Item 0902
DESIGN: UniCopter ~
Trim, Stability & Control - Stability - Static - Longitudinal (Speed Stability)
Drawing:
This is Muse-C
Parasitic Drag of Fuselage and Landing Gear:
The UniCopter will have negative static speed stability due to the parisitic drag of the fuselage and landing gear. This problem is offset on conventional helicopters by
nonuniform induced velocity up to around 40 kts and then by flapback due to the coning angle at higher speeds.Solutions: In order of effectiveness.
Rotor Torque - Pitch X-coupling:
The torque of the rotors, when driven by the engine, will cause a nose up pitching moment. This torque moment will disappear during autorotation. Fortunately, the
obliqueness of the Unicopter is significantly less than previous intermeshing helicopter and this cross coupling will be less significant.For moment value see;
DESIGN: UniCopter ~ Trim, Stability & Control - Trim - Rotors (Port & Starboard)Notes:
Minimizing the amount of parasite drag of the fuselage (flat plate area) and the distance from the center of its drag to the plane of the disks will help. The fuselage should also be aerodynamically shaped to minimize downward drag. The amount of drag will increase as the square of the forward velocity.
By locating the horizontal stabilizer above the rotor disks (T-tail) its (small) drag component will assist. Are there any disadvantages in locating it there? All of the vertical stabilizer should probably be above the rotor disks as well.
The Flettner was changed so that the advancing blades were the higher ones. This was done to give longitudinal stability; in that at the start of autorotation the nose wants to drop. This feature of wanting to rotate the craft positively about the Y-axis will help the Unicopter, but will it be enough? It is interesting to note that some of the Kaman Huskies incorporated a large diameter exhaust pipe that extended back to the tail and then pointed downward. Apparently, this was done to neutralize some of rotor torque about the Y-axis and the effect upon loss of rotor torque. This should not be as large a problem with the UniCopter since the 'V' angle is reduced to 18º.
It is intended to sense the forward velocity and apply lateral cyclic to negate dissymitry of lift. Perhaps this sensing of the forward velocity should also apply aft cyclic.
Make sure that as the forward speed increases the angle attack of the horizontal stabilizer does not increase so much that it stalls, and maybe looses a lot of its downward force. A larger and further aft stabilizer will reduce the angle of incidence.
Idea for Solution to Nose Down Pitching:
DESIGN: UniCopter ~ Rotor - Disk - Pusher Prop Assist.
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|
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Equivalent Flat Plate Area: [f] * |
Drag: |
Vertical Arm: ** |
Horizontal Arm: *** |
Moment: Basis for Moment? |
|
|
Fuselage |
1.24 ft2 |
|
-2 ft. |
3 ft. |
-4.47 |
|
|
Landing Gear |
0.14 ft2 |
|
-5.5 ft. |
0 ft. |
-0.77 |
|
|
Vertical Stabilizer |
0.0325 ft2 |
|
1.0 ft. |
7.7 ft. |
+0.25 |
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|
Winglets |
0.01 ft2 |
|
2.4 ft. |
7.7 ft |
+0.18 |
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|
Horizontal Stabilizer |
0.159 ft2 |
|
2.4 ft. |
7.7 ft. |
+1.28 |
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H.S. Downward Thrust |
|
|
2.4 ft. |
7.7 ft |
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|
|
|
|
Sum: |
-3.53 |
* From
DESIGN: UniCopter ~ Dimension, Area & Drag - Drag - Parasitic, in forward Flight** From X-Z plane of rotor hub centers. *** From Y-Z-plane of rotors.
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Last Revised: February 17, 2005