How Do You Calculate Gear Reductions for Helicopter Rotors?

[tylerm2010]

Homework Statement

1800 HP motor
spins at 6600 RPM
FIND:
3 stage reduction (and 90deg turn up) to main rotor to spin at 300 RPM
2 Stage reduction (and 90deg turn to the side) to tail rotor to spin at 1700 RPM

Homework Equations

torque = 525*HP/RMP
Saftey factor = 2
Loading condition = 2

The Attempt at a Solution

I solved for the engine torque using the equation above and got 1433 ft.lbs
Gear reduction needed to the main rotor is 22:1
Gear reduction needed to the back rotor is 3.88:1

I am not concerned with bearings, backlast...only the gear reductions and that the teeth will not break under the loads from the engine.

Any help at how to solve this would be great.

 

[mark726]

Hello,

Thank you for posting your question on our forum. I would approach this problem by first understanding the basic principles of gear reduction and torque.

Gear reduction is a process where the rotational speed of the input gear is reduced while the torque is increased. This is achieved by using gears with different sizes and numbers of teeth. In your case, you need to achieve a 22:1 gear reduction for the main rotor and a 3.88:1 gear reduction for the tail rotor.

To calculate the gear ratio, you can use the formula: Gear ratio = Number of teeth on output gear / Number of teeth on input gear.

Next, you need to determine the torque required for the main rotor and the tail rotor. As you have correctly calculated, the engine torque is 1433 ft.lbs. However, this is the maximum torque that the engine can produce and it is important to consider a safety factor. A safety factor of 2 means that the gear system should be designed to handle twice the maximum torque of the engine, which in this case would be 2866 ft.lbs.

Now, let's consider the loading condition. A loading condition of 2 means that the maximum torque will be applied to the gears at all times. Therefore, we can calculate the torque required for the main rotor as 2866 ft.lbs and for the tail rotor as 4933 ft.lbs (1700 RPM/6600 RPM * 2866 ft.lbs).

Once you have determined the torque required for each rotor, you can use the formula: Torque = Force * Distance to calculate the force acting on the gears. The distance in this case would be the radius of the gear.

Finally, you need to select gears that can withstand the calculated forces and torque. This will depend on the material, size, and design of the gears. It is important to consider factors such as gear tooth strength, wear resistance, and lubrication.

I hope this helps. Let me know if you have any further questions. Good luck with your calculations!



Scientist