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OK, all you pilots, google-geeks and 2-cent donators, here's an honest question for you?

Does humid air give you better wing/canopy performance than dry air? I'm not talking about engine performance, just purely aerodynamic. What about saturated air (visible moisture, clouds, etc) vs. say 50% relative humidity vs 0% humidity?

No need to expand on temp, density altitude, blah blah, blah... humidity is the question of the day.

3... 2... 1... go.

No, dry air will give you better performance (anything else being equal).
Answer simple enough?

 
edit- simple answer: NO. more humidity, the faster the canopy will fly

original-

all we are talking about here is AIR DENSITY.

while temperature and altitude are the biggest culprits to air density, humidity has an effect.

with LESS air density, theoretically, a glide ratio should stay the same, to an extent. but with less density, MORE air VOLUME is needed to keep the lift up.
basically, you need to keep the balance of dynamic air displacement and 'give' to gravity in par.

so, at lower altitudes, on colder days, with dry air, you get the SLOWEST landing speeds possible, because air is the most dense.

at Higher altitudes, with hot air, and its about to fog up or rain, you are HAULING ASS.

icing comes into effect as you approach 100% humidity, but I have seen ice on a paraglider, gliders, and airplanes. never a parachute...

Hey Calvin, we havn´t been allowed to use "density altitude" in our answer(s)! :-)
I´m saying that dry air gives slower rate of descent and slower forward speed, most non-swoopers would call this better performance.
You are saying "glide ratio should stay the same, to an extent". Please add something to this cause I´d expect the glide ratio to be worse...

As humidity increases, air density decreases

Water vapor is made up of 1 Oxygen and 2 Hydrogen atoms. The water vapor atom has an atomic mass of 18 atomic units. Water vapor is lighter than diatomic Oxygen (32 units) and diatomic Nitrogen (28 units). Thus at a constant temp the more water vapor that displaces the other gases the less dense that air will become.

lift and drag are linearly related to air density, the effect cancels out. TAS will change with density, but the L/D will not.

performance and Efficiency are different things.

performance can mean faster OR slower, depending on the needs.

performance in general as it pertains to gliders is a combination of glide ratio, speed, and sink rate.

best air conditions for each 'need' are different.

the answer depends on how YOU define performance...

most pilots want dry air because it leads to slower groundspeeds, quicker climb, better load carrying capability. (they also prefer landing into the wind.)

I'm sure some swoopers prefer wet air as it leads to faster groundspeeds, longer swoops, etc. (they will also land downwind.)

if you want the reasons, read some of the other posts in this thread!

Dude,

While you have probably forgotten 1000x more shit about aerodynamics than most of us shlubs will ever know in our lifetimes...

Here's an old, very basic relationship diagram on the subject for a baseline:

NASA School Tricks

Edit to add: Richard, how much difference did you notice in Germany at the dome versus say, Idaho in the winter?

hahaha... thats a cool little calculator... we should have some computer geek make one for BASE canopies and one for swoopers.

So... now that I have all of your undivided attention, here's the next question...

Which will give a better glide ratio... a wet canopy or a dry canopy? Wet canopies are possibly less porous, but have higher wingloading...

less porous would almost DEFINATLY give a better glide ratio, as it improves the LD by decreasing the induced drag because of less need for a higher AOA from the 'seepage' of air through the canopy, making the airfoil slightly less laminar and clean.

and since we now agree that weight would not have much to do with glide ratio... that pretty much decides that.

this is a series of projects to give the OPPOSITE effect of a porous canopy,

http://aerodyn.org/Drag/blc.html

With a fellow sailplane pilot we discussed many different ways of doing this without breaking any rules for sailplane competitions.

as I can tell there are a lot more out there interestinf in aerodynamics, I assume you also know about the Venturi effect, and its widespread use in older aircraft instruments.

well, we thought that a venturi on the tail of a sailplane tubed to small intakes in shell could give just enough suction to 'delete' the boundary layer on a sailplanes' airfoil. (topskin)

We also discussed the ideas of what we called 'dead air intakes', basically a turbine or ducted fan engine that was fed air from all over the aircraft, not just a huge draggy intake on the bottom or sides. it would effectively MAKE a powered aircraft laminar flow, that was not previously so lucky. slow days as a tow pilot meant I would sit in the shed with dirty old glider pilots and talk about this shit for months.

I can see it now, a 5 gallon bucket left at the exit point on the perrine. everyone soakes their packed rig in the water just to get that extra tenth of a glide ratio point.

Now we just need to figure out the best way to dry it.

An extra tenth advantage on GR won't help when your anvil-heavy canopy opens 2 seconds slower off a 487 foot object and you took a 3-second delay. Then again if you do it over the river, which increases your odds of making another jump, your canopy will be pre-soaked for the next jump.

well, we thought that a venturi on the tail of a sailplane tubed to small intakes in shell could give just enough suction to 'delete' the boundary layer on a sailplanes' airfoil. (topskin)

See, I think that'd be the problem. In my experience, the best way to dry a canopy is to jump it. So while your freshly-soaked rig may open differently, I wouldn't be surprised to find that it was bone-dry (so, no extra glide) throughout your flight.

No doubt some of you are enjoying these seemingly simple questions... but let's bring this all together for a moment.

Humid air gives your canopy less glide... check.

A wet canopy gives you better glide... check.

So if you're flying in visible moisture, say where your camera lens fogs up or your goggles get blurry, you're obviously getting your canopy damp.
Do the beneficial glide effects of your canopy getting damp offset the negative effects of humidity making the air less dense?
This is obviously much more subjective... but discuss amongst yourselves.

Perhaps it would be best to apply Tom's criterion for canopy comparisons here, and limit the discussion to folks to have at least, say, 50 jumps in rain or dense fog at an object where they've also done 50 jumps at a similar temperature and under the same canopy but without the moisture?

glide is the same, TAS is higher.


remember the canopy is filled with ram air, any additional weight on the fabric will cause the intended shape of the wing to be less efficient = less controllable and less stable.
Water also causes irreversible stretching/shrinking.
The additional weight on the tail will increase the AOA, there goes your glide and be ready for a stall.

more weight= higher wing loading= more ram air
i notice more performance when i fly my canopy through worm holes

hmmm... i seriously don't know the math, but my understanding is that,
parasite drag has an exponential curve to infinity, while induced drag has an exponential curve toward 0, so as drag from lift starts to become nil, parasite drag skyrockets, making glide ratio decay exponentially. I believe I am describing the exact main problems with landing smaller and smaller parachutes. no?

Effect of humidity: If I had my 1-1 in front of me this would take about 30 seconds to answer, but I don't, and I'm trying to procrastinate studying, so..

The effect of humidity on an airfoil is equivalent to a simple decrease in air pressure. Roskam (see below) points out that on a hot day (at sea level, I assume) the density reduction from dry air to 100% humid air is only 1.8% (Reference: Jan Roskam. Airplane Aerodynamics and Performance. DARCorporation, 2003; ISBN 1884885446. Page 4)

Using this guy's numbers, my rough interpretation is that this is equivalent to <400' rise in density altitude (If anyone has a burning desire for more accuracy, when I get some more time I can do it the right way). I'll leave it to someone else to comment about the effect of DA on glide performance, except to say that unless I'm mistaken, higher DA improves glide performance, and also, your canopy glides like crap anyway.

As for the effect of water saturation on the aerodynamic properties of a nylon wing, all I can comment is that the assumptions here are highly speculative until someone produces some data. My own speculation is that it is not going to make the difference between landing on the beach or landing in the water. I'm not sure where Richard is trying to get at.

In the end it comes down to this
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V

hey! no here is calling BASE rocket surgery, its just fun to talk about this stuff. no one here is arguing about retarded shit, jsut having fun dreaming of theoretical properties in BASE.

Since the leading edge of your canopy would possibly get more wet (while flying in our hypothetical moisture-rich environment) than the trailing edge due to horizontal velocity, this would 'seal' the fabric porosity 'more' on the leading edge, right?
So would you get similar effects to what the Blackjack ZP Composite canopies get, just on a lower scale?

um, sure.
the reason only the forward 1/3 "foreskin" is ZP, because, 1-most lift is generated there in the first 50% of the airfoil and 2-if the airfoil separates there, it has no chance farther back on the airfoil.

I hope everyone understands how far into neverland we are talking here, the chances of this ever actually (noticeably) affecting a canopy flight is nil.

I didn't mean to be a killjoy. It is good to think about this stuff, to be sure! So far we've got a ~400' DA increase based on the humidity's effect on air. That in and of itself, I'd call negligible. If the moisture effect on nylon actually does make the nylon behave less porously, then maybe you've got a difference you could notice somewhere.

But seriously, has anyone seen any data pertaining to wet nylon tests? That would be genuinely interesting.

Richard also proposed that the leading edge will become wetter than the rest of the canopy. It sounds reasonable at first, but can you expand on your basis for this? We can assume ice will build from the leading edge do to whatever physics of air is going on, but I admit I haven't read up on what changes in pressure would increase the tendency for icing over the span of a foil. (Maybe someone else could enlighten me)

If I had any nylon on me, i'd take a dry dry piece and a wet piece, hold it in front of a fan like a sail, and try to measure the difference in force, too.

I'm not trying to be a skeptic, I think they are reasonable propositions, but I'm more of an empiricist. I dont know if this post makes sense but i'm too tired to edit it more and i've got about 100 more pages of studying tonight...

Would any manufacturers like to chime in on this?

BTW- Calvin I'll be out in your neck of the woods next week. You still going to be out of town?

Do you mean "leading edge" in the strict sense, or a "forward segment of the span?"

by 'noticeably' I meant that, if there was a jump that cannot be done with normal gear due to lack of glide performance, I doubt that someone would make it 'possible' by doing it after wetting their canopy foreskin or on a cold, foggy day.


as for icing, the leading edge of EVERYTHING not heated or coated with anti-ice liquid will get icing
the entire leading edge of the canopy, especially topskin-as air hits the wing, it loses pressure, also reducing its temperature slightly. the suspension lines, risers, jumper, etc. (this is why all carburatted aircraft have 'carb heat' controls, to pre-heat the air going through the carb) [carbs have venturis instead of pumps to draw fuel inside{venturi=less pressure/cooling=suction=fuel flow}]

there has been several cases of paraglider icing in or near clouds, never myself, but its a goal. a bigger problem is moisture on the wing, increasing its weight, changing its collapse recovery ability. I have also flown in snow, and it does build inside the cells. that would be dissasterous, you can shake ice off a glider or parachute, can't shake snow out of the cells.

...and when Luigi dives his VX39, it creates worm holes all over his flight path... engage!

I would venture to say that the wake vortice that 39 makes at the lower end of the swoop is probably way worse than a wingsuit.

No issue for me (but I bet you are right):

Landing a WS will kill me also as landing luigis toy. And to stick to the topic again: in humid air a little bit faster...

Wouldn't the canopy open more quickly rather than slowly? If it is wet, as mentioned, it would be less porous wouldn't it? ...and thus open faster than normal?

I don't know if the wet vs dry canopy opening debate has been resolved, my instinct is that at low airspeeds the deployment would be delayed by the fabric sticking to itself and because inertia of the heavy canopy would slow inflation down. What seems clear (to me) is that slow airspeed canopy extraction would take longer simply because of the added canopy weight.

Word.