I have a 4 star 40 that I'm rebuilding from a crash in which the stab separated from the fuselage. 4 star plans specify stab incidence as zero degrees. If I'm building the plane originally from the kit, I can probably safely assume that mounting the horizontal stab on the fuselage surface carefully will achieve the zero degrees incidence. However, given the damage incurred in the crash at the point where the stab joins the fuselage, I can no longer make that assumption. What I'm having difficulty with is determining a longitudinal reference line against which I can make incidence measurements. Can anybody please explain to me how to establish a line of reference for the purpose of measuring stab and/or wing incidence? Thanks. .. Ken

I use one of these -

http://www.greatplanes.com/accys/gpmr4020.html

It is accurate and the notches will give a good indication for most any wing or airfoil you put it on. Mount the wing on the fuselage since you want the angles relative to the wing and not the fuselage. Adjust the tail until it is the same relative angle to the wing as shown on the plans. It will be OK then. The device can be used for many years and will pay for itself in knowing that you have a properly set up airplane.

Or

Use the side view on the plans. Measuring from the bottom of the plans to the bottom of the fuselage get a front and aft distance from the bottom of the fuse to the bottom of the plans. Pick points that can be easily measured on the actual model and that weren't broken. Block the fuselage to that position.

Pick a point on the leading edge and trailing edge and mark them. Do the same measuring thing for the tail to position it with respect to the bottom of the plans. Adjust the actual tail/fuselage intersection until the measurements are the same as on the plans.

Or

Lay the actual fuselage over the side view of the fuselage on the plans and adjust the stab seat until it matches the plans.

But I recommend the Great Planes laser thing plus it is fun to play with and shoot across the shop to chase bugs, etc.

Thanks Ben. Those are excellent suggestions. I just happen to already own 2 of the laser incidence meters to which you allude. Where I've had difficulty, tho, is in using the meters on wings with ailerons installed, or horizontal stab with elevator installed. Unless the control surface is absolutely zeroed (guesswork at best) the angle of incidence will be affected. How do you deal with that, or do you always measure the incidence before you've mounted the control surfaces. .. Ken

No I usually forget too.

For ailerons or tail surfaces I use two straight popscicle sticks (or something equally straight) and lay one on the top of the aileron (chordwise) overlaping the wing and one on the bottom of the aileron (still chordwise) overlaping the bottom. Then use a clothes pin or something similar to spring load them in place. You can see the stick become tangent to the gap between the surface and touch it equally on either side.

Put one every foot or so across the surface with a minimum of two per surface. It pretty well automatically centers the movable part with respect to the fixed part. It will also hold it firmly enough to use the incidence meters on the whole wing/surface.