I have been doing the annual condition inspection, oiling the hinges, making sure nuts are tight everywhere including the elevator balance weight, and not once considered that it may be an unnecessary item. Consensus appears to be that indeed the balanced elevator on a KR-2 is not needed. Doing a little weight and balance math on my moving the cg issue, if this 2.6 pound elevator balance mass is removed, then I could remove 8.8 pounds of ballast from the engine mount and still get the same cg that I was working towards. And the airplane would be 11.4 pounds lighter. Thanks all for the reality check.
Sid Wood Tri-gear KR-2 N6242 Mechanicsville, MD, USA ---------------------------------------------------------------------------------------------------- Hi Ya Jeff I reckon it's bit more complex than just moving the wing. As a weight alone, moving the wing back away from the CoG increases weight on the tail for sure. To this extent Mike was correct in his comments on 10th May about moving the wing forward to offset the tail heaviness. However, the centre of lift is also moved backward which could act aerodynamically to counteract this which I think is what Sid was getting at. The extent to which these two interact and are then influenced by the other two vectors of thrust and drag is what ultimately determines whether the nose or the tail hits the ground first and whether the elevator has the authority to control it before it happens. Sid has added 49 lbs at about say 24" in front which suggests he has about say 20 in the tail at about 60". It may well be those elevator weights are a significant part of the problem. It all seems academic now. Sid will either fly or he won't. Cheers John John Martindale 29 Jane Circuit Toormina NSW 2452 Australia ------------------------------------------------------------------------------------- Hi John, You are correct in that the fuselage was extended to address elevator sensitivity and the firewall moved forward to move the engine forward to make the plane easier to balance. Sid just stated it a different way by saying the wing was moved back by 2". Either statement is correct. I don't think the CG envelope changed at all between the 2 and 2S as far as CG range relative to the wing cord. I don't know why Sid's plane is so terribly tail heavy, but adding a ton of weight to it isn't the way I would go about fixing it. As someone pointed out, he has balance weights on the elevator. Those are really unnecessary on the KRs. I'd lose those in a heartbeat. When I rebuilt the tail on mine to a much larger elevator and stab, I designed it to accommodate a set of balance weights, but when it came down to it, I couldn't convince myself to add 4# of lead to the tail. Sid seems determined to fly his plane as equipped. That seems fool hardy to me and others have implied the same on the net. Hopefully he won't hurt himself in it. Best regards, -Jeff >I reckon it's bit more complex than just moving the wing. As a weight >alone, moving the wing back away from the CoG increases weight on the tail >for sure. To this extent Mike was correct in his comments on 10th May about >moving the wing forward to offset the tail heaviness. > >However, the centre of lift is also moved backward which could act >aerodynamically to counteract this which I think is what Sid was getting >at. ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ This issue of W&B is being made much more complicated than necessary. Kids figure it out every day on the play ground on the tedder toter. The fat kid moves in toward the pivot point or the skinny kid moves away from the pivot point to achieve balance. In our case we want to achieve balance slightly ahead of the Center of Lift for stability in the air and then position our landing gear to achieve balance on the ground. In the case of a tail dragger we place the gear to give us tail weight and a nose wheel configuration we want nose weight on the ground. Moving the wing back would in fact move weight to the tail but we also move the C of L to the rear, thus adding mass forward to the C of L, decrease mass aft of the C of L, and making the airplane more nose heavy in the air. Gear placement would have to be considered with such a change. In our case, with the airplane built, we don't move the wing but we move other items to get our center of mass slightly forward of the C of L, engine, battery, etc. In case of a gross error in the design or building, balance may not be achievable without radical changes. In our case we know that moving the engine mass a few inches forward of the C of L is usually enough to correct the problem. That was with the standard KR with a VW engine. As builders make changes , lengthen fuselage, heavier engines, fuel tank changes, balanced elevators, etc., they must take in to account this balancing act. The further you get in to the project and realize an error, the harder it is to correct. So, if the fat kid is setting on the tail, move the skinny kid further out on the nose, or make the fat kid lose weight, or make the skinny kid gain weight, the options are numerous. It's as simple as that. :-) Just remember, it's the C of L we need to work around, that being basically the C.G. spec's given in the plans. Larry Flesner
