Helicopter tail rotor thrust requirement

In summary, the amount of thrust needed by the tail rotor of a helicopter to counter the torque of the main rotor depends on the horsepower and rpm of the main rotor. To calculate the torque, you can use the formula T = 63025*hp/rpm. By increasing the length of the tail boom, the required thrust can be reduced. Using the given example of a model helicopter with a 3.5 foot long tail boom, the required thrust for the tail rotor would be 0.25 lbs. However, further calculations are needed to determine the exact amount of thrust needed for different tail boom lengths.
  • #1
PaulHP
6
0
How can you calculate the amount of thrust needed by the tail rotor of a helicopter to counter the torque of the main rotor?
 
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  • #2
Welcome to PF.

The answer to the question depends on what you know. If you know the horsepower and rpm of the main rotor, you can calculate the torque easily enough. More information is needed before we can help you...
 
  • #3
lets say that this is for a model helicopter with .05 hp (37 watts), has blades that rotate at 300 rpm and has a 3.5 foot long tail boom. Wouldn't the required thrust of the tail rotor be cut in half if the tail boom length is doubled?
 
  • #4
Making the tail boom longer would decrease the power requirements of the tail rotor.
 
  • #5
Thanks, I thought it would, but how would you determine exactly how much thrust would be needed for the tail rotor at various tail boom lengths?
 
  • #6
Just do a moment balance.
 
  • #7
Well, you have the horsepower and rpm. Torque is horsepower/rpm...
 
  • #8
ah. So, 0.88 ft-lb would be required to counter balance to main rotor and the thrust required for the tail rotor at 3.5 feet would be 0.25 lbs, right?
 
  • #9
I can tell you yes or no if you show some steps as to how you got to your final answer.
 
  • #10
0.05 hp X 5252= 262.6/300 rpm = 0.88 ft-lb
0.88/3.5 ft= 0.25 lbs of thrust
 
  • #11
T = 63025*hp/rpm

this "0.05 hp X 5252= 262.6/300 rpm = 0.88 ft-lb" Makes no sense to me.

I get 3lbs of thrust.
 
  • #12
Cyrus said:
T = 63025*hp/rpm

this "0.05 hp X 5252= 262.6/300 rpm = 0.88 ft-lb" Makes no sense to me.

I get 3lbs of thrust.

T = 63025*hp/rpm is to find torque in in-lbs, and T-5252*hp/rpm is to find it in ft-lbs..
 
  • #13
PaulHP said:
T = 63025*hp/rpm is to find torque in in-lbs, and T-5252*hp/rpm is to find it in ft-lbs..

Yep you're right :tongue:
 

1. What is a helicopter tail rotor?

A helicopter tail rotor is a rotary wing located at the tail of a helicopter that is responsible for generating thrust to counteract the torque produced by the main rotor and provide directional control.

2. Why is tail rotor thrust necessary?

Tail rotor thrust is necessary to counteract the torque produced by the main rotor, which causes the helicopter body to rotate in the opposite direction. Without this counteracting force, the helicopter would spin uncontrollably.

3. How is the amount of tail rotor thrust determined?

The amount of tail rotor thrust required is determined by the torque produced by the main rotor, which depends on factors such as the helicopter's weight, power, and airspeed. The tail rotor must provide enough thrust to counteract this torque and provide directional control.

4. What factors affect the tail rotor thrust requirement?

The tail rotor thrust requirement is affected by various factors such as the weight and distribution of the helicopter, the power and airspeed of the main rotor, the altitude and air density, and the direction and intensity of the wind.

5. Can the tail rotor thrust requirement change during flight?

Yes, the tail rotor thrust requirement can change during flight due to changes in the factors that affect it. For example, as the helicopter's weight decreases due to fuel consumption, the tail rotor thrust requirement will also decrease. Pilots must continuously monitor and adjust the tail rotor thrust to maintain control and stability during flight.

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