Negative Incidence
by Jerry Kelly
Incidence is the angle formed by a line through the leading edge and the trailing edge of the wing and a similar line through the horizontal stab and elevator (at neutral). When the line through the wing points down, in relation to the stab line, it is called “negative incidence” or a lifting tail.
In flight the symptoms are:
1. A lot of up elevator trim is required to keep the plane from diving.
2. When throttled back, the plane climbs. The more serious the problem, the more noticeable the climb.
3. In a dive the airspeed increases and the lifting tail causes the nose to drop and the speed to increase even more. A very vicious circle.
The fix is to adjust the wing saddle so that the wing lifts and not the tail. The best way to know is to take very careful measurements or more risky trial and error.