Weight-shift control (WSC) aircraft come in an array of shapes and sizes, but the basic design features are fundamentally the same. All WSC consist of a flexible wing made with a sail fitted over a rigid airframe. A separate carriage is the fuselage which consists of the flight deck, propulsion system, and landing gear. [Figure 3-1]
Figure 3-1. Wing and carriage of WSC aircraft.
The Wing – Weight-Shift Control Aircraft
The wing has a structural frame that the sail fits over. Although the wing structure is rigid, it is designed to move and allow the sail to flex and the wing to deform or “warp,” to provide a simple control system with no pulleys, pushrods, hinges, control cables, or separate control surfaces. This simplifies maintenance and reduces the cost and weight of the wing. Each wing is built from high-quality aircraft parts including alloyed aluminum tubes, stainless steel cables, hardware, and specially designed sail cloth.
Wing Frame Components
The structural frame of the wing is composed of the leading edges, keel, crossbar, pilot control frame, king post and wires/ struts. The wing frame is a number of structural triangles formed by the wing components. These triangles, braced by wires and struts, provide a strong and lightweight frame to support the flexible sail. [Figure 3-2]
Leading Edges
Leading edges are tube assemblies that are at the front of the wing, the leading edges of the wing airfoil. These are swept back to form the front shape of the wing and attached to each other with nose plates. The leading edges support the airfoil and are designed to flex as part of the wing structure.
The leading edges are each made up of two main sections, an inboard and an outboard section, as shown in Figures 3-2 and 3-3. Additional tubing “sleeves” are typically used for added strength where the leading edge attaches to the nose plates, and where the inboard and outboard tubes join at the crossbar attachment. This sleeving can be internal or external depending on the specific manufacturer’s design. Typically, additional sleeving is used throughout the leading edges at various locations to strengthen and vary the flex for the particular design of the wing. Each manufacturer and make/model uses different internal and external sleeving to accomplish specific strength and flex characteristics. Generally, the inboard sections are stiffer and the outboard leading-edge section flexes as part of the flexible wing design. Sleeving is commonly added throughout the aircraft where bolt holes are drilled through the tubing to reinforce it around the bolt hole.
The outboard leading edge sections can be removed to pack up the wing into a “short pack” which is commonly used for shipping. [Figure 3-3]
Keel
The wing keel is like that of a boat keel, the center of the wing, fore and aft. It attaches to the leading edges at the nose plate and performs a number of important functions. It is the structure where the carriage attaches to the wing, and it is the wing structure that connects the center section of the sail at the “keel pocket” (discussed later in this chapter in the sail section). The control frame and king post (if so equipped) also attaches to the keel. It also provides structure for the upper and lower wires (if so equipped) and a reference or anchor for the crossbar which needs some movement in relation to the keel for roll control.
The keel is rigid and is not designed to flex nor is it highly stressed like the leading edges except where the undercarriage attaches to the wing. Sleeving is normally added to strengthen this middle area as well at the nose attachment and rear cable attachments.
Crossbar
The crossbar is two aluminum tube sections hinged above the keel that attach to the leading edges. The crossbar is tensioned back with the crossbar tensioning cables, which pushes the leading edges forward to conform to the sail. These crossbar tensioning cables are attached at the rear of the keel when the wing is tensioned into flying position. [Figure 3-4]
Figure 3-4. View looking inside left hand wing from the tip showing crossbar tensioned and pushing the leading edges into the sail. Notice the slight bending of the leading edges to fit into the sail (top). Crossbar tensioning cables attached to rear of keel in flying position detail. See specific location on airframe with figure 3-2. (bottom).
These crossbar sections are under a compression load and designed to be stiff with no bending. A larger diameter tube is typically used to avoid any bending when the wing is flying. A ding, dent, or bend in the crossbar could spell disaster during flight because it is one of the main structural members that holds leading edges into position during flight.
For wing take down and packing, the crossbar haul back cables are released, the crossbar hinged center moves forward, and the leading edges rotate in toward the keel about the nose plates and come together, allowing the wing to fold down into a long tube for transport and/or storage.
Control Frame
The triangle-shaped control frame serves two main purposes. It provides the lower structure for the wing and is the control bar for the pilot. The control frame is bolted to the keel with two downtubes extending from the keel attachment to the horizontal base tube, which is the pilot’s control bar. [Figures 3-2, 3-5, and 3-6]
Figure 3-5. Control frame corner bracket with wire attachments.
Notice the thick structural ⅛ -inch flying wires that support the wing and smaller 3/32-inch cables holding the control frame in place fore and aft.
Control frame corner brackets at the bottom of the downtubes provide the wing structural attachments for the flying cables or struts that attach to each leading edge/crossbar junction, and secure the control bar fore and aft to the wing with the front and back wires attached to nose plates and the aft section of the keel. [Figures 3-5 and 3-6]
Figure 3-6. Control frame with downtubes, control bar, and corner bracket with flying wing wires, and control frame fore and aft wires.
During flight, the downtubes are similar in compression to the crossbar and must be stiff and straight to maintain structural integrity. The base tube/control bar is under tension during flight.
Front and rear flying wires hold the control frame in place fore and aft. Side flying wires hold the control frame in place side to side and provide structure to hold the wings in place while flying. [Figures 3-2, 3-5, and 3-6] Strutted wings use struts in place of the side flying wires, which is discussed later in this chapter.
Training bars are added for dual controls so the person in back can fly the aircraft. These are typically used by an instructor for training but can be used by a passenger in the back also. [Figure 3-7]
Figure 3-7. Passenger using training bars which are also used by the instructor during training.
King Post With Wires-on-Top Wing Design
Similar to the lower control frame holding the wing in position during flight, the king post is attached to the keel and supports the upper ground wires which hold the wing in position on the ground and negative loads during flight. [Figure 3-2] It also provides a structure for reflex lines which is discussed later in wing systems.
Topless Wings With Struts
Similar to airplanes with struts to support the wings, some WSC aircraft replace side flying wires with struts, eliminating the king post and ground wires on top of the wing. This provides a number of benefits, but primarily, no king post is needed because the struts can take a compression load and hold the wings upon the ground and also take the negative loads during flight. With struts, a WSC aircraft is much shorter in height allowing it to fit into hangars with lower doors and ceilings. This can make a big difference in finding a suitable storage for the aircraft if leaving it set up. [Figure 3-8]
Figure 3-8. Strutted wing on WSC aircraft carriage.
Some strutted designs allow the wings to be folded back while still on the carriage. This can also be helpful when using a smaller space for storage by folding the wing up without taking it off the carriage. [Figure 3-9] It is also convenient for sea trikes since the aircraft does not have to be taken out of the water to fold up the wing.
Figure 3-9. A strutted wing folded back so it can fit into a trailer for storage and easy transport (top). Strutted wing with wings folded back for easy storage (bottom).
Strutted wings have a clean upper surface with no holes required for the king post or wires to go through the top of the sail. This reduces interference drag on the top of the wing. Increasing overall efficiency, no holes in the sail also eliminates any high-pressure leakage from underneath the wing getting sucked up to the lower pressure on top of the wing. [Figure 3-10]
Figure 3-10. Clean upper surface of strutted wing.
Sail Components
The sail is a highly refined design that integrates with its wing frame. Each sail and wing frame are designed for each other and are not interchangeable with other sails or wings. Modern sails are designed with complex geometry and sewn to precision to achieve a highly efficient design. Because of the flexibility of the wing frame and the modern techniques in sail design, the leading edge can have a curved shape which adds to the efficiency and stability of the wing. [Figure 3-11]
Figure 3-11. Curved leading edge sail design.
Battens and Leading Edge Stiffener
As discussed in the aerodynamics section, stiff preformed battens are the airfoil ribs that maintain the airfoil shape from the root to the tips. Additionally, a foam or mylar stiffener is inserted in a pocket at the leading edge to keep a rigid airfoil shape between the battens from the leading edge up to the airfoil high point. Double surface wings have additional ribs on the bottom surface that are straight or formed to maintain the bottom surface camber.
Sail Material and Panels
Sail material is a combination of polyester materials designed with different weaves, thickness, and orientation to fit the design mission of the wing. Panels are cut to different shapes and laid down at different angles to provide the stiffness and flexibility where needed for the specific wing design. Automated machines typically cut the fabric to precision tolerances and the panels are sewn together with high strength thread.
Pockets and Hardware
Pockets are added for battens and hardware is installed for the wing frame and wire attachments. Trailing edge line or wires are sometimes added for reinforcement and can be used for tuning. Battens are held in with a variety of batten ties or other methods unique to the manufacturer. [Figure 3-12]
Figure 3-12. Trailing edge of the sail showing reinforcement panels, trailing edge line, and batten ties with attachment hardware.
Sail Attachment to Wing Frame
The sail is attached to the wing frame at the nose and the tips. A keel pocket towards the back of the sail secures the sail to the wing keel. [Figure 3-13]
Figure 3-13. Keel pocket.
Cables and Hardware – Weight-Shift Control Aircraft
Cables are used throughout the wing frame and sail to hold components in place and act as structure to carry loads. Flight and ground cables are stainless steel and attach to components with tangs or other hardware depending on the application. Cables are secured at each end with thimbles and swaged fittings. Figure 3-5 shows detail of typical swaged fittings. A variety of hardware is used for attaching these swaged cable fittings to the airframe. Each manufacturer has different hardware for wing components. [Figures 3-14 and 3-15]
Figure 3-14. Crossbar tensioning junction attachment example.
Figure 3-15. View inside wing showing top wire coming though sail that is reinforced, being attached to the crossbar by a tang, an aircraft bolt, washers, and lock nut.
Wing Systems
Reflex Systems
As discussed in the aerodynamics section, the trailing edge near the root and the tips must stay up during unusually low or negative angles of attack [Figure 2-29] to maintain a positive pitch stability for the aircraft. There are a number of reflex systems used to accomplish this in emergency situations.
Figure 2-29. Emergency vertical dive recovery for a WSC wing.
Reflex cables—most wings with a king post use cables to hold the trailing edge up at unusually low or negative angles of attack. These reflex cables are secured to the top of the king post and attach to several positions on the trailing edge where the battens are located. Different manufacturers have different positions where these are attached, depending on the design of the wing. Refl ex cables also provide additional reflex at high speeds because the drag of the wires pulls up the trailing edge, creating more reflex at these higher speeds. [Figure 3-16]
Figure 3-16. Reflex cables.
Washout struts—tubes near the tips that keep the tip trailing edge up during very low or negative angles of attack. They can be inside or outside the double surface of a wing. The refl ex cables may not go to the wingtip, so washout struts are used to hold up the trailing edge at the tip at very low and negative angles of attack. [Figure 3-17]
Figure 3-17. Washout struts.
Sprogs—for wings using struts with no king post, sprogs are used to keep the inboard trailing edge up in place of the reflex cables. A wire attached to the top of the leading edge holds the sprog up in place. [Figure 3-18]
Figure 3-18. Sprogs for strutted wing.
Pitch Control System
The pitch control system is a simple hinge on the keel at the hang point that allows the pilot to push the control bar out and pull the control bar in to control pitch. This wing attachment is different for each manufacturer, but all designs have this hang point wing attachment so the control bar is always perpendicular to the longitudinal axis of the aircraft. This raising and lowering of the nose is the pitch control system for the WSC aircraft. [Figures 2-7 and 3-19]
Figure 2-7. Angle of incidence.
Figure 3-19. Hang point wing attachment.
Roll Control System
Control bar movement from side to side controls the roll about the longitudinal axis. The wing attachment hang point allows the carriage to roll around the wing keel. Thus, it can also be looked at from the carriage point of view, when the control bar is moved side to side, the wing rotates around the wing keel relative to the carriage. [Figures 2-31 and 3-19]
Figure 2-31. Pilot induced moments about wing/carriage hang point and resultant CG rolling moment.
It would first appear that moving the control bar to one side, thus shifting weight to the opposite side, could alone bank the aircraft. It is true that shifting weight to the right would naturally bank the aircraft to the right and put it into a right-hand turn. However, the weight alone is not enough to provide adequate roll control for practical flight.
As weight is moved to one side, the keel is pulled closer to that side’s leading edge. The actual keel movement is limited to only 1 to 2 inches each side of center. However, this limited keel movement is sufficient to warp the wing, changing the twist side to side (as discussed earlier in the aerodynamics section) to roll the aircraft [Figure 2-24] by changing the lift side to side. Simply, the shifting of weight from side to side pulls the keel toward the leading edge on that side and warps the wing to roll the aircraft.
Figure 2-24. Shifting weight to one side warps the wing by increasing the twist on the loaded side and decreasing the twist on the unloaded side.
Besides the keel shifting relative to the leading edges and crossbar, overall roll control is adjusted by the designers to fit the mission of the wing through sail material/stiffness, leading edge stiffness/flexibility, amount of twist, amount of travel the keel is allowed, airfoil shape, and the planform of the wing. [Figures 3-20 and 3-21]
Figure 3-20. Shifting weight to the right pulls the keel to the right (or lets the crossbar shift to the left) and increases twist on the right side for roll control.
Figure 3-21. Crossbar travel limiter.
Trim Systems
There are a number of trim systems to relieve the control pressures for pilots to fly at different “hands off” trim speeds. Ground adjustable trim allows the pilot to adjust the trim speed of the wing on the ground and remain at one speed during flight, while flight adjustable trim systems can change the trim speed in flight.
Ground Adjustable Trim Systems
The most common ground adjustable trim system, and typical of most aircraft, is moving the wing attachment hang point forward for faster trim speeds and aft for slower trim speeds. Each manufacturer has different hardware, but the basics of sliding the carriage wing hang point forward and backward on the keel is similar for all. As an example, moving the hang point at the furthest aft position to the furthest forward position could speed the wing up 20 knots. This in turn moves the control bar position back to a new “hands off” trim speed.
Another less commonly used method of increasing trim speed is to increase tension on the crossbar by pulling it back further, slightly increasing the nose angle and reducing twist. This increases the angle of attack (AOA) of the tips producing more lift, and it lowers the nose to a higher trim speed. This is a typical in-flight trim adjustment for high performance hang gliders. The roll control is diminished with this faster and stiffer wing.
Ground adjustable trim systems are described in the Pilot’s Operating Handbook (POH) for each aircraft. Different loads may require different pitch settings.
Inflight Adjustable Trim Systems
Being able to adjust the trim systems in flight has a number of advantages as discussed later in the flight sections. A number of inflight adjustable systems are available with different manufacturers. A common in-flight adjustable trim system is raising and lowering the trailing edge. Raising the trailing edge increases airfoil reflex and slows the wing. Lowering the trailing edge decreases airfoil reflex and speeds up the wing. Typically, a crank on a downtube controls a wire that runs up the downtube to the top of the wing. As a result of moving the crank, the trailing edge wires are raised and lowered and the trim speed changed. [Figure 3-22] Hydraulic or electrical systems can move the hang point on the wing for other inflight trim systems. [Figure 3-23]
Figure 3-22. A crank on the downtube of the control bar that adjusts the trailing edge reflex during flight.
Figure 3-23. Hydraulic inflight trim systems that move the hang point in flight controlled by the pilot.
Another pilot-actuated trim system in flight is an elastic system in which the pilot increases tension on the elastic system which raises the nose for climb and slower flight. [Figure 3-24]
Figure 3-24. More tension on elastic pulling down on the rear of the wing keel reduces the trim speed and is controlled by the pilot in flight.
Carriage – Weight-Shift Control Aircraft (Part One)
The carriage is a completely separate structure from the wing. Without the wing, the carriage can be driven around if needed. Most of the weight and cost of the WSC aircraft is in the carriage. There is a wide range of carriage designs from the most simple and basic open trikes to the more sophisticated and complex trikes that integrate cowlings and offer a number of adjustments for the pilot and passenger, resulting in comfort and less fatigue during flying. Generally, the more complex the trike, the more it costs, weighs, and the more power it requires for similar wings. [Figure 3-25]
Structure
Similar to the wing, the carriage is designed with a number of structural triangles for optimum strength and minimum weight. Each manufacturer and model have specific details that vary, but the carriage structure is typically a mast, keel, and front tube that form the main triangle components of the carriage structure with the wing attachment at the top of the mast. A seat frame attached to the mast and keel provides rigidity to the main components while providing structure for the pilot and passenger. [Figure 3-26]
Figure 3-26. Basic components of the carriage structure.
Landing struts attached to the rear wheels provide structure for the main landing gear, and a front fork provides the landing gear structure for the front wheel. An engine mount attaches to the mast, providing structure for the propulsion system to attach to the carriage. [Figure 3-26]
Landing Gear
The landing gear provides support to the WSC aircraft on the ground and absorbs the shock to reduce the stresses on the pilot and the aircraft during landings.
The landing gear is made up of the front wheel, which has a lighter load and is used for steering, and the main or rear landing gear, which takes most of the load for the aircraft. [Figure 3-26] The front steering fork for the nosewheel has foot rests attached that the pilot uses for steering the WSC aircraft on the ground. Besides ground steering, the foot controls are similar to driving a car, left foot pedal is brakes on the ground only, and right foot is throttle and power on the ground and in flight. [Figure 3-27] The front fork typically has camber so it naturally tracks in the direction of travel similar to a motorcycle front fork.
Figure 3-27. Large foot rests used for steering the aircraft on the ground (left hand ground brake shown).
For training, a second steering control is installed with a connecting rod so the instructor can sit in back and steer the carriage on the ground using the nosewheel. [Figure 3-28] Steering dampers are sometimes used to stabilize the front wheel from shimmying at higher speeds during takeoff and landing. [Figure 3-29] The front wheel sometimes has shock absorbers or the tire itself can act as the shock absorber. The front wheel typically has a disk or a drum brake, mechanical or hydraulic. [Figures 3-30 and 3-31] A front brake is lighter and simpler than rear brakes, but some carriage brake systems utilize the rear brakes.
Figure 3-28. Foot steering control for instructor in the back seat and connecting rod to front fork.
Figure 3-29. Steering rod damper.
Figure 3-30. Mechanical drum brake system.
Figure 3-31. Hydraulic disk brake system.
A parking brake is extremely useful for securing the aircraft on the ground without needing chocks for securing the aircraft before takeoff and after landing. A number of parking brake systems are utilized by different manufacturers. [Figure 3-32]
Figure 3-32. Mechanical parking brake system.
The main landing gear is the two rear wheels of the WSC aircraft. Since the center of gravity (CG) is much closer to the rear wheels, most of the weight for the aircraft is carried on the rear wheels for taxi, takeoff, and landings.
There are a number of different configurations for the main gear. A conventional configuration has two separate systems for each rear wheel. Each side is two structural triangles, one horizontal and one vertical. The horizontal triangle consists of a drag strut from the wheel forward to the keel or forward structure to maintain the wheel’s fore and aft position, and the main landing gear strut. Both the main and the drag struts can pivot about the attachment to the keel as part of the shock system.
Figure 3-33. Conventional landing gear configuration.
The vertical triangle consists of the main landing strut and the shock strut attached to the wheel and up to the keel structure [Figure 3-36] or other structure such as the engine mount shown in Figure 3-33, which houses the compressed nitrogen and oil “oleo” shock absorber.
Figure 3-34. Alternate vertical system utilizing streamlined wires and bungee cords.
There are a number of other main landing gear configurations and shock absorbing systems such as wire bracing with bungee cord shocks [Figure 3-34], fiberglass or flexible (fiberglass or steel) main gears with no struts [Figure 3-35], and any variation of these. Carriages designed for faster speeds may have streamlined landing gear systems. [Figures 3-36 and 3-37]
Figure 3-35. Solid flexible main gear.
Figure 3-36. Conventional landing gear with streamlined drag and main struts.
Figure 3-37. Solid flexible main landing gear that is streamlined.
As discussed in the nosewheel section, the carriage can have main landing gear brakes on both main landing gear wheels that can be drum or disk and controlled by mechanical or hydraulic actuation. Each manufacturer has different designs and options.
Tires can also assist as shock absorbers for landings. Large tundra tires add significant shock absorbing capability and are used for operations on soft fields, rough fields, and sand. [Figure 3-38] Generally, the faster WSC aircraft used for airport operations have narrower tires to eliminate drag.
Figure 3-38. WSC aircraft with large tundra tires for soft or rough field operations.
Carriage – Weight-Shift Control Aircraft (Part Two)
Landing Gear for Water and Snow
Besides landing gear for land, there are landing gear systems for water (Weight-Shift Control Sea) and snow (ski-equipped). If ski-equipped, skis are added to the bottom of the wheels or replace the wheels. If sea-equipped, a complete system provides aircraft flotation and steering using rudders similar to a boat. The water rudders are foot controlled, similar to WSCL steering on the ground. Two types of sea equipped systems are the flying boat and pontoon.
The flying boat is a solid or inflatable boat that the WSC aircraft fits into, and its fuselage is secured to as well. [Figure 3-39] This is generally used for rougher seas in the ocean and, with the extra drag of the boat itself, this typically uses a larger wing and is therefore a slower flying WSC aircraft. The boat design is known to be more stable in rough seas and assists in keeping less water from splashing up so pilot and passenger stay dryer.
Figure 3-39. Flying boat.
The pontoon system is used for calmer water, has less drag while flying, and therefore can accommodate faster, smaller wings. [Figure 3-40] Both the flying boat and the pontoon system need more horsepower than land operations for two reasons: first, to provide enough thrust to accelerate to takeoff speed with the extra drag of the boat or pontoons on the water, and second, to provide enough extra thrust to overcome the additional drag of the boat or pontoons in the air for flight.
Figure 3-40. Pontoon system.
Electrical Systems
WSC aircraft are typically equipped with a 12-volt direct current (DC) electrical system. A basic WSC aircraft electrical system consists of a magneto/generator, voltage regulator, battery, master/battery switch, and associated electrical wiring. Electrical energy stored in a battery provides a source of electrical power for starting the engine and other electrical loads for the WSC aircraft.
The electrical system is typically turned on or off with a master switch. Turning the master switch to the on position provides electrical energy from the battery to all the electrical equipment circuits with the exception of the ignition system. Equipment that commonly uses the electrical system energy includes:
- Position lights
- Anticollision lights
- Instrument lights
- Radio equipment
- Navigation equipment
- Electronic instrumentation
- Electric fuel pump
- Starting motor
- Electric heating systems (gloves, socks, pants, vests, jackets, etc.)
Fuses or circuit breakers are used in the electrical system to protect the circuits and equipment from electrical overload. Spare fuses of the proper amperage should be carried in the WSC aircraft to replace defective or blown fuses. Circuit breakers have the same function as a fuse but can be manually reset, rather than replaced, if an overload condition occurs in the electrical system. Placards at the fuse or circuit breaker panel identify the circuit by name and show the amperage limit.
An ammeter may be used to monitor the performance of the electrical system. The ammeter shows if the magneto/ generator is producing an adequate supply of electrical power. It also indicates whether or not the battery is receiving an electrical charge. A voltage meter also provides electrical information about battery voltage, an additional status of the electrical system.
Ballistic Parachute
An additional safety system available is a ballistic parachute system. In the case of a structural failure because of a mid-air collision or an engine out over hostile terrain such as a forest, the ballistic parachute provides an added safety system. The parachute is sized so that when used, the complete aircraft comes down under canopy. Details of ballistic parachute system use are covered in more detail in Chapter 13, Abnormal and Emergency Operations.
When the system is activated, a rocket shoots out, pulling the parachute system to full line stretch, and forcing the parachute out and away from the carriage and wing.
Figure 3-41. Located under the pilot’s legs, the canister will blow through the break-away panel in the cowling.
The preferred point of attachment for the parachute is on top of the wing at the hang point. This allows the WSC aircraft to descend level and land on the wheels, helping to absorb the shock. This requires routing from the chute to the top of the wing with “O” rings to be able to remove this routing to easily take the wing off the carriage. Alternate attach points where there is no routing to the top of the wing are the mast and engine attachment points; however, this has the WSC aircraft descending nose down when activated.
Figure 3-42. Canister mounted under engine.
The ballistic parachute canister can be mounted in a number of locations on the WSC, typically on the carriage pointed sideways to avoid entanglement with the propeller. The actuation handle is mounted in the flight deck for pilot use when needed. [Figures 3-41 and 3-42]
Flight Deck – Weight-Shift Control Aircraft (Part One)
The flight deck is where the pilot and passenger sit. It is typically a tandem seating with the pilot in front and the passenger in back. When the WSC aircraft is used for instruction, the instructor typically sits in back and must have access to the flight controls.
The pilot in the front has ground and flight controls. The right foot controls a foot throttle and the left foot controls the brake. This is similar to throttle and brake controls on an automobile. The feet also control ground steering by moving the front fork with the foot pedals. A foot throttle and foot brake can be added to optional ground steering control for use by an instructor sitting in back.
A hand cruise throttle is typically used when the pilot can set it and it stays set. This cruise throttle is usually in a position where the instructor in the back seat can also operate it. [Figures 3-43]
Figure 3-43. Cruise throttle control and ignition switches.
The wing flight control bar is in a position at chest height for the pilot in the front seat. Additional extensions are added for a passenger or instructor to use if seated in the back seat. [Figure 3-7]
Figure 3-7. Passenger using training bars which are also used by the instructor during training.
Ignition switches are sometimes included in the cruise control throttle housing or as a separate set of switches. If a WSC is used for instruction, the ignition switches should be within reach of the instructor sitting in the back seat. [Figures 3-43]
The ballistic parachute handle must be accessible for use when needed but not put in a position where it could be accidentally deployed. Some WSC aircraft have two handles, one for the front and one for the back. Additional controls for starting, such as the choke or enricher, must be accessible to the pilot.
Dashboards and Instrument Panels
The instrument panel is in front of the pilot and provides engine, flight, navigation, and communications information. The pilot is responsible for maintaining collision avoidance with a proper and continuous visual scan around the aircraft, as well as monitoring the information available from the instrument panel. The pilot must process the outside cues along with the instrumentation throughout the flight for a sound decision-making process.
The ignition switches, which may be located on the instrument panel or within the instructors reach for WSC used for instruction, has two positions: ON, which allows power to make contact with the spark plugs, or OFF, which is a closed switch to GROUND and removes the power source from the spark plugs. Typically, WSC engines have two spark plugs per cylinder, two switches, and two completely separate ignition systems. Some single-place WSCs with smaller engines have only one spark plug per cylinder, one ignition switch, and a single ignition system.
For example, for a two-stroke liquid-cooled engine, the manufacturer may require instrumentation to monitor engine exhaust gas temperatures (EGT), water temperatures, and revolutions per minute (rpm). Additionally, for a four-stroke engine, the manufacturer may additionally require oil temperature and pressure gauges. For a simple two-stroke air-cooled engine, the manufacturer’s requirement may be EGT, cylinder head temperature (CHT) and rpm instrumentation. Generally, most electrical or engine controls are located on the dashboard unless required to be reached by the instructor for flight instruction.
Dashboards are as varied as the manufacturers and the purpose of the aircraft, from simple to complex. Classical analog gauges are common, but digital instruments are becoming more popular with light-sport aircraft (LSA).
Overall, no instrumentation is required for E-LSA, but for S-LSA an airspeed indicator is usually required, and engine manufacturers require certain instruments be installed on the aircraft to monitor the performance of the particular engine.
Flight Instruments
The specific theory of operation and details of instruments is covered in the Pilot’s Handbook of Aeronautical Knowledge, and is a prerequisite to this section on flight instruments. The altimeter is the most important flight instrument and should be on every WSC aircraft. It is used to maintain the proper altitude at airports, during cruise, and provides other aircraft position information for the safety of all.
The vertical speed indicator (VSI) is one tool to assist the pilot with the performance of the aircraft. The airspeed indicator (ASI) is used to optimize performance of the aircraft, compare predicted to actual performance, and to operate within the limitations of the aircraft.
Navigation Instruments
A global positioning system (GPS) is typically used as a navigation and flight aid for most WSC aircraft. A magnetic compass is commonly used as a primary navigation system or as a backup when a GPS system is used.
Engine Instruments
There is a variety of engine instruments that are used. The most basic is the engine rpm, which determines the power of the engine. Specific engine instruments are discussed in the powerplant section.
Instrument Panel Arrangements
Instrument panels vary greatly from the basic to the complex. Figure 3-44 depicts a standard instrument panel supplied by the manufacturer with a portable GPS added in the middle. Electrical components are neatly arranged along the top. Large analog airspeed (left) and altitude (right) flight instruments are installed in the middle with the portable GPS installed between the two. The bottom stack consists of the basic engine instruments for a simple two-stroke air-cooled engine: RPM for power (top), CHT (middle) and EGT (bottom).
Figure 3-44. Basic analog flight and engine instruments.
A more advanced analog panel with a user radio and GPS added is shown in Figure 3-45. Airspeed, vertical speed indicator, and altitude large flight instruments are along the top. A navigational gyro is in the middle of the panel. The bottom row consists of four-stroke engine instruments, electrical and remote fuel gauge. The user installed radio and GPS complete a well equipped instrument panel. A hybrid panel of analog, digital, and portable instruments is shown in Figure 3-46.
Figure 3-45. Full analog instruments.
Figure 3-46. Instrument hybrid—analog airspeed and compass indicator with separate digital instruments.
The integrated digital panel does provide more options in a smaller space. One panel can now have aircraft performance screens, engine systems screens, navigation screens, communications screens, attitude indicator, and any combination of these. [Figure 3-47]
Figure 3-47. Digital instrument panel.
Communications
There are three types of communications systems used in WSC aircraft:
- Communications between the pilot and passenger while inside the aircraft.
- Aircraft radio communications with other aircraft and control towers.
- Radar position indicator communications from the WSC aircraft to control towers (transponder).
Easy and clear communications between the pilot and passenger, or between the instructor and student inside the flight deck is important for the safety and enjoyment of both. Modern communications systems have advanced noise canceling systems in headphones and microphones to reduce engine noise and blast of air. Each system is unique, and the quality of the sound and noise canceling capability of the system varies. Some use voice-activated systems in which headphones activate only when someone is speaking into the microphone; others have a steady state in which there is no additional control of the voice activation. Since there is a large difference in systems available, it is best to test systems to determine what is best for the WSC aircraft being flown. [Figure 3-48]
Figure 3-48. Basic pilot-to-passenger communication system.
An aircraft radio is required for flying in any tower controlled airspace. Using a radio is not required at airports without a control tower but it is recommended for the safety of self, passengers, pilots in the air, and people/property on the ground. To broadcast to a tower or other aircraft, press a Push To Talk (PTT) button. A complete flight deck radio and accessory system schematic is shown in Figure 3-49.
A radar signal receiver/transmitter system is required at busy commercial airports (Classes C and B) and at altitudes above 10,000 feet mean sea level (MSL) (unless the aircraft was certified without an electrical system to power the unit). This is known as a Mode C transponder that sends a signal giving the control tower an exact location and altitude of aircraft. [Figure 3-47]
Flight Deck – Weight-Shift Control Aircraft (Part Two)
Powerplant System
The powerplant system is composed of the fuel system, engine, gearbox, and propeller. Here we will point out the basic components of these systems with their function and details covered in Chapter 4, Powerplant System.
Fuel System Components
The WSC aircraft is equipped with fuel tanks usually ranging in capacity from 5 to 20 gallons. As with any aircraft, knowing how much fuel the tank holds is crucial to flight operations. The LSA definition has no limitations on the size of the fuel tank, unlike its ultralight vehicle predecessor.
Figure 3-50. Fuel tank with visible fuel quantity.
Generally, the fuel tank is located close to the CG, so fuel burn does not affect the balance of the carriage. Some fuel tanks are clear for visual inspection of the amount of fuel on board [Figure 3-50], while others have tanks that are not visible and require fuel level probes for instrument panel indication of fuel. [Figure 3-51]
Figure 3-51. Fuel fill to fuel tank under passengers seat.
Fuel lines exit the fuel tank, and may incorporate a primer bulb, fuel filters, fuel pump, and/or a primer system, all of which must be integrated into the carriage. A fuel venting system is also required, which can be a hole in the fuel filler or lines running to vent at an appropriate location.
A fuel shut-off valve may be installed and can be located anywhere in the fuel line. Some designs have a fuel tank sump drain valve to remove water and solid contaminants.
Engine and Gearbox
The typical WSC aircraft engine can be two or four-stroke, liquid or air-cooled, and normally ranges from 50 to 100 horsepower. Some engines have electric starters and some have pull starters. Most WSC aircraft engines have reduction drives that, when attached, reduce the propeller rpm from ½ to ¼ the engine rpm. [Figure 3-52]
Figure 3-52. Engine gearbox.
A significant amount of the total aircraft empty weight is determined by the powerplant (engine, gearbox, and propeller) and mounting configuration. When trailering the WSC aircraft over bumpy terrain or over long trips, the bouncing of the carriage in the trailer can put extreme stress on this mounting system. In addition, repeated hard landings of the carriage can also stress the welds of the engine mount. Consistent detailed inspections of the engine mount should be an important part of every preflight and postflight inspection.
The powerplant systems are as varied as the WSC aircraft they power. Modern technology has allowed these systems to become lighter, quieter, more efficient, and, most importantly, dependable.
The Propeller
Propellers are “power converters” that change the engine horsepower into thrust. Thrust is the force that propels the aircraft through the air by pushing the WSC aircraft forward. Aerodynamically speaking, a propeller is a rotating airfoil and the same principles that apply to the wing applies to the propeller, except the propeller provides a horizontal force of thrust.
Figure 3-53. Four-blade propeller.
Propellers typically consist of two, three, or four blades. [Figures 3-53 and 3-54] Propellers can be ground adjustable or fixed pitch. Variable pitch flight propellers are not allowed on LSA. The pitch should be properly set for your WSC aircraft to provide the recommended rpm of the engine at full power. The POH should be consulted if there is any question about the propeller rpm and adjusting or replacing the propeller. Propellers are specifically matched to the engine power, gear reduction and speed range of the aircraft. Therefore, not just any propeller may be put on any engine. The POH requires specific propellers that are matched for each aircraft.
Figure 3-54. Three-blade propeller.
As with an airplane propeller, the WSC aircraft propeller turns at such high speeds that it becomes invisible when in motion. The dangers of a turning propeller require every pilot to maintain the highest level of safety and respect for the consequences of body parts, pets, and debris coming in contact with a rotating propeller. Debris on the takeoff/ landing field is a danger to the propeller, as well as to the people who may be in the prop-wash area behind or on the side of the propeller. Stones, small pieces of metal, and sticks can become dangerous projectiles if kicked into the propeller during start-up, taxi, takeoff, and landing. Just as with any airframe or wing component of a WSC aircraft, if the propeller becomes damaged, nicked, or dinged, the aircraft’s performance can be greatly affected. Some pilots elect to use tape or rock deflector guards to protect the leading edge from rock/debris damage. Regardless, taking proper care of the propeller is as critical as proper engine and wing care.
