Big 2 stroke

Discussion in '2-Stroke Aircaft Engines' started by captarmour, Feb 9, 2013.

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  1. Feb 9, 2013 #1

    captarmour

    captarmour

    captarmour

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    2 strokes have long been known to wear out a lot quicker than 4 strokes. What about building a long stroke 1200 cc 2 stroke instead of a small 600 2 stroke.

    I envision a twin cylinder, opposed cylinder firing together to make a 'twingle' using crankcase induction. Maybe a 100mm bore and 200 mm stroke making about 1500cc. Revving to about 3000 rpm. The icing on the cake would be direct injection, but maybe simple is better. With such a long stroke and mid porting maybe very little port timing overlap may reduce fuel economy.

    On a different note, i am looking at patenting an electric reduction box that will also work as a hybrid, that should be very interesting as the model using rc electric motors I made is very interesting.
     
  2. Feb 9, 2013 #2

    rtfm

    rtfm

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    Hi,
    Nice to have a new voice on the forum. Welcome.
     
  3. Feb 9, 2013 #3

    Lemans

    Lemans

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    Hi Captarmour,


    Good to see new blood on the 'engine department'. Wearing out has less to do at witch rpm's the
    engine is running. Important here is piston speed and the actual weight of the oscillating parts.
    Your big stroke engine could wear out faster than a small one.
    You could read this: 'Designing/building of my 4-stroke (direct-drive) engine to replace the 277/477 Rotax' in the Member Project Logs.
    The engine is based upon the same piston movements you mentioned.
    I have no intention of 'protecting' the design. Feel free to build one too.
    Theory shows interesting figures - still yet to be proved in the real world.
    Minor point is the need to use a 2-stroke mixture in a 4-stroke engine (lubrication of crank,pistons and piston pins)


    see you arround.
     
  4. Feb 9, 2013 #4

    captarmour

    captarmour

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    Oops, initially I was thinking real low rpm like say 1500 rpm for a single cylinder. The twin would be a 100mm bore 100mm stroke. Lower rpm could be used too.
    With additional complications like forced injection, oil pump lubrication could be used. Heavy fuel could be an option with direct injection and maybe even compression ignition.
    I'll have a look at the thread. For 4 stroke I like the flat head design, very simple and light. A nice mod would be a flat head to fit the VW engine coupled with a longer stroke/lower rpm.
     
  5. Feb 9, 2013 #5

    Dana

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    Problem with low RPM is you also have low HP unless the torque is very high, so you're back to a highly stressed (and probably heavy) engine... losing most of the advantage of a 2-stroke over a 4-stroke.

    -Dana

    The citizens of the United States are getting the government they deserve. The problem is that I'm also getting the government they deserve.
     
  6. Feb 9, 2013 #6

    sachaknoop

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    Dana, I understand what you mean, but I wonder if this could be backed up by numbers, in a kind of comparison with 2 engines with the same thrust, on the same plane. One would be a 2 stroke, and the other a 4 stroke, both direct drive.
    I think the Trabant engine is a long(er) 2 stroke, and was installed on the first SD-minisport. there is also a 4 stroke version. Might be a good comparison platform. Of course the Trabant engine is heavy built which is a shame....but I like the sound better than a 2 stroke with reduction drive (less RPM)!



    Sacha
     
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  7. Feb 11, 2013 #7

    captarmour

    captarmour

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    Is this video the one with the Trabant engine? It sounded much higher revving than the Briggs.

    I still think that the 2 stroke if built same size and tuned to equal the output of the 4 stroke may be just as reliable.

    On another note has anyone ever produced a flat head for the VW engine? That could save some weight with no rocker arms and associated hardware and a much more compact head something like the D-Motor. At 3000 rpm who really needs overhead valves?
     
  8. Feb 11, 2013 #8

    BBerson

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    I don't know if its been done yet. But I have considered doing it myself.
    The two cylinder Onan was used on the tiny Quickie airplane and was flat head. Of course, the Onan was just too small.
     
  9. Feb 11, 2013 #9

    sachaknoop

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    Hi Captarmour, yes, in the video the first plane has the Trabant engine, reliability in Trabant cars is very good, it used to do a lot more Km's than a comparable 4 stroke of these days. Saab was one of the latest car manufacturers that switched from 2 stroke to 4 stroke because they could not find a 4 stroke that was as reliable as their 2 stroke engines. They did 500000 km easily.

    Still the Trabant engine in the sd-1 minisport was abandoned, and I guess it is because the engine is too heavy (just guessing).

    Sacha
     
  10. Feb 11, 2013 #10

    captarmour

    captarmour

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    Thanks Sacha, I'll look it up.
     
  11. Feb 11, 2013 #11

    Lemans

    Lemans

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    Is this video the one with the Trabant engine? It sounded much higher revving than the Briggs.”


    Trabant engine red line is 5000 rpm. The B&S red line is 3500 rpm.Trabant is 2-stroke / twice the explosion of the B&S. So for every explosion in the B&S you get 3 explosions of the Trabant.


    At 3000 rpm who really needs overhead valves?
    Even at 1500 rpm, good designed heads makes a huge difference. Industrial engines don't use flat heads anymore. You would be surprised howmuch power you lose.
    Download the software from Lotus and play a bit with different valve setups.It's free for single cylinder engines.


    I still think that the 2 stroke if built same size and tuned to equal the output of the 4 stroke may be just as reliable.
    May be a turbo compressed 2-stroke could shake some incredible figures on the tables. But on the other hand ...fuel consumption would go sky high.
     
  12. Feb 15, 2013 #12

    captarmour

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    Direct injection although complex would reduce fuel consumption to as good as a 4 stroke as fuel is injected after exhaust ports are closed. Many outboards and a few scooters are using direct injection. Some are multifuel as well, spark ignition diesel for example.

    BTW, Why don't we see more outboard aero conversions? They operate under constant loads like airplane engines.
     
  13. Feb 15, 2013 #13

    Jay Kempf

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    I really don't know. It makes all the sense in the world. There are a lot of nice engines to pick from in the 1-2 liter range. They are mostly higher revving engines requiring PSRUs to get them in the right range for an air prop. But these engines run through PSRUs all day long anyway. Some will tell you that you can't convert an engine that was made to use lake or sea water as cooling which is preposterous. Some/most of these engines merge cooling water early in the exhaust near or in the head. But that is solvable.
     
  14. Feb 16, 2013 #14

    captarmour

    captarmour

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    BTW I have designed and built a working model of a reduction box using an a brushless motor as a generator. My thoughts are why have a gearbox that is basically dead weight when you could use it to power everything as well augment the power of the engine? My model uses another brushless motor to represent an IC engine.
    the beauty is when in generator mode it is always in regenerative braking mode, not just when decelerating.
    as soon as I patent it I'll be able to say more.
     
  15. Feb 16, 2013 #15

    Kram

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    Loop scavenge 2 strokes wear faster because rings have to pass over ports/port edges and also rings are fixed, ie: unable to rotate in their lands as a 4 stroke ring does so the rings tend to cause scoring going up and down in the same location.

    2 strokes with uniflow scavenging aren't as prone to wear as they usually cross the lubricating inlet ports at slow speed near BDC and their rings are able to rotate in their lands. Most diesel 2 strokes are uniflow.
     
  16. Feb 16, 2013 #16

    captarmour

    captarmour

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    Thanks, that makes sense. The Detroit diesels have the uniflow cylinders. I always wondered if a 4 stroke cam was spun at same speed with crank, valve timing sorted and forced induction could it not work as a 2 stroke?
     
  17. Feb 16, 2013 #17

    captarmour

    captarmour

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    Jay K, at one time I even thought of modifying the leg to mount the prop, flipping it upside down for a seaplane application needing a high mounted prop. They do tend to be on the heavy side though.
     
  18. Feb 17, 2013 #18

    Dan Thomas

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    The reduction ratio of the outboard's gears is rather small. Boat props aren't so RPM-limited as airplane propellers are. They can turn well over 4000 RPM without any hassle; the 12-inch propeller I had on my straight-shaft inboard turned at engine speed, with the redline at 4800. Two-stroke outboards have higher redlines than that.

    The outboard's gearbox relies on the surrounding water for cooling, and its bearings would not handle an airplane prop's huge gyroscopic loads well.

    Dan
     
  19. Feb 17, 2013 #19

    captarmour

    captarmour

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    Ok makes sense.

    Going back to the issue, some half VW are 1200 cc and producing about 40 hp, whereas I think the 582 Rotax is about 600cc and produces about 65 hp. I think that's an unfair comparison when we talking longevity. I'm wondering if restricted to 20 hp to equal the power/displacement ratio of the 1/2 VW how many hours it would do? Remember at 20 hp it would probably be direct drive so to compare power to weight we would need to remove the g/box.

    if we wanted to use an off the shelf 2 stroke to go head to head with the Rotax 912, in power and displacement, what would be a good choice? Any ideas?

    Most outboards have a few different power outputs on the same block, the most reliable would be the least power choice in that series.

    talking about reliability, a friend had a Yamaha DT 175 motorcycle who rode it for nine years on average 5 days a week commuting to work, with only plug changes. The relatively unstressed engines can go a long time.
     
  20. Feb 18, 2013 #20

    deskpilot

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    Not many comments re your 'twingle' (love it) suggestion. Nice to have someone on board rethinking 2 strokes. Here's another one.

    http://www.p119.info/archives/10968 Only just found it. In the past, I've been looking at the Balandin/Parsons motor but can't figure out how it pressurizes it's cranks for each of the 4 cylinders.

    Two-stroke radial engine Balandin-Parsons - YouTube

    This is a cut-away view but it's not very clear on the dividing walls etc.
    B & P diagram.jpg

    Comments.......anyone?
     

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