R44 200ftAGL engine out Autorotation video

[[email protected]]

Thanks JohnR81 - that explains some of the confusion. I wonder if the guy in the video was often swapping between Raven and Raven II - it would go some way to explaining the switch cock-up.

As I said, why would Robinson not keep a standard layout between models - just a HF accident waiting to happen.

[topradio]

If he used a checklist he wouldn't have made the cock-up even if they had moved the switch to above his head. Models change and evolve that's why we have variance training.
The switch had to be faulty (intermittent?) and normally he would have found his error when starting up but on this occasion it caught him out.

[aa777888]

Originally Posted by [email protected]

Thanks JohnR81 - that explains some of the confusion. I wonder if the guy in the video was often swapping between Raven and Raven II - it would go some way to explaining the switch cock-up.

As I said, why would Robinson not keep a standard layout between models - just a HF accident waiting to happen.

As someone who actually does fly both Raven I and Raven II helicopters, it's not really an issue. It's the same switch in both helicopters. Nobody pays attention to how it is clocked in the instrument panel. It's all about the number of clicks.

On the Raven I you turn it until you hit START, get the engine running, then release the switch out of its momentary START position into the BOTH position.

On the Raven II you turn it until you hit PRIME (the momentary position of the switch is used to run the electric primer of the fuel injection on the Raven II), prime for however many seconds you want, then release the switch out of its momentary PRIME position into the BOTH position. Then you use one of the two identical starter buttons, one located on the cyclic, the other on the collective, to start the engine.

After that both variants are the same for the mag checks: two clicks back to R, then two clicks forward to BOTH, then one click back to L, then once click forward to BOTH. The muscle memory is identical.

The real danger in switching back and forth between the two variants is that the carbureted Raven I requires you to manage carb heat. If you are coming out of the Raven II and forget to do that it can really ruin your day.

BREAK

In re-watching both the front and rear seat videos, it would seem that there might have been some concern about engine performance, and that would be commensurate with running on only one mag. In the rear seat video particularly, the pilot picks up and sets down a couple of times. And if you listen carefully I think I heard the word "engine" on the audio track. Also, on the front seat video, the manifold pressures look exceedingly high for the conditions they probably had in TX in January. If I had picked up on, say, a 15 or 20C day at TX altitudes and saw nearly 25" that would be most unusual and concerning. And the MP is sitting at 20" when they were on the skids, which is very high if the collective is all the way down, even with just one mag it doesn't do that, so perhaps he still had some collective pulled in, not sure why.

Anyhow, it seems we'll never really know, because there does not appear to be an FAA or NTSB investigation opened up on this incident, at least not in any publicly accessible database.

[John R81]

If it is N322SH ROBINSON HELICOPTER R44 II

Then

NTSB Status - In Work

Preliminary
"On January 9, 2021, about 1010 central standard time, a Robinson R44 helicopter, N322SH, was
substantially damaged when it was involved in an accident near Albany, Texas. The pilot and two
passengers were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations
(CFR) Part 91 hog hunting flight.
The pilot reported that it was the third flight of the day and the helicopter took off uneventfully. About
120 ft above the ground, the engine sputtered temporarily before it lost complete power. The pilot
performed an autorotation to a field. During the descent, the helicopter impacted trees and landed hard
right skid low. Subsequently, the main rotor blade contacted, and separated, the tail boom.
The helicopter has been recovered to a secure location for further examination."

[aa777888]

Thanks, John. I see I'm looking in the wrong place. I didn't know they had switched over to this "CAROL" site.

[[email protected]]

aa777888 - it's fine if someone always follows the correct procedures as you shouldn't get caught out - the HF element comes when a cursory glance doesn't identify that something looks wrong - if he flys both types and is used to seeing different pictures in each for normal flying configuration, he might forget which he is in and the subconscious alarm bells don't ring to get him to take a closer look.

Notwithstanding that, the engine performance should have been a big clue if it is at such variance from the norm as you describe.

Whichever way you cut it, it seems the fault lays firmly with the guy in the right hand seat.

[Robbiee]

Originally Posted by aa777888

The real danger in switching back and forth between the two variants is that the carbureted Raven I requires you to manage carb heat. If you are coming out of the Raven II and forget to do that it can really ruin your day.

Maybe if you were initially trained in a Raven II? Having been trained in the R22 my pre-takoff/landing check has always been, Lights out, Speed is green, Guages are green, Fuel, Carb heat, Trim. No matter which Robby I'm flying muscle memory has me saying (and looking for) those things everytime,...even when they're not there.

As for the key, yeah muscle memory with how to check it, but up until this accident if you'd of asked me which way the key points, I'd of just stared back like a deer in the headlights,...as that's not something I've ever paid attention to,...let alone memorized.

Funny though, I've complained about Robby's lack of standardization with regards to instrument placement (mainly when I get into a ten-hole) but never even noticed the inconsistent key setup,...?

[Nineteen84]

Interestingly, the R44 checklist includes a mag check on each mag to ensure the engine doesn't cut out on only one mag and that the RPM drop is insignificant, and then returning the key to the 'both' position and checking the RPM returns to normal...it's the same on the checklist of the Piper PA-32 using the Lycoming O-540/IO-540...so if this was followed the key would be in the 'both' position

[aa777888]

Lack of standardization seems to be an issue in many helicopter models. Look how many variants of the Squirrel/Astar there are. Single vs. dual hydraulics, different engines, FADEC/no FADEC, etc. Lot's of different panels in helicopters that have been around a long time, like the MD500, the 206, etc.

[rotorspeed]

Doesn’t seem too smart to have a big floppy key fob that significantly obscures the position of the key beneath it - particularly when that position is critical. Surely a more rigid coloured small flag on the key would be more sensible, to enable instant visual recognition of key position?

[aa777888]

Originally Posted by BDAttitude

That's what you do in a SEP - watching for the RPM drop when when switching BOTH-L and BOTH-R. You don't have to watch the gauges - not being deaf is enough. I have no idea how practical this is with a rotor and its significantly higher inertia.

You don't appear to have read the entire topic. See posts 22 and 132. Inertia is not an issue, piston helicopters all use a freewheeling device between the engine and the transmission. On the Robinson it's a sprag clutch.

[aa777888]

Originally Posted by BDAttitude

Switching an ignition circuit off leads to a step in power produced by the engine, not a step in engine speed. So no freewheeling.
On a prop with low inertia and no constant speed governor active, the new power level will lead to a nearly instantaneous drop in speed due to low masses and high aerodynamic resistance.
I strongly suspect that I will take a little longer for the rotational masses in a R44 to settle for the new power level.

Freewheeling does occur. The sprag clutch leaves the engine free to decelerate to the extent that switching a mag off will make it decelerate without any inertial effects from the transmission or rotor system. Also, this test is performed at 75% RPM which is, intentionally of course or you could not perform the test, below the 80% point at which the governor takes over, so that is not a factor either. The only rotational masses the engine has to contend with during this test are those of the engine itself. Thus your assertions are not entirely correct. However, it is true that, because of the sprag clutch, there are no frictional or drag forces loading the engine from the transmission or rotor system, so that does have some affect on the deceleration of the engine.

I was asking how long that takes and if this magneto check is practical therefore.

A tired mag will approach the 7% in 2 second limit, so not long in that case. I brand new mag can take 5 or even 10 seconds to show even a small drop, say 2%. One must be careful and patient to detect a bad P lead. I suspect most do it by ear, but I like to visualize a discrete drop in RPM. In any case the check is eminently practical.

[212man]

Freewheeling does occur. The sprag clutch leaves the engine free to decelerate to the extent that switching a mag off will make it decelerate without any inertial effects from the transmission or rotor system

So you are saying there is a needle split when you do the mag check? There are some instructional videos available that would tend to suggest otherwise.

[aa777888]

Originally Posted by 212man

So you are saying there is a needle split when you do the mag check? There are some instructional videos available that would tend to suggest otherwise.

No, the needles don't split, but that's just energy being removed from the transmission and rotor system and at the low energy state of 75% it tends to bleed off at the same speed as the engine when a magneto is removed from the equation. Nevertheless, don't be fooled by that. By definition, because of the sprag clutch, the transmission and rotor system are not "dragged down" by the engine, and the engine is not "dragged up" by transmission and rotor system. The sprag clutch is a one way valve for energy (ignoring the tiny friction losses in the sprag clutch itself). If that was not true then you could never achieve a needle split under any circumstances, and of course you can.

[Vessbot]

Could it be that the clutch carries a small amount of negative torque that has to be overcome before freewheeling happens? And, if so, a mag check does not overcome this small amount, so they stay engaged? Because if we're talking 5-10 seconds to see a mag drop, there's definitely something "dragging up" the engine RPM, which, in an airplane takes more like an eighth of a second (i.e., near instantaneous) to change.

[aa777888]

Originally Posted by Vessbot

Could it be that the clutch carries a small amount of negative torque that has to be overcome before freewheeling happens? And, if so, a mag check does not overcome this small amount, so they stay engaged? Because if we're talking 5-10 seconds to see a mag drop, there's definitely something "dragging up" the engine RPM, which, in an airplane takes more like an eighth of a second (i.e., near instantaneous) to change.

Perhaps. I am now logging a Knowledge Limit Exceedance

[Vessbot]

Originally Posted by BDAttitude

The engine delivers positive torque at all time during the magneto check, just slighltly less when on one ignition circuit. The entire powertain therefore decelerates until the new power setting (pi/30*rpm*torque, torque up, rpm down) is in balance with the aero forces. It‘s the same as if you decelerate your car without coasting (dragging the engine).

Thank you aa777888 for that up to 10s. I doubt the majority of operators will have the discipline.

The transmission is carrying positive torque (engine driving rotor) during steady state running in BOTH and slightly less positive torque in steady state running in L or R. But the question is, during the RPM reduction from BOTH to one mag, why does the change take 5-10 seconds instead of being nearly instantaneous, as it should be if the engine was under only its own influence? During that ramp-down (let's say 3 seconds into the 10 seconds), something is keeping the engine RPM higher than it should be with no external influence. So what is that something?

[aa777888]

One thing I didn't think of is that the engine is turning that big squirrel cage fan right off the crankshaft, right where a prop would be on an airplane.

[Gauges and Dials]

In a normally aspirated piston engine, manifold pressure is determined by throttle position and engine RPM. Mags on / mags off; mixture full rich or idle cut-off; engine producing power or no power, fuel tanks full or empty; the air in the manifold doesn't know about any of that; only how how fast the engine is turning and what the throttle position is.

A surprising number of piston pilots will get this wrong until they think it through.

[megan]

why does the change take 5-10 seconds instead of being nearly instantaneous, as it should be

It doesn't take a number of seconds, the change, as you say, is instantaneous. There seems to be a lack of appreciation of what is happening when you switch to one mag, besides the fact that one mag is now not operating. The sole reason for the mag drop is that it takes longer for the flame front from that one operating mag to spread right across the cylinder ie total combustion within the entire cylinder volume will be reached at a slower rate. The torque drop is instantaneous. For those of you with the latest engine instrument installations, why does the EGT rise when switching to one mag?

freewheeling doesn't occur during a mag drop check, there is a power reduction, not a removal of power.