Moment arm is a physics concept to do with levers (for example crowbars, wrenches, shovels etc...) You know how with a long lever you can move more than with a short lever? That's because the moment arm is longer. Force applied to an object with a lever is proportional to lever length AND
force at the end of the lever.
With me so far? If we are still having language issues the pics here should be helpful: http://en.wikipedia.org/wiki/Lever
So anyway, back to the SP
. The fin holds the plane stable in yaw and the rudder actually yaws on command. With longer fuselage, the rudder and fin are further from the center of yaw and can be made smaller since the moment arm (length of the lever) is longer. The SP
is shorter than the garden variety 747, so the moment arm is shorter. Thus more force need to be applied. So the fin and rudder were sized up.
is to the plain vanilla 747 as if you were digging with a shovel and all of a sudden had to use a 20% shorter handle. You would need to apply more force to the handle at your end to lift the same amount.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo