PPRuNe Forums - View Single Post - Question on forces acting on an aircraft in climb
Old 9th Jul 2010, 12:29
  #117 (permalink)  
Wizofoz
 
Join Date: Jun 2001
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Insofar as Aviators are generally not dumb, and are usually interested in scientific discussions, sure, why not.

I in fact raised the issue on a more "Sciency" forum (JREF) and got replies which were interesting.

I'm not saying they refuted you, as it was me putting my interpretation on things you said, and I may well have mis-represented you and your arguments, but one poster (who I know to have a PhD in Physical Sciences) participateded in this exchange:-

me-

Hi guys,

I need some help from a physics Guru, even if it is to tell me I'm wrong so I can drop it.

On an Aviation forum, a discussion came up regarding the forces on an aircraft in a turn.

As you'd be aware, and aircraft in a 60deg Angle of Bank turn experiences 2g. People started refering to this as the Aircrafts "Apparent Weight".

I chimed in and said it was meaningless calling it "Apparent Weight" as it was indestiguishable from "Real" weght. Basically the the opposite force felt as a reault of the aircrafts acceleration was the same thing as that due to Gravity, so it was incorrect to label them as different things.

I got pretty soundly shouted down, and one posted invoked that I was using "Operationalsim" which was out-moded.

What are the physics heavy-weights opinions?

Thanks
Sol Invictus (PhD dude):-

There's a deep principle of physics - the equivalence principle - which says you're right. Inside a sufficiently small laboratory, you cannot tell whether you're in a gravitational field ("sufficiently small" means too small to measure tidal effects). If you feel an acceleration it could be because you're in a room or plane that's being supported against the force of gravity by the ground or air, or because the room or plane is accelerating in zero gravity due to something else (like an elevator cable or a banked turn), or some combination of the two as in your example.

Of course you could also just look out the window and observe you're flying over earth, and use your knowledge of its mass to determine which component of your weight is "real" and which is "apparent". But I suppose you consider that cheating.

ps - I'm not sure what "operationalism" is, but I think I believe in it.
Me (Responding to a query)

Well, I copped a speil and a link to a philosophical document, and was told

"The view of science that quantities which you cannot discriminate with instruments are the same thing is about the only philosophy of physics which has been definitively discredited in the last hundred years. So it is rather inappropriate to try it on here, don't you think?"

I didn't understand what he meant...

Sol:-

Insofar as I can parse that, I disagree with it completely. The idea that the only real things are those we can (in principle) measure not only has not been discredited, it's one of the most powerful ideas around. It has repeatedly proven its worth over the last century (the equivalence principle being an excellent example).
So, firstly you can see that EVERYONE (including me) knows that at a practical level, invoking the Earth as a Frame of Reference makes sense in the real world, but also that from a purerly theoretical standpoint, operationalism appears to be alive and well.

The thread is here:-http://forums.randi.org/showthread.php?t=179962
If you'd like to read or participate in it.
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