Lessons from a Lucky Wind Dummy - Edith's 12/28

[brianvh]

Oh, and about water vapor. It's only about 3% of the volume in the summer, and since a water molecule is about 2/3 the density of an average air molecule, it only makes roughly a 1% difference in density. Negligible in this context.

Since thermals are only a few degrees warmer than the surroundings (as compared to 30 degrees in summer versus winter) the water vapor difference does make a noticeable impact for buoyancy high up in the atmosphere. Low in the atmosphere the water content variation between thermal and the surroundings are not so large so makes a small impact, plus temperature differences are larger. You have to be halfway to cloudbase before water vapor affects buoyancy to any significant degree.

[Danny Brotto]

Thanks Brian,

The laws of physics... they are not a suggestion, they are the law.

Danny Brotto

[mingram]

Good stuff guys. I've flown in strong wind and noticed increased speed/penetration with ~4kg of ballast (I was carrying an extra gallon of water). My bet is the little gain in speed is more noticeable on PG because they fly slower and don't have much ability to change speed compared to HG.

At this site we will have to be more cautious in strong, right cross wind to stay upwind of the LZ. Preferred turn direction after launch is to the right which will keep you upwind and on the better slope of the ridge and give you time to judge penetration.

[Dan T]

Thanks Brian, your write up was very informative.

I watched Krista's whole flight from launch. Her issues penetrating into the wind would not have been an issue for any VG equipped HG.

The cross wind would have increased the effective length of the field along the axis that Brian landed his Falcon.

[thermalup]

Here are a few words from a CrossCountry Magazine link sent to my e-mail inbox just now (I believe John E. referred to this information earlier). Great discussion that you started here and most of of what is below was brought up in earlier comments. I fly HGs but over the years I have witnessed several non-penetrating PGs end up in the trees/rotor behind our ridge sites. Afterwards, many of these pilots commented that they wish they had flown with ballast. But, as noted in earlier comments here, ballast (on a flexible wing) is not a very effective cure for penetration issues.

Wing Loading and Ballast
"People often ask how heavy they should be relative to the weight range on their wing.
The aerodynamic effects of wing loading are fairly simple, but the choice of loading depends on where you fly, how you fly, and what you want to get out of your flying.
Wing-loading doesn’t affect glide (unless the wing is distorted by the weight): you just go down the same glide angle at a higher speed if you are heavier.
Increasing wing loading increases speed by only the square root of the weight change. On any particular glider if you can double your weight without distorting the wing then your speed will go up by a factor of 1.41.
Carrying ballast to increase speed is almost always a waste of time in recreational flying. Even if you carry 10kg of ballast, your speed only goes up by about 3%.
A 3% increase in speed means going from a trim speed of 36km/h to 37.08km/h: not very dramatic – and certainly not enough to stop you being blown over the back of the hill if the wind picks up.
However, in competition small differences matter, and the topguns burning down final glide at 65km/h, block-to-block on speed bar, might give anything for a 3% increase in speed."

[mingram]

I got permission from Steve Wendt to cross-post this:

Many of you have mentioned that losing weight as a way to gain performance is in your future. Weight loss can add to certain factors and reduce others. Here are the basics ........

Decreasing weight changes critical speeds by about one-half mph for each 10 pounds lost. Meaning if your stall speed was 20 mph, after losing 10 pounds it is now 19.5 mph. If your best glide speed was 28 mph, now it is 27.5 mph. Add a Mosquito at around 40 lbs and we have increased our stall speed by 2 mph . The actual glide ratio doesn't change, just the speed at which it occurs in no wind. These numbers may seem minimal.

Though it doesn't change the actual glide through the air in no wind, In a headwind , adding weight improves your glide over the ground, while reducing weight improves your glide over the ground with a tailwind, due to a better sink rate.

Sailplanes do it all the time. They add over a hundred pounds of water in their wings to head up wind early in their soaring day more quickly, then dump the water for the downwind run to get home, because you get a better glide downwind if you are lighter.

Dan mentioned the other day at Woodstock he felt he had less glide when heading to the landing field. Some of that would be his weight loss, and trying to glide upwind, which would mean reduction in glide...( plus sitting in ridge lift for an hour gives us a false sense of an incredible glide).

Your sink rate improves by about "4 feet per minute" for losing 10 pounds. Doesn't seem like much , but if you flew for an hour , 10 pounds lighter would be 240 feet higher on average . John Shurte lost close to 30 pounds, and as a result, his sink rate improved by about 12 fpm, and his speed to fly were reduced by 1.5 mph, which may or may not be an improvement on a windy day. These numbers seem small but.......If 'Old John' and 'New John' left the same thermal at cloud base at the same altitude in no wind , and flew in a straight line for one hour, ' New John' would be 720 feet higher, but ' Old John' ( though 720 feet lower) would be 1.5 miles further away , or 1.5 times the length of our tow field for reference.

So, put that donut down now, or add the cheesecake to your dinner, but either way, think about the type of performance you want and need.

Basically , lighter is better for climbing and drifting downwind if making it happen quickly isn't a factor. Heavier is better for heading upwind and better handling, as well as a slightly higher speed range.

[pvanoevelen]

Thanks all for the very informative points. Most of them are made though based upon ideal conditions, meaning no variations in wind speed (turbulent air) and consequent wing deformation. On a paraglider those things can make a big difference. Having flown for years over the top of the range of my glider I had quite a difficulty in soaring under light conditions (prevailing on the East Coast) at the same time I had rarely collapses and learned to respond to the quicker dynamic behaviour of the wing. Flying an EN-C wing now vs the High End En-B before at a little above the recommended weight it is all quite a different experience, more agile (higher performance wing) yet gentler.
Krista did learn a lot from what happened at EG and I am glad she shared that experience so we do not have to make similar errors of judgement. (Btw this discussion also indicates EG is for PG at least P2 with observer in my book)

Just my 2 cts.

- Cheers Peter