Chapter 12 – Part D Design of Control Surfaces

Chapter 12 – Part D Design of Control Surfaces
Aircraft Design; A Systems Engineering Approach Mohammad Sadraey Wiley, 2012 Chapter 12 – Part D Design of Control Surfaces Grumman E-2C Hawkeye 2000 (G-123) (Courtesy of Antony Osborne) Copyright © Wiley. Permission required for reproduction or display.

Chapter 12. Design of Control Surfaces
Overview Introduction Configuration Selection of Control Surfaces Handling Qualities Aileron Design Elevator Design Rudder Design Aerodynamic Balance and Mass Balance Chapter Examples 11/27/2018 Chapter 12. Design of Control Surfaces

7. Aerodynamic Balance and Mass Balance
Saab Tp100C (340B-Plus) (Reproduced from permission of A J Best) 11/27/2018 Chapter 12. Design of Control Surfaces

Aerodynamic Balance and Mass Balance
The hinge moment created by a control surface must be such that the pilot is capable of handling the moment comfortably, as well as the effort should also be small enough to ensure that the pilot does not tire in a prolong application. The aerodynamic force produced by a control surface; if not managed properly; may interact with inertia and generate an undesirable structural phenomenon called flutter. Two main objectives of aerodynamic and mass balance are: Reduction of required force felt by pilot Avoiding flutter 11/27/2018 Chapter 12. Design of Control Surfaces

Hinge moment The hinge moment created by a control surface: Hinge moment coefficient: Two non-dimensional derivatives: 11/27/2018 Chapter 12. Design of Control Surfaces

Pilot stick force The stick/yoke/pedal force (Fs) is related to the hinge moment: GC (gearing ratio) is the ratio between the linear/angular movement of the stick/wheel to deflection of the control surface: For stick/pedal: For yoke/wheel: 11/27/2018 Chapter 12. Design of Control Surfaces

1. Aerodynamic Balance In order to insure that the pilot is fully and comfortably capable of moving the stick/pedal and deflect the control surfaces, the aerodynamic force and hinge moment of a control surface must be balanced or reduced. 11/27/2018 Chapter 12. Design of Control Surfaces

Aerodynamic balance The technique of aerodynamic balance is applied not only to manually controlled control surfaces, but also to power-assisted surfaces. In large transport aircraft, artificial feel is often incorporated into the controls so that the pilot has a sense of feel in the controls. The designer must be careful not to overbalance the control surface 11/27/2018 Chapter 12. Design of Control Surfaces

Ways to aerodynamically balance
Horn Balance Overhanging balance Internal Sealed Frise Balance Trim Tab Balance Tab Servo Tab Spring Tab 11/27/2018 Chapter 12. Design of Control Surfaces

1. Horn Balance A horn balance is the addition of an extra surface to the control surface ahead of the hinge line. A horn balance is a low cost and simple technique and is used mostly on older and GA aircraft. The effectiveness of a horn balance depends upon the area and moment of the horn ahead of the hinge, to the area and moment of the horn behind the hinge. By careful design of the horn, the pilot stick force is significantly reduced. 11/27/2018 Chapter 12. Design of Control Surfaces

Two types Horn extends to the leading edge of the lifting surface, and is called unshielded horn. Horn has part of the lifting surface ahead of it and is said to be shielded horn. 11/27/2018 Chapter 12. Design of Control Surfaces

Short 360-100 (Reproduced from permission of Jenny Coffey) 11/27/2018
Chapter 12. Design of Control Surfaces

Control surface balance
The control surface balance is defined as the ratio between the control surface area forward of hinge line to that of aft of hinge line. The most popular application of the horn balance is elevator, and next is the rudder. Horn balance is rarely used on aileron. 11/27/2018 Chapter 12. Design of Control Surfaces

2. Overhanging balance When the hinge line is moved aft (set back), closer to the control surface center of pressure, the surface is said to be aerodynamically balanced using nose overhang. The shape of leading edge of control surface is essential in effectiveness of the overhang balance. The nose contour must be shaped such that the nose does not protrude into the airstream even at high control surface deflections. A highly curved protrusion, which would generate large suctions on the nose, would overbalance the surface, tending to move it to a higher deflection. 11/27/2018 Chapter 12. Design of Control Surfaces

Overhanging balance If the gap between the leading edge of control surface and trailing edge of lifting surface is not sealed, the airflow leaks through the gap; tends to improve the balance. 11/27/2018 Chapter 12. Design of Control Surfaces

Overhanging balance The leading edge of the control surface could be either blunted or sharpened. A blunt leading edge (either round or elliptic) will cause a suction flow around the radius and lightens the surface. Sharpening the leading edge reduces the suction ahead of the hinge when the surface is deflected and heavies the surface. A blunt nose has a greater effect on hinge moment than a sharp nose, but it may create non-linearities at small deflections. 11/27/2018 Chapter 12. Design of Control Surfaces

3. Internal Sealed Internal sealed utilizes an internal flexible, airtight seal to feel the pressure difference between the top and bottom surfaces and to provide the balancing moment. Each side of the seal is open to atmosphere at the shroud trailing edges. 11/27/2018 Chapter 12. Design of Control Surfaces

Internal Sealed The advantages mainly are that the seal prevents the energy loss and flow from high pressure surface to the low pressure one; and that the non-linearities do not occur. This results in a reduction of the induced drag by as much as about 5% of the total induced drag. The internal overhang effectiveness is comparable to the overhang balance. 11/27/2018 Chapter 12. Design of Control Surfaces

4. Frise Balance A Frise balance is applied by making the control surface to have an unsymmetrical nose profile. At small angles of deflection the up-going aileron is overbalanced, and this helps to deflect the down going aileron on the other side. 11/27/2018 Chapter 12. Design of Control Surfaces

Frise Balance The advantages of frise ailerons are a large balance effect with a small setback hinge; and they are relatively easy to construct. The behavior of the control surface at low deflection angle is nonlinear; rotating up overbalances the surface, while rotating down creates a heavy force. The effectiveness of the frise balance is a function of rigging point, hence a careful rigging is needed for an effective balance. 11/27/2018 Chapter 12. Design of Control Surfaces

5. Trim Tab Tabs are secondary control surfaces placed at the trailing edges of the primary control surfaces. Trim tabs are used to reduce the force the pilot applies to the stick to zero. Trim tabs are frequently used in reversible flight control systems (e.g., mechanical). Trailing edge tabs are employed as variable trimming devices, operated by stick/wheel directly from the cockpit. 11/27/2018 Chapter 12. Design of Control Surfaces

Trim Tab Trim tabs are utilized even in very large transport aircraft (such as KC-135); due to the fact that, the loss of all engines are conceivable; thus pilot must be able to trim the jumbo aircraft with his/her body force. For instance, in the past history flight of Boeing 747, there is at least three cases where all four engines become inoperative. 11/27/2018 Chapter 12. Design of Control Surfaces

B-747, one incident One incident involved British Airways Flight 9, a scheduled flight from London Heathrow to Auckland. On 24 June 1982, a Boeing 747 aircraft flew into a cloud of volcanic ash thrown up by the eruption of Mount Galunggung, resulting in the failure of all four engines. The aircraft was diverted to Jakarta in the hope that enough engines could be restarted to allow it to land there. The aircraft was able to glide far enough to exit the ash cloud, and all engines were restarted, allowing the aircraft to land safely at the Halim Perdanakusuma Airport in Jakarta. Anne Deus 11/27/2018 Chapter 12. Design of Control Surfaces

Trim tab To achieve a zero cockpit control force, the trim tab is deflected opposite to the elevator deflection. Trim tabs may be adjusted when the aircraft is on the ground; or may be manually operated and set by the pilot during flight. 11/27/2018 Chapter 12. Design of Control Surfaces

Trim tab When a lifting surface is equipped with a tab, the hinge moment coefficient; Ch is given by: where dt represents the tab deflection, and the parameter is a non-dimensional derivative: The tab-to-control-surface-chord ratio is usually about 0.2 to 0.4. 11/27/2018 Chapter 12. Design of Control Surfaces

Trim wheel Trim tabs are usually deflected by a device referred to as the trim wheel. Trim wheel and trim tab assist a pilot to longitudinally trim a large aircraft with his/her hand force (say 50 lbf), and to keep a large elevator at any deflection needed at any speed. Cockpit of BAC FG One-Eleven (Reproduced from permission of A J Best) 11/27/2018 Chapter 12. Design of Control Surfaces

Compensate for any imperfection in production
In an RC model aircraft, homebuilt aircraft, and even in a small GA aircraft, a simple plate (i.e., tab) may be permanently added to the vertical tail to directionally balance the aircraft and to compensate for any imperfection in production. This makes the aircraft symmetric about xz plane. The need for such tab is not revealed until the first flight test. 11/27/2018 Chapter 12. Design of Control Surfaces

Cessna Citation 500 Large transport aircraft such as Boeing 747 and Boeing 737 are equipped with horizontal tail trim tab, as well as the vertical tail trim tab. Business jets such as Cessna Citation 500 are equipped with vertical tail trim tab. (Reproduced from permission of Jenny Coffey) 11/27/2018 Chapter 12. Design of Control Surfaces

6. Balance Tab The balance tab (sometimes called geared tab, geared balance tab, or link tab) is geared to the primary control surface in such a way that it moves in a given ratio to the control surface movement, and in the opposite direction. 11/27/2018 Chapter 12. Design of Control Surfaces

Balance Tab The geared tab lift is in the direction opposite to that of the basic control surface and thereby reduces the effectiveness of the surface. The tab creates a hinge moment about its own hinge as well as a hinge moment about the hinge of control surface tending to increase the surface angle. The tab is directly connected to the lifting surface via a mechanical link; the length of the link may be adjusted. The tab neutral position (i.e., angle) with respect to control surface can be easily adjusted to obtain the desired amount of balance. 11/27/2018 Chapter 12. Design of Control Surfaces

Balance Tab A balance tab may be employed as a trim tab by making the tab follower link variable in length and by providing the pilot with the authority to vary the length of the link. This is often applied with the help of an electro-mechanical jackscrew in the tab arm. A version of balancing tab is called an anti-balance tab where the tab moves in the same direction as the surface, due to different connection to the lifting surface. Due to the opposite direction of the balance tab and the anti-balance balance tab, the balance tab is a exhibiting a lagging behavior, while an anti-balance tab is exhibiting a leading behavior. 11/27/2018 Chapter 12. Design of Control Surfaces

7. Servo Tab A servo tab is a tab in which the stick/wheel is connected directly to the tab, which is hinged to the control surface. In the cases of trim tab and balance tab, the stick/wheel is connected to the control surface. 11/27/2018 Chapter 12. Design of Control Surfaces

Servo Tab In the cases of trim tab and balance tab, when the pilot moves stick/rotates wheel, the control surface is deflected; while in the case of servo tab, when the pilot moves stick/rotates wheel, the tab is deflected. The deflection of the control surface is performed via servo tab. Pilot controls the servo tab, but servo tab controls the control surface. The stick/wheel force depends on the hinge moment of both control surface and the tab. 11/27/2018 Chapter 12. Design of Control Surfaces

Servo Tab The servo tab effectiveness is a function of the ratio between two arms of tab and control surface (i.e. z1/z2). The servo tab in not employed in many modern aircraft, since its effectiveness at low speeds (particularly at stall) is not reliable. A very low stick/wheel force is achieved for a small arm ratio (z1/z2); however, the control is easily overbalanced. 11/27/2018 Chapter 12. Design of Control Surfaces

Lockheed C-130 Hercules Large transport aircraft such as Boeing KC-135 and Boeing 707 are equipped with horizontal tail trim tab, as well as the vertical tail trim tab. Military transport aircraft Lockheed C-130B is equipped with horizontal tail trim tab, as well as the servo tab. Lockheed Martin C-130J Hercules C5 (L-382) (Reproduced from permission of Jenny Coffey) 11/27/2018 Chapter 12. Design of Control Surfaces

Elevator and flap mass balance in CAP Aviation CAP-232
(Courtesy of Jenny Coffey) 11/27/2018 Chapter 12. Design of Control Surfaces

Rudder tab of Boeing 707 (Courtesy of A J Best) 11/27/2018 Chapter 12. Design of Control Surfaces

Aileron, elevator, and rudder tabs of ATR-72-600
(Courtesy of Antony Osborne) 11/27/2018 Chapter 12. Design of Control Surfaces

Rudder tab of Mudry CAP-10B
(Courtesy of Jenny Coffey) 11/27/2018 Chapter 12. Design of Control Surfaces

8. Spring Tab A spring tab is basically similar to a servo tab except a spring is added. The spring is connecting the tab to either lifting surface or control surface. The addition of a spring to a servo tab will further reduce the stick/wheel force, so a spring tab may be assumed as a variable servo tab. 11/27/2018 Chapter 12. Design of Control Surfaces

Spring tab The effectiveness of the spring tab ( ) is a function of the ratio z1/z2 and spring constant. The control force varies moderately with speed, since the effectiveness of the spring tab decreases with airspeed. Unlike servo tab, the servo tab is not overbalanced even at stall speed, since the tab deflects only when there is a load on the control surface. 11/27/2018 Chapter 12. Design of Control Surfaces

Spring tab Unlike servo tab, the servo tab is not overbalanced even at stall speed, since the tab deflects only when there is a load on the control surface. One undesirable side effect of the spring tab originates from the addition of a springy element. The response to pilot command is relatively slow, due to the floating action of the control surface. Spring tab may be pre-loaded to avoid them from coming into effect for small pilot force. 11/27/2018 Chapter 12. Design of Control Surfaces

2. Mass Balance There are many aircraft; with reversible or irreversible flight control systems; that are equipped with a mechanism which allows the aircraft to fly with a condition usually referred to as control-free, stick-free, or yoke-free. Such mechanism permits the control surface to be left on place (i.e., free to move); since the control surface’s hinge moment has been set to zero by devices such as tab. When aircraft is operating with the controls-free, the control surfaces will oscillate when a gust moves the control surface from the trimmed position. 11/27/2018 Chapter 12. Design of Control Surfaces

Flutter A freely oscillating control surface (e.g. elevator) may create an undesirable phenomenon called flutter. Flutter is a dynamic phenomenon and may lead to dynamic instability of the airplane that cannot be tolerated. Flutter is characterized as a high frequency oscillation of the control surface caused by an interaction between the aerodynamic force (e.g. local lift) and weight of the control surface. This undesirable phenomenon can be prevented by stiffening the lifting surface’s structure (wing, horizontal tail, and vertical tail) in bending and torsion. Another solution is to move the control surface center of gravity near or in front of the hinge line. 11/27/2018 Chapter 12. Design of Control Surfaces

Mass Balance Control surfaces are deflected around their hinge axes, which is close to their leading edges (about 5% - 10% of the chord). The center of gravity of a control surface is a little more aft (about 20% - 40% of the chord). This implies that the center of gravity and hinge axis of a control surface do not coincide. A counterbalancing mass needs to be set ahead of the surface to shift the center of gravity of a control surface forward to coincide with the hinge line. 11/27/2018 Chapter 12. Design of Control Surfaces

Mass balance Many light aircraft and gliders which do not fly fast do not possess mass balanced control surfaces. Except for very low speed aircraft, the flight control surfaces in an aircraft with a reversible flight control system are almost always mass balanced. The exact same effect of mass balance can be produced with the application of mechanical spring. 11/27/2018 Chapter 12. Design of Control Surfaces

Un-mass balancing In an aircraft with irreversible flight control system, there is no need for mass balance. Repainted an aircraft causes un-mass balancing, since the point goes over the entire surface, and even the mass. It is noticeable that the application of mass and spring balancing also improves stick-free stability of an aircraft; as well it reduces the pilot force to deflect a control surface. In order to reduce the drag of the bare mass, it could be covered, faired, or aerodynamically shaped. 11/27/2018 Chapter 12. Design of Control Surfaces

Lockheed C-5 Galaxy Transport aircraft Lockheed C-130 Hercules and Lockheed C-5 Galaxy are mass balanced with Uranium, so their control surfaces have a thick skin. 11/27/2018 Chapter 12. Design of Control Surfaces

Lockheed C-5B Galaxy (Courtesy of Antony Osborne) 11/27/2018 Chapter 12. Design of Control Surfaces

Example 12.4: Aileron Design Example
Problem statement: Design the roll control surface(s) for a land-based military transport aircraft to meet roll control MIL-STD requirements. The aircraft has a conventional configuration and the following geometry and weight characteristics: mTO = 6,500 kg, S = 21 m2, AR = 8,  = 0.7, Sh = 5.3 m2, Sv = 4.2 m2, Vs = 80 knot, = 4.5 1/rad, Ixx = 28,000 kg.m2 Furthermore, the control surface must be of low cost and manufacturable. The high-lift device has been already designed and the outboard flap location is determined to be at 60% of the wing semispan. The wing rear spar is located at 75% of the wing chord. 11/27/2018 Chapter 12. Design of Control Surfaces

Example 12.4: Solution The geometry of each aileron is as follows: 11/27/2018 Chapter 12. Design of Control Surfaces

Example 12.5: Elevator Design Example
Problem statement: Figure illustrates the geometry of a high-wing twin jet engine light utility aircraft which is equipped with a tricycle landing gear. Design an elevator for this aircraft which has the following characteristics. mTO = 20,000 kg, Vs = 85 KEAS, Iyy = 150,000 kg.m2, Tmax = 2×28 kN, Lf = 23 m, VC = 360 KTAS (at 25,000 ft), CLo = 0.24, CDoC = 0.024, CDoTO = 0.038, CLa = 5.7 1/rad Wing: S = 70 m2, AR = 8, CLawf = CLaw = 5.7 1/rad, e = 0.88,  = 1, DCLflapTO = 0.5, Cmacwf = 0.05, iw = 2 deg, ho = 0.25, asTO = 12 deg Horizontal tail: Sh = 16 m2, bh = 9 m, CLah = 4.3 1/rad, ih = -1 deg, h = 1, hh = 0.96, ah_s = 14 deg, Airfoil section: NACA 0009, atwist = 0, 11/27/2018 Chapter 12. Design of Control Surfaces

Example 12.5 Aircraft geometry 11/27/2018 Chapter 12. Design of Control Surfaces

Example 12.5: Solution Geometry of the elevator 11/27/2018 Chapter 12. Design of Control Surfaces

Example 12.6: Rudder Design Example
Problem Statement: A large transport aircraft with a maximum take-off mass of 260,000 kg is equipped with four turbofan engines each generating 140 kN of thrust. The distance between the most aft and the most forward cg is 1.5 m. The top-view and side-view of the aircraft are shown in Figure 12.51; fuselage has a cylindrical shape. Other characteristics of the aircraft are as follows: S = 365 m2; b = 60 m; SV = 50 m2; Vs = 120 knot; ; hv = 0.97; Lf = 63 m; Df = 5.5 m; The aircraft is not spinnable, and is required to be able to land safely when there is a crosswind of 40 knots. Design a rudder for this aircraft. 11/27/2018 Chapter 12. Design of Control Surfaces

Example 12.6 Top-view and side-view of the aircraft 11/27/2018 Chapter 12. Design of Control Surfaces

Example 12.6 Center of projected side area 11/27/2018 Chapter 12. Design of Control Surfaces

Example 12.6 The geometry of the rudder 11/27/2018 Chapter 12. Design of Control Surfaces

References Hawkins F. H., Human Factors in Flight, 2nd edition, Ashgate, 1998 Bridger R.S., Introduction to Ergonomics, 3rd Edition, R.S. Bridger, CRC Press, 2008 Kroemer K.H.E., Kroemer H.B., Kroemer-Elbert K.E., Ergonomics: How to Design for Ease and Efficiency, 2nd Edition, Prentice Hall; 2nd edition, 2000 Salyendy G., Handbook of Human Factors and Ergonomics, 3rd edition, Wiley, 2006 Vink P., Aircraft Interior Comfort and Design; Ergonomics Design Management: Theory and Applications, CRC Press, 2011 Federal Aviation Regulations, Part 23, Airworthiness Standards: Normal, Utility, Aerobatic, and Commuter Category Airplanes, Federal Aviation Administration, Department of Transportation, Washington DC Federal Aviation Regulations, Part 25, Airworthiness Standards: Transport Category Airplanes, Federal Aviation Administration, Department of Transportation, Washington DC MIL-STD-1797, Flying Qualities of Piloted Aircraft, Department of Defense, Washington DC, 1997 MIL-F-8785C, Military Specification: Flying Qualities of Piloted Airplanes, Department of Defense, Washington DC, 1980 Harper R. P. and Cooper G. E., Handling Qualities and Pilot Evaluation, Journal of Guidance, Control, and Dynamics, Vol. 9, No. 5, 1986, pp Stevens B. L., and Lewis F. L., Aircraft Control and Simulation, 2nd edition, Wiley, 2003 Roskam J., Airplane Flight Dynamics and Automatic Flight Control, DAR Corp., 2007 Mclean D., Automatic Flight Control Systems, Prentice-Hall, 1990 Nelson R., Flight Stability and Automatic Control, McGraw Hill, 1989 McCormick, B.W., Aerodynamics, Aeronautics and Flight Mechanics, Wiley, 1979 Etkin B. and Reid L. D., Dynamics of Flight-Stability and Control, Third edition, Wiley, 1996 JAR-23: Normal, Utility, Aerobatic, and Commuter Category Aeroplanes, European Aviation Safety Agency, Joint Aviation Authorities, Netherlands, 2007 Joint Aviation Requirements JAR-25, Large Aeroplanes, European Aviation Safety Agency, Joint Aviation Authorities, Netherlands, 2007 Hoak D. E., Ellison D. E., et al, “USAF Stability and Control DATCOM,” Flight Control Division, Air Force Flight Dynamics Laboratory, Wright-Patterson AFB, Ohio, 1978 Spiegel M. R. and Liu J., Mathematical handbook of Formulas and tables, second edition, Schaum’s Outlines, McGraw-Hill, 1999 Abbott I.H. & Von Doenhoff A.F., Theory of Wing Sections, Dover, New York, 1959 Spiegel M. R. and Liu J., Schaum’s Outline Series in mathematical handbook of formulas and tables, McGraw-Hill, 1999 Sadraey M. and Colgren R., Derivations of Major Coupling Derivatives, and the State Space Formulation of the Coupled Equations of Motion, AIAA , 6th AIAA Aviation Technology, Integration and Operations Conference (ATIO), Wichita, Kansas, Sep , 2006 Roskam J., Airplane Design, DAR Corp., 2003 Torenbeek, E, Synthesis of subsonic airplane design, Delft University Press, 1996 Stinton D., The Design of the Aeroplane, AIAA, 2001 Jackson P., Jane’s All the World’s Aircraft, Jane’s information group, Various years 11/27/2018 Chapter 12. Design of Control Surfaces

Dassault-Dornier Alpha Jet A
(Reproduced from permission of Antony Osborne) 11/27/2018 Chapter 12. Design of Control Surfaces

Grumman EA-6B Prowler (G-128)
(Reproduced from permission of Antony Osborne) 11/27/2018 Chapter 12. Design of Control Surfaces

Chapter 12 – Part D Design of Control Surfaces

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