1332

Item 1332

DESIGN: SynchroLite ~ Rotor - Hub - 3-blade - CVJ & HS - Blade Generated Forces - Preliminary

Overview:

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:

1. Fatigue:

a. General Comments:

b. Ferrous and Non-ferrous Metals:

c. Heat Treatment:

d. Surface Finish:

e. Section Changes:

f. Discontinuities:

g. Protective Coatings:

h. Corrosion:

i. Size Effect:

2. Design Considerations:

a. Flight Conditions:

a1. Normal Operating Conditions:

Blade's CG - Adjusted for Offset: ~ 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".

Blade's Weight - Adjusted SynchroLite Blade: ~ by DBJ

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 W_b = ((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

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 = C_F = 0.000341 * W_b * 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 * C_F)) = 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 = T_b = T / b = 188 / 3 = 63 lbf-ft = 85 N-m

Lag Offset = e = T_b / C_F= XXXX

Normal lag angle = sin^-1(e/a) + sin^-1(e/r₁) = XXXX

a2. Full Power Flight:

For appropriate load factors and safety factor see OTHER: Flight Dynamics - Definitions ~ Limit Load Factor

Centrifugal load factor of 4.0 and the torque safety factor of 2.25 are used to give reasonable operating stresses = 9.0

a3. Autorotation at Ceiling:

Use, conservatively, an rpm = 2.0 times normal

b. Ground Conditions:

b1. Combined Flapping and Drag Moment:

b2. Brake Torque:

For appropriate load factors and safety factor see OTHER: Flight Dynamics - Definitions ~ Limit Load Factor

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.

b. Bearings:

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:

a. General:

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:

a. General:

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:-

b2. Autorotation:-

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