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Copyright 1996 by Leonard G. Barton. Revised 9/30/96

The RC Sailplane Page

New for 2002 Hikenfly, a new design optimized for rough country slope and thermal soraing.

As far as I know these are the first model aircraft plans published on the web. (Let me know if you if you know otherwise. Click here for more info.

Why radio control soaring?

No matter what kind of radio control flying you want to do (power scale, power stunt, helicopter, flatland soaring, or ridge soaring), radio control sailplanes are the best way to learn to fly for several reasons:


Easier to build. No fussing with starting batteries or fuel.

Easier to repair. While radio control boats seldom sink and cars are pretty rugged, when learning to fly model aircraft you will crash (although the frequency and likelihood can be reduced through proper training with an experienced pilot). Since a training glider is much lighter and does not have a powerplant assisting its descent, damage and risk of injury will be less than with a powered model.


No dangerous prop or chopped fingers. A training sailplane will be light weight with sufficient drag to prevent extreme speed build up.

Fewer controls:

A training sailplane will have only elevator and rudder, important when learning to fly.

Less expensive:

A complete training setup, kit, materials, and all essential tools can be had for about US $250 with careful shopping.


My favorite recreation is to hike and fly our Mount Diablo foothill ridgelands. Even flying from a large flat field with a "high start" (rubber tubing and string) will give you plenty of exercise.

Kit, scratch built or ready built?

I recommend kit building for the beginner. Since it is inevitable that you will have to repair your sailplane at some point, you will have developed most of the skills and knowledge required by building from a kit. (By kit, I do not mean assembly of a "Ready to Finish" (RTF) or "Almost Ready to Fly" (ARF) aircraft.

Important note:

Model sailplane construction and operation is both a hobby and a sport. The hobby part is the construction, maintenance, and repair of airframes and equipment, while the sport is the development and use of skills in operation. Although forms of the hobby can be pursued without the sport (e.g., building display models), the sport is most economically enjoyed by involvement with the hobby.

What is the best kit for the beginner?

Features important to the beginner are simple construction, a rudder/elevator design (no ailerons), a thick, flat bottomed wing (for easy construction, low sink rate and to avoid rapid speed buildup). A "turbulated" leading edge, with spanwise square stock across the upper surface forward of the spar will exhibit a low sink rate at slow speed. Foam core wings, while durable, may be too heavy for easy slow flight, and "D" tube sheeted leading edge wings are difficult for the beginner to build and repair.


Good examples of aircraft suitable for the beginner are the "2 by 6" (72 inch span) and the "Pussycat" (2 meter, or 78 inch span, shown above). These have low parts count, simple fuselages of rectangular cross section and simple wing designs with flat bottomed airfoils. The "Gentle Lady", although popular, and flyable over a wider range of conditions, has (in my opinion) an overly complex structure.

Kit modifications and construction

Kits can greatly improved for durability while adding very little weight. Most of the modifications suggested here are to improve durability for rough country flying and beginner's flying errors and to ease repair tasks by localizing damage.

Use spruce in place of some balsa.

A simple change is to use 1/8" spruce for the wing turbulators (in place of balsa) and to use spruce spar caps in all wing panels. The spruce turbulators add little weight in this small size and are much more durable, especially when the wing is handled. Using spruce instead of balsa in the outboard panels will add some weight, but with a big payoff in ruggedness.

Modify the wing leading edges

The Pussycat is designed with cedar arrowshaft leading edges. These leading edges are too durable, in that a collision with a rock or fencepost will often cause the failure of three to five ribs as in addition to a difficult to repair broken leading edge. When building the wing you can easily replace the arrowshaft with 5/16" square hard balsa (reshaping the leading edge notches in the ribs to accommodate this). Combined with fiber tape as suggested below this leading edge will be tough and will localize damage to a small area.



Left view above: turbulators, hard balsa leading edge, "C" beam spar webbing, closed trailing edge.

Right view above: "T" section forward ribs. Red object in wing tip is a glued in push-pin for static balance (balanced prior to covering).

Add underwing rib caps

By removing 1/16 inch from the bottom of each rib (except the center ribs, which are already relieved for the center sheeting), you may then add strips of 1/16 by 1/4 strip stock between the spar and leading edge. This transforms the rib cross section to an inverted "T", which adds much collision strength to the leading edge. You can cut these strips from sheet stock.

Modify the spar webbing

The Pussycat was designed with "I" beam spars, which are not only difficult to build, they are not as strong as "C" spars, where the webbing extends from the top to the bottom surface on one side of the spar. Buy a sheet of 1/16 inch medium hardness balsa for the webbing. The webbing between the top and bottom spars should be extended all the way to the tip. This and the spruce outer spars will make the wing much more durable if the tip is driven into the ground. The grain of the webbing must be vertical - running from spar cap to spar cap.

Modify the trailing edges

The trailing edges of the Pussycat are simple 1/16" sheet forming a triangle open on one side. By closing the open side of this triangle with 1/16" sheet strips between each rib, the wing will be much more durable when handled. Unlike the spar webbing, you do not need to put the wood grain vertical - simple grainwise strips will do.

Tape the leading and trailing edges and the spar caps.

Use a fiber reinforced packing tape, torn into 1/4" strips, to reinforce the transverse wing elements. This will not add working strength but will prevent shattering in a crash and will hold broken pieces together. It is then often possible to repair a damaged wing leading or trailing edge by aligning the parts and using thin CA glue to rejoin the pieces. (Repair of a broken spar is usually more difficult, requiring a sawn scarf (angle cut) joint and replacement section glued with epoxy.)

Modify the after fuselage shape

The after fuselage of the Pussycat (and most other aircraft) tapers evenly to the end. By making the fuselage a little wider near the end and then increasing the taper, the fuselage is considerably strengthened just forward of the stabilizer. This location is a common point of breakage without this modification.


Side view showing fuselage ramp for easy wing pop-off. Rudder is "Bobcat" sized, for use of fuselage with a Bobcat (aileron control) wing. The only substantial difference between a Pussycat fuselage and that of a Bobcat is the larger rudder and the Bobcat has a "T" tail. This "T" tail is fragile, heavy, and not worth the trouble. The main advantage of a "T" tail is that it is up out of long grass and twigs. This is more effectly addressed with a "V" tail (to be the subject of a future page).

Aircraft shown is entirely scratch built from dimension materials, with 1/32" plywood fuselage and other modifications described here.

Modify the fuselage at the wing leading edge

The fuselage of the Pussycat hooks the leading edge of the wing. This is a bad design feature since a hard nose in into the ground (common in ridge soaring) can break the wing, rather than allowing it to pop off. Instead of this hook, modify the fuselage to form a ramp, where the wing can slide forward and upward. If you do not like the appearance of the gap formed, add a fairing to the wing. Filling this gap is not recommended for a trainer since it will inhibit wing rotation about the fuselage when a tip digs into the ground.

Modify the wing hold down pins


The wing hold down dowels across the fuselage accept rubber bands across the top of the wing. In an extreme crash the rubber bands will break, but a more readily releasable wing can be obtained by using short angled pins made from the same material. The rear pins (not shown) point backward. These pins should anchor both in the fuselage side and in the nearby transverse bulkhead. Glue them in with a little 5 minute epoxy.

Use piano wire in tubing

Also seen in the previous picture is part of the wire control system. I use the inner (moving part) of a Nyrod(TM) as an outer guide for a wire pushrod, with an appropriate attachment to the servo arm. These are readily adjustable and are much more stable under temperature changes than is the nyrod, while being much lighter than steel cable in plastic tubing. Short segments of nyrod are used where the wire is accessible, with a continuous segment in the tailcone. An alternative (used in hand launch gliders) is to use short segments of aluminum tubing as guides, with no ability to remove and rethread the wire. It is best to be able to remove the wire since it can rust and may need polishing or replacement.

Add fuselage gussets under the wing.

The fuselage opening under the wing has a central bulkhead. By adding a triangular gusset inside the fuselage between this bulkhead (on the after side) and the fuselage side, the fuselage is greatly strengthened. These gussets increase the resistance of the fuselage to twisting, which is one of the failure modes in an extreme crash. You can also add a simple cross panel gusset at the after end of the fuselage opening (just under the trailing edge of the wing).

Build a lightweight plywood fuselage.

A durable, lightweight fuselage may be built of 1/32" spruce plywood, edged with 1/8" spruce. The spruce edge stringers are doubled at the equipment hatch and wing opening. The portion of the sides under and forward of the wing should be infilled with 1/8" balsa, with the grain vertical. While not trivial to build, such a fuselage is lighter than a "light ply" fuselage and is much more durable than either balsa or light ply. In general, keeping the after part of the fuselage and empenage light will greatly reduce or eliminate the need for nose ballast. Any weight saved on the tail will thus be multiplied in overall weight savings. It is possible to build too light, resulting in a lack of penetration and a tendency to wallow in flight, so don't go overboard. Light weight construction is much more important for "Grenade Launch" (hand launched) gliders.

Use cloth "Z" hinges.

You can heat seal two 1/2" wide strips of heat shrinkable polyester cloth covering material together (glue side to glue side on a 1/8" overlap). Be sure that you have a strong joint. Cut this into 2" strips and use for "Z" hinges. Use shorter length strips at each end of the moving control surface. These provide both hinging and aerodynamic sealing and unlike mechanical hinges, strengthen the related components (stabilizer/elevator or fin/rudder). Note that this is not recommended for use on powered aircraft.

Use "Eilen's Tacky Glue" for wing and empenage.

Available at craft shops, this glue is appropriate for wing and empenange construction. It dries to a tough and somewhat flexible joint, reducing the tendency for wood to fail just off of the glue joint. It is a water based glue and so is easy to clean up. (It is also ideal for attaching bubble canopies as it dries almost clear.) Unlike CA, it looses weight as it dries.

Use thick CA for other construction.

Thick Cyanoacrilic glue will not soak into the balsa and will reduce the overall weight of your model. It can also be used for tacking in combination with Eilen's glue, giving the advantage of fast, pinless construction and light weight with toughness

Save your wing rib punch-outs.

Most kit plans do not include drawings of every different rib. Carefully preserve the sheet from which the ribs were removed. By carefully removing the ribs the remaining material will form a useful pattern form making whole or part replacement ribs. If your kit has loose (usually pre-sanded) ribs, trace each distinct rib shape onto paper before use.

Add keys to ensure wing alignment.

Add some small, low protrusions on the bottom of the wing that will ensure accurate alignment. If you use protrusions, be sure that the wing can still rotate and slide in a hard landing without damaging any components. Better yet, you can simply add some alignment marks which you check before every launch.

Wing building tips.

Click here for wing assembly tips. This improved method may help you build a lighter, stronger, more accurate and more easily constructed multi-panel wing.

Align and balance.

Make sure all surface are free of warps, that the wing is balanced from side to side, that the fore and aft balance (CG, or Center of Gravity) is where the designer specified (in a fore and aft sense), and that the stabalizer is parallel to a line across the wingtips. While a little nose heaviness can make the aircraft more stable in pitch, moving the CG back of the design location (typically 25% of chord for a trainer) can result in an unflyable aircraft.

Flight trim.

A pilot with basic flying skills can fine tune the center of gravity by observing the flight response. This is best done by ridge soaring, where you can fly the aircraft back and forth and observe the pitch response at eye level. First adjust the pitch trim control on the transmitter for level flight at moderate speed. Pick up additional speed by flying a shallow dive and release the control. The aircraft should gently pull out into a shallow climb. If it pulls up sharply, you have too much nose weight (the center of gravity is too far forward), while if it continues in or steepens the dive the nose is too light. While this may not seem sensible at first, consider that additional nose weight is countered by additional up elevator in level flight. This up elevator becomes more effective as speed increases. You may notice that even though the aircraft will recover by itself from a shallow dive, it will not self recover from a fast, steep dive. The reason for this is that the center of lift moves aft as the angle of attack decreases. The angle of attack decreases because the required lift is produced at a lower angle due to the increased speed. The aftward movement of the center of pressure is a characteristic of asymmetrical airfoils, such as the flat bottom wing used in a trainer.

Assuming that the rudder, fin, and stabilizer are properly aligned, then if the aircraft tends to turn in a dive then the wing is warped. If the aircraft tends to turn to one side when the aircraft is slowed, then the wing half toward that side of the turn is heavier than its opposite (the center of gravity is not on the centerline).

Flight rules.

Beginners should find an experienced pilot to guide them. It is especially important for a beginner that the aircraft be properly set up and trimmed. Do not fly in conditions beyond your capability. Repairing damage can be time consuming and frustrating to a beginner.

Before each launch, put up the antenna, turn on the transmitter and receiver and check that your controls operate. This will keep you from launching into free flight.

Inspect your aircraft after every hard landing. Damage, even if minor, should be repaired before flight. If you think you want to do field repairs, carry a sharp knife or razor blade, thin CA, thick CA, accelerator, and transparent tape.

Rough country flying tips.

If you intend to carry your transmitter about (and your plane is not flying), put the antenna down. (This absolutely requires that you put it back up before your next flight!)

If you are carrying your plane on a steep slope, hold it on the downslope side. If you slip and fall, your feet will go out from under you in the downslope direction and you will land upslope and not atop your glider.


I have found the "Stylus", a one meter designed for hand launch, an excellent "Hike and Fly" plane. Not intended for beginner construction, it is difficult to build to its 11 ounce (308 gram) design weight, but that doesn't matter much for hike and fly. Mine is 14 ounces (392 gram) and is flyable over a wide range of terrain and wind conditions. It uses "micro" servos and small battery pack, but a standard sized receiver. The ability to toss it to a reasonable altitude is very useful when hiking ridge tops under light or no wind conditions, while its small size light weight, and pop-off wing give it an unexpected ruggedness (mine has spruce leading edges for this type of flying). The big advantage of flying this kind of ship (no ailerons) is that you can "park" it in the air. You can set up a stable course and take your eyes off of it long enough to ensure your footing (or even enjoy the view) while moving about. This is not practical with a low dihedral aileron ship, which must be flown at all times. The small wingspan aids in carrying the ship through brush, where a 2 meter ship is inconviently large.

The design and construction of a slightly larger, easier to build ship for this use will is now in progress as noted at the beginning of this page.

Bungee launching (high start)

You can fly from flat fields using the equipment and methods shown here.

For more info e-mail me with subject "RC Sailplanes" at the address shown below in the graphic (this is to foil spambots, net spiders that collect e-mail addresses for mass mailings). Note that our politicians won't stop spam (they could) - $why not?



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