CG limits, CG effects and the load sheet

Why the tail pushes down

Throw a dart. Heavy end first, it flies true.

Its weight is ahead of its feathers. Knock it, and it swings back.

Watch it go. A wobble, and it straightens itself.

Now weight it at the tail. It tumbles.

No one can throw a tail-heavy dart straight.

It goes end over end.

An aeroplane is built the same way. Its CG sits ahead of the centre of lift.

Lift behind the CG tips the nose down, always, at any speed.

So the tail pushes down. That downward push balances the nose-down tip, and it grows with speed.

Fly faster and the tail pushes harder, so the nose comes up. Slow down, and it drops. The aeroplane looks after itself.

Now a gust knocks the nose up.

Scroll on: it swings back on its own. That is stability: it wants to return.

CG ahead of the centre of lift: stable. The further ahead, the more stable.

CG too far forward

Slide the CG forward.

The arm to the lift grows, so the tail must push down harder. That push is load the wing must carry as well. It acts like extra weight.

More lift needed means a higher angle of attack, so more drag. And so:

A gust barely moves it. Very stable, and very hard to manoeuvre.

Past the limit, the elevators may not lift the nose at rotation or flare at landing.

CG too far aft

This lesson is part of the Navigation plan. See plans

Heavier

This lesson is part of the Navigation plan. See plans

The load and trim sheet

This lesson is part of the Navigation plan. See plans