It would entail multiple powerplants, long drive shafts, and pusher propellers mounted on the extreme aft end of an aircraft. Well-stocked from the war effort with a robust team of engineers and faced with a dwindling number of military contracts, the company tasked a team to investigate and develop the concept.

• READ MORE: Cessna 407: Full Steam Ahead, Right Up Until the End

The company’s first attempt at integrating the new design resulted in the XB-42 “Mixmaster”—an experimental military bomber with twin contra-rotating propellers mounted to a common drive shaft. Although the company built and flew two examples, the military quickly lost interest in piston engines, and Douglas pivoted, ultimately reworking the XB-42 into the jet-powered XB-43. Neither aircraft would advance beyond the development stage.

Undeterred, Douglas unveiled a proposal for the same twin-powerplant, pusher-propeller concept in 1945, which was applied to a conceptual airliner. Called the Douglas DC-8 “Skybus,” it would utilize the same Allison V-12 engines as in the XB-42, this time buried in the forward fuselage section and linked to the aft propellers with a series of shafts that extended nearly the entire length of the 77-foot aircraft. The Skybus never left the drawing board.

Douglas would try one last time to make the unconventional design work, this time in the form of a 39-foot-long, 5,085-pound, five-passenger GA aircraft. With a large, bulbous forward fuselage section and low wing, the Cloudster II housed two 6-cylinder Continental piston engines behind the passenger compartment. Douglas designed the aircraft around two 250 hp engines but explained in a 1947 press release that it would be flown initially with 200 hp engines until the more powerful ones became available.

As unique as the pusher design was, it was not without precedent. Just two years earlier, Lockheed had built and flown its Model 34 “Big Dipper,” and WACO’s Aristocraft made its first flight only a few months before the Cloudster II. The companies touted many of the same theoretical advantages, including unrestricted visibility from the cabin, no spiraling slipstream effect from a forward-mounted (tractor) propeller, and a quieter cabin. 

• READ MORE: Interstate TDR Developed as Unusual Kamikaze Machine

Moulton Taylor, the designer of the similarly configured roadable “Aerocar” that would fly a couple of years later, added that at idle a propeller mounted to the extreme aft end of the fuselage has the effect of an anti-spin drag chute, adding stability and aiding recovery from spins. Taylor defended the pusher configuration passionately, observing, “Who ever saw a boat with a tractor propeller?”

Another benefit of the design had to do with controllability in the event of an engine failure. Like the Cessna Skymaster, the Cloudster II utilized centerline thrust, meaning that if an engine failed, the remaining engine could power the aircraft without introducing asymmetric thrust and the associated handling challenges. Of course, because the Cloudster II utilized just one prop and drive shaft, a single point of failure of any of these components would leave the aircraft entirely unpowered, illustrating the lack of redundancy compared to a traditional twin.

When the Cloudster II finally flew, it encountered problems that were both predictable and serious. The lengthy drive shafts produced significant vibration through the airframe, a problem that would require careful engineering and multiple isolation units to address. Additionally, the location of the engines mounted side by side, deep within the airframe, introduced cooling issues. While more airflow could be ducted onto the engines easily enough, this would come at the expense of significant drag. 

• READ MORE: The Ryan YO-51 Wowed with STOL Performance

Ultimately, development of the Cloudster II was abandoned in late 1947. Douglas reportedly donated it to a local Boy Scout troop for ground training before it was scrapped sometime after 1958. The concept was then left for WACO to pursue, also unsuccessfully, with its Aristocraft.

In the early 1960s, Jim Bede attempted to make it work with the Bede XBD-2. Later, in the 1980s, the twin-turboprop Lear Fan 2100 attempted to resurrect the concept yet again, but despite building and flying three examples, it once again fizzled out.

The post The Bold, Bulbous Douglas Cloudster II appeared first on FLYING Magazine.

But then again, most engineers aren’t Jim Bede. 

While still enrolled in the aeronautical engineering program at Wichita University, Bede designed an aircraft that would incorporate a number of unique technologies. His vision was to integrate these technologies to provide superior performance to existing designs. Integrating new systems and complexity into an entirely new aircraft design, however, would prove to be challenging even for him. 

Bede started with an entirely clean-sheet design. Envisioning an eventual family of multiple aircraft varying in size and passenger capacity, he began with an experimental prototype of the Bede BD-2, which he called the XBD-2. Intended as a proof-of-concept and testbed and first flown in July of 1961, it was boxier and more utilitarian than the sleek, streamlined concepts he endeavored to build, but it would function well for its intended purpose.

At first glance, even an experienced pilot or engineer might not guess the XBD-2 is a twin-engine aircraft. But it is, and two 145 horsepower six-cylinder Continental O-300s are snugly nestled in the aft fuselage, stacked one above the other. While such an engine configuration is decidedly unconventional, Bede was of the opinion that it offered several advantages.

Most obviously, housing the engines within the fuselage provides for a clean wing, undisturbed by engine nacelles and far more aerodynamically efficient. From a controllability perspective, an engine failure would be a non-event, as there would be no risk of asymmetric thrust. The lack of engine nacelles helped to reduce overall drag, enabling an 18:1 glide ratio. 

A system of 10 belts and multiple clutches enabled operation at any combination of engine power, and the pilot could shut one engine down completely to maximize endurance. Bede even mounted each engine on a slide-out rack, a design he claimed enabled an engine to be removed in only 30 minutes. Presumably, little time was required to decouple an engine from the system of drive belts.

It was a complex system, but Bede wasn’t finished. With the assistance of Mississippi State University’s aerophysics department, he introduced further complexity to the aircraft by integrating a Boundary Layer Control, or BLC system, into the design. Utilizing 160,000 strategically-placed pinholes in the upper wing and aileron surfaces—holes roughly 30-50 percent as large as those in a typical air hockey table—the system would draw air into the wing to create additional lift. By causing the boundary layer to stick to the wing at high angles of attack, the system effectively increased lift and lowered the stall speed.

The BLC system drew air into the wing via a pump driven by the propeller shaft. So long as the propeller was being turned by at least one engine, the BLC system would operate. Ingested air was ducted back to the engines to provide additional cooling. The system proved to be effective, lowering the stall speed from 64 mph to only 42 mph—an impressively slow speed for an airplane with a gross weight of 3,300 pounds. Bede even claimed that the system would be undeterred by rain.

The most visually notable feature of the XBD-2 is the shrouded propeller. Bede was of the opinion that the aerodynamics at the tips of a standard propeller was one of the greatest sources of inefficiency, and he claimed his testing found that “a correctly-designed shroud” would increase the static thrust of a given propeller by over 100 percent. While many would be interested in seeing figures to back up this rather extreme claim, his other claim that a shroud greatly reduces propeller noise is perhaps more palatable and easy to accept.

The basic performance figures of the XBD-2 are impressive. At 9,000 feet, max cruise speed was said to be 179 mph at 16 gallons per hour. Max rate of climb at maximum gross weight was listed as 1,050 feet per minute with both engines operating and 720 feet per minute with one engine shut down, and the service ceiling was 21,000 feet on two engines and 14,500 feet on one. 

Takeoff distances were similarly impressive. While the company didn’t specify at what weight the numbers were achievable, they claimed only 300 feet was required for the takeoff roll, and 500 feet was required to clear a 50-foot obstacle. 

Ultimately, the XBD-2 logged approximately 50 hours of flight time before being permanently retired. No further derivatives were ever produced, and neither the BLC system, the coupled twin engine configuration, nor the shrouded propeller would make an appearance in any of Bede’s subsequent designs. Today, the sole XBD-2 is on display at the Manitowoc County Airport in Manitowoc, Wisconsin.

The post Bede XBD-2: Experimental Prototype for Unique Technologies appeared first on FLYING Magazine.