project pattern
es, embedded in last month’s col- umn was a spoiler alert that Yuri had been flown, and that fact is now abundantly evidenced by some great airborne shots, courtesy of Paul Osin - ski. Most will note the additional side area in the form of a ventral strake on the fuse bot- tom, fences or SFGs (side force generators) on the stabilizers, and a very small strake on the top of the canopy. In its stock form, Yuri flies extremely well, but I found for my per- sonal style and setup, the additions are a minor improvement for some of the maneu- vers unique to the FAI F3A sequences. Backtracking slightly to the moments be- fore the test flight, Yuri hit the scale and weighed in at 3,690 grams (8 pounds, 2 ounces), less the motor Li-Po. With the addi- tion of the pair of Thunder Power 5s5000 G8 ProLites, the ready-to-fly weight registered at 4,870 grams (10 pounds, 12 ounces)—well under the legal limit of 5,000 grams, and quite respectable for a large volume and very rigid 2M ship. As noted previously, since the “birthing” of Yuri, RC-Composit has made several improvements, shedding approximately 230 grams (8 ounces) in the production process, making it possible to stay under the 5,000 gram weight limit with an extremely wide range of equipment. The recommended center of gravity (c.g.) is 210 mm from the leading edge of the wing (just behind the center of the wing tube); with a range of 200 mm (windy conditions) to 215 mm (calm conditions). The test flight was completed at 205 mm with a very stan- dard 21–14 Falcon carbon fiber prop. Immediately noticeable were the sensi- tivity of the rudder and the lack of air- frame drag. Yuri required very little pow- er to maintain good pace even in long uplines. Downlines were a bit on the fast side, even with the brake engaged. Swap- ping to a 21–13W was an improvement, and changing to the 22–12 PT carbon fiber prop yielded the flight envelope I was look- ing for; sufficient downline braking to fly a relaxed pace in calm air, and still enough
Y PHOTO: RON LOCKHART Dave and Yuriat the field for another day of Pattern practice.
speed to fly in moderately windy/turbulent conditions.
Without a doubt, smaller motors (such as
the AXI 5325) running 20–13 propellers are capable of providing Yuri with the needed speed and vertical in all but the windiest of conditions. And for those that routinely fly in windy conditions, Yuri can easily handle those conditions with a 21–14 without put- ting undo stress on the power system. Before delving into a detailed evaluation
of Yuri’s flight characteristics and minor setup tweaks, I think it is important to pro- vide some background/context as to my ex- pectations and personal preferences for “proper” Pattern plane behavior. I am very particular as to not only how a plane reacts to specific control inputs and combinations of control inputs, but also how the plane re- acts to variable weather conditions. My bottom line is that the best airplane (and trim setup) is the one requiring the fewest control inputs to complete maneu-
vers and has a performance envelope suffi- cient to handle the majority of weather con- ditions without changes to the power setup or flight conditions. In terms of how aerody- namic theory (and law, per se) applies to Pattern models and what methods achieve the desired state of trim, there are most cer- tainly differences of opinion. I am not locked into the idea that one trim method will be equally successful on all designs, or that a single trim method may produce the best trim setup for all pilot preferences. That said, there are a couple realities that I be- lieve are essentially aerodynamic law and non-negotiable:
1) Spiral airflow exists, and has an effect on Pattern models. Additional asymmetric factors generated by the power system (sin- gle propeller for purposes of this discussion) include torque, gyroscopic precession, and P-Factor. There are no absolute fixes (save counter rotating propeller setups) to negate the effects of the listed asymmetries; howev-
Redux
by dave lockhart with algirdas ungulaitis You can reach Dave Lockhart via e-mail at
davel322@comcast.net
PHOTOS: DAVE LOCKHART
Dave’s dad, Ron, shows the simple and very visible color scheme (at left) on the bottom of the Yuri. The color scheme on Yuri(above) is designed to be very visible with long lines to reinforce Yuri’sPattern mission.
56 NOVEMBER 2013
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