To expand on what Brian stated, there are some constants in aviation about CG movement and adding weight that we CIF's teach. More thorough discussions can be found in the Pilot's Handbook of Aeronautical Knowledge, and the Airplane Flying Handbook both available at any decent pilot store printed by ASA.
First when adding weight aircraft speeds will go up, stall speeds, lift off speed, climb speed (to achieve the same rate of climb as solo if enough hp is available) while cruise speed typically reduces as does top speed (depending on CG & hp). A look at two aircraft that are similar will show that all things the same, the heavier plane will fly slower at the same power setting. Again, I will not re-write the book here, more can be found in the two texts I referenced, and I strongly recommend ALL who are testing read or re-read these two texts at least where aircraft performance and behavior sections are in them. A rearward CG changes the airplane's flight characteristics in known ways. What isn't known is HOW MUCH each KR example will be effected in these ways. An aft or rearward CG makes the airplane fly faster due to the supplemental lift received from the tail due to having to hold the tail up with elevator, since the weight moving back tends to lower the tail. This action allows a lower angle of attack and less drag for the available horsepower, hence flies faster. Better fuel economy, range and speed result. The downside to this CG location is that the arm, or simply the leverage the elevator has over the rest of the plane just got less. Your "prybar" for moving the tail around just got shorter by how ever many inches the CG moved to the rear. This has the effect of making the elevator less effective, since you cannot change how much it moves, or how big it is. So to get the same response from the plane requires larger inputs. How much depends on the speed, the slower the speed, the more drastic the effect is. It is possible to get slow enough that you will lose virtually all effective control of the plane and not be able to raise the tail or maintain level flight due to lack of elevator effectiveness. Remember you weigh more also so it takes more speed to maintain any flight regime even though the aft CG works to lower those speeds; a challenging paradox to test for. The most dangerous part is that when practicing (or not practicing) stalls, the aft CG tends to make the plane enter a flat spin, which in most cases is not recoverable due to how the resulting spin removes the control from the surfaces. The most uncomfortable part is that the Center of Lift is now close to the Center of Gravity which you can simulate by standing on one foot and balancing for awhile. That is why a KR with two on board gets pretty "busy". I may get flamed for this comment, but the above explanation is why I bumped my speeds in the pattern and landing up to what it takes for two on board and use them all the time. Other aircraft publish speeds that work in any flight configuration, as long as you are in the CG envelope. I was copying their pattern of publishing. Yes our KR can get slower, but my habits will allow for safe flying no matter what my load, or winds. If I wanted a bush plane I would have gotten a Kitfox or Cub. I am not bothered by using 1500 feet to land, or take off. Test carefully and with deliberate safety in mind.... Colin Rainey KSFB
