A friend has a Profile Cardinal, and I reminded him about Brett's suggestion to trim 1/2" to 5/8" off the TE of the flaps, to improve the corner. My friend replied and asked why he couldn't just reduce flap motion and get the same result.

Other than knowing that the wider chord on both moveable surfaces increases the control loads, reducing control responsiveness, I can't 'splain it further.  Would the negative pitching moment be reduced as the travel increases? What's the scoop?   Steve

Flap hinge moment goes up with the square of flap chord.

Ted,
When did your article come out and which magazine was it in?

Thanks,
Roger

If the flap deflection on a profile Cardinal were reduced without cutting the flaps, and the linkage adjusted to give the same elevator deflection as the cut-flap version, what would be the difference(s) in flight characteristics between the cut and uncut versions.  (The mechanical practicality of doing this to a Cardinal control system is not part of the question--just the aerodynamics). Thanks.

Ted,
Yes, I thought your flap experiment described in the article was very clever and informative.  Experimentation is a lot of fun IMO, especially when the results turn on cartoon lightbulbs over my head.  I have tried to stall the Imitation by banging the corners of the triangles hard, and it has plowed through very nicely even at a fairly porky 60 oz.  I am currently on crutches with a pinched nerve in the back, but when and if I am able to fly again, the next thing will be to add a wart to the outboard flap to damp the roll in maneuvers, which has been a problem with most every plane I've flown. 

Another ongoing problem is level-flight stability.  I have found the point in control sensitivity adjustment where total groove is achieved on the Imitation.  It happens to be right at the point where required handle input for good performance becomes excessive, i.e. controls not sensitive enough.  I have been curious about the "bit of slop" theory of groove achievement, so had a friend machine a custom link with a bit of slop.  Interestingly, that helped but it also produced a flat spot not at the intersection of the horizontal eights where the controls obviously switch direction, but 1/4 loop later at the top of the second inside loop of the H8s.  Interesting.  If any slop is tolerable, it ain't much.  Then I read Randy's post about a bit of added drag at the far aft end of the plane helping groove.  He had good results with a 3/8" wide strip (a "drag strip" you might call it) attached to the TE of the rudder of the plane he was flying, which had a vertical TE.  Never in a million years would that idea have occurred to me.  Since the Imitation doesn't have a vertical rudder TE, some other vertical drag device test arrangement will present itself.  Wing turbulators at 10% of MAC may be another area of experimentation.  I suspect that the pilot's neurological limitations are also a factor which are probably beyond correction.  The Imitation is a wonderful, stable platform for boys who like to play science project.

Thanks for reading.