Flaps, Ailerons, and Flaperons
Full span ailerons, which also act as full span flaps, are thus used (called flaperons). The full span provides maximum high lift (flaps) for the entire wing and roll controllability (ailerons) at a minimal weight since both functions are shared by the same control surface (flaperon), with a simple mechanical ‘mixer’ controller.
We all know that close to the airfoil, the air is slowed down by friction. This slowed down layer of air is called the boundary layer. The boundary layer builds up thicker when moving from the front of the airfoil toward the wing trailing edge. Another factor is called the Reynolds effect, which means that the slower we fly, the thicker the boundary layer becomes. Friction and the Reynolds effect result in an approximately ½" thick boundary layer toward the rear portion of a 4 to 5 ft. chord wing designed to fly at low speeds.
A conventional flap or aileron thus would have 1 or 2 degrees of deflection with very little control effectiveness because it deflects in this not very aerodynamically active boundary layer. To avoid this loss of controllability, the flaperon can be designed as a separate small wing, moving outside of the wing’s boundary layer and slipstream. Additionally, such a flaperon system (often called a "Junker" flaperon) is effective even at high angles of attack because it is positioned below the wing and thus continues to get ‘fresh’ undisturbed air even when the wing is at the extreme angle of attack (see Figure 8).
Figure 8 – Boundary Layer
Horizontal Tail
Also, because a high lift wing is designed to fly at an unusually high angle of attack (30 degrees compared to 15 to 17 degrees for a conventional wing) we need to achieve this high angle by pushing the tail down much more than with a conventional wing. Short of building a very large horizontal tail, we need a large negative lift coefficient on the tail. This is achieved first with an inverted stabilizer airfoil, and secondly with a virtual venturi. Let me explain: From an aerodynamics standpoint we know that a venturi provides lower pressure and higher speeds at the smallest section, as illustrated in Figure 9.
Figures 9, 10 & 11 – Venturi
The increased speed will overcome the tendency of separation when the flow is deflected. We also know that when we have a half venturi (Figure 10) the airflow creates a mirror image and follows the principles of a complete venturi (Figure 11), and thus the increased speed from the venturi effect follows the elevator of the horizontal tail even when deflected in the trailing edge down position (thus the virtual venturi effect).
Rudder
I’ve used the all-flying vertical tail (rudder) on my STOL designs that I’ve used on many of my earlier designs because it provides exceptional crosswind capability. With a STOL design, when the crosswind is higher than the aircraft’s stall speed (this actually happens!) you can just face the airplane into the wind and literally take-off vertically (even if you have to face across the runway)! Another advantage of the all-flying vertical tail is that it is physically smaller (and shorter) than a corresponding conventional fin and rudder vertical tail, and thus lighter; and being a single piece it is easier to construct. It also provides excellent spin recovery capability because the actual moving part (rudder) is larger. The rudder itself is an actual symmetrical airfoil (and not just a flat ‘board’), helping to make it effective and responsive even at lower speeds.
The main wings of the STOL designs taper at the wing root to allow undisturbed air to flow from the propeller to the empennage (tail sections). The position of the tail above the fuselage, with the direct undisturbed air from the prop, provides excellent and responsive control from the tail sections, compared to the sluggish response a conventional configuration provides at slow flight.
Short take-off / Landing
To best achieve short take-off performance, the wing’s high angle of attack must be achieved at or near the ground, and we thus need a general aircraft configuration that permits this high angle of attack. We can do this either by using a very long main gear in tailwheel configuration (raising the nose) or by raising the rear fuselage (in tricycle gear configuration).
Figure 12 – Landing Gear Configuration
With the taildragger configuration, the whole cabin is awkwardly inclined on the ground, and the long gear legs mean that the landing gear structure is either weak or heavy. The inclined cabin and high gear make access to the cabin difficult, especially for passengers or cargo loading, and can severely limit the pilot’s forward visibility while on the ground (taxiing and take-off).
Figure 13 – Cabin Angle
Most pilots today are much more comfortable (and safer) with a tricycle gear configuration, as nearly all trainers are tricycles. A tricycle gear is very stable on the ground, whereas a taildragger gear is not and needs continuous control input, especially in crosswind conditions. Aircraft insurance rates reflect this.
In a tricycle gear configuration, the wing is at a "neutral" angle of attack while the aircraft is on the ground, as opposed to a maximum lift angle with a taildragger (see Figure 12). Tailwheel airplanes are thus much more susceptible to the wind while taxiing the aircraft, or even while parked outdoors (this will be where the aircraft will spend the vast majority of its life, unless hangared).
Despite the many advantages of a tricycle gear system, many older aircraft designs (as well as many modern STOL designs) use a tailwheel configuration – this is mainly because the technology and expertise did not exist to build a lightweight and strong nosewheel system, and many designers today have little experience (or interest) in landing gear structures.
Off-airport operation dictates that a STOL aircraft have a durable and forgiving landing gear system. Landing gear systems seem to be a major weakness on many light aircraft designs, requiring that these aircraft be operated from paved runways, despite their capability to take off and land in short distances. 
Figure 14 – Landing Gear
With my STOL designs, I have used a simple single-piece double cantilever spring leaf for the main gear. While it’s not the lightest gear system around, it provides excellent rough-field capability when combined with large tires, and is very durable, simple and virtually maintenance-free. The nosewheel strut is steerable, with direct linkage to the rudder pedals, and uses a single heavy-duty bungee for shock absorbency. The STOL CH 801 borrows the nosegear assembly from the ZENITH CH 2000, my type-certificated production trainer design. The main wheels are also equipped with individual hydraulic disk brakes (activated with toe brake pedals) for exceptional ground handling. Experience has shown these landing gear systems to be well-suited for grass field operation, while being appropriate for low-time pilots. (Nosewheel system wear is minimized by reducing the pressure on the nosegear by using the appropriate elevator inputs – the effectiveness of the elevator makes this easy with my STOL designs).
FUSELAGE
The rectangular cabin offers maximum usable space for occupants and cargo. The 4-seat STOL CH 801 cabin is long enough to fit a stretcher along the right side of the aircraft across the folded co-pilot seat, while still providing adequate space for the pilot and one passenger, or two 50-gallons drums can be carried in the rear. Of course, for those using the STOL CH 801 as a sport utility plane, there’s enough room inside for two to camp in, and more than enough baggage area for extended cross-country trips. The two-seat STOL CH 701 is surprisingly roomy for an aircraft it’s size and weight.
The large doors offer easy access to the cabin for occupants and bulky baggage, and the aircraft can be operated with the doors removed for maximum visibility and ‘outdoor’ feel.
While it’s maybe not the most aesthetically pleasing, the square fuselage is very simple to build and helps to provide good yaw stability and spin dampening (resistance) due to its flat sides and distinct corners.
CABIN / VISIBILITY
Pilot and passenger visibility is an important element of aircraft design, and is often overlooked by designers. Good visibility is especially important in a STOL aircraft – where the pilot needs to be able to see obstacles when "bush" flying. Passengers also need good visibility to enjoy "low and slow" flying – they don’t want a small window the same size as in a commercial jetliner.
While an open cockpit provides unobstructed visibility, bugs, wind, and cold air all dictate an enclosed cockpit for a modern aircraft - to provide a minimum level of comfort that we’ve grown accustomed to. An enclosed cabin also allows for good ventilation and heat, and protects avionics and baggage. Large doors provide easy access to the cockpit (and can be removed for better visibility and "ventilation")
A high-wing configuration provides the best downward visibility to enjoy the views provided by low and slow flying, and provides the pilot with the required visibility to be able to safely operate into unimproved areas – to be able to see and avoid obstacles. With my STOL designs, I’ve used an "above-cab" wing position, where the wing is located above the cabin. This design feature maximizes visibility for a high-wing configuration: Horizontal visibility is augmented by raising the wing over the pilot’s head, and upward visibility is achieved by decreasing the wing thickness at the inboard end where it meets the cabin, and the top of the cabin can thus be fitted with a full window. A ‘skylight’ provides important visibility to the pilot in a highly maneuverable aircraft.
Figure 15 - Visibility
The tapered wing root and top window provide good visibility in turns. The wing design minimizes the frontal area in the propeller slipstream for increased performance, and also provides direct prop blast to the tail sections for superior controllability in slow flight.
The additional benefit of this tapered "above cab" wing configuration chosen for visibility is also its smaller frontal area, which means less drag (a faster airplane with the same amount of power) and excellent controllability at low speeds because the air is directed without disturbance from the propeller to the tail.
As with most modern aircraft, I’ve chosen a side-by-side seating arrangement to maximize pilot and passenger comfort. Throughout, the cabin is ergonomically designed for pilot productivity, comfort and flexibility. The STOL CH 801 cabin interior is designed to provide comfort for four large adults, while being easy to convert for cargo-carrying applications. Large doors on either side allow easy access to the cabin from both sides. The adjustable front seats fold forward for easy access to the rear seats / cargo area. With anticipated applications for mission use, the rear seat area can be converted for cargo use (included 50 gallon drums), or the cabin can be reconfigured for a berth (patient on a stretcher) across the front and back right-hand seats, with the pilot in the front left seat and a doctor or nurse in the left rear seat. Recreational pilots can literally camp out of the STOL CH 801.
All-Metal Durability
Bush planes need to be rugged, reliable and simple to maintain. "Field maintenance" takes on a new meaning where the pilot literally needs to be able to perform basic maintenance and repair functions in the field.
Both the STOL CH 701 and STOL CH 801 are built of all-metal construction. I have over 30 years experience designing and building all-metal aircraft, and there is more than 60 years experience in the industry with stressed-skin, semi-monocoque construction. Far from being obsolete, metal (aluminum alloy) construction continues to dominate as manufacturers’ choice of construction. Aluminum alloys provide the following benefits:Low weight / high strength relationship;
Corrosion resistance, especially with newer alloys and modern primers;
Low cost and widespread availability;
Proven durability, and resistance to sun and moisture exposure
Existence of vast amounts of empirical data on its properties
Easy to work with: requires simple tools and processes, and does not require a temperature-controlled or dust-free environment, as with composites. Modern blind rivet fasteners have greatly simplified all-metal kit aircraft construction;
Malleability: easy to form into many shapes, with almost no limit to the shapes it can be formed into;
Environmentally friendly: no health hazards to worry about when working with sheet metal; recyclable;
Easy to inspect: construction or materials flaws are easily detected, as are defective parts and damage.
Simple to repair: rivets and fasteners can be easily removed to replace damaged parts or sections, and individual parts can be replaced without having to replace or rework an entire airframe section.
Thus, aluminum-alloy construction provides the best airframe for a bush plane: 1) Suitable for continuous outdoor storage; 2) Durable and rugged, and; 3) Easy to inspect, maintain, and perform field maintenance. For example, a simple sheet-metal patch can easily be blind riveted onto a damaged area to fly the airplane home.
A well-designed sheet-metal aircraft also provides superior crashworthiness, as an impact’s energy is absorbed by progressively collapsing (deforming) the metal structure, as opposed to splintering or shattering upon impact. The landing gear of my STOL aircraft absorbs a lot of energy. It then requires more energy to "rip" it out, and the aluminum stringer frame and stressed-skin construction then need much more energy to start to bend, buckle and twist. The sturdy "cabin frame" will protect the occupants even in an unlikely nose-over of a tricycle gear airplane where the wings, positioned quite a bit higher than the occupants’ heads, will absorb the impact’s energy. Another important advantage often overlooked is the inherent lightning protection that a metal airframe offers.
As an aeronautical engineer, it’s easy for me to design a complicated aircraft, and much more challenging to design a simple one. For a kit aircraft to be successful, it must be relatively simple in terms of construction, assembly and systems: Not only is a simple design easier and more affordable to build, but it will be well-constructed by the amateur builder, as there will be less opportunity for errors or poor workmanship. With a simple design, building time will be lower, and less tools and skills will be needed to put the aircraft together, equating to much higher completion rates than complex projects, and once completed, the aircraft will be easier to operate and maintain. Simple systems maximize reliability, while minimizing pilot workload. With 24 years experience designing and making kit aircraft for amateur builders, we’ve learned to develop aircraft specifically for the amateur builders and sport pilots, offering them complete kits that are quick and easy to build, with minimal tools and skills.
With form following function, my two STOL aircraft designs have an inherent beauty that is more than skin deep once one understands the aerodynamic and construction features that have gone into these designs, making them highly effective short take-off and landing aircraft, while being simple to build and maintain, and providing excellent durability and flexibility.
The STOL CH 701 offers excellent off-airport performance in a lightweight and very economical two-seat design that is easy and fun to fly, while the new STOL CH 801 is a true sport utility vehicle, with 1,000 lbs useful load. 
Actual photo of a short take-off!
As a designer, it is truly rewarding to see how my designs have been put to use around the world, whether for mission or relief work in remote areas, or a recreational pilot writing me that the plane ‘takes off like a cork out of a champagne bottle
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