Simanaitis Says

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LUIGI STIPA’S INTUBED PROPELLER concept may have been derided as the “flying barrel,” but Stipa had done his homework. Here in Part 2, we’ll see whether theory translated into practice. Briefly, it didn’t, and it did. 

Flight Testing. The Stipa-Caproni first flew on October 7, 1932. Indeed, just as Stipa had calculated, it was reported that the intubed prop increased the engine’s efficiency. What’s more, additional lift of the duct’s airfoil allowed a very low landing speed of only 42 mph. The lift gave the Stipa-Caproni a higher rate of climb than other aircraft of similar power and wing loading. The aircraft also proved noticeably quieter than others of the era. 

Quite amazingly, there’s film footage of this experimental aircraft in testing. 

The Stipa-Caproni under test. This and the following image from YouTube.

On the other hand, the design invoked aerodynamic drag to the point of cancelling out its engine’s efficiency: Top speed proved to be a mediocre 81 mph. 

Pilots reported that the Stipa-Caproni was extremely stable; indeed, so much so that it was difficult to change course.

The Regia Aeronautica cancelled further development; nor was the envisioned flying wing ever built. The latter’s powerplants would have been embedded in multiple ducts within its giant wing, thus mitigating the drag of the Stipa-Caproni’s fuselage.   

Other Ducted Fans. The ducted fan concept was not unique to Stipa. For example, Henri Coandă may have flown a ducted-fan biplane in 1910.

Above, the Coandă-10 as seen at the Second International Aeronautic Salon in Paris, 1910. Below, my GMax Coandă buzzing Notre Dame. 

Others of my GMax projects were also ducted-fan propelled. Jim Miller’s Texas Gem Formula One air racer most definitely flew in ducted-fan form 1973-1975 and continued as an unducted pusher through 1986.

My GMax Texas Gem.

In 1981, the Mapanare I aircraft was designed by IUPFAN, Instituto Universitario Politécnico de las Fuerzas Armadas Nacionales, in Maracay, Venezuela. Its ducted fan was turbine-driven.

My GMax Mapanare I.

Wikipedia notes, “The modern turbofan engine is thought by some aviation historians to be a descendant of the “intubed propeller” demonstrated in the Stipa-Caproni.” 

Last, having mentioned the giant flying wing concept, I’m reminded of the Bel Geddes’ Number 4. This airliner proposed in 1929 had its twenty engines perched above the wing. But wouldn’t this thick wing section have been a natural for intubed propulsion? 

My GMax Bel Geddes Number 4 over Long Beach.

Hmm… Maybe I should consider staring at the Stipa-Caproni for hours. ds 

© Dennis Simanaitis,, 2022


  1. Bob Storck
    October 14, 2022

    Two alternatives for your perusal, Dennis … perhaps more attractive and important in aviation developments.
    The Caproni-Campini Nr. 1 did not have a jet engine in the sense that we know today. Rather, a 670 hp Isotta Fraschini L. 121/R.C. 40 piston engine drove a compressor, which forced compressed air into a combustion chamber where it was mixed with fuel and ignited. The exhaust produced by this combustion propelled the aircraft forward. This ‘motorjet’ concept had been investigated in the US by GE and Kettering, and discarded in favor of pure turbines, although the scheme was pursued in WWII by the Soviets. (MiG-13 and Sukhoi Su-5)
    Then my mentor at Mississippi State, Dr. Gus Raspet developed and flew the XV-11 Marvel which should appeal to you for its elegant engineering and appearance. Probably, it tried to get too much bang for the buck, investigating then emerging composite structures, boundary layer control, a combined ducted fan thruster and control surface, an innovative rough surface landing gear, and flexing wings that dispensed with hinged flaps and ailerons.
    The Aerophysics department developed masterful canopies, both elegant in shape and distortion free optically. You should appreciate the results with your artistic eye.

  2. Bert SWIFT
    October 14, 2022

    Well, I show up a day late and find that tomorrow came today! Great test video, still very cool! I understand if you felt you’ve built enough similar examples that this is just another picket in the fence. But, thanks for sharing I really enjoyed it!

    Your friend,
    Bert Swift

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