project pattern
W
Redux
ith all the construction details completed and the ESC pro- grammed, the remaining items to be addressed before test fly- ing are control throws, radio setup, and inci- dences. While control throws are pretty straightforward, the radio setup can be very complex, depending on pilot preferences and the plethora of programming options avail- able on the modern high end transmitters. Incidence setup is seemingly quite straight- forward, but can also be quite complex as it can influence the trimming process. Of course, the ultimate goal of the trimming process is to have an aircraft that is 100% pure in response on all control axes in all flight regimes, but how to achieve that state of trim is a never ending subject of debate. Somewhat related to incidence settings is the physical alignment of the fuselage wings stabilizers. I’ve not discussed this previous- ly, as the wing and stabilizer tubes for Yuri are pre-installed by RC-Composit (as were the wing adjusters and incidence of the wing).
Pre-installed wing and stabilizer tubes are typical with the modern day com- posite Pattern “kits”, but that does not mean the alignment should not be checked. Aircraft alignment has been discussed many a time by many authors in many mediums, so I won’t cover it in detail again. The wing and stabilizer need to be parallel to each other (in the same plane), and per- pendicular to the rudder post. The wing tips need to be equidistant from the rudder post, and the stabilizer tips need to be equidistant from the rudder post. Of course the individ- ual structures need to be free of any warps. As delivered from RC-Composit, all of the
critical dimensions for Yuri were +/– 1⁄32 inch, within tolerance of what I can repeatedly measure accurately. In general, I will not ad- dress any alignment issues unless one or more critical dimensions are off by more than
by dave lockhart with algirdas ungulaitis You can reach Dave Lockhart via e-mail at
davel322@comcast.net
PHOTOGRAPHY: DAVE LOCKHART
Using a Robart Incidence Meter as a base fixture, the attached Smart Level digital inclinometer can be used to precisely check the incidence of the wing and stabilizer panels to within 0.1 degree.
1⁄16 inch. Small alignment errors can general- ly be corrected by very lightly sanding the in- side edge of the wing/stabilizer sockets in fuselage, and then building up the opposite side of the socket(s) with thin layered appli- cations of thin CA or laminating resin. This is a very tedious, repetitive, and an- noying process, but worth it in my opinion to avoid potential trim issues that could result from misalignment. Substantial alignment errors require breaking loose and re-setting the socket(s) on at least one side. Care must be taken to not pre-load any of the struc- tures; i.e., perfect alignment must be main- tained without any force being applied to any of the structures. Gluing any of the struc- tures in place with a degree of pre-load will likely result in aircraft alignment that con- tinually changes with temperature and hu- midity and aerodynamic forces on the plane. Determining the exact incidence of each
surface is never a task I enjoy. Initially, a ref- erence, datum, zero line, or centerline of the fuselage must be established as a basis to measure against for the incidence of each surface. Some planes utilize the baseline of the canopy or small dimples molded into the fuselage side as the baseline, and others may use a long level paint line on the fuselage. In the case of Yuri, there is no specific ref- erence line, but the wing incidence is pre- set. I chose to use the long white centerline stripe on the fuselage as the centerline, as- suming the incidence of the white line to be 0 degrees. The incidence of the wings meas- ured positive, at +0.6 degrees each (leading edge high). The incidence of the stabilizers measured positive, at +0.3 degrees each. The weighted needle on the time tested Robart incidence meter is sufficient for de- termining incidence within 0.25 degrees, which is quite coarse for Pattern needs.
Portable and simple to use, the CRC Products Throw Meter (above left) easily attaches to any control surface and allows control throw measurements to a resolution of approximately 0.25 degree. Requiring a 4–7-volt power source and
48
a bit of geometric setup, the Budd Engineering Laser Measurement System (above right) allows measurements of control surface throws to a resolution of less than 0.1 degree.
OCTOBER 2013
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