OS GT15HZ 600 + OS Trex 600 Conversion... First Impressions

[Sowa]

I've had quite a few people PM me and ask about this setup, I postponed my judgement until I was able to get acquainted with my bird.

The build:

The OS conversion is really nice, everything seems to be of high quality and I did not have any fitment issues. The carbon frame halves were a bonus as some other conversions tend to use G10. One aspect of the conversion I really like was canopy fitment. I believe the conversion moves the rear canopy mounting point forward as it's in a different location than in the manual. This can make it an issue for some if using aftermarket canopy mounting options. I ended up starting off with lynx thumb screw mounts and if it wasn't for the flat spots on the support it would not have fit. I have since then moved to booya mounts. But the canopy fits just as it does in the stock model with no frame sticking below the bottom of the canopy. This is only a visual thing and has no effect on performance of the model but I still like my heli's to look good, and not like a Frankenstein build.

The frame halves were cut to fit a standard size throttle servo, in order to shave some weight off the model I opted for a Hitec HS82mg, this uses a standard splined output but saved almost an ounce of weight over the servo I had in my nitro rig. Every gram counts!

During the build I also did a little research and decided to ditch the stock tank, as I did not care for a 30 min flight time, out of an 8oz tank I get about 14 min of flight time with no issues of a lean condition towards the end of the tank. I might even go to a smaller 6 oz nalgene bottle setup for better fitment, but I like the clear fourtitude tank as its easy to see how much fuel is in the tank from a distance. But this was a huge weight savings in the end. I believe the stock tank is around 15 oz, and I saved over an ounce just between the stock and fourtitude tank (no fuel). With fuel the savings are greater. Here is a link on how to build your own.

The heli came out to 4kg on the dot (8.81 lbs) with a full tank of fuel.

The DFC head uses very hard dampers, these heads are usually flown around 2200rpm, With a ratio of 7.73 this put the motor around 17k which is to high for my comfort. I went ahead and swapped it out for a KDE SXT setup with KBDD green dampers, I have the head running around 2000 with no bobbles or wobbles. I also went ahead and installed the KDE performance tail upgrade.

Issues: One thing I didn't really pay attention to during the build was the clutch and bell tolerance. The gap was too large for the clutch to engage properly and within 3 flights I had smoked the liner. Worried about the stock clutch I went ahead a replaced it with a QuickUK clutch I was able to find on sale, the liner was also replaced with Trex 700n liner as it was much thicker. No issues with slipping yet, but I will keep you guys posted.

Advice: Definitely put some 2nd pieces of fuel tubing over the pump connections (as per manual), I had the line from the crankcase to pump come loose in flight, and I didn't notice it until my telemetry alarm went off, the motor will run without crankcase pressure to the pump and will go into an instant lean condition. I had a hard time to shut it off when this happened. Put some fuel tubing over the line and haven't had an issue.

The motor

My first impression with the engine... This thing is huge! Compared of course to my OS55, now keep in mind this a .90 class motor vs a .50 class which has a much smaller foot print.

1st start up was nothing spectacular motor ran and idled very nicely, it does seem to have more vibes at idle than my old 50. The tolerance between the piston and sleeve is quite large, so I always get my motor above 160F before taking off. It's pretty loud on the bench when it's cold, but cleans up real nice once it gets up to temp. I would definitely recommend letting it get up to temp before taking off, otherwise you will start to develop more and more piston slap. This is something very serious with forged pistons in cars.

The electronic ignition system does not use much power, I am putting back in about 830mah back into my 2s 21000mah LiFe, meaning I can get about 2 flights out of a charge. I did have a smaller 1450mah pack to save weight initially but it seemed the current draw was too high as the pack would sag in voltage pretty tough. I am having no issues running the larger RX pack.

Issues: To those that have been following my posts, I did have a wrist pin retainer come loose on my 4th flight. It was very frustrating because all I wanted to do was fly and I ended up watching the days past by as my motor was being sent out to Japan for repair. OS did stand behind the motor and claimed it was assembled incorrectly.

Break in

I took my time with break in, I believe I'm still in the process as it runs better and better every time I go out and fly (less finicky). I started break in at the stock needle settings (3 out on the main, left the slow in the stock setting), this did well for about the first half gallon. What I noticed about half a gallon in was the plug beginning to foul about halfway through the flight. I did a lot of slow circuits and hovering and about 6 min in the motor would stumble and loose head speed. Trying to get it running right I kept playing with the main needle, that was incorrect. It seems that the slow jet has a lot more effect around hover than the main. The more fuel I run through this motor the more I have to lean out the slow jet. I am about 4 clicks lean (from 3 out) on the main and half a turn in on the slow. It was really rich on the low end, to the point where it wouldn't start unless I pinched the fuel line to the pump.

Advice: This motor will let you know when it's too lean by hanging on the pipe. I would really notice this holding a hover and then hitting throttle hold, the motor would sing for a bit before dying down to idle. This motor is pretty sensitive to the low end needle adjustments with about a 20 degree window at which it's happy. I will use telemetry to help judge where the slow needle is set, after getting the motor up to temp I will land and watch the engine temp, if it drops off rapidly then it's to rich, if it keeps going up then it's to lean. It should go up a few degrees then drop back down again close to operating temp once it's in the right range, but never cool the engine down too much.

Tuning

"Your nitro is too lean!!! .... It's not a nitro, it's a gasser!" I get that a lot at the field!

The 15HZ is much more sensitive to needle adjustments than a nitro. My nitro had a wide window at which it was happy and made good power. The 15HZ... not so much, it seems very sensitive to adjustments so much so it might be frustrating to someone who is new at this, I went through a weekend were I just kept fiddling with the settings to get it to start and keep running, but I would consider myself below average when it comes to tuning gas engines (this is my 1st one).

I have been flying the motor on throttle curves with no issues. The 1st time around I started with the gov on and just kept leaning it out until it took off and flew. That was a HUGE mistake as I ended up 5 click under two turns out.... way too lean. It flies at the recommended factory setting of 3 turns out great, still rich but plenty of power for loops, flips and rolls.

Advice: Make sure the motor is up to temp before beginning any tuning adjustments, there is a huge difference in power output between 180F and 250F, so make sure you give it some time in the beginning.

OS55 vs GT15HZ

The model is heavier with the gasoline setup, the model came out just over a quarter of a pound heavier than my friends N5C (full tank comparison), I had my OS55 in a velcity 50n2 so I have no direct comparison, sorry guys. The extra weight can be felt, but it's not that bad, it feels a little lighter than an electric (disk loading wise). That being said, this motor does feel more powerful than my OS55. The biggest difference, is flight time and cost of fuel I love the cheap fuel costs and long flight times (I think the other pilots are jealous!) Its a perfect trainer which is what I built it for.

I currently have about a gallon through the engine, which is over 4 hours of flight time (equivalent to around $120 in nitro!). Still running strong, still running rich, but I'm loving it. Today was just a gas and go day with no fiddling of the needles started up, ran great, actually made it look like I knew what I was doing!

I think with proper care and careful tuning this motor can run for a long time. It's just special in it's own needs and requires a lot of patience! If that changes and it eats itself, you guys will be the first to know.

[joecass2]

Did they give you a hole new engine or just fixed it. I have a GT15HZ that the wrist pin retainer fell out of it. I'm sending it out now. never made it past brake in.

it's good to hear that it makes more power than the OS 55.

how did you mount your micro throttle servo in the frame? do you have any pictures of it?

[brw0513]

Mitsu,

Nice write up. I like your approach. I bought the OS conversion and a GT15HZ but you're ahead of my progress.

Is that the Hatori SB-15 you have fitted? Did you ever try the OS PowerBoost pipe? If so can you make any comment.

What head speed are you running while hovering?

What blades are you using? Length?

Thanks, and keep up the good work!

[joecass2]

What clunk are you using in the tank?

[Sowa]

Originally Posted by joecass2

Did they give you a hole new engine or just fixed it. I have a GT15HZ that the wrist pin retainer fell out of it. I'm sending it out now. never made it past brake in.

OS did not send me a new motor, they just fixed the one I purchased.

Originally Posted by joecass2

how did you mount your micro throttle servo in the frame? do you have any pictures of it?

Align makes a handy kit P/N: AGNHN6070, bolts right into the existing cutout in the OS or Align frame halves. I forgot to mention I also added frame bolts in the standard servo holes to stiffen the are up front, it felt flimsy.

Originally Posted by brw0513

Is that the Hatori SB-15 you have fitted? Did you ever try the OS PowerBoost pipe? If so can you make any comment.

Yes it is a Hatori Pipe, I never tried the OS PowerBoost pipe. The price difference between the PowerBoost and Hatori was only $40 from rcjapan.net so I opted for the Hatori. Also while talking to Carey about the PowerBoost vs Hatori he suggested using the Hatori as it moves the powerband higher and runs stronger.

Originally Posted by brw0513

What head speed are you running while hovering?

~2000 rpm, is what my phone and ears are telling me, but I don't have an optical tach to really know.

Originally Posted by brw0513

What blades are you using? Length?

Rail 606/Rail 96, I have a set of Edge 623s and a trex 700 boom and torque tube to cut down and stretch the heli. I feel this motor should swing a 623 blade with no problem, and bring me closer in disk loading to a 50 class nitro. I will let you guys know how that goes.

Originally Posted by joecass2

What clunk are you using in the tank?

I am using a felt clunk that is supplied in the fourtitude rc tank. I have been able to find that clunk for sale in regular chainsaw stores (Sten 610-186). It has been working great with no bubbles in the fuel line.

[joecass2]

thanks for the reply. can it do tic toc with out bogging?

[TheFriendsOfMrGyro]

And I was worried about the little spring in my G290's throttle arm against a DS615 servo

Nice birdy, happy flying.

[Sowa]

Originally Posted by joecass2

thanks for the reply. can it do tic toc with out bogging?

Yessir, it has enough power to tic toc, but this isn't a powerhouse, you need good collective management to continuously do them. It makes a little more power than an OS55HZ only ~450 watts more (.6 hp), so it has very similar power to a 50 class nitro. Adding the extra weight probably makes the power to weight ratio very similar.

I just turned the gov on today and started tuning it.There was quite the difference going from throttle curves to a governed setup, the motor sounded stronger and actually held head speed quite nicely, while making more power. Unfortunately my flying day was cut short due to mysterious overheating servos (too hot to touch after a 14min flight). I didn't want to take my chances with one burning up so I packed it up after 4 flights (almost 1 hour of flight time, that's nuts! ), but I was having a blast just swapping rx packs and gassing up.

I wonder if some of the gasser guru's can chime in, but I've come to realize that fuel mixture doesn't have much of an effect on power (within reasonable means). Tuning car engines, all of your power is made off your ignition map, not your air fuel ratio. What I noticed with glow engines (nitro) is power is hugely effected by the mixture. But, unlike a gasoline engine in which spark and ignition are separate, as you lean out a glow engine you also advance the timing as the glow plug is hotter from the previous combustion cycle.

Today it was a little hotter in LA then yesterday, being that i'm still learning my telemetery readout i'm slowly bumping up the alarm to higher temps until I start to hear/see a lean condition. I've actually richened the main needle today two click out from 3 turns, and the motor made enough power to keep me happy. OS suggests 3-2.5 out for break in

On a side note, I highly encourage a backup solution. I installed Scorpion backup guard on this one and it saved my heli today, I put 2200mah into a 2100mah rx pack don't know how that happened, especially since I bought a cell checker today.

[joecass2]

that sounds really good. I had a OS 55 in a X50. the power was pretty good. can't wait to get my engine back from japan. thanks for all the info.

[Doug Darby]

Fuel mixture on gassers can sometimes be masked by the gov. But it still takes a trained ear to detect changes in power based on fuel mix.. The really great pilots (Tim Jones, Mitch Pricer, etc) can detect power changes just from feel... Unfortunately I cant do that as well...
Its also important to experiment with different Head Speeds to find your engines peak power band. Every engine will be a little different and it not only effects power but also how quickly the engine recovers from a full collective pull...

Glad to hear you are enjoying your gasser...

[joecass2]

What was your throttle carves for brake in?

What FBL controller are you using?

What gov?

[Sowa]

Normal 15, 37, 42, 48, 100

I believe I initially had a lower curve, like 15, 35, 38,41, 100 for the first half gallon I tried to keep the motor out of the power band. Kept the head speed pretty low.

Idle up 100, 62, 43, 62, 100

Idle up worked ok, it may not be the best curve as it would bog in full pitch climb out after 5sec. Not sure why but the gov cleaned that up.

I'm flying the ikon using it's internal gov, had to turn up the spoolup rate to get it to work with the 15HZ.

[joecass2]

How much fuel do you have though it now? Still waiting to get mine back from Japan.

[Sowa]

It's been grounded need to figure out why my servos are coming down burning hot.

Still a little over a gallon.

[rcnut]

So where did you buy your motor from? The GT15-600? I have a Compass 3D+ I would like to try it in!

[Sowa]

Rcjapan.net, pm me for a coupon code or sign up for their news letter.

Does anyone have a good reference on tuned pipes for 2 stroke engines. I'm in contact with escomposites to try and get a carbon tuned pipe for this motor.

[LoveToFly1]

Originally Posted by mitsudriver274

Rcjapan.net, pm me for a coupon code or sign up for their news letter.

Does anyone have a good reference on tuned pipes for 2 stroke engines. I'm in contact with escomposites to try and get a carbon tuned pipe for this motor.

I don't think there is a tuned pipe for that motor other than the pipe that comes with it.....

Carbon is not an ideal composition for a tuned pipe either I wouldn't think. Tuned pipes work by using heat and sound waves.....

[Sowa]

Originally Posted by LoveToFly1

I don't think there is a tuned pipe for that motor other than the pipe that comes with it.....

Carbon is not an ideal composition for a tuned pipe either I wouldn't think. Tuned pipes work by using heat and sound waves.....

To my knowledge the only pipes that are available are the Hatori and OS pipe.

The reviews I've read on the es composites stuff has been really good (in the planker community), why wouldn't carbon be a good material for an expansion chamber? If the correct carbon fiber is used then it will have a higher modulus than its aluminum counterpart, and if the correct epoxy is used than it should deal with the heat just fine. The carbon pipes have a tendency to run hotter but that shouldn't be an issue in heli's. I think the biggest hurdle will be packaging the whole unit.

I did end up getting another flight in today, only 2min though as I touched my servos and they were burning hot again. I may have found the issue but I will find out for sure tomorrow. I did however swap out the kbdd lime green dampers for the regular trex 600N dampers and the heli flew much better at 2050. No more bobbles or wobbles (after turning the gov on I realized I was probably flying 2100+). If I can just get the servos to behave this will be an awesome flying bird.

[LoveToFly1]

Originally Posted by mitsudriver274

To my knowledge the only pipes that are available are the Hatori and OS pipe.

The reviews I've read on the es composites stuff has been really good (in the planker community), why wouldn't carbon be a good material for an expansion chamber? If the correct carbon fiber is used then it will have a higher modulus than its aluminum counterpart, and if the correct epoxy is used than it should deal with the heat just fine. The carbon pipes have a tendency to run hotter but that shouldn't be an issue in heli's. I think the biggest hurdle will be packaging the whole unit.

I did end up getting another flight in today, only 2min though as I touched my servos and they were burning hot again. I may have found the issue but I will find out for sure tomorrow. I did however swap out the kbdd lime green dampers for the regular trex 600N dampers and the heli flew much better at 2050. No more bobbles or wobbles (after turning the gov on I realized I was probably flying 2100+). If I can just get the servos to behave this will be an awesome flying bird.

aluminum isn't a good material either for a TUNED pipe. for a muffler, it works perfectly fine. but a TUNED pipe works off of the sound waves an heat. I cant explain it as well as some others probably could, but most TUNED pipes are made from steel. steel doesn't absorb any of the sound waves, thus working much better and more efficient than a softer material like aluminum. the chamber on the tuned pipe uses the sound waves like an exhaust and intake valve. by the sound waves bouncing back from the end of the pipe to actually stop the fresh charge from escaping the motor that has just filled the chamber from the transfer ports.

I understand that nitro motors call the round mufflers tuned pipes all the time, and they may work that way for a nitro motor. but for the gas motors, the QD pipe is the design that I understand works the best. with the cone shape.

I have seen baseball bat type designs for gas motors too, and they seem to work as well. but all my reading and research has shown that the cone type design is the best for a 2 stroke.....

but to answer the original question, a material that will absorb the sound waves and prevent them for working efficiently and 100%, is not ideal. titanium may be the best material honestly, light and very strong and rigid.

I may be totally wrong...who knows......lol...someone correct me if I am. Tom and Doug are pretty much the authority on the tuned pipe around here from my experience.

[Dylanss180]

I was thinking of making a muffler out of titanium. But I would need a tuned pipe to measure in order to make a new one.

The beauty of making it out of 6AL4V titanium is if you get in a crash the material will not dent or break. Unfortunately it is really hard to work with. But, I might give it a shot if the opportunity arises.