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Re: JSBSim Piper J-3 Cub

Postby Bomber » Sun Aug 06, 2017 5:14 pm

Thorsten wrote in Sun Aug 06, 2017 4:49 pm:
Is it a joke?


No, as I said above, it's playing games.


Can you please show some respect and not make this personal....

It's about the dihedral that the fdm authors used on the shuttle and Cub.
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Re: JSBSim Piper J-3 Cub

Postby Thorsten » Sun Aug 06, 2017 5:28 pm

Right...

Simple suggestion - if you have something to say, say it. Otherwise leave it.
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Re: JSBSim Piper J-3 Cub

Postby Hooray » Sun Aug 06, 2017 5:30 pm

Stop the flirting guys, or just get a room ...
Please don't send support requests by PM, instead post your questions on the forum so that all users can contribute and benefit
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Re: JSBSim Piper J-3 Cub

Postby Bomber » Sun Aug 06, 2017 5:31 pm

Right,

So now you want to hear what I got to say ?

Simple question of you...

With zero dihedral do the wings produce side force ?

You answer that, I'll sing like a canary.
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Re: JSBSim Piper J-3 Cub

Postby Thorsten » Sun Aug 06, 2017 5:35 pm

Okay, find someone else to entertain you then.
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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Sun Aug 06, 2017 5:40 pm

I'm not sure how relevant this is, but a two minute search of actual cub users gives a "total" dihedral of everything from 0 to as much as 4". Sounds like the Cub and PA-18 dihedral are notoriously non uniform and also not very straight for measuring.
I guess my point here is this model can theoretically use any number within that range and be accurate as to reality.

But please, get to the point.
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Re: JSBSim Piper J-3 Cub

Postby Bomber » Sun Aug 06, 2017 6:00 pm

Wlbragg,

It's very simple.... I'm trying to make the point that following others work and extrapolating it to meet your own planes requirements doesn't necessarily make it correct.

All because it's been done before like something, doesn't mean the somethings correct... and the more people doing it one way doesn't add gravitas to the method.

Question question question.

Does a wing with zero dihedral and no beta produce any side force ?

If the answers no..... then how do ailerons produce side force ?

Simon.
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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Sun Aug 06, 2017 6:13 pm

OK, here is the problem I am having. I can't very well question something I have no knowledge of. I wouldn't know what question to ask.
I started this out indicating I don't want to be an FDM expert. Do I like to learn, yes, so it is interesting when I am introduced to concepts like dihedral.
Now your introducing another question about "how do ailerons produce side force" when I don't believe we were even talking about ailerons.

Now to expand on my unwanted FDM education. We are discussing the dihedra of the wings, but any meaningful use of that feature seems to also relate to "dihedra effect" which is during slipstream. If you have an aileron deflection during slipstream then I guess you would have a surface of the aileron at an angle to the wind. Not only forward but sideways.
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Re: JSBSim Piper J-3 Cub

Postby Bomber » Sun Aug 06, 2017 6:17 pm

Well isn't it about the code used and whether it produces side forces by its aileron deflection...

I don't know what your planes fdm has been modeled to reflect... zero dihedral or 4 degs ? Or somewhere in between.

It's why I ask the question.... to save jumping to conclusions and being pulled up on it
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Re: JSBSim Piper J-3 Cub

Postby Bomber » Sun Aug 06, 2017 6:22 pm

Also.... I'm asking about zero dihedral...

Yes there might well be dihedral effect with a zero value but how does that differ from a positive or for that matter a negative value.

Those that throw maths and convention in our face should be able to answer these simple questions on there own without having to use reference materials or write paragraph after paragraph in an attempt to confuse with its complicated.
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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Sun Aug 06, 2017 6:24 pm

Something else is stuck in my mind.

This would be my order of priority in regards to an FDM.

A perfectly modeled FDM, all the FDM data match the published numbers spot on and the simulation matches that of reality.

An FDM were there was some cheating done because the published data and the FDM data could be reconciled, but the simulation matches that of reality.

A perfectly modeled FDM, all the FDM data match the published numbers spot on, but the simulation doesn't match that of reality.
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Re: JSBSim Piper J-3 Cub

Postby Bomber » Sun Aug 06, 2017 6:31 pm

Well you and a lot of planes are clearly in the 3rd paragraph.

A question to ask then is how to move up to paragraph 2 .

Alan recognises that in flight modelling where the results don't match reality there is some level of 'art' involved....

The past few pages have been about acknowledging this and maybe maybe being able to talk about this 'art'....

Without being accused of insulting people's work.
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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Sun Aug 06, 2017 6:32 pm

Well isn't it about the code used and whether it produces side forces by its aileron deflection...

Well, there you go, I thought it was about pitch. This whole thing started out with a request to correct an issue with a perceived lack of elevator strength.

Which then turned into an issue with how tight the aircrafts response was. I assumed, mostly in relation to the issue being front and center which was elevator and pitch.

So I am indeed getting confused here.

Maybe that is one reason I don't respond well to only open ended questions without points. I need it spelled out.
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Re: JSBSim Piper J-3 Cub

Postby Bomber » Sun Aug 06, 2017 6:46 pm

Yes it's a divergence.... the reason why I've created another topic.

But no more a divergence, where people are told not to listen to what I'm saying because of a flight model I did 3 years ago....

I'm simply asking if the shuttles wing has zero dihedral then why do its ailerons add side force with deflection.... where is rhis vector coming from ?

Maybe Thorsten who'd have others follow and extrapolate code for their planes could answer... but I doubt he's playing the silly game of open and honest development discussion.

But instead using words like red herring and such.

Simon.
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Re: JSBSim Piper J-3 Cub

Postby wlbragg » Sun Aug 06, 2017 6:57 pm

I'm simply asking if the shuttles wing has zero dihedral then why do its ailerons add side force with deflection.... where is rhis vector coming from ?

That isn't as obvious as it is to me?

Doesn't deflection cause the aileron to put a surface opposing the sideways wind force, even more so in a slip or a trailing v wing. While dihedral would also cause the same thing on a different plane, it isn't the only way, right?
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