Question

CLE 0.05 0.33 0.355 -0.923 TABLE B.1 General aviation airplane: NAVION Longitudinal се се CLE Co. C CL C Cu C Cou C M-0.158 Sea level 0.41 4.44 -0.683 0.0 - 4.36 3.8 -9.96 0.0 00 0.0 Lateral C C CH Ca C M-0.158 Sea level -0.564 -0.074 -0.071 -0.410 -0.0575 0.107 -0.125 -0.134 -0.0035 0.157 0.107 -0.072 Note: All derivatives are per radian. ca C c c Center of gravity and mass characteristics W - 2,750 lbs CG at 29.5% MAC - 1048 slug.ft - 3000 slug ft -3530 slug.ft Reference geometry S - 184 ft b = 33.4ft - 5.7 ft AUTO FIGURE B.1 Three-view sketch and stability data for a general 2.5. Using the data for the business jet aircraft included in Appendix B, determine the following longitudinal stability information at subsonic speeds: (a) Wing contribution to the pitching moment (b) Tail contribution to the pitching moment (c) Fuselage contribution to the pitching moment, (d) Total pitching moment (e) Plot the various contributions (Estimate the stick fixed neutral point

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Answer 1

For a business jet aircraft

Wing contribution to the pitching moment:-

In pitching moment, the lift and drag are always perpendicular and parallel to the virtual wind. Because of this it not suitable to use these forces to obtain the moments for their arms to the center of gravity will change with angle of the attack. For this reason, all forces are determined into normal and chord wise forces whose axes remain fixed with the airplane and whose arms are for that reason constant.

Tail contribution to the pitching moment:-

The tail contribution to stability was found to be

dcm/dcl = dcn/dcl VB nt

For the small angles of attack, the lift curve slope of the tail is very nearly the same as the slope of the normal force curve.

The expression nt is the ratio of the tail dynamic pressure to the wing dynamic pressure and nt varies with the location of the tail with respect to wing wake, prop slipstream, etc. For power-off considerations nt varies from 0.645 to 0.949 due to boundary layer losses.

Fuselage contribution to the pitching moment:-

The fuselage contribution is complicated to divide from the wing terms because it was strongly influenced by interference from the wing flow field. Wind tunnel tests of the wing-body blend are used by airplane designers to obtain information about the fuselage influence on stability. A fuselage by itself is almost always destabilizing because the center of pressure is usually ahead of the center of gravity. The magnitude of the 'destabilization effects of the fuselage requires their consideration in the equilibrium and stability equations.

Total pitching movement:-

The pitching moment on an airfoil is produced by the force on the airfoil if that aerodynamic power is considered to be applied, not at the center of pressure. The pitching moment on the wing of an airplane is part of the total moment that must be balanced using the lift on the horizontal stabilizer. More generally, a pitching moment is any moment acting on the pitch axis of a moving body.

Plot the various contributions:-

The normal force involvement a prop or turbojet is destabilizing if the prop of the air plane cg.

Estimate the stick fixed neutral point:-

The stick fixed value is almost equal to the cg-hn.

The stick fixed force gradient will increase by using body weight.

Hope it helps...