09/11/2018
RANS S-21 OUTBOUND
TEXT MANUAL
160
Adjusting Wing Root Angle of Incidence
In some cases adjusting the wing at the root can be effective. Raising the rear spar may
be the better choice over trim bumps, or in combination with trim bumps, if roll is strong.
In this case always raise a wing, since this is the better loading on the spar. The amount
you raise the wing has to be at least 0.2" to offer adequate edge distance from the
existing holes. Prior to removing the two 10-32 bolts in the fitting, mark a line where the
fitting meets the spar web, this will create a reference line for the 0.2". Use the fitting as
a drill guide. Be sure to raise the wing opposite of the roll. If rolling left, raise the right
wing to reduce lift to diminish the roll.
Adjusting Horizontal Stabilizer Angle of Incidence
The Horizontal stab is adjustable for a couple of reasons, one to optimize speed and if
pitch trim is unable to hold level flight throughout the speed range, with and without
flaps. The latter would be the case where an engine of greater than flight tested weights
is installed. The S-21 was designed to accommodate a wide range of engines, from the
100 HP Rotax up to Lycoming 360's with constant speed props. A good test for
optimum incidence is the ability to hold a trim speed, and how well it returns to trim
speed after a positive or negative pitch diversion. A lack of incidence will also impact the
stick pressure in the stall, worst case forward CG and full flaps. Our flight testing has
shown this adjustment to be fairly forgiving, and on our demo plane we went to full
negative, while the sister ship was about midway. We saw little speed difference and
only slight changes in stick pressure in pitch in the stall. This will be the case with the
heavier engines, but incidence changes will show a stronger impact on the Rotax
912ULS powered planes. A simple rule of thumb is to start full down adjustment for the
Titan, and full up for the Rotax. Check for neutral trim speed by finding the speed the
elevator is flush. This can be a wide speed range. We have adjusted from 65 MPH IAS
to 85 MPH IAS on the Rotax powered plane. For the Titan shoot for 95 to 100, go back
to more incidence if holding trim speed is affected.
