PPRuNe Forums - View Single Post - Helicopter crashes into the Hudson River NYC
Old 25th May 2019, 18:27
  #28 (permalink)  
lennystyles
 
Join Date: Feb 2008
Location: Netherlands
Age: 30
Posts: 2
Originally Posted by Two's in View Post
The problem was when he lost forward airspeed, the torque reaction from the main rotor began to overcome the anti-torque moment provided by the tail rotor. This caused the aircraft to yaw to the right despite full left pedal. The combination of a tail wind component, high power and zero airspeed overcame the tail rotor authority. The application of more power simply made the situation worse and increased the torque driven yaw, so no, he couldn't (and didn't!) "power" his way out of it. He had a number of options, all of them poor. He could have lowered the nose and attempted to regain positive airspeed, this would have provided aerodynamic forces to counter the yaw, but in this case he would have been descending and accelerating towards the river bank and structures, so this may not have been appealing. He could have reduced the power until the anti-torque force countered the yaw, but again, this meant descending towards the river and the bank waiting for the rotation to stop, not an obvious choice. Or, if he could have maintained a more stable platform, the rotational speed might have decayed as the aircraft came back into the wind, allowing him to transition away into the wind and regain positive airspeed quicker, but again, it's a brave man who can hold it in a level flat spin waiting for the rotation to slow down.

As you see from the video, all this happened very quickly, and this guy was only thinking of repositioning to a spot following a refuel. He probably wasn't considering the finer points of countering an unstable rotational acceleration with a limited anti-torque force following the loss of translational lift in a down wind configuration. But he will next time.
Thanks for the detailed explanation. Really appreciated. I' ack some of the basics such as the interaction between main rotor and tail rotor etc so i'll be checking google/youtube. The rest I did understand.
I find it interesting to see, that for the eye, these are two similar jobs, but if you just take a bit of time to think about it, there are several more dimensions you guys have to think about.
lennystyles is offline