But doesn,t the 727 bacicly have the same airframe as the 737 and 757.I do understand that the wings are a little more heavyer since they don,t have engines under them.
To answer that part of the original question: no, it's not basically the same airframe. The 707/727/737/757 have the same basic fuselage cross-section, but everything else is specific to type. (There was a joke that Boeing made fuselages by the mile and sawed it off by the yard for the different types..........................) The wings of all those are wholly different, and the 757 has a different nose shape. The 727-100 was designed for a specific task out of LGA, I believe, so had triple-slotted flaps to make the takeoff performance needed. But, with weight increases on later models, the field performance was not so good. No, I did not operate it, just read about it, watched a few, and flew in the back.
Try
Boeing 727 - Wikipedia, the free encyclopedia for more info.