Making the Best Better - Soloy's Cessna Turboprops PDF Print E-mail
Thursday, 19 April 2012 08:56

To understand the origin of Joe Soloy’s idea for the turboprop Cessna, it is necessary to go back to Soloy’s original conversions of the piston-powered Bell 47 and Hiller UH-12 helicopters. As a Hiller operator in the wilds of Alaska in the 1960s, Joe always thought about how much more user-friendly it would be if he had a lightweight, powerful turbine engine in place of the very heavy, low-powered piston engine installed in these first-generation commercial helicopters.

The advent of the Allison 250 series of engines was just what was needed, and the engines soon found their way into the new generation of military and commercial helicopters, as well as, thanks to Joe, the legacy helicopters which had built an industry. The removal of the heavy piston engine and its replacement with a lightweight, more-powerful turbine engine gave these helicopters a new lease on life; after 40 years of continuous service, the engine is still being enjoyed by several operators today.

Joe’s thought process was, “If it worked for the helicopter operators, why not provide a similar option for the many utility and agricultural operators of the piston aircraft currently in use?” First, it was necessary to select a turboprop engine that would have power to spare and be suitable for use in the harsh environment of agricultural and bush strip operations. Of the types available in the early 1980s, none met the requirement, and it was decided to produce a Soloy reduction gearbox and attain an STC to convert the Allison 250-C20B turboshaft engine into a turboprop. The design parameters were based on those used in the successful Soloy Bell and Hiller reduction gearbox. It had to be strong, simple, and geared to produce a slow propeller speed for minimum noise levels. The gearbox and Turbine-Pac components were mated to a specially adapted Allison 250-C20S engine. The gearbox first flew in a Cessna 185 test bed, which was used to refine the systems and production configuration of the new powerplant. Further experience was gained in Cessna 210 and Cessna 337 test beds.

The Cessna 206 was chosen as the best candidate for a fully certified conversion. The prototype engine was installed, which allowed a certification program for the Part 23 airframe and Part 33 engine to be conducted concurrently with two STCs to be issued in May 1984.

The conversion of customer aircraft commenced immediately, with the latest Cessna (a JAARS C207) being converted last year. While the total numbers are not huge in OEM expectations, many 206s and 207s, which were the next airplanes to follow the 206, have been in constant service in a variety of operations for almost 30 years.

Although the Soloy units have been used in a multitude of operations, such as government agencies, skydiving, fishing guide services, tourism, and personnel transport, Soloy felt that it has only scratched the surface of the light utility turboprop market. With this in mind, it was decided that the company should develop the Cessna 206 Mark II, a new installation using the Rolls-Royce (formerly Allison) 250-B17F turboprop engine. This is the latest version, and it is a lightweight turboprop engine having a strengthened gearbox, stronger compressor, and an increased thermodynamic power rating. The use of this engine is for a more compact installation with cowl lines designed to make the 206 look like it was meant to be a turboprop from day one. Not only does it look right, but the technical aspects of the installation have the look of the OEM’s hand, producing an aircraft that would not look out of place rolling off Cessna’s Independence production line.

The Mark II is already in service, with three used for skydiving in Europe, where the low noise level is a significant factor in its acceptance. It is now being seen as a bridge between the piston utility single and the growing number of expensive turboprop singles, sharing what is becoming a very significant market segment, brought about by increasing cost and reduced availability of avgas.

With the growing emphasis on airborne security and surveillance platforms, we Soloy sees the Mark II as a very economical option when compared to modern helicopters, which are often used for general patrols. The Mark II platform is half the price of a similarly sized helicopter, costs a third as much to maintain, and requires a fraction of the comparable costs for initial and recurrent crew training.

Soloy’s Sentinel Edition of the Mark II comes equipped with a swiveling observer seat with camera display and control mounts, large observer window, and wing-mounted hard point capable of supporting one of a large selection of cameras.