Some of us on the list are getting hung up on the CG range as a percent of mean aerodynamic chord. To an aircraft designer, expessing the CG range this way is used for preliminary design purposes only --we want to make sure that we have a usable product that can support real world loading conditions, and also to know where the landing gear needs to be. (It's bad when the airplane falls on its tail when the pilot throws a suitcase in the back...)
Once the airplane is built and in flight test, we determine the real CG limits by ballasting the airplane to different CGs and doing the following:
1) Determining the maximum forward CG by determining where tail power becomes insufficient to flare on landing. This is actually not hard to calculate and simply verify during flight tests.
2) Determining the aft CG at which the handling qualities become unacceptable. As I mentioned in an earlier posting, this depends on the intended pilot population (is it a trainer or an advanced fighter jet) and its mission (is it a trainer, a Bonanza-class airplane or an airliner). This is very difficult to determine analytically, hence the intial reliance on rules of thumb. (Since you can't calculate it precisely, you might as well use a quick estimate that's just as good.)
Again, rules of thumb (such as a range of 15% - 30% MAC -- this depends on airfoil section and the aft-loaded NLF airfoils are different from the NACA 65-series, for example) are used only to estimate those actual CG limits which are verified in flight test.
Scott Krueger is abolutely right when he says that there are multiple factors which influence pitch sensitivity, not all of which were mentioned in the CAFE reports. First and foremost is CG. Other factors are (in the 320 series) the elevator bellcrank arm and the tail size. And then there are odd airplanes like Dom Crain's, which has the pitch damping of a large tail but (I'm guessing) the tail power of the small tail. He likes it.
Here's one suggestion to non-builder owners of 320 and 360 airplanes. If you think the pitch sensitivity is too high, measure the distance between the elevator axis of rotation and the bolt hole to which the elevator pushrod is attached. There were two versions of this bellcrank. Original ones had a longer distance and the newer ones were 1 inch shorter. I have a copy of the Lancair factory newsletter in the hangar addressing this change and I'll post it in the next week or so. The shorter distance gives higher stick forces but less control stick throw. You will notice the stick force change but probably not the change in stick throw. You can modify your bellcrank without replacing it, if you want. You just drill one hole, although you'll have to remove at least one elevator (maybe both) in order to do it, and you should check the rigging afterwards to make sure the neutral position is still where you want it. Elevator range of motion will be unaffected but with the elevator in trail the stick might be tilted forward or aft a little.
- Rob Wolf