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  1. #1
    RC-Captain's Avatar
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    pros and cons of 2 and 4 stroke engines ?

    I'm fairly new to flying a glow trainer. Have been flying it for almost a year now.
    I'm not sure if I understand the difference between a 2 stroke or a 4 stroke engine.

    All I know is 2 stroke cranks twice before refiring and 4 stroke cranks 4 times before firing.
    I finally broke bread and bought a real charger , THE TRITON 2............

  2. #2
    tIANci's Avatar
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    RE: pros and cons of 2 and 4 stroke engines ?

    RC - what you say is not really right, the 2C does not crank twice, the shaft would have turned 360 degrees for every power cycle, the 4C engine would turn 720 degrees. The 4C engine has proper combustion cycle in that the fuel so called completely burnt.

    Four stroke engine:

    Try this --> http://www.k-wz.de/vmotor/v_omotore.html and this --> http://www.keveney.com/otto.html

    Two stroke engine:

    try this --> http://www.keveney.com/twostroke.html

    General difference between 2C and 4C is:

    RPM - 4C is usually running at 10,500 RPM max but 2C is generally about 12,000 RPM, some can even touch 22,000 RPM.
    Torque - 4C has more torque at a certain RPM than a 2C engine of the same capacity, 4C torque also comes at a lower RPM
    Fuel - 4C has a lower fuel consumption
    Maintenance - 4C needs more care in operating and maintenance
    Tuning - both are the same in terms of ease

    They are very different creatures but both have their own purpose.
    Its nice to be important, but its more important to be nice ...
    Revver Brotherhood No. 232

  3. #3
    RC-Captain's Avatar
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    RE: pros and cons of 2 and 4 stroke engines ?

    tIANci ....thanks for explaining and the links really helped me understand .

    it looks as if the gears in the four stroke good easily cause problems.
    I finally broke bread and bought a real charger , THE TRITON 2............

  4. #4
    tIANci's Avatar
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    RE: pros and cons of 2 and 4 stroke engines ?

    RC - my first 4C engine was a Saito 72, used ... about 1.5 years old ... it would still tach about 10,400 RPM easily. A new one should be able to hit about 10,750. So you tell me how worn is the engine? Like all engines it needs Tender Loving Care!

    When you fly 2C engines you will notice that your throttle is usually at 70% onwards to get the plane to pull well. That is because the power comes at higher RPMs with a 2C engine. When I first flew the 2C engine it was like a total difference, I had to learn to use throttle management differently. The power comes at about 45% to 80%, after 85% there was not much more difference in speed. But you know what is best? An electric brushless motor with good batteries! Totally linear throttle!!! I love EP.
    Its nice to be important, but its more important to be nice ...
    Revver Brotherhood No. 232

  5. #5

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    RE: pros and cons of 2 and 4 stroke engines ?

    A 2-stroke engine has a power stroke every revolution of the engine's crankshaft, so each time the piston reaches the top of its stroke, it fires. As the piston travels down in the power stroke, it also exhausts the spent fuel/air charge through the exhaust port and begins to take in a new fuel/air charge through the intake and transfer port, which is coming from the crankcase, which is under pressure from the descending piston. As the piston passes bottom dead center and starts up on a new compression stroke, the pressure in the crankcase is reversed, making a partial vacuum and drawing fuel and air from the carburetor into the crankcase. As the piston reaches the top of the stroke, it fires again, and the cycle repeats. SO--- one stroke up, and one stroke down, there's your 2 stroke cycle.

    A four stroke engine has a power stroke every other revolution of the crankshaft. Since it does not depend on crankcase pressure to move the fuel/air mix, it has to draw the mix in through a valve, controlled by a camshaft which is geared to the crank at a 1 : 2 ratio ( the camshaft rotates once to two turns for the crank). As the piston starts down, the cam opens the intake valve, and the fuel/air mix enters the cylinder from the carburetor. As the piston reaches the bottom of its stroke, the cam closes the intake valve, and the piston starts back up again, compressing the mixture, which fires at the top of the stroke from compression heat and catalytic reaction of methanol and platinum (the glow element), and then you have the power stroke as the piston is pushed down by the burning mix. As the piston reaches the bottom of the power stroke, the rotating cam then opens the exhaust valve, and the rising piston pushes the spent charge out the exhaust. As the piston reaches the top, the intake opens and the cycle repeats. SO-- one stroke up, compression, one stroke down, power, one stroke up exhaust, one stroke down, intake, and there's your 4-stroke cycle.

    Part of the reason there's so much difference in how 2- and 4- strokes make power lies in the combination of strokes in the 2- stroke cycle. Since the intake and exhaust ports are about half way down the cylinder, as the piston is moving down on the power stroke, as soon as the exhaust port is uncovered, the pressure pushing the piston is released through the port, so only about half of the downward travel of the piston actually produces power. A 4-stoke, on the other hand, has the piston "pushed" almost its full travel on the power stroke before the exhaust valve opens and releases the pressure, so more power is made for each downward motion of the piston. I compare it to the difference between having someone shove you in the chest, vs someone punching you in the chest. Both are going to produce motion (power), but the 2-stroke is dependent on the more frequent power pulses and a generally higher rate of making them (RPM), where a 4-stroke gets more energy per stroke but makes them less frequently and at a generally lower rate. This translates into the greater torque at lower rpm's in a 4-stroke vs a 2-stroke, but the overall higher horsepower at higher rpm's in a 2-stroke.

    This is a fairly simplified explanation, because there are many variables to consider, such as port size and timing(2-strokes) and valve size and overlap (4-strokes), ignition advance, fuel mix, etc. But these are the basics for 2- and 4-stroke operation
    Club Saito #2, WACO Brotherhood #20. What other trouble can I get into?

  6. #6
    tIANci's Avatar
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    RE: pros and cons of 2 and 4 stroke engines ?

    Khodges - my epxplanation is better ... I got MOVING pictures ... hahahahaaa ... I hate to read!
    Its nice to be important, but its more important to be nice ...
    Revver Brotherhood No. 232

  7. #7

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    RE: pros and cons of 2 and 4 stroke engines ?

    Ditto on all...
    It all boils down to personal preference, the kind of flying and the kind of planes you fly.
    Some guy's think 4stk. engines are too complicated, the only maintenance involved is valve adjustments and that's no big deal.
    If I have to adjust the valves on my two Saito 180's twice a year that's allot.
    4stk. engines sound more realistic than 2stk.s, idle at a much lower RPM, don't flood as easily when mounted inverted and have smaller mufflers to hide.
    Training with a 4stk can be more difficult because you can't hear them over the 2stk's in the air, not a problem where I live now, only 60 members, my old club had 300.

  8. #8
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    RE: pros and cons of 2 and 4 stroke engines ?

    Khodges - my epxplanation is better ... I got MOVING pictures ... hahahahaaa ... I hate to read!
    I agree and fully understand both engines.

    khodges did you really come up with and type all of that information? It doesn't matter thanks alot , I really appreciate the information.
    I finally broke bread and bought a real charger , THE TRITON 2............

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    RE: pros and cons of 2 and 4 stroke engines ?

    ORIGINAL: RC-FIEND

    Khodges - my epxplanation is better ... I got MOVING pictures ... hahahahaaa ... I hate to read!
    I agree and fully understand both engines.

    khodges did you really come up with and type all of that information? It doesn't matter thanks alot , I really appreciate the information.
    Nah, it's all a lie, made every bit of it up, and I beat my kid until she agreed to type it for me. I didn't look at the link that tIANci posted, so I don't know what "moving pictures" he had; just hope he can read better than he spells (e-p-x-p-l-a-n-a-t-i-o-n)[X(]
    Club Saito #2, WACO Brotherhood #20. What other trouble can I get into?

  10. #10
    RC-Captain's Avatar
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    RE: pros and cons of 2 and 4 stroke engines ?

    .............LMAO ........
    I finally broke bread and bought a real charger , THE TRITON 2............

  11. #11

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    RE: pros and cons of 2 and 4 stroke engines ?

    Glad you enjoyed it. I've been screwing around with engines (motorcycles mostly) for a long time, the basics are the same for airplanes, motorcycles, cars, etc, and they don't change. BTW, my kid will be fine, no broken bones.
    Club Saito #2, WACO Brotherhood #20. What other trouble can I get into?

  12. #12

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    RE: pros and cons of 2 and 4 stroke engines ?

    Glad you enjoyed it. I've been screwing around with engines (motorcycles mostly) for a long time, the basics are the same for airplanes, motorcycles, cars, etc, and they don't change. BTW, my kid will be fine, no broken bones.
    Club Saito #2, WACO Brotherhood #20. What other trouble can I get into?

  13. #13
    tIANci's Avatar
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    RE: pros and cons of 2 and 4 stroke engines ?

    Khodges - what is your full name and address please ... I am calling social services!!!
    Its nice to be important, but its more important to be nice ...
    Revver Brotherhood No. 232

  14. #14
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    RE: pros and cons of 2 and 4 stroke engines ?

    Hi, I was wondering about cooling in a cowling. Will a 2c heat up any faster than a 4c? Would there be any difference air flow needed across the engine. Is either one any easier to mount in a nose cowl with exhaust being considered. I was inerested in a GP spacewalker and considering something like an OS 91fx and 91fs.

    Happy New
    Dave
    \"This isn\'\'t flying. This is falling with style.\"

  15. #15
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    RE: pros and cons of 2 and 4 stroke engines ?

    A 2 stroke fires on every other stroke or one complete revolution of the crankshaft. Bang! Piston goes down, comes back up and Bang! Repeat.
    A 4 stroke fires once every fourth stroke. Bang!, blow, suck, squeeze.
    2 strokes spin faster. 4 strokes can turn bigger props and have more torque.
    4 stroke use less fuel (usually) and sound real *****in. Best choice for a scale plane or warbird.
    \"B Positive to ground, over...\"

  16. #16
    tIANci's Avatar
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    RE: pros and cons of 2 and 4 stroke engines ?

    Dave ... both will overheat if there is insufficient cooling or if over leaned. For a Spacewalker go for a 4C, it sounds very cool! Its nice to hear it with a 4C puttering around. You can go with a 2C but you will need a Pitts muffler if not the stock muffler will make the plane look bad. Go with a 4C throwing a nice 15x6 prop. Read the reviews and see what they use and how it flies.
    Its nice to be important, but its more important to be nice ...
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  17. #17
    RC-Captain's Avatar
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    RE: pros and cons of 2 and 4 stroke engines ?

    another engine question please

    As Im typing I'm looking at the January AMA mag. and I found two engines that have the needle moounted to the carb. and doesn't have any fuel tubbing in between . Any benifits to this or do the engine run the same with this set up ?
    I finally broke bread and bought a real charger , THE TRITON 2............

  18. #18
    tIANci's Avatar
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    RE: pros and cons of 2 and 4 stroke engines ?

    RC - the engines with a fuel tube between are what you call remote needle valves. Its a new design thing and its to move the needle away from the prop, also you can adjust that angle you might want it to suit the plane. There is no real difference in performance.
    Its nice to be important, but its more important to be nice ...
    Revver Brotherhood No. 232

  19. #19
    RC-Captain's Avatar
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    RE: pros and cons of 2 and 4 stroke engines ?

    tIANci

    I'm not sure the fuel tube between the carb and needle is new. The two engines are OS .50 and Super Tiger's engine which all of them eliminate the fuel tubing.

    Also if you are eliminating a tube then this has to be better for the pressure in the fuel tank and in the cylinder. Have you flown a plane with both set ups?

    I'm going to order a new engine and really need to now the performance difference . Thanks [8D].
    I finally broke bread and bought a real charger , THE TRITON 2............

  20. #20
    tIANci's Avatar
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    RE: pros and cons of 2 and 4 stroke engines ?

    RC ... not flown remote needle valves but from all literature from manufactures none of them state that the remote needle valve assists in enhancing performance (more RPM/HP/Torque). Its a matter of safety and ease of use/set up. Today my friend's OS46AX was not behaving ... its only about 6 tanks old. He is experienced and I am keen to see what went wrong.

    Oh yes ... when I said new I mean the remote needle valve set up is a new thing. Only thing I find not nice with ST engines is that you will have a hard time in adding an extention to the needle valve. So far all my planes using the G90 do not need extensions. If you fly a YAK 54 or an SU31 you are in trouble! The cowling will swallow the whole engine with ease and the needle valve too.
    Its nice to be important, but its more important to be nice ...
    Revver Brotherhood No. 232

  21. #21
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    RE: pros and cons of 2 and 4 stroke engines ?

    With the needle mounted on the carb, there are less places to develop air leaks. Also brings your knuckles very close to the prop. Rear needle engines are sometimes more difficult to mount due to the rear needle not allowing the engine to be mounted as far back as you might need it to before coming into contact with the firewall.
    \"B Positive to ground, over...\"

  22. #22
    RC-Captain's Avatar
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    RE: pros and cons of 2 and 4 stroke engines ?

    I dont think I like putting my hand so close to the prop so I will probably stick to the rear mounted needle. you think the would make the connection in the rear with somthing other than surgical tubbing .
    I finally broke bread and bought a real charger , THE TRITON 2............

  23. #23
    tIANci's Avatar
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    RE: pros and cons of 2 and 4 stroke engines ?

    Many years flying and never met the prop! Always focus and it will not happen.
    Its nice to be important, but its more important to be nice ...
    Revver Brotherhood No. 232

  24. #24

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    RE: pros and cons of 2 and 4 stroke engines ?

    There actually is a potential problem in the use of a remote needle valve with two stroke engines.

    The main pressure drop in the fuel delivery system occurs across the needle valve. With a needle valve in the carb this does not present a problem, & in fact, assists in fuel vaporization. However, with a remote needle valve the pressure drop is still at the needle, but the fuel now discharges into an additional length of fuel line, which also causes a frictional pressure drop. Additionally, the suction (negative) pressure from the carb throat further lowers the pressure in the fuel delivery tube to the carb. If the combined pressure reductions exceed the vapour pressure of the methanol in the fuel, it will vapourize in the delivery line & produce bubbles (flashing). Flashing is even more likely if the delivery tube lies near the engine case & is heated by the engine. The whole business is even more compromized by operation at high ambient temps (a nice warm sunny day).

    Flashing does not always occur with this remote configuration, but it happens often enough to be a pain. Many fruitless hrs have been spent by modellers searching for pinholes in tubing & various other causes for the bubbles that plague their fuel delivery & tuning when, in fact, it is flashing. I avoid remote needle valves on 2-strokes like the plague.


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