Incidence Angle
It is confusing at first but is critical to understand and get right. Remember the water skier analogy? A water skier is pulled at a point above the CG, drag occurs below at the water, skis angled up relative to the line of pull by the boat.
Understanding that helps makes sense of why the angles are different for low wing, mid wing, biplane and parasol winged aircraft. A line through the motor to the tail for a low wing plane such as the P51 is the line of force and very similar to the skier. The wings are like the skis and are tipped up. That is a positive incidence angle relative to the stabilizer set at zero (the water's surface is at zero). The motor is downthrust 2 degrees. This creates drag at the TE of the wing and the tail surfaces to keep the plane straight and level.
A Parasol wing plane is quite different. The drag of the wing is above the line of force and will tend to pitch the nose up so the wing is set at zero, the motor downthrust might be 3 degrees, and the stabilizer might be set -1 degree to keep the nose down.
A biplane should be set with the wings parallel with the stabilizer with the line of force running right through the CG to the tail. There is drag above and below the line of force. Giving 1-2 degrees up elevator and 2 degrees downthrust will give stability and level flight. It is much easier to set the wings parallel with the stabilizer and then add some up elevator with a slight bend.
A mid wing behaves much like a low wing plane and should be set with 2 degrees down thrust relative to the stabilizer angle of zero. A low wing plane with its drag below the line of force will tend to pitch down with power which makes a large stabilizer important. Even though the nose may pitch down the wing provides more lift as speed increases. A fast flier will have a zero to 3 degree positive angle on the wing (LE high) A slow flier can have 5 degrees positive which will behave much like a plane with flaps deployed. It will take more power to overcome the drag but will be very stable at slower speeds.
EZ set wing incidence for OG planes:
Just about every model in the OG foamboard plans can have the wing incidence set by using the thickness of the foamboard (3/16") under the LE and verifying that a line drawn from that thickness back to the underside of the TE is parallel with stabilizer. From there trimming can be done at the field with only a slight bend to the stabilizer required.
Understanding that helps makes sense of why the angles are different for low wing, mid wing, biplane and parasol winged aircraft. A line through the motor to the tail for a low wing plane such as the P51 is the line of force and very similar to the skier. The wings are like the skis and are tipped up. That is a positive incidence angle relative to the stabilizer set at zero (the water's surface is at zero). The motor is downthrust 2 degrees. This creates drag at the TE of the wing and the tail surfaces to keep the plane straight and level.
A Parasol wing plane is quite different. The drag of the wing is above the line of force and will tend to pitch the nose up so the wing is set at zero, the motor downthrust might be 3 degrees, and the stabilizer might be set -1 degree to keep the nose down.
A biplane should be set with the wings parallel with the stabilizer with the line of force running right through the CG to the tail. There is drag above and below the line of force. Giving 1-2 degrees up elevator and 2 degrees downthrust will give stability and level flight. It is much easier to set the wings parallel with the stabilizer and then add some up elevator with a slight bend.
A mid wing behaves much like a low wing plane and should be set with 2 degrees down thrust relative to the stabilizer angle of zero. A low wing plane with its drag below the line of force will tend to pitch down with power which makes a large stabilizer important. Even though the nose may pitch down the wing provides more lift as speed increases. A fast flier will have a zero to 3 degree positive angle on the wing (LE high) A slow flier can have 5 degrees positive which will behave much like a plane with flaps deployed. It will take more power to overcome the drag but will be very stable at slower speeds.
EZ set wing incidence for OG planes:
Just about every model in the OG foamboard plans can have the wing incidence set by using the thickness of the foamboard (3/16") under the LE and verifying that a line drawn from that thickness back to the underside of the TE is parallel with stabilizer. From there trimming can be done at the field with only a slight bend to the stabilizer required.
Motor Side Thrust Angle
There is a difference between types of plane's motor thrust.
A high drag model like a biplane, or triplane needs more power to move fast enough to generate lift. That doesn't mean it flies faster, just that it needs more power to achieve that slow flight. A big prop like the 8 x 4 does the job, but it generates a lot of opposite torque on the plane. The plane will want to roll left as you apply more power. To compensate we adjust the motor thrust line to the right. A biplane will need 2-3 degrees right thrust to calm the left roll.
A narrower wing span will need more right thrust than a wider span.
A WWII fighter with its single wing has less drag and takes less power to generate lift. So the torque on the airframe is less. The right thrust needed may be 1-2 degrees right. The plane may actually fly faster than a biplane but with less power needed.
While test trimming each plane it is best to shim the airframe so that the 1System pod doesn't need trimming when you switch planes. Card stock folded makes a good trim at the field. Once you have it trimmed, make a note of the location and thickness and then make a permanent shim at home with balsa or cardstock glued in place.
A high drag model like a biplane, or triplane needs more power to move fast enough to generate lift. That doesn't mean it flies faster, just that it needs more power to achieve that slow flight. A big prop like the 8 x 4 does the job, but it generates a lot of opposite torque on the plane. The plane will want to roll left as you apply more power. To compensate we adjust the motor thrust line to the right. A biplane will need 2-3 degrees right thrust to calm the left roll.
A narrower wing span will need more right thrust than a wider span.
A WWII fighter with its single wing has less drag and takes less power to generate lift. So the torque on the airframe is less. The right thrust needed may be 1-2 degrees right. The plane may actually fly faster than a biplane but with less power needed.
While test trimming each plane it is best to shim the airframe so that the 1System pod doesn't need trimming when you switch planes. Card stock folded makes a good trim at the field. Once you have it trimmed, make a note of the location and thickness and then make a permanent shim at home with balsa or cardstock glued in place.
