Wright Stuff is flying Mon and Tues 2-5. Read this beforehand. Pass on to Michael, Joe, Bobby, Matthew, Adam, Kim, and Brian if you know they arent on here--- Science Olympiad 2015 - Wright Stuff Airplane Trimming December 29, 2014 Five Variables to Consider: Decalage Angle: angular difference between the wing and stabilizer Increased decalage angle, which usually requires moving the CG forward, increases drag (reducing duration) and increases pitch stability. More pitch stability means that the airplane recovers from air disturbances quicker and usually without losing as much altitude. Once desired CG is established, decalage is adjusted to just less than stall; usually by building the airplane with a little excess wing incidence and gradually over the course of a couple test flights, reducing the wing incidence until the stall disappears. Decalage is adjusted by slightly pushing in or pulling out one of the wingposts from the tissue tube, which reduces the wing incidence and decalage. Usually, this adjustment is done one degree or less at a time (1/16”=1 degree) Left wing washin: small positive angular difference in the left wing relative to the right wing Too little washin results in the left wing hanging down during climb, especially in the initial, high powered, portion of the climb, which may lead to poor initial climb or no initial climb. Too much washin may result in too rapid climb and/or a too large turn circle. A reduction in washin from an initial setting of 1/8” wing LE higher than TE to a new setting of 1/16” can change the climb from relatively rapid (3-4 circles to 21’) to relatively slow (more desirable 6-7 circles to 21’) resulting in longer duration. Small changes can have a big effect. In rough air, a relatively rapid climb may be desirable and may produce more duration because the airplane will “punch through” the bad air better and gain more altitude. Decalage and left wing washin both have the effect of increasing the wing’s overall angle to the free air stream. If washin is reduced, it may be a good idea to also increase the overall wing incidence in a subsequent test flight and thereby the overall decalage angle in order to bring the airplane closer to stall. Center of Gravity (CG) and location of clay ballast: CG is usually predetermined by the airplane design (size of the wing, size of the stab, tail moment arm, planned decalage angle) so that the CG is an appropriate distance from the neutral point (NP) CG distance from NP is expressed as a percent of wing chord and is called the static stability margin (SSM). A typical range for this type of airplane is 15% to 25% although as little as 10% is sometimes possible. Optimum decalage angle for a particular CG will produce flight trim that is just short of stall. If pitch stability is not adequate (If the airplane loses more than one foot of altitude after an air current induced stall) then the CG may be moved forward slightly by moving the ballast in increments of ¼”, which for the Freedom Flight kit airplane moves the CG about 1/16” to 1/8”, which increases the static stability margin (SSM) about 2% to 4%. Stabilizer tilt The tailboom can be heated with your breath near its midpoint or wetted (if necessary) with saliva and twisted to increase or decrease tilt. Twist moderately hard to about 4x the amount you want to change, heat the center of the twist area with your breath repeatedly and hold for about a minute and check the result. Repeat till you get the result you want. If stabilizer tilt is increased, wing incidence (and thereby decalage) should be increased in a subsequent test flight to bring the airplane again to just less than stall. This is necessary as increasing stabilizer tilt causes the airplane to spin in slightly (spinning in is evidenced by a dive or reduced climb rate or slight rolling as it circles). Slightly increased decalage should remove this tendency to spin in. Tailboom offset for left turn Can be used in combination with stabilizer tilt change to increase or decrease the turn circle size. A larger turn circle (greater than 25’) will lead to longer duration, but the limitations of the flying site will probably require a circle of less than 25’ or even less than 20’. Remember that the LCC Regionals site, if setup as in past years, allows a clear area of about a 45’ diameter circle. Tightening the turn circle can be accomplished by slightly increasing tailboom offset combined with slightly increasing stabilizer tilt.
Posted on: Sun, 28 Dec 2014 02:02:44 +0000
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