Blade Buddy

Wondering if anyone else has had bearing failures in the Wren44 Turboprop Engine.
I purchased the engine in May 08 through the local agent in Australia.
After recieving it I built a test stand and ran it a number of times to familiarise myself with its operation [about 1hr total time on Fadec], the engine performed well on all occasions.
I then scratch built a 1/6 scale Lama Helicopter to put it on. The project took a little over a year. It flies like a dream and the turbine performs well, however a couple of problems have arisen which concern me.
All appeared well up until about 7hrs total run time. After each shutdown the output shaft appeared locked up however after rotating it back and forth a few times by hand it would free up and then feel ok. This began to get worse over the next few runs and working the shaft back and forth was becomming less effective in freeing it up.
At this time I decided to dismantle the hot end and investigate the problem. [After 40 years repairingprecision equipment I consider myself competentto do so]
Internally all of the gearbox components appeared ok with the gears showing no significant signs of wear, the planet gear bearings felt smooth and free as did the output shaft bearings,and all appeared well lubricated.
Further investigation revealed the turbine shaft support bearingadjacent to the power turbine was badly coked up with burnt oil residue, the shaft bearing at the gearbox end was fine.
I cleaned the components, replaced the faulty bearing with a new one, reassembled and test ran the engine and it was fine.
At about 13hrs total time the problem began to reoccurr. At 13.9hrs I dismantled the hot end again to find that the bearing was again serverely coked up.
This time however I found another problem, one of the planet bearings had thrown its cage and was on the verge of collapse.
I have since rebuilt the hot end and replaced the turbine bearing and all of the planet bearings and the engine again is running fine. It is up to about 16hrs now but I fear the problem will be ongoing.
I was expecting at least 25hrs TBO on the engine.

I am using Jet A-1 with 5% Aeroshell 500 Turbine oil.
The engine is being run between 54% and 81% throttle settings which should equate to approx 29% to 66% power output, [nowhere near maximum]and a typical flight of approx 10minutes consumes 800 to 900mls of fuel. Gear ratios in the helicopters transmissionhave been arranged for the engine output shaft to run at 6300rpm.
My shutdown proceedure is to run at around 20% throttle setting for 20 seconds then to idle for 30 seconds then shutdown.
Startups have been fine [except for the odd glow plug failure] and shutdowns normal.

I have had no problems with the gas producer at this time, only with the output stage [ Hot End ].
Has anyone else had any similar problems with the Wren44 Turboprop ?

I have ordered a spare engine for the helicopter which should be here soon, I'm hoping the problems will not occurr with the new one .

Wren Turbines USA

My Feedback: (39)

Blade Buddy,

Your title is a bit confusing, as you are have a problem with the 44 HELI gearbox, but title it as a Turboprop motor????? Two completely different gearboxes......

I have forwarded this to England for their analysis.

Ron

Chris Bergen

I have seen where Jet-A can leave a residue, typically in teh exhaust area, whereas kerosene leaves the exhaust pristine clean.

It's possible the coking is from the use of Jet-A and whatever additives are used locally.

As for the bearing problem, Wren does specify that the 44 Turbines, including gearboxes, are NOT user serviceable. Maybe it would have been money well spent to have them do the servicing, saving you the grief of continued bearing problems....

Blade Buddy

The engine is in factthe Wren44 Turboprop, not the Heli engine. It is used without any modification to drive into the transmission of my helicopter.
Two problems exist
1: The continued severe coking of the bearing behind the power turbine [after about every 7hrs ] there is no residue in the exhaust system and the power turbine wheel is clean.
the prolem seems to be a buildup of burnt oil residue after a few operating hours, this being pretty much the hottest part of the engine. The shaft tunnel of the output stage is only cooled by airflow inside the tunnel and the outside is radiated with heat [ 500 deg C ] from the exhaust shroud only a few millimetres away, whereas the shaft tunnel of the gas producer is cooled both by airflow inside the tunnel and cool air around the tunnel inside the gas producer.

2: The failure of one of the planet bearings @ 13.9Hrs.

As for servicing the engine , I have no problems with this as I rebuild precision equipment for a living.

The continuing problem is the coking of the turbine shaft bearing,

The bearing failure in the gearbox has only happened once at 13.9 hrs

Blade Buddy

Hi Ron here is my Wren44 Turboprop engine set up on my Lama[img][/img]

Wren Turbines USA

My Feedback: (39)

Blade,

After consulting with Mike Murphy in England, we have agreed that if you will send it to them (England), the gearbox will be rebuilt with flange floating bearings at no charge...except for shipping. Please advise as to your decision.

Blade Buddy

Hi Ron,
I will be happy to accept Mike Murphy"s offer.
The new Wren44 Turboprop engine I ordered should be here soon.
As soon as it arrives I'll put it in service. Then I can send the other one back to Wren for attention.

Can you confirm Wren's address and contact details?
Should I email Mike Murphy direct and advise him of my intentions.
Best regards
Bob

Wren Turbines USA

My Feedback: (39)

Call Wren and explain to Terry. I'll forward a heads up to them. Let me know if you need anything else.

Ron

Blade Buddy

Thanks Ron will do
Best regards
Bob