Effect of Leading edge shape and Hinge line location on hinge moment characteristics
of NACA0012 Airfoil
M. Vijayakumar+, Barsha Rani-, N. Lakshmi-, S. Sindu- ,
+ Scientist, Aerodynamics Division, ADE, Bangalore
- Final year B.E. (Aero) student, Acharya Institute of Technology, Bangalore
Email:vijayakumarm06@gmail.com, barshar94@gmail.com
Abstract
The control surface Leading Edge shape and Hinge line location of control surface have an important effect on the
Hinge Moment characteristics of the elevator, rudder, flap and aileron. This two parameters control the power to be given by the
actuator to the control surface, i.e. it defines the actuator power requirement.
To study the Hinge moment characteristics of flap/elevator computationally using CFD++ code, NACA0012 airfoil
with flap/elevator of 31.2% of total chord was selected. There are three hinge line locations at 13.46%, 23.1% & 32.7% of flap
chord aft of the leading edge and also three modified flap nose Leading Edge radius were selected. The parameters considered
were nose shape of the flap/elevator, location of hinge line and the comparison between CFD and ESDU (Engineering Science
Data Unit) theoretical calculation.
The floating characteristics of the control surface as well as the magnitude of the hinge moment coefficient depend on
the magnitude of the parameters Chα and Chδ. As the hinge line is moved aft, the moment about the hinge line will reduce and if
the hinge line is moved far enough aft, the resultant moment is reversed, and the control is said to be overbalanced. Reduction in
flap chord decreases the lift of the airplane slightly, but also reduces the hinge moments.
Hence as the hinge moment is reduced, the control power given by actuator to the control surface is minimized. This
will result in reduced weight of the actuator.
Keywords: Leading Edge shape, Hinge line location, CFD++ code, ESDU data, actuator, Chα and Chδ
1. Introduction
The requirements of high speed and low speed airfoils are different as high speed airfoil requires a sharp leading edge
and a low speed airfoil requires a round or blunt leading edge and these requirements are analyzed in the preliminary design
phase of an aircraft wing. Both the leading edge shape and hinge point location of the control surface affect the hinge moment
characteristics of the wing and hence it is important to study these effects.
The deflection of any control surface involves a hinge moment. The hinge moments are the aerodynamic moments that
must be overcome to deflect the control surfaces. It governs the magnitude of augmented pilot force required to move the
corresponding actuator to deflect the control surface. To minimize the size and thus the cost of the actuation system, the control
surfaces should be designed so that the control forces are as low as possible. The objective of this project is to study the hinge
moment characteristics of flap by selecting three hinge line locations for flap deflection and also modifying the leading edge
nose radius of the flap to check the reduction in hinge moment. The reduction in hinge moment will reduce the actuator power
requirement. This will result in reduced weight of the actuator.
2. Geometry and grid detail for NACA0012 airfoil with flap
a. Geometry Details
Figure.1.NACA0012 airfoil with flap.
Figure.2. NACA0012 airfoil with 10% reduction in flap leading Edge nose radius.
Figure.2. NACA0012 airfoil with 20% reduction in flap leading Edge nose radius.
b. Mesh Details
Fig.3 Unstructured Mesh on Naca0012 airfoil with 0º flap deflection
Grid Type
Total No of cells
Number of Tetra cells
Number of Penda cells
No of Prism Layer
Table.1
Unstructured
8.739758 millions
3.717236 million
4.786032 million
24 layer with Y+ = 1
4 Flow Conditions & Solver Details
The free-stream flow conditions are summarized in Table.2
Reynolds Number
3.2 millions (M=0.13)
Static Pressure
101325 Pascal
Static temperature
293.5 K
Angle of attack
-8 to 18 deg
Solver Details
CFD++ software has been used in numerical simulation. In CFD++ software preconditioned compressible-Implicit N-S
solver with S-A turbulence model selected for computation.
5. Results & Discussion
CFD analysis has been carried out on NACA0012 airfoil with flap, three hinge line location (HP=0.73, 0.76, 0.79
from leading edge) and three leading edge nose shape to study hinge moment characteristics using CFD++ software with
unstructured mesh.
(i) The comparison hinge moment vs AOA at Flap deflection = 30º about three hinge line shows that (Shown in Fig-4)
the hinge line location at 79% of the flap chord aft to the leading edge, gives less hinge moment (approx. 60%) when
compared with 73% and 76% hinge line.
(ii) Similarly, the comparison hinge moment vs flap deflection at AOA = 0º shows that (Shown in Fig-5), the hinge line
location at 79% of the flap chord aft to the leading edge, gives less hinge moment when compared with 73% and 76%
hinge line.
(iii) The comparison of hinge moment vs AOA at Flap deflection = 30º for different leading edge nose radius at
Hinge point =0.73, 0.76 m shows that (Shown in Fig-6 & 7), 10% reduction in leading edge nose radius
gives
less hinge moment(5%) when compared with original & 20% reduction of leading edge nose
radius. Up to 15
degree flap deflection, there is a minor increase in hinge moment of maximum 10% is
observed. After 15 degree flap deflection there is a reduction of hinge moment between 15 - 28% observed.
(iv) The comparison between CFD & ESDU data for hinge moment vs AOA at Flap deflection = 30º for Hinge point =0.73
shows that (Shown in Fig-8), there is a deviation 16% is observed. It is due to the non-linear effects which is not captured
by the ESDU data.
(v) Figure.9 shows the Pressure Contour over NACA0012 Airfoil with 30 deg flap deflection and angle of attack, α=0°.
The detailed results will be shown in final paper.
..
Ch v/s AOA
5
10
δ=
30
°
0
0
Ch
-0.01
15
C…
C…
-0.02
-0.03
α(degree)
Figure.4. Hinge moment coefficient vs angle of attack about different hinge line locations at 30º flap deflection.
Ch v/s δ for AOA=0
5.00E-03
α
0.00E+00
0
5
10
15
20
25
Ch
-5.00E-03
-1.00E-02
-1.50E-02
-2.00E-02
Ch_0.
73HP
δ(degree)
Figure.5. Hinge moment coefficient vs flap deflection at different hinge line locations at AOA = 0º.
Figure.6. Hinge moment coefficient vs angle of attack for different LE nose radius at 30º flap deflection at
HP = 0.73m.
Figure.7. Hinge moment coefficient vs angle of attack for different LE nose radius at 30º flap deflection at
HP = 0.76m.
0
-5
Ch v/s AOA
0
-0.1
5
δ=
-0.2
Ch
10
Ch…
-0.3
-0.4
-0.5
α(degree)
Figure.8. Hinge moment coefficient v/s angle of attack at 0.73HP
Figure. 9. Pressure Contour over NACA0012 Airfoil with 30 deg flap deflection and angle of attack, α=0°
6. Conclusion
From the CFD analysis and ESDU calculation carried out to study the Hinge moment characteristics of NACA0012
airfoil with flap by modifying the leading edge shape and hinge line location the following observations are made.
1. When compared on the basis of hinge line, Hinge line 0.79% gives less hinge moment than 0.73% and 0.76% hinge
lines though there is a reduction in maximum lift coefficient. But in real cases the flap may not be deflected to higher
angles (eg: δ=25° or 30°) when the stall angle is reached, hence 0.79% hinge line can be preferred over other hinge
lines.
2. When compared on the basis of leading edge shape, 10 percent reduction of flap leading edge nose radius shape gives
better beneficial results for reducing hinge moment above 15 degree flap deflection. Up to 15 degree flap deflection,
there is a minor increase in Hinge moment of maximum 10% is observed.
3. When the data generated using CFD code is compared with ESDU theoretical data, a deviation of 20 to 30 percent is
observed between CFD and ESDU data for all flap deflection except 5 deg deflection at HP 0.73%. It is because CFD
data predict the non-linear flow behaviour where flow become unsteady after separation, but ESDU data is suitable
only for linear behaviour. So this deviation is expected.
Acknowledgment
The authors wish to thank Mr. N Balachandran, Scientist, GD, ADE, Mr. G Sankar, Scientist, ADE, for their support &
guidance during the code development work.
References
[1]NACA TR 528, “Reduction of Hinge moment of Airplane Control Surface Characteristics by Tabs,” by T.A Harris, 1935.
[2]NACA TR 675, “Effect of Elevator Nose Shape, Gap, Balance and Tabs on the Aerodynamic Characteristics of a Horizontal
Tail Surface,” by Goett and Reeder, 1939.
[3] NACA TR 721, “Determination of Control Surface Characteristics from NACA Plain flap and Tab Data, “ by Ames and
Sears, 19441.
[4] NACA WR L-663, “Wind-Tunnel Data on the Aerodynamic Characteristics of Airplane Control surfaces”, by R. I. Sears,
1943.
[5]NACA WR A-11 “Computation of Hinge Moment Characteristics of Horizontal Tails from section Data,” by R. M Crane,
1945.
[6] Jack D. Brewer and M.J., “Wind-Tunnel Investigation of Tab Balance on Tab and Control Surface Characteristics”, August
14 1947
[7] Harold T. Johnson, “Measurements of Aerodynamic Characteristics at Transonic Speeds of an Unswept and Untapered
NACA 65-009 Airfoil”, June 10, 1953
[8] James M. Luckring, “A Survey of Factors Affecting Blunt Leading-Edge,
Separation for Swept and Semi-Slender
Wings”, NASA Langley Research Center, Hampton, VA, 1992
[9] M. L. Eglington, “Control of a Leading-Edge Flap using the Nose Pressure
Distribution”, N&O Joernaal Julie, 1992
[10] D.M. Somers, “Effect of Flap Deflection on Section Characteristics of S813 Airfoil”, State College, Pennsylvania, January
2005
[11] Drela, Mark. “XFOIL Subsonic Airfoil Development System.” 12 Feb 2008.