So you know that, but you asked… [8D]
However your answer to my question was:
Anyhow, let's say that your definition of stability is the same as mine.
So, my simple question now is:
What makes your little foamies so neutrally stable?
Why aren't they positive or negative stable instead?
Have you any idea Dick?

yes - first -no formed dihedral- the wing is flat.
secondly -the wing is an ellipse of very low aspect ratio- quite insensitive to yaw induced assymetrical lift.
The proof - you can apply hard rudder and with no cross control - the plane turns tight flat circles -very tight just a few spans long.
looks almost like a flat spin but is not.
The rudder when applied-produces an adverse yaw -which balances the lift differences in the wing panels (more lift on faster moving outboard panel)
The lateral area of the fuselage is such that there is a very high % of area foward of the CG- not enough to self servo or wiggle but enough to make yawing extremely easy.
the loading is quite low under 4 oz ft so that AOA for normal flight is at an angle not much above zero .
very clean setup .
What are your thoughts on how this works?
I have never seen textbook data which applies.
the fact is - the model acts much like a round planform wing - -totally insensitive to yaw -the Leading Edge, is a smooth constant curve from one tip to the other.

Zero wieght airframe? Would you please describe your idea of one. Because what I have in mind would require lift from a source lighter than air, as the propulsion system would have wieght. If you are getting your lift from that source, then an airfoil is not required and typical design would not follow. So you are making a mute point.
(Blimps are zero wieght)

Who says a garbage pail wouldn't fly? You? Then you are going against your own steppin out theories. If I put a 400 hp engine on it, and big enough control surfaces, I probably could make it "fly"

The hard fast rules, are just that, hard fast rules to make any design work "better". Notice I said "better", not "at all"
Your foamies are designed to a certain thing, fly crazy. If you wanted them to fly across the English channel, then you find yourself going back to the hard fast rules to make it fly more effeciently, and further on a charge.

Put a cargo in your foamie, find its maximum cargo. I'm sure it would carry more if we used the hard fast rules.

Can you explain technically which hard fast rules you broke to make a plane fly better?

awe - shucks- you apparantly don't fly models so none of what I said makes sense to you
If I wanted a plane to cross the channel in a self stabilizing mode - I think I could do that -- I have one rc setup I take out once a year - and fly to about 200 ft then turn off the system -it holds , due to a thing called PCM HOLD in the RX design
the plane will circle - and does gain and loose altitude (self corrects for speed ) till I get tired of watching it -
My foamy design does not fly crazy - tho it will do maneuvers which -apparantly you are not familiar with.
I hoped to explain why - but if you are looking for something from a text book - I can't help you.
Technical explanations are a waste of time if they are not clearly applicable to situation at hand.
as for zero weight - -it is a hypothetical example .
This means that IF the plane was of zero weight - how would that ZERO wingloading affect flight.

Dick,
Your description makes sense but I guess it refers only to why your foamies are neutrally stable regarding just two axis: Directional and/or lateral stability (yaw and/or in roll).
However, I'm quite curious to hear your description why your foamies also are neutrally stable regarding longitudinal stability (stability in pitch)?

Awe shucks you still didn't answer my question. And you missed my point completely.
Your point still makes no sense whats so ever.
So what if you can make a piece of stryofoam fly. (I have several) I'm saying you can make it fly better using hard fast rules.
I fly 3d so I know exactly what your talking about. But you still don't make a valid point.

Hypothetical example of zero weight is of no use in your ideas. All designs are based on lift, which requires weight.
Lets see, if the world was square and the atmosphere was made of molten metal, how would we fly? Who cares?

Thank you for the kindegarden explination of PCM hold, my 9cap does that, now I know why.

I am not an engineer or an aerodynamics expert, just have a good sense of physics. Don't be upset if I prove you wrong.
Because you fly 3d foamies, and they are a little tail heavy with no airfoil, doesn't mean that the hard fast rules are still not applicable to make your plane fly better and more efficiently. Thats all the rules are meant for. Those hard fast rules were never meant to make planes do 3d

I once made a paper airplane cross the East River in NYC from a 10 story building. The plane had no airfoil, and very light wing loading. What does that mean? Nothing. It could have flown better with an airfoil.

If a plane is hovering, is it really a plane anymore?

Webster has this to say:

One entry found for airplane.
Main Entry: air·plane
Pronunciation: 'ar-"plAn, 'er-
Function: noun
Etymology: alteration of aeroplane
: a powered heavier-than-air aircraft that has fixed wings from which it derives most of its lift

Notice the heavier than air part.

When a plane is hovering, it is no longer flying like a airplane anymore, therefor the hard fast rules that apply for airplanes would not apply anymore.
Of course. If this is what you are trying to say, then I agree.

Ah--- pitch stability - I really don't get excied about that -
I just adjust cg for easy control--and extreme pitch--the radio settings of expo make this possible.
these things do fly hands off quite well -- nothing like my
trainer designs but then -I don't expect them to do that.

Ants lake - you have said nothing to "prove me wrong".
I used hypothetical examples to look at the extreme ends of what happens .
Webster's "airplane" is close enough for folk music.
for those who still believe that some textbook airfoil will improve models in the small light foam stuff- I have a very simple answer .
Build one - You make it as good as you can - then show me what facet of flight is improved.
In case anyone forgot. airfoils are designed to a criteria.
In this instance - the criteria is simple: minimum weight for strength and wingloading far exceed any other criteria.

I don't think the issue here was a question about what makes you excited, but about whether or not the CG location matters regarding an aircraft's stability.
And for me it still does matter as well as for you.

Exactly Adam.
And an airfoil would make it fly better. May not make a difference when hovering or doing 3-d, but again, thats what the rules are not for.

You can't tell me that a tail heavy foamie, flying through the air with its tail dragging lower than the nose is flying at its most efficient.
It'll fly longer on a given charge just by changing cg to where its supposed to be, and even further on a charge by creating an airfoil for it.

The reason I put websters definition is to show you that once a plane is not using it's wings for lift anymore, then it's really not a plane anymore, and the rules written for planes, and wings wouldn't apply, of course.

I think your trying to be "cutting edge" but instead you went over the edge and made some claims that just aren't true.
Usless hypotheticals have no place in trying to prove that hard fast rules aren't hard fast anymore, they just don't apply.

I think you need to approach the whole thing from a different angle, to make it more appealing to people. Because I get what your saying, but I just don't agree with how your saying it.

antslake - that is incorrect .
Have you flown these?
Or are you just guessing?
These do not drag around at a high AOA- they fly very flat -even at very low speeds -
the wingloading is under 5 oz ft.
They do sink rapidly at min speed -but are completely controllable .
The "rules for planes " concept is fine for very basic trainers .
With the power available - even on full scale - the old rules have evolved - a lot.
What is an Ospry? a plane - a helicopter?
The thin flat plate as a lifting device is excellent -as long as the AOA is controlled.
As an aerobat - when pitched quickly, it has the excellent property of instantly stalling and snapping - then easily, quickly recovering due to very low inertia.
For you - that may be a terrible thing - for me -it is exactly what I want!
If my hypotheticals are useless to you - ignore them .
However - unless you research the capability of a concept - to infinity or to zero - you really have not thoroughly explored it.
If the basic textbook approach make you more comfortable - stick with it.

Dick,
You seem to be forgetting that on page one, post #16, of this thread I explained to you that I have explored the low wing loading area further than this. CG matters. Airfoil matters.

You can make your planes fly the way you like because they are light and slow... so you can compensate for the fact that they are not positively stable in pitch by using RC. The flat plate works well enough for you that you don't think any improvement is possible. That's fine... but let the airfoil engineers work on the problem and I guarantee they will come up with something that meets all of your criteria and still is more efficient.

Dick,
Below are just some of your "interesting" statements posted earlier in this thread:
Honestly, I don't know whether you were kidding or just shooting at all directions in order to get some hits…

Yes I have flown these, put one in a wind tunnel and you will see.

guess what?
a wind tunnel is NOT a real world enviroment.
For this application the tunnel is of no real value.

Now your just getting silly.

Just admit it, it could be better with an airfoil.

If it really could - I would do it -
the thin flat plate is well suited to this application.
it is simple strong twist free in the planfom I use and the benifits of a curve in it have no merit.
but - hey- you do it and show me where I missed out!

Dick,
I'm sure an airfoil would give it better flying characteristics, but I guess it just wouldn't be exciting enough for you…

It is an airfoil -just not one you are used to seeing --

The thin flat plate is not the best airfoil, even if the foamie's wingloading and inertia are low. You can manage it just thanks to its low inertia not because your "airfoil" is the best.

I just got back from a flying session with it -
in doing rolling circles etc - where pitch is constantly changing -- the model will keep an even track -not pitch sensitive -
I had to increase expo somewhat to desensitize it - but still the ability of the wing to do this -PLUS offer instant flick rolls -which are totally predictable confirms my earlier thouht on this concept .
You an theorize till the cows come home - but actual practice is the real world.
The thick winged models of the same size /weight are terrible on the flick rolls - they simply refuse to stall.

Avoiding stall is often the main goal - especially beginners wouldn't appreciate flying a plane that stalls easy.
You may keep practising until the rivers get dry, but the laws of physics are always there to be considered, regardless you like them or not.

I am using them - that's why it works !
Maybe I should have said "stall on command ".

You keep telling us how well you can handle your foamie but I don't think that's the point here.
The pilot's commands don't make a plane more stable even if the pilot is capable to fly it safely.
The plane's degree of stability/instability is always there regardless pilot's skills.

it will trim hands off in straight level flight - and fly for a looong distance -as far as I can see to control it -