> > >The KR2s is specified to have an gross weight of 980 lbs. Is this >independent of the size of the motor.
Yes. The motor has nothing to do with it. It is a factor of the structures capability to support the weight. >I mean surely if you have a 140Hp >motor in stead of a 70Hp motor you can lift more. I understand that gliding >will be an issue on a heavier plane. You can "lift" more because you are able to generate more thrust to overcome the drag caused when generating lift. It's not a free lunch however. You now have more weight to carry with the larger motor and probably more fuel on board also for the larger engine. Now you're having to use part of the extra HP just to lift the extra weight. It's a vicious circle. The larger motor does nothing to change the ability of the structure to carry additional weight so all you've really gained is a bit better climb rate and a slightly faster cruise. With the extra weight and no changes to the wing, you will probably increase your takeoff run and will need to increase your approach speed also. Like I said, there is no free lunch. >What I am actually asking is this. How >do they spec gross weight? Can I get past this limitation? The designer specifies the gross weight as a function of the structural design and the amount of weight it can support with a predetermined safety factor. Very generally, this is usually a factor of the wing structure. The KR is capable of carrying more weight than the 980 gross weight limitation but above that you are reducing the safety margin. Can you get past that limitation? Yes, but don't go there without a total understanding of structural design and limitations. You can catch a 6 pound fish on 6 pound test line attached to a fly rod. If you want to catch a 10 pound fish on the same line you can't make the line stronger by attaching it to a 2" X 4" plank. > I am a big boy 335 Lbs. I have a heavy >Soob motor and I am seriously considering adding weight by placing the >cooling system under a wing. >Jannie The Soob motor is heavy with the added weight of the cooling system. It doesn't matter where you place it, weight is weight. The factor that will change with where you mount the cooling system is the center of gravity or C.G. That is the point where the aircraft balances, like a see saw, and that balance point must fall within a certain range as specified by the designer. It would be difficult to build a KR with a SOOB engine and keep the empty weight at 650 pounds or less. If you weight 335 pounds then you're already at 985 pounds and you haven't added any fuel yet. Even in the U.S. where we can specify a higher gross weight, you're looking at a heavy single place. Without more information that we have been given, I'd say you have two options. One, loose 135 pounds, or two, pick a different design. Please don't shoot the messenger. Good luck....... Larry Flesner
