CH701:  Beginning Once Again

Of all the contemporary homebuilt aircraft, the Zenith CH701 is one of the few that needs no introduction.  It is a single engine, two place, aluminum construction, high-wing aircraft and enjoys widely celebrated short-field, STOL, capabilities -- when properly flown and appropriately powered.  The CH701 is the smallest of three visually similar Zenith aircraft that owe their existence to the innovative genius of  Chris Heintz.  Even its occasional detractors acknowledge that if your payload requirements are modest and you need to land short, and take off even shorter, then the CH701 is worth serious consideration.

Zenith Workshop, Many Years Ago (great way to start)

Occasionally referred to as a “Sky-Jeep,” hundreds of the venerable CH701s have been built world-wide for back-country flying by sportsmen, adventurers and explorers, not to mention missionaries as well as by ordinary private pilots desiring a forgiving, recreational aircraft capable of operating from  unimproved landing strips, or primitive terrain where there is no landing strip at all.  Either from kits and Zenith supplied assemblies, or starting from raw materials, aluminum sheet and rivets, the Zenith CH701 was designed to be built by amateur hobbyists using straightforward, shop tools and techniques, and relying on extensive use of blind-riveted 6061T6 aluminum construction.  In short, the CH701 is an authentic recreational STOL designed for real people with normal skills and an active sense of adventure.

The CH701 was originally designed to take advantage of the once ubiquitous Rotax 503 and 532 series of engines (back when Avid Flyer and KitFox used the same smallish engines and lighter gross weights -- we all weighed less back then I'd guess), although the current iteration has a 1100 pound designed gross and has accepted an assortment of engines of  65 to 100 horsepower; the widely-renowned 4-cycle Rotax  912 series currently being the most fashionable power plant.  The 701 wings are draggy, forgiving and fat, really fat, and the external ailerons and flaps are combined as flaperons (ala Junkers) and usually operated by a central control stick through a series of bell cranks and a flap mixer. The low-speed lift of Chris Heintz' plump wing is greatly enhanced by the use of fixed, Handley-Page style, leading-edge slats -- although some notable builders, apparently attempting to move the 701's cruise speeds up in the mach-numbers, have experimented with wing-mounted vortex generators (VGs) as a lower-drag alternative to the fixed slats.  

Those fat wings are constant chord and do provide great lift, but together with a boxy, rather utilitarian fuselage, combine to make a draggy aircraft whose sweet-spot is closer to low end of its flight envelop  -- it is my humble opinion that those who yearn for faster and faster cruise speeds are wasting their time and probably should quit flogging the faithful steed that was designed to be content with the modest 503 Rotax --  and, just choose a different design more suitable to their mach-number cravings (vis. my own flirtation with the speed question, distractions of Wittman and Sonerai birds -- or perhaps the Zenith Cruzer).  Although the CH701 design has remained visually the same for decades, Zenith has introduced many noteworthy enhancements over the years, including a higher useful load, easier and quicker build kits, matched hole assembly, as well as a variety of option packages including longer-range fuel capacity, tundra landing gear, streamlined lift struts and new flap handle as well as more detailed construction drawings together with step-by-step pictorial assembly instructions.  Zenith seems to support everything from scratch builder who simply buy the plans, to those who purchase fast-build kits where everything the FAA will permit under the 51% rule is factory assembled, and everything in between -- you can buy a little of a lot.

Mine is mostly scratch-built so far, and a few scrounged parts, but I'm not a purist and fully intend to get Zenith to sell me those time-consuming assemblies that will help me get done in this lifetime -- hopefully with enough time left to fly a bit.  I’ve been around airplanes, or dreamed of them, since my kindergarten days well over half a century ago. First from my earliest memories as a kid on my dad’s shoulders at a 1950s USAF air-show (in the Dakotas), through childhood to my first real job as a mass-properties analyst with GE’s Flight Propulsion Divisions near Cincinnati, at the same time bumming rides and taking a few hours of lessons at the nearby Dayton airport, and eventually as an aircrew in the Army’s 1st Cavalry Division MedEvac Hueys – and that was all still in the late 1960s and very early 1970s -- nearly two decades before I finally completed my private ticket (okay, I'm slow... this will become embarrassingly obvious).

Roger's well-known Zenith CH701 -- Rotax powered for many hundreds of hours.(Zenith photo)

Roger provides a CH701 overview and narrates a short demo flight;

           https://www.youtube.com/watch?v=1Y_lrhx-RPU

The CH701's Design Features are well known -- but worth noting again (Zenith figure)

You may surmise the builder lacks serious aviation credentials -- and you'd be correct; no 25,000 hour ATP logbook, no A&P certification, no Alaska bush experience or turbine time, no CFI qualifications, no engineering degree or glider experience either, no IFR qualifications (but, passed the written long, long ago), and no FBO experience -- nor any documentable experience even cleaning restrooms at the local airdrome.  He’s just an geriatric hobbyist who has been hanging around one shop or another for the past 8-10 years, attempting one aircraft project or another -- none have flow, most were sold.   Let’s face it; when it comes to actually building a real airplane, a lifelong fantasy, I’m far better at daydreaming than building. As much as I am in awe of those accomplished craftsmen who can speedily hand-form a breathtakingly exquisite aircraft (or other mechanical marvels), I’m as slow as molasses in January when it comes to actually accomplishing anything serious in the shop.

The "Dave brake" was built some years ago -- will bend 8' of  0.040" 2024

So, I'm returning to the project I first began; the CH701 Through several abortive projects on several LSA designs (and a few that were not so LSA), I have managed to continue to acquire my engine, a fairly standard Corvair – built by Bill Clapp (Azalea Aviation – yes, I’m aware there is another Corvair purveyor, but Bill picks up the phone when I call… ).  There ain't no free lunch, and as entrancing as the other projects have been, I keep returning to the simpler, little CH701; it fits the bill more or less -- and although the Rotax is the favorite engine, and the heavier Corvair is acknowledged to be less than optimum for authentic STOL activities, it is what I have -- so that is what I'll use.  

The CH701 construction will use up my leftover stock of aluminum for the wings, as well as using the parts and assemblies I long-ago built for the cabin structure and empennage -- I do love the smell of argon (or acetylene) in a summer morning, so the small amount of welding should suitably entertain me when needed.  The Zenith Company has kept the CH701 plans available for "scratch" building for many, many years and although pseudo-competitors appear to come and go, the CH701's popularity seemed to go on and on -- its younger brother, the larger CH750 and progeny, seems to be the CH701's most formidable competitor --  having eclipsed the smaller CH701 both in the market-place and in press coverage; oh well, I'm sure the sibling rivalry hasn't hurt Zenith's bottom line.  I expect my 701 will probably be one of the occasional long-wing variants (with slats, or not, I am not sure…), since those longer webs are the spar webs I cut out, and will powered by my Azalea Corvair.

The Corvair with IFB (Azalea photo)

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