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.
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]
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]
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.
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.
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.
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.