Safest most reliable way to operate a 2 stroke?

Discussion in '2-Stroke Aircaft Engines' started by JayKoit, Feb 11, 2013.

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  1. Feb 11, 2013 #1

    JayKoit

    JayKoit

    JayKoit

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    Hi All,

    I've been reading a few threads here about two stroke reliability, and have heard different views on their operation, maintenance, safety, reliability, etc. And although the two aircraft I'm looking at have FWF kits for the 912, they also offer them for the Rotax 582, Simonini Victor, and Hirth 3503, and I just can't get around the 7-10K I'd save by going two stroke (I'd save even more if I buy a zero timed 582 from Rotax Rick). I know it's possible to have hundreds of worry free flight hours behind a 2 stroke, so I'd like to hear from some 2 stroke owners who have successfully flown for hundreds of hours on their engines:

    - What is the safest, most reliable way to operate a 2 stroke aircraft engine, day to day, week to week, and year to year for every flight?

    - Do you premix or inject?

    - What are your maintenance and overhaul schedules regardless of what the manufacturer says?

    - Warm up and cool down methods?

    - Type of fuel?

    - Best way to avoid cold seizure -- or ANY type of seizure?

    - Does throttling back in cruise make a difference?

    - Anything else I'm missing?

    I'd love to hear from you. Thanks!
     
  2. Feb 12, 2013 #2

    N8053H

    N8053H

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    Some very good questions.
    I share my hangar with a man who flies with a rotax and has for years. He has hundreds of hrs flying using rotax.
    Now I have had nothing but problems using two strokes but not everyone has these issue's. The biggest thing do not buy any two stroke that has been setting any length of time. Rotax recomends to thier dealers to rotate their stock every 5 years. If a rotax is setting on the shelf for 5 years Rotax wants that engine back. They are concerned with seals.
    As for Rotax Rick, he is the best. He will explain everything you need to know to operate your two stroke. I wish I had met him sooner in my flying, I would not of had all these issue's.
    Fire up your engine and bring her up to around 200 on the CHT gauges before you move. Then go out and run her or taxi for 5 mins. You do the 5 min taxi to make sure your fuel system is on and everything is working as it should. Then go to the hold short line or the end of the runway, what have you. At this point, run her up and do your mag check. Now you should have been running in total with warm up, taxi and mag check around 10-15 mins. By this time you have heat soaked the engine. You may apply full power and take off.
    If you do not allow your engine to heat soak you take a chance of a cold siezer. Notice I say take a chance, it may not happen, but then again it may. I have done this before, a Newbee mistake. Do not blame the two stroke if you sieaze one with improper warm up.
    Talk to rotax Rick he will advise on a lot of this. he has a recomendation for oil and rpm's he wants to see in flat out running. He built me a 503 that replaced my 447. I could take off at 5000 rpm's. I could cruise at 4200 rpm's.

    Premix, some use injection but Rick will want you to premix.

    Here is a video of this airplane. When you see this video the pilot is using 5000 rpm for take off. Only once I took off at 6500 rpms and at half field I was at 800'. The field is 4000' long.

    Hi-Max with Rotax 503 DCDI - YouTube

    Watch this to learn more about your two stroke.

    EAA Video Player - Your Source for Aviation Videos

    Good luck and fly smart.
     
  3. Feb 12, 2013 #3

    tpelle

    tpelle

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    I have absolutely '0' experience flying behind a 2-stroke, but like the OP I have been researching the issues. I gather that another operational method that may result in a cold seizure is making a long descent at idle with the propellor windmilling, and that proper technique would be to throttle back a little (but not all the way to idle), reduce speed by increasing the angle of attack, then using the throttle to set the desired rate of sink - essentially keeping the propellor "loaded" all of the time, and thus the engine producing power. The theory, as I understand it, is that the heat-soaked engine remains hot internally due to the reduced cooling fuel flow with the throttle closed, but the cylinder cools down rapidly due to airflow. You want the engine to keep making power.

    I also gather that the shock cooling effect is moderated somewhat on the water-cool 582, due to circulating thermal mass of the coolant.

    Have I described this correctly? Is that a valid technique?
     
  4. Feb 12, 2013 #4

    N8053H

    N8053H

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    Watch the last Video I posted on my last response to this question and you will have all these questions answered.

    You never " Windmill " a two stroke. Watch that video and learn all this and more.

    Fly Smart
     
  5. Feb 13, 2013 #5

    JayKoit

    JayKoit

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    N8053H, thanks for the info on Rotax Rick. I'll contact him directly to talk shop. I just finished that EAA webinar you linked to in your above post. It does answer all my questions. tpelle, I highly recommend. Great video!
     
  6. Feb 13, 2013 #6

    fly_boy_bc

    fly_boy_bc

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    I learned all about this when training in Canada for 1300 pound ultralights 15 years ago. Rotax knew about this issue BEFORE they started manufacturing aircraft engines! When Rotax powered snowmobiles are "coasted downhill" they would shock cool and when they were run downhill at full power they would overspeed.

    Just like the way we are told to fly them now. Don't "coast" when descending and no FULL power diving!
    Warm and cool them properly and be careful when descending and you should make it to TBO and beyond! (with correct maintenance).
     
  7. Feb 14, 2013 #7

    PONCH

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    It has been my experience that a properly used and maintained 2-stroke can be very reliable and durable. To properly use and maintain such an engine one needs to understand how it works, how it fails, and why it fails. Premix your fuel and use top shelf oil. These engines get all thier lubrication from the oil in the fuel and oil injection pumps have failed, doesn't happen all the time but it has happened and the results are catastophic engine failure. One of the leading cause of engine failure is a lean running condition, fuel cools internal parts and again, the oil is in the fuel. That's why they should not me coasted, as mentioned above, because coasting forces the engine to operate at a given speed without the corresponding fuel/oil supply. The crank case and intake must remain air tight. If gaskts or seals are in poor condition the engine could suck in air thus creating a lean running condition. Visual inspection of the engine could often reveal such a problem and it must be repaired immediately. It is good practice to check your spark plugs regularly, especially if you make any tuning adjustments or experience any loss of power. Dirty carbs or contaminated fuel system can, and often will, cause the engine to run lean resulting in scored cylinders, burned pistons, or worse. This is the most common cause of death in any 2-stroke application. Never try to make a sick 2-stroke run, you'll likely blow it up. Some people are nervous about using an engine at high RPM for extended periods, however these engines are designed and constructed for such use. They have very few moving parts compared to a 4-stroke therefore less metal on metal, less complication, less to go wrong, and less weight. Basically the only moving parts are the piston, rod, and crank (and the water pump impeller on some models) while a comperable 4-stroke has at lease 3 times more moving parts which don't fare well to prolonged high RPM. It's not apples to apples. Maintainence and proper use is not the same for a 2-stroke, it's a different mind set all together. I have faith in any engine that can survive a jet-ski. With proper care you shouldn't have any surprises and the simplicity of these engines makes them easy to inspect and maintain. I'd take the Rotax...
     
  8. Feb 19, 2013 #8

    Kram

    Kram

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    I did my first apprentiship from 15 at a Yamaha and Stihl dealership in the 70's and have raced motocross all my life and still at it now in my 50's racing Classic motocross.

    Premix is an absolute but I have found that certain brand oils suit certain brands of engines and the price of it has little bearing on it, in fact cheap common blue Mobil 2 stroke oil is one of my favorites and the more expensive Castrol TT for example is one I dislike. With each brand engine find out who's having a good run and find out which brand oil they use and don't fall for the ultra lean mixture rubbish, stick with the mixture recommended by the engine manufacturer.
     
    Last edited: Feb 19, 2013
  9. Feb 19, 2013 #9

    Beaver550

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    I have flown behind (actually in front of) two strokes for over 1000 hours over a 25 1/2 year period and have had no problems that I did not cause myself. I have run out of fuel (forgot to switch tanks) a couple of times, had water in the fuel, and did have an in flight seize that was my own fault. I had just about 300 hours on my 582 with out doing any service work. Rotax recommends decarbonizing the engine at 150 hours and now I follow that recommendation. Learned the hard way; the piston rings had carbon build up underneath until they expanded out to the point where they stuck which resulted in a mild seize.

    Two strokes are relatively simple but my opinion is that you have to make up for that with your operating techniques. The devil is in the details. What helped me the most was going to one of Rotax's Service Centre Two Stroke Operation and Servicing Training Workshops. Most Rotax Service Centres offer a two day course. If you are going to fly a two stroke it is well worth the time and money. Brian Carpenter's video previously linked is but a small bit of the info that you will get from one of these courses. The video is well worth the watch and so is the course. TAKE a Rotax workshop!

    I used to follow my own methods and service schedule. The more I fly and gain experience, the more closely I follow Rotax's recommendations. There is too much at stake to take chances. Rotax knows what works and that is what is in their manuals and servicing recommendations. Ignorance and ignoring the known and published recommendations is what causes so many problems. I have flown multiple multi-thousand mile trips all in front of a two stroke (Rotax). They are a great engine if respected and operated correctly.

    Regards,
    Joe
     
  10. Feb 19, 2013 #10

    tpelle

    tpelle

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    I have been doing a LOT of (internet) research on the 582, and, bearing in mind I have 0 practical experience, I have become convinced that the Rotax oil injection system appears to be the way to go, as opposed to pre-mix. My resons are as follows:

    1. Pre-mixed gasoline does not "store" well, so you can't just land and put your airplane away for a week or two waiting for good flying weather, as the fuel/oil mix will separate. There is no really good way to re-agitate the fuel/oil mix. Wit the oil injection system you have only pure gasoline in the fuel tank, and oil in the oil tank.
    2. Pre-mixing introduces a probability of error in getting the proportions right, especially on a cross-country when you are refuelling at a strange airport.
    3. The argument that the oil pump may fail really doesn't hold water, as 4-strokes have oil pumps too, and in either case a failed oil pump will bring either engine to a stop quite rapidly.

    It seems to me that most of the things that stop a 2-stroke (contaminated fuel, ignition problems, running out of fuel, running out of oil, carb ice, internal component failure) will also stop a 4-stroke. It's theoretically possible that the 2-stroke may even be MORE reliable than a 4-stroke in one category, that being internal component failure, since the 2-stroke simply has fewer components. Of course the Rotax 582 has the additional complication of a liquid cooling system, with it's water pump, hoses and fittings, radiator, etc. But so do some 4-strokes - specifically the popular Rotax 912-series of engines. But I gather that the liquid cooling of the 582 may help compensate for what I see as the most likely failure of the "generic" 2-stroke, that being the shock cooling siezure.

    Again, my position is that of someone who has never sat behind or in front of a 2-stroke airplane engine. But if I were to spend my money on one today I think it would be a Rotax 582 with oil injection, and with that English carb heat system that consists of a set of adapter plates through which coolant flows to warm the carb bodies.
     
  11. Feb 20, 2013 #11

    Kram

    Kram

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    As you are talking about a week to 2 week time frame I will respectfully disagree with you, the fuel will not "go off" or oil separation to any worthwhile degree in that short a time frame but when you start talking months you may have issues.

    Because the specific weights aren't so far apart, the moment you start moving the vehicle around, let alone start the vibrating engine, the fuel will immediately and thoroughly remix what little may have seperated (which would be next to none in a week to 2 week time span). If anything one benefit is the carby bowl will actually have a stronger oil mix for initial cranking at start up as the gasoline has vapoured off a little.
     
  12. Mar 4, 2013 #12

    nickjaxe

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    Lots of very good info here...re letting the motor soak up lots of heat before gunning the throttle to take off...one thing I would add that I try to do on climb out after take off with a wide open throttle....when I am ready to reduce power...normally for me once I pass around 500ft agl I reduce power in small segments letting the pistons stabilize heat wise....my theory being......

    If after a WOT climb out I suddenly reduce power from 6500rpm to 5500rpm for a cruise climb the very hot piston is suddenly robbed of a lot of the cooling/lubing effect of the incoming petrol/oil charge...so I throttle back to say 6300 for around 30secs then 6000 again 30 secs gradually down to the req new lower RPM and hopefully giving the piston a chance to cool and not get to tight in the bore,

    Dont forget guys when the engine is suddenly dropped down to idle speed from a higher RPM for say a descent...that Rotax set the idle mixture quite high on the rich mixture side to cool that piston.

    Nick.
     
  13. Mar 5, 2013 #13

    captarmour

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    My 2 cents is 4 strokes are more reliable mainly because size for size they are working half as hard. Either manufacturers build bigger engines for the same hp or we operate a 65 hp as a 40 hp as an example. If 2 strokes were built big enough to make max power at 3000 rpm for direct drive operations they may last a lot longer.

    direct injection is complex but has advantages. Besides much better fuel economy and cleaner running, with a crankcase seal leak the engine should run richer instead of leaner, thus preventing lean mixture seizure.

    i wonder if a 582 were direct drive how many pounds of thrust would it produce with the biggest prop that could spin at about 3000 rpm without tips going sonic? How could it be tuned for more low end torque? How about adding a blower to boost low end torque?
     
  14. Mar 5, 2013 #14

    N8053H

    N8053H

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    If you where to see a graph showing a 4 stroke and 2 stroke engine, you would see that RPM, HP, and Torque curves are different for these two engines.

    A 4 stroke has a very flat torque and HP curve in all rpm ranges.

    The 2 stroke has a very sharp curve. The curve would start almost on the bottom of the scale at low RPM and would stay there untill over mid rpm. Then the curve would come up very steep in both HP and Torque as RPM go up.

    If you do not run this 2 stroke in this higher rpm's you are producing less power then your 4 stroke at idle.

    So a 2 stroke must run in its upper rpm limits to make any power or torque. This is why we see reduction units on 2 strokes. If they could have been removed they would have done it years ago.

    Add a blower and thats more weight the plane has to carry, its a trade off and not a good one for these little planes we are talking about here.

    Fly Smart
     
  15. Mar 5, 2013 #15

    captarmour

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    How would prop it(582) up to reduce rpm to where we want(say 4500 rpm)at full throttle with the gbox?

    Or prop it up to run at 3000 rpm at full throttle direct drive?

    How would that affect reliability?
     
  16. Mar 5, 2013 #16

    Dana

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    The 582 produces 50HP at 6000 rpm, 36HP at 4500 rpm, 18HP at 3000 RPM. At those lower rpms a 4-stroke would have a better power to weight ratio.

    Dana

    Keep skunks, lawyers, and bankers at a distance.
     
  17. Mar 5, 2013 #17

    captarmour

    captarmour

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    That's not much. Off the shelf would not work. Compared to the 35 hp half vw it is just over half the size, 580 cc compared to 1037cc and without gbox weighs 82 lbs compared to 85 lbs. Really 3000 rpm is ridiculously low considering it is tuned for max torque at 6000 rpm. I wonder how much more it could produce if tuned for max power at 3400 like the half VW?

    the idea of a big 2 stroke to equal the 4 strokes cc for cc is for another thread though so I'll stop here. Pls go to big 2 stroke thread.
     

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