While Zenith gives CH 701 builders various approved ways to customize their aircraft, many builders find themselves going "beyond the plans" to a greater or lesser extent in the hope of building an airplane more suitable for their purposes. Modifications fall into two general categories: those designed to remedy a shortcoming in the original design, and those designed to increase the capabilities of the airplane. Hopefully, very few modifications of the first type are necessary, as that would imply design shortcomings the kit manufacturer has not addressed. Modifications of the second type are more common, and more justifiable, but almost always compromise both weight and complexity for the added capability.

The author's primary goal for his CH 701 is to complete an aircraft that he is comfortable flying with a useful load of at least 520 lbs. (two 200 lb. occupants and a full tank of fuel) and with minimal operating costs. While Zenith specifies the CH 701 as having a 580 lb. empty weight, giving a 520 lb. useful load at 1100 lb. gross weight, at least one Jabiru 2200-equipped CH 701 has come in at only 540 lb. empty. Operating costs of the CH 701 are strongly dependent on fuel consumption. Fuel consumption can be minimized by reducing cruise horsepower (by reducing weight to reduce induced drag, by reducing cruise speed to reduce parasitic drag, and by directly reducing form drag through fairing and other means) and by choosing an engine and propeller combination that produces the required cruise thrust efficiently. All modifications must be evaluated in light of how they help and hinder the author's goals. Not all of the modifications discussed here will end up being selected for the final aircraft.

The most significant modification planned is that of the elimination of the CH 701's leading edge slats and their replacement with vortex generators. More than any other feature, the slats are what define the CH 701. But experimental evidence shows that nearly-equivalent STOL performance can be maintained without the slats, and in exchange not only is the most difficult part of the build averted, but a couple pounds are saved and a significant source of drag is completely eliminated. Read more...

Other modifications have been pioneered to reduce form drag, and thereby increase efficiency and cruise speed, in exchange for a shallower "steep approach." The CH 701's struts are a major source of drag, and many builders have faired them in one way or another. Similarly, the large tundra tires used to give good soft- and rough-field performance are a large source of drag in the air; wheel fairings can have a significant impact here. Both of these modifications add additional non-structural weight for drag reduction only, offering a straightforward trade-off. Read more...

As additional fall-out of its quest for minimum weight (and therefore maximum useful load), the CH 701 design uses very thin skins in many places. In order to make construction simpler, many of these thin skins are flat panels. A result of this is a tendency for certain surfaces to oil-can or ripple slightly. This is most often reported with the large flat panels of the rear fuselage, but has also been detected with the wing skins. The consequences of this oil-canning is increased cabin noise and a less perfect appearance, especially with polished finishes. Fixes for this problem include using thicker skins, which adds large amounts of weight for minimal improvement, or the addition of strategically placed, lightweight stiffeners, which can resolve the issue with little penalty. Read more...

The CH 701 is also very light on access panels, making inspection of various parts of the aircraft structure difficult once the build is completed. This saves weight, as access panel cut-outs require reinforcement to avoid decreasing strength, but makes certain tasks, such as changing ELT batteries, difficult. Read more...

The empty weight of the CH 701, as given by Zenith, includes only those components absolutely required for flight, and certain minimal avionics. The addition of permanently installed safety equipment can cut into useful load significantly, but in exchange guarantees that such equipment will always be available. Safety equipment that can be permanently installed in this manner include ballistic parachutes, crash survival kits, fire extinguishers, etc. Read more...