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Incredible Scratch-Built Rotary Engine

Incredible Scratch-Built Rotary Engine

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.

Updated: July 27, 2015 — 9:49 AM
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  1. I think this motor is a “radial” and not a “rotary”

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

  3. 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. 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
    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. 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. Thanks. That was wonderful.

  8. Nearly as good as my husbands avro judy clarrkson

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

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

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

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

    1. 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. 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 .

  15. I love scale RC aircrafts and would like to know, how this rotary ( not radial ) engine was build ?
    I have a selfmade 1/5 scale Fokker Dr.1 ! Might be, it fits ? With kind Regards Hans Dieter

  16. Good day to you all,
    I’m Andy Johnston and have just discovered this site whilst browsing images for the aero windscreen for the Avro on Google.
    What a surprise, as I am a UK resident I have never heard of Model Airplane News.I never got round to making these and now I’m trying to get the detailing finished.

    To clear up a few of your questions above, the Bentley was researched from photos I took at the Shuttleworth Collection workshops in 1998, a visit to the Kensington Science Museum in London and the Imperial War Museum, Duxford where I got the close-up of the makers plate which I has photo-etched.
    Armed with Lew Blackmore’s book on how he built the engine in the 1980’s, I set to with my lathe Myford and a vertical milling machine to fashion all the parts with great success as it turned out.
    The aircraft was researched, again from the airworthy full size at Shuttleworth Collection, Old Warden, Bedfordshire (a must-see venue, look it up on the net).

    I managed to obtain a set of plans for the Avro, scaled them up and got on with fashioning all the parts including all the rigging turnbuckles, folder metal control surface horns etc. Every part required which is why it took 2 years.

    The ignition is electronic using a TIM 6 Jerry E Howell self build kit and the coil HT is supplied via a distributor disc with contacts timed for every alternate cylinder as is required in a nine cylinder four-stroke.
    The spark plugs were Rimfire purchased form Paul Knapp of Arizona, I didn’t fancy making my own, it is akin to fitting poor quality re-tread tyres to your Lamborghini!!!

    The carburettor is a commercial Walboro suitable for a 38cc size petrol two-stoke engine and is perfect.I run a 50:1 oil/petrol mix and the main oil feed pump is engine driven and I only use Bel-Ray H1-R fully synthetic.

    So there you have it, to date I have had 62 flights, the majority at model air shows.

    I’m thinking of retiring it as the odds of a mishap get very short the more you fly. I’ll also be 74 in three months time and my confidence is less now.

    Thanks for your interest, there are one or two more videos on YouTube apart from the one here.

    Bye for now,
    Corsley Heath

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