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The STOL CH 750 Super Duty Design
Wings | Fuselage | Cabin | Tail | Gear

The STOL CH 750 Super Duty is based on the decades of aeronautical design experience Chris Heintz accumulated over his long career as a kitplane designer. It is the latest member of a line of practical, simple, light STOL aircraft that started in 1986 with the CH 701. With a gross weight more than twice that of the original 701, the 750 Super Duty is an excellent example of the continual development and improvement that is such a part of Zenith Aircraft Company.

The Super Duty is quite similar to the original STOL CH 750, but it has been enlarged and strengthened to give a higher useful load and the ability to use larger engines. The wing is longer and stronger, and the fuselage has been changed slightly to make room for a third seat in the baggage compartment area. The rudder and horizontal tail are larger as well.

However, many of the lessons learned with the rest of the Zenith STOL lineup still apply to the Super Duty. Like the rest, it was designed with maximum short-field performance and ease of building and maintenance as central goals.

It still features the same idiosyncratic, yet ideally suited to the job at hand, wing design, with leading edge slotted flaps and flaperons hung beneath the trailing edge.

WING DESIGN:The STOL CH 750 SD uses a special airfoil design to achieve very high lift, low stall speeds, and high strength. A thick wing, full-length leading-edge slats and trailing edge Junker type flaperons develop a maximum wing lift coefficient of 3.10.

The flaperons act as both full-span ailerons and full-span flaps. For maximum reliability and to keep construction simple, the leading edge slats are engineered to remain in a fixed position in all flight attitudes, and do not retract.

In 2004, Kitplanes magazine had the following to say about the original CH 701: “Thanks to its thick, high-lift wing, full-span flaperons and fixed, full-span leading-edge slats, the 701 needs little more runway space than the typical backyard with clear access at the ends.” The CH 701 has a takeoff roll of about 90 feet. The much heavier Super Duty still only requires 115 feet to get off the ground.

TAIL DESIGN: The STOL CH 750 Super Duty has the same all-moving rudder tail section as the rest of the Zenith STOL family. Making the entire rudder / vertical stabilizer pivot results in very strong rudder authority, yet a rather small total vertical stabilizer area. The small area means the Zenith rudder is less affected by crosswinds than a plane with a larger rudder would be. The all-moving rudder / vertical stabilizer gives the Super Duty strong and responsive rudder authority, particularly at lower speeds.

The “upside down” airfoil of the horizontal tail is another seemingly odd feature that actually fulfills a very specific purpose. It provides the negative lift (downward force) necessary to get the tail down and nose up early in the takeoff run, reaching the high angle of attack where the high-lift wing features work best as soon as possible. Perhaps counterintuitively from a non-aeronautical engineering perspective, a definite downward force on the tail actually enables the airplane to fly sooner.

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CONTROL SYSTEM: The STOL CH 750 SD’s large control surfaces provide excellent controllability at very low flying speeds – a necessity for good short take-off and landing performance – while remaining light and balanced.

The Super Duty control system is simple and easy to maintain. There are no moving parts inside the wings, and the system is easily accessible through a large inspection / service panel on the bottom of the fuselage.

The ailerons are actuated by push-pull rods attached to a torque tube which rotates when the stick is moved left and right. The flap motor is attached to the aileron system so that pushing the “flaps down” switch essentially lowers the whole aileron system, dropping the ailerons and giving them their double function as flaperons. The flaperon system is easy to disconnect for wing removal.

The elevator and rudder systems are very simple and conventional, consisting of cables from the stick and rudder pedals. Pushrods directly link the rudder pedals to the nosegear strut. Hydraulic disk brakes are standard, with individual toe pedals on the pilot’s side.

The standard fuel system consists of two tanks located inside the wings behind the wing spars. Each factory-welded aluminum fuel tank has a capacity of 24 US gallons, for a total capacity of 48 gallons, plenty of fuel to feed the high-performance engines the Super Duty can accommodate.

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VISIBILITY: All Chris Heintz STOL designs contain many design features for excellent visibility. The Super Duty’s wings are positioned above the cabin and fuselage, rather than directly at the occupant’s eye level as in many high-wing aircraft. You can see directly to the side without ducking to look under the wing root. There is no conventional roof, just a clear skylight for an excellent view out of the top as well. The wing root is tapered to allow a greater field of view above. This tapering also puts the rudder more directly in the propellor blast, contributing to rudder control.

LANDING GEAR: While it is somewhat unusual for an aircraft intended for serious off-airport operation to have tricycle gear, this was a deliberate choice by Chris Heintz, and like all other design choices was made for very specific reasons. Heintz has always intended his planes to be flown by everyday low-time recreational pilots, and almost all pilots are familiar with tricycle landing gear. The gear on the STOL CH 750 SD is not as much of a compromise as it might seem. The negative lift provided by the horizontal tail gets the nose off the ground quickly, and the swept-up tail enables taildragger-or-greater takeoff and climb angles. At the same time, the Super Duty rests level on the ground, which gives easy ground handling, superior visibility, and wind resistance.

The main landing gear is a single massive piece of 6061-T6 aluminum, bolted to the bottom of the fuselage. This is a very sturdy and shock-resistant system. The nose fork is similarly beefy, and can accept large tundra tires. The Super Duty kit comes standard with large tires suitable for off-airport use, and the huge tundra tires seen on the Zenith demonstrator aircraft are optional. While tailwheel aircraft have traditionally dominated in off-airport applications, the Super Duty’s tricycle gear offers both rough field capability and all the advantages of a tricycle-gear aircraft.

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FLOAT OPERATION: Zenith Aircraft’s Canadian sister company, Zenair, produces all-metal floats which are ideal for use on the CH 750 Super Duty. The floats are mounted on a monoleaf main spring for the same shock absorption on water that pilots are used to on land. Floats are available finished, as predrilled kits, or as basic parts kits. Zenair floats are available in straight (water operation only) or amphibious models. The amphibious floats feature pneumatically activated retractable main wheels and a single unique retractable steerable nose wheel.

See the Zenair Floats page for details.

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Zenith designs always respect and encourage builders’ choices about how they choose to use and equip their airplane. The Super Duty airframe itself is designed to allow maximum customization by the actual builder. Zenith aircraft are not designed around any specific engine, allowing for custom powerplant installations by builders.

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Construction of the STOL CH 750 Super Duty kit is modular, i.e., each section of the aircraft is built separately on the workbench. Many builders choose to buy component kits instead of buying the complete kit at once, purchasing kit sections as they progress through the project. This method of construction requires minimal workshop space; most builders construct the kit in a single-car garage or basement workshop. Once all the airframe sections have been assembled, the wing and tail sections are bolted to the fuselage and the landing gear, controls, and fuel system are installed.

Throughout, the STOL CH 750 Super Duty is designed to optimize STOL performance and to provide excellent flight characteristics. The aircraft is also designed to be easy and quick to build, and to provide a durable airframe that is well-suited for its utility role. Finally, but importantly, it is designed to be low-cost to build, to own and to operate.

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