By Frederick A. Johnsen
It is gray and subdued, an understated exterior for a smooth custom homebuilt firmly rooted in the plans of the legendary Marcel Jurca. But the Sperocco that visited AirVenture Oshkosh 2021 reveals a number of structural and aerodynamic touches applied by owner/builder Lowell Manary, EAA Lifetime 52692.
The Sperocco is all wood, save for aluminum wheel wells and compound curve fairings made with composites, Lowell said. After researching aerodynamics, he chose the Riblett airfoil for his airplane.
The basis for Lowell’s efforts is the Jurca Sirocco design. Lowell said it is a Special Sirocco, or simply the Sperocco. Lowell had earlier completed a Jurca MJ-5 Sirocco and enjoyed the project and the flying.
Jurca’s original Sperocco plans did not address a six-cylinder engine as large as Lowell wanted for his customized project, so he negotiated with Marcel Jurca to make design changes that would beef up the fuselage to meet Lowell’s desires. The fuselage is stressed to accommodate engines up to 350 hp. The spar design was widened by 40 millimeters.
A manufacturing engineer by trade, Lowell said that he knows how to “look stuff up” to inform his choices on the Sperocco. He read the books of German aerodynamicist Dr. Sighard F. Hoerner as the Sperocco’s important aerodynamic details were taking shape.
A close look at the trailing edges of the aircraft’s control surfaces shows a deliberate effort to square the edges instead of tapering or rounding them. Lowell said this increases the amount of effective get a grip on area while reducing drag caused by turbulence at the edge of many control surfaces.
Early construction of this special Sperocco began in Connecticut. Lowell and his wife, Dee, retired and moved to Colorado with the unfinished airplane project. Work progressed on the engine of choice — a Lycoming O-540 parallel-valve engine obtained from a Piper Aztec.
First flight of the Sperocco came on July 6, 2019. It has 125 hours on it at the time of AirVenture 2021. Lowell likes to describe its characteristics. He said it is super light on the controls. “It cruises 200-plus over the ground at 10 gallons per hour, ” he added — and that’s in miles per hour. His Sperocco stalls at 60 mph, and Lowell has established an approach speed of 80. “It’s got a docile stall that makes the Cessna 150 a wild stall, ” Lowell said. For a no-flap landing, he adds 10 mph to the stall and approach speeds.
The Sperocco celebrated another first upon landing at Oshkosh. “This is the lowest altitude it’s ever been. ” Home field elevation in Colorado is 5, 190 feet; Oshkosh sits at 808 feet unless it is even lower this week from the weight of all the airplanes on the ground, as one wag has suggested.
(With special thanks to Alan Collins [EAA Lifetime 1175453] who provided details of the Sperocco’s performance and construction. )