Item 1374
DESIGN:
UniCopter ~ Rotor - Hub - ARR - Blade Generated Forces - Preliminary:The preliminary rough calculations of the blade generated forces at the rotor hub.
Mechanical Design and Description ~ Rotor Hub section is the source of this page and the calculations.
[Source ~ MDD p.4-48]Calculations are for 3-blade and 4-blade rotors.
B. Rotor Hubs:
2. Design Considerations:
a. Flight Conditions:
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3-blade Rotors |
4-blade Rotors |
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Rotor speed: N |
480 rpm |
480 rpm |
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Number of blades per rotor: b |
3 |
4 |
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Lift of one rotor: L |
575 lbs |
575 lbs |
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Radius to the GG of the blade: r = 0.42R = |
0.42 * 9.5' = 4.0'' |
0.42 * 9.2' = 3.89'' |
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Weight of the blades: 1071.html , Wb |
21 lbs |
16 lbs |
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Normal centrifugal effect: CF = 0.000341 * Wb * r * N2 |
= 0.000341 * 21 * 4.00 * 230,400 = 6,600 lbs = 29,358 N |
= 0.000341 * 16 * 3.89 * 230,400 = 4,890 lbs = 21,752 N |
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Average coning angle: β0 = tan-1 (L / (b * CF)) |
tan-1 (575 / (3 * 6,600)) = 1.66º |
tan-1 (575 / (4 * 4,890)) = 1.68º |
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Normal operating torque: (1 rotor) T = 63,000 * hp / N |
7875 in/lb = 656 ft-lb |
7875 in/lb = 656 ft-lb |
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Torque per blade: Tb = T / b |
656 / 3 = 219 ft-lb |
656 / 4 = 164 ft-lb |
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Lag Offset: e = Tb / CF |
219 / 6,600 = 0.033 ft? |
164 / 4,890 = 0.034 ft? |
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Normal lag angle: sin-1(e/a) + sin-1(e/r1) |
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Same Page ~ Different Craft:
~ Dragonfly ~ SynchroLite (CVJ)For comparable calculations on 2-blade SynchroLite see;
DESIGN: SynchroLite ~ Rotor ~ Initial Rough Calculations for Rotor
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Last Revised: November 5, 2004