Text by Budd Davisson, Sport Aviation, Oct, 1997, Photos: Jim Koepnick, EAA
| The Ellipse kits may or may not be available by the time you read this. These kinds of projects,unfortunately, come and go. |
The Ellipse Some people whistle, play piano or watch television, when they have a few free moments on their hands. Not Dean Wilson, of Grangeville, Idaho. Best known as the father of the Avid Flyer, Wilson designs airplanes when things slow down. Lots and lots of airplanes. He explains, "I design a new airplane every two or three months, then every five years or so, I take the best one and build it. I think when you die and go to heaven, your reward is you get to build airplanes. I like the mental challenge and can't think of anything I'd rather do."
A self taught engineer ("...I quit school to go to A and E school), at one point Wilson held more STC's for light aircraft modifications than almost anyone. He's also designed and built a sizable number of aircraft ranging from the little Avid Flyer to the immense Eagle Ag plane. The most recent of his designs to see light under its tires is the Ellipse, a relatively unique appearing four-place, 150 horsepower airplane with folding wings. Just saying it is a 150 hp four place, homebuilt makes it unique enough, but the rest of its features make it a very singular breed. "I looked around and decided I didn't want to design a 172," he says, "because there are ten million of them out there. It looked to me as if there is a need for a fast, low-powered four place, especially in Europe where gas prices are so high." In pursuit of his goal of speed with low horsepower while still being able to carry a sizable load, he gave his airplane relatively long, narrow wings with an elliptical plan form. "The elliptical wing is the most efficient shape because of the relationship between the lift distribution and the drag," he says. "Then, combine that with high aspect ratio and low span loading to get a good rate of climb. With a Hershey bar wing, you'd have 22% more wetted area and drag. Square wings are cheap to build, but, as the price of fuel goes up, you can afford to spend more time building the elliptical wing for better performance." The wing's aspect ratio is a relatively high 10 1/2 to one with about 25% of the trailing edge being ailerons. The flaps take up the rest of the wing and only deflect to about 15 degrees. Total wing area is 128 square feet. Every designer uses the materials with which is he most comfortable, which in Deans' case, means rag and tube fuselage and wood wings. The wing is skinned in 1/16", 45 degree mahogany plywood which raises the inevitable questions about the compound curves normally required when skinning an elliptical wing in wood. First of all, the builder doesn't have to worry about that because in the kit the wings come completely fabricated and ready for finish. Even if the wings were scratch built, however, the builder would find that Wilson has come up with a clever way of handling the compound curve problem: The leading edge is not a single, smooth curve, but tapers back in several steps. This allows the skins to wrap back from straight sections at an angle which eliminates the need for a compound curve. The first joint is 72 inches in from the tip and then every 42 inches from there on to the root and the ribs are eight inches on center.
There is a span-wise stringer every two and a half inches as you move across the chord, which means there are a lot of stringers. About half of the stringers run out of the leading edge before reaching the tip. The box spars are at 15% and 65%. Dean says, "There are one thousand forty-one pieces in each wing panel, including 25 different ribs because of the elliptical plan form. That's one reason we complete the wing for the builder." The fuselage is typical Wilson, with a multitude of smaller pieces of tubing rather than a smaller number of large tubes. This gives a lighter, stronger structure, but adds to the complexity. Here too, however, the builder doesn't have to concern him or herself with that because the fuselage comes finish welded. The fuselage is 43" wide in front and the back seats are another inch wider. The front door is on the left, so the pilot can load his front seat passenger first and then climb in. The back seat is entered from the right. The door hinges up completely out of the way, which makes getting into the airplane much easier then in some aircraft with normally hinged doors.
Certainly one of the first things people notice about the airplane is its rather unusual struts. There's a reason they are shaped that way: When the wings are folded, the back strut conforms to the fuselage side which lets the wing tips come almost completely against the vertical fin. For the rear strut to be bent in that manner requires additional bracing in the middle of the strut which makes for a very high drag arrangement. Rather than leaving the tubing intersection out in the wind, Wilson faired it over. The small slot is a handhold for folding the wings or moving the airplane. I forgot to ask, but since it's a stressed skin wing, it may only need a single strut for flight but needs two to safely fold the wing. Folding the wings requires pulling a safety pin out of each spar-pin in the cockpit and inserting a small tubing handle in a slot in the wing root to lever the spar-pin out. The controls automatically connect and disconnect. With the pin out, the wing easily swings back where it lays against the vertical fin and is held in position by a simple triangular tubing truss. The process takes about 90 seconds per wing including putting the truss in place. Wilson then bolts a long, narrow, tubing truss tow-bar to the bottom of the rear fuselage and tows the airplane on its main gear. Wilson carried the elliptical low-drag shape over to the tail surfaces. At first they don't look elliptical, but that's because he put a slight peak in the tip of the trailing edge of each for appearances sake. The engine in the prototype Ellipse is a dead-stock 0-320 out of a Tri-pacer. Wilson says the builder can use anything from 125 to 200 horses in the machine. After flying it, we can state categorically that 180 hp up would make this airplane into a near rocket ship because with just 150 hp, it really gets the job done.
When I backed up and sat down on the seat to swing my legs over the stick and inside, I noticed the tachometer showed only a single tenth past exactly 100 hours indicating how much time they had on the airplane. 45 of that 100 hours was spent doing performance testing so they could give their performance numbers to the Oshkosh audience with no fear of being wrong. Glancing at the charts they had developed, it was obvious that what ever performance numbers Dean gave were accurate. When sitting in the airplane, you're immediately aware of how bright and uncluttered it feels. That's partially because the sheet metal framing around the windshield and windows is extremely narrow and doesn't obstruct vision at all. Also, you sit fairly high in the airplane and the windshield wraps around and down quite a ways. The result is great visibility. The nose just barely cuts into the ground visibility but slopes to the sides so quickly, you can see most of the runway around the edges of it. After we lit the fire under the Lycoming, I unconsciously glanced up at the slots cut in each wing root over our heads. I could easily see the safety pins in place which kept the wing locking pins from moving. At the same time I checked the sight gages on both wing tanks. These tanks feed into a header tank in front of our knees for a total of 41 gallons. That's something like five hours of fuel. The header tank is interesting because the sight gage is not only marked in gallons, but the last few gallons are subdivided into quarts. It looks as if Dean likes to know exactly how close to running out he really is. Dean had just topped the tanks and, with the two of us on board ,we had used up only about 650 of the 1023 pounds of useful load available. Figuring another 350 pounds for back passengers that would still leave another 25 or 30 pounds for baggage. Taxiing the airplane is brain-dead-simple since it follows the rudders so nicely and visibility is so good. Although the panel is fairly wide (it's big enough to easily accept any normal instrument load up to IFR), I was sitting high enough I was not conscious of a blind spot on the other side of the nose, as with some side-by-side tailwheel airplanes. In fact, you're sitting so high, and it handles so obediently, it would be easy to forget you're in a taildragger. Even taking into account that we were only at about 65% of gross weight, takeoff was something of a surprise for only 150 hp. For one thing, acceleration was at least that of a lightly loaded C-182, while the ground roll was hardly worth mentioning. At 1177 pounds empty, the airplane is light, but not overly so, still it got with the program as if it had a 180 on board. I was seeing one of the many benefits of high aspect ratio and low span loading. As we climbed away from the airport, we were showing right at 1000 fpm climb. Dean made that first takeoff, but on subsequent ones, I found the ground handling I'd seen during taxiing extended to the takeoff as well. In other words, my feet weren't doing anything noteworthy on takeoff. During some of the takeoffs and landings we had a slight right cross wind and my feet still weren't getting any exercise. Also, because the visibility, which is already good, increases to a dramatic level as soon as the tail is brought up, there's a tendency to keep the tail a little low so the airplane leaves the ground almost immediately. He's saying it takes 1100 feet at full gross but we were using little over half of that. While we were doing the air-to-air photography with the camera ship, I found the one and only thing about the airplane I didn't like and fortunately it's a fairly easy fix. For my taste (I repeat, for MY taste) the ailerons are too heavy. The pressures coming out of neutral (break-out forces) are higher than with most airplanes and those forces blend into aileron pressures that are equally as high. They don't increase dramatically with stick deflection (the force gradient isn't very steep), they just start at a higher level is all. At first, there's the perception that the airplane has a lower than normal roll rate, which could be expected with wings that long. That however is not the case. The roll rate, when you put your shoulder into the ailerons to get some deflection, is at least on a par with Cessna products, but the higher-than-normal pressures make it seem slower. Dean is aware of this and is working on it. The easiest fix would be spades. The cleanest fix would be moving the hinge point back.
The airplane lets you know immediately that it is much cleaner than most airplanes of its type. In fact, considering the span and strut arrangement, you'd expect it to be a little draggy, but it definitely is not. For one thing, it has absolutely no trouble in giving Dean's claimed cruise of 150 mph TAS at 2,500 rpm. For another, it doesn't like to slow down, when the power is brought back and dropping the nose even a few degrees builds the speed up immediately. When I started setting up for stalls, it seem to take forever to get the speed down under 90 mph and even when it got there, I had to work to keep it slow. This sucker is clean. As the speed bled off, I just kept working until the stick was securely nailed against the stop and I held it there for a few seconds. Clean, we were down around 60 mph and it was only mushing. With flaps full-down, which is to say about 15 degrees, the airspeed would go down another 5 mph and the stall stayed just as benign. Releasing any back pressure at all put it back flying again. I tried to accelerated it in both situations and the stall refused to get any more dramatic. I'd forgotten to ask whether he'd spun the airplane or not, so I didn't do any cross controlled stalls. We did the usual phugoid test thing and upon release at ten knots below trim speed, nose high, it slowly pitched back towards level flight indicating positive static stability, but it wasn't strongly positive. As the nose came down, however, it barely overshot trim speed and settled down to original trim speed in two to three cycles, so it is well within the ball park "normal" airplanes have established as being acceptable. All of my landing approaches involved lots of high angle slips because I couldn't get used to an airplane that glides as well as this one does. Fortunately, it slips as well as it glides. In fact, I found I could slip it right down to the grass off the end of the runway and let it's natural gliding ability carry us to the numbers.
We were coming over the threshold de-accelerating through about 75 mph which gave just enough float to set it up in a three-point attitude. In truth, because you have such good visibility, I had a tendency to slightly over-rotate and tick the tailwheel on first. It's hard to get used to not having the nose up in front of you. Landing roll-out was an absolute non-event. At least once, I got it on a little crooked because of the crosswind, but the airplane didn't want to swerve or do anything out of the ordinary. As tailwheel airplanes go, it has some of the best runway manners the genre' has to offer. It appears Dean has once again accomplished his goals, which in this case, included designing a 150 hp, four-place airplane that would do 150 mph. This is no small task, especially when you're not willing to compromise on low speed handling and landing speeds. He's taken what he's learned over the years and combined it into an airframe that is not only efficient, but can hide in your garage, when it's not out flying. Basically, what he has designed is a truly useful airplane. contact: (This may not be current info)
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