Foamie Slopers


A review by Brett Jaffee,
from the July 1995 issue of Radio Control Soaring Digest.

Rubber Duck

Type: Ready to fly elastic tailless slope glider.
Radio: 2ch required (aileron/elevator via elevons with mechanical mixer).
Standard gear okay.
Span: 35"
Airfoil: Modified EH210. 10% thick, 2% camber.
Wing Area: 351 sq. inches.
Overall Length: 18 1/8"
Observed Flying Weight: 20 oz
Observed Wing Loading: 8.21oz/sq. ft.

Several years ago, at the International Model Show in Pasadena, I came across an unusual airplane. It was a tailless slope glider made of a material that I had never before seen used in an R/C model. The plane was the Rubber Duck, a ready to fly sloper designed by Steve Hinderks, and sold by his company, The Birdworks.

The plane seemed perfect for slope combat or just for fun. It also looked like it would make a great "pathfinder" plane, i.e. the plane you throw off the cliff to check out the lift when you don't want to risk your multi-hundred dollar composite glider. With this in mind, I finally decided to take the plunge and try out the Rubber Duck.

The Rubber Duck arrived at my house in a large, odd shaped box. Even though it's an RTF type plane, I had still expected to find at least a few bags of hardware and assorted parts when I opened it up. I got a surprise with the Duck, though, because I found only two items: an instruction sheet and one fully assembled airplane. Everything needed to fly the plane (except the radio) was already installed, including the control horns, push rods and clevises. The Rubber Duck is 99% ready to go. All that's needed to get it flying is to push your radio parts in place and hook up three clevises.

My first impression of the plane was that it appeared to be very well made. The foam wings were immaculate, with a smooth, even surface and no warps or other imperfections. The foam was firm and resilient, almost like that used in Nerf footballs, but denser. The installed balsa elevons were fitted perfectly to the wing and hinged at the top with fiberglass filament packing tape. The black triangular fin plates which capped the wing tips were made of a different type of foam than the wing, but they were also tough, yet flexible. Their trailing edges were capped with tapered balsa. Made from yet another type of foam, the stubby gray fuselage seemed a bit softer then the other components. It had holes pre-cut for the servos, elevator, and battery.


The two pre-cut servo holes in the fuse are sized for standard servos, which simply press in place. Small holes have been provided between all the radio equipment cut-outs to allow the servo leads to be routed through the fuselage.

Located up front is the pre-cut battery bay, which will hold a 500 mAh square pack tightly. Steve recommends gluing the battery in with either hot glue or contact cement in order to add strength to the forward fuselage

The receiver cut-out appeared to be sized for the typical seven channel FM unit. Since I was using a Futaba four channel AM receiver, the hole was much too large. In order to get a good fit, I cut up a piece of the discarded foam plug material that had been in the radio holes when the plane came out of the box. This gave the receiver a tight and secure fit. A nyrod, which I tack glued to the side of the fuselage, was used to allow the antenna to trail out beyond the elevons.

Once the radio is in, it's a simple matter of connecting the servos to the push rods. The push rods control the elevons via a mechanical mixer, which comes already installed. The mixer consists of a couple of brass parts that link the elevon horns and push rods. It is simple and elegant, and worked flawlessly the very first time it was connected.

The instructions are somewhat vague about control throws. They simply state to use a small servo arm for novices, or a big arm for experts. Feeling fairly confident, I choose the biggest servos arms that I could find. Next, I set the elevons with a bit of reflex, as is indicated in the instructions. This is set by placing a straightedge across the top of the wing and measuring the gap between it and the hinge line.

With everything in place, I checked the balance. The CG is located 1 3/8 to 1 3/4 inches behind the leading edge. My plane balanced towards the rear of this range, with no additional weighting required. Final flying weight was 20 ounces.

For finishing the plane, there is the option of reinforcing the fuselage by wrapping it from the nose to the leading edge of the wing with electrical or cloth tape. For the initial flights, at least, I chose not to do this. The wing can also be painted, if desired, with enamel or epoxy paint.


The first trim flights were made at our local hill, which has a steep grass and brush covered face that rises approximately 150 feet from the ground below. Upon arrival at the slope, we found that we had zero wind, so the Duck was taken to the top of the hill and simply heaved off. I wasn't sure what to expect, having never flown a tailless airplane before. The Duck held no surprises, though, as it glided easily down the ridge, with the controls being responsive, even at slow speed.

The wind did eventually pick up, but lift conditions were less then ideal. I estimated the wind speed at about five mph, with the slope lift being relatively weak. During these flights, I noted that the Duck needed absolutely no aileron trim changes, however, it was taking increasing amounts of elevator trim to remain airborne. The glider would continue to descend, and after a few turns in the pattern, I would be forced to land on the face of the hill.

Eventually, the wind picked up to ten to fifteen mph, and the Duck began to feel more in its element. I was now able to easily keep the plane in the pattern. In flight, as on the ground, the Rubber Duck a unique-looking airplane. Everyone seems to have an opinion about what it looks like. One friend said it looked like a space ship or U.F.O., while another commented that it resembled a flying TV dinner tray. Personally, I think it looks like the nose from an IndyCar. It certainly doesn't resemble anything else you are likely to see on the slope.

Despite having no dihedral, I found the plane stable and easy to fly. Stalls are gentle, and the plane tends to mush forward without falling to either side. It also seemed very resistant to tip stalling. One of the things I found interesting is that the Duck will begin to bob its nose up and down before the onset of a stall. The plane does not like to be given large elevator inputs, especially at lower speeds. A "bank and yank" type turn will result in a few pitch oscillations before the plane loses most of its speed and sort of skids around the corner. Keeping the elevator movements small, smooth, and progressive is necessary to get tight turns when flying slow, though this isn't as critical when the Duck is going faster. Despite this it is very easy to fly the Duck though a tight pattern. In better lift, the Rubber Duck will carve through the turns nicely.

One consequence of the Duck's pitch response is that loops can be a bit tricky to do. At first, I found it hard to get the plane through the top of the loop. Often, it would get to the top and stop before getting completely on its back. This would result in the plane somersaulting through the last half, rather then completing a smooth circle. Once I got the hang of using the elevator correctly, though, I was able to perform loops properly


The roll rate is fairly fast, but not blisteringly so. Rolls that the Rubber Duck produces in lighter lift conditions are from axial, needing quite a bit of elevator correction throughout to keep the plane "on a wire". They tighten up as the plane gets some speed going, though, and I eventually found myself confidently rolling the plane while flying only inches off the ground.

Inverted flight is possible, but it does take a fair amount of lift to get it to maintain altitude. Quite a bit of down elevator is needed, but the plane is very easy to fly upside-down.

Eventually, I got the opportunity to test the Rubber Duck on a high-wind day. One thing that becomes apparent is that relatively large trim changes are needed for varying conditions. In light wind, quite a bit of reflex is needed in the elevons. As the lift improves, much or all of the up elevator can be neutralized.

The Duck will never break any speed records, but unbalasted, it still moves around at good clip in high wind, and penetration is good as well. When doing a high speed dive, I found that the plane was becoming overly pitch sensitive, as though it were tail heavy. To counter this, I taped a half ounce weight to the nose, which smoothed everything out. This weight was removed when the lift got light, as it tended to make the turns more sluggish at low speeds and increased the amount of up trim needed when the wind started to taper off.


The Rubber Duck has held up remarkably well after being put through a great amount of intentional thrashing and abuse (see sidebar). The bottom of the fuselage had some gouges caused by slide-in-the-dirt landings made before it was tape-reinforced. One of the balsa trailing edge fins had broken off early in flight testing but it was easily glued back in place. The surface of the wing got a few small punctures, caused by crashes on sharp twigs, as well as some scratches caused by mid-air collisions. The leading edge did pick up a few nicks before I taped it, but over all, it held up very well, showing no obvious areas where impacts have occurred. What's interesting is that when the wing gets dented, the foam in the damaged area will often expand back to its original shape after a few hours. Aside from the broken balsa trailing edge fin, the only repair I had to make was a quick one to the wing center and saddle. Early on, it appeared that the seam between the two wing halves had widened a bit, and the wing seemed to be a bit loose on the saddle. This problem also occurred on a Rubber Duck owned by a friend and another one I saw as well. It was quickly fixed with a few dabs of hot glue in the affected areas (you can use contact cement for repairs too). The problem has not reoccurred, despite even more harsh punishment after this repair was made.


The Rubber Duck is an extremely fun little sloper, a real grin machine. In the course of writing this article, I let about a half-dozen people take the controls. Without exception, they said that it was a neat plane to fly, and all commented on how much they were impressed by the unusual construction materials. It is one of the most durable gliders that I have ever flown. This plane laughs at danger and shrugs off crashes, whether they are from mid-air collisions, or dumb-thumbing into the ground. What this does is make the Duck a totally care-free flying machine. It's ideal for the times when you just want to have fun buzzing the slope just inches off the ground, do a little combat with you buddies, or simply relax after flying your expensive, high performance gliders. The ability to absorb mistakes, along with its stability and friendly personality seem to make the plane a good aileron trainer. In fact, I've seen a couple neighborhood kids use it successfully as a first airplane. The Rubber Duck's unusual design is sure to attract attention anywhere it flies, and it's small size makes it very portable. In fact, you can just throw it (literally!) into the front seat of you car.

I feel that the Rubber Duck is also a great deal, at $55 (plus shipping). For that price, you get a fun flying airplane that is 100% assembled right out of the box, and can be made ready to fly in less then thirty minutes. The Rubber Duck is available from The Birdworks, P.O. Box 1302, Port Orford, OR. 97465, or call Steve Hinderks at (503)332-0194. It is available with either red or blue wings.


What's the point of having a "bouncible" slope glider if you don't try to bounce it once in a while? With that it mind, my friends and I put the Rubber Duck through the wringer.

The first step involved touch and goes in the brush and some target practice. The Duck excelled at this, and seemed to have the unusual ability to skim through the grass for relatively long periods before pulling up and flying off. Next, an aluminum can was set up on top of a tall, thin branch, and the Duck was given the job of knocking it off. It was very easy to line the plane up to hit the can, though in many cases it ended aiming slightly low and hitting the branch. At one point, the branch knocked it out of control, and the plane cartwheeled into the thick skull of the unsuspecting photographer (me) before tumbling across the ground. There was no damage to either the photographer or the Duck. In a later, slightly more successful attempt, the Duck managed to break the twig in two and send the can hurtling skyward. I was able to snap a picture of this at the instant it happened. The photo showed off the Duck's amazing resiliency. In it, the plane's wing can be seen being heavily deformed as it hits the branch. Despite this, there was no evidence of leading edge damage or deformity on the wing. The plane is truly an "elastic sloper," as the manufacturer claims.

The final step was combat. Although it seemed capable of absorbing plenty of abuse, I decided give the Rubber Duck some extra reinforcement. I wrapped the forward portion of the fuselage with red duct tape in order to prevent the possibility of it being torn in a mid-air or the resulting crash. I also taped the leading edge of the wing. Because the trailing edge of this plane would be totally exposed in the event of a rear-end collision, I felt that it would be a good idea to reinforce this too, so I taped the balsa elevons with two layers of heavy, clear packing tape.

The Duck proved itself to be a durable and tough plane in combat. When hit, it usually simply bounced off the other plane. A hard enough hit would knock the Duck out of control, sending it spinning like the rotor of a helicopter. Often, the Duck would recover and continue to fly while the other plane involved would go spinning into the ground. About the only thing that's really tricky to pull out of is a collision that puts the Duck inverted and at low altitude. One thing I really liked was the Duck's unusual ability to get into the area between the wing and tail of conventionally designed gliders without getting tangled up. Usually when this type of hit occurs at lower speeds, the planes tend to lock together and spiral to the ground in a deadly embrace (okay, so maybe it's not all that dramatic, but it looks cool when it happens). Since the Duck has no tail, it would not lock into the other plane. Instead, the victim would be sent cartwheeling or spinning, while the Duck flew on like nothing had happened.

Although we usually try to avoid them, head-on collisions eventually occur. The Duck took some horrendous head-ons in the course of combat testing, both with other types of combat gliders as well as other Rubber Ducks. These hard hits at low levels would often end with an equally horrendous impact with the ground. Despite this, nothing on the plane ever actually broke off. Time after time, I would watch the plane hit the slope, and then be amazed to find it on the ground, undamaged. With out a doubt, the Duck is one "bouncible" airplane.

Note: The Birdworks no longer makes the Rubber Duck, but they do make an improved version called the "Geek." Check it out on the Birdworks The Birdworks webpage