This all looks like a lot of fun. I'm sure the bumblebees are very excited as well.

The balloon looks great. It looks like a larger version of the 5.5 foot balloon used by Public Lab folks. It doesn't say how thick the chloroprene is. If it is similar to the 5.5 foot balloons, that might make it a bit more fragile when fully inflated. But maybe the chloroprene is thicker. If one knew math one could figure that out from the size and weight of the balloons (8 foot diameter and 600 grams vs 5.5 foot diameter and ??? grams). So maybe I will never know.

The lift from that balloon fully inflated (8 foot diam.) with pure He should be almost 8 kg. So you should be good to go with it inflated to about 6 feet diameter. A handy lift table is here: http://www.chem.hawaii.edu/uham/lift.html

Balloons usually pop when they touch something (trees or buildings) or while they are being inflated. A new balloon inflated to under it's recommended limit and flown away from obstacles will generally not pop.

That braided line looks a little fishy. There is no indication what material the line is made from. 80 pound test line is probably strong enough because you will have three lines, but it might be minimal. Without more information about the line I would be worried. That big balloon will pull hard if a little wind comes up, so I would recommend three tethers of 100 to 150 pound test of braided polyester (e.g. Dacron). You don't need to counteract 300 pounds of lift, but better line gives you more tolerance for knicks, abrasions, weak knots, and one or more lines failing some other way. Don't forget gloves for the line handlers.

A simple pendulum suspension might be more effective than a Picavet. It depends on the angle of the lines and how variable that angle will be.

Filling and launching a 5.5 foot balloon is not hard with a few people to help. It is not hard to hold onto, although it is important that everyone involved remember not to let go. You will have twice the lift and a bigger target for wind, so it will be harder to hold onto, but probably doable. A net is a good idea but it has to be very soft so it doesn't damage the balloon which is quite fragile when inflated.

I can't wait to get the bumblebees' side of this story.

Chris
The KAPtery

Awesome post! I'm sharing it with the Public Lab Grassroots Mapping google group incase other people want to ping in here. Great project!

Thanks cfastie and stevie. @stevie: I feel I've not put enough detail in yet to explain how it works: I'll make a new note to explain it properly when I've actually flown it.

@cfastie: Thanks for this brilliant post!

Really useful info - good question about the balloon strength: there's not much info to let us compare balloons.

You gave especially useful info about the line, on the basis of your message: - I've cancelled the reel order on Amazon. - I'm thinking this looks more promising: http://www.ebay.co.uk/itm/301394084365?var=600368435007 it's described as Dacron Polyester Braided Line. The 110lb one is £18 for 300m, 165lb is £35 for 300m. Length: I'm not sure how high it could go - as I've no idea really what range might work, but I'm thinking of at least allowing for the possibility of going over 150m would be good (as the lines are at an angle, over 200m of line might be needed, so 300m is an ok length). Which strength is ok? The publiclab one is 110lb, so I guess that's adequate? Also the stronger one is I guess heavier - but I couldn't see a weight. So I'll go for three reels of the 300m 110lbs line.

Sorry I'm not buying straight from PublicLab - I'm too impatient to wait for intl shipping :)

Finally (for now): I need some reel winders, I've had a look on amazon, and there's quite mixed reviews - also most of them seem to be for children! Do you have any recommendations?

Thanks again for all the help!

I'll do a full explanation of the design/experiment when I've got it working a bit more.

The two camera flashes have arrived today. I'm also going to look at how to power the camera with external batteries. Will rig four canon batteries in parallel (carefully - ensure same batch/charge/etc before I do that) and build a 'fake battery' to put in the camera to get the power to the battery pins. Bit of a pain, but found that the onboard flash runs it down quite quickly, and I might want it up for a few hours.

First, the maths.
8 foot diameter balloon weighs 600 grams, so when inflated each cm² weighs 0.00321 grams
5.5 foot diameter balloon weighs 350 grams, so when inflated each cm² weighs 0.00397 grams
(this ignores the nozzle part)

So the chloroprene in the big balloon gets stretched thinner (81% less material/cm²) than the little balloon which has 47% less surface area. So the material in the big balloon is a little thicker than in the little balloon, but not in proportion with the inflated size difference. But since you will only fill it to a diameter of about 6 or 7 feet, it will not be stretched as thin as a little balloon inflated to 5.5 feet diameter. (The preceding information is not intended for application in the real world where you should consult with someone who has actual knowledge of the issue at hand.)

Does it take too long to get things shipped from the Netherlands? The KAPshop has good kite line deals. 600 feet of 90 pound line on a 6 inch winder for €10.10. http://www.kapshop.com/p142/Winder-with-line-(40-kg)/product_info.html.

Those don't look like the nice Shanti hoop winders, but I can't tell. Shanti hoop winders are the industry standard but are distributed only by Shanti kites, so they cost more than other winders. But other winders don't say "Unbreakable" on them. I'm pretty sure those are not Shanti winders because they don't cost enough. They must be the winders on this page: https://www.funwithwind.com/store/ListCategoriesAndProducts2.asp?idCategory=174&idparent=168. The other less expensive winders are like these: https://goodwinds.com/line-winders/winder-reels/halo-reels.html. Any of these will work, but for serious and extended flying, most KAPers seem to like the Shanti hoop winders like this or the ones near the bottom of this page: http://www.brooxes.com/newsite/BBKK/kitesales.html. The 500 feet of 110 pound line from store.publiclab.org is just what you need for this. They are Shanti winders, but they don't say what size winder that is.

Flash photos of bumblebees 200 feet above ground? I'd say some explanation is required.

Chris

Good work on the balloon maths - hopefully will come in useful for other people. Also your research into which lines and winders - quite a common question probably.

I'll go with the one you recommended (from KAPshop). Is 90lbs strong enough? Also they don't say they're Dacron, but the other lines on their page are.

The reels look simple enough. I noticed some online have a handle/bearings/etc to let you wind it in/out but I assume that's not really necessary.

Thanks again for all your advice!

I'll definitely explain the flash thing soon :)

I assume the kite line sold at the KAPshop is good braided polyester. Dacron is DuPont's brand of polyester, so it does not have to be Dacron. The 90 pound line is too light to use for kite photography but might be fine for your use. KAPers generally fly with 150 to 250 pound line. The forces rarely exceed 30-40 pounds, but lots of things can weaken a single point in the line, so to use the same line for many flights it's good to start with sturdier line. It's also easier to handle. I might select 110 pound line for a triple tether on a seven foot balloon with no knowledge about who will be tying knots, handling the line, or deciding if there is too much wind. You might also decide that in some conditions one or two tethers is all you need, in which case 90 pound line will be minimal. Maybe one line should be heavier and one or two additional lines could be lighter.

Those crank winders (http://www.amazon.com/Professional-7-5-Kite-Reel-Lock/dp/B0053AU2JG) are rather useless for kite photography because there is barely enough leverage to reel in line when there is enough wind to lift a camera.

But for balloon flying in zero wind they might make it easier on your tether sergeants.

Chris

Another rather important topic is the strict altitude limitations for kites and balloons in the UK. Kites are not allowed to be more than 60m above the ground. Special permission is required for higher flights. Balloons might be allowed higher than kites but decorations are required.

From: http://www.thekitesociety.org.uk/KiteRules.htm

Rule 53 Captive Balloons and Kites by Day
53. (1) A captive balloon flying by day at a height exceeding 60 metres above the surface shall have attached to its mooring cable tubular streamers which are
(a) not less than 40 centimetres in diameter and 2 metres in length; and
(b) marked with alternate bands of red and white 50 centimetres wide at intervals of not more than 200 metres measured from the basket or, if there is no basket, from the lowest part of the balloon.

This might save you some money on kite line.
Chris

This suggests that UK balloons, like UK kites, must be kept under 60 m agl without special permission. There are similar restrictions in the US but they apply only to kites weighing over five pounds or balloons more than 6 feet in diameter. So we are quite free to use lots of kite line.

`2. REGULATORY BACKGROUND

`2.1 Within UK airspace, the operation of balloons and kites are subject to the provisions and requirements set out at Articles 163 and 164 of the UK Air Navigation Order 2009 (which is contained in CAP 393). Amongst other things, these Articles provide that CAA permission is required to operate a tethered balloon or kite more than 60m above ground level (agl)

`3. Whilst proposals to operate a tethered balloon or kite above the 60m threshold are considered on a case-by-case basis, associated concerns are routinely very similar. Given potential difficulties associated with the visual acquisition of cables, such concerns focus on the fact that a tethered balloon/kite operation cable as well as the balloon or kite could present a significant flight safety hazard to other airspace users.

From: http://publicapps.caa.co.uk/docs/33/20130301PolicyStatementTetheredBalloons.pdf

cfastie, don't worry, we've got this covered. We just need to apply to the Civil Aviation Authority, as you've identified. I'm just ensuring I've got the landowner's permission first, as that's a requirement of the CAA's application process (note: it's open access land). As the balloon will between 60 and 150m it seems (from what others have said) that the application process is quite easy. There are no airfields/airports near the site, etc either, so it should be fairly straight forward, however paragliders do use the peaks, so it is something to think about. In particular using sufficient streamers on the lines - which is something I'd not thought of in relation to the experiment -it's vital they're not in shot! Could be a problem :)

I'll let people on here know how the application process goes.

For reference, the form I need to complete can be found here: https://publicapps.caa.co.uk/modalapplication.aspx?catid=1&pagetype=65&appid=11&mode=form&id=4409

Thanks though for raising this, especially if anyone else finds this thread in the future.