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glider design

Old 05-14-2010, 03:02 PM
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pitts M 12
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Default glider design

are alirons a good feature on a 50 inch unpowered sailplane?
Is the covered leading edge of a glider a required feature?

JM
Old 05-14-2010, 07:27 PM
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limeybob
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Default RE: glider design

need a bit more info.
Purpose of the glider.
Aspect ratio
Do you mean a sheeted leading edge?
bob
Old 05-14-2010, 10:09 PM
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Dsegal
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Default RE: glider design

Gliders turn very tightly on rudder alone (on a plane designed for 3 channels). There is no requirement to have a sheeted leading edge.
Old 05-15-2010, 11:31 AM
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Default RE: glider design

More information on what type of glider and how it'll be used would help. For example if this will be a light thermal model then you can easily get away with a greater dihedral setup and no ailerons. But if this will be a slope soaring model then ailerons would be highly desireable and almost mandatory.

Same issue with sheeting on the wing. If it's a lightweight lazy summer evening slow flyer then there's no big requirement for sheeting the leading edge. Even up to a moderate performance the airfoil shape and use of mutiple turbulator spars to support the covering can sub in for sheeting. But at some performance point and with some airfoils sheeting is highly worthwhile.

So toss us some more information on if this is your own design you're working on or if you're adapting a kit or whatever the project is about.
Old 05-17-2010, 11:07 AM
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pitts M 12
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Default RE: glider design

It is to be a dual purpose model.
JM
Old 05-17-2010, 01:55 PM
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Default RE: glider design

WHICH two purposes? Don't be so stingy with your words! We're not going to charge you for the bandwidth!


EDIT; Also moving this to Gliders and Sailplanes where it's more appropriate.
Old 05-19-2010, 09:37 PM
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pitts M 12
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Default RE: glider design

It will be a thermal model. The fuselage is 30 inches long. wing is held on with rubber bands. wing has no spars but 3 1/8 stringers chord is 7.5 inch.

JM
Old 05-20-2010, 09:24 AM
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Default RE: glider design

At this point, I would say 50" x 30" is a little outta proportion, maybe 50"ws x 20" fuse would be much closer to being a good proportion. But you'll never know, if the design looks right to you, build it and try it out. The worst case scenario is it won't fly like you want it to, or it might be exactly what you wanted.
Old 05-20-2010, 10:18 AM
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pitts M 12
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Default RE: glider design

as in dual purpose i mean a slope soaring  and a thermal soaring model.

JM
Old 05-20-2010, 07:54 PM
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Default RE: glider design

Well, first off a 50 inch model that is heavy and strong enough to survive at the slopes is not going to be a great thermal model. The wing loading is likely going to be too heavy to thermal well or too light to slope well. Also unless you're using a sheeted wing the fact that it has no really significant spars worrys me. Slope models at high speeds generate a lot of G force. Much the same sort of G forces you get during a hi start launch on a thermal model. So unless there's something more holding this wing from bending I think you may have to deal with that for starters.

Anyhow, to get back to your original question. If slope flying is in the mix then yeah, ailerons would be wise and far more fun. But when flying slow in a thermal situation you need to learn to use very small control inputs. Otherwise the done traveling aileron can cause the angle of attack of that wing to rise to where the wing stalls. Aileron induced tip stalling is a big cause of "unexplainable" crashes during slow landing approaches. They are only "unexplainable" because the pilot didn't understand that his too large an aileron input caused the problem.
Old 05-20-2010, 09:07 PM
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Default RE: glider design

At a span of 50 inches, such a design would make for a nice slope plane but not all that great a thermal flier. Ailerons are nice on a slope plane but like BMathews said, they can get you into trouble if you're not used to them.

At 50 inches, to be a good thermal plane you would need to keep it as light as possible. Think something like a DLG here. Light, strong and with a good airfoil. The drawback to that layout is that they're not really good in winds. If you ballast it up, you'll increase how well it can penetrate the wind, but loose it's floater characteristics.

For thermal flying, the old saying of "bigger is better" is very true. At 50 inches, your plane would fall well below the 2 meter span range which is by many considered to be the lower end of a good thermal ship. I for one love the 2 meter class and have had some great ships in that range over the years. If built right, they will handle slope flying well and still be able to thermal. If you have room to build and haul a 2 meter ship, I think that may be more towards what you'd really like in a "Combo" ship.

There's also the airfoil to consider when designing a sailplane. This is usually chosen by the type of flying that you intend to do with the ship. Most thermal ships have airfoils that are flat to semi-symmetrical in shape while many of the fully aerobatic slope planes will use an airfoil that is closer to being fully symmetrical. The projected weight of the ship will also have an impact on airfoil selection.

As to sheeting the LE of the wing, It has both good and bad points to it. The good being that you get a much cleaner shape to your airfoil LE as well as extra strength in the wing. The bad being that you end up with a lot more weight to have to provide lift to over come. My current design project includes a full "D-tube" leading edge and full house controls (Flaps, Ailerons and Spoilers) on the wing but I've also got 196 inches of span to provide lift. AT 50 inches you're going to need to keep it as light as possible or you may end up with a plane that will only fly on a slope with strong winds hitting it.

EDIT:ANOTHERTHOUGHTHERE...

At 50" X 30" you're going to need a lot more lead in the nose to bring her into balance. The further back from the wing you have the tail feathers, the more weight it's going to take in front of the wing to offset that weight. Look through some of the on-line shops to get a better idea of proportions of sailplanes that are already flying and on the market. The "wish-books" can provide you with a lot of information. Span, length, airfoil used weights etc.

Old 05-26-2010, 09:21 AM
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pitts M 12
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Default RE: glider design

perhaps I will scale up my design to a 2 meter and see how it looks. though the "slope " is the type of thing that you would see on a dike so that is the reason that I would like a smaller model. Thanks

JM
Old 05-26-2010, 11:46 AM
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Default RE: glider design

If your "slope" is going to be something more modest such as a dike or line of tightly growing trees that you may happen to find then a lightly built 60'ish inch DGL (Discus Launched Glider) would be something that is quite appropriate. But keep in mind that the lift zone from modest features like these is quite limited. It will hold up a 1.5 to 2 meter model just fine but it won't lift it up to much more than twice the height of the feature that is creating the lift. The smaller lift ridges of this sort don't affect the airflow over a big enough area to do more than create just a little hiccup of this sort that doesn't extend very far from the feature. So while they will hold up the glider they won't generate the big lift zone needed to get enough altitude to do any aerobatics.

I've soared off lift from a tight tree line on occasion and if there isn't a guy with a stopwatch breathing down your neck counting down to the "max time" for a contest task it actually gets pretty boring, pretty quickly. It's fun at first to know you can do such things but it's more of a "survival" trick for getting your flight time.

As a result I'd suggest you think about it in this light and figure out if you want to optimize the thermal aspects moreso over the small feature slope soaring aspects. And this mostly means size. A 2 meter or larger thermal glider will do far better at thermaling in all aspects than a small one. And if it should come down to needing that "survival lift" off a dike or tree line it can still use the lift as well as a small model. The ONLY advantage of the smaller model would be for slope flying on a much larger hill or cliff where you want quicker handling. My own feelings are that for general sport soaring a 2 meter to 100 inch model is a great size. It's big enough to stay in good view while ranging out farther to look for lift. But they also break down well for transport and storage. Smaller models get small too fast and you will find that you just can't search anywhere near as big a block of air for lift. Now if you're confined to fairly small parks then perhaps a "vest pocket" soaring solution IS a good idea. But only if this will be how you'll fly it all the time. A smaller model can be made to a lighter weight and turn far tighter. And that can help a lot of you're dealing with a lot of smaller thermals and other small spotty lift in tighter fields. For example a park with a couple of soccer fields or 2 baseball fields in one area would be perfect for a 50 to 60 inch model. You could certainly fly the bigger ones there as well but the smaller size would let you work some of the smaller lift pockets more effectively.

Getting back to the ailerons again. If you've flown and are very comfortable with polyhedral designs and can handle the perspective issues of flying out at a far distance then ailerons can really help you to sharpen up your glider handling. But if you don't have a huge amount of flying time with poly ships then go real easy on the aileron size and throw. They should be set up so that they are about as responsive as a power trainer model and no more than that. Otherwise even small control inputs will get you into big trouble when you're way downwind in a thermal and are flying the model as much on habit as you are on visual.
Old 05-28-2010, 06:05 PM
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pitts M 12
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Default RE: glider design

I'm actually going to build  a CF spar on the CG for stiffness there.
JM
Old 08-27-2010, 10:32 AM
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pitts M 12
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Default RE: glider design

Thanks for all the advice as this is my first glider and big  scratch build and my most advanced model is my parkzone wildcat.

JM
Old 08-27-2010, 12:33 PM
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Default RE: glider design

ORIGINAL: pitts M 12

Perhaps I will scale up my design to a 2 meter and see how it looks.
If 2 meter appeals to you, why not to use, as a base of your own unpowered sailplane, a proven design which can thermal and slope soar decently?

http://www.rcmplans.com/index.php?ma...oducts_id=1605

manuals.hobbico.com/gpm/gpma1960-manual.pdf
Old 09-03-2010, 06:57 PM
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pitts M 12
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Default RE: glider design

the 50 inch version is based on a great planes fling

JM

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