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What makes a good engine?

Guest jimbo_xyz

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Guest jimbo_xyz

Pardon my ignorance but I'm hoping this is a good place for me to learn a little.


I'm wondering what makes engines like the Rotax and Jabiru so popular?


The Rotax seems so complex. What are the advantages of these over others like Hirth, Aerovee or Rotec Radial? (which seem cheaper)


Also I'm assuming for Rec planes like Jabiru, Hornet STOL or Aeropup that 4-stroke is preferable.


I ask this as I want to build a kit aircraft in the near future and with little flying experince I don't have hands on knowledge. Just at the research stage.


Any and all input appreciated.







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Hi James,


I think a lot of popularity is due to what engine is supplied or recommended by the kit supplier - and some suppliers are "agents" for certain engines too.


And reliability history once an engine type has become established helps spread the word (or not).


The difficult question is what about the newer entrants - ULpower and Rotormax for instance.


You have to decide what limitations and features are tolerable to achieve the power / weight demands of the particular installation.


Geared engines can deliver good power but usually need liquid cooling and multiple carbs to do that. Earlier Hirths got a poor reputation and with Rotax ramping down 2 stroke production there is only the Siminoni that looks a possibility, theres just so few around here that its impossible to know if they are OK. Direct drive has limitations as to prop types and rpm (power) useable, but the simplicity of installation and ease of maintenance helps. In some countries the manufacturers recommentations are mandatory and that means a Rotax 2 stoke has major work and crank replacement every 300 hrs. This sort of policy really distorts the market because some makers publish proper service bulletin data some dont (bother to publish any)


Apologies for not being able to answer the question - leave your engine choice as late as possible we will all know a lot more about whats best then.





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Guest jimbo_xyz

Thanks for the info Ralph.


I see Diesels are being improved all the time too. It will be great when they're a viable option. I've read a few kit building stories and it seems that if you get the engine straight up and aren't careful they can degrade before they are used.


I like your advice of leaving it as late as possible.





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