Item 0881
DESIGN:
UniCopter ~ Rotor - Hub - ARR - Design ConsiderationsInitial information from
[Source ~ MDD p.4+]
Drawing:
Profile:
"The test results indicate that substantial drag reduction can be attained through the use of a cambered hub fairing with circular arc upper surface and flat lower surface."
Fatigue:
General Comments:
Mechanical Properties:
Ferrous and Non-ferrous Metals:
Hear Treatment:
Surface Finish:
Section Changes:
Discontinuities:
Protective Coatings:
Corrosion:
Size Effect:
Design Considerations:
Flight Conditions:
Normal Operating Condition:
Full Power Flight:
Limit load factor for rotor thrust loads = 4.0
Limit load factor for centrifugal loads = 4.0
Safety factor to be used with above loads = 1.5
Limit load factor for torque loads = 2.0
Safety factor to be used with torque loads = 2.25
Autorotation at Ceiling:
Same factors as above except RRPM to be 2.0 x normal [200% RRPM]
Ground Conditions:
Inverted Load:
Limit load factor = 2.0 x weight of craft. Inverted flight will require an increased LLF factor.
Blade Pitch Mounting:
General Discussion:
Approximate change of pitch angle from -5º to + 23º. This incorporates both -5º to +15º of collective and +/- 10º of cyclic. Inverted flight will require an increased negative value for the collective. Note that inverted flight will put the tail in the rotors' downwash.
The blade attachment bearings must be designed to handle; centrifugal load, thrust load (from the collective), moment load (from the cyclic) and torque load.
Bearings:
See UniCopter ~
Give serious consideration to elastomeric bearings, because of lower bearing friction and no seal friction. See: UniCopter -
DESIGN: UniCopter ~ Rotor - Hub - Pitch Bearing - Elastomeric.The bearing's rated thrust capacity
[ Is this just centrifugal force? ] should be calculated for an average life of 2,500 hours at 500 RPM. For light series bearings, 60% of this calculated capacity may be used as the allowable operating load to which it should be subjected. For a medium series bearing, 75 to 80% of the rated capacity may be used. When two such bearings are used in tandem, the combined capacity should be taken as 190% of one bearing and 280% for three bearings.The bearing can be of the "full type"
The CarterCopter uses a hinge less system also. The blades are one
piece from tip to tip. The control rods "twist" the beam for pitch
control. There is a lot of mass in the weighted tips so getting a
bearing to turn under those loads was the hard way to do it.
Might consider torsion straps but centrifugal effect is not going to present the main loading.
Torsion straps might reduce the OD of the pitch bearing area and thereby reduce the obliquity slightly.
Drag and Flapping Pivots:
Note
Stress in Hub Parts:
In autorotation, it is possible to have speeds of 173% RRPM i.e. 3G.
Teeter Rotor Mounting:
Note
Rotating Axle:
Note
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Last Revised: February 28, 2005