Two-Stage Gear Train Ratios

Having an accurate gear ratio for the main and tail rotor is essential for Rotorflight accurate RPM Filters performance.

Therefore it is best to count the tooth on the main and tail gear/pulley reduction sets and enter the values into the configurator.

This is relatively easy in single stage drive train that are used on most helicopters.

Broadly there are three types of two-stage ratios which are dependent on where the tail gear is connected. Review your helicopters gear arrangement and choose the calculator that matches below.

note

Select the helicopter from the dropdown or count the gear teeth for your helicopter and enter the count into the calculator.

Type 1 - Two-stage gears

Many SAB and ALIGN helicopters use this method.

Chose your helicopter and modify the motor pinion to match what you are installing.

Type 1: two stage gear

Choose HelicopterType 1 CustomSAB Goblin 500 SportSAB Black Thunder 700SAB Kraken 580SAB Kraken 700SAB Raw 580SAB Raw 580 NitroSAB Raw 700SAB Raw 700 NitroSAB Raw 700 PiumaSAB ilGoblin 700SAB ilGoblin 700 SUTALIGN TB40 Top ComboALIGN TB60 Top ComboALIGN TB60 Super ComboALIGN TB70 Top ComboALIGN TB70 Super Combo

: Calculated Main Ratio

: Calculated Tail Ratio

Type 2 - Two-stage gears

Chose your helicopter and modify the motor pinion to match what you are installing.

Type 2: two stage gear

Choose HelicopterType 2 CustomKDS Agile A5KDS Agile 7.2KDS Agile A7Align TN70

: Calculated Main Ratio

: Calculated Tail Ratio

Type 3 - Two-stage gears

This gear system was used for the Gaui Hurricane.

Type 3: two stage gear

Type 3 CustomGaui Hurricane

: Calculated Main Ratio

: Calculated Tail Ratio

Calculations

The following section is an example for the calculations that are used in the above. This can be used if you wish to know more or to calculate the ratios yourself.

Type 1

For example for the SAB ilGoblin 700 with STD 21T motor pulley, the calculation will be as follow:

SAB ilGoblin 700

z1: 21 teeth
z2: 56 teeth
z3: 18 teeth
z4: 68 teeth
z5: 34 teeth
z6: 26 teeth

• motor pinion = (Z1 x Z3) = (21 x 18) = 378.
• main gear = (Z2 x Z4) = (56 x 69) = 3808.
• tail pulley = (Z3 x Z6) = (18 x 26) = 468.
• front pulley = (Z4 x Z5) = (69 x 34) = 2312.

Type 2

For example for the KDS Agile A5 with STD 21T motor pulley, the calculation will be as follow:

KDS Agile A5

z1: 21 teeth
z2: 54 teeth
z3: 17 teeth
z4: 66 teeth
z5: 57 teeth
z6: 14 teeth

• motor pinion = (Z1 x Z3) = (21 x 17) = 357.
• main gear = (Z2 x Z4) = (54 x 66) = 3564.
• tail pulley = (Z6) = (14) = 14.
• front pulley = (Z5) = (57) = 57.

Type 3

This gear train type has a two-stage Main rotor and two-stage tail ratios. This design was used for helicopters such as the Gaui Hurricane.

Gaui Hurricane

z1: 13 teeth
z2: 42 teeth
z3: 19 teeth
z4: 61 teeth
z5: 14 teeth
z6: 9 teeth
z7: 9 teeth

• motor pinion = (Z1 x Z3) = (13 x 19) = 247.
• main gear = (Z2 x Z4) = (42 x 61) = 2562.
• tail pulley = (Z5 x Z7) = (14 x 9) = 126.
• front pulley = (z4z6)* = (61 x 9) = 549.