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Thread: 300 CI "Rotax" type motor

  1. #1
    skukum12's Avatar
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    300 CI "Rotax" type motor

    As we are aware, traditional avgas is on the way out. A suitable replacement doesn't seem to be available any time soon. Rotax motors run on auto fuel, put out a fair amount of power for their size and are becoming increasingly popular. Their displacement is small at around 75 cubes therefore high rpms and gear reduction is required.

    So, why not a Rotax style motor in the more traditional 300+ cubic inch range? Less rpms, no gear reduction, auto fuel, air cooled cylinders and liquid cooled heads.

    NO POLITICAL COMMENTS PLEASE!!!

    Why or why wouldn't this be feasible? Cost? Weight? Complexity? Let's keep it to experimental for now.
    "Always looking up"

  2. #2
    skywagon8a's Avatar
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    Continental built a liquid cooled 0-200.
    https://airandspace.si.edu/collectio...m_A19870381000
    And a liquid cooled IO-550.
    https://mooneyspace.com/gallery/imag...cooled-engine/
    N1PA

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    If demand ever pushes manufacturing to expand their engine line? Make mine a diesel. http://www.continental.aero/diesel/diesel-engines.aspx They're getting 1-1/2 hp per cubic inch of displacement while sipping fuel.
    Last edited by stewartb; 01-08-2021 at 07:04 AM.
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    The main thing that needs to be done is to modernize the combustion chamber design. The frying pan design still dates back to the '30s while technology has move far beyond that. Even the angle valve engines do not use a suitable squshband combustion chamber allowing for a properly controlled flame front.
    Back in the '90s Continental worked with Honda in an engineering study on cylinder heads. I have not seen any mention of this since the original external photos of the engine were released.
    A properly designed cylinder head would have a higher eternal volume as we see in all the vehicles made in recent history. This can easily be compensated with a more compact ridged engine core. The crankshaft would utilize a more ridged design, narrow bearings as all engines utilize today.
    There is no reason a 300 ci direct drive engine could not put out 300+ HP and accept boost or gear reduction for far more power. All of these options can live happily on 87 to 91 Oct Non Ethanol that is readily available.

    To do this the world would need to allow a new and more streamlined certification program allowing for incorporating today's modern lubricants.
    This can easily be done since none of this requires any ground breaking development. Just needs the freedom of a different mindset.
    Regards, Charlie
    Super Coupe E-AB build in process
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    A second part to the above, to utilize current engines. Unleaded fuel utilizes thinner piston rings that what the current air engines run. The auto industry made this change about 1977. The valve train reliability would greatly benefit from eliminate lead. The small dia valve stems and narrow seat areas in modern engines would be a simple engineering change.
    This would allow reuse of the current engines but without the great increase of efficiency of the modern combustion chamber designs.
    Regards, Charlie
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    Utah-Jay's Avatar
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    It really seems like a no brained to switch over to MoGas. AND not being political at all, but in today’s times it seems like the certification process could be streamlined to help speed up the transition away from AVGas. It is just common sense really.

    Let’s get to Turbo Fuel Injection as soon as possible.

    Diamond seems to have a pretty good Diesel engine they run reliably. I am FAR from a gear head, but is that 180hp engine they run a reasonable weight? I know is sips fuel at about 7-8 gallons per hour at 75%

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    I wish Honda or Yamaha would build an airplane specific engine to give Rotax a little competition. 150-200 HP on MoGas, sipping under 5 gallons an hour. Yes, please!
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    Quote Originally Posted by 1934A View Post
    I wish Honda or Yamaha would build an airplane specific engine to give Rotax a little competition. 150-200 HP on MoGas, sipping under 5 gallons an hour. Yes, please!
    That would be sweet. We would truly need allot of reform of the certification system to make it happen.
    Regards, Charlie
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    E-AB is the reform.
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    Dave Calkins's Avatar
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    Quote Originally Posted by stewartb View Post
    If demand ever pushes manufacturing to expand their engine line? Make mine a diesel.
    make mine a turbine
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  11. #11

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    Quote Originally Posted by stewartb View Post
    E-AB is the reform.
    And the market is big enough for development and research. Someday we can have engines that do not get less reliable with every engineering change.
    Regards, Charlie
    Super Coupe E-AB build in process

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    Like a hand-built ported, balanced, high compression 390 with improved induction, improved injection, improved ignition, and improved exhaust? I put my money in an updated version of a legacy design and I'm all smiles. I have a lot of respect for these old airplane engines. They do the work and keep on ticking. I would enjoy a single lever controlled 300hp diesel and matched prop on my 180. Diesel torque would be sweet. No mags, no plugs, no mixture or manifold pressure to manage? Giddy up! But in the near term? A cross flow IO-550 would be fun, and that's here now. Certificated, too.
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  13. #13

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    And how many months have you patiently waited for crank replacements and other parts.
    Regards, Charlie
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    So far the new motor's been great. As for the recalled one? It was part of the journey. I rolled the dice and lost. C'est la vie.

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    Let’s face it, aviation engines are decades behind the rest of the industries with regards to innovation, efficiency and dependability.

    Cars in the 1960’s (the era that typical certified stuff originated) were not nearly as reliable as the current technology, not as light and not as fuel efficient.

    We can do better and should expect/demand better, but it seems everyone is happy with 30-60 year old technology, go figure
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    Quote Originally Posted by Dave Calkins View Post
    make mine a turbine
    Dave, How do you justify the fuel consumption in a small turbine? Turbines love fuel and are expensive to build. The lowest fuel burn I've seen in a turbine was 20 gph in a Soloy 206.

    Quote Originally Posted by Utah-Jay View Post
    We can do better and should expect/demand better, but it seems everyone is happy with 30-60 year old technology, go figure
    Not hard to figure with an annual market of a few hundred airplane engines while millions of auto engines are produced.
    The car engines also don't have to deal with the FAA.
    N1PA
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    Quote Originally Posted by skywagon8a View Post
    The car engines also don't have to deal with the FAA.
    THIS ^^^^^

    Experimental is the way to go for sure IF you can

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    too bad Subaru engines are junk, they're about the closest to the correct configuration. UL Power engines seem like a step in the right direction.

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    Deltahawk is a diesel aircraft engine manufacturer in Racine Wisconsin. Their direct drive 180 hp two stroke diesel engine R&D project has been around since 1996. They keep promising and things are still “Just around the Corner.”

    I have visited their big booth at Oshkosh and hear their open ended promises. I heard crickets when I asked them about deliveries And how long they’ve been Developing it.

    However, I don’t think they are like Bede, who receive money for kit orders and Never delivered. Their latest promos say FAA certification expected in late 2020, 80 million invested so far.

    I hope they come out with a 180 hp turbo charged unit around 300 pounds and under $40,000. I expect 375 pounds and $80,000.

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    Click image for larger version. 

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    Just around the corner.
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    Marine outboard engines are high horsepower, lightweight, fuel efficient and it seems we could learn a lot from what they have been able to do.

    Horsepower up to 450 and beyond is commonplace in a small light package.


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    They are also liquid cooled.

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    The big 6s are anything but light! Evinrude's Etec had a weight advatage but Evinrude is history.

    From the Mercury website-
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    Last edited by stewartb; 01-10-2021 at 11:59 AM.

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    Quote Originally Posted by stewartb View Post
    The big 6s are anything but light! Evinrude's Etec had a weight advatage but Evinrude is history.

    From the Mercury website-
    You are reading misleading weights as the weights you are looking at include an entire propulsion system as well as steering mechanisms. You need to look up the weights of just the dressed powerheads.

    You will find the actual engines to be only a few hundred pounds. Pretty good for 300-400 plus horsepower!


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    You'll need a reduction unit and radiator. Add those back in.
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    Quote Originally Posted by stewartb View Post
    You'll need a reduction unit and radiator. Add those back in.
    For sure you would need those. Itís not so much about adapting the engines themselves as it is adapting the technology to a suitable configuration. I think a aircraft engine manufacturer could replicate a lot of what the outboard industry has done.


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    What about just redesigned cyl heads? Get to a more efficient design that could handle 91 octane with even 10:1 compression or turbo normalizing
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    Quote Originally Posted by gahi View Post
    What about just redesigned cyl heads? Get to a more efficient design that could handle 91 octane with even 10:1 compression or turbo normalizing
    You mention head design and this is exactly what I mean by looking at what is being done with outboard power. Yamahas 425 HP engine uses a direct injection on their gas engine allowing compression ratio of over 11:1 on pump gas. A lot to learn here.


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    Utah-Jay's Avatar
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    Let’s hope MOGAS is the future as it is less expensive and much more available.

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    Quote Originally Posted by JeffP View Post
    You mention head design and this is exactly what I mean by looking at what is being done with outboard power. Yamahas 425 HP engine uses a direct injection on their gas engine allowing compression ratio of over 11:1 on pump gas. A lot to learn here.
    That family of engines as well as the new Suzuki outboards are about the best engineered out there that are happy with continued high power use.
    Regards, Charlie
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    gbflyer's Avatar
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    Drone applications are why Rotax continues to innovate with their small engines. GA is a sideline. Maybe there will be a commercial need for a 300hp recip powerplant in a drone eventually and they will spool up production for one. Probably not going to be a viable option for a 60 year old Cessna though.

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    wireweinie's Avatar
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    Quote Originally Posted by gbflyer View Post
    Probably not going to be a viable option for a 60 year old Cessna though.
    Why not? Look at the aircraft from as far back as the 40's with turbine engines fitted to them.

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    300 CI "Rotax" type motor

    Quote Originally Posted by wireweinie View Post
    Why not? Look at the aircraft from as far back as the 40's with turbine engines fitted to them.

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    Probably because a turbo Beaver or Otter has viable commercial use? The recips are quickly going away in the 135 market. I donít think manufacturers will be clambering over one another to produce an engine for the average certified GA aircraft that usually only gets overhauled or replaced in 30 years?

    Hope Iím wrong. It would be great to see a resurgence.

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