TAIL DESIGN AND ITS CONFIGURATION TYPES

B.TECH

1. MODULE-III TAIL DESIGN Horizontal Tail and Vertical Tail LECTURE BY Dr S Kishore Kumar Department of Aerospace Engineering

2. Introduction-Tail Design Define Design Requirements Select Tail Configuration Determine Tail Sizing Aerodynamic Considerations Structural Design Control Surface Design Stability Analysis Iterative Refinement Integration with Other Systems Compliance with Regulations Final Design and Documentation

3. Tail in conventional aircraft The tail in a conventional aircraft often has two components: horizontal tail and vertical tail carries two primary functions: Trim (longitudinal and directional) . Stability (longitudinal and directional). Since two conventional control surfaces (i.e., elevator and rudder) are indeed parts of the tail to implement control, it is proper to add the following item as the third function of a tail: 3. Control (longitudinal and directional).

4. Three functions are described in brief here: Tail Design The first and primary function of a horizontal tail is longitudinal trim, also referred to as equilibrium or balance. The second function of the tails is to provide stability. The horizontal tail is responsible for maintaining longitudinal stability, while the vertical tail is responsible for maintaining directional stability. The third primary function of the tails is control. The elevator as part of the horizontal tail is designed to provide longitudinal control, while the rudder as part of the vertical tail is responsible for providing directional control.

5. The following are the tail parameters which need to be determined during the design process: In general, the tail is designed based on trim requirements but later revised based on stability and control requirements.

6. There are a few other intermediate parameters, such as downwash angle, sidewash angle, and effective angle of attack The above parameters are used to calculate some tail parameters.

7. Illustrates a block diagram of the Tail design process

8. Tail volume coefficients of several aircraft [5]

9. The aircraft trim must be maintained about three axes (x, y, and z): (i) the lateral axis (x), (ii) the longitudinal axis (y), and (iii) the directional axis (z). When the summation of all forces in the x direction (such as drag and thrust) is zero, and the summation of all moments, including aerodynamic pitching moment about the y-axis, is zero, the aircraft is said to have longitudinal trim:

10. The horizontal tail is responsible for maintaining longitudinal trim and making the summations zero, by generating a necessary horizontal tail lift and contributing in the summation of moments about the y-axis. A horizontal tail can be installed behind the fuselage or close to the fuselage nose. The first is called a conventional tail or aft tail, while the second is referred to as a first tail, fore plane, or canard

11. The vertical tail is responsible for maintaining directional trim and making the summations zero, by generating a necessary vertical tail lift and contributing in the summation of moments about the y-axis. When the summation of all forces in the z direction (such as lift and weight) is zero, and the summation of all moments including aerodynamic rolling moment about the x-axis is zero, the aircraft is said to have directional trim:

12. Tail Configuration The list of design requirements that must be considered and satisfied in the selection of tail configurations is as follows:

13. In general, the following tail configurations are available that are capable of satisfying the design requirements in one way or another:

14. Based on the statistics The majority of aircraft designers (about 85%) select the aft tail configuration. About 10% of current aircraft have a canard. About 5% of today’s aircraft have other configurations that could be called unconventional tail configurations.

15. Aft Tail Configuration An Aft Tail Configuration is a traditional aircraft design where the tail section, also known as the empennage , is positioned at the rear of the aircraft. The tail typically consists of a horizontal stabilizer and a vertical stabilizer , providing pitch and yaw stability and control, respectively.

16. aft tail configurations The aft tail configurations are as follows: (i) conventional, (ii)T-shape, (iii) cruciform (+), (iv) H-shape, (v) triple-tail, (vi) V-tail, (vii) inverted V-tail, (viii) improved V-tail, (ix) Y-tail, (x) twin vertical tail, (xi) boom-mounted, (xii) inverted boom-mounted, (xiii) ring-shape, (xiv) twin T, (xv) half T, and (xvi) U-tail

17. Practical Design Steps-Tail Design Process 1. The tail design procedure is as follows: 2. Select tail configuration - (Ex-V Tail, H Tail or any other) Horizontal tail 3. Select horizontal tail location (aft or forward (canard); 4.Select horizontal tail volume coefficient, V H 5. Calculate optimum tail moment arm ( lopt ) to minimize the aircraft drag and weight 6. Calculate horizontal tail planform area, S h

18. 7. Calculate wing/fuselage aerodynamic pitching moment coefficient. where C maf is the wing airfoil section pitching moment coefficient, AR is the wing aspect ratio, is the wing sweep angle, and αt is the wing twist angle (in degrees). 8. Calculate cruise lift coefficient, C LC 9. Calculate horizontal tail desired lift coefficient at cruise from trim

19. 10. Select horizontal tail airfoil section 11.Select horizontal tail sweep angle and dihedral . 12. Select horizontal tail aspect ratio and taper ratio . 13. Determine horizontal tail lift curve slope, C L α_ h 14. Calculate the horizontal tail angle of attack at cruise.

20. 15. Determine the downwash angle at the tail 16. Calculate the horizontal tail incidence angle; i t 17. Calculate tail span, tail root chord, tail tip chord, and tail MAC

21. 18. Calculate the horizontal tail-generated lift coefficient at cruise. 19. If the horizontal tail generated lift coefficient (step 17) is not equal to the horizontal tail required lift coefficient (step 8), adjust the tail incidence. Check the horizontal tail stall. Calculate the horizontal tail contribution to the static longitudinal stability derivative (C mα ). The value for the Cmα derivative must be negative to insure a stabilizing contribution. If the design requirements are not satisfied, redesign the tail.

22. 21. Analyze the dynamic longitudinal stability. If the design requirements are not satisfied, redesign the tail. 22. Optimize the horizontal tail. Reminder: Tail design is an iterative process. When the other aircraft components (such as fuselage and wing) are designed, the aircraft dynamic longitudinal-directional stability needs to be analyzed, and based on that, the tail design may need some adjustments.