Hi Wayne and all

Basically, the drag force is exerted by the surrounding air. If the air is doing 60 kph sideways (ie wind), the raindrop will soon be doing 60 kph sideways with the air. Think leaves and dust.

It's worth noting that if the raindrops are bigger than 3 mm, which they can be, and if they started very high up in the sky, they can be going a bit faster than 20 mph by the time they hit.

Ever been hit by storm-driven hail?

Cheers

"The group experimented with raindrops of different sizes, falling heights, and speeds. They found that slow falling raindrops generate the most energy because raindrops falling at high speeds often lose some energy due to splash."

http://www.physorg.com/news120216714.html

" the electrical energy is proportional to the square of the drop’s mechanical energy, while voltage and mechanical energy are directly proportional.

The largest raindrops caused the largest vibrations on the PVDF, and therefore generated the greatest amount of electrical energy. The researchers demonstrated that their system could generate 1 microwatt of continuous power as a worst-case scenario, while simulations showed that a single large raindrop might generate up to 12 milliwatts of power. "

How does their measurement of 2 µJ from 1 mJ compare to Richard's estimate of 5.35E-04 joules?

Edited by oware on 03/25/2011 04:22:58 MDT.

"How does their measurement of 2 µJ from 1 mJ compare to Richard's estimate of 5.35E-04 joules?"

5.35E-04 joules = 0.535 mJ, so the calculation is at least in correct range.

To All,

This topic is like beating a dead horse so I just edited my post and I am throwing in the towel..

Best Regards,
Lawson

Edited by Mountainfitter on 03/25/2011 06:49:55 MDT.

Lawson - come on, Man. This is what BPL is all about. Lets figure this 'stuff' out. If anything. there will be a sample of fabrics tested by BPL now which is good for all concerned.

I appreciate your input - we need(!) both sides to any story to make an eventual informed decision. Keep posting!!!

A very interesting thread, which I've just read straight through. It seems what's needed is a balance between lab results and real world experience. Just how do the two relate.

With regard to cuben fiber the only product I've tested is the Terra Nova Laser Ultra 1 tent. I used this in February in very heavy rain with 100% humidity and 40mph winds and it has stayed dry inside. In calmer conditions in wet mist there has been condensation inside, as I would expect in any shelter. The inner tent kept this off my down sleeping bag. The tent has been pitched three times on sodden ground out of which water bubbled when pressure was applied and the cuben fiber floor hasn't leaked. I didn't use any other groundsheet. My interest now is in durability - the low weight is amazing but so is the cost. To justify the latter the tent needs to be last.

Paramo/FurTech garments were mentioned earlier as having a thick fleece lining. They don't, they have a very thin fleece lining. These garments are waterproof in use but don't meet any waterproof standards. I think of them as functionally waterproof. They are the most breathable and condensation free shell garments I've used but the inner lining does make them warm. For me - I run hot - they are for temperatures below 40F. Of course for shelters they are irrelevant.

Most recently I have been trying Polartec Neoshell and my tentative findings are pretty good. The makes say it has a hydrostatic head of 10,000mm. Again, I want to test the durability before I come to firm conclusions.

Great findings, Richard, and please keep your highly interesting posts coming - very much looking forward to the findings of you, Roger and Greg's little quick n dirty experiment! A bit odd that Ron hasn't yet weighed in, though - maybe he's busy designing ;) ?!

I own and have used a HMG Echo I for a few weeks outdoors, but it yet has to rain on it. As I generally pitch fairly high, condensation also never has been an issue yet. Maybe I take it up north (or another cuben shelter) next week to see how it copes in the late Arctic winter and chip in if there's any blizzards or serious snowing going on.




On a side note, some of the other posters might want to read up on netiquette. The tone of voice is at times pretty unfriendly & very un-BPL-like, and considering that some of these represent a business I'd re-think how I appear in public. It is OK to be of a different opinion, hough friendliness shouldn't get lost in the heat of the typing =)

I've been following this thread, and it reminds me of the quote, 'there are lies, damned lies, and statistics'.
I've no experience of using Cuben yet, but can't help feeling that 'lab' results may not be absolutely relevant to 'real world' experience, especially from such a small test sample.
As in Richards previous finding that baffled and stitch through down garments show little difference in warmth retention in the lab, i find a different result in 'real world' experience.
This is in no way a dig at your work Richard, as i'm thankful that you are doing this kind of research on our behalf.

The more research, the better.

Here's the deal for me. I am not a scientist, but can do a little research and make/confirm calculations. Just need to determine which theory or scientific testing protocol makes logical sense to me. I think this is a great start to look at a particular type of gear (shelters) and do some investigations that may not have been done in the past, with a different methodology. All, keep up the good dialogue, good work, good thinking, and good science.

It's time for me to set up my camo HMG Echo II system, and document (with pictures), for the next few days...

Requests? (tell me what you want!)

This is the current forecast for the next five days: I suppose this weather is good for something...

This morning I received an email from forum member Ken L with an idea to independently test a constitute component of Cuben which is Mylar. His question was, “Have you ever tested Mylar balloon material through the HH tester?

I had a new in the package “Original Space Emergency Blanket” which I promptly unwrapped, measured its thickness and HH tested it both pre and post Ziff Aging. An important caveat is I have no idea if this is the same formulation of Mylar used in Cuben. Further clouding the applicability is that it was coated with aluminum.

Thickness: .01mm
Virgin Hydrostatic Head: >3,515 mm H2O

I then followed Ziff’s “scrunch and un-scrunch 5 minute aging cycle”

Aged Hydrostatic Head: >3,515 mm H2O

According to ISO 811, materials with a hydrostatic head of more than 1,500mm H2O can be designated, in general, as rainproof. So in the strictest sense, .01mm Mylar, used in the “Original Space Emergency Blanket”, is rainproof both in its virgin form and in its Ziff Aged form.


Picture of virgin Mylar pretest




Picture of Ziff Aged Mylar pretest





Picture of Ziff Conditioned Mylar at 3,515 mm H2O

Edited by richard295 on 03/25/2011 14:21:12 MDT.

Nice test Richard. Did you happen to notice if the mylar failed dramatically (ie. a small rip occurred?) or did it just start seeping through?

Dan,

There was NO leakage during either test.

Just a thought, Here are some of the makers specs:
http://www.cubictechnology.com/index.htm (Note that it is advertised as waterproof.)
http://www.cubenfiber.com/cfhistory.html
http://www.cubictechnology.com/CTF3%20PRODUCT%20INFO%20PACK%2007192010_4c.pdf
http://www.cubictechnology.com/Technical%20Fabrics%20for%20Aerospace%20Applications.pdf

Richard - so if there was no leakage is that 3515 the limit of your tester's pressure capability?

I found this very fitting :)

Edited by skullmonkey on 03/26/2011 13:34:42 MDT.

Paul,

Yes, that is the current limit. I can modify the configuration for higher pressure testing in the future, if required.

For my current UL shelter material testing, the critical range where I want the most measurement granularity is between 1,500mm H2O - 2,112mm H2O to test rainproofness. Per the International Standards Organization 811, materials require a MINIMUM hydrostatic head of 150 cm (1,500mm) to be designated, in general, as rainproof. For US weather, 2,112mm H2O is a prudent level to be rainproof. Some US storms will require more than 2,112mm H2O HH to be rainproof.

The term waterproof is frequently used as a marketing buzz word; it has no precise meaning without qualifying it in each context used. For example, water jets are routinely used to cut metal and so even metal is not waterproof without a precise qualification of the water pressure force.

Only if I were doing rainproof tests for UL shelters to be used in the Brazil and Marshall Islands areas would I have to configure my tester for measuring pressures higher than 3,515mm H2O. Also if was focusing on flooring material, would I have to configure my tester for measuring pressures higher than 3,515mm H2O.

Edited by richard295 on 03/26/2011 15:14:28 MDT.

Roger,

"Basically, the drag force is exerted by the surrounding air. If the air is doing 60 kph sideways (ie wind), the raindrop will soon be doing 60 kph sideways with the air. Think leaves and dust."

So if the rain drop is going sideways at the same exact speed of the wind, then it would not fall to the ground? Or would the wind slow its downward velocity (resistance)? Does the wind cause the raindrops to hit each other resulting in spliting rain drops or possible allowing some to merge and gain size?

Hi Nick

Separate out the two directions. The rain will likely travel sideways with the wind at the wind speed, but gravity will still have its way as well. The rain will fall.

Mind you, having experienced rain going upwards in places ... :-)

> Does the wind cause the raindrops to hit each other resulting in spliting rain drops or
> possible allowing some to merge and gain size?
I rather doubt it. I would imagine that all the rain drops would fall together at the same rate. They might even drag some air with them.

Cheers

Edited by rcaffin on 03/26/2011 16:10:49 MDT.

Stuart Robb was the first to submit a Protocol B submission. His air mail envelope arrived from Scotland about 1/2 hour ago. His test results were immediately emailed to both Stuart R. and Roger C. I am going to start a new thread this evening entitled "Protocol B Test Results". A complete report of Stuart's submission, sans the aging test cycle, will be included. Without divulging the results, this pure silnylon tested higher than pure silnylon I have tested from any US source so far(his source was Denmark).

Edited by richard295 on 03/29/2011 00:42:49 MDT.