This is basically the way the air flows across the wing when the wing is at flying level and there is no yaw (This assumes a 2D model with no circulation around the wingtips). With a pen, draw lines that are parallel to the centerline of the wing/fuse on the paper. Take two pieces of paper that are stiff enough to hold some shape.Some paper models best illustrate the concept. He informed me that he used the dihedral joint method of glider washout technique in the early 1950’s. He believes to be the originator of the technique. ** I recently received correspondence from Lee Hines. Ron Whitman’s Super Sweep model had this feature, but it’s unknown whether he originated this idea.** After spending many hours talking to some great modelers about this subject, it was concluded that cutting the dihedral skew to the centerline of the wing can add washout or wash-in. Recently, in the last 30 years, many glider designs cut the dihedral joint (poly-dihedral designs, outer dihedral joints only) skew to the centerline of the wing. Still, an approximation is better than nothing and some numbers are needed, so intelligent design choices can be made. The angle of attack typically decreases as you move to the tip of the wing this is not a constant number using the typical washout method. Now, this is an approximation, since wings are typically tapered or some other interesting elliptical shape. Therefore, the change in angle of attack is: To get an average angle of attack, the dimensions were taken at the midpoint between the dihedral joint and the end of the wing. The following dimensions are taken from Super Sweep plans. Tan = height washed up (H)/wing chord at this location (Wc) Next, set a line that passes through the front point of the leading edge and trailing edge where the trailing edge has washed up. Calculate the angle between these two lines. To calculate the washout in terms of angle of attack, set a reference line that passes through the front point of the leading edge and trailing edge of the normal airfoil. To quantify the washout using this typical washout method, it was decided that the change in angle of attack is the parameter of most interest. To calculate this change in angle of attack, some trigonometry was applied. Typical Washout Methodįor years, washout appeared in many glider designs. Bending or sanding the wingtips at the trailing edge up about 1 / 16” added washout. This was thought to improve the glide of the model, along with the transition from launch velocities to glide velocities. The disadvantages of washout are added drag, and the possible added roll to the model. Bending tabs on any flying surface is thought to be very velocity dependent. This means that the characteristics of the model will change dramatically with velocity. Since gliders go through a large range of velocities, this is thought to be a concern. Also, at high velocities, the concern of the up tab bending or flexing is an issue. When parts of a glider flex/bend or the model is velocity dependent, the trimming of the model becomes very difficult. The other is to cut the dihedral joint skew to the centerline of the wing. One method is the typical way of shaping/sanding the wingtips. Yaw makes the washout issues even more complicated, so to keep things simple, no yaw is made.Ĭurrently, there are two methods typically used in glider designs to add washout to a wing. Also, it is important that both wingtips are washed out equally otherwise, a roll or aileron effect is created. Angle of Attack” graph to understand why this theory is believed to be true. It is believed that washout is desirable because the tips stall first and putting the tips negative, compared to the rest of the wing, prevents this from happening. When discussing glider designs, whether indoor or outdoor hand launch gliders (HLG) or catapult launch gliders (CLG), the subject of washout is typically brought up. Washout is usually thought of as twisting, shaping/sanding or adding an up tab to the trailing edge of the tips of a wing, so wing tips are at a negative angle of attack, compared to the root of the wing. Originally by Kurt Krempetz for AMA Glider

Homemade hang glider plans