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Spinster
08-03-2011, 08:18 PM
Okay,

Everybody knows that a fly arranged OVER the tent makes the tent cooler inside than it would be without it. (Even better, in this sort of weather, a fly INSTEAD of a tent tends to provide more air circulation and thus be cooler) . And, any moment, RJ will be along with pictures or a link to show how THEY did it, THEN, as opposed to how we are sometimes bad to do it incorrectly in this day and age.

My question is----HOW and WHY does it make it cooler? How and Why does this provide a better shield against rain?

For various reasons, too onerous to list, my over tent fly is in one place, and I am another. I need to be able to compensate next week, as I'll be at Wilson's Creek for six days.

I do have a huge painted canvas floorcloth I could throw over the tent and ridgepole for an additional shade layer. I have no way to elevate it to provide an air pocket between it and the tent.

So, is this compensating mechanism a decent idea? One that actually happened? Or too stupid for words?

jda3rd
08-03-2011, 08:44 PM
Well, my supposition is that with the fly elevated a few inches above the tent roof, it's a bit like setting up your tent in the shade. I'd guess that there is an optimum distance, and that the closer it is, the less effective. Similarly, the fly over the tent acts as an umbrella in the rain, protecting the tent roof from being the initial water barrier.

Frank Brower
Jeff Davis Artillery

billwatson2
08-03-2011, 09:39 PM
It's reflecting sunlight. The fly might heat up, but it keeps the tent from doing the same, by virtue of that little air barrier. The tent canvas will get as hot as the ambient air, but not "extra" hot from absorbing heat from the sunlight. And so it won't heat the air in the tent, either.
That's my theory and I'm sticking to it. :-) We'll have to run experiments some time with little thermometers.

TheQM
08-03-2011, 11:34 PM
Mrs. Lawson,

I made a extra ridge pole that goes on top of my tents. (Both Comman & Wall) That leaves a 2.5" gap between the tent and the fly on top. The difference is amazing. As was already mentioned, the shade and air flow keeps the tent much, much cooler. Since the fly extend out beyond the edge of the tent, it also keeps you drier when it rains.

This extra ridge pole is also used when I use my fly as a porch, or a free standing tent without ends.

Julio C. Zangroniz
08-04-2011, 01:53 AM
To fly or not to fly...that is the question?
I own both an A-frame and a primitive lean-to.
At this year's Battle of Gettysburg, I packed my fly poles, ropes and stakes, but forgot the canvas. Thus, my A-frame sat in the sun the entire day, and it was simply unberable during the day. I could have baked bread in it.
Mercifully, I was better prepared at the Battle of First Manassas, because I packed both A-frame, fly and all poles and stakes. I set the fly over the tent and the difference it made was astonishing, keeping the tent out of the direct sun through most of the day. I was actually able to lie down inside without passing out. And as everyone knows by now, we all needed that extra difference at First Manassas.
This week, I'm heading for Wilson's Creek and I'm taking two suitcases just for the A-frame and the canvas. I will have to cut new poles after I leave Kansas City, but so what?
My pole arrangement for the fly uses only four poles. Two about eight feet, at the rear, and two up front, about 6 1/2 feet. The difference causes a "gentle slope" that directs any precipitation away from the tent.
And as I recall at that very location in Year 2000, there was PLENTY of precipitation at the so-called Wilson's "Leak." Hopefully, we all will be more fortunate, weather-wise, this year.
In a nutshell, the fly over the tent simply works better.
But Spinster, I don't know how well an extra layer, placed directly over the tent, would work. If at all possible, perhaps you might want to find a nearby wood-line, or even a single, very large tree, and tie the upper ends of your floor cover to high branches while setting up your tent underneath?
Buena suerte!
Julio

RJSamp
08-04-2011, 06:30 PM
Actually, you all are dancing around the physics 'above' this....

Think air flow in your attic.

Think air as an insulator.

and although the canvas can reflect sunlight.....the fly over the top 'physics' works with dark canvas that absorbs sunlight as well.

For water repellency, think slowing down of the water and a primary shedder of 99% of the rain.....the underlying tent canvas then has zero issues with what little trickles through the fly.

I'm on the road or I'd post a few hundred fly over the tent pictures.....or front porch gables matching the tent/fly gable profile (angled of course, not flat).

As an observation, I'd say we are much improved on this issue from 10 years ago when I first went on a rant.....

Julio C. Zangroniz
08-04-2011, 07:46 PM
That's because you are mellowing with age, RJ...
Julio