MAC limits?

[newmei]

In general on a big a/c what are normal MAC limits? Like say forom .22 to .41 MAC? Do you even have a particular MAC limit published like a envelope on a small a/c? I would think so but this confuses me.

Thanks

 

[mar]

Close but not quite

Hi Newmei--Here's a paragraph from my DC6 W/B section. I wouldn't know how they do it on modern jet transports but I'm guessing it does *not* involve a sharp pencil and a straight-edge.

"The forward center of gravity limit for DC-6A and Swing-tail cargo operation is 11.0% from the empty weight up to 85,600 lbs. with a straight line variation from 11.0% to 14.1% at 102,000 lbs. and then a straight line variation between 14.1% at 102,200 lbs. and 16.9% at 107,000 lbs. These limits are based on wheels down operation. The forward CG limit is allowed to shift further forward with the landing gear up, however, since a wheels down take off or landing is the most restrictive case only those limits are shown. The aft loading limit is the same for both wheels up and wheels down operation. The maximum aft center of gravity is 33.0%."

So. Yeah, if you were to trace those limits out graph-wise you'd end up with an "envelope"--or more precisely a trapezoid.

On our W/B worksheet we just follow the arrows left and right (less or more weight) and extend that line down into the envelope. Then we come across with the takeoff and landing weights e voila' we can record both MACs.

Piece of cake!
Fly safe.