Robinson Main Rotor Blade AD

[Velocity173]

I'm talking about power available at the rotor shaft, not translated to flight. If the loss of the engine reduced the power available at the shaft, it would reduce the destructive force available regardless RPM.

Yeah you'll still have the same power to the main rotor shaft.

Each engine is set at 100 % engine Np. Depending on the engine model, it's ECU or DEC is reading those percentages. When an engine fails, the other engine will droop slightly while the rotor drags it down. The amount of droop will vary with weight, speed, DA etc. The ECU / DEC for that particular engine senses this droop and immediately increases fuel flow to maintain 100 % Np / Nr. So, like above, if you were pulling 45 % trq a side before to maintain flight, that remaining engine now has to put out 90 % to maintain flight and 100 % Nr.

Only really becomes a problem below min SE speed or above max SE speed. If you're below, which is usually around ETL, you better get the nose down and accelerate or you'll be mushing out of the sky as the rotor droops. If you're at a high cruise speed, say 150 KIAS, you better reduce collective quickly or you're gonna have a severe rotor droop as well. In either case you run the risk of an over TRQ if you don't react quickly.

 

[Ted]

Them are some lucky sums a *******......

When it's not your time, it's not your time.

A friend wrecked his 414 last year. Plane ended crashing upside-down in some woods, caught fire. He broke his back and got burned but opened the emergency exit and got out.

Wasn't his time.

 

[Henning]

Yeah you'll still have the same power to the main rotor shaft.

Each engine is set at 100 % engine Np. Depending on the engine model, it's ECU or DEC is reading those percentages. When an engine fails, the other engine will droop slightly while the rotor drags it down. The amount of droop will vary with weight, speed, DA etc. The ECU / DEC for that particular engine senses this droop and immediately increases fuel flow to maintain 100 % Np / Nr. So, like above, if you were pulling 45 % trq a side before to maintain flight, that remaining engine now has to put out 90 % to maintain flight and 100 % Nr.

Only really becomes a problem below min SE speed or above max SE speed. If you're below, which is usually around ETL, you better get the nose down and accelerate or you'll be mushing out of the sky as the rotor droops. If you're at a high cruise speed, say 150 KIAS, you better reduce collective quickly or you're gonna have a severe rotor droop as well. In either case you run the risk of an over TRQ if you don't react quickly.

Ah, so if the engine spooling up power to take up the slack hits the drooping rotor under load you can get an over torque? That would likely make a bad day worse. What is going to break?

 

[Velocity173]

Ah, so if the engine spooling up power to take up the slack hits the drooping rotor under load you can get an over torque? That would likely make a bad day worse. What is going to break?

If the engine fails and your indicated speed is above your min SE airspeed and less than your max SE airspeed, you're good. She'll have a transient droop because it takes a bit for the engine to spool up and take the load but you're talking a few % and then it'll go back to 100 % Nr.

Now, if you're slower than your min SE airspeed or greater than your max SE airspeed and you do nothing with the collective, you're gonna droop and stay there. The engine just can't over come the drag of the rotor at that high of collective and resulting angle of incidence. If you haven't exceeded a structural torque limit, then nothing is going to break. Most likely you've reached your environmental torque limit. That's when the engine has tried to meet the demand of the torque you want out of it but it's TGT limiting is keeping you from hurting itself. The engine MAY allow sustained flight if you do nothing with the colective but at a reduced Nr. Probably have the generators drop off line though. So, when the engine fails outside the SE envelope, gotta get the collective down and either increase or decrease speed to get back within the envelope.

Since the engines rarely fail, most rotor droop accidents occur with both engines running. This usually happens at high altitude and heavy weights where the crew attempts to bring the aircraft to an OGE hover and they just don't have the power to pull it off. Happened a few times in Afghanistan, also happened to a 160th aircraft out in Colorado a few years back. Perfect example is the Mt Hood accident years ago with the AF HH-60. They were right at the hovering limit of the aircraft. All it took was a gust of wind, the rotor droops and you have settling with power. Some refer to that as settling with too little power but I won't go into splitting hairs on proper terminology.

 

[Henning]

Ok, thanks for the explanation, I think I get the issue now and what you mean by droop. So, in short, if you are operating inside the parameters where the timing of the transfer works out without a significant amount of rotor energy loss, or droop, involved, then the engine can catch up the extra duty without temping out getting the rotor back to its target energy. However if you are operating outside those parameters, then the energy can decay, or droop, to the point where the single engine can no longer restore the rotor to its proper energy before hitting the temp limiter unless you reduce the load with collective quickly before the energy degrades so far it's unrecoverable. Do I have that right?

 

[Velocity173]

Ok, thanks for the explanation, I think I get the issue now and what you mean by droop. So, in short, if you are operating inside the parameters where the timing of the transfer works out without a significant amount of rotor energy loss, or droop, involved, then the engine can catch up the extra duty without temping out getting the rotor back to its target energy. However if you are operating outside those parameters, then the energy can decay, or droop, to the point where the single engine can no longer restore the rotor to its proper energy before hitting the temp limiter unless you reduce the load with collective quickly before the energy degrades so far it's unrecoverable. Do I have that right?

Precisely.

 

[RogerT]

Larry .. if I recall right ... the blade part number in the OZ AD was C016-7. A friend has an R44 we fly quite a bit and I immediately checked the blades on that one when I read about it.

RT

 

[Geico266]

Larry .. if I recall right ... the blade part number in the OZ AD was C016-7. A friend has an R44 we fly quite a bit and I immediately checked the blades on that one when I read about it.

RT

Was his included in the AD? I assume that is the PN for all R-44?

You have your helo rating right?

 

[Gerhardt]

And people get worked up over ADs on 2-bladed machines. The severe vibration mentioned here is on a 4-blade aircraft.

 

[Warlock]

Watched a Blackhawk on short final 300-400 ft or so chunk a blade at Ft Rucker. The violence which ensued prior to impact was nothing I ever want to see again...we were grounded for a week prior to allowing us to fly again. I remember we were flying a UH-1 into Tac X like it was yesterday (1985) and the UH-60 was going into a stage field called Runkel. I was pointing out the traffic when it happened...they made a design change and beefed up the spindle that held on the blades...