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Thread: Two cycles, Boy some folks sure hate them

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    bwilson4web's Avatar
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    Two cycles, Boy some folks sure hate them

    Hi,

    I am rebuilding a 1987 built, Viking Dragonfly, a two-place, foam-and-fiberglass plane that came with a 60 hp, 1983 era, 1835cc VW engine. In 25 years, there have a few technical improvements so I did a 'trade study' to find engine options that (1) improve useful load, and (2) preserve the 500 mile range. But when I announced the results, some of the reactions were not technical.

    My trade study came up with three candidates:
    • 625 cc Hirth 3503 - two cycle, water cooled, oil injected, fuel injection, geared, two cylinders.
    • 1800 cc Jibaru - four cycle, air cooled, carb, four cylinders.
    • 680 cc HKS 700E - four cycle, air cooled, carb, geared, two cylinders.
    Details about my project, requirements and study are here:
    http://hiwaay.net/~bzwilson/dragonfly/

    I need to find productive sources about two cycle engines and had already joined the YahooGroup Hirth group. But I suspect there may be other forums and sources with hands-on, experience with larger, two cycle engines. Any recommendations?

    You know the funny thing is I can be persuaded by facts and data but I can't be brow-beaten.

    Thanks,
    Bob Wilson

  2. #2

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    There's a 2-stroke section on homebuiltairplanes.com.

    2-strokes have their advantages and disadvantages. Advantages are better power to weight ration than any 4-stroke, simpler construction, and lower cost. Disadvantages are higher fuel consumption (so maintaining range compared to a 4-stroke might be a problem), need to mix oil and gas, and and critical mixture (run too lean and the engine fries, too rich and you foul a plug). Also many (not all) 2-strokes are single ignition, which reflects the snowmobile heritage of many designs.

    A lot (but not all) of 2-strokes bad reputation is from the early days when most 2-strokes were straight snowmobile conversions. People tried to ignore them and treat them like a Contentinal (add fuel, turn the key, and push the throttle forward), and had troubles. They do require more attention than a 4-stroke, with seasonal carburetor jetting adjustments and preventive maintenance. As one example, a leaking crankcase shaft seal: in a 4-stroke, you lose a bit of oil and maybe have to wipe it off, while on a 2-stroke it's an air leak that fries your engine.

    But even though I've been flying 2-strokes for over 10 years (and never had an engine failure related to the fact that it's a 2-stroke), I'd install a 4-stroke if feasible.

  3. #3

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    Quote Originally Posted by Dana View Post
    There's a 2-stroke section on homebuiltairplanes.com.

    2-strokes have their advantages and disadvantages. Advantages are better power to weight ration than any 4-stroke, simpler construction, and lower cost. Disadvantages are higher fuel consumption (so maintaining range compared to a 4-stroke might be a problem), need to mix oil and gas, and and critical mixture (run too lean and the engine fries, too rich and you foul a plug). Also many (not all) 2-strokes are single ignition, which reflects the snowmobile heritage of many designs.

    A lot (but not all) of 2-strokes bad reputation is from the early days when most 2-strokes were straight snowmobile conversions. People tried to ignore them and treat them like a Contentinal (add fuel, turn the key, and push the throttle forward), and had troubles. They do require more attention than a 4-stroke, with seasonal carburetor jetting adjustments and preventive maintenance. As one example, a leaking crankcase shaft seal: in a 4-stroke, you lose a bit of oil and maybe have to wipe it off, while on a 2-stroke it's an air leak that fries your engine.

    But even though I've been flying 2-strokes for over 10 years (and never had an engine failure related to the fact that it's a 2-stroke), I'd install a 4-stroke if feasible.
    Well said.

    The only two-strokes with a prop I work on are airboats. Lots of fried engines every summer. All due to lack of maintenance or improper operation. That said, because they are not very forgiving, I'd prefer not to fly behind one. Flying requires enough concentration and attention to detail as it is. No need to make it harder if an alternative exists. Most of my engines come from crashed ultralights where a piston melted.

    I have to question the requirement to maintain the 500 mile range, even if it means switching to a less reliable engine. From the website: "Adding the ballistic chute means 'reliability' gets a reduced valuation when the final engine selection is made." I'm shocked to hear someone who is analyzing this to death and will only accept hard data, jump to this conclusion. Deploying the chute is not free. There is no guarantee it will work successfully. If it does there will be airframe damage, the cost to repack the chute and recovery of the aircraft. There may be injuries or death or third party damage depending on where it comes down. If you want to crunch some numbers, figure how often you will be using the 500 mile range vs. shorter flights. Is staying in the air for an extra, say, 1/2 hour, worth the added risk and tremendous cost for the few times it will be used? If so, is the Dragonfly really the right plane for your mission or are you trying to beat it into submission?

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    bwilson4web's Avatar
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    Thank you!

    I had visited them briefly when Google pointed to a couple of postings but moved on. I went back and sure enough I'm finding serious two-cycle information. I like the EAA and certainly it has a wealth of information and expertise but I'm finding it is also a good source of pointers to other technical resources.

    Bob Wilson

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    bwilson4web's Avatar
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    Quote Originally Posted by turtle View Post
    . . .
    I have to question the requirement to maintain the 500 mile range, even if it means switching to a less reliable engine.
    I bought this plane to move a maximum, useful payload at least 500 miles in a 'bladder's time.' N19WT has over 100 hours of acceptable performance that I plan to maximize using current technology.

    I've added emphasis to this quoted material to make sure everyone understands what we agree about:
    Quote Originally Posted by turtle View Post
    . . .
    From the website: "Adding the ballistic chute means 'reliability' gets a reduced valuation when the final engine selection is made." I'm shocked to hear someone who is analyzing this to death and will only accept hard data, jump to this conclusion. Deploying the chute is not free. There is no guarantee it will work successfully. If it does there will be airframe damage, the cost to repack the chute and recovery of the aircraft.
    Yes, we fully agree. We agree about the technical challenges of adding a ballistics parachute. The alternative is to have parachutes used as the seat cushions for both me and the passenger and "GOOD LUCK!" to everyone on the ground.

    This part is special:
    Quote Originally Posted by turtle View Post
    . . .
    There may be injuries or death or third party damage depending on where it comes down.
    So the options are:
    • four-stroke engines never fail
    • airplanes gliding down at 60+ mph never crash and injure those below
    • flying at night and into IFR weather never leads to accidents
    This is an especially foolish claim when considering the alternatives. I have no problem with a mandatory, insurance driven requirement for a tested, ballistics parachute. In the meanwhile, I choose safety.

    Quote Originally Posted by turtle View Post
    . . .
    If you want to crunch some numbers, figure how often you will be using the 500 mile range vs. shorter flights. Is staying in the air for an extra, say, 1/2 hour, worth the added risk and tremendous cost for the few times it will be used?
    Yes, the cost is well within my budget and the requirements can be met by:
    • Hirth 3503 - best combination of payload and range
    • HKS 700e - better payload and less but acceptable range
    • Jabiru - acceptable payload and range
    Yes, the Dragonfly really is the right plane for my mission. I have long wondered about modern two-cycle engines and admired the safety aspects of ballistics parachutes. Both are commonly used in ultralight aircraft. BTW, this is the Ultralight discussion group where such technologies are common. Will you also disrespect the other ultralights too?

    Quote Originally Posted by turtle View Post
    . . . If so, is the Dragonfly really the right plane for your mission or are you trying to beat it into submission?
    Since I bought N19WT, I had not considered 'beating' to be effective aircraft or engineering approach. But I am Southern which means I can be persuaded but I won't be brow-beaten into your point of view.

    Bob Wilson

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    Nice job at twisting words. On your website you imply that a ballistic chute can compensate for a less reliable engine. "Adding the ballistic chute means 'reliability' gets a reduced valuation when the final engine selection is made." So you are fine with pulling the chute and causing whatever carnage you may cause just so you can get a little more distance. This isn't about installing a chute as a secondary, incidental safety measure. The reasoning on your site is to allow you to create an unsafe condition and be able to recover from it.

    There is no disrespecting ultralights here. They serve a purpose but they do have a higher risk. I don't think anyone will deny that. Even the manufacturers of the engines put a low TBO on them because of their failure history. What people don't consider is that we are all in this together. An accident due to someone cutting corners or hotdogging affects everyone from the UL flyer to the millionaire with the Turbo Beaver. It's up to us to choose safety over function. If someone needs to reduce tubing thickness and thereby reduce the safety factor to get more useful load, he chose the wrong aircraft. If the range and load aren't enough without sacrificing reliability, he chose the wrong aircraft. Spec sheets and computer modeling don't keep you in the air. Ask Airbus with the 380. The high-tech Rotax 914 is a poor substitute for the ancient IO-240, as was proven by flight schools across the country with the DA20. Throwing technology at a problem that was caused by poor planning is a bad idea. Using armchair engineering to justify reducing the safety level is worse.

    Useful load - Range - Reliability


    You can only pick two.

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    bwilson4web's Avatar
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    Quote Originally Posted by turtle View Post
    Nice job at twisting words. . . .
    No, thank you for providing such easy words. Still I understand you may have other questions about my project but this is the wrong thread.

    If you would like to go through a semi-formal, NASA style review, let me know. I'll send a note to the moderators and ask which forum they would prefer to see the reviews posted.

    Thanks,
    Bob Wilson

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    bwilson4web's Avatar
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    Quote Originally Posted by Dana View Post
    There's a 2-stroke section on homebuiltairplanes.com.
    . . .
    As follow-up, I got a recommendation about Ultralight Propulsion by Glenn Brinks, 1982, and ordered a copy. I have some ideas to test and this may provide some additional technical details.

    Thanks again,
    Bob Wilson

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    I too question the relationship between a BRS and engine reliability. A BRS is not a substitute for a reliable engine. A BRS should not even be considered an option in case of engine failure... under nearly all circumstances, it's better to fly the aircraft to a forced landing than to pull the chute and become a passenger in what will certainly be a hard touchdown. You use the chute when the wings fall off, or you have a midair collision, not when the engine quits (unless, perhaps, you're IFR over ground fog or on a dark night, in which case the choice of anything but the most reliable engine might be questioned).

  10. #10
    bwilson4web's Avatar
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    Quote Originally Posted by Dana View Post
    I too question . . .
    That is OK but I came here to discuss two-cycle engines. If you are interested in a NASA style, project review of N19WT, let me know. I've already sent a note to the moderators asking where I should post it.

    Bob Wilson

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