DESIGN: SynchroLite ~ Rotor - Hub - 3-blade - CVJ & HS - Blade Generated Forces - Preliminary
The preliminary rough calculations for the Constant Velocity Joint w/ Hub Spring Rotor.
Mechanical Design and Description ~ Rotor Hub section is the source of this page and the calculations. [Source ~ MDD p.4-48]
B. Rotor Hubs:
a. General Comments:
b. Ferrous and Non-ferrous Metals:
c. Heat Treatment:
d. Surface Finish:
e. Section Changes:
g. Protective Coatings:
i. Size Effect:
2. Design Considerations:
a. Flight Conditions:
a1. Normal Operating Conditions:
~ by DBJ
- Blade's CG - Adjusted for Offset:
Blade's Weight - Adjusted SynchroLite Blade: ~ by DBJ
- This book considers the blade's CG to be 0.45R for a tapered spar and plan or be 0.48R for a constant spar section. The radius of the rotor is 96". Therefore, the blade's CG will be 0.45 * 96 = 43.2".
Rotor rpm = N = 650 [rpm]
Number of blades per rotor = b = 3
Lift of one rotor = L = 275 [lb].
Radius to the GG of the blade. From above, the radius to the CG of the blade is 0.453R. Therefor r = (D / 2) * 0.45 = (16.0 / 2) * 0.45 = 3.6 ft = 1.1 M
Normal centrifugal effect = CF = 0.000341 * Wb * r * N2. = 0.000341 * 6.5 * 3.6 * 422,500 = 3,371 lbs = 15.000 N [Comment ~ this value is not much less then the Initial Rough SynchroLite calculation, and also, the SynchroLite's rough calculation is very close to the more detailed one.]
Average coning angle = β0 = tan-1 (L / (b * CF)) = tan-1 (275 / (3 * 3,371)) = 1.56 degrees
For the more detailed calculation see; DESIGN: Dragonfly ~ Rotor - Disk - Coning Angle
Normal operating torque (1 rotor) = T = 63,000 * hp / 700 = 63,000 * (50 / 2) / 700 = 2250 lbf-in = 188 lbf-ft = 254 N-m
For the more accurate value see; FORM: Dragonfly ~ Power Train
Torque per blade = Tb = T / b = 188 / 3 = 63 lbf-ft = 85 N-m
Lag Offset = e = Tb / CF = XXXX
Normal lag angle = sin-1(e/a) + sin-1(e/r1) = XXXX
- The blade weight of the SynchroLite's VR-7 is 6.25 lbs. This includes a 1 lb tip weight. It has a 5.25' chord, no taper, and a rotor radius of 8.67 ft. For confirmation, see: OTHER: Helicopter Specification - SynchroLite
- The SynchroLite's grip weighs 1.5 lbs.
- The SynchroLite CVJ has a 4.58" ? chord, no taper, a rotor radius of 8.0 ft.
- The cross sectional area of the SynchroLite CVJ 's blade will be (4.58 / 5.25)2 = 0.76 that of the SynchroLite's blade, and the grip and tip weight will be (4.58 / 5.25)3 = 0.66
- Assuming that the tip weights have the same 0.76 ratio, the weight of one SynchroLite CVJ blade will be Wb = ((6.25 - 1) * 0.76) + ((1 + 1.50) * 0.66) = 5.64 lbs = 2.56 Kg.
- The SynchroLite CVJ 's blade will be slightly larger than 2/3's that of the SynchroLite and stronger therefore 1.15 * 5.64 lbs = 6.5 lbs = 2.96 K
a2. Full Power Flight:
a3. Autorotation at Ceiling:
- Use, conservatively, an rpm = 2.0 times normal
b. Ground Conditions:
b1. Combined Flapping and Drag Moment:
b2. Brake Torque:
b3. Inverted Loads:
- GW/2 with a Limit Load Factor of 2.0 = (550/2) * 2 = 550 lbs.
b4. Review for Fatigue:
3. Blade Pitch Mounting:
a. General Discussion:
- Normal blade pitch change from approximately -5º to +25º.
- If grease is used in lieu of oil then the bearings should have a 15 to 20 percent higher capacity.
- For angular thrust bearings, the selection should be based on an average life of 2,500 hours at 500 rpm. For a light series bearing 60% of this calculated capacity may be used as the allowable operating load to which it should be subjected. When used in tandem the combined capacity should be taken as 190% of one bearing.
c. Location of Pitch Mounting:
4. Drag and Flapping Pivots:
a. General Comments:
b. Geometric Relationship:
c. Drag Pivots:
d. Flapping Pivot:
5. Stress in Hub Parts:
b. Design Considerations:
b1. Design of Section AA:
b2. Normal Operating Stress in Section AA:
b3. Autorotational Stress :- Section AA:
b4. Alowable Fluctuating Stresses :- Section AA:
6. Teetering Rotor Mounting:
b. Design Loads:
b1. Accelerated Flight:
b2. Autorotational Condition:
b3. Inverted Load Condition:
b4. Combined Flapping and Torque:
b. Axle Terminal:
7. Rotating Axle:
a. Design Considerations
a1. Flight Condition:-
a2. Combined Flapping and Torque:-
b. Operating Stresses (Section BB)
b1. Normal Flight:-
c. Other Sections
Same Page ~ Different Craft: ~ Dragonfly ~ UniCopter
For comparable calculations on SynchroLite (2-blade) see; DESIGN: SynchroLite ~ Rotor ~ Initial Rough Calculations for Rotor
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Last Revised: November 5, 2004