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May 21, 2019, 05:42 PM
A man with a plan
Balsaworkbench's Avatar
Thread OP
Question

how much slope is needed for slope soaring


I've been threatening to get into gliders for a long time, and now I'm finally building a 10 foot thermal plane. But I'm also wondering how much of a slope is needed for slope soaring. In my part of Missouri we have some hills, but nothing really outrageous. There's a big cliff with a river at the bottom and no access except by boat. I know that would work because I see the eagles getting tons of lift there, but I don't want to mess with it. In addition to the limited access at the bottom, there's not a good place to land the plane at the top. Mostly what we have are gentle hills, where a 40 acre pasture may be 20 feet lower in the middle than at the edge. We get some days with 15 mph wind all day, especially in the spring.

We fly at the local airport, where the land slopes away in all directions, and there are a couple of lines of tall trees alongside the runway in various places. I've noticed lift where the wind hits the trees.

I know this is kind of vague, but does this sound like the kind of place where a slope plane might be able to stay up? I can post a few photos if that would help. Is there some kind of formula for the minimum workable slope soaring conditions?
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May 21, 2019, 06:49 PM
The Mr. Rogers of RC soaring
rdwoebke's Avatar
Generally what is in front of the slope and the width of the slope is the most important. For example at the beach a small beach rise that is long is a decent slope for light wing loading gliders. In southern Indiana there are a lot of hills but the hills are always hills next to hills and there isn’t an open space next to them for the air to get smooth and hit the hill.

Feel free to post pictures. But keep in mind from pictures it is often tough to really visually see the rise of the slope

Ryan
May 21, 2019, 06:55 PM
That thing almost hit me
Tahoed's Avatar
All depends on the plane. An Alula https://dream-flight.com/products/alula-trek can pretty much fly off an ant hill. Post some pictures of the slope.

Alula. Small slope. Playing with the crows. (2 min 33 sec)
May 21, 2019, 07:50 PM
A man with a plan
Balsaworkbench's Avatar
Thread OP
Quote:
Originally Posted by rdwoebke
Generally what is in front of the slope and the width of the slope is the most important.
That part about the width took me by surprise. When you explain it, it makes sense. But I wouldn't have thought of it.

To the south of our current flying area is the runway, a large part of which is between lines of trees. To the southwest is a bunch of trees and a school building. It's pretty clean to the northeast, north, and west. Just wide fields sloping up to the runway.

I'll see if I can get a couple of photos tomorrow.
May 21, 2019, 08:19 PM
The Mr. Rogers of RC soaring
rdwoebke's Avatar
My experience is you can work slope lift off a surprising amount of things with a floaty glider. Tree lines, buildings, small changes in elevation. I even heard one guy that is well respected in the soaring community say he worked the edge of a crop field with a DLG. But to fly what folks might call a "slope plane" aka something heavy and fast then my experience is you need a more "real" slope.


Ryan
May 22, 2019, 06:49 AM
Registered User
The lenght of the slope forces the air to go above it (generating lift) instead of around it. The airstream has to be rather perpendicular to the slope, again to be forced to go above it instead of around it . Around 30 degrees out of perpendicular is still flyable.

Small elevation, plenty of lift for a full sized Ka6....

Dune Running with K6 glider and GoPro (4 min 19 sec)


Cheers
Joao
May 22, 2019, 08:51 AM
Registered User
Quote:
Originally Posted by rdwoebke
Generally what is in front of the slope and the width of the slope is the most important. For example at the beach a small beach rise that is long is a decent slope for light wing loading gliders. In southern Indiana there are a lot of hills but the hills are always hills next to hills and there isn’t an open space next to them for the air to get smooth and hit the hill.


Ryan

This proves true in my area. I haven't found a slope around here where there is a long enough fetch in front for the air to smooth out. (unless you go to a mountain top that rises above surrounding terrain) Seems upwind there is something, a tree line, another hill, mountain, buildings, that forces turbulence into the air making it difficult to ride. Think of water turbulence downstream of rocks, same thing in air. That's why good lift can be found so easily along beach areas. With the wind blowing steadily off the ocean, there is nothing to introduce turbulence and the smallest rise produced good lift. And as Ryan said, the wind cannot go around, it has to go over.

Edit to add; Just a thought. If there is a large reservoir in your area, if you can find a rise of land on the downwind shoreline that's fairly open, that could possibly offer an opportunity. Also think of a dam or spillway as a possibility though may need special permission to access those areas.
May 22, 2019, 10:44 AM
A man with a plan
Balsaworkbench's Avatar
Thread OP
I live a few miles from Truman Lake. The shoreline is owned by the Corps of Engineers and is mostly trees, so probably not good. The dam is about a 45 minute drive away. Unfortunately it faces east, and the wind rarely comes from that direction. I think my best bet is a hill.

I'm glad I asked this question, because you guys have given me a lot of insight into slope lift.
May 22, 2019, 12:35 PM
Registered User

Whatís a slope?


I once won a contest by sloping a stand of trees. Watch for birds. If they donít flap but donít loose altitude they may be in slope lift.
May 22, 2019, 12:49 PM
The Mr. Rogers of RC soaring
rdwoebke's Avatar
A person can definitely work slope lift with a decent glider off a lot of things. Warehouses, tree lines, clumps of trees, etc. But if a person is wanting to build what people often refer to as a "slope plane" and fly it like a slope plane (doing aerobatics and stunts and what not) then one needs a bit more of a "real" slope. I mention this because the OP uses the word "slope plane" in his initial post. If your plan is to fly a regular type sailplane and want to see where you can work slope lift (also sometimes called ridge lift or mechanical lift) then yes there are lots of "slopes".


Ryan
May 22, 2019, 01:02 PM
A man with a plan
Balsaworkbench's Avatar
Thread OP
In 30+ years I've flown lots of powered models, including really floaty powered models such as Buzzard Bombshell, Q-Tee, Whimpy, etc. I have very limited glider experience, but I have flown my floaty planes on available lift.

I think you guys are making a pretty good point. Based on prior experience, I'd say I have a fairly good grasp of tree deflection, watching birds, finding hot spots, etc. I was just wondering where the dividing line is between a thermal plane and a heavy slope glider. In other words, if I can keep a thermal plane in the air over a tree line, there comes a point when it starts getting blown around too much and it isn't as much fun any more. Is that the point where you switch to a heavier slope plane, or is there a gap between good thermal plane conditions and good slope plane conditions? I think I just answered my own question, because you probably adjust your wing loading for the amount of wind, right?
May 22, 2019, 01:16 PM
The Mr. Rogers of RC soaring
rdwoebke's Avatar
If you can't move the plane around well enough to get to or work the lift you need to work then we add ballast. As a general rule of thumb I like to increase wing loading in 1 ounce per square foot increments. So if my plane has 1,000 square inches then I start with 8 ounces of ballast kind of deal.



Ryan
May 22, 2019, 01:26 PM
Registered User
Quote:
Originally Posted by Balsaworkbench
In 30+ years I've flown lots of powered models, including really floaty powered models such as Buzzard Bombshell, Q-Tee, Whimpy, etc. I have very limited glider experience, but I have flown my floaty planes on available lift.

I think you guys are making a pretty good point. Based on prior experience, I'd say I have a fairly good grasp of tree deflection, watching birds, finding hot spots, etc. I was just wondering where the dividing line is between a thermal plane and a heavy slope glider. In other words, if I can keep a thermal plane in the air over a tree line, there comes a point when it starts getting blown around too much and it isn't as much fun any more. Is that the point where you switch to a heavier slope plane, or is there a gap between good thermal plane conditions and good slope plane conditions? I think I just answered my own question, because you probably adjust your wing loading for the amount of wind, right?
Ahh those names bring back memories from the 1970's. Man named Paul in the club flew a Buzzard Bombshell. One day he had it turned into the wind, throttled back, just floating stationary couple hundred feet up. Suddenly the wing dowels broke, the fuselage came screaming straight down like a missile and dead centered the roof of MY car. I was just a teenager. It took some convincing my folks I hadn't been involved in some nefarious activity as it was hard to believe a "model airplane" could cause that much damage. Paul stopped by on his way home to talk to my folks and I believe only then did they actually believe my story. It caved in the whole roof which had to be cut off and a new roof installed.
I flew a Q-Tee into the ground. (Literally several times) Just flew it to death with a Cox .051 engine. Once threw it airborne forgetting to turn on the receiver switch. Jumped in my car and chased it over a mile before it came down right beside the road. Had a Square Soar glider, knew little-nothing about finding thermals but managed a few times to stumble into one. Lost it downwind once, took me over a day to find it.
Good times.
As far as your question. Some thermal planes will slope just fine and vice versa. I'm not the one to answer your questions though with any specifics.
May 22, 2019, 10:42 PM
DWA
DWA
1Corinthians 13:1-8
DWA's Avatar
This slope has stuff in-front of it and it is not very long but its a good slope. It is about 200 feet to the bottom of the hill so that helps.

Quick video of my flying one of my P-51 gliders at a slope called Lilly Shapell
(0 min 53 sec)
May 22, 2019, 11:19 PM
A man with a plan
Balsaworkbench's Avatar
Thread OP
Wow, that's very nice. Thanks for posting.

What is the wing loading on that model?


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