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Why do most sailplanes have only rudder and elevator?

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Old 06-13-2015, 07:14 PM
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YellowBlueBird
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Default Why do most sailplanes have only rudder and elevator?

While looking for a sailplane with ailerons observed that most don't have them. ?

Is there a kit sailplane with full house controls?
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Old 06-16-2015, 11:41 AM
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are you kidding.
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Old 06-16-2015, 12:37 PM
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I'm going to assume you're serious. Sailplanes are primarily designed for catching thermals and staying in the air - therefore, only rudder & elevator are necessary or wanted. Some have spoilers to assist in coming back down.

Ailerons are primarily for banking, sharp turning, maneuvers - something completely alien to a sailplane. There are GLIDERS with ailerons, but they're primarily slope gliders. They have much higher performance parameters, some are even scale models of WW2 warbirds.
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Old 06-16-2015, 02:34 PM
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Originally Posted by skylark-flier View Post
I'm going to assume you're serious. Sailplanes are primarily designed for catching thermals and staying in the air - therefore, only rudder & elevator are necessary or wanted. Some have spoilers to assist in coming back down.

Ailerons are primarily for banking, sharp turning, maneuvers - something completely alien to a sailplane. There are GLIDERS with ailerons, but they're primarily slope gliders. They have much higher performance parameters, some are even scale models of WW2 warbirds.
Thanks Skylark,

My first and so far only sail plane is a Great Planes Spectra. It seems a bit hard to control. Once it gets passed a certain point in a turn the wing wants to drop sharply and the airplane tends to dive. This is not what I expected from a sailplane. I have done many dead stick landings over the years and a properly coordinated rudder aileron turn resulted in less loss of altitude. My vintage rudder only planes did not have this problem. Is it possible that this plane is simply out of trim?

What type of work did you do In the air force? I was in radar and spent a year in Vietnam..

Jerry
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Old 06-16-2015, 05:23 PM
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Not sure where you were looking when you concluded most sailplanes lack ailerons. Most high-end sailplanes do have ailerons. All things being equal and over the long run, a sailplane with ailerons and flaps will outperform one without. This is not denigrating RES. A plane with only rudder, elevator and spoilers can have spectacular performance. Not fiddling with ailerons and flaps (for camber control) is more relaxing and it gives you more time to figure out where the thermals are.

There are few sailplane kits on the market compared to twenty or thirty years ago. Those that are have 2-meters or less wingspans. You need a larger sailplane to carry the extra weight of the wing servos. There just isn’t a market for a three-meter plus, full-house, sailplane kit.

Your Spectra may have a trim problem. Usually an extremely hard rudder will only result in a steep spiral turn and not a spin or dive. You might try washing out the outer panels’ incidence. That is, make sure they have less angle of attack than the inner panels.

Allan
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Old 06-16-2015, 05:37 PM
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Sailplanes are designed to fly as efficiently as possible, getting the most lift out of even the lightest thermal. The more control surfaces you have the more servos and linkages you need, and that translates into weight. Really, unless you are flying competition rudder and elevator are all you really need. Some add spoilers to get the planes back down if it gets into a really strong thermal.
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Old 06-16-2015, 07:18 PM
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Hey Brother Jerry! I started USAF during that time period, never got the call to go over there. I was in Security Service (SS) until it morphed into Electronic Security Command, finished my near 22-yr in ESC. Multiply-rated linguist, beyond that I can't say.

I know the Spectra - it's a good plane, but sometimes rather "spirited" for a sailplane. I fly the old Spirit-100, larger and unpowered version of the Spectra. Allan's got some excellent points in his reply too - especially the washout issue. I've also heard of guys putting small winglets on the tips to settle them down a bit. For starters though, I would definitely look at that trim & balance - you might also just have a heavy wingtip on one side or the other. After that, check the motor for mount stability. If it's loose in the mounts she can make a plane do wierd things at wierd times - turning especially.

Hey Flywheel! I like that Dorfmann ref - outstanding! ... and soooo true.
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Old 06-17-2015, 01:51 PM
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Default Ailerons????

i beg to differ with a lot of the comments on this subject.

A rudder and ailerons offer different control aspect in flight.

A true glider should have a full house of controls.

If a simple glider has enough dihedral, than it can achieve some of the banking as a full house glider does, but it cannot respond nearly as fast as one with ailerons.

Rudder is yaw...keeps the nose pointed into the relative wind. Combine with dihedral and elevator, the glider can bank.

Ailerons control roll. In order to turn an airplane properly, especially one without excessive dihedral, ailerons, rudder and elevator are needed. Exception, canard airplanes.

To suggest that most gliders only need rudder and elevator is completely incorrect, and an insult to what gliders are capable of.

In full siize sailplanes and in complex models, banking angles in excess of 60 degrees are common. The tighter the thermal, the smaller the core is and the more bank angle is required. This is also true when closer to the ground or the source of the lift.

When banked over in excess of 60 degrees and the thermal kicks your tail around, or you leave the lift and need to get back into it, you need as much control as possible to keep control and get back in or remain in the lift.

Here is a glider with a lot of dihedral and a full house of controls. The second picture offers a view of a relatively tight turn. The yaw string on top of the canopy allows the pilot to keep the nose pointed into the relative wind and that is controlled by using the rudder.
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Old 06-17-2015, 06:40 PM
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Originally Posted by skylark-flier View Post
Hey Flywheel! I like that Dorfmann ref - outstanding! ... and soooo true.
Thanks.
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Old 06-17-2015, 09:42 PM
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You do need to put washout in the outer wing panels. These things were known to tip stall. I have one and fly it quite often. If it is trimmed out and the wash out applied the plane flies great.
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Old 06-18-2015, 01:45 AM
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Thunder and lighting have walked about all night and continues this morning. Looks like this will be an all day In the shop. Washout it will be., Does anyone know of a kit sailplane, about 90 inches, with full house setup. I have found Skybench aero but they don' seem to be active.

Thanks to many who have made suggistions
Jerry
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Old 06-18-2015, 02:07 AM
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Sierratango, If you don't have full house controls there is no ball to step on. Is that structure on the left side of the hanger just decorations?
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Old 06-18-2015, 06:12 AM
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The photo was taken at the Mammoth Lakes airport. The structure on the left is decoration, a facade of sorts like the front side of the hangers facing the runway.

I have never flown inside an airplane that only had rudder and elevator to know for certain what you are stating.

I presume you are saying that ailerons produce asymmetrical lift and drag and therefore a rudder and yaw string are needed.

However, with long span gliders, one might argue that the outside wing in a turn is traveling faster than the inside wing and thus producing more lift and drag and thus stepping on the ball or on the gapped side of the yaw string would still be necessary.

Mother nature gave us five fingers on each hand and radio control tranmitter manufactures are giving us multichannels. Why not use everything you can and build as light as possible and grow into your model rather than grow out of it.

It it is all fun anyway. Really fun!
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Old 06-18-2015, 10:07 AM
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Mine has all of them.
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Old 06-18-2015, 10:55 AM
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Usually ailerons are found on higher performance machines while rudder control for turning is found on lower performance machines.

Several factors to consider here.

1. Rudder alone for turning is lighter weight
2. Rudder alone for turning is simpler
3. Rudder alone for turning works well on aircraft designed for it
4. Rudder alone for turning is usually more effective than ailerons at very slow speeds
5. Glider wings are long and thin and usually not as stiff as power plane wings. Hard to hide the aileron servos or you need very long torque rods.
6. A thermalling glider fliies at a speed very close to stall for minimum sink, an aileron moving up will decrease lift on that wing panel at a time when maximum lift is required.
7. 2 Ailerons are higher drag than a single rudder, considering wing/aileron gap.
8. Gliders are generally not designed for aerobatics so ailerons are not required.

Having said all of this, ailerons DO have their place on HIGH PERFORMANE gliders. They allow the modification of the airfoil for launching and thermalling, they allow the pilot to apply high drag on demand by both ailerons moving in the same direction together and they are very effective at higher speeds used to travel from one thermal to another. They are also great fun for gliders designed for aerobatics and slope flying.
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Old 06-20-2015, 05:01 AM
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Originally Posted by Aquila1954 View Post
You do need to put washout in the outer wing panels. These things were known to tip stall. I have one and fly it quite often. If it is trimmed out and the wash out applied the plane flies great.
The Introduction F5J is slightly larger than you asked for, but it seems to be a model who lives up to it's name: http://www.hoelleinshop.com/Models-H...=12327&p=12327

From the same producer - which is very well renowned here in Europe - is also the Climaxx Evolution and Thermal Instinct:
http://www.hoelleinshop.com/Models-H...=12327&p=12327


http://www.hoelleinshop.com/Models-H...=12327&p=12327
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Old 06-20-2015, 12:33 PM
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Originally Posted by YellowBlueBird View Post
While looking for a sailplane with ailerons observed that most don't have them. ?

Is there a kit sailplane with full house controls?
Time for me to jump in with my 2 cents.

I belong to a glider club and fly gliders and e-gliders 90% of the time. I have a fleet of molded high end competition gliders as well as wood and foam gliders.

Gliders can have whatever controls you like and you should have no trouble finding just about any combination you wish:

R/E
R/E/S
R/E/A
R/E/F
R/E/A/F
R/E/A/F/S
Elevons (Flying Wings)
Rudervators (V Tail)

With or without motors for launching.

You say you have a Spectra. That is the motorized version of the Gentle Lady. Are you still flying it with the old brushed motor and NiCd batteries? If you are you should at least toss the NiCds and switch to Lipo batteries to save 8-12 ounces. Makes a HUGE difference in how the glider will fly and thermal. If it doesn't have a motor than it is a Gentle Lady or a converted Spectra.

If you are having problems with it tip stalling the inside wing in a turn then you are likely flying too slowly for the weight of the glider. Adding some washout will help but really this is a piloting error. Or you may have it set up nose heavy in which case it will tend to drop the nose into the turn if you get it getting too slow. That is a set-up error.

Now, whatever control you want, you can have them.

R/E gliders are extremely popular because they fly so well and because they thermal so well. The high dihedral wing that is required for a R/E only glider also makes it very stable and easy to fly. When you fly them high and out far, near visual limit, the R/E high dihedral design makes them very easy to control and to see.

If you are shopping for full house gliders, RES, R/E or any other combination these sites offer a nice selection:

Esprit Models
http://www.espritmodel.com/

Kennedy Composites
My Supras, Blaster 2 and AVA are from Kennedy)
http://www.kennedycomposites.com/

Art Hobby
http://www.arthobby.com/

Soaring USA
http://www.soaringusa.com/


Let us know if you find something at one of these that strikes your fancy.



If you are interested, here is my fleet. Does not include some small electric planes or micro helis.

I have a Spirit, which is a 2M R/ES glider that is similar to the Spectra, but ho motor. I used to put my Spirit into a thermal, put in a click or two of rudder trim, and let it fly itself while I put the radio on the ground and had lunch. Wonderful. In addition to the Spirit I have a Radian R/E/motor glider, An AVA and a Bubble Dancer, all of which are RES gliders.

My DLGs, 1.5 M discus launched gliders, tend to be R/E/A where the ailerons are full span and can be set up as flapperons. I have a Blaster 2 and an XP5.

I have one 1.3M R/E/A/Motor glider called a sky runner. This is more of a warmliner than a thermal glider.

Then I have 3 Supras, a Stork, a Mantis and a Graphite which are all high end full house gliders between 3.2M and 3.45M for the winch.

For one Supra and the Mantis I have a pure glider fuse and an electric glider fuse that share the same wing.

I have a 3.4 M Ventus 2C for aerotowing that has R/E/A/F and spoilers.

For the slope I can fly any of the above gliders and often do. I also have a Zagi flying wing (Elevons) a R/E/ailerorn foam glider and a Boomer flying wing (elevons)


Ed

Last edited by aeajr; 06-20-2015 at 12:47 PM.
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Old 06-23-2015, 03:36 PM
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Old 06-23-2015, 03:37 PM
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Old 06-23-2015, 03:38 PM
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Old 06-23-2015, 03:39 PM
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Old 06-23-2015, 03:41 PM
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Old 06-23-2015, 07:26 PM
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Ya know Greg you can put more than one link in a post.
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Old 07-31-2015, 02:56 AM
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Originally Posted by FlyWheel View Post
Sailplanes are designed to fly as efficiently as possible, getting the most lift out of even the lightest thermal. The more control surfaces you have the more servos and linkages you need, and that translates into weight. Really, unless you are flying competition rudder and elevator are all you really need. Some add spoilers to get the planes back down if it gets into a really strong thermal.

Going back some 20 years ago I heard the same comment from several different glow Pilots while flying my full house ( six servo) 3 meter SailPlane , "wow this flies just like a real plane ( meaning one of their models )".
So yes there is a difference, and my first 6-servo 2 Meter was about 10 oz LIGHTER than a Gentle Lady and will still out climb them all day long.
The Real Problem with the older designs of RE's is that they have a much narrower "comfort Zone" when it comes to wind speed. They take a long time to do a 180 deg turn and they are getting blown downwind the entire time they are turning. I've seen people get into trouble try to land in a day that got windy

jim
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Old 03-28-2016, 07:43 PM
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Hey Dave W. I was AFSS 1969-72. DLIWC and Yokota AB. Skivvy Nine forever.
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