I am not familiar with the datcom method. I have begun to read about it here:
http://en.wikipedia.org/wiki/USAF_Stability_and_Control_DATCOM
I am sorry this is long, and maybe this is more for myself, to clarify what I do and do not know, but here is my understanding of the Raymer neutral point formula.
What I know, or at least what I think I know.
- X_np
The neutral point of the wing in reference to every other point. This is calculated from the Raymer formula.
- C_L_alpha
The coefficient of lift with respect to angle of attack of the wing. This is calculated from PLLT.
- C_m_alpha_fuselage
The coefficient of moment with respect to angle of attack of the fuselage. The only way I can think of to calculate this is to run a CFD program like Fluent.
- eta_h
The efficiency factor of the horizontal stabilizer. This is equal to the dynamic pressure at the horizontal stabilizer over the free stream dynamic pressure. Normally this is just one. I do not know how to calculate this value without the use of CFD.
- S_h
The planform area of the horizontal stabilizer. This is a simple projected area formula, not sure if that is the right term, but you get what I mean.
- S_w
The planform area of the wing. Again, this is a simple projected area formula.
- C_L_alpha_h
The coefficient of lift with respect to angle of attack of the horizontal stabilizer. I assume this is also calculated from PLLT.
- q
The dynamic pressure, using the standard formula q = 0.5*rho*v_inf^2
What I kind of know.
- Xbar_acw
The aerodynamic center of the wing as a fraction of the wing mean chord. I think this is calculated by this formula:
(2/3)*(W_cr+W_ct-W_cr*W_ct/(W_cr+W_ct))
where,
W_cr = Wing chord root
W_ct = Wing chord tip
- (del alpha_h)/(del alpha)
This is the change in angle of attack of the horizontal stabilizer with respect to the change in angle of attack of the wing. I think to do this you have to find the change the aerodynamic center of the entire aircraft, then geometrically calculate how much a change in angle of attack changes the angle of attack of the horizontal stabilizer.
- Xbar_ach
The aerodynamic center of the horizontal stabilizer as a fraction of the horizontal stabilizer mean chord. I think this is calculated by this formula:
(2/3)*(H_cr+H_ct-H_cr*H_ct/(H_cr+H_ct))
where,
H_cr = Horizontal stabilizer chord root
H_ct = Horizontal stabilizer chord tip
- (del alpha_p)/(del alpha)
This is the change in angle of attack of pressure on the wing with respect to the change in angle of attack of the wing. I don't have the formula on me, but I think I could find it.
- Xbar_p
The center of pressure on the wing as a fraction of the wing mean chord. Again I do not have the formula on me, but I think I'll be able to find it somewhere.
What I definitely do not know.
- F_p_alpha
I think this is the force of pressure with respect to alpha on the wing, but I have no idea how to calculate it.
