bum steer

[bomber]

"somewhat misleading"... Is a bit non committal

Yet he's quite clear what it isn't.... And that's the centre of pressure...

Even though I've been explicit and clear in saying we're not talking about the wing but the plane as a whole...

The point at which the lift, drag and side forces..... Or pressure for want of another word act.

We can talk semantics if we wish, others will try misrepresentation and even others will downright be disengenuous.

I may not be able to call bullshit on the FG forum or on discord, but I can here.

Simon

[mue]

What you're missing is that mue et al are not correct...

You cannot apply the equivalent force at the nose....end of.

Why do you neglect applying of moments?

The aero reference point in JBSim is not equal to the centre of pressure. It is just a reference point for the aerodynamic forces and moments - it can be (almost?) anywhere (e.g. at the nose).

I tried to explain it with a simple example:
https://forum.flightgear.org/viewtopic. ... 07#p370607

[bomber]

Moments and inertia are calculated around the cog in JSBsim....that's just how it is, I didn't write JSBsim.

The facts are he was wrong, laughable, and you were wrong to support him......

You show me a plane with the aerorp at the nose which hasn't had to have some serious smoke and mirrors magic to make it work..

It is not as written the reference point.... And the correct term is datum point and it is this point that can be anywhere on the plane or off it, including the nose...

He made a mistake, accept it and accept that you supported a mistake.

Simon

[bomber]

At ref point 1.) acts the force F and a negative (nose down) moment of -0.3m * F
At ref point 2.) acts the force F and no moment
At ref point 3.) acts the force F and a positve (nose up) moment of 0.7m * F
All three combinations (consisting of ref point, force and moment) describe the same force acting at the center of pressure (0.3m behind the leading edge) and therefore are equivalent. It's called "Equivalent force systems". You can describe any force and moment acting at one point by a force and moment acting on another (arbitrary) point

If it was an equivalent force and moment....... Why aren't they equivalent ?

Nose down, no moment, nose up ?
Surely by definition they should all be the same ?

Aerorp defines a moment between where the forces of lift, drag and side are applied and the planes cog..... Defined from the datum point.... A point which can be anywhere.

Simon.

[mue]

If it was an equivalent force and moment....... Why aren't they equivalent ?

Nose down, no moment, nose up ?
Surely by definition they should all be the same ?

As I said, you didn't understand equivalent force systems...

...and you still don't.

[bomber]

Like talking to a 5 year old this is......

How is your flight modelling coming on..... I love flying your planes as they're so realistic....

Which one is it again ?

Flight modelling zealots...... Why can't you simply answer his question on how to move the aerorp position ?

This is what he wants to do, it's not your place to preach to him the Bible of aerodynamics scripture by scripture.... Either answer his question or don't answer....

But you're like a man on the dock side giving swimming critic to a drowning man..... Throw him the bouancy ring, that's the help he wants.

Simon

[Richard]

AERORP is simply the centre of gravity when the aerodynamics were measured (or calculated from).

... Why not call it the neutral point ?

The neutral point is something else; AERORP is usually defined as I stated.

It is possible that AERORP could be at the neutral point but AERORP does not have to be at the neutral point.

No intended sleights of hand - I tried to write a response that was clear.

Normally AERORP will be in the permissible CG range - and it is impossible that it could ever be at the nose unless you could have a CG on the nose also.

[bomber]

AeroRP - the location where the aerodynamic forces are applied to the model. If this location is not exactly equal to the center of gravity (CoG) then moments, or twisting forces, will be created. Conventional aircraft need AeroRP to be aft of the CoG for stability.

This is how JSBsim wiki defines it...

http://wiki.flightgear.org/JSBSim_Aerod ... 0stability.

If moments are being created because the aerorp is not at the CoG, then it's clear that the armature is the distance between the aerorp and the CoG... yet the forces of lift, side and drag are applied at aerorp, this is a JSBsim fact... and by this very fact it's clear that moments are calculated within JSBsim around the CoG.

Normally AERORP will be in the permissible CG range - and it is impossible that it could ever be at the nose unless you could have a CG on the nose also.

Hopefully certain parties will read your sentence and accept it..... equivalent force my arse !
Flight modeling is not easy, yet it's not as hard as some people persist in making it out to be.

SImon

[mue]

Hopefully certain parties will read your sentence and accept it..... equivalent force my arse !

I'm not surprised anymore that you, bomber, don't understand basic mechanics.

But I'm surprised that Richard doesn't know or maybe I should say forgot about Equivalent Force Systems. Because in the past he himself used Equivalent Force Systems to change the aero reference point by adding the appropriate moment (or as he wrote "effectively balanced out by the proportionate value of the forces..."): https://sourceforge.net/p/jsbsim/mailman/message/32743744/. And thats effectively the formula for Equivalent Force Systems: The system of force F_a and moment M_a at point A is equivalent to the system of force F_b and moment M_b at point B with F_b = F_a and M_b = M_a + (position point b - position point a) x F_b.

[Edit: corrected cross product)

[bomber]

There ya go, resorting to the tried and trusted FG forum technique of telling everyone what a person doesn't know.
In the hope that by doing so others think how much more intelligent you must there fore be, because you do know something.

I create flight models in a completely different way to everyone else using JSBsim..

If I didn't understand something it'd be reflected in the flight model performance.
And along the way there's been a lot of reflection in the performance that required me to adjust my thinking.... I've had to learn a lot that I wasn't born knowing.

As I said this is a tried and trusted technique to discredit someone in FG.

Alant was publicly critical about my bi-plane flight model couldn't have one wings forces effecting the other... I sent him the spreadsheet of my working out and reference docs and not another word from him was said.... not even a gentlemanly retraction.

Richards publicly critical that my flight models don't have rotational damping... ever built a flight model without such a thing ? In a spin, (and yes as I have differential wing lift my flight models spins both ways without any smoke and mirrors) without rotational damping the planes spin gets faster and faster and eventually FG crashes to desk top... So as my flight models don't do that what is the conclusion ? Rotational damping in my Flight models isn't a factor on the force generated but right at the start on the angle of attack so preventing the incorrect force being generated in the first place.

I show all my working out, generate spreadsheets for prop, engine, weight & mass and flight model aerodynamics and I issue these with my flight models...

So by all means tell everyone what I don't know.... I'll just continue on with my hobby of gaining greater and greater understanding of flight modeling.