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Old 06-11-2013, 10:20 AM   #1 (permalink)
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Default Pros & Cons of Kero Start

Hi Guys,
I have purchased a new Kero Plug for my Vario Bell 412 with the JetCat PHT3-3 turbine, but I am having an anxiety attack about doing it after reading some of these threads that are talking about the problems they are having with failed starts, engine fires, etc. I would like to get your pros and cons about using Kero Start! Thanks.
Richard

Last edited by avconslt; 06-11-2013 at 12:32 PM..
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Old 06-11-2013, 10:38 AM   #2 (permalink)
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I am thinking the same but I guess the gas is out weighing kero right now. But i could be persuaded. The only thing that i worry about is fire, and especially the scale guys with fuselages. also what else has to be done besides the kero plug and the right program(v6).
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Old 06-11-2013, 11:35 AM   #3 (permalink)
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While my JC heli motor is the PHT2, I have had my fair share of fail starts and fires due to weak batt, but the most prominent cause of the fail starts for me was the turbine wheel rubbing against the EGV during startup. It was caused by the EGV not fully expanded during the preheating phase. Once I sorted that issue out, I haven't seen fail starts since. I do like the Kero burner so far.
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Old 06-11-2013, 12:08 PM   #4 (permalink)
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apologies avconslt if your thread on dark side went off topic slightly.

The downer of Kero is if something goes wrong you can end up with a turbine combustion chamber full of fuel, the worse that can happen on gas is a loud POP which does make people run but can lower the life of your bearings over time if you allow it to run too long on gas only as Gas is a hotter way of starting.

If I was going over to kero I would take the mechanics out and bench run the turbine until I got the kero consistently starting without having to touch the start up parameters.

I do like the kero start up as it is less pipes and clutter on board and it is a very realistic sound.

But for simplicity Gas is an easy option.=, and as I have an older Wren Mw54 the kero option is expensive to upgrade to, in my case.

Good luck with what ever you choose.

Matt
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Old 06-12-2013, 07:45 AM   #5 (permalink)
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Either system can have it's share of issues, and both can be very reliable.

The biggest pro of kero start is not having to locate, carry, and keep full, the can of propane. It's simply one less thing to worry about.

I do enjoy the POP that I get with my Propane start MW54, it gets attention no doubt! After not having started this particular engine for a little while, I struggled recently getting the parameters and the regulator set to get consistent reliable starts, but to be fair, I also swapped in a new ECU.

I have also struggled with Kero starts initially on both my Wren 44 and Jetcat SPH5's, but again, once the settings are dialed in, the become very reliable. So Matt's suggestion is certainly valid, get them dialed in BEFORE putting them in a Fuse. And keeping that Battery topped off in a Kero start system is a MUST.
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Old 06-12-2013, 02:22 PM   #6 (permalink)
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I've had the burner orifice carbon up and clog twice now on my MW44 and cause no-starts. I've also had one element short but that was after 3 failed start attempts at the field when the orifice clogged the second time. I knew based on symptoms (slightly sluggish previous start) that the orifice was likely restricted and needed to be cleaned. Unfortunately I didn't have the right size socket on me to swap to my spare burner element and I *really* wanted to fly once more-- so I tried to start the turbine 3 additional times. Finally I decided to call it a day and upon getting home I hooked up the handbox and attempted one more start and saw the error message for a shorted burner. When I removed the burner it was totally carboned up and and clogged; I think the lack of fuel flowing over the element during those 3 start attempts at the field with the clogged orifice caused it to overheat and fail.

One thing I've noticed common to both situations was when the element and banjo housing were removed for cleaning or replacement is that the lower o-ring on the banjo housing sheds small pieces of rubber back up into the banjo fitting where it can either pass through or clog the two small holes leading to the burner element; I have a hunch small pieces of o-ring are making it to the hot element where they melt and clog up the orifice.

I did notice when I received the rebuilt element back from Wren they provided what appear to be teflon o-rings for the banjo fitting instead of the original viton o-rings. Maybe these will prevent the small shredded pieces of o-ring from entering the element and clogging it.

I have been removing and cleaning the burner orifice about every 20-25 starts now; during the next cleaning I'll switch to the newer teflon o-rings and see if that points to the lower viton o-ring "shedding" little pieces of rubber as the cause of the carbon buildup problem

I can't comment on gas-start turbines as I've never had one but with the exception of the 2 instances of clogged burner orifices causing failed starts (2 failures in 120-something total starts) I've been extremely happy with the kero start-- it's a much "cleaner" installation and one less thing to remember to refill or bring to the field.

For installation in a scale heli, depending on turbine placement and exhaust exit location I might reconsider going kero start just because a delayed ignition condition can leave a lot of puddled kero inside the turbine and lead to a fire. It seems the risk of a fire / hot start is less with a gas start system.
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Old 06-13-2013, 04:04 PM   #7 (permalink)
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Lot's of food for thought here guys! Thanks. BTW: one drawback of Teflon O-rings is creep. They will take a permanent shape, generally making them single use seals. Lot's of experience here with PTFE components in big laser systems.
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Old 06-13-2013, 08:29 PM   #8 (permalink)
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Very true Brent, teflon certainly does like to creep and take a set.

Wren didn't say exactly what the new o-rings were made of but they sure look and feel a lot like teflon. They could be some other kind of fluoropolymer-- but I'm expecting them to take a set based on look and feel. As long as they don't leak or start shedding little pieces up into the banjo fitting and then into the burner they should be better than the current viton o-rings.

I can say that after being installed for 20-25 starts the viton o-rings, especially the lower one, take a definite set and the little bit of the bottom o-ring that extrudes up into the banjo fitting from contact with the burner threads and compression loads starts to "shed" small pieces.
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