Homebuilt Experimental Aircraft, IV
Building your own homebuilt aircraft means dedicating a huge amount of time, perseverance and resources into your personal project. Do not think that this can be done without too much trouble, it will not. It will take a lot of effort, time and dedication to finish.
Propellers create thrust from the power of the engine thereby moving the machine forward and in doing that the engine uses fuel from the fuel tanks. And this process is our subject here.
The power from an engine, be it an AVgas or diesel, must be transformed to useful thrust. Or else there isn't much flying going on. Propellers are used for that purpose. They come in two, three and more blades and can be made from metal, wood or composites. This depends (among other things) on the designer or on how much power, torque and RPM the engine has.
Fixed or controllable
Propellers can be fixed (for climb or cruise purposes) or adjustable (ground or during flight). Adjustable propellers have an advantage over fixed types: they can be set for start, climb and cruise RPMs. Constant-speed propellers keep the preset rpm constant relieving the pilot from this task.
These propellers are controlled by either an electric motor in the spinner or a cylinder actuated by oil pressure from the engine. The electric types can be made rather sophisticated by a microprocessor controller with settings like: feather, take-off, cruise, climb, manual control and hysteresis function. All values can be set by the pilot for the right conditions.
Choosing the right propeller for your aircraft is a difficult task as a number of variables, like engine RPM, torque, power, noise limitations (regulatory) type of aircraft (its ideal cruise and climb speeds) influence each other so that usually the chosen propeller design is a compromise of all these variables.
Read more about this subject in our propeller section.
Aircraft Fuel and Fuel system
Piston powered aircraft generally consume AVgas, aviation gasoline. It is like a high octane auto gas, only more expensive (in Europe about 10 USD/gallon), high lead (despite its LL, low lead, designation) and it is more controlled and more stable. Problem is that the future of AVgas is not certain. No surprise that diesel engines are getting more and more popular. These engines can use JET-A(1), road diesel, agricultural (red) diesel and even biodiesel is possible.
Small airplanes like the Pelican PL, Zenair types and the likes mostly have a Rotax 912, 912iS or the 914 turbo engine capable of running on Mogas. Much cheaper but not certified and the fuel is not controlled the way AVgas is. The composition of Mogas can vary daily but AVgas hasn't changed in the last decade or two. There are also some issues with bio-alcohol in Mogas.
That being said, I have been flying for years with Mogas and found no real issues apart from the alcohol in some type of aircraft.
Usually, high wing models like your average Cessna, Murphy etc. have a fuel tank in each wing. Aluminum fuel lines run then to a fuel selector in the cabin with Left, Right, Both (not always) and Off selections. The Cessna 150/2 has a On, Off type of selector and both tanks feed the engine at the same time. Fuel is gravity feed and sometimes a low pressure fuel pump is added to aid starting and used when switching tanks during flight and on take-off and landing.
Low wing models normally would have a tank in each wing, fuel selector in the cabin and have an separate electrical fuel pump. Gravity feed is more difficult as the wing (and fuel) sits lower than the engine and the pump needs to push the fuel to the engine. There are some type of aircraft (Lancair has one) that have an extra header tank behind the instrument panel.
Some aircraft have extra or auxiliary tanks in the wings or fuselage enabling them to fly extended ranges or for longer times. Fuel in these tanks is pumped to the main tanks via extra fuel pumps. More to be found in the fuel management section.