Item 0912
DESIGN: UniCopter ~
Trim, Stability & Control - Stability - Speed Stability and the Horizontal StabilizerOverview:
Considerations regarding the improvements to Speed Stability, by the Horizontal Stabilizer.
Lift
[L]:An aerodynamic force caused by air flowing over an airfoil.
etc. etc. etc.For an airplane wing:
LW = (ρ / 2) * V2 * S * CL . Where S is the area of the wing.c
l = L / ((ρ * A * Vfwd ^ 2) / 2)c
d = D / ((ρ * A * Vfwd ^ 2) / 2)
add incidence and angle of attack (see draring in prouty
Physical Parameters:
A
= 3 ft.2Aeff
= ? ft.2x
H = -7.67 ft.z
H = 2.4 ft.x
CG = 0.265 ft.z
CG = -2.18 ft.H.S. Airfoil: NACA 0012
This will be changed to an inverted asymmetrical.Aerodynamic Parameters:
Forward velocity: [100 MPH] V = 146.7 ft. sec.??
Density
ρ = 0.002378 slug/ft.^3 At sea level, standard conditions
Calculated Values:
α
H = iH + ΘNote that the area in the 2 equations below should maybe reduced to whatever the effective area will be?
L = (ρ / 2) * V
2 * A * CLD = (ρ / 2) * V
2 * A * CD(ρ / 2) * V
2 * A = 76.77Note forward speed will change as angle of attack increased
In the case of a sudden dive the above may not be true.
C
m = m / ((ρ * A * Vfwd ^ 2) / 2) Pitching moment coefficient.
|
Angle of Attack: [αH] |
Coeff. of Lift: [cl] |
Coeff. of Drag: [cd] |
Coeff. of Momentum: [cm] |
Lift: [L] |
Drag: [D] |
H-force: [H] |
Lift x Arm: |
Drag x Arm: |
Moment: [m] |
|
|
|
0.0 |
0.0 |
0.006 |
0.0 |
0.0 |
0.46 |
|
0 |
1 |
1 |
|
|
2.0 |
0.2 |
0.006 |
-0.003 |
15.3 |
0.46 |
|
117 |
1 |
118 |
|
|
4.0 |
0.4 |
0.007 |
|
|
|
|
|
|
|
|
|
6.0 |
|
|
|
|
|
|
|
|
|
|
|
8.0 |
0.9 |
0.009 |
-0.01 |
69.1 |
0.77 |
|
530 |
2 |
532 |
|
|
10.0 |
|
0.011 |
|
|
|
|
|
|
|
|
|
12.0 |
1.3 |
0.016 |
-0.015 |
99.8 |
1.2 |
|
765 |
3 |
768 |
|
|
14.0 |
|
0.22 |
|
|
|
|
|
|
|
|
|
16.0 |
1.6 |
0.09 |
|
122.8 |
6.9 |
|
942 |
17 |
959 |
|
|
18.0 |
1.0 |
0.2 |
|
76.8 |
15.3 |
|
589 |
37 |
626 |
|
|
20.0 |
0.8 |
0.3 |
|
61.4 |
23.0 |
|
471 |
55 |
526 |
Note that the horizontal stabilizer losses its lift very suddenly at -16 degree. In other words; the increasing drag does not contribute very much to speed stability. The H.S. must never get neer this angle.
I wonder if sweeping the last 20% of the chord upward (ie. negative trim tab) will help this situation?
Miscellaneous:
The horizontal stabilizer will play no roll in trim during hover. It will have some nose up pitching effect during vertical climb. Perhaps it should be linked to the collective, for basically the same reasons it should be linked for autorotation.
"The price of increased stability is less agility. The tailplane introduces a powerful stabilizing stiffness and damping. One way to circumvent this dichotomy is to use a moving tail plane, providing stability against atmospheric disturbances and agility in respect to pilot control inputs." ~
[Source ~ HFD p.314]
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Last Revised: November 1, 2001