How much weight should be added to a tennis ball ... for ... the average sitflier
Just enough to create a small crater when he loses it
It will take about 1.72 lbs. of lead (probably less) to fill an average tennis ball (calculated by volume/weight of ball/lead).
From here you can use this:
¼ A * v2term = mg
where vterm is the terminal speed, A is the area of the ball’s cross section, m is the mass of the ball, and g is acceleration due to gravity. From this expression we find the expression for the terminal speed as vterm = Root of 4mg/A
(This post was edited by frost on Jul 2, 2008, 8:32 AM)
Yep... The tail is gonna change everything ! I won't give the «secret recipe» online but I think a freefly ball should go around 160m/h , and you can head down or sit with it. If you can't sitfly at 160, you probably should'nt jump a ball... If you decide to experiment and go for the «trial and error» method, make sure you have a clear spot ;) Have fun !
From the experience I have, the average freefly speed we should be aiming for is around 160-165 miles per hour. I do most VRW around that speed, all the record jumps and big ways I was in were around that speed. Sometimes we speed it up but rarely over an average of 170-175. How fast do you usually freefly (average) ? Curious to know. If I remember correctly, the test for the Atm Dolphin (skyball) is around those speeds, (165) ?
Posting this kind of information online would be silly because there WILL be someone who goes and makes one, can't catch it, and bam... incident. It only takes one ball going in at the wrong place and causing damage/injury to alert the FAA. Then spaceball flights would be banned for us all.
I do disagree that a ball should only be built for 160mph though. I currently have 7 balls built for different speeds that I use for coaching. Everything from 115mph to 170mph. The ball in the video above was 140mph. Some S-L-O-W sitfly training.
Bottom line is that you shouldn't be worried about the specifics because you shouldn't be making one without some experience with all of it first. It's quite a whole different beast, but explaining that now would take pages and I've got to get out to the DZ. It sounds like there are plenty of people here who would be happy to work with you in person. This would allow them to gauge you skills properly and do some ball jumps with you to specifically fit your learning needs. Once you've done some work with a ball master as far as chasing, catching, spotting, etc then you will probably be given direct insight into all the theory of spaceball building (weights, tail lenghts, fill, etc.). It's a great training tool and I love to teach it, but certainly not online. You will probably have to do a little traveling and meet with a ball master in person.