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STOL CH 701 PILOT REPORT: Kitplanes Magazine

More than Just a
Pretty Face

Zenair's STOL CH 701 fills the light utility role.
By LeRoy Cook

During the last decade, an entire category of light aircraft has evolved, bringing, us back to the beginnings of our general aviation industry. Powered by small, high-output engines, these are two-place, high-wing airplanes with less than 500 pounds of empty weight. A typical gross weight of less than 1000 pounds gives them excellent takeoff and climb performance. Among others, this class of aircraft includes the RANS S-6, Kitfox, Avid Flyer, Rebel, Merlin and Zenair STOL CH 701. They fill a void between heavyweight ultralights and the smallest certificated trainers.

We've been here before. In the mid-1930s, during the depths of a continuing Great Depression, the old Wright Whirlwind-powered cabin cruisers were simply too much aircraft for the times. Few people could afford them, and something was needed to give the common man wines. The Taylor Cub and Aeronca C-2, using newly developed 37- to 50-hp engines, made economical backyard flying possible and infected a fresh crop of pilots with the aviation bug.

Today's Version

Chris Heintz's CH 701 has brought us full circle. I caught up with it at the Zenith Aircraft factory in Mexico, Missouri. The first product of Zenair's new U.S. plant, N701ZA was painted in appropriate red, white and blue colors, decals on the rudder and wingtips. Heintz's STOL bushplane design was introduced in 1986-a response to the need for a small but rugged airplane that could be fitted with wheels, skis and floats. Naturally, Heintz developed an aluminum float kit that could be built with techniques like those used for the airplane.

Adding Simplicity

Heintz's philosophy of design is one of paramount simplicity. Even before he moved to Canada from his native France in 1973, he had created a homebuilt airplane that could be assembled with ordinary hand tools-the sort that could be found in any home workshop. Aluminum structures were used throughout Heintz's new Zenith; metal, he reasoned, is stable through a wide range of temperatures, resists attacks from moisture and sunlight, is essentially non-toxic, and needs no special skills if a carefully designed kit of component parts is supplied.

As with the previous Chris Heintz designs, the STOL CH 701 embodies these tenets. Compound curves are nowhere to be found, other than on the fiberglass cowling. Pulled rather than driven rivets allow easy one-person assembly in a residential neighborhood. The main gear is carried by a one-piece aluminum spring: a leak-proof, shock-absorbing method for the rigors of Canadian winter. While a full airframe kit is available, complete even to optional firewall-forward engine packages, Zenair still offers a plans-only option for the scratch builder.

Pretty Is as Pretty Does

The CH 701 may or may not win beauty contests, depending, on the judge's tastes. But its slab sides allow easier construction, the notched inboard wing root enhances visibility and improves wing efficiency, and the high tail is well clear of water or brush. Tricycle gear is standard, although conventional gear is optional; the trigear's ease of handling overcomes any slight concession to rough-field weaknesses. As we were to see in our evaluation flight, the powerful elevator control and c.g. location allow the bungee-cushioned nosegear to float over hazards. Full 16-inch tires are installed for high flotation, with the mainwheels equipped with hydraulic drum brakes.

Form follows function, of course. The CH 701 is a STOL airplane, true to its name. As such, it has the necessary extra complication of a set of fixed, full-span leading edge slats, along with below-the-trailing-edge flaperons that simply remain in the slipstream at all times. These additions to a basic high-lift airfoil produce a quoted 3.10 maximum lift coefficient, approaching that of a Boeing 727 wing and allowing the CH 701 to hang in the air at impossibly slow speeds. Similarly, the horizontal tail embodies a deeply-lofted profile; its upsidedown camber is visible from the other side of the ramp, in both stabilizer and elevator.

The vertical tail is an all-moving surface aft of the dorsal fin: a Heintz trademark. The CH 701's rudder is taller than that of the less-athletic Zenair airplanes - the CH 601 series - and the horizontal tail is mounted above the fuselage tail cone, rather than buried artfully within to create a builder's roadblock. An optional electrically actuated trim tab is located on the left elevator. The wings fold back along the fuselage to create a width of 7.3 feet for storage or trailering. Quick-disconnect fittings for the control linkages are installed at the wingroot. The demonstrator had only a 12-gallon nose tank, but optional wing tanks can be installed to add another 12.5 gallons, or to allow the use for a smaller 6-gallon nose tank for increased avionics space.

How It's Built

Structurally, the CH 701 is built almost entirely of corrosion-resistant 6061-T6 aluminum, which normally requires no zinc chromating for preservation. The more common 2024-T3 is slightly stronger but would not have the same enduring qualities in its unprotected state. The fat high-lift airfoil has a deep spar, braced by tubular lift struts and attached to a cabin carry-through structure. Streamlining fairings are available for the lift struts, but their effect on speed is minimal, Heintz says. Hoerner wingtips extend the effective span of the wing by 12 inches, Zenair calculates.

A Rotax 582 liquid-cooled, 65-hp, two-stroke engine is standard, equipped with oil injection to eliminate mixing oil with fuel and fitted with a two-blade, fixed-pitch wooden propeller from GSC. The demonstrator aircraft was equipped with a 64-inch ground-adjustable propeller for test purposes, however. The 582 is installed with its cylinders down in the STOL CH 701, so modifications were needed to the crankcase, water pump and exhaust manifold. An 80-hp Rotax 912 four-cylinder, four-stroke engine is optional, turning a three-blade ground-adjustable propeller, although the Rotax 582 gives plenty of performance, thanks to a gross weight well below 1000 pounds. A large coolant radiator is found under the belly. Cabin heat is taken from an exhaust shroud: a welcome winter option to supplement the greenhouse heating through the Plexiglas overhead. I noted a large panel under the aft fuselage, an access hatch for control linkages and the tail cone area. A generous baggage shelf behind the cabin holds up to 40 pounds of parkas, swim fins or provisions. Zenair's floats attach to the trigear mounting points, retaining the main gear's shock absorption. Amphibious floats are available, swinging the main tires up into wells behind the step area; the nosegear is simply left in place, with an extended strut to allow it to reach below the floats. Its minimal water drag is only present during displacement taxiing.

The Inside Story

Nicholas Heintz, chief pilot at Zenith Aircraft, waved us aboard so we could sample the CH 701 in the air. The large 34-inch doors swing 180' for rapid boarding or fending off. Half doors or sliding windows are warm-weather options. There was ample room in the 40-inch-wide cabin, even with bulky clothing. Zenair's center-mounted Y-shape control yoke increased room and access by providing a handle for either pilot at no cost in knee space. Dual throttles are also installed. Toe brakes, however, were found only on the left side, although the nosegear steering was available through both sets of pedals.

A standard VFR panel is part of the CH 701 kit, with the addition of other gadgetry left up to the individual builder. The demonstrator carried an airspeed indicator, non-sensitive single-pointer altimeter, slip ball, tachometer, coolant temperature and pressure, and a magnetic compass. The fuel gauge was a simple and reliable sight tube. Electric pitch trim is controlled by a switch near the left-hand throttle. The flaperon control is a sliding handle on the floor, under the pilot's knees that hooks into one of three notches; either half or full flaps may be selected below 60 mph. The linkage was purposely designed to require slowing down so the slipstream forces would allow extension, easing loads on the fittings, Nicholas said.

Thanks to the 12-volt electrical system, starting was as simple as adding some choke and engaging the starter. The willing little Rotax hummed into life, and we taxied away with a nudge of the T-handle throttle rod protruding from the comer of the panel. Despite the nosehigh profile presented by the CH 701, forward visibility was good, thanks to the narrow cowling. Nosegear steering is firm but responsive, and one can always employ a touch of brake to tighten the radius.

Going, Going, Gone

At runway's end, the simple checklist calls for controls and trim checks, setting the altimeter, running the engine up to 5000 or so to test each of the two electronic ignition modules in turn, and scanning the skies for approaching traffic. No avionics were installed, so we simply lined up with the runway and blasted off-and I do mean blasted! With no special technique, we were off in about one runway light length - around 200 feet - climbing away steeply at 48 mph. The horizon was near the bottom of the windshield, and while the rate of climb was probably around 1000 fpm, the angle of climb was spectacular.

Leveling at 2500 feet AGL, we turned the engine down to 5800 rpm and saw a respectable 80 mph for its efforts. The seating is comfortable and the control forces light and powerful. Strong adverse yaw requires forceful rudder inputs, another Cub-like characteristic. One doesn't build a CH 701 for extensive cross-country cruising, however. Its forté is low-speed work, so we undertook a set of stalls under various combinations of power, flap setting, and control displacement, finding the STOL CH 701 thoroughly benign. The actual stall, such as it was, occurred at 35 mph or so, and only when flaps were lowered and power was retained did the airplane offer to exhibit a breaking stall.

The flaps may be lowered at any airspeed below 60 mph, although Heintz says he prefers to slow to about 50 mph to lessen the pull on the handle. For landing approaches, Nicholas suggested 50 mph as a starting point, Gradually working down to 45 or so in normal operation. As with all STOL aircraft, maximum performance is achieved at the corners of the envelope. This means that a sudden reduction of power at slow speed, delayed until near the ground, will "dump" the airplane onto the chosen landing spot. We used around 400 feet for stopping.

The STOL CH 701 is an excellent choice for first-time builders needing the ability to fly into strips less than 1000 feet in length. It flies in a straightforward manner, uses rugged construction methods, and has been around enough years to acquire a service history. The little airplane can do a big job, on floats as well as wheels. Thanks to the relatively uncomplicated construction techniques, Zenair estimates construction time at only 350 hours. It's worth a sample flight of your own.

KITPLANES Magazine, May 1995, by LeRoy Cook, pages 66-70.
© Kitplanes Magazine

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NOTE: This article represents the viewpoints of the author, and not necessarily those of Zenith Aircraft Company.

© Zenith Aircraft Company
2007-06-29