1) The Aerodynamic Center is never referred to as the "Neutral Point". The Neutral Point is vastly different and must not be confused with anything else except what it represents - it is that position on the MAC where the airplane is neutrally stable (static stability criteria). If the CG is located forward but near the NP it may be twitchy and difficult to fly. If it's at the NP it will have no significant stabilizing behavior and will most likely be close to unflyable. If the CG is past the NP then the airplane is unstable and uncontrollable.The MAC is 42" and the AC [ Aerodynamic Center] some times called the neutral point is about 25% of the a MAC. Sweping the wing forward 3-5 degrees would move the AC forward. I know the aircraft CG should be forward of the AC. But what should the range be in inches?
The ac is the property of the airfoil and also of the whole wing - part of the stability calculation involves finding the ac position of the three dimensional wing. For a rectangular planform it's pretty much the same as for the airfoil section but I have seen slight shifts also, so just in case, it's a good idea to go through the calculation exercise anyway.Just to make sure I've got the terminology down (I'm pretty sure I've got the principles down):
-the AC is a property of the wing?
-the neutral point is a property of the whole aircraft?
-or is it that AC is for the aircraft geometrically, and NP accounts for pitcing moment and stuff?
I've flown models of conventional tractor configuration where the c.g. was at greater than 100 percent MAC. It's true they had very large tails.
And assuming I'm reading it right, your last statement is highly improbable. Which airplane are you referring to?
Ironically enough, it was a month ago on this thread - just a couple of pages back.1) About a month ago i posted an excerpt from one of my programs that shows some of the calculation steps used in deriving this part of the airplane's characteristics (I forget now which thread that was in - anyone?). Doing it right does involve a bit of work.
Sorry, my mind (and I was assuming our discussion) was rooted in conventionally configured aircraft. Yes, it is true the cg can be located in a wide variety of locations (including off the main wing), depending on wing sizing and loading, and lifting configuration, but the actual "allowable" range of motion tends to be very small for those layouts in order to still arrive at a safe and controllable airplane. Case in point, the allowable ranges of most canards are about three quarters to half of what an equivalent conventional airplane would have.