PHOTO: EARL HAURY


The large scale and small pinpoint laser dot, circled (at left) of the Budd Engineering Laser Measurement System make it easy to see small adjustments to control surface throws. The AeroPerfect MU-9000X USB (above) is a dual axis MEMs type inclinometer for the ultimate in precision measurement of control surface throws and incidences to an accuracy of 0.01 degree.


With the addition of a Smart Level incli- nometer to the Robart, digital readings can be obtained to within 0.1 degrees. Obtaining accurate and consistent inci- dence readings can be troublesome, owing primarily to two factors; 1) the airplane must be 100% secure and unable to move if bumped during measuring, 2) the incidence meter needs to be securely and accurately attached for each reading.


My solution for the first problem is to use a large cradle to support the fuselage, elimi- nating the possibility of squashing the wheels or landing gear. The second problem is a little more difficult, but primarily comes down to having consistent technique, and I take multiple measurements and use an av- erage reading.


During construction, the motor thrustline was not measured, but set to match the fuse- lage nosering. Measuring the amount of downthrust can easily be done by mounting a long straight stick (1-inch square balsa works well) as a “propeller” against the spin- ner backplate, and then using the Smart Level on the balsa stick. Downthrust for Yuri measured in at negative 1.5 degrees. The above incidences are relative to the white paint line on the fuselage, and while useful for record keeping, testing, and eval- uation of different incidences, they are un- likely the actual incidences in flight. In practice, the stabilizer is likely very close to zero degrees during straight and level flight. This puts the effective incidences for Yuri at +0.3 for the wings, 0 for the stabilizers, and approximately 1.8 degrees of downthrust. Determining the control throws requires little more than a finely graded ruler, meas- uring the movement at the trailing edge of each control surface. However, there are a variety of device systems that allow more efficient measurement of control throws. If I need to check throw coarsely (chang- ing a servo at the field), I will use a clip-on style throw meter like the CRC Products throw meter (available from Central Hob- bies). Benefits are no setup time and no bat- teries needed, but the accuracy is limited to approximately 0.25 degrees.


FLYING MODELS


Driven largely by the need for greater res- olution, my preferred system is the Budd Engineering Laser Measurement System. While it takes a little bit of effort to set up, the large scale and focused laser pointer eas- ily allow control throws to be measured to 0.1 degree increments.


One of the newest systems for measuring control throws (and incidences) is the MU- 9000X USB from AeroPerfect. The MU- 9000X USB is a dual axis inclinometer that utilizes a MEMs (micro electro mechanical system) sensor to detect angles as small as 0.01 degrees. The sensing unit attaches to the control surface or wing stabilizer panel and sends measurement information to a PC. Very slick system, and on my list of tools to acquire (temporarily unavailable at the time of this column).


Moving on to the actual control throws for


Yuri, I will note that my general preferences are to use individual rate switches and I rarely use flight modes. This allows me the greatest amount of flexibility to choose indi- vidual rates and combinations of rates for specific maneuvers.


And now, in the interest of brevity, I must advise of a bit of a spoiler alert. Yuri has flown, and flies quite well. The control throws that appear in the box at right are the actual control throws I have found to be the best for my flying style and allow Yuri to complete the full range of Pattern maneu- vers, up to and including those found in the FAI catalog for generating unknown sequences.


My standard or normal flying rates are low aileron, low elevator, and high rudder. I tend to fly a fairly sensitive rudder, moder- ate elevator, and moderate to slow ailerons. Spins are completed using elevator and rud- der only, with a slight nudge of aileron to initiate the spin. For reversing spins, I use high rate aileron (briefly) during the spin re- versal. For snaps, I switch to high rate aileron, and for


vertical upline snaps I


switch to low rate rudder. Many pilots would prefer to fly on low rate rudder, switching to high rate for snaps, spins, and stall turns. Of note, the apparent asymmetries in


the control throws are very intentional. Yuri utilizes a “live skin” type of top hinge. The geometry of the top hinge results in slightly decreased deflected surface area for “down” movement in comparison to “up” movement. To have the same effective deflected control surface area, the “down” aileron must move slightly further than the “up” aileron. Similarly, the down eleva- tor movement is greater than the up eleva- tor movement, but the full throw authority is equal.


Exponential for down elevator is reduced slightly, and this gives Yuri a more balanced feel in pitch, compensating for the small amount of down elevator needed for inverted flight. The rudder is center hinged, so the throw is equal in each direction to ensure spin rates are equal to the left and right. However, the exponential for the rudder is less to the left, compensating for the right thrust.


Control Throws for Yuri Low Rates Aileron 9.7° up


10.8° down 43% exponential


Elevator 13.4° up, 40% exponential 16.2° down, 32% exponential


Rudder 4.25″ right, 38% exponential 4.25″ left, 31% exponential


(as measured at the bottom of the rudder) High Rates


Aileron 20.1° up 22.1° down


70% exponential


Elevator 20.3° up, 60% exponential 22.8° down, 51% exponential


Rudder 5.25″ right, 55% exponential 5.25″ left, 45% exponential


(as measured at the bottom of the rudder) 49


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