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Discussion
Is ridge soaring possible in this situation
Our club has a flying field located in a valley . Our flying field and runway is located about 1000 feet from the bottom and 4000 feet from the top of a several mile long steep tree lined ridge that rises 900 feet from our field elevation. There is also valley on the other side of this ridge.
Last summer with crosswind toward the ridge a UMX Cub blew out of control range and by itself circled and flew over the ridge. Would a powered glider or perhaps a plane like a Bixler find enough lift to ridge soar in this situation with a decent wind blowing toward the ridge? If so, how close to the ridge would one have to get? Would it be necessary to be near the top of the ridge? What windspeed might be required. It would of course be pretty hard to see a small plane at 4000' away although we were able to see the little Cub circle up. It is hard to know how close to the ridge it actually was. Just curious. |
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What you're asking about is known as "slope soaring". But with a twist added that you want to soar from a location at the bottom of the slope instead of the top.
If you get winds that run onto that slope either directly or at some angle up to roughly 45 degrees to the face there's no doubt that you could slope soar along that cliff. And for a good enough wind and light enough model you don't need to be right at the cliff. But the lift becomes weaker as you move away unless there are other hills to form a valley where the air is ducted up along the slope. In such a case the lift can extend out ahead of the slope by quite a lot of distance. Most slope soaring involves standing at the top of the cliff and throwing the model out into the lift. But that's because such models don't normally have a way to get up to the lift from below. But to fly from the top of the cliff you need access to the top or some point well up the side and you need a place to land when you have had enough. Locally I'm surrounded by suitable hills for slope soaring model gliders. But all of them are covered with trees. It's a rain forest here don'cha know.... So the slopes are not what any reasonable person would call accessible for this sort of model flying activity. If you're asking about flying over to the slope from your present field I'd say that's a bit of a stretch. The model is going to be pretty darn small to see at that point and you'll lose a lot of the fun of flying unpowered aerobatics that are best enjoyed when up close to the action. But if you just wanted to fly a suitable glider or lighter powered model over that way and soar in the lift while the engine is at idle or the electric motor is off that's quite possible. And by doing so you may find that you can get enough lift well off the actual slope. |
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Thanks. Yes, before posting I looked up slope soaring and did discover that it was done from the top of the ridge. This ridge is totally tree covered and not accessible. So I was curious if it could be done from the bottom. I have flown at this field for years but never ventured very far "out".
Is more encouraging than I actually expected. We often have a pretty good crosswind. I have set up a couple of planes that might be suitable for this (Bixler, Zeta F-61 Wing) and maybe I'll venture out toward the ridge on a day with a good crosswind wind and see if I get any lift. Attached is a Goggle Earth image of the area. The yellow line goes from the runway to the ridgeline is is about 4000'. Elevation of ridge is 900' above field and river, so it rises 900 feet in about 3000'. Perhaps I don't need to get out as far as the top of the ridge. |
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Last edited by u2builder; Jan 29, 2018 at 03:59 PM.
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The real question is what's upwind. You said the field was in a valley. How close is the ridge upwind? It's hard to predict these things, but sometimes obstacles upwind will ruin slope soaring, even if they're not quite as high as the slope. We used to have a site that would be unpredictable, and almost always weaker than you'd expect by just looking at the slope. It's amazing how low a slope can be and still work if the wind is coming in off the ocean. It won't get the model very high, but for a good floater, a couple of feet will keep it flying.
An alternative explanation for the UMX is thermal lift. Could be either one or both. If I understand the description, your ridge ought to work very well, and it shouldn't take very much wind. Especially if you're flying a big, efficient glider. Keep in mind that if you're close to the top of the hill, the wind may be somewhat stronger there, with the potential to blow you back over the ridge, where there may be "rotor" even if you can still see the model just over the crest of the hill. But unless you've got amazingly good eyes, you'll have real t rouble seeing a Bixler at that distance. Try a Sailaire*. ;-) *I don't have one, that's just a picture I found on the web. |
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Thanks. There are no obstacles other than pretty uniform forestation, and the ridge is very "linear" or straight and quite flat on top. I would guess it could be quite turbulent as the ridge slopes down sharply on the other side. I could probably "see" a glider like in the attachment pretty far out!
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Well, I'd say that 1000 feet away is as far as you would really want to fly in any circumstances if you're not flying a pretty large model. I've done so with a larger glider out to probably 1500 feet. But it rapidly turns into a white knuckle event or calm "trust the Force" event due to being so familiar with the model. At that distance the model becomes invisible for a couple of seconds each time it turns end on to me. Something like a Bixler or anything of 2M or smaller span and you'd be at your comfortable visual limit by the time you reach the base of the slope. Never mind heading up the slope even further away where the lift will be stronger. So even soaring along the base of the slope is a bit of a reach that should not be taken lightly.
And of course that slope is DOWNWIND of your launch point by that far during the cross wind that provides the lift off the slope. And that means you will want either some good height or a power source to get back to the landing area against the wind. I also see that there isn't anywhere else closer to use for a takeoff and landing area which would let you soar on the slope. So all in all if someone shows up with an electric power 3M sailplane they can likely reach and use the lift along the slope. For the rest of you? I'd stay closer to home. |
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