The project plane concept has been alive at Tri-State Kite Sales for many years. As a long time dealer for the Quicksilver line of aircraft, I always felt that given the chance, I could greatly improve the way the plane feels in the air, handles in the air and on the ground, plus improve the long term quality of the airframe.
With the advent of this sport pilot thing, I also see a great incentive to get the plane back solidly into the ultralight category weight wise.
To this end, I started with a project called 'shorty'. Now shorty was never intended to be a great flyer, although it was. My goal was to make a plane that was low using an idea I had from many years ago. The advent of the double kingpost was a good news bad news thing. The good news was that the overall height was less with the dual kingposts, and the bad news was, the plane got a lot more sloppy in handling and stiffness.
But by incorporating the dual kingpost and a straight tri-bar crosstube, I endes up with a plane just over 8 feet tall, almost 1 1/2 feet shorter than the stock MX series with the single kingpost.
Back in the 1985 production, Quicksilver started making the MXL II with the straight tri-bar crosstube. This design lowered the wire atach point, made for a stronger plane, and a stiffer plane. They deleted the upper tail wire which hurt the overall strength of the plane and the long term quality though. The large diameter prop almost required the wire be removed. I worked an upper tail wire guard into my designs and restored the wire for better preload on the tail parts and better long term quality of the plane.
But back to the project plane. The straight tri-bar crosstube could only be done if the engine were relocated back further on the airframe. Then the tri-bar could be straight acroos without the 8 inch sag built in, and reduce the overall height of the plane. Weight reductions are rather impressive when the wing span, the overall height and the axle width and such are reduced. Another significant reduction resulted from going to the gearbox drive.
One long term problem I've had with the MX and the MXLs is the flexing of the trike portion during aerobatics. I don't mean loops and such but just the normal steep turns and flying we normally do.
The flex can be felt when moving the elevator abruptly, and noting the movement of the throttle assembly relative to the axle strut. I felt that any project plane would certainly need to address this stiffness issue for sure.
Shorty started as a trike only project and ended up being a full plane using a set of pretty grey sails with navy markings. It was intended to possibly be used as a float plane so I had some grey floats started for it. I also installed a yoke that I designed for the MX, MXL series many years ago. IT flew fine, felt great, use a 447 with gear box for power, had a 66 inch prop, got great mileage off the 6 gallons of fuel and all in all, was good plane to fly.
I designed a double aframe trike single place frame for it. This eliminated the flex of the trike during hard maneuvers for sure. The plane felt good and solid even with the 32 foot standard length wings.
This design also eliminated the trike wires in the back from the root tube to the axle and also the pesky lower nose wires that always seem to be in the way during flight and getting in and out.
This picture shows the plane with a pilot standing in front of it. The lower profile is obvious as he can easily see over the wing.
Another important feature is the wide open access for getting in and out. Also see the yoke control. The double aframes are not visible since they are one behind the other. This next picture shows them pretty well.
Notice that the front frame sits just ahead of the gas tank and the aft frame is well behind the pilots shoulders. This affords great access, visibility, and strengthens the frame very well over the double set of wires on a stock plane.
You can also se the clearance above the pilots head. Even with the lower frame height, there is plenty of room for a helmet and movement. The valve for the fuel is just above his head out of the way, but a bit closer than on a stock plane.
This plane was flown by students and rental too. No problems, and most liked the yoke control. The full wingspan made for a bit more trouble in sever turbulence, but the dihedral of the wing was lowered to 4 degrees, half that of a stock Sport single place plane. This made it handle better then with the longer wingspan of 32 feet.
Some small details were worked out on this plane such as the need for a much lower push pull tube location to clear the prop. Rudder cables also got an extra set of pullies at the axle to assure they would stay clear of the large prop.
This plane was never weighed but an idea of the weight compared to a stock plane can be made. First, the gearbox removes about fifteen pounds of weight since there are no belts, pullies, flex coupler, pillow block bearings, root tube bearings or prop shaft. Just a B box replacing all these items. A flex coupler weighs about 8 pounds and the B box is listed at just under 10. The rest of the parts are weight saved using the gearbox over the belt system. The advantages of the gearbox over the belts extends much further than the weight. Friction reductions adds about ten percent to the thrust. Belt slippage is also eliminated using the box.
But the project had showed that a light weight, low plane is possible, flies very well, and also showed the double aframe works extremely well to. Time to get a bit more serious in the overall redesign.
The next plane is still called the project plane, not shorty as the grey one was dubbed. It sports a bright orange sail mainly because I had a lot of orange material and it shows up pretty good too. The wingspan was reduced to 28 feet matching the Spint and Sport. The airfoil chosen was the original MX which offers good top speed and pretty good climb. the Sprint is really slow and the sail on the Sport with all the double surface and zippers adds a lot of extra weight without adding much drag reduction over the old MX airfoil.
The double a-frame was retained, the new 4 degree dihedral was reused, the tail is stock and the overall height is still just over eight feet. Some new items were added to remove excess weight and revise some overall problems with the stock Sprint/Sport. The steering on the stock singles is pretty crappy. It works and is a mile better than none at all, but the rods crossing each other and the need to offset them makes for poor steering one way and worse the other.
I eliminated the large gooseneck with its huge thick plate. The fork was redesigned following a pattern I designed several years ago using only one leg rather than two and an axle. This eliminated a lot of weight, raised the pedals a bit and allowed the steering rods to come off the bottom of the pedals rather than the upper sides. This eliminated the need for them to cross to provide the push right to go right steering we are used to. Lots of weight removed just doing these small redesigns.
The main axle was shortened almost a foot, the landing gear downtubes were made using thinner material, axle struts were also redesigned reducing weight. The final product is shown in the next photo.
I forgot to mention that the ailerons were shortened even more than we normally shorten them. Overall length is about 80 inches. the bellcrank was moved to the outer wing wire to catch the aileron. We used the best of the controls, push rods with rod ends. this eliminated the cables and the hassle during assembly trying to get the last cable on each side attached. Threading the cables through the wing makes the change well worth the extra effort and parts.
This is by far the most maneuverable plane using the quicksilver design, ie, wires and tubes. It feels great with no airframe flexing noticed, steers almost on the inner wheel, takes off in about twenty feet and has an exceptionally low stall speed. Since the design isn't finished, specifics won't be quoted but all in all, it flies very well. One thing that was a bit surprising, the fuel tank on this one is only the legal five gallons. Mileage seems about 2 1/2 gallons per hour or less. The 447 does very well turning the 66 inch prop, quiet and powerful with almost no vibration since the entire motor and drive is mounted on rubber. The prop shaft in the root tube can't match this one no matter how well the prop is balanced.
While many of the design features are considered standard locally, I will list them for those of you that are used to stock Quicksilvers. Push rod aileron rather than cables, rod ends rather than the forks, rudder brace kit, coated rudder cables, B gearbox, rudder plates, rudder horn stiffener bolt, stabilizer ribs, upper tail wires, screw up aft kingpost, double aframe, high rate steering, wide seat, low friction throttle cable, extra shortened ailerons, and a few I can't remember,,,,,,,, One area that doesn't get much attention but creates a lot of the problems with the Sprint/Sport designs is the fact that the dual upper kingposts don't match up to the single aframe on the bottom. This misalignment makes for some serious stresses in the root tube. This causes bending and flexing, and during accidents, the root tube is often bent or just as likely broken. Flexing of the root tube causes the airframe to flex and as the wing wires get tightened, the lower wires, both nose and aft root tube get looser. This allows the lower frame to move fore and aft during harsh flying.
Another area of concern is the lack of upper tail wires. Removing the wires allowed the 66 inch prop to be retained but it removed any possibility of preloading the tail to the rest of the airframe. Without any preload, the bolted junctions get serious additional wear, hole elongation and wear against the sides of the tubes.
With the upper tail wires installed, the airframe is preloaded and there is no movement at any bolted joints until the load is high enough to reverse the load due to the preload. Lower tail tubes, tail brace and diagonals get serious wear without the top tail wires and virtually none with top tail wires.
All in all, this plane is a great success. Meeting the FAR 103 limit of 254 is the goal, and it has been meet. Some small changes are still planned such as a fiberglass engine shroud which removes 4 pounds of heavy sheet metal and smaller tires which removes about 6 pounds. Other changes will require ordering different materials than what I normally stock.
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Tri-State Kite Sales 9230 Caborn Rd S Mt Vernon, IN 47620