View Full Version : Ground Stability W&B

nobbyknownowt

19th Jun 2007, 14:22

Here's one for you.

How can you calculate the %MAC CG that the aircraft will tip up at during loading?

I guess its when there is less than zero on the nose wheel but how to calculate that?

If you use normal W&B formulae like CG=D-((F*L)/W) and F=0 then the answer is always D

Just curious:}

cheers

Nobby

When the CoG moves aft of the vertical plane through the line between the two aftmost supporting points of the potentially tipping rigid body is the geometrical answer.

In your formula, D would be the distance to the CoG from datum prior to applying the force F at a distance L from the center of gravity of a body with the weight W. If F is zero, D will indeed remain exactly D.

If you are really asking how you can calculate if the aircraft will tip over, the answer is that you need to calculate the CoG of the aircraft and compare it with the (hopefully) known limiting location given by the geometry of the landing gear.

Mad (Flt) Scientist

19th Jun 2007, 21:21

One caveat to a simple calculation.

The cg "during loading" will be moving about as the cargo is actually loaded. There may also be (small) forces exerted by the motion of the cargo in the aircraft. I can certainly conceive of a situation where I think I'm loading the aircraft such that it cannot tip over in the final loaded configuration but where in fact there's a risk of tip-over during loading

I'd say the vast majority of incidents where aircraft tip over on the ramp stem not from poor load plans but from poor planning of loading or unloading. "Hey, let's just get the front cargo hold emptied while the catering are blocking the rear". :ouch:

nobbyknownowt

20th Jun 2007, 13:42

Course it is:D

take length of MAC and length of MAC minus distance of main wheels to aft edge of MAC and work out the percentage!

DOH!

cheers

Nobby