[snip]
... when I changed flaps design from full to partial and back, the Flaps are "not" the same size, they are calculated to be the same "area " that is moving, My planes also have very differant tips than yours or Paul's, that maybe another difference,
and Your right I agree, i also encourage people try it and see which way it works best for you. [snip]
Regards
Randy
Hi Randy,
Have to make a comment about the above. I'm sure you're more than aware of the following but just in case others try to make that simple assumption...
Matching "area" of the movable part of the wing (the flaps) when shortening or lengthening the span of the flaps is not a one for one exercise. Much more changes when (for instance) you shorten the flaps from full span to (for instance) two thirds span and simply increase the chord of the movable part of the flap to match the "moving area" of the full span version.
First, it isn't the "flap area" in and of itself that increases the lift coefficient of the total wing. The moving flap is nothing more than a part of the wing that moves so as to change the part of the wing to which it is hinged from a symmetrical to a cambered (higher co-efficient of lift) airfoil. Thus, if you shorten the flaps on a sixty inch span wing (ignore the fuse for simplicity of illustration) by one third you have reduced the "enhanced" part of the entire wing by 20". A full one third of the wing has lost its ability to change camber and, thus, create more lift than it is capable of doing as a simple symmetrical section. The overall lift of which the wing is capable will suffer as a result.
Increasing the chord of the 40 remaining inches of movable flap will recoup a percentage of what is lost by the unflapped 20 but not remotely as effectively as having the entire span flapped with the same amount of longer but narrower flap. If you don't need the lift (and most ships don't) that's not a big deal, But......
The only way to retain the same amount of area in that shorter span is to increase the chord of the movable flap (probably by one third) so that instead of a three inch chord for 40 inches you'll have a four inch chord (this is, I understand, a distorted example but is done so purposely to make the effect of increasing the chord more obvious). Increasing the chord of a movable surface exponentially impacts the hinge load (torque) required to deflect the surface. Increasing the chord of a flap by one third will increased the force necessary to deflect the same amount of area as the longer flap by much more than 1/3. (Howard or Igor or Brett can do the math). In addition, after a point, the effectiveness of the longer chord flap to increase lift versus the drag it produces to do so becomes much less efficient.
Let's make the example really extreme and say we'll make the flaps only 1/3 span but retain the same area as a "conventional aspect ratio" full span flap. Now the span of the flap will only be twenty inches but the original three inch chord will have extended to eight inches. The torque required to deflect such flaps will likely exceed the line tension available to apply it enough to generate the pitch change necessary to fly a stunt pattern. In addition, the amount of lift generated by a wing which only has 1/3 span flaps that are very hard to deflect will be significantly less than the same wing with "conventional" aspect ratio, full span flaps (less "high lift" flapped span and a less efficient spread of fixed vice movable chord for the 20 inches of flapped wing).
Again, without going into a classic "Fancher marathon meltdown", the bottom line to this discussion is determining how best to achieve the lift that is "necessary" to support the airplane flying corners as tight as the pilot is capable of flying them competitively. A large part of this equation, IMHO, is reducing necessary control forces as much as possible to allow the airplane to be flown precisely with a preponderance of small muscle inputs using a firm but light grip on the handle.
Bill Netzeband in his CL Aerodynamics Made Painless articles 40 or so years ago addressed the phenomenon of hinge loading and it is the primary source of the now infamous "Netzeband Wall" which most of us know is the point at which inadequate line tension exists for the control system to overcome the airloads on the movable surfaces. I encourage every who is interested in Stunt Design to get their hands on Wild Bill's priceless exposition on how these things (stunt ships) work. There is maybe 10% of it that I don't think is gospel and even that 10% would be primarily argument over details. They can be found in the Jul/Aug, Sept/Oct 1966 and the Dec 1967 American Modeler magazines (the AMA publication of the era and, thus available at the Museum library in Muncie). The math is pretty heavy reading and the nomographs a bit clumsy to use but the text can be read carefully, pulling theory and effect from between all the numbers, to make the reader a pretty informed individual.
Ted