By Dan Johnson

Every Aviator Magazine reader has probably heard of off-road vehicles. How about an "off-airport" flying machine? You may not have used the term but you probably know one of the candidates: Zenith Aircraft's highly functional CH 701. Dan Johnson investigates.

No one calls the CH 701 the most handsome aircraft in the fleet. That title may be better reserved for sleek carbon fiber jobs. But as a practical aircraft appealing to ultralight enthusiasts, the Chris Heintz design with a 20-year history is head of its class. While the design has not changed much in those two decades, the kit has changed quite a bit to make the builder's effort easier.

The designs of engineer Chris Heintz have been around a long time, beginning with his early Zipper ultralight-like aircraft. A prolific and versatile creator, his aircraft models have put nearly 3,000 builders in the air. The low-wing CH 601/650 B series is the most popular at better than 60 per cent of all Zenith models followed by more than 700 CH 701's now flying around the world.

Ultralight enthusiasts who have built kits will find the all-metal CH 701 a reasonable project and quite ultralight-like to fly, though it also has the cabin comforts associated with light sport aircraft.

OFF-AIRPORT SKY JEEP
The Zenith Aircraft Company, based in Mexico, Missouri, is run by Sebastien Heintz, one of a family of brothers in the aviation business. Mathieu runs AMD, which fully manufactures the CH 650B/CH 750 LSA and other Heintz designs, Michael runs a West Coast dealership selling both kits and fully built Zodiacs (as the line is also known), and Nicholas partners with Sebastien as head of the Zenith's technical support. A Canadaian / USA based businesses was operated for years by patriarch Chris Heintz, who now lives in the south of France. When the Heintz men get together at air shows they make quite a team.

On numerous occasions, Zenith Aircraft demonstrated at air shows that the assembly of one of their kits could be accomplished in a week - albeit a busy one with long hours - complete with a test flight at the end.

Chris Heintz first introduced his CH 701 in 1986 "as an 'off-airport' short takeoff and landing (STOL) kit aircraft." It was intended to address the desires of sport pilots, yet it had to be a project that first-time builders could successfully undertake.

Zenith Aircraft Company was formed in '92 to manufacture and market the Chris Heintz designs created by Zenair. The STOL CH 701 was never meant to be just another pretty light aircraft, according to Chris. Instead it was engineered to bring outstanding STOL performance, all-metal durability, and remarkable ease of construction. These are all qualities that should endear the CH 701 to the ultralight enthusiast looking for an all-metal design with ATV instincts.

Indeed, the STOL CH 701 is a great example of form following function, to borrow an architectural metaphor. Some owners affectionately call their 701 a "Sky Jeep."

With the STOL CH 701, designer Chris Heintz combined the construction of conventional aircraft with the short-field capabilities of an ultralight aircraft. The CH 701 features fixed leading-edge slats for high lift, full-span flaperons (combined ailerons and flaps), an all-flying rudder, and well-proven all-metal construction.

The Heintz "Sky Jeep" excels in short-field performance. The CH 701 I flew, powered with a 100-hp Rotax 912S engine, was airborne in well under 100 feet of asphalt runway. Rotation came barely after I applied full throttle and lift-off began at around 22 knots. The CH 701 leaped into the sky within four seconds from standstill. Naturally, a headwind would further shorten both time and distance for takeoff. In a word: impressive!

EASY ENTRY
Entry from in front of the wing strut with the gull-wing door opening wide against the bottom of the wing was simple. You merely sit down and swing your legs in, though I helped pull my feet with my hands to clear the front cowl post.

The door closed with a single latch that was easily seen at approximately my outside knee. When opening, a friction latch appeared to prop open the door securely. The CH 701 seats were comfortable and the interior was nicely finished with carpeting.

Shoulder belts are standard on both seats. The CH 701 offered for this flight test was equipped with a good range of instruments that offered all the information needed without technical overload, which seemed appropriate.

I loved the great visibility out of the skylight. These windows are quite useful in turns opposite of the side on which you're sitting. To your side, you'll have to look out the side window before turning.

Some folks have been critical of the way the wings "end" or flatten at the canopy, which is located well below the top of the wings. It does look somewhat unorthodox, but one benefit is that your head remains below the wing rather than slightly up inside it. The result is improved lateral visibility. Remember, this design is about function, not stylish beauty.

Visibility is not as enormous as the company's clear-canopy CH 601/650 B, but it was more than adequate in the CH 701. Of course, the design provided the downward visibility of all high-wings that many pilots prefer for aerial sightseeing. Flying over the green countryside, I was pleased to have a great viewing platform.

Despite the wide cabin, my headset sometimes bumped a cross member overhead, suggesting that the wearing of a helmet is unlikely except for shorter occupants.

The CH 701's instrument panel switches were easy to reach and instruments could be clearly read. Adequate room was available for a variety of instruments and radios if you simply must load it up with such gear, though in my opinion, doing so starts to violate the simple effectiveness of this design.

Chris Heintz's Y-shaped joystick handle worked well to my side (in the left seat), but I found it a bit more awkward moving it to the right. With a right-seat occupant, I found motions to that side bumped into the other person's leg. The left side of the stick was equipped with multiple switches for trim control and radio-transmit. The Y-stick should work excellently for training and yields more legroom than dual joysticks.

Powerful hydraulic brakes slowed the 1,100-pound aircraft well and the gear has generous ground clearance for off-field landings. According to others, the CH 701 slab gear is extremely stout. Thankfully, I never tested this ability.

When you open the throttle of a 100-hp Rotax 912S-powered CH 701, be prepared for action. Much like a Quicksilver ultralight, ground break is extremely fast on takeoff. This is a central feature of the design. Its leading edge slots and full-flying flaperons were created to provide fast liftoffs from unimproved airstrips. Believe me, the concept works!

Takeoffs were easy if you were prepared. Landings took a bit more finesse though the aeroplane can certainly handle rough touchdowns.

I found I needed to keep the stick aft to prevent bobbing. My check pilot said the wing tries to start flying again unless you keep the angle high. Once you've started to raise the nose in preparation for final touchdown, keep it up. The wing can fly so slowly at such high angles of attack that lowering the nose just a tiny bit makes the 701 want to resume normal flight.

Approaches were made at around 43 knots with a bit of power, though it was obvious that I could come in much slower once I was ready to manage the plane's special low-speed performance characteristics.

The mechanical flaps were difficult for me to fully deploy. I could get enough flaps down for normal operations, but needed a better technique to get them out all the way. You reach down (where a seat adjustment might be) and must pull forward, an awkward motion that I could only manage to the first notch. Since the company offers electric flaps as an option, I'd recommend them despite a modest weight penalty.

Fortunately slips were very effective in either direction, thanks to the slab-side finish of the design. Given its slow approach speed potential, I can't imagine using slips to land very often. Standard large tyres can make off-field landings no problem.

BLAST OFF
The CH 701's climb angle expressed as deck angle is very steep yet this is not unreasonable as the fixed-slat wing provides genuine STOL characteristics. I measured climb with the Rotax 912S at better than 1,000 fpm dual and nearly 1,500 fpm solo. All measurements were done at about 1,000 msl on a cool 20°F day.

The leading edge slots account for some of the CH 701s capability in fast takeoffs and high rates of climb, but the Hoerner wing tips - angled up to a extended upper surface line rather than rounded tips - help increase effective span by pushing the wake vortices beyond the span.

I cruised at near red line, about 90 KNOTS, thanks to the 100-hp Rotax 912S. Frankly, I found it too much engine for the plane and others have agreed. I'd save the extra expense for a 912S and stick with the highly reliable 80-hp Rotax 912. However, if you want amphibious floats, fly at high elevations, or intend to fill the plane to gross weight on all flights, the 100-hp 912S may be the right selection for you.

Several CH 701 pilots with whom I've spoken agreed that the 701 has a rather high sink rate. This is a deliberate design feature that helps you get into tight fields, but I encourage guarding your altitude when not near a landing field, even if a landing field can be mighty small. I was told, "At 1,000 feet agl, you'll be on the ground in 60 seconds without power." Later trials showed the 1,000-fpm sink rate to be about right despite the high-lift wing. Wing loading is 9 pounds per square foot, much higher than most ultralights; here's where such differences show.

In a demonstration of superior low-speed performance, a CH 701 was configured to tow hang gliders in Germany. These aircraft prefer tows below 26 knots and the CH 701 can do it. The low stall speed and excellent climb performance of the aircraft make the STOL CH 701 an ideal tow plane for the slow-flying hang gliders.

As is often the case in my line of work, I got to fly a nearly new aeroplane. As is also often the case, all the pulley wheels and linkages were still a bit tight. Consequently, the CH 701 rudders were rather stiff. They tended to stay where they were put, which gave false impressions of handling. I once thought the plane had a left turn only to realise (from the ball's position) that I had the rudder slightly depressed from a previous manoeuvre. Such tightness will loosen in time and should not be an ongoing problem.

Contrasting with the rudders were very responsive ailerons, virtually regardless of speed. When I flew at a low (though probably not minimum) speed, roll pressures seemed almost as light as at cruise speed, though the response degree lessened somewhat due to slower airflows past the surfaces. My Dutch roll coordination exercises were sloppy owing to the stiff rudders. At speed very little rudder is needed while at slow speeds more is needed (logically).

A medium-power stall did break and went rather sharply to the right side, rapidly enough that my check pilot started to reach toward the controls. Despite the abrupt manoeuvre, recovery was easy. One factor affecting this behaviour may have been the powerful engine and a propeller set up for fast climb. Stick with the 80-hp engine and a medium prop and you may never experience a sharper break. Contrarily, low-power stalls never broke and were extremely well behaved.

With stalls coming at nearly 26 knots and with top cruise nearly 85 (in the 100-hp Rotax 912S-powered version), the CH 701 has a wide speed envelope of better than three to one.

WHY CROSS COUNTRY?
The CH 701 is not your ideal cross-country cruiser. It wasn't designed for that kind of flying; Zenith's CH 601/650 B will prove much better in this realm of flight.

But if you fly from unimproved, short, or soft airstrips, the CH 701 may be your dream plane. Like 4x4 off-road vehicles, the CH 701 is not a pretty aeroplane, but it can take off from airstrips you wouldn't think of using in your composite LSA. Lots of ultralight pilots can enjoy such gutsy performance.
While no CH 701 will be envied for its striking good looks, the STOL design more than makes up for its workhorse appearance with toughness and outstanding short-field performance. And a 20-year-plus history in the field speaks volumes to the model's market and aerodynamic success.

I once drove behind a Chrysler Jeep, which had a wide bumper sticker across the top of the rear window that read, "It's a Jeep thing. You wouldn't understand." If you're an off-airport CH 701 "Sky Jeep" buyer, you probably do understand.

CH 701/750
SPECIFICATIONS
Seating:                                 2, side-by-side
Empty weight:                       263kg (580 pounds)
Gross weight:                       499kg (1,100 pounds)
Wingspan:                             27 feet
Wing area:                            122 square feet
Wing loading:                       9.0 pounds/square foot
Useful Load:                         235.9kg (520 pounds)
Payload (with full fuel):       181.4kg (400 pounds)
Cabin Interior:                      40 inches at shoulder (44” with the bubble door option)
Length:                                                  20.9 feet
Height:                                   8.6 feet
Fuel Capacity:                      75.71 litres (20 gallons)