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Old Apr 21, 2015, 11:13 AM
old1104 is offline
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Design Question

I am new to RC and even newer to RC gliders. Have been flying free flights off and on since the 50's design my own planes. I used to fly A2 gliders and used to do real well well at regional contests.

I had asked earlier about flying in turbulent air. I have two different gliders. One low inertia in roll and yaw (own design and was built to see what it takes to fly electric RC gliders). The second has high inertia in roll and yaw. Both gliders are rudder elevator pod and boom gliders. The heavy glider wing was built for winching and the other was built for electric. Both are flown as electric only. . I crashed the high inertia glider when changing it over to the DX9 radio. I rebuilt it but changed the tail section and the boom. I lengthed the boom and made the vertical much bigger horizontal. Before the high inertia glider would have problems with yaw oscillations if I over controlled it. High inertia glider was adapted to a pod and boom that was set up for an OLYII boom lenght and tail section size. The glider was to heavy for an OLYII. I built a center section for the hevy wing to fit it to the OLYII pod and boom set up. I assume the longer tail boom and much larger vertical would reduce the yaw issues. The additional nose wt made the glider even heavy. The high inertia glider has SD8040 10% airfoil and 113 inch span. I had purchased the wing at a swap meet. The low inertia glider has a AG24 9.2% airfoil and 120 inch span.

Now I assume the the high inertia glider would handle turbulent air better than the low inertia glider. It would not respond the turbulence than the low inertia glider. The make reading thermal harder.

As set up the low inertia glider has 6.5 lb/ft sq wing loading while the the high inertia glider has 10.6 lbft sq wing loading. I could add weight the the low inertia glider if that would be the better glider in high turbulence.

I realize a full house glider will do better in turbulence as ailerons allow for much better control. I am trying to learn how to control a glider with ailerons but need a lot more experience before I can successfully fly an aileron glider and make proper turns. Using ailerons, rudder and elevator properly seems to be a little problem for me. I have two smaller gliders with ailerons and need a lot more time before I can fly them and do thermal flying as well as I can the rudder elevator gliders..

I will be building all my own gliders as I can not afford the high performance gliders. So I am trying to understand the design trade offs for gliders design. I plan to build a full house glider next winter. I will most like use an average thickness of about 7%. 8% at the center section and 6% at the tip.

I only fly electric since no one near by flies winch glider and our field is to small for even high start. It is a small landing and take off area attached to a farm. There are high voltage power lines right next to the field and the wind is often across the field.

Art
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Old Apr 21, 2015, 11:41 AM
Bernd Brunner is online now
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dare to thermal
Mannheim, Germany
Joined May 2004
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Art, i couldnīt see a question, but i can tell, that eg in F3J (thatīs a high performance thermal class) we are flying very light planes with low inertia. When the wind picks up, ballast in the fuselage is added. Only in very,very strong wind >20kts heavier buildt planes where used.

So my answer would be: build a low inertia plane which can be ballasted. Check out the charlesriver pages! http://www.charlesriverrc.org/articl...edancer-3m.htm

/Bernd
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Old Apr 21, 2015, 11:58 AM
marc.pujol is online now
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You want to have your own plane that is quiet optimized? Good.
Look at RCSD around 2011 and Nov 2012. There are articles on yawing stability and the Genoma2 plane with lots of information on its design and how to construct it.

And I can assure you that is fly realy realy well.

Marc
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Old Apr 24, 2015, 10:03 PM
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Given the same wing loading, I'll take the lower inertia model since it will require less control movement.

Models are using thinner airfoil which is a bigger building challenge but they work well without adding as much weight.

Enjoy building. It's a disappearing skill.
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Old Apr 24, 2015, 11:11 PM
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Thanks Malchow. I flew today and the high inertia glider was harder to control but also did not bounce around like the low inertia glider. My limited experience with RC gliders confuses me as to what is best in turbulent air. I guess I will go with your suggestion of keeping the inertia as low as possible.

Art
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Old Yesterday, 07:47 AM
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You are pretty well right in your conclusions. I had two identical F3B models, one very light and one very sturdy. I have used them mostly slope soaring at the mountain, which is basically a combination of thermal and slope lift. In rough and turbulent conditions the heavy model was like a locomotive in the air, but kinda sluggish and unhappy when going slow in light conditions. The light model was relatively easy and responsive in light lift, but became quite jumpy and a handful to control when ballasted and going fast in rough conditions. I think the heavy one was more suited as basically a slope soarer more than a thermal glider.
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Old Today, 12:29 PM
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In regard to highly turbulent wind, are you particularly trying to fly in a spot that's unusual? Having flown super light planes to super heavies, turbulence considerations, for me have only really come into play in high wind areas like slope soaring. For thermalling, aside from the occassional anomaly, for the most part, in normal 0-10 mph winds, I stick with traditional thermal plane design and have no trouble. A lighter and more center massed (majority of weight in fuse, with as light of wingtips as reasonable) plane will react better and faster to thermal "turbulence" and is desirable.

If you are trying to fly during storms, or something like near a helicopter pad, or maybe you can only fly in a city with highrise buildings, etc, try looking for more typical flying locations that are generally considered acceptable for the plane you're trying to fly.

Build light, with options for ballasting, as previously mentioned. Only use enough mass to maintain an ability to make forward flight reasonable.

Unless, perhaps you've somehow gotten into dynamic soaring conditions and have mistaken that as typical thermal flying.

There may always be conditions that surprise you, where a wild pocket of wind comes out of nowhere, but do not build to specifically handle that odd condition, rather build to suit the 95th percentile of flight conditions.
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