MTK

Rick the OS is a beast on compression. On par with my fully broken in DLE55, which has a great seal in ddition to great compression.

The dynatron had no trouble turning over the SAP180 two years ago when it was needed

MTK

Bob,

I am hoping that after we figure out how to do it, it will be easy. Others apparently are not having the woes I have with mine. So maybe I got a lemon

MTK

I've not run the stock muffler anywhere

cmoulder

I hope it isn't the piped set-up that is the problem.

PlaneKrazee

My Feedback: (14)

The first time you started it in your temptress (after getting it back from Hobby Services)only took three flips. The second time took 100 flips to get it going. Something is different from when you received it from Hobby services to when you started it the second time in the plane.

Running the carb dry or having the needles too lean to draw fuel on choke? I'd have to say you were not getting a prime. They put prime bulbs on some lawn mowers and weed wackers for a reason. The choke plate with the hole in it doesn't allow all engines to prime well.

Take the cowl off, fuel it, set the choke and see if the fuel line fills with gas after you flip it or rock it 10 times. If it doesn't you have figured out the problem. Block the hole in the choke plate and try again. If it still won't prime mount it on the bench, stuff your thumb over the carb and see if it will prime.

Where is the little smiley beating it's head against a brick wall when you need it?

What oil are you using?

MTK

The engine draws fuel fine. It actually floods after several flips without popping. I see the gas getting to the carb. I doubt my needles are set lean. Once it's going, there is no problem with transition

I bench ran it about 5 times at home (in my plane fully set-up as if I was ready to fly). Then at the field it took about 45 minutes of flipping to finally get one in.

It may all be part of the learning curve. I'll just have to see on this one, and use 24 volts on the dynatron.

If I'm still having starting problems after 3 or 4 gallons through it, Ill chalk it up to experience and move on....But, not yet

speedracerntrixie

My Feedback: (29)

Matt, How about trying a different oil in the fuel? I know you have a puzzled look on your face and are saying to yourself that it's not drinking time in CA yet however, What I am thinking is that it works great at home and maybe it's being stored in a temp controled enviroment. When you get out to the field where it is colder the oil from the fuel that has now evaporated leaving just the oil and is cold so the viscocity is higher just may be enough to keep the reeds closed under crankcase vacuum. As you prop and prop the new fuel slowly works it's way in and unsticks the reeds. Far fetched but maybe worth a try?

choihjin

My Feedback: (1)

Dear Matt;
I hope it is helpful.
My OS GT now runs with Mijzlik carbon fiber prop 18x10. It reached 8200 rpm, but I set to 8000 rpm. The prop noisy is too sharp and loud.
As I mentioned already, It runs on Hyde soft mount and with Hatori header/Canister muffler. Even it rotates carbon prop much faster than other wooden props such as Menz, Hawk (18x10, 7500 rpm), I feel less trust pulling my Smaragd which is much over than 5.0 kg. I am looking for 19x10 carbon prop, but difficult to find this size of prop. Ans also I am struggling to take off some weight now.
I hope to hear your good weekend flight news.
Regards

MTK

Don't be afraid to modify the wooden prop if it presents too high a load. I suspect the Hawk is a wide blade design. We don't really need wide blades in pattern. Just make sure that blade shape is preserved on both blades.

Rather than a 19x10, let me suggest an 18x12 apc. The engine seems to be comfortable turning in mid 7's so more pitch will be better and quieter.

If you can't find a 19x10 carbon and you really want one, I have one I will sell you. PM me with address

choihjin

My Feedback: (1)

Thanks Matt;
Menz 18x12 wooden prop caused too much shake on my soft mount. Menz 19x10 was good to start engine easily, but rotated just 6800 rpm only. I think carbon fiber prop 19x10 will rotate faster. Two sources for carbon prop searched by google are Australia and France. I will contact to you.

MTK

I got to use the dynatron starter on the OS33GT. Well, guess what? The dynatron doesn't have enough guts to spool the 33GT up. Spool it up, hell, it doesn't even turn it over, on fully charged 6S lipo, 25 Volts.

But it turns the Mintor 38 with no problem. The OS has tremendous compression quite likely higher compression ratio than the other 30cc offerings, to be able to put out the power it does. In addition the Bore to Stroke ratio is far more advantageous compared to other 30cc engines. OS did many things right on the engine but did not make it user friendly, at least not yet, early in the learning curve....

airborne2.4

Hey guys,
Need to start the week off with a laugh? Here ya go
http://www.rcuniverse.com/forum/m_10...m.htm#10907375

MTK

What a great sense of humor! I enjoyed this video and will share it with my wife tonight....I'm sure she'll get a kick out of it

jrpav1

My Feedback: (17)

Matt,
Sounds like the OS needs a compression release like we sometimes use on long-stroke Harleys. Is there any place on the head where you can machine a spot to put one in? You'd have to make a little tiny compression release device too but this may fix your problem.

That being said, the engine should start with a hand flip IF the ignition is firing at the correct time since you said it definitely has fuel (Spark + Fuel + Compression = Should run!). I know it sounds like a trivial thing but if the ignition system is an "auto advance" type it may not know where the piston is unless the engine has rotated a few times at a steady speed. I actually built a single-fire ignition for Harley engines a few years ago and I learned a lot about ignition sytems and how they work. Some simply fire when they see an input from the crank sensor but an auto-advance type is more complicated. Depending on how it's designed it may not be able to figure out exactly where the piston is under all conditions - especially when hand-starting. On the one that I built I used two hall sensors and a wheel with notches in it. This gave me two pulses per cylinder - one was at 45 degrees BTDC and the other was at TDC. To get the advance curve I delayed by a certain time after I saw the 45 degree pulse (timing was never more than 45 degrees BTDC) but to get the thing started I couldn't use this method. The reason being that converting between "degrees" and "time" will only work when the engine is running. The trick was to use the other pulse at TDC: I ALWAYS made sure the coil was triggered at this time. Until I figured this out I had lots of trouble getting engines to start because big Harleys tend to crank fairly slow. This may explain why you're having so much trouble hand starting the OS. Not knowing how they designed the ignition system I can only point this out as an FYI - it may not even apply to your situation.

Doesn't Ed have one of the gear-reduction starters with a LiPo pack attached to it? That may be all you need. High-voltage on a Dynatron is OK but as you've seen it doesn't always work. The gear-reduction types generally work better at starting the stubborn high-compression stuff. A 4S LiPo pack on a gear reduction starter (Kavan, Magnum, etc.) is pretty nasty!

John Pavlick

airborne2.4

My wife loved it

choihjin

My Feedback: (1)

In the manual, 'the ignition module set not to operate below 120 rpm for safety'.
OS should reconsider this ignition module setting. Based on their claim, hand start below 120 rpm should not operate, and should not start backward. Many are experencing backward start, which is more dangerous than any other engine's no limit setting. How about setting below 80-100 rpm for safety?
Starting by an electric starter is recomended. And also starting with a Chicken stick or gloved hand is instructed in the manual with a mistake: 1, 2, 3, 4. Open (Close?) the choke valve fully. 5, 6, 7. Open the choke valve fully.
Even some faults, I love this powerful gasser, and hope OS upgrade the ignition module.

bjr_93tz

I figure OS means that once the engine is running, that if the rpm (calculated from the pickup pulse frequency) drops below X rpm then the cdi will automatically cut so as to prevent that one last backfire before stopping or kicking back into reverse opersation.

Unless it's actually measuring the pulse width as well then there's absolutely no way the cdi knows how fast you're cranking it for a single flick with 2-3 seconds between pulses so I'd expect the "minimum rpm" function to be disabled because I doubt too many people flick the prop over 3-4 times per second giving the cdi enough pulses to calculate an rpm.

MTK, could you please run a little test for me to put to bed my understanding/misunderstanding of this whole "minimum rpm" thing? If you get the time could pop a spare plug into the plug cap, turn the motor over by hand at a constant rpm 30-60 rpm and let me know if it sparks each time.

Cheers
Brett

MTK

BJ

I have done that several times. The OS CDI indeed does not fire.

Same plug, same flip rpm and same set-up except RCEXl CDI, the plug fires every time. What does that prove? The OS CDI does what it was designed to do.

MTK

b

cmoulder

Matt,

You probably mentioned - or have tried - this already and I forgot it, but have you run the engine with the RCExcel ignition? Timing or advance not compatible?

choihjin

My Feedback: (1)

Based on all information we have discussed above, summarize and darely conclude as follows;
Becaude of minimum rpm setup, the first flip over Hall sensor can not make CDI to ignite how faster you crank the prop, but second flip passing over Hall sensor will ignite depending on the rpm higher than 120 rpm. Because CDI fires at BTDC, the rotating propeller with enough momentum passing through TDC will start forward, otherwise it will rotate backword due to very strong compression of OS GT gassers. That is why OS recommend to use an electric starter, I think.
In my case 19x10 wooden peopellers (more momemtum) started forward easier than 18x10 prop (less momentum). Someone (I have to wait until weekend) do test it with chicken stick. Crank it one complete rotation of propeller passing through second TDC faster than 120 rpm enough making CDI to ignite, like an electric starter, not just hitting prop with groved hand.

MTK

Attempted again last night and was successful in turning the engine over with the dynatron starter and successful in starting the engine: Here's what I did:

Choked the engine and throttle to full
Ignition off
Flipped the prop by hand about 10 times until you could tell fuel was in the engine (felt much looser)
Turned ignition on and flipped by hand until I heard a pop (2 flips)
Ignition still on, throttle to just above idle, choke off; prop turned all the way back to BDC to get a running start
Bumped the starter and it immediately fired right up
COOOOOOLLLL!!

That will be my new starting procedure. We are supposed to get decent weather Sunday. I hope to get a few flights in

PlaneKrazee

My Feedback: (14)

Congratulations! Now if it will pull your plane for a thousand flights....

airborne2.4

That's what I'm waiting to hear.

TimBle

you're going to wait a long time then