Wren 44 questions

[cbdane]

Hey guys, just got my 44 back from the UK with the kero-start upgrade and I have a couple of questions. I could bug Wren but it's more fun to ask here!

1. I opted for the internal kero-start upgrade. The external upgrade would have been fine since they recommended no internal work (bearings, etc.) on the gas generator but I figured after such a long trip across the Atlantic, might as well crack it open while it was there. With the internal upgrade, can I still simply unscrew the burner for maintenance? I noticed that the Wren website only lists the external burner core under spares. Is it the same unit for both internal and external?

2. The way my engine is plumbed and after reading through the manual, it appears that the filter is placed after the "Y" and the fuel valves, only on the main line. Wouldn't it make more sense to place the filter before the "Y" since the kero-burner must also be sensitive to possible debris? I understand that the filter should not be placed on the suction side of the pump but it seems like it would work equally well anywhere on the pressure side and placing it before the split would also protect the valve mechanisms and burner core from debris.

Thanks in advance for your input!

[flymustangs]

Don't have any input on #1, but on #2 I don't see any reason not to move the filter. On my original 44 Magnum I moved the filter to in between the pump and the solenoid valve. I plan on putting the filter in between the pump and Y on this one, just as you mentioned. I bought it partially built and it has another filter between the UAT and the pump. That will obviously have to go. Now I'm debating the manual fuel valve...again!

[Kiba]

I'm not filtering my kero burner (per Wren's fuel line diagram) and it's never been an issue. The orifices in the kero burner are much larger than the tubes & orifices in the main injector assembly and will be less susceptible to clogging. I agree that a more thorough way would be to place the filter after the pump and before the Y heading to both solenoids or even run dual filters, one on the main fuel line and one on the kero burner fuel line.

I've never seen an internal kero start up close but it appears to use the same burner element and burner housing of the external version, only with the internal version does away with the external fuel line and banjo fitting of the external version.

Brent, I have to ask... what did the UK repair/replace after the dirt nap? I'm curious how it held up given the severity of the impact. I'm also very happy to see you repaired it and plan on using it again.

[cbdane]

Originally Posted by Kiba

Brent, I have to ask... what did the UK repair/replace after the dirt nap? I'm curious how it held up given the severity of the impact. I'm also very happy to see you repaired it and plan on using it again.

As it turns out, the damage was minor. Only two parts were replaced: the SS exhaust (of course) and the machined web that sits behind the driven wheel in the secondary and holds the output shaft bearing. As I mentioned, they suggested that the gas generator didn't even need to be opened but I liked the idea of the internal kero-start upgrade. This required a new combustion chamber which of course increased the cost of the conversion; the external burner would have used the original chamber. I added a few bits and bobbles like the green anodized gas generator mount. Remember mine used the older black powder-coated steel version that bubbles up and looks a little tacky after a while.

You can see maintenance costs now posted on their website. However, it is important to consider the cost of shipping back and forth. Not cheap, especially if you obtain shipping insurance.

Looking forward to getting the engine back into a heli! Since the mishap in June, I had a big home improvement project at home that sucked up 4 months of my life. I'm now getting back on track with my helis!

[Kiba]

So all it really needed was just the hot side sheetmetal and the web? That's seriously impressive.

I think you'll like the kero start, once you do a little tweaking for startup parameters it works very well and takes some weight & clutter off the heli. I do strongly suggest buying a spare burner and keep it with your field spares. I've had one burner fail and since I thought ahead and had a spare on hand I was able to swap it out and keep flying while I sent the dead one back to Ron for a fresh element.

I need to come out to Livermore again for a play day once I get my Diabolo finished. I'm 95% done but just found out that the kit is missing one spacer for the bearing stack in the tail grips and Chuck's webpage shows they're out of stock. Hopefully he has one sitting around...

[cbergen]

Curious to your thoughts on if the placement of the engine (rearward vs forward facing) had any impact on the lack of severe damage to the turbine....

Yes, it's conjecture, but an eyewitness to the impact may have an idea...

[cbdane]

Originally Posted by cbergen

Curious to your thoughts on if the placement of the engine (rearward vs forward facing) had any impact on the lack of severe damage to the turbine....

Yes, it's conjecture, but an eyewitness to the impact may have an idea...

Chris, the impact was nearly exactly on the side so turbine orientation probably wasn't a big factor. This said, however, the cushioning effect of the fuel bottle crumpling flat couldn't have been a bad thing.

[Skiddz]

Wow, the nozzle guide vane got tweaked enough to be replaced? That's a pretty stout piece. No wonder the heli didn't survive.

[cbdane]

Originally Posted by Skiddz

Wow, the nozzle guide vane got tweaked enough to be replaced? That's a pretty stout piece. No wonder the heli didn't survive.

On the 44 the vanes are pretty thin. When you look at it, it's not immediately obvious that it's bent without careful study. Wren returned both parts, including the crunched exhaust! They offered me $80 for my gas-start Fadec which I happily agreed to. My only regret there is I now realize I didn't download the last four flights on the day of the accident. I logged every one until then.

[cbdane]

Could someone confirm that the fuel bottle volume (each) for a Magnum is 600cc? Mine were a bit mashed and I didn't hang onto them.

[Kiba]

Correct, mine are 600mL.

[cbdane]

Originally Posted by Kiba

Correct, mine are 600mL.

Thanks!

[cbdane]

Originally Posted by Kiba

I think you'll like the kero start, once you do a little tweaking for startup parameters it works very well and takes some weight & clutter off the heli. I do strongly suggest buying a spare burner and keep it with your field spares. I've had one burner fail and since I thought ahead and had a spare on hand I was able to swap it out and keep flying while I sent the dead one back to Ron for a fresh element.

I realized I never closed the loop on this based on what I learned from Wren. It turns out, the internal burner does indeed use a different part than the external burner. I went ahead and ordered a spare as was recommended here but, interestingly, Wren (Leonie) indicates that it is less necessary for the internal kero ignition system. Here's what he said:

Originally Posted by Wren Turbines

I have received your accessories order & replaced the external for an internal burner (I will get this added to the web site). The coking problem does not appear to be a problem with the internal burners. When Wren initially started building kero start engines this could be a problem, but we have now made the burner body wider so any build up does not coat the element and the wider aperture allows for the residue of oil/fuel to be burned away more efficiently. Repeat start/stops of the engine are the main cause of this ie tinkering – if the engine is allowed to run/fly once it is started the oil/fuel deposit is burned off."

So, no tinkering guys. Let me just say that working with Wren on the service of my engine was a joy. They were amazingly responsive with excellent email communication and very patient with any question that I had. Turbines are pricey, as we all know, and their service is no exception. However, I felt that I truly received excellent return on my investment during this inspection/repair/upgrade process! Thank you Wren!

[Kiba]

Glad to hear Wren UK is as easy to work with as Ron here in the US. I haven't had any dealings with Wren UK yet but Ron is amazingly responsive and very helpful-- even on odd hours on weekends!

Interesting to hear Wren opened up the burner orifice on the internal burners. While my external burner 44 would coke up the orifice every 25 cycles or so initially now after ~1900 minutes of use and about 200 cycles there haven't been any coking issues to speak of in the last 50 starts or so. I have noticed the external burner housing seems to have eroded somewhat internally and opened up some after 200-something starts and perhaps that larger orifice is leading to extended burner cleaning intervals.

I still need to make it back out to Livermore to chat and fly. I recently rebuilt the heli-organizer in the back of my car to fit the Diabolo as it formerly fit the Goblin so now the helis will be safe and secure for longer trips.

[cbdane]

Originally Posted by Kiba

Glad to hear Wren UK is as easy to work with as Ron here in the US. I haven't had any dealings with Wren UK yet but Ron is amazingly responsive and very helpful-- even on odd hours on weekends!

Does Ron ever plan to do 44 service work in the future?

[Kiba]

I'm not sure. Last time I talked to him he could perform some service on the 44 at his shop but given the tolerances of the 44 some operations requires equipment that he doesn't have here in the US so they had to return to the UK.

However, on Wren USA's new webpage there is now an option for "complete 1st and 2nd stage service" and it mentions shipping the turbine to the USA facility. Might be worth talking to Ron to clarify...

[lperagallo]

I believe that Ron could service the gas generator but not the gear box. Glad to see he is services the complete system now.

Lou