - or no rig - your body position make the bigest impact to your speed.
- Best measurement results if ProTracks are mounted as told before.

Check these two links:
www.zct.co.uk/skydivemag/latestnews/june03-jmsnewsround.html middle of the page
www.manchestereveningnews.co.uk/news/business/s/123/123129_wind_tunnel_helps_mark_go_that_extra_mile.html

[Dean]

Hello Arnold,

Thank you very much for that detailed answer and the links! I had no idea so much effort had gone into finding the proper location for the Protracks. I will certainly abide by their findings and mount it on the harness.

Dean