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  • Is a four stroke worth the bother?

    Sometimes doubt my motive for persisting with the Briggs, am getting just under seven litres per hour. John just sent over his latest prices and says
    Polini Thor 250 does around 7 litres. Mini 3 around 6.5 per hour, although do wonder what the lifespan of a high power two stroke is compared to a dozy four stroke. I'm not interested in swapping airframes again but the price including engine seems ridiculously cheap, just over £7k for the soaring wings, just under £8k for the 447 Cyclone delivered Southampton port, including engine, built

    Attached files pricing-page.pdf (347.3 KB) sample-3.pdf (1022.7 KB) sample-2.pdf (1.2 MB)
    G-KEVA
    BMAA 5696

    "If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me: it's all balls."

    R.J. Mitchell :- Designer of the Supermarine Spitfire

  • #2
    Is a four stroke worth the bother?

    Hi Kev,

    I am using about 5.5 litres an hour with the Polini on the Airplay Aviation Polini Dragon Chaser demonstrator and know I can get better with a little more work but does it really matter?

    The only practical implication is range and weight as cost when you work it out relative to the purchase price and hours used is a very small percentage of the real cost.

    Reliability is another none issue when comparing two or four stroke , the fact that the two stoke is rotating a lot faster does not add to either wear or reliability problems but what does make a difference is the number of engines sold and operating so you know the problems and the state of tune.
    If you can maintain control over the heat generated and the lubrication then if its a two or four stroke the reliability is then down to the design and the stage it has reached in the refinement to make it work.

    So probably the choice is a very personal one of which type you fancy for all sorts of reasons be it past experiences or image or even the level of performance you want with the two stoke in a good position up to say 50hp and the four stoke losing its weight disadvantage above that.

    One thing you should never underestimate is the effect of weight when dealing with the lighter end of plane as the engine weight is a bigger percentage so it is very easy to lose any advantage when adding a bigger and more powerful engine and remember its not just the engine weight difference but also stronger mountings , bigger tank and so on.
    Mick Broom
    Member 909
    Shadow G-MWTN

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    • #3
      Is a four stroke worth the bother?

      Kev what would the cost be with the Briggs?
      As an ssdr innovator your ideas and assistance are invaluable. I for one am constantly wondering who is going to come up with what next and usually it's you!
      Although many of us tinkerers don't say much the steady flow of information always gives food for thought even if funds or expertise do not allow thought to become reality.
      Keep up the good work!
      Dom

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      • #4
        Is a four stroke worth the bother?

        The current trend for more powerful paramotors has helped us no end by giving us engines like the thor 250. Whilst the engine is great, loads of smooth power, light weight and relatively frugal. I have concerns about the reliability of them. I have a 8 month old barrel that's porous and looks like they won't cover it under warranty. The thor 200 was released on to the market with loads of problems and a crap carb that couldn't be kept in tune. I'm getting 5 litres/hour with mine which I'm really happy with 35hp for 20kg. It's the reliability that worries me. I'm a member of two Facebook groups for the polini thor 200/250 engines, information from which has proved invaluable in keeping me airborne. Funnily enough there aren't any groups for simonini or rotax two strokes.

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        • #5
          Is a four stroke worth the bother?

          Kev,

          When comparing the reliability factors between 2 stroke and 4 stroke engines I think you'll find that the cooling method is important. Water cooled 2 strokes don't normally suffer from cold seizures in the way that air cooled 2 strokes do, as the barrel distortion is much less with water cooling. Also, the water cooling has the added benefit of allowing a much tighter fit of piston to bore than can be achieved with air cooled 2 strokes for the same reason, i.e. less barrel distortion due to hot spots. So the reliability factor goes up substantially with water cooling on 2 strokes. There is also the added benefit of being able to use some of the hot water from the water jacket to help keep the carb and intake tract warm and thus ice free. So although there is a weight penalty to pay, the advantages I think outweigh the disadvantages, and put the water cooled 2 strokes almost on a par with 4 stroke engines for reliability. Furthermore, they are a little quieter than air cooled engines, so there is another added benefit.

          In contrast with the simple design of the 2 stroke engine, the 4 stroke has to have a proper scavenging and filtering lubrication system, valve gear and cams, etc. all of which add to weight and complexity. They also put out much less power per cc than the equivalent 2 stroke, and have to make up for this with higher revs. So it is a fine balance that has to be drawn between them both as power plants when it comes to making the decision of whether to go 4 stroke, or stick with 2 stroke power.

          As you know, I've sung the praises many times of the stepped piston 2 strokes from Bernard Hooper, and I only wish I had the money to persuade him to build us some test engines. The power to weight ratio of his designs is very impressive, and would change the microlight industry in a heartbeat if he entered the market as a rival to Rotax.

          Best regards,
          XL's forever! Well, one of them anyway. It's all I can afford, not to mention the Raven and the Mini-Max. Oh, and I almost forgot the Spectrum as well :-)

          Comment


          • #6
            Is a four stroke worth the bother?

            Kev, I suspect that ultimately it's not about which engine is 'better' by any set of standards.

            Are you building you V twins simply because there's a slim chance of getting a better engine out of the exercise, or do you actually derive more satisfaction from the process?

            I am fully aware that I am building my engine for my own entertainment. I expect to learn a lot in the process and at the end of it, I'll have a big, noisy toy. Neither of these things justify the time and money that will be consumed.

            Why do you feel the need to justify your actions? If you are happy developing the V twin, carry on!

            I look forward to the EFI supercharged version.
            Pete T.

            "A closed mouth gathers no feet".

            Comment


            • #7
              Is a four stroke worth the bother?

              Peter Twissell wrote: Kev, I suspect that ultimately it's not about which engine is 'better' by any set of standards.

              Are you building you V twins simply because there's a slim chance of getting a better engine out of the exercise, or do you actually derive more satisfaction from the process?

              I am fully aware that I am building my engine for my own entertainment. I expect to learn a lot in the process and at the end of it, I'll have a big, noisy toy. Neither of these things justify the time and money that will be consumed.

              Why do you feel the need to justify your actions? If you are happy developing the V twin, carry on!

              I look forward to the EFI supercharged version.
              That's summed it up nicely. Kev's a tinkerer, and one that's had good results. I'd love to see a 35hp v twin based on honda monkey engines. Loads of tuning parts available but would need a custom crankcase and crank making. Could be a bit lighter than the vanguard engines.

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              • #8
                Is a four stroke worth the bother?

                Another thing is that most of us aren't blessed with engineering skills/facilities that allow custom engine creating and are looking for an off the shelf solution. So that usually means two stroke.

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                • #9
                  Is a four stroke worth the bother?

                  John Kendall wrote:
                  That's summed it up nicely. Kev's a tinkerer, and one that's had good results. I'd love to see a 35hp v twin based on honda monkey engines. Loads of tuning parts available but would need a custom crankcase and crank making. Could be a bit lighter than the vanguard engines.
                  Saw a Bailey of the same at the very last NEC Flying Show, 2013, but have heard nothing since.

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                  • #10
                    Is a four stroke worth the bother?

                    Been swapping notes with a Brazilian flex pilot, he's fitted an Ace Aviation reduction drive, fettled the motor with a couple of Honda motorbike CV carbs and got flying.

                    However his mate didn't bother with all that tuning stuff...

                    Got this message via WhatsApp...

                    hello kevin sr, we use a 627cc engine all original Briggs, gearless, direct propeller shaft and look at the flight!

                    The video shows a slow weightshift cruising around, using a stock 23hp motor just parked on the back and no redrive. At just over a grand this is seriously cheap flying, although I might warn him that a prop on one end of the crank and heavy flywheel on the other has been known to bust cranks. Certainly with reduction added, governor clutter removed and a spot of machining to knock three kilos off the flywheel if you aren't after a hotshot this is budget aviation

                    Kev
                    G-KEVA
                    BMAA 5696

                    "If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me: it's all balls."

                    R.J. Mitchell :- Designer of the Supermarine Spitfire

                    Comment


                    • #11
                      Is a four stroke worth the bother?

                      Excellent stuff Kev. Driving down the cost of aviation by experimentation and the sharing of innovation. Ssdr may not be for everyone but I'm sure the masses will benefit in the long run.

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                      • #12
                        Is a four stroke worth the bother?

                        It is a source of gentle frustration to me that Flylight and Ace Aviation develop trikes that will run on lower power, say, 22-25hp, fitting screaming two strokes to them and limiting their appeal to fun local flyers.

                        On G-KEVA Iíve gone for good speed and climb, so have tuned the Briggs engine quite highly, but the standard off the shelf Briggs and Chinese copies do 23-28hp pretty much off the shelf; they are heavy (around 35-40 kilos when Johnís reduction Drive is added) but are really dozy and will run forever, and sip fuel. Not only that they are tough and able to be fixed anywhere in the world with spares from any garden machinery shop.

                        Some shy away from what they think might be complex engine work, I understand this but the basic engine with mild parts added is cheap and not a fat lot needs doing to power it to maybe abit less horsepower than mine, so if a Laser or slightly bigger and slower wing than my Cyclone is fitted, this makes a grand little easy -going touring trike, or even just a fun machine that will last years longer than the little screamer two strokes.

                        Such a toy would be fine with a small tank as they only burn 6 litres per hour, and the few changes to make it work in a trike are ready to hand with my input. A Brazilian crowd are flying exactly this sort of trike, Kleber Alvez Adorno has sent over several videos.

                        Have a look how simple it is to put a Ďhotterí camshaft into the engine to make 28hp, two cheap and simple tweaks to the valve springs (washers under the springs to make them keep them keep the valves pressed home at high revs) and rip off all the governor rubbish and youíve got a nice little aeroplane motor. After all, Johnís already got the reduction belt drive sorted, and that engine is Japanese built and available all over the world.

                        Check these video out to see what I mean about simple engines; once the governor rubbish is scrapped the engine gets lighter and simpler as well

                        https://www.youtube.com/watch?v=6nlUMtZUcgk&index=15&list=FL1fpKf7jwjf8laM HVjesx-g

                        https://www.youtube.com/watch?v=Cx7x65mtvtk&index=16&list=FL1fpKf7jwjf8laM HVjesx-g

                        Dan Curtis and Billy Brooks had overheating bothers, but they scrapped the fan cooling for free air; with fan cooling I've had zero issues, even bashing mine to 6000'plus

                        Just a thought

                        Kev
                        G-KEVA
                        BMAA 5696

                        "If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me: it's all balls."

                        R.J. Mitchell :- Designer of the Supermarine Spitfire

                        Comment


                        • #13
                          Is a four stroke worth the bother?

                          Hi Kev,

                          Power to your elbow for pushing four stroke power but you cannot make a case for the four stroke using fuel burn or high revs.

                          High revs would be vibration which with a balancer shaft is a thing of the past, maybe high wear rate , not the case if lubrication is ok on the two stroke but possibly component life is shorter and the parts are more expensive but they are fewer in number.

                          Fuel burn is efficiency which is effected by weight but the Polini can match your fuel burn and have a better power to weight figure.

                          Down side is cost so keep working on the four stroke to get it sorted but if into comparable power to weight you will need to spin your four strokes a lot faster to get the results and you still need to lose a bit of weight.

                          When are you going to come down and try the Dragon???

                          Mick
                          Home soon ;-(
                          Mick Broom
                          Member 909
                          Shadow G-MWTN

                          Comment


                          • #14
                            Is a four stroke worth the bother?

                            Love to

                            Spinning my engine at 4000 cruise and 4250 climb full chat

                            British Hovercraft selling 28hp with governor stripped out and cam upgrade for £1200 but when you ring pretend it's not for an aircraft or Ross Pullen refuses to supply

                            Ace reduction drive is a bargain too, Brit Hover have some left over big carbs from converting 990cc units and they perk up 630cc engines nicely, at half price
                            G-KEVA
                            BMAA 5696

                            "If anybody ever tells you anything about an aeroplane which is so bloody complicated you can't understand it, take it from me: it's all balls."

                            R.J. Mitchell :- Designer of the Supermarine Spitfire

                            Comment

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