My Fav

[hjajr]

Hate to hear all that Bryan.
Doesn't sound good.
I have no issue with a Rotax. I believe for the money they are hard to beat now a days. Used ones anyways. The 4 bangers are just to high.

Did the engine do ok?

 

[hjajr]

What happened after 100 hours on the mini?

 

[bryancobb]

What happened after 100 hours on the mini?

Got scared and sold it. Never had a single issue with the engine but B.J. convinced me that my Dykes ring was just about ready to break out at the piston top edge.

 

[bryancobb]

...I have no issue with a Rotax...

I don't either. I have 200 hours behind a fan cooled SINGLE IGNITION 503 in a Tierra!

Low too! At 50' above the trees. The engine ran like a champ.

The 582 in the Mini-500 never gave a hint of a problem but you could tell it was being taxed right up to its max. Again, without problems.

I do consider myself pretty skilled at operating a 2-stroke properly and any 2-stroke in an aircraft, especially a helicopter, is NOT a crank-it-n-forget-it powerplant. They do require one of the following:

1) Run them slobbery rich, never letting their personality be shown, and accept the carbon buildup...

ORRRR

2) Lean 'em out, get 'em into the power band, and let them show off.

A 2-STROKE IS DESIGNED TO RUN BEST JUST ON THE EDGE OF MELTING. I was 100% comfortable running my 582 in the Mini with 1200 EGT's.

I was FINATICAL about my gauges being accurate on my EGT's and I watched them closely.

I think an aluminum piston starts to SMEAR like butter on the cylinder walls at about 1350. If I jetted the Mini for 1050, I could barely hover in cool weather.

It's a fine line.

 

[hjajr]

Mine are running right at 1100 and 1150.
I messed up one time with a gyro and raised the needle one time and ruined the engine . I believe it was hitting around 1200 degrees. I dont care to hit 1200 again.
1175 is hot enough . I'm not saying it wont run better.
Well rick is building me a 670 for the mini. hope it holds up. I know there are some that he has built gyros engines for. One had a engine out and I believe it was posted on here. I believe rick fixed it for no charge. Hopefully that wont happen in the mini. Most of my flying is close to home and high enough to get over the trees to the next field. Still building up my faith in it. just 3 or 4 hours now.It does manuaver very well.
Bryan how does it auto? what is a good mininium speed for autos? Surely its not like the Mosquito autos?

 

[bryancobb]

... Bryan how does it auto? what is a good mininium speed for autos? Surely its not like the Mosquito autos?

I don't remember doing a lot of autos in it. I did do a few to power recovery and I remember it doing just fine.

Mine had the old radial ball bearings in the MRGB on the input shaft and there was some concerns at the time that the abrupt from "driivng" to "coasting" loaded the bearings differently which would cause them to fail. Because of that, I stayed away from doing autos just for fun. I felt confident that it would get me down if the engine ever quit.

I personally saw with my own eyes, a little fella doing OGE autos to the ground from a 200' hover. This was 1997 Sun-N-Fun. I was impressed. He did get the blade tips VERRRRY close to the boom in them though.

It never hit but it was CLOOOOOSE!

 

[bryancobb]

hj,

HERE'S WHAT WILL KILL YOU IN A 2-STROKE MINI... a normal descent at 500FPM...if you do not know what you are doing with the MIDRANGE jetting circuit.

As you gradually lower collective to descend, when the task of metering fuel/air changes from the mains to the "jet-needle/needle-jet" team, it better be jetted right in the midrange or you will seize it instantly.

GET THIS SET CORRECTLY ON THE GROUND WITH 500 LBS OF SANDBAGS ON THE SKIDS. You know it's right when the EGT's NEVER start getting hotter as you slowly decrease collective from full to 1/4.

 

[hjajr]

I said that I changed the needles. I believe I changed the jets just down one size. That is all it took to make it run to hot.
Its a good thing I have a EIS on it so I can watch it some. It always seems to be right. I will watch it more closely Byran. I don't never cut the throttle but maybe 200 RPM's doing anything in this ship no matter where the collective is do I don't even hit mid range except for running it up and shutting it down.
If I remember right this has had the PEP jet update.

 

[bryancobb]

HJ,

As you know, the Mini-500 rotor should be kept as close to 100% (546 RPM), from liftoff to a hover, during all flying, and all the way till landing and sitting on the skids for shutdown.

Are you aware that when you lower the collective to do a normal descent, at 546 RPM, the carburetor closes proportionate to how much you lower the collective EVEN THOUGH ENGINE AND ROTOR RPM IS KEPT UP to 546?

After you takeoff and climb out ( on the main jets and at 546 RPM ) then you level off to cruise ( still at 546 RPM ). At this cruise setting, the carburetors are just BARELY above the point where the main jets hand off the responsibility to the jet-needle/needle-jet team. Your engine is running on the main jets but just barely.

Then you get where you are headed and get ready to descend and land. You lower the collective a little (still keeping 546 RPM) and believe-it-or-not, you are now on the MIDRANGE jets. I.E. the jet-needle/needle-jet team. This is usually when a seizure happens.

 

[davh12]

Excellent photos. Thanks. Very intriguing platform.

 

[Jason Knight]

HJ,

As you know, the Mini-500 rotor should be kept as close to 100% (546 RPM), from liftoff to a hover, during all flying, and all the way till landing and sitting on the skids for shutdown.

Are you aware that when you lower the collective to do a normal descent, at 546 RPM, the carburetor closes proportionate to how much you lower the collective EVEN THOUGH ENGINE AND ROTOR RPM IS KEPT UP to 546?

After you takeoff and climb out ( on the main jets and at 546 RPM ) then you level off to cruise ( still at 546 RPM ). At this cruise setting, the carburetors are just BARELY above the point where the main jets hand off the responsibility to the jet-needle/needle-jet team. Your engine is running on the main jets but just barely.

Then you get where you are headed and get ready to descend and land. You lower the collective a little (still keeping 546 RPM) and believe-it-or-not, you are now on the MIDRANGE jets. I.E. the jet-needle/needle-jet team. This is usually when a seizure happens.

How you do you counteract this issue?

 

[cburg]

Especially when you figure the Heli pilot rating to fly a non-103 is between $10,000-$15,000.

 

[bryancobb]

How you do you counteract this issue?

You learn to properly jet the engine for use in a constant-RPM, varying-load, helicopter application.

 

[Low level lover]

Hello Gentlemen

Not sure I agree with the statement about just barely running on the needle jets in cruise flight. Maybe altitude plays a roll in this, but I had a situation where with the wrong needle jets (should have caught on when the rotors spooled up more than normal on warm up) in cruise flight I could not keep the EGT's from exceeding the redline. I had to apply more power than needed (running back on main jets) to stay within parameters. So I elected to do a quick go around to set up for a successful auto (rolled engine to idle) from 500 ft agl where I had just departed from. At the bottom of the auto did a power recovery where the main jets take over again and all was well. Changed out the needle jets and off I went again with no problems.

Take note, if your rotors spool up more than normal when idling you may be running too lean a needle jet.

Kirt

 

[bryancobb]

Kirt,

My "barely on the __________ jets" statement was really just an example to make a point. The point being ...there is a threshold where the changeover happens, somewhere fairly close to the cruise power setting. You need to be jetted correctly ABOVE that threshold (main jets) and BELOW that threshold (needle-jet/jet-needle team) to avoid seizure.

On takeoff and climb, this is a list of some of the most common things that will seize your engine:
* Cold Seizure (not letting the engine warm up long enough before takeoff)
* Main Jets too lean
* Obstructed fuel supply (kinked or decayed lines, clogged filters, tiny speck across main jet orifice...etc)

On normal descent, this is a list of some of the most common things that will seize your engine:
* Wrong jet-needles or needle-jets, or both (EGT Limits exceeded)
* Wrong clip position on jet-needles (EGT Limits exceeded)
These things may or may not show up during normal cruise depending on how fat you are and how much fuel you have in the tank, as well as density altitude.

 

[Danough]

Jetting suggestion?

Jetting suggestion?

So Bryan,

Would you care to share a good starting point for main jets, jet needles, needle jets, and needle position for a Rotax 503 in a helicopter? I know what the literature recommends but they are assuming use in a fixed wing.

 

[bryancobb]

Dan,

A 503?
I don't know of a helicopter that it will fly! What is it 56 HP? I think even a Mosquito Air weighs more than 560 pounds with pilot and fuel.


Anyway, to answer your question, I would fasten the ship firmly to the ground. Then change main Jets (starting very rich) so at full throttle with as much blade pitch as can be applied without RPM bleedoff the full throttle mixture is correct. Get leaner gradually as you monitor EGT's. Keep applying more blade pitch as you lean it out. At some point when your EGT's are stable at about 1175, and Rotor RPM is at your constant flight RPM the manufacturer calls for, you now have the MAIN JETS CORRECT.

Now comes the tricky part and if you do it wrong you will melt your cylinders and seize it up. As you GRADUALLY and slowly lower collective and maintain constant RPM, watch for THE SLIGHTEST INCREASE in EGT's. If they rise at all, your NEEDLE JETS are too lean. This will show up at about 75% power and lower. As a starting point, I would install needle jets that are 4 steps richer than what comes stock in the engine. That will probably keep you from melting it as you "sneak up" on the correct ones. The midrange is jetted right if there is no rise in EGT's as you lower collective from full up to full down while keeping full RPM.

Don't change the clip position of the jet needle. Put it in the bottom slot (richest) and leave it there. In a Mini-500 with a 582 and a PEP pipe, 11K2 jet needles have the proper profile. For your machine and exhaust, I have no Idea what jet needle will customize the engine for your machine and setup.

Hope that helps.