Incredible Scratch-Built Rotary Engine

Jul 29, 2013 16 Comments by

Andy Johnston must take his RC modeling very seriously … why else would he spend over 3 years building a true-to-scale, rotary Bentley engine spending another 2 years building an Avro 504K from plans, specifically for the engine?  The 9-cylinder powerplant has cast-iron liners that are 1mm thick, aluminum finned barrels and a total of 347cc displacement for a range of 700 to 3500rpm with a 25.5×23 prop that has a scale blade shape.  The engine spins, just like its full-size counterpart! The Avro 504K is enlarged to 27% scale  from 1/4-scale David Boddington plans and has a 116-inch wingspan. It is covered in linen solartex and has freehand markings. Andy notes, “The Avro was designed around the Bentley with the provision for exchanging it for a Zenoah 62. The Avro’s maiden flight was on 31st March 2012 with the 62 (and 3kg lead up front, the difference in weight between it and the Bentley) to prove the airframe and it was a great success so a further six flights were made to complete the CAA tests on that day before making the swap and further tests. The Bentley engine build started in August 2004, it’s test run was 9th January 2008 and the maiden flight in the Avro was 6th April 2012. There are no noticeable effects of gyroscopic precession from the rotating Bentley affecting the handling unduly, just a slight difference in left and right which may be due to torque and the coarse-pitch propeller. Twenty-two flights with Bentley to date.” Enjoy this video, courtesy of tbobborap1, our videographer friend across the pond.

Debra Cleghorn, Featured News

About the author

Model Airplane News Executive editor. About me: I’m a publishing professional who has a passion for aviation and RC, and I love creating issues, books and a website that help RC pilots to enjoy this sport even more. I admire scale aircraft and enjoy the convenience of flying smaller electrics.

16 Responses to “Incredible Scratch-Built Rotary Engine”

  1. Barry says:

    I think this motor is a “radial” and not a “rotary”

    • Joe B says:

      Barry. when the whole engine crankcase and cylindars spin around the crankshaft its a rotary engine. When the crankshft spins inside the crankcase its a radial engine. Rotary engines were popular choices for ww1 aircraft like the Foker Dr1 and such.

  2. Bruce Cochran says:

    Very impressive!
    Looks like this was at an old RAF base judging by the “Bunkers” in the background?

  3. John Burke says:

    At first look I thought it was a radial engine but when I looked at the picture I realized it truly was a rotary engine – Too Cool

  4. Roger Engelbrecht--long time modler says:

    Some piece of work. It must have a whale of a lot of torque. Does he have a way to blip the engine when landing as the WWI fighters had to?

  5. Roger Engelbrecht Anchient Modler says:

    What a piece of work!!! It must have a lot of torque. I wonder if he has a blip switch like the WWI fighters needed when landing..Barry:I’ll excuse you for not knowing the shaft was stationary and the
    prop was fastened to the engine which rotated. Not a great thing !!!

  6. Mike C says:

    No, it is a rotary. The crankshaft is bolted to the firewall and the whole engine spins. Not to be confused with a Wankel rotary engine.

  7. Girish Kalvade says:

    Thanks. That was wonderful.

  8. Judy clarkson says:

    Nearly as good as my husbands avro judy clarrkson

  9. Terry B says:

    I assume it is gas powered, where would the carb be and how is the spark delievered to each cyld? Any idea’s?

  10. Roger says:

    I remember a guy named Ray (forget his last name) from New York, built exactly the same engine and the same airplane and exactly the same scale, a coincidence I presume, so I am wondering if this guy here simply purchased Ray airplane/engine combo or actually built this one.. but one thing for sure , it is a work of art…I first saw it in Ottawa, Ontario…

  11. Mark says:

    It sounds like it’s revs are controlled by the ignition like the full sized orginal, rather than a carby

  12. Nigel Davidson says:

    Magnificent, thoughtful edits and no daft music making it very watchable and interesting, thank you.

  13. Eric says:

    How in the world does the fuel supply and throttle servo get the motor if it’s spinning like that?

    • Joe Frisbie says:

      The crank shaft is hollow and the carb is mounted on the end of the shaft. On a real (original) aircraft that put it right in the middle between the pilots knees. One benefit of the cylinders rotating was that there was never a overheating problem, constant airflow over the cylinders.

  14. Martin Woodhall says:

    Not only a great model with incredible detail but beautiful flying too! My father earned his Wings in an Avro 504k in 1925 and it a ways remained one of his favourite aircraft .

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