Homebuilt Experimental Aircraft, III

Building your own homebuilt, experimental aircraft means dedicating a huge amount of time, perseverance and resources into your aircraft 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.

But when your aircraft is finished and knowing that you are the one that has built this with your own two hands, the smoking start of the engine running for the first time, initial taxi and test runs and then the exiting first flight before flying off between the clouds into the sunset...makes it really all worth your while!

Aircraft usually need some type of power to get them in the air and remain flying. Gliders get themselves in the air by either a towing airplane in front of them or through a winch and cable, after which they use thermals trying to delay the inevitable return to mother earth. Us guys in powered airplanes use an engine with a propeller and some maybe even an exotic turbofan.

Aircraft Engines

Engines come in all kinds of shapes and sizes. Most common types are: 4, 6 and 8 opposed cylinders from Lycoming or Continental, Rotax, Jabiru and Subaru engine types. Radial engines like the 7 or 9 cylinder Rotec (a very impressive piece of work). Diesel engines running JET-A can also be seen on the platform. The smaller two stroke engines from Rotax or Hirth are usually installed in small ultralights.

The TBO (time between overhaul) is determined by the manufacturer and is usually around 2000 hours. JET engines have a much higher TBO, ranging from 3500 hours and higher.

The power of aircraft engines in this class is usually between 80 Hp and 180 Hp (for the small two place types) and between 200 and 350 Hp for the larger four seat Lancair type of aircraft. Exception is the Murphy Moose which has a nine cylinder radial engine with 360 - 400 Hp.

Compression Ignited Engines

Also known as diesel engines. They are capable of running on diesel, JET and biodiesel fuel. A bit heavier built due to stronger torque pulses in the engine but as they have a higher efficiency than gasoline engines their range is improved and with no special ignition system they are more reliable. A number of diesel engine manufacturers are busy in this field.

Spark Ignited Engines

These are your everyday AVgas engines: Lycoming, Continental to name a few. Technology from early last century as they use a dual magneto system to ignite the fuel / air mixture. Modern avgas engines use electronic ignitions and are even microprocessor controlled (FADEC).

Engines with a turbo compressor

Basically, turbos are exhaust gas driven air compressors. This compressed (and warmed) air is then fed into the intake of the engine, sometimes through an intercooler. The advantage is that energy (heat and speed) in the exhaust gasses are used which would otherwise have been lost in space.

This principle can be used two-ways: add more air (pressurize the intake) or keep the pressure of the air in the intake manifold at a preset value. The first type is called turbocharging and the second turbo normalizing. With turbo normalizing the intake is kept at a constant sea level pressure (30") regardless of altitude (or until the system reaches its limit).

This imposes a lot less stress on the engine compared to turbocharging. With turbocharging the intake is usually pressurized to 39-40" MAP (there are exceptions), more air means that more fuel can be added and the engine will produce more power. This overboosting is time limited, usually 1-5 minutes, depending on engine design.

Diesel engines usually have a turbo compressor to create even more power.

Electric Engines

There is some active development to power very light aircraft and gliders with an electric motor. The firm Pipistrel (see: http://www.pipistrel.si) is test flying with a glider. Hopefully, when solar cells obtain a much higher yield (about 16% now), it should be possible to exclusively run on electric power by recharging the onboard batteries through the solar cells on the wings, even while flying!

Another flying example of electric powered airplane is the Electra Flyer, this is a single seat aircraft build by Electric Aircraft Corp. It has a 18 hp electric motor and cruises at 70 mph, stalls at 45 mph with a duration of 1 to 1,5 hours. Climb rate with a two bladed prop from Powerfin is about 500 - 600 ft/min. The electric engine draws its power from a 78 lb rechargeable lithium polymer battery of 5.6 kWh.

Flightstar has successfully completed flight tests with the e-Spyder which is driven by a 20 kW (26,8 hp) electric motor with an engine controller and lithium batteries developed by the Chinese firm Yuneec. It will take at least 7 years of development (2010) before electric aircraft wil have the same endurance as fuel powered aircraft, about 4 h.