OS GT55

Glow/Nitro and gas engines, propellers, fuel and other stuff associated with making lots of noise and thrust.

OS GT55

Postby MikeA » Wed Jun 23, 2010 12:22 am

I just took the plunge and ordered an OS GT55 gas engine. There isn't too much experience with these being posted in the "mainstream" RC discussion forums, but there's no end of speculation! ya what else is new? What little there is has generally been positive - it seems to run well.

When mine arrive's I'll post some notes on my experience with it, but in the meantime maybe someone else has some real-world experience to share?
Last edited by MikeA on Sun Aug 29, 2010 9:18 am, edited 1 time in total.
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Re: OS GT55

Postby RCModelReviews » Wed Jun 23, 2010 1:16 am

That'd be great. I've been looking at that engine and noted that (for an OS) it's pretty well priced.

However, it's a big step for OS (from glow to gas) so I think everyone's hanging out to see just how well it works before risking their own cash.
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Quick update

Postby MikeA » Wed Aug 04, 2010 1:04 am

Hard to believe I ordered this engine in late June and haven't been able to fire it up yet. I ordered a Jtec wraparound Pitts muffler for it based on some good comments from some flying friends. I wanted to have the quietest possible setup without compromising too much on power, so I ordered the large version with the snufflers on the stingers, which are really small mufflers, so I'd have a two-stage muffler. It finally arrived in late July, but I was amazed at just how huge it is.

The OS 55 is going into my trusty Hangar 9 Carden Yak 54 to replace a nuthin-but-trouble Evolution 58. The Evolution 58 is a very powerful engine and can be a joy to fly when it runs well, but it's proven to be very unreliable. I lost the 2009 IMAC season While I sorted out various things and just when I thought I had everything running just right it gave me more grief on the eve of the 2010 IMAC season opener event. I was just too steamed to want to try to figure out it's newest problem, so I shelved it and ordered the OS.

Size matters. This is one of the things about the JTEC site (http://www.jtecrc.com/wraparoundpittsstylemufflers.htm) that ticks me off - they don't publish clearance dimensions. In fact many sites lack basic overall dimension sketches. But that's a whole other rant. So I ordered the large version without consulting their sales team etc for dimensions and got burned. I would have to cut out pretty much the bottom of the Yak's cowl to make it fit and I'd have to protrude the engine farther forward than I'd want to, just to clear the motor box. That cowl really needs the support that comes with a minimal cut-out.

Anyway, I finally consulted the sales dept at Jtec and got the dimensions for the regular wraparound pitts muffler without the shufflers, plus I talked to a local guy who had just installed the same muffler in the same plane, but on a DLE 55 and he told me it was a great fit. So I ordered the regular pitts muffler.

The waiting game: Jtec's business model is to produce only what's ordered, so one could expect a week or so to make it then another 3 or 4 weeks shipping time from the USA to Canada. But I got a little lucky because they had one already made and sent it. So it may be the end of August before this thing get's fired up and in the air.
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Re: OS GT55

Postby RCModelReviews » Wed Aug 04, 2010 1:46 am

It's a pretty looking engine -- and from reports I've read they perform pretty well too.

Was it the OS brand that attracted you to this engine rather than something like the DLE55?

I must admit that I'd have been tempted to modify the engine box so that it would accommodate the muffler and allow the engine to be moved back to the desired position.
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Re: OS GT55

Postby MikeA » Sun Aug 29, 2010 9:14 am

RCModelReviews wrote:It's a pretty looking engine -- and from reports I've read they perform pretty well too.
Was it the OS brand that attracted you to this engine rather than something like the DLE55?


I'd say yes. I want something with an expectation of bullet-proof reliability by starting every time and running the same every flight with good, clean throttle response. Couple that with Japanese engineering and manufacturing and quality control and I could feel assured that my luck would have nothing to do with getting a good or bad version. For me the cost didn't factor in. Yes, the DLE55 is cheaper and I have fellow flyers that love them, but I was willing to take a chance on a realatively new product from OS because it was from OS.

BTW I finally fired it up a few days ago and hope to get it flying tomorrow. It starts easily, using the procedure in the OS manual, which has a lot of ignition-off choking. In the first few minutes of run time I was getting ~6900 rpm on a Xoar 23x8 (2 blade) prop. Curiously, the JTec pitts muffler / Xoar prop combo was 1 dB quieter that the evolution 58 on a canister - BUT the Evolution was turning a 24x10 prop at around 6500 rpm. I expect to go to a 24x8 prop after break-in.

I did some needle tweaking going a little lean then a little rich and finally settled just about where it was set out of the box.

One other thought - If Saito made a four stroke (gas) that could turn a 24" prop between 6000 & 6500 rpm I would have bought that. :)
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Re: OS GT55

Postby hazzbro » Mon Aug 30, 2010 12:54 pm

Got to see one fly in person this weekend on an Extreme Flight 88" Yak. The OS engine ran very well. It had about 1/2 a gallon through it at the beginning of the evening (not sure how much at the end) and was pulling a Xoar (in think) 22-8 at ~7400 RPM. Jeff was running the motor on Redline oil at 32:1 (I think) for break in. As the evening went along the idle was able to be lowered successively and really smoothed out. The power was more than sufficient for good 3D flight even though the motor is still not totally broken it. It was also being run on a ES composites tuned pipe. The only thing I didn't like was the amount of misses you could hear in the lower rpm ranges. I know most 2-stroke gassers do this but this seemed to have more than normal. Could it be the higher break in oil content???? Oh yeah, one other think I like about OS's ignition module is you can use a 2-cell lipo w/o a regulator.
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Re: OS GT55

Postby RCModelReviews » Mon Aug 30, 2010 11:23 pm

Thanks for the update.

Yes, I too have noticed that a fair few of the 2-stroke gasers have an annoying miss at some throttle settings. Some of the cheaper 26cc engines also have a miss that occurs at full throttle for a few seconds after the throttle is opened and no amount of tuning will get rid of it.

Sounds like the OS is a keeper then!
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Re: OS GT55

Postby MikeA » Wed Sep 08, 2010 2:32 am

hazzbro wrote:Jeff was running the motor on Redline oil at 32:1 (I think) for break in. . . . . The only thing I didn't like was the amount of misses you could hear in the lower rpm ranges. I know most 2-stroke gassers do this but this seemed to have more than normal. Could it be the higher break in oil content????

I got my H9 Carden Yak in the air finally on Monday. I also experienced the rough-running 4-cycling just off idle up to about one third-ish throttle. The idle has a noticeable bang-bang-bang sound. I'm running 40:1 synthetic so I'd say the oil content isn't a cause. I'm expecting the low end to smooth out as I lean it out a bit. Right now I can't go anly leaner on the low end without it coughing & dying when snapped open from idle, so I'm hoping more run time will allow me to lean it out.

Top end is fine.
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Re: OS GT55

Postby RCModelReviews » Wed Sep 08, 2010 8:32 am

Most 50cc engines have a burble to the midrange at some range of throttle openings but if it's "banging" at idle are you sure the timing is right?
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Re: OS GT55

Postby MikeA » Wed Sep 08, 2010 4:16 pm

RCModelReviews wrote:Most 50cc engines have a burble to the midrange at some range of throttle openings but if it's "banging" at idle are you sure the timing is right?

Perhaps "bang-bang-bang" was a poor choice of sound-effect wording. More like pop-pop-pop, which I take to be a a "normal" 4 stroking sound. It's just a bit more pronounced than my other gas engines. No worries.
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