Osprey Two (oz8401)

About this Plan

Osprey Two. Radio control pattern model for .40 to .51 power.

Quote: "This mid-wing .45 powered beauty is a real performing aircraft designed by Alex Bouluraight for all-around sport flying, and will sharpen up your pattern maneuvers. Osprey Two by Alex Bouknight.

The mid-wing airplane has long been known to offer some real advantages in terms of aerodynamics over conventional type arrangements such as high or low wing versions when dealing with aerobatics. The longitudinal center of mass is closely related to the position of the wing on the fuselage and is a little above the centerline of the airfoil on a low wing design. This means that there is more of the mass of the fuselage and fin/rudder area on top of this center of mass than on the bottom. When you apply rudder only in level flight, you get what is called rudder or roll coupling. This condition results in an adverse yaw to the opposite direction intended and often drops the nose. This condition shows up on maneuvers like knife-edge or 4-point rolls where cross controlling is needed to compensate for the effect to keep the flight path true.

By raising the wing position to a middle area, it is easier to design a fuselage with a closer to equal area above and below this centerline. This also enables the engine thrust line and the stab to be positioned on this same line which produces fantastic rolls because everything is revolving around a central axis. This eliminates the barrrel rolling effect where the nose moves in a spiral instead of staying on the axis line.

The problem is where to put the radio gear with a wing panel running through the middle of the radio compartment. The answer is to have two separate wing panels positioned on a strong aluminum tube running through the fuselage. The tube gives
the necessary strength to hold the panels and yet does not take up much room in the radio compartment, allowing for a standard radio gear installation.

Two dowels near the leading and trailing edge establish the correct incidence and keep the wing panel from rotating around the tube. The panels are held to the sides of the fuselage with wing bolts running from the inside of the fuselage out into a spruce block in the wing that has been tapped. This makes for easy transport to the field, too, since there are two shorter panels instead of one long wing.

This method of attachment allows for super accuracy concerning incidence and dihedral if you use great care when doing your drilling and layout work. I will explain a little trick 1 used that will produce good results. The tube used is 1/2 in T2024 aircraft grade aluminum and you will need two pieces, one for the actual tube and one for a cutting tool. The aircraft tube needs to be 15-3/4 in long; long enough to run from the outside edge of the #3 rib, through the finished fuselage, to the outside edge of the #3 rib in the other panel when in position. The other tube needs to be about 12 in long. I filed the inside edge of this tube razor sharp with a small pencil file while keeping the outside diameter the same 1/2 in.

After the holes in the fuselage are drilled, this tube can be used to cut the holes in the ribs and ply plates with the wing panel in position. Making sure that your tubes are perfectly straight and the original fuselage holes are positioned accurately, the cutting tool will cut exact size holes in exactly the right place. Block the panel into an accurate position and rotate the cutting tube to cut the holes. This eliminates the problem of drill bits drifting or tearing the edges of the holes. The holes in the fuselage should be drilled undersized and sanded to the correct size using sandpaper wrapped around a smaller dowel. This will clean up the drilled hole and allow for some realignment in case the bit drifted. Take your time here; an accurate fit of the tube in the fuselage will prevent slop in the panels which leads to uncontrollable wing flex in flight.

This system works great when done correctly and very unfavorably when done sloppily. There is a servo in each wing panel connected to a chord to drive the strip ailerons. This will produce very precise, no slop linkages, using a simple wire connecting rod attached to the control horns. The servos should be positioned in the panel so the top edge of the servo case is flush with the sheeting. If the servo sticks up too high, the laminar flow will be disturbed in the form of turbulence.

The airfoil sections chosen are the NACA632A series with the maximum camber at 35% of the chord. These airfoils were designed to achieve low profile drag and high lift while preserving as much laminar flow over the largest wing area possible. I chose to use a root airfoil on the wing panels of 17% with sheeting, and a tip airfoil of 18.5% with sheeting..."

David, Excellent scans! The file contains both the fuselage and the wing. File is bit map (monochrome) and is at 300dpi. Gene

Supplementary file notes

Article pages thanks to hlsat, JHatton.

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