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project pattern


W


Redux


hen I previously mentioned Yuri had been test flown, did I neg- lect to mention that the takeoff roll was perfectly straight, liftoff was gentle and true, and only after four passes did I notice a single click of trim was needed? Nope, I did not neglect to men- tion these hyperboles. In truth, Yuri did need a couple clicks of trim (with the trim sensitivity on the smallest increment), but any well-built and setup Pattern plane should need minimal trim on the test flight. Far more important is the “trim condition” of the plane.


Trim condition, described in detail last month, is, in brief, how the plane performs in a variety of attitudes (uplines, downlines, knife edge, etc.); how well it handles turbu- lence; and how easy it is to fly through a wide range of maneuvers. The plane that completes a maneuver or sequence of ma- neuvers with the fewest inputs from the pi- lot is in the best trim condition. On the trim flight, I had the c.g. for Yuri set at 205 mm aft of the leading edge of the wing, roughly in the middle of the recom- mended 200 mm (windy weather) to 215 mm (calm air). The thought process behind dif- fering c.g. locations for differing weather conditions is fairly common, and most cer- tainly has basis. A more forward c.g. is more stable, and of greater benefit in turbulent conditions. A more aft c.g. allows the plane to fly more efficiently; requiring smaller ele- vator and rudder inputs to complete a given maneuver, and often the plane is less sensi- tive to trim changes with variations in speed.


As a general rule, I don’t change the c.g.


for different weather conditions. Changing the c.g. can also affect the entries and exits to snap rolls and spins, and affect the pitch- ing characteristics in uplines (minimally, if at all), downlines, (more forward c.g. will pull to the canopy), and knife edge (more for- ward c.g. will pull to the canopy). I find it more beneficial to leave the c.g. in one place to have the most consistent response possi- ble, as opposed to adapting to differing re- sponses for very small performance gains. With the c.g. at 205 mm, I found Yuri to be well settled and comfortable in pitch; a good balance of responsiveness and groove. Ele- vator authority on spin entries was good, positive right up until the point of stall. Snap entries were clean with no tendency to wind up (increase rotation rate). Long up- lines pulled ever so slightly to the canopy, and long downlines pulled slightly to the canopy.


In the yaw axis, Yuri was very responsive, and while the tracking in a crosswind was quite good, the damping in turbulence was a little less than I prefer. Keep in mind that the yaw behavior I am describing is very common with current day 2-meter Pattern planes—it is simply a tradeoff of having strong rudder authority for knife edge inten- sive maneuvers versus a more locked-in “groove” in yaw.


38


Horizontal knife edge flight was very good, with only the slightest pull to the canopy, and a small bit of adverse roll (rolling against the direction of rudder in- put). In knife edge loops, as a slip angle (skidding per se) became evident, the pull to the canopy became more pronounced (not


unexpected). So, with Yuri in relatively good trim, where to begin to improve the trim condition? The trim faults I am describing are truly minor; small enough that they would be hard to detect in the course of fly- ing through a Masters pattern.


Firstly, I made some very small adjust- FEBRUARY 2014


by dave lockhart with algirdas ungulaitis You can reach Dave Lockhart via e-mail at davel322@comcast.net


PHOTOGRAPHY: DAVE LOCKHART


To eliminate undesired adverse roll, a linear programmable mix (above) in the JR 12X is used. At full rudder deflection (below), the ailerons deflect approximately 3⁄32 inch (inset); mix values of 6% (left aileron with left rudder) and 7% (right rudder with right aileron). This mix amount is, in practice, very small when considering Yuri’sability to complete knife edge loops with little more than half rudder deflection. A throttle “stick switch” value of 10 renders the mix inactive on the bottom 4 clicks of the throttle stick to avoid undesired effects on stall turns and spins.


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