Wednesday, August 30, 2006

The flight home from New York was good, the weather is beautiful in Toronto today. The passengers were happy, and I really have nothing to report.

Tomorrow, I'm heading back to New York city for 4 days, so I'm gonna tour Manhattan and buy some dodgy fake Rolex watches, maybe a handgun or two, and of course some crack. Kidding, kidding, I'd never buy a handgun.

Anyway, pilot geek stuff coming right up:

Suck, Squeeze, Bang, Blow.

No, that's not what you think it means at all, it's how engines operate, whether they be piston or turbine. Today I'm bored, so I'll quickly run through how a turbine engine works. It's pretty simple, and it won't take long.

At it's most basic : compress some air, add fuel and ignite it. The expanding hot gases are channeled out the back of the engine, pushing the engine forward. The engine is attached to the airplane, so the airplane is pushed forward.


Click on this to make it bigger


At the front of a jet engine is a fan (called a compressor) that spins at a very high speed - our jet engine compressors spin at around 35,000 rpm in normal flight. When air enters the engine, the spinning fan blows the air into a small chamber. This compresses the air, hence the name. In the small chamber, the air combines with fuel and the fuel/air mixture is ignited, causing the air to greatly expand. The expanding air rushes out toward the back end, but in order for it to get out the rear of the engine, it has to run through a pinwheel (called a turbine) in the back, causing the pinwheel to spin. After going through the pinwheel, it shoots out the back of the engine, and that pushes the engine forward. We call this thrust. What does the pinwheel near the back of the engine do? Well, the pinwheel in the back is linked to the fan at the front, so spinning the pinwheel causes the fan to spin, which compresses the air which goes through the engine which burns and shoots out the back, spinning the pinwheel, causing the front fan to spin and so on and so on in an endless cycle.

There are 2 basic types of applications of turbine engines in aviation - turboprops, and jets. A turboprop is essentially a plane that uses jet engines to spin propellors, while a pure jet dispenses with propellors entirely, using the thrust of the air out the back of the engine to move the plane forward.

In a turboprop airplane, the pinwheel also spins the propellors, which takes up most of the energy of the air rushing out the back. The thrust out the back of a turboprop is generally a small part of the total power produced - I think in the last turboprop I flew - the MU-2 - for engines that were over 700 horsepower each, the residual thrust each engine produced was only like 50 pounds, the majority of the power was as a result of the spinning propellors. In a jet, there are no props to spin, so the air blowing out the back of the engine makes up all the thrust.

The reason most turbine airplanes fly high up in the air is because the air is generally colder at a high altitude. When the air is cold, the air molecules huddle closer together and that provides greater expansion when the air/fuel mixture is ignited in the engine, which helps increase the efficiency of the engine. Above a certain altitude, say around 35,000', the air stops getting colder so most aircraft don't bother climbing up higher than that because the engine efficiency stops getting much better above that altitude. Most turbine engines run on jet fuel, which is essentially kerosene. That being said, if we are in a pinch we can run our turbine engine safely on just about any kind of gasoline with a few restrictions and as long as we don't run it for very many hours before replacing the fuel with real jet fuel.

Turbine engines are very reliable and actually really easy to operate - you run the engine faster to produce more power (subject to temperature and rpm limitations - you don't want to melt the engine or overspeed it but that's generally not easy to do accidentally). They are very light for the amount of power they produce, and a jet engine can easily put out far more power than a piston engine of the same size. They do cost a hell of a lot of money though - a new engine for our jet can run around half a million dollars and a single engine for a large passenger airplane can easily run to ten million dollars or more.

I went to flight school for 2 years to learn that, and now you know it all for free in about 2 minutes :D

4 comments:

Anonymous said...

You sir, are a NERD!!!!!

heh.

:)

Anonymous said...

When do we get the test? Multiple choice/essays/fill n the blanks/group take home /
they are all so fun
PS have a wonderful time in New York. esp the MOMA (Museum of Modern Art)KM/nanaimo

christine said...

Ha, ha -- I'm smart for FREE!
-C.

phil said...

I thought the reason jets fly high is to get to the thinner air and so reduce drag.

btw great blog