Saturday, October 31, 2009

DHRUV CRASH UPDATE #5: The Cyclic Limit Theory

The three member HAL-team of experts, which includes company official KM Bhat, along with Chief Test Pilot Wg Cdr (Retd) Unnikrishna Pillai (who trained the Ecuadorian pilots in 2008) and HAL's Chief Designer of the Rotary Wing R&D Centre, Prasad Sampath, have started work alongside the Accident Investigation Board inquiring into Tuesday's Dhruv crash. Incidentally, the two pilots who miraculously survived the accident, were discharged from hospital yesterday and on the same day, also provided testimony to the Board.

Ok here's the very latest. According to my sources in Ecuador, the ill-fated helicopter is likely to have come under the air forced downward by the rotors (rotorwash) of one of the other Dhruv's flying in the formation. At this point, complications may have started when the pilots Luis Armas and Ivan Abril made an attempt to recover from the ensuing sharp left bank (this is visible in the video). In technical terms, the pilot encountered a cyclic limit to the right (saturation of cyclic - the stick for lateral movement of the helicopter), as a result of which they found they had no further cyclic available at their disposal to stabilise or roll back out of the left turn. In well-documented helicopter flight dynamics, when cyclic saturation is reached, there is an abrupt loss of available lift to counter the turn.

It is understood that the Dhruv flight manual and training programme contains a specific module on recovering from a cyclic limit situation, and the Ecuadorian pilots underwent this process as part of their training in 2008. The training however, taught them how to recover from this situation when the chopper's altitude was at least 1,000 feet. Therefore, considering that the Dhruvs were flying at just 70-meters above the ground -- and if this theory holds -- then the pilots would not have had a chance to recover either way.

8 comments :

Anonymous said...

i would agree with this theory. from the visuals of the crash, it can quite easily be made out to be the case. loss of cyclic during a turn kills lift drastically. this is quite likely to be the real reason why the helicopter went down.

Anonymous said...

could it have had something to do with vortex ring state?

Anonymous said...

Quite possible that voretx rings had something to do with it considering the formation flying and the lack of altitude that would have been needed to recover

hey lets just write the design off eh...why bother investigating...

Gagan said...

These pilots seem to be competent enough if one goes by their long flying hours they've accumulated over the years.
If this theory is true, and the chopper was indeed too low to recover, the next aspect is the copter's design which saved the lives of the two pilots.
They literally fell 70m from the air onto the ground. The chopper cabin could have just caved in around them, the fuel tanks could have just ignited, their seats could have torn off the floor and impaled them across the dashboard - Nothing of the sort happened. They walked out alive.

That's a tremendous chopper there. I am glad this one's made in india.

Jai Ho and all that.

Murali said...

Well, if what said here is indeed the reason. then why did this not happen when they tried it the formation first time around or is this the first time for these pilots?

Was the chopper flown at 70M deliberately for this maneuver, if so wasn't this done at practice earlier ?

Anonymous said...

The otherwise superior performance of the Dhruv made the pilots somewhat overconfident to attempt a risky maneuver?

Anonymous said...

you are spot on, mr aroor. this is precisely what happened.

Anonymous said...

airports are equipped to identify microbursts or windshear, the boundary of a rotor wash generated one is too tiny to detect? or

guidelines for formation flying are violated?