AOPA Rod Machado article

[shdw]

For example, gravity is a constant and two skydivers should freefall at the same speed.

Only in a vacuum. On earth, friction screws it all up.

Edit: I was beat to the punch

 

[USMCmech]

What's unfortunate, though, is that academic understanding does not always directly translate to understanding of practical application, and frequently we end up with two discussions -- one academic and one practical -- without the ability to directly connect the two logically. IMHO, that's exactly what's happened with this discussion of load factors and bank angle.

That is exactly what has happend with this dicussion, one party is viewing it through a theortical understanding (which is not wrong BTW), and another is simply discussing the real world effects of a given configuration (which is not wrong either).

 

[Douglas]

The root cause was actually experiences I've had while flying warbirds with pilots who got squeamish when that happened. The airplanes were legal to be there, and so were the parachutes.

I still categorize that as "GA", which is probably the root cause of the misunderstanding.

Ah, my bad.
I'm pretty sure it is criminal to not take a war bird past 60.
"There will be wing-overs."

 

[tgrayson]

I didn't have a G meter installed, but I know the difference between 1G and 2G. I've done 60 deg constant altitude turns and I've done 60 deg descend;ing turns. They do NOT have the same load factor.

Well, no, as I pointed out, you probably have about 1.97. ;-) I accept that your perception of the load factor is different, but that's not meaningful. Human perceptions are very unreliable and are easily influenced by other environmental factors, which is why instrumentation, such as load meters, were developed.

If what you say is true, then how can acro planes fly stabilzed knife edge, 90 deg bank, constant altitude, 1G?

In this instance, the weight of the aircraft is being sustained by fuselage lift, not wing lift. That's a whole different flight regime from normal banked flight.

 

[USMCmech]

Only in a vacuum. On earth, friction screws it all up.

Then why does adding weight belts inside the jumpsuit of the lighter diver fix the problem?

There is no obvious change in drag, but changing the variable that doesn't matter (weight) changed the result.

I've never gotten a good explaination, but I know that both things are true. One is a law of physics, while the other is a result of a real world problem.

 

[shdw]

That's not really what I meant when I wrote that, but the point is taken.

Fair enough. Don't drop any bombs on me for misunderstanding though, ok? Thanks.

one academic and one practical

My problem with this is when someone refutes the academic because of a perceived practical experience. Science is rarely ever what we see the first time around. You know this though.

 

[USMCmech]

Well, no, as I pointed out, you probably have about 1.97. ;-) I accept that your perception of the load factor is different, but that's not meaningful. Human perceptions are very unreliable and are easily influenced by other environmental factors, which is why instrumentation, such as load meters, were developed.

Obviously I don't have a calibrated butt either, but the difference in load factor is quite obvious.

And perception is VERY meaningful, it is how we interact with the world. As pilots we should be far more concerned with the "real world" results of our actions than scientific theory (IMHO). In many cases, we don't even need to understand these matters. Go back to the dozens of threads about "how is lift created". The theory gets presented hundreds of ways, but all a pilot really needs know is velocity and AOA.

That is not to say that we don't need to understand the theory of course, but I fall much more to the practical. I'm a mechanic, not an Engineer.

 

[shdw]

Then why does adding weight belts inside the jumpsuit of the lighter diver fix the problem?

I'm going to take a stab at this, though I am by no means certain. Weight is used to overcome drag. The big fat guy has a little more drag (surface area) but a lot more weight. The skinny guy has less drag but far less weight. Give the skinny guy more weight so he can accelerate as quick as the fat guy and vuala! Skinny guy and fat guy accelerate together.

Not certain if that is accurate, but I'm sure tgray can correct any error I may have here.

 

[tgrayson]

is that academic understanding does not always directly translate to understanding of practical application

I've found that a proper, thorough understanding of the academic always, always, always translates to understanding the practical application in almost every area of human endeavor. The real problem is that people often don't have a adequate academic understanding, hence they can't apply it.

 

[darrenf]

but changing the variable that doesn't matter (weight) changed the result.

Why do you assume that weight does not matter? Again, this is not in a vacuum.

 

[Douglas]

But your mom is.

 

[tgrayson]

Then why does adding weight belts inside the jumpsuit of the lighter diver fix the problem?

A falling body accelerates until the drag equals the weight of the body. When the diver is light, a relatively low velocity will produce enough drag to stop his acceleration; when the diver is heavier, he must accelerate to a higher velocity to achieve the drag necessary to stop his acceleration. Drag is proportional to velocity squared.

 

[shdw]

I've found that a proper, thorough understanding of the academic always, always, always translates to understanding the practical application in almost every area of human endeavor. The real problem is that people often don't have a adequate academic understanding, hence they can't apply it.

Along the same lines, primacy! Learning solid academics first and then applying them to a controlled environment is far easier than learning how a descending turn works after 10,000 hours of flying. You have 10,000 hours of perceived situations in uncontrolled environments to contend with. To me that is just torturous to the human brain.

I tend to be one of those guys that just blindly believes the science. This makes it far easier for me to toss out past experiences in an attempt to understand the science. I recently started working with a 90 hour student who has learned nothing about aerodynamics in her training. I'm finding it near impossible to make even basic claims because of the 100s of false perceptions that have gone uncorrected throughout her training. Some brains simply refuse to believe it until it is physically seen. Nothing wrong with that, but it is why we need g-meters and AOA indicators in all basic trainers!

 

[TwoTwoLeft]

Funny, the Examiner on my CFI initial ride told me I should never let that happen - that I must grab the controls as soon as a wing drops, unless the student is receiving instruction for a CFI ride.

His reasoning was that exceeding bank and pitch limits was only legal when necessary for a certificate or rating without a parachute. While technically true, I sincerely believe that that instructional value is real - and that instructors should have more leeway here.

That examiner needs to go review AC 61-67. It is completely legal to give stall/spin training with out parachutes to some one not going for a specific certificate or rating.

 

[USMCmech]

Why do you assume that weight does not matter? Again, this is not in a vacuum.

Two different weighted objects with the same size, shape, and drag "should" fall at the same rate, even outside a vacum. A 15lb and a 8lb bowling ball dropped from the same height at the same time will hit the ground at the same time, you can try it.

In the example of the skydivers, I understand that there is a lot more going on. This means that the simple bowling ball experiment is not a valid example to use for skydivers.

 

[shdw]

Two different weighted objects with the same size, shape, and drag "should" fall at the same rate, even outside a vacum. A 15lb and a 8lb bowling ball dropped from the same height at the same time will hit the ground at the same time.

Assuming drag is equal and the distance is short enough that the lighter ball doesn't hit terminal velocity (drag = weight), this would be true. As you can see, though, there are a quite a few assumptions one must make to make this a true statement.

A falling body accelerates until the drag equals the weight of the body.

Gah, simplicity. Up forces equal down forces. I just didn't define my up and down forces, even though I knew them. Thanks.

 

[tgrayson]

A 15lb and a 8lb bowling ball dropped from the same height at the same time will hit the ground at the same time, you can try it.

No, they won't, even Galileo knew that. From a small height, the difference will be invisible, but you'd see a much bigger difference as the height increased. Let me point out again, this isn't a problem with the theory, it's a problem with the understanding of the theory. I predict that you will never in your lifetime observe any phenomenon that isn't explainable using freshman science courses.

 

[USMCmech]

A falling body accelerates until the drag equals the weight of the body. When the diver is light, a relatively low velocity will produce enough drag to stop his acceleration; when the diver is heavier, he must accelerate to a higher velocity to achieve the drag necessary to stop his acceleration. Drag is proportional to velocity squared.

Back to the "bowling ball off a tower" experiment,

Both the 15lb and the 8 lb bowling ball will acclerate at the same speed, but the heaver one will keep speeding up to a higher terminal velocity.

Is that correct?

 

[shdw]

Back to the "bowling ball off a tower" experiment,

Both the 15lb and the 8 lb bowling ball will acclerate at the same speed, but the heaver one will keep speeding up to a higher terminal velocity.

Is that correct?

The bowling balls still must overcome drag. If drag were identical, then yes. Otherwise, the ball with less drag would accelerate more quickly.

I'm not certain if weight plays a role in the acceleration. Taylor, help me? Edit: Greater difference in weight versus drag equates to faster acceleration? Similarly to excess powers relationship to weight and climb in an airplane? Am I on the right track? Thanks again.

 

[USMCmech]

The bowling balls still must overcome drag. If drag were identical, then yes.

Bowling balls are the same size (and presumably the same drag) no matter what the wieght, which is why my physics teacher used them in his obviously inaccurate example.