Simanaitis Says

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SENSING MY PENCHANT for GMax modeling of odd aircraft, a reader recently asked me about doing a Stipa-Caproni “Flying Barrel.”

Surely it’s one of the oddest things ever to take to the air, and I must say I am tempted. However, it does violate one of my GMax rules: “Never take on a project you wouldn’t mind staring at for hours.” Here in Parts 1 and 2 today and tomorrow are tidbits concerning this quandary.

The 1932 Stipa-Caproni. This and other images from Wikipedia.

The problem is, the Stipa-Caproni is pug-ugly. 

A Valid Proof-in-Concept. On the other hand, Luigi Stipa didn’t see the aircraft as a final design. Rather, it was a proof-in-concept for his “intubed propeller” idea destined for use in a multi-engine flying wing, in which it might have made sense.

As noted in Wikipedia, Stipa applied Bernoulli’s Principle in having the fuselage form a  venturi tube in which the engine’s propeller would operate more efficiently than in the open. 

“Stipa,” Wikipedia notes, “spent years studying the idea mathematically while working in the Engineering Division of the Italian Ministry of Air Force, eventually determining that the venturi tube’s inner surface needed to be shaped like an airfoil in order to achieve the greatest efficiency.”

Wikipedia continues, “He also determined the optimum shape of the propeller, the most efficient distance between the leading edge of the tube and the propeller, and the best rate of revolution of the propeller. Finally, he petitioned the Italian Fascist government to produce a prototype aircraft. The government, seeking to showcase Italian technological achievement —particularly in aviation— contracted the Caproni company to construct the aircraft in 1932.”

This was the same era, note, that Italo Balbo was commissioned to fly his fleet of 24 Savoia-Marchetti SM.55X flying boats from Italy to the 1933 Chicago World’s Fair. 

The Stipa-Caproni monoplane

The Stipa-Caproni Design. Wikipedia notes, “The resultant aircraft was a mid-wing monoplane of mostly wooden construction dubbed the Stipa-Caproni or Caproni Stipa. The fuselage was a barrel-like tube, short and fat, open at both ends to form the tapered duct, with twin open cockpits in tandem mounted in a hump on top of it. The wings were elliptical and passed through the duct and the engine nacelle inside it.” 

Wikipedia describes, “The duct itself had a profile similar to that of the airfoils, and a fairly small rudder and elevators were mounted on the trailing edge of the duct, allowing the ducted propeller wash to flow directly over them as it exited the fuselage to improve handling. The propeller was mounted inside the fuselage tube, flush with the leading edge of the fuselage, and the 120-horsepower (89-kW) de Havilland Gipsy engine that powered it was mounted within the duct behind it at the midpoint of the fuselage.”

Tomorrow in Part 2, we’ll see how the Stipa-Caproni faired in flight testing. Nor was its intubed propulsion unique, neither before nor afterward. ds 

© Dennis Simanaitis,, 2022


  1. Tom Austin
    October 13, 2022

    Flying Manicotti! Creativity sometimes requires taking bold risks (cooked almost gently in boiling water) Can’t wait for your next post!


  2. Jack Albrecht
    October 13, 2022

    Not being an aerospace engineer, how different is this to a turbine engine, in principle?

    • Bill
      October 13, 2022

      Fundamentally. A turbine converts the energy of a moving fluid to mechanical energy. The fluid can be most anything – water, wind, exhaust gases from a piston engine (exhaust drives the turbine & turbine drives a compressor aka turbosupercharger), combustion products from flame cans in the case of a turboprop, even LNG in the case of a cryogenic turbine.

  3. Mike B
    October 13, 2022

    Ducted fan. I’ve heard of these many times, and vaguely recall some having been done as model aircraft. But to Jack A’s question, isn’t this in principle the turbofan engine, but with a “fan” of only 2 blades powered by a piston engine rather than a turbine? Modern turbofans generate most of their thrust from the air bypassing the turbine itself, with the turbine mainly providing the power needed to spin the fan…

    • Dennis
      October 13, 2022

      One oddity of the Stipa, of course, is the presence of a traditional gasoline engine driving the propeller. In a modern turbofan engine, the fans compress the intake air, with fuel added later to combust and generate the thrust. See

  4. Bert SWIFT
    October 14, 2022

    Dennis, I love this one. I think you should do it if you can muster up the excitement! What a wacky yet brilliant idea. Can’t wait to see where this goes tomorrow!

    It looks simple enough. But I’ve never built anything in GMax…

    Your friend,
    Bert SWIFT

    • Dennis
      October 14, 2022

      Hi, Bert,
      Good to hear from you. In fact, GMax has a fairly steep learning curve. But once comfy with it (even only its basics, actually), it’s absolutely a ball.

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