i took the agk yesterday. and i got it 80. but there are a few questions that i havent seen in the book. such as

1)what is fuel ice?

2)what is purpose of the "run down" procedure a) for lubrication b) release pressure c)wastegate closed...( i forgot the rest of the answers).

3) switching off the magneto : primary circuit grounded or secondary circuit grounded

4)the definition of the fuel/ air mixture . weight of fuel or air into cylinder. am i correct??

5) if the mechanical fuel pump fail, will the boost pump provide sufficient pressure into the cylinder?

Hi Dennis,

Fuel ice is a type of icing that occurs through the vaporization process during the mixing with air within the carby. Basically, it's a release of Latent heat chilling the air. Combined with the venturi effect, it makes up what we know as Carby Ice.

Run down procedure applies to turbocharged engines. Turbos take usually around 5 minutes to slow down and cool down after flight. The run down procedure is there to keep circulating oil through the bearings for lubrication and cooling.

Switching off the magneto grounds the primary circuit. Secondary circuit is always grounded through the coil from memory.

Feul/air mixture is the ratio of an amount of fuel is mixed with a an amount of air for combustion to occur within the cylinder. It can be expressed as a weight depending on which book you're reading at the time but they are all referring to both fuel and air.

The Boost pump provides sufficent pressure to the engine's fuel delivery system such as the Carby or Fuel injection system, not directly to the cylinder. With the expection of fuel injectors, the only part of the fuel system that feeds directly into the cylinders are primer lines. They only supply a given amount and only while you are pumping it.


Hope this helps.

Regards,
Mister W.

Thanks mister.
I don't understand what is the primary circuit and secondary circuit? Are they regarding with the impulse coupling?
And one more question that I don't understand, in the dry sump engine, the little high temperature gauge associate with the low pressure , what is the problem of the engine? The engine pump goes fail or The screnvrnge pump fail(I forgot the rest of the answer)

Hi Dennis,
Basically, the primary circuit builds electrical voltage and passes it on to the secondary circuit which has even more wire windings on it stepping the voltage up from say 200 volts to 20,000 volts. When the breaker contacts open the magnetic field that has built up collapses and causes the voltage to spike large enough to arc across the gap of a spark plug. For this happen the magneto needs to be spinning fairly quickly. At startup the magneto isn't spinning faster enough to create the spark it needs to fire the spark plugs. This is where the impulse coupling comes into play. Most aero engines fire the spark plugs at about 25° BTDC. Way too early for start up and could make the engine momentarly run backwards causing allsorts of damage. The spring in the impulse coupling winds up until the right moment to fire, about TDC or shortly after. At that moment, the spring is released and it spins the magneto shaft at a higher RPM providing the spark we need. Once the engine is running the impulse coupling detaches and engine timing returns to normal.

Dry sump engines- engine pump feeds it with oil for the oil tank. Scavenger pumps suck the oil out and return it to the oil tank completing the cycle. If you have high temp and low pressure, this would mean that the engine is not being fed enough oil from the engine pump. With the scavenger pump doing a better job taking the oil away will only add to the engines woes, reducing pressure and since part of the oils job is to cool as well as clean and lubricate, it will run hotter.

Hope this helps.

Cheers,
Mister W