DESIGN: UniCopter ~Landing Gear - Retractable - Reasons For
Nose Down Pitch in Fast Forward Flight:
The thrust of the rotor disks must provide vertical lift to overcome gravity. They must also have a horizontal component to provide a forward propulsive force. This forward force must offset the parasitic drag of the fuselage, theparasitic drag of the landing gear and the H-force resulting from the blades. The ratio of lift to drag will determine the forward pitch of the craft. As well, the plan view of the helicopter probably has more drag the front profile and the pitch of the craft will cause 'plan view' profile drag.
Another consideration is that the drag below the rotor disk(s) must be offset by the negative lift and drag of the horizontal stabilizer. The landing gear is the lowest part of the craft and therefor it will have the greatest moment arm that must be offset by the tail.
Retractable landing gear will increase the weight of the craft but this weight is handled by yhe vertical component of the rotors' thrust.
More on Drag:
Note:The moment arm from the rotor disk up to the horizontal stabilizer is 30". The moment arm from the rotor disk to the center of landing gear drag is 60". This means that for every one pound of drag on the landing gear an additional two pounds of drag must be developed by the horizontal stabilizer. This means that the landing gear drag has a 3:1 penalty. Consider making one or all the legs retractable.
Consider having the three retractable skids (pads) that are convex rectangular segments of the lower fuselage. They are reinforced and have a hard-wearing surface. When extended they are three skid pads and when retracted they are shape conforming parts of the fuselage.
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Last Revised: August 5, 2002