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in2jumping

Re: [The111] Fatality - Tampa Bay, FL - 20 Jan 2010

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>This is the reason in my original example that I replaced the earth with a
>theoretical plane that does not move.

Yes, I saw that. I'm putting this back in the real world. And in that real world, that eastbound car is moving at 860mph relative to the earth, not 60mph. Does that mean it's harder to stop when it's driving east? After all, it has 860mph worth of momentum!

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Thats wher gravity helps deminish this effect and, in your case, if the car is on the earth and stops moving its still on the earth and therefore only slows down to 800mph which is still only a deceleration of 60mph.

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Okay, real world: Airplane is moving at 60mph and banks left and pulls back so hard (45degree deflection on the elevator) that it quickly decelerates to 0mph facing the opposite direction. With a 2:1 thrust to wieght ratio the airplane accelerates back to 60 mph and full flight. Now there is a 20mph headwind. The plane is going 60mph relative to wind but 40 to the ground. It makes the same adrupt turn coming to a stop facing the opposite direction before accelerating back to 60mph relative to the wind and 80 mph to the ground. What is the total acceleration and inertial effect on the aircraft? Is it the same in both scenarios?

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This is the greatest dz.com thread in a long time. Lets keep this alive forever. Who is going to be the next troll/amateur physicist/aviator to step up and prove these guys wrong with their personal experiences.

I know inertia is a tough thing to wrap the head around but pick up a text book, or search the interwebs.

And if you ever manage to find yourself in a fixed wing aircraft at 0mph in its airmass i hope you have some altitude on your side or an appropriately designed parachute.

I really hope this has all been troll fodder, but im entertained either way.

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And if you ever manage to find yourself in a fixed wing aircraft at 0mph in its airmass i hope you have some altitude on your side or an appropriately designed parachute.


Also, that is why I said when doing this maneuver I must have more altitude when the winds are higher...... which means the winds do have an effect.

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If you assume the plane comes to a stop in relation to the ground in both cases, then you're comparing apples to oranges. The plane is coming to a stop in relation to the air. There'll be a 20 mph difference in ground speeds when it is stopped with wind vs no wind. The accelerations will be identical.

Dave

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They can't be identical if in one case you are going from 0mph ground speed to 60 in one case and 0mph ground speed to 80 in the other.
Now just make the turn a little less dramatic each time and it is easier to overcome the inertia until the turn is so smooth that inertia seems to have no effect and everything is just moving with the wind.

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Here is something else. For years physics teachers have been using a simple example to illustrate inertia. They take a ball in a little spring loaded cannon on a cart and roll the cart. The spring shoot the ball and the ball lands back in the cannon while moving. They then teach the equation to explain this. However, they don't included wind resistance of the ball, deceleration of the cart due to friction of the axles, etc. Does that mean these things aren't having an effect and if replicated in much larger scenerios that it will working without taking wind resitances and friction into effect? No, they are still present just ignored and in extreme examples must be taken into account.
The same is happening in this example. The slowly circling plane works within the framework of ignoring inertia but in extreme cases with extreme winds and sharp turns and such inertia must be taken into account properly.

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They can't be identical if in one case you are going from 0mph ground speed to 60 in one case and 0mph ground speed to 80 in the other.



My point exactly. They won't both have zero ground speed. You are completely mixing up the concepts of ground speed and airspeed. When the pilot applies a certain control input, the plane will respond exactly the same way, regardless of wind. The ground speed of the plane will vary... which has absolutely no affect on the plane.

Go back to your plane circling around inside a car... but lose the car...

First assume zero wind. The pilot picks an object on the ground and flies a perfect circle around it. He just puts his controls in the required position and holds still. The plane just keeps following the same path over the ground in a perfect circle.

Now the wind starts to pick up. The plane's path over the ground becomes a... well... whatever you'd call that shape. Looks kind of like the way you'd draw a spring. If the pilot had his eyes closed, he'll still feel like he's flying in a perfect circle. The plane will feel like it's flying in a circle. If he had a cloud layer right below him, he'd even look like he was flying a perfect circle over the clouds.

The plane's airspeed is contant throughout the maneuver. When the wind is coming from behind, his ground speed increases. His airspeed does not. The wind has no affect on how the plane flies.

Dave

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Your probably also being confused by the slope of the recovery relative to the ground, which will be steeper shallower depending on upwind or downwind. Just like the take off that seemed climb faster into the wind.

Or if your flying your rc in an area with vertical terrain creating rising and falling air then there is a lot more going on that this discussion isn't aimed at.

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Yes, in a slow standard circle inertial differences are not apparent. However, if you look at the original example of the car on a non-moving plane: if things work as you describe then things could move faster than the speed of light if you were to put something in an object moving at the speed of light and move the inside object forward. However, that doesn't work because the inside object would be moving faster than the speed of light and thats not possible. The point being that true speed as determined by non-motion is relevant particularly when determining the inertia of an object or its resistance to a change in velocity. Therefore you must look at true velocity not its velocity as compared to its surroundings which is what you do when you look at airspeed only to determine the inertia of the object and its change in direction, which is so small it is does not show up in the circling plane but will show up in the quick high performance maneuvers.

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>Thats wher gravity helps deminish this effect . . .

No, gravity is the same in all cases. In the car's case, the force caused by gravity is resisted by the air pressure in the tires; in the airplane's case, the force caused by gravity is resisted by the air pressure above/below the wings.

> if the car is on the earth and stops moving its still on the earth and
>therefore only slows down to 800mph which is still only a deceleration of
>60mph.

You are correct! It only slows down 60mph WITH RESPECT TO THE ROAD. That's all that matters. Likewise, airplanes only fly/turn/climb WITH RESPECT TO THE AIR. That's all that matters.

>Also, if anyone can fly any size aircraft at 20mph in a car going 60
>please let me know!

Try it sometime with a 5mph RC airplane (they exist and are tiny) and a van going 60mph; prove this stuff to yourself.

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>Airplane is moving at 60mph and banks left and pulls back so hard
>(45degree deflection on the elevator) that it quickly decelerates to 0mph
>facing the opposite direction.

1) You can't decelerate to 0mph in an airplane without some fancy maneuvering (like doing a hammerhead stall with the plane entirely vertical.)

2) Sounds like you are describing a maximum performance turn, often called a chandelle. These work the same way no matter which way the wind is blowing.


>With a 2:1 thrust to wieght ratio the airplane accelerates back to 60
>mph and full flight. Now there is a 20mph headwind. The plane is
>going 60mph relative to wind but 40 to the ground. It makes the
>same adrupt turn coming to a stop facing the opposite direction before
>accelerating back to 60mph relative to the wind and 80 mph to the
>ground. What is the total acceleration and inertial effect on the
>aircraft? Is it the same in both scenarios?

Yes - provided that in all cases you are referring to airspeed when discussing the initial, intermediate and final speeds of the aircraft. (Keep in mind that in the second case your "0mph" really means "0mph airspeed, 20mph groundspeed.")

>if things work as you describe then things could move faster than the
>speed of light if you were to put something in an object moving at the
>speed of light and move the inside object forward.

a) no you can't; relativistic time dilation will prevent that.

b) even that only happens at speeds approaching the speed of light. It's a separate phenomenon that does not occur in speeds seen in aviation.

>Therefore you must look at true velocity not its velocity as compared to
>its surroundings . . .

There's no such thing as "true velocity," only velocity relative to a frame of reference. That's why pilots do 99% of their flying referencing their airspeed indicator and not their GPS groundspeed display.

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Try it sometime with a 5mph RC airplane (they exist and are tiny) and a van going 60mph; prove this stuff to yourself.



Or better yet, try it with a tiny R/C plane in a van, then have the van go backwards at 25mph in the cargo hold of a C-5.

And then have the C-5 go both with a 150kt jetstream wind and then against it.

Woo Hoo!!:P
"There are NO situations which do not call for a French Maid outfit." Lucky McSwervy

"~ya don't GET old by being weak & stupid!" - Airtwardo

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Okay, I see my gap. If your going foward at 60 and reverse and go back at 60 the total reversal is 120. If you have a twenty mile per hour headwind then your speed going forward relative to a fixed object is 40 and downwind is 80 so the total reversal is 120. So in both cases 120 is the velocity used to calculate inertia meaning inertia is the same in both cases.
My problem was I compared 60 to 40 and 60 to 80 instead of totaling them like I did above and compare the totals. I was comparing the wrong numbers. Time is another part of the equation so if you make the turn the exact same way in both scenarios then the amount of time it takes to make the turn is the same so the inertial effects are the same in both cases.
I will admit I was wrong but I find it interesting that no one could find this flaw in my example earlier. It would have made for a much shorter debate and a lot less confusion.
So, true speed or velocity does matter but the inertial results are the same whether you use true velocity or relative as you are only looking at the reversal.
Also, that means that gravity has nothing to do with the scenario as the car or plane has the same lateral inertial effects with or without gravity.

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I will admit I was wrong but I find it interesting that no one could find this flaw in my example earlier. It would have made for a much shorter debate and a lot less confusion.



What I find interesting is how you haven't realized that they were saying that! What you're so close to discovering is that the change is airspeed is the same no matter what the wind is doing, which is what all the others were saying with things like "Groundspeed doesn't matter."

You keep using the phrase "true velocity." Bill said earlier (and was correct in saying so) that velocity only has a meaning in some reference frame. What do you mean when you say "true velocity?"
Well, the door was open...

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I will admit I was wrong



Sometimes all the explanation and insistance in the world that something is wrong, isn't enough to convince someone -- until they can fit the situation into their own mental model to see where & why the model is flawed.

Looks like we all might be getting somewhere now!

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Okay, real world: Airplane is moving at 60mph and banks left and pulls back so hard (45degree deflection on the elevator) that it quickly decelerates to 0mph facing the opposite direction. With a 2:1 thrust to wieght ratio the airplane accelerates back to 60 mph and full flight. Now there is a 20mph headwind. The plane is going 60mph relative to wind but 40 to the ground. It makes the same adrupt turn coming to a stop facing the opposite direction before accelerating back to 60mph relative to the wind and 80 mph to the ground. What is the total acceleration and inertial effect on the aircraft? Is it the same in both scenarios?


>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Is the above a chandelle?
I still want to know about landing without gear and flaps.
This thread is dead, capute, is no more!
:D

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Can you tell which way the wind is blowing, or how strong the wind is blowing, under canopy with your eyes closed?

If so, please explain how.



Magical canopy faeries tell me which way the wind blows.



Most of the voices in my head don't like your faeries!! :)
Birdshit & Fools Productions

"Son, only two things fall from the sky."

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