28 April 2008


I teach.
Well, it might be better to say "I try to teach."
More and more, I find students expecting me to tilt their heads upward, open their mouths, and spoon in the information they need to become helicopter pilots. That ain't the way it works, folks.
True learning only comes when you know "Why".

All flying things are fascinating, aren't they?
In my opinion, helicopters are even more so because they have so many things spinning this-way-and-that in order to accomplish lift without twisting themselves into a death spiral. There are SO MANY things a student needs to fully comprehend before he can fly safely. In order to react properly to an emergency, the student needs to really understand the "why".

My latest question, so appropriate today, is "Why do we need fuel?"
Wouldn't it be great if we could commit aviation without using any fuel?!

Students are initially puzzled by the question. Then, when they answer, they try taking the easy route... "Because it makes the engine run."
Yeah, of course.
But WHY?
Or maybe more appropriately here... how?
Why DO we need fuel?

Pilots and non-pilots... do you know?
Some of you only THINK you do.
Yeah, we gotta have fuel, but down to the kernel of it, what does fuel do for us, and...


PlasticPilot said...

Some students also have strange questions... When I was studying for my PPL, someone asked, after the end of the weight and balance chapter:
"Does all planes have a center of gravity, or is that an option ?".

No more comment.

nec Timide said...

I try to teach as well, though only those who strive to qualify for a scholarship, but still try to concentrate on "why" as well. I got it from my high school physics teacher who also took that attitude.

So, my whiskers are telling me there may be a mouse trap here, but fair is fair I've laid a few of my own for students so I'll stick my toe in.

Flying is about (amongst other things) energy management. Fuel is chemical energy that, with our engine, propeller, rotors and wings we convert into kinetic energy (thrust and lift) to overcome gravity and drag, and to modify our kinetic and potential energies. Aircraft don't crash when pilots run out of, or mismanage, fuel (or they shouldn't). Energy management just becomes more difficult.

Greybeard said...

Nec, all that is true, but that's not the basic "why" I'm trying to get students to understand. Let me give you a hint:
Our engines are referred to as "air pumps".
Ooooookay... if fuel is such a critical thing, why aren't they called "fuel pumps"?

Anonymous said...

Fuel is mixed with air in the right proportions (approx 11:1 ratio) and enters the cylinders via the intake manifold. This mixture combined with the spark from the plugs during the compression stroke completes the fire triangle (oxygen, fuel, light). This chemical energy derived from the production of heat is converted into mechanical energy via piston/connecting rods which subsequently rotates the crankshaft. Rotating crankshaft = lift

No fuel no combustion no fun!

Ian said...

In that case, how about we need fuel to make the air pumps to so we can "commit aviation"?

p.s. "commit aviation" is genious. I love it.

Greybeard said...

11:1 huh?
That's my point entirely, Rodolfo. We're using FAR more air than fuel...
The fuel is used to heat and expand the air, which forces the piston down in the cylinder. (And no, it is NOT an explosion!)
But that's why we need fuel. If you can figure out how to expand that gas to force the piston down without using fuel, you can be a millionaire tomorrow...
(or maybe dead, if the oil companies get wind of it.)

Here's my point. Ask the next person you meet how a reciprocating engine works. Unless, like Rodolfo, they're working toward becoming an A&E, you may be surprised/saddened by the answer you get.
And if they regularly "commit aviation", they've missed a lesson they should have learned.

Ian said...

Out of curiosity, does anybody know the approximate ratio for a turbine powered engine?

Greybeard said...

How long do you want your turbine to last, Ian? Good article here, and it looks like the ratio is about 15:1 if you want good TBO's.

nec Timide said...

So turbine mixture and piston mixture are judged on the same metric, how long you want it to last ;-)

Back to your original question, it didn't occur to me that you were looking for that low level detail. But I guess that was your point.


Jeff Bucchino said...

We need fuel in order to make aviation as expensive as possible, otherwise everyone would do it.

JLeonard said...

Heck, I'm just a lowly trauma nurse that wants to fly in the helicopter...but they keep mumbling something about a weight limit...Jim