The removable nose block serves two purposes. One is to make thrust line adjustments easier when trimming the model to fly. Without some kind of adjustable nose block you have to try to put tiny wedges of wood or paper behind the edge of the thrust button to adjust the thrust line...not easy to do. The second is to provide better access to the fuselage when loading and winding a motor.
The thrust line must be adjusted to get flying stability under power. After you get the model to glide properly, you need to adjust the thrust line, up, down, right, or left, so that the torque of the motor does not spin the model into the ground and so that it is not pulled into the ground or made to climb too fast and stall. You do this by putting wedges between the nose block and the first former to tilt the nose block in the desired direction. Torque, with a usual right-handed propeller (turns clockwise when viewed from the rear), tends to pull the model to the left. This is more noticeable with a low winged model like the Skyraider. Since the model will tend to turn to the left and climb too fast with the burst of power that you get from a rubber motor when first released, a good place to start with thrust line adjustments is 2 degrees right thrust and 2 degrees down thrust. Start with a low number of winds on the motor and test fly, working up to the number of winds necessary for long flights as you adjust. Low winged models, flown outdoors, tend to fly left under power and glide right. High winged models usually fly right, right.
It is important when making an adjustable nose block to have some kind of key that fits snuggly into the first former and only fits in one direction. A loose nose block will cause bad flights. Often modelers use tiny rare earth magnets, (Like I used for the landing gear.) facing each other or a thin piece of steel, to hold the nose block in place. The trapezoidal box key, that you see in the picture above, works well although there are many other ways to do it. In the case of the Skyraider, I filled the plastic cowl with a balsa former that has the 1/64" plywood on the back face and the key built into the back of it. An identical piece of plywood is glued to the front of the first former in the fuselage. The plywood is just there to give some additional durability since the balsa is soft. All these parts were carefully laid out before the fuselage was assembled so that they would line up.
Here is an example of a trapezoidal key built into the nose of another model.
I hope this is not too confusing and helps you.
Howard
