Left yaw in a hovering auto???

[Weads]

What causes the helicopter to yaw left when throttle has is rolled off? (Counter clockwise system) In my limited knowledge it seems that once throttle is rolled off, thus removing torque effect, that right pedal would not be needed nor left since we don't have the torque effect to counter. Contrary to my thinking we need lots and lots of right pedal but why??? Any insight would be greatly appreciated! Thanks in advance

[iChris]

What causes the helicopter to yaw left when throttle has is rolled off? (Counter clockwise system) In my limited knowledge it seems that once throttle is rolled off, thus removing torque effect, that right pedal would not be needed nor left since we don't have the torque effect to counter. Contrary to my thinking we need lots and lots of right pedal but why??? Any insight would be greatly appreciated! Thanks in advance

 

Too much left pedal applied during the torque reduction.

 

The answer is already in your question, “we don't have the torque effect to counter.” The answer is also in the needle split you see on your dual tac when you rolled off the throttle. Tail rotor thrust is a function of rotor RPM and the torque couple is a function of engine RPM.

 

You were in equilibrium before you rounded off the throttle, tail rotor thrust equal to the main rotor torque couple. What happen? It’s right there on your dual tac. Again, from your question, “we don't have the torque effect to counter.”

 

Clue, after the throttle chop, the engine RPM reduction leads rotor RPM reduction. The effect, the torque couple is decreasing faster than the reduction in tail rotor thrust required to maintain equilibrium. Therefore, what do you need to do?

 

Reduced tail rotor thrust (tail rotor pitch) with right pedal; thereby, regaining equilibrium and arresting the left yaw. In other words, you need to compensate for the reduction in torque with a reduction in anti torque.

 

Edited April 25, 2017 by iChris

[HawaiiCFII]

You have the left pedal pushed in for hovering power conditions. Once you roll off the throttle the tail rotor is still spinning with the same amount of pitch. To match the power off condition you need to push in right pedal and remove all of that pitch in the blades.

 

You'll notice that if you are slow on getting that pedal in it doesn't work very well and you have yawed a good amount. You might try pushing a lot of pedal to try and get the nose back to the position it was at but it's mushy. This is due to the reduced rotor rpm and reduced effectiveness of the tail rotor as Chris mentioned.