Robinson R44

[helo_44]

R44 Raven 2 - Ring gear failure

Hi all....last week I had to (at great expense to management ) replace the ring gear on my Raven 2 after just 250 hours.

Sitting alongside were two other Raven 2s undergoing the same surgery.

The engineers put the high failure rate down to an incorrect starting procedure used by most pilots.....basically beginning to feed in mixture BEFORE releasing the starter button.

I am a little sceptical and would be interested in feedback regarding:

- experience with with incidence ring gear failure around the traps and if it is higher on Raven 2s than other machines,

- technical thoughts on the explanation offered.

Thanks!

[Lu Zuckerman]

Sometimes the factory is right but sometimes they are wrong.

To: helo_44


What Robinson has told you may very well be correct but three failures for the same reason on three helicopters in the same area (Improper starting procedures). Gears fail for many reasons one of which is abuse and overstress. However they also fail due to improper machining (A lot of S-58 T tail rotor gear boxes failed for this reason). Other gears fail due to faulty heat-treat where the gears are either too hard or not hard enough. (There were 43 B-214s that had bull gears that were too soft and had premature wear). There is such a thing, as batch sensitivity where parts are made at the same time and if one has a problem then there is a strong possibility that the other parts made at the same time will have the same problem.

When the gears are removed if you can check the manufacturing date to see if they were made at the same time. Even if they were not made at the same time have your maintenance engineer check the wear pattern and the Brinell hardness of the gear body.

[chopperchav]

I've got a raven 2 with 18 hours on clock. I have found that on starting, the blades will start rotating with clutch disengaged. Im putting this down to the clutch belts being tight as it is still very new. Is this normal or should I be getting something done?
Consequently it can be a **** to start and I find myself with the starter button pressed with mixture full in as the drag of the blades keeps stalling the engine. Am I doing some damage to my ring gear by doing this then? What is ring gear anyway?

[Choppersquad]

you might post correct start up on the 44 if you have spoken to
robo on this matter.

cs

[helicopter-redeye]

I have found that on starting, the blades will start rotating with clutch disengaged. Im putting this down to the clutch belts being tight as it is still very new. Is this normal or should I be getting something done?

POH, "Blades turning within 5 seconds"

On a 600hr Raven 1 they turn very early on as well and the engineers say that this is correct.

New R44's can be a bit difficult to start but settle down within about 70hrs. It's then a case of throttle management during the clutch process to ensure it does not stall as the belts tighten.

I've found 62% engine tach reading by the time the belts are going tight gives a smooth start (POH is 50- 60 with clutch light on) but this has also varied between machines (56 - 63 range) and also if it is the first start of the day or the sixth.

Also recall it was harder to start all engines in Maryland, USA, but this may have been because it was much colder outside ...

[Vfrpilotpb]

The mighty Ford Corporation had a very costly time in the early 70's and then the 80's with the ring gears of many Capri 1600 and 2litre engines ring gears failures, and as Lu has already said it was the heat treatment of the teeth making them not hard enough, the secret in starting equipment is to make the smallest and least costly piece of kit the one most likley to fail, Ie the starter pinion should be the weakest item, ring gear next and then engine last.

Vfr

[chopperchav]

Helicopter- redeye, the problem I am having is blades turning with clutch switch 'disengaged'.

[headsethair]

"Helicopter- redeye, the problem I am having is blades turning with clutch switch 'disengaged'."

Easily fixed with a phone call to Wycombe and a little visit to their workshop........it's a belt thing.

[helicopter-redeye]

Correct, on start up (as you turn the key/ press the button in RII) the blades turn. As the engine lights, before you throw the brown guard switch, the blades will be turning about 1 rev per 2 secs.

I'm told that this is normal and expected (the engine likes load). Older machines (& I recall most of the Astros I ever flew) this did not happen.

I've just had a new clutch actuater fitted (the springs lost springiness on the original) and the blades noticably turn more as it is new (engineer says this is fine too).

Check with your engineer if uncertain or if the clutch is not disenganging correctly. 50 to 62 seconds on the timer from switch to clutch light on depanding on usage.

[chopperchav]

Thanks for the info, glad that is normal.

[CRAZYBROADSWORD]

You will find that blades often turn when you start if the aircraft was shut down the day before on a warm day then left overnight in the cold. try engaging then disengaging the clutch before you start the thing up as this should put the belts back to the right tension.

[helo_44]

Hmmmmm....lots of stuff here....but the missing bits seem to be:

What is a ring gear - a gear (usually attached to the flywheel area) that the starter motor engages with to turn the crankshaft of the engine during start up

What happened before/after failure - since close to new and during start up the starter motor would occaisonally fail to engage with the ring gear. this made a sound like high pitched whizz...rather than the usual aruuuugha during a normal piston engine start.....usually stopping the start procedure and waiting about 30 secs remedied the situation.....this happened more frequently until the engine failed to start at all.

What happened - the ring gear had big chunks out of the side of it and rounded teeth in some parts...I will try to recover the failed gear and get some pics....as a matter of interest one of the machines being repaired was from Brisbane....a long way from Sydney so with different pilots....

What is the required starting procedure - of course this is in the manual....but my take on it is (check this with your engineer!!!)

Main switch on
Area clear
Throttle closed
Mixture full rich
Prime (cold engine 6 secs, warm engine 3 secs)
Mixture full lean
Press starter button on collective with left hand
As soon as engine fires release starter button
Quickly feed in mixture to full rich with right hand
Alternator, clutch, oil pressure, etc

The important thing (according to my engineer) is to ensure that the starter is released BEFORE feeding in the mixture rich lever.....

I am still interested if anybody else has had similar issues as I am having difficulty understanding how the damage I obsered was caused by the starting sequence.....

PC

[Gaseous]

Lots of experience of ring gear failure with Enstroms. Mine is on its seventh. (its 29 years old). Looking through the log books it has been a problem all its life so its not likely to be pilot induced or a batch production problem. Enstrom is Bendix fuel injected with Bendix mags which I think is the same as a Raven 2. Enstrom starting procedure exactly as described above.

I assume the R44 uses 2 sets of contact breaker points.

Mode of failure is ususally when the engine doesn't fire until the instant the switch is released. What then happens is that the advanced cb points are then activated causing the engine to fire. If there is not enough momentum to carry it over TDC, the engine will rapidly revolve in reverse for half a revolution. If the starter motor gear is still egaged, something breaks. Ususally its the ring gear but can be the starter motor casting. Ive even had it chew up the sprag clutch in the starter motor.

The next time the starter is tried there is a gnashing of gears. Very unpleasant.

As the starter drops out of mesh with the ring gear pretty quick, it can only happen if the button is released at exactly the moment the advanced points open. This is why it doesn't happen very often.

There is an unauthorised fix for this by putting a switch to hold the retard points on until the engine is actually running but as far as I know there is no authorised fix for this.

Its worse for helicopter engines than fixed wing as the belt drags a bit and there is arguably less flywheel effect. (no prop)

I don't believe it is a problem of wrong starting procedure. It happens if you are unfortunate enough to release the starter at the wrong time, which you have no way of knowing. Crap design.


You gotta live with it.

Gear failure can also be caused if the relay that switches to to retarded points fails but that is not likely in a new 44.

Pushing the start button with the engine running is not good either.

[Lu Zuckerman]

A horse of a different colo(u)r.

TO: helo_44

You were addressing the starter ring gear on the engine. I thought you were addressing the transmission. My statement still stands and it applies to the engine ring gear as well as the gears in the transmission. Now that I know what you are talking about I have to agree with the starting techniques being the culprit. However faulty manufacturing processes can also effect the gears longevity.

[Doucheman]

R44 Barrell Roll

As a quick question, is there any particular reason that an R44 couldn't do a barrell roll given that it is a 1G positive manouvre??
Look forward to your input
Thanks
Douche

[moosp]

I'll start with a couple of reasons why not.

1) It is against the POH and therefore against CASA regulations and therefore illegal.

2) You WILL crash.

[Flight Safety]

It's unthinkable with a teetering rotor head (the R44). Only possible with a fully articulated or semi-rigid rotor head.

[Gomer Pylot]

Perfectly done, it's theoretically possible. But not with me in the aircraft, or anywhere near it.

[Flight Safety]

Gomer, yes, it's theoretically possible. But unlike the fully articulated and semi-rigid designs, there is no margin for error with the teetering rotor head. The execution would have to be textbook perfect, which is not likely on your first (and last) attempt.

I'm with you, I'd be out fishing that day.

[Gomer Pylot]

FS, theoretically possible and practically possible aren't the same thing. While it is theoretically possible to do it in an R22, trying it is only for the terminally stupid who play in the shallow end of the gene pool. Like I said, it won't be attempted if I'm in the aircraft.