Slope Soaring Tips for Beginners

by Akkana Peck

My husband and I are learning to fly slope gliders (after already flying electric-powered model airplanes). I didn't find much on the web about learning to slope soar, so I'm writing this page as something that might be helpful to new slope soarers.

Differences between slope soaring and other types of flying

Of course the obvious attraction of slope soaring was the lack of mechanism: no noisy motors (not that modern electric motors are very loud), no complicated winch setup like the thermal gliders use, relatively small and simple airframes. It has a purity, as much as anything requiring $150+ of radio equipment can seem pure. But the first thing we learned was that another difference is that it's much more physical than other types of flying. First, there are no slope sites anywhere near a road. If you live very near the ocean, you may have ocean cliffs with parking lots nearby, but anywhere inland, you'll probably have a pretty significant hike to get to anywhere with lift. I knew the slope sites had a little bit of hiking, but when I visited them I was impressed with the significance of the climbs these people were doing carrying equipment. People who do other types of R/C flying mostly don't seem like they're much into physical activity.

That was part of the attraction, for me: Dave and I like to hike anyway, and spending all our time standing in a field flying electric planes was making it hard to get much exercise. But be aware of it: visit your local slope sites before purchasing a glider to make sure you're up to it.

We didn't realize until later that hiking to the slope site is only part of the exercise. Once you're there, you'll also expend lots of energy chasing up and down the hill to retrieve your glider when it lands in unexpected places. Or you can try discus-launching at a flat site, in which case you'll be running halfway across the field and back every minute or so to retrieve the plane.

Rule 1 of slope soaring: If you build a glider, there will be no wind ever again.

We ordered our mini-Weasels partly because it had been extremely windy, so windy that most of our electric planes were having trouble flying. We finished them in a few days, tossed them in the car and drove up to a local site known as Windy Hill (that's the name of the park, not just a nickname given by glider people -- it's always windy there.) It was dead still. We spent a frustrating afternoon tossing our Weasels down the slope, or standing atop the hill waiting for a tiny gust.

A few days later, we went on a trip to visit friends in Arizona. Our route took us over Pacheco pass, a known wind tunnel with a wind power generation station, and over Tehachapi pass, which has an even bigger fleet of windmills. We stopped at roadside rest areas with the Weasels. They were still. The windmills were barely turning. Same story at other roadside rest areas in usually windy areas, like California's central valley.

After we got home, we hovered over the weather pages. There's a "live wind map" page for the bay area which shows directional arrows supposedly indicating the wind direction everywhere. But it turns out that they don't have very many wind-reporting stations, and in particular, they don't have any in the hills where we normally hike. So the arrows are all interpolated. More than once, we saw nice green arrows over our hiking areas, and rushed up the hill to find dead calm along the ridgetops.

Corollary 1 to Rule 1: When you finally get wind, it will be too much wind.

After two weeks of dead calm with a new slope glider, you think that there could be no such thing as too much wind. Until you find yourself on a hilltop with your new carefully-built slope glider, trying to stand up in the 20mph gale, and contemplate tossing your precious toy into that and seeing it swept away forever.

Corollary 2: or in the wrong direction.

We drove over to the coast, where there's always an onshore wind. Not that day -- the wind was actually blowing from the land out to sea. I didn't think that ever happened. None of the cliffs point that way, either; they all face the sea. Dave thought that just having wind at all might be enough for slope soaring, but it doesn't seem to work well unless the wind is blowing at least partially onto the slope, so it gets forced upward.

We ended up driving up the coast about 30 miles, stopping at every beach, until finally we found one that had a little cove with a hill that pointed in the right direction. Then we had a great time -- really our first slope experience.

Corollary 3: or with no recovery zone.

Actually, we did find a few cliffs with the wind blowing onto them -- but note the word "cliff". Experienced glider pilots can toss a slope glider off a cliff and expect to bring it back and land it at their feet, but when you're learning, you want a place where you'll be able to hike down and retrieve it.

What to do with your slope glider when there's no wind

Dave and I discovered "Weasel hiking". We'd drive to a trail in the hills hoping for wind, hike up to the highest hilltop, spend a little time there tossing our gliders out into the dead air. Maybe we'd hike around (we like hiking anyway, though it's nicer when you don't have to carry a heavy transmitter everywhere). But the hike back down turned out to be fun. See, even when you don't have wind, you can fly a fair distance if you don't mind landing downhill from you. So you toss your glider as high as you can, then fly it down the trail as far as you can, trying to land somewhere near the trail; hike down to it, then toss it again. You can actually get in a reasonable amount of flying this way, and learn something about the characteristics of your glider.

This may not work quite so well if your first slope glider is large and unweildy.

Things to watch out for while glider-hiking.

On our first windless outing, I got the clever idea that I'd climb up on Eagle Rock (maybe 15' above the trail) and toss the glider off the rock. But my launch technique was pretty inconsistent, and the Weasel flopped nose-first in the bushes at the foot of the rock. Unfortunately, the bushes turned out to be poison oak. I had to carry the Weasel, by the tip of its fragile tail, all the way back down the trail (no more flying for me that day!) and carefully wash it off with Simple Green as soon as I got home. Be aware of the foliage around you before you throw.

(It also helps to put some brightly colored surfaces on your plane, especially if you fly in places will tall grass. Can you find the Weasel in this photo?)

Other things to watch out for: trail visibility (don't throw if you can't see the trail for a good distance ahead), hikers who might get hit (if you're new and your control isn't so good, you might hit someone), potentially dangerous trail users (like groups of hikers with kids who might run over and damage your glider), cliffs, poo (especially on equestrian trails), ticks, snakes, and other denizens of the tall grass through which you search to retrieve your plane.

When you finally find wind

Huzzah! You're at a likely ridge with the wind blowing in the right direction, onto the ridge. Now what?

Watch the birds.

My first really successful (staying up for a while, being able to do aerobatics) slope flight was at a launch point I picked because I saw a whole flock of swifts playing just off the hillside. Sometimes a good ridge doesn't look that different from any other place, but if you see a hawk circling to stay above a particular point, or a flock of swifts playing there, you know it's a good spot. Hawks and swifts are professionals: they're better at finding lift than you'll ever be.

Launch into the wind.

Our Weasels, at least, launch much better if you throw them into the wind, even if you'll be flying along the ridge line once you're in the air. This takes some nerve at first, since you feel like you're throwing the plane out across the lift into the zone where it'll drop like a rock into the valley below. And sometimes it might (remember what I said about a recovery zone?)

Follow the ridge line.

A good slope soaring hill usually has a cliff or steep area aligned more or less facing the wind. The wind hits the cliff and gets directed upward. You need to stay above that area -- so once you're in the air, turn to fly crosswind along the ridge line, then turn fairly sharply and fly back the way you came.

Turn into the wind, away from the hill

When you're flying crosswind along the slope, turning into the wind will give you some additional lift. (This is part of the more advanced technique called "dynamic soaring", or DS.) So when you make your turn to fly back the way you came, turn away from the hill, not toward it.

This can be psychologically difficult for the novice. Turning toward the hill is safe -- if something goes wrong, the plane ends up fairly near where the pilot is standing. Turning away from the hill, into the wind, is unsafe -- if something goes wrong, the plane ends up waaaay down the hill and you have a long hike to get it back.

Trust me. If you want to stay up and in the lift, work up your nerve and turn into the wind.

Watch the plane: don't assume you know where the lift is

Slope lift seems really straightforward. The wind hits a hill, it bounces upward, the lift is right above that, right? But it's not so simple. Sometimes the lift will be better above a cliff, sometimes above a gentle slope; sometimes it'll be a bit downwind of the cliff edge, other times out from the cliff. Sometimes you'll be getting great lift at one point along a ridge, then suddenly the lift will die, even though the wind hasn't stopped, but fifty feet to the left, a spot that didn't have lift before will suddenly come an elevator. Maybe experienced slope pilots understand all this, but I don't. Watch what your plane does, notice when it takes off and learn how to stay near that spot, and notice when it stops climbing and be ready to go hunting for lift somewhere else.

And watch the birds (swifts and hawks). They play in one spot for a while, then move on. And if you fly with other glider pilots, watch them, too. You can help each other by calling out where the lift is good.

Trade off between speed and altitude, and use ground effect.

Airplanes (all planes, not just slope gliders) can trade speed for altitude, and altitude for speed. (This comes from the Newtonian physics concept of the equivalence of potential and kinetic energy. Altitude, combined with the earth's gravitation, gives you potential energy, mgh; speed means kinetic energy, .5*m*v²; and they can be traded for one another. This is how a rollercoaster operates, too.). Knowing about this can be useful: for instance, you can dive below the edge of the cliff and not be in any risk, as long as you have enough speed to trade that kinetic energy for potential energy and climb back up. Play with this (preferably when you're already fairly high) and get a feel for it: you can use it to your advantage.

Ground effect is the phenomenon that when an airplane is flying very close to the ground, it can fly faster and experiences more lift than when it's high in the air. (The effect is caused by a reduction fo turbulence from the airplane's wingtips. Some birds, such as pelicans, use ground effect very effectively as they skim just above the water.) One way this becomes useful in slope soaring is when you have a gentle slope above you. Remember I said to make your turns away from the hill? It sometimes happens that you make a turn toward the hill instead, fly out of the lift zone, and start to sink toward the hillside. Don't panic: if you approach the hillside smoothly, you may be able to use ground effect to skim along the hillside, gain speed, then climb out, turn back into the wind (which gives you lift, remember DS?) and make it back to the lift zone.

How much elevator can you use?

I don't know if other slope planes exhibit this effect, but the mini Weasel, when you give it too much aileron, porpoises, flying a sawtooth pattern as it repeatedly stalls and recovers. I found this helpful when feeling out how much elevator I could give it.

Get familiar with your trim tabs

The right trim varies depending on what the wind is doing. If you're getting good lift, you might want to add a couple of notches of up trim to take advantage of that (without having to hold the stick back constantly). If the wind is blowing you back and you want the glider to penetrate better and stay in the lift zone, you might want a few notches of down to help with that. Adjusting up and down as the conditions change can make flying more fun.

More...

... as I learn it! I guess that means I'd better go out there and do some more research!

Happy soaring ...

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