B301

DESIGN: UniCopter ~ Power Train - Reduction - Final

Outside Information:

Gear calculations for outside helicopters: DESIGN: SynchroLite ~ Power Train - Secondary Reduction

Gears MUST be strong. See [Source ~ MMD p.49-50]

Also see: OTHER: Helicopter - Outside - Intermeshing - Kaman - K-MAX ~ Transmission

The 2 tables and related notes in this section are probably obsolete

Rough Calculation for Final Gears:

FORM: Gear - Bevel - Arrow:

 

Arrow Pinion Part No.

6P45L15 (mod. to 81º) Item 0275 (mod.)

55P48L16 (mod. to 81º) Item 0868 (mod.)

 

 

Arrow Gear Part No.

6P15R45 (mod. to 81º) Item 0274 (mod.)

55P16R48 (mod. to 81º) Item 0867 (mod.)

 

 

Horsepower;

53.9

75 **

 

 

Pinion Speed:

1964

1659

 

 

Pinion Working Torque:

1729.7

2849.2

 

 

Estimated Rated Pinion Torque:

3459.3

5698.5

 

 

Catalog Rated Pinion Torque:

2381

3468

 

 

Catalog Pinion Pitch Diameter:

2.5

2.909

 

 

Pitch Line Velocity:

1286.4

1264.4

 

 

Dynamic Factor:

0.8277

0.8288

 

 

Allowable Pinion Torque:

1970.6

2874

 

 

Service Factor: *

1.1393

1.0088

 

* The final reduction should have a greater service factor because it is located after the overrunning clutch and it is responsible for rotor-rotor synchronization. Note: The blades, hub and frame are extremely rigid, therefor if the rotational twisting of the 3 shafts is kept extremely small, there will be no chance of an oscillation taking place between the two rotors. Rotational spike dampening between the engine and rotors will also help.

** Based on 3/4 of a reduced 100 total hp. being delivered to one rotor.

FORM: Hamilton Bevel Gear Selection.

 

Pinion Speed

1659

1659

rpm

 

 

Catalog Pinion Pitch Dia.

2.91

3.2

in.

 

 

Pitch Line Velocity

1,264.4

1,390.9

ft/min

 

 

Diametral Pitch

5.5

5

 

 

 

Face Width

1.25

1.5

in

 

 

Allowable Contact Stress

190,000

190,000

Steel Rockwell 50 min.

 

 

Allowable Bending Stress

30,000

30,000

Steel Rockwell C 50 min.

 

 

Elastic Coefficient

Pinion & Gear - Steel

Pinion & Gear - Steel

 

 

 

Load Distribution Factor

One member straddle mounted

One member straddle mounted

 

 

 

Geometry Factor [I]

.103

.103

 

 

 

Geometry Factor [J]

.227

.227

 

 

 

Durability (1)

56.22

81.63

hp. Service factor is 1

 

 

Strength (1)

75.3

109.3

hp. Service factor is 1

 

 

See form for additional data.

 

 

 

(1) The values are too light. Increasing the face width up to 1.5" will take the durability to 67.46 hp. and the strength to 90.36 hp. Is there any way to speed up the pinion; by increasing the teeth in the gear and/or increasing the RRPM? De-rate the engine, minimize spiking from engine, lighten the empty weight, use VR-7/8 airfoil etc.

Increasing the gear to 38 teeth means that the pinion speed can go from 1658 rpm to 1750 rpm. With the 1.5" face width the durability goes from 67.46 hp to 72.54 hp. and the strength goes from 90.36 hp to 97 hp.

The DP 5.5, 36 teeth gear has an OD of 6.544"

The DP 5.5, 38 teeth gear has an OD of 6.907" This may be the best choice, especially if the engine is derated.

The DP 5, 36 teeth gear has an OD of 7.219"

See the above table for using 5 DP with 16/36 teeth and standard face width of 1.5". The OD of this gear is 7.2771, and the face width could probably be increased slightly. The drawing is Item 1028. Consider spreading the flight control rods and using this gear. Maybe increase the face width also.

___________________________

When one looks at the K-Max, and particularly the Mini 500 gears linked to above, it makes the use of a 5 Diametrical pitch look too big.

Notes:

The hand of the spiral has no influence on the smoothness, quietness or efficiency of operation, regardless of the direction of rotation.

Spiral bevel gears will carry substantially higher loads than straight tooth. Spiral bevel gears are quieter.

Straight bevel gears are only good for 1000 fpm at the large end of the teeth. It looks like the pitch line velocity is going to be 1,600 to 1,700 fpm.

Van Gear and United gear can only produce straight bevel gears, but 99 degrees is no problem.

Increasing the speed of the rotor will increase the safety factor.

Housing:

Taper the forward face of the housings down and back so that it does not interfer with the flow of air into the engine compartment. If enough fins are cast into the housings an external source of oil cooling may not be required. Just use a splash system.

Additional Related Information:

OTHER: Mechanics ~ Casting: Information on castings for housings etc..

OTHER: Mechanics ~ Machining: Information on machining of castings and billets.

OTHER: Helicopter - Outside - Intermeshing - Kaman - K-MAX ~ Transmission

 Notes:

As an alternate supplier, consider Curtis Machine Company Inc. http://www.curtismachine.com/

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Last Revised: February 9, 2005