PPL question about CG
 

Hi there,

Is there any effects of CG being fwd or aft of the limit in case of steep turn situation?

Yes.
Think it through and you'll probably understand it well.

Very broadly, as the CG moves aft the aeroplane becomes less stable in the pitching plane. As you go aft of the CG limit the aeroplane will be come more and more "pitchy" then, at some point (possibly not very far aft of the limit) it will become uncontrollable. With a forward CG it will become more strongly stable, this will reduce its controlability!

So, the short answer, yes, there will be an effect. The advice - don't try this at home!! Really, DO NOT TRY THIS AT HOME!!

Happy landings

3 Point

That's true whether or not in a steep turn.
The question is with respect to a steep turn.
But rather than give the answer, I suggest thinking this through, what happens in a steep turn that could have any bearing on how the aeroplane handles with different CG positions?

Okay, i think we can put it this way..

- if the CG is aft of the limits, the full deflection of the elevator would not be enough to recover from a steep rurn.

and

- if the CG is fwd of the limits, the full deflection of all control would not be enough to recover from a steep rurn.

or its the other way around.

Think about the stall speed as well. In a steep turn the stall speed will increase in any case. But if the CG was beyond the forward limit........

The centre of pressure will move forward as the AoA increases when entering a steep turn. The distance between the CoP and CoG will change and this must have some effect on stability.

Hi Sam.

As the C of G is moved further forward, the stick force, and control deflection to maintain altitude in a steep turn, will increase, until it reaches a point where either the force becomes too great for the pilot to maintain, or the elevator reaches the limit of it's travel. In either case, the aircraft will be unable to maintain altitude.

As the C of G is moved further aft, the stick force/deflection will reduce until a point is reached where the aircraft becomes unstable, pitches uncontrollably into the turn, and stalls/spins, a condition from which it may be unable to recover.

As Dobbin mentioned earlier, the C of P moves forward in a steep turn, so there will be a rearward C of G position where the aircraft is marginally stable in level flight, but becomes unstable as a steep turn is entered.

Hope that helps.


MJ:ok:

Ps. As 3 point says, Please don't try either of these at home!

Everyone jumped in with the answers, I was hoping to try to get Sam to figure out by himself.
In short, the effects of having the CG "out of limits" or even "close" to the limits, are emphasized within a steep turn.
Where you might be able to get the plane to fly when it's "just outside the CG limits", you risk losing control in a turning manoeuvre.

Interestingly, this has been one of the issues with Permit to Fly IFR since a number of aircraft types at the aft C of G have very low elevator stick force per g.

ifitaint...

Indeed, ifitaintboeing! I recall doing an SEP renewal (free of charge - PtoF aeroplane....) in a very nice RV-4. The CG was probably quite aft with 2 PoB and while the aeroplane had nicely responsive controls, trying to fly it accurately for any length of time wasn't all that easy due to rather limited pitch stability. So for flying in IMC it would be rather tiring, I would imagine.

I'm told the early Spitfires were rather like that too.

Good to have seen you last night!

'Twas good to catch up, albeit briefly.

ifitaint...