Hi guys,
I want to know how to set correct incidence on my airplane which i build from kits having plans and having no plans. Kindly also let me know about setting correct incidence on ARFS.

As far as ARF's go, incidence is usually set by screwing the wing on, the saddle will only allow the wing to fit one way, and it's usually close enough. As far as your kit built plane, what is it? If you reference the thrust line as zero, you can probably start with between 0 and +1.5 and have a flyable plane. Sometimes you can use the horizontal tail as zero reference. It would really help to know what your model is, somebody out there may have plans and specific info. Good luck.

If the plane is supposed to have incidence it is NORMALLY INDICATED ON THE PLANS.

For setting the incidence you will need an incidence meter. I use the Great Planes laser incidence meter.

How I set the plane up is:

For positive/negative incidence:

I block the plane up and use a small level on the horizontal stab to insure that this is level. Then I "zero out" the incidence guage on a level surface and clamp it to the main wing. At that point I adjust (shim ) the wing as needed to get the incidence I need.

For ARFS and other planes:

For ARFs and other planes with no incidence given, I assume it is a 0/0 incidence (0 incidence on the main wing and 0 incidence on the horizontal stab ). With these planes I zero out the incidence meter and clamp it to the main wing. Then I block the plane up until the incidence meter reads 0. Then using a small level, I make sure the horizontal stab is at 0 degrees.

The reason I do it differently for ARFs and other types of planes is that it is usually easier (less work ) to shim/adjust the horizontal stab than the main wing. I ALWAYS check the incidence on ARFs. While it is unusal, I have found a couple of ARFs that had positive/negative incidence, even though the manufacturer has stated that it should be a 0/0 incidence.

Hope this helps.

As far as how to set the incidence on a plane that YOU designed, there is no set rule on what the incidence SHOULD be set at. Setting different incidences will give different flying characteristics. This will also change from one design to another.

For a symmetrical airfoil type plane, draw a line right through the center of the wing for your reference line. For a totally flat bottomed wing (unusual), the flat bottom is the line to use. For a semisymetrical (that's an oxymoron...) wing draw the line from the center of the rounded leading through the trailing edge. Set these lines at 0 degrees with the stab for starters.

I'm open for corrections MinnFlyer; also thanks for the description of using the GP incidence meter. I need one!

Ernie

Actually, you shouldn't use the wing sandle of a flat bottom wing to measure incedence. I know. I have done it. When you put a meter on a flat bottom wing, the meter will measure a more positive value than the saddle, ( or the bottom surface of the wing).

Incidence with a typical semi-symmetrical/flat-bottom wing on a typical kit..

Pilotfighter, most flat bottom wings are of the semi type like in Paul's drawing. (thanks Paul) This is a modified flat bottom wing that has a rounded leading edge, called a "Phillips entry". This causes the chord line not to be parallel to the flat bottom line.

A true flat bottom wing has no rounded leading edge, but a totally flat bottom right up to the leading edge. The incidence meter should then clamp on parallel to the flat bottom I think.

Ernie