@erik,
I have the impression of some misunderstanding, at first view I partly disagree.
To be clear:
- When I speak about 'lift' in this context, it is not the wing lift or the wings + tail. It's only the tail contribution (hstab or hstab+elevator)
- Usually, the CG is before the aerodynamic focus, making the aircraft wanting to pitch down without the tail effect. Hence, the tail lift is negative in steady flight to counteract.
Now, let's imagine two steady flight situations at low airspeed, high alpha:
1 - Usual one:
The aircraft tends to pitch down with the elevator at or close to neutral. The pilot holds the stick pulled back to get a high AoA. The elevator (up deflection) makes negative lift. The hstab, seeing an incident wind from below (high alpha), makes positive lift. The sum of both is still negative to keep the steady equilibrium, steady pitch up moment (counteract the nose down tendency).
- The elevator tends to make the aircraft pitching up, with its own area and deflection,
- the hstab tends to make the aircraft pitching down (because of alpha)
with its own hsatb area only.
2 - Unusual one in steady conditions, only to explain:
The CG is
aft the aerodynamic wing focus, located to get the same velocity, attitude, alpha than example 1
with the elevator at neutral.
- The hstab+elevator exert a positive lift,
- The area to take into account for the moment vs alpha (if some alpha appears) is the [hstab+elevator] one.
This equilibrium with aft CG doesn't exist usually, I imagine such steady conditions only to explain. But they (high alpha, elevator at neutral) can dynamically be encountered,
shortly, on an aircraft with the usual CG location.
Just to say that, in these conditions, the area which makes the pitch-alpha moment is [hstab+elevator]. I say it again: this is temporary a situation, shorter than in the usual example.
Many (if not most) aircraft in FG decouple the elevator-deflection and hsatb-vs-alpha contributions. In this simplified case, to give priority to the stall behavior, I think it is better to take only the hstab area into account for its moment vs alpha.
But,
Thorsten wrote in Sun Aug 06, 2017 5:07 am:........ it is quite possible to capture the effects of hstab and elevator in one deflection-angle independent term and one term that depends on alpha and deflection angle.