Shoe,

None, unfortunately. I had my OCS/flight school application approved and all tests except physical passed and the Marine Corps (Navy) docs found a touch of a color perception problem so it was a no-go. They said if I really wanted to pursue it that perhaps the Army would let me fly helos. Since I had already been to Vietnam as a tactical air control radio operator (1965) and since the year was 1969 and the bullets were flying even thicker than '65, I politely declined their offer. I finished my 12 years as a Marine Corps radar/computer technician and got out. I am just a (former---lost my medical) private pilot with a deep curiosity about and interest in aerodynamics and Naval Aviation history. BTW, I would have given my left .... to have attended flight training with the best. Their "Handbook for Naval Aviators" was the aero-standard for a long time and I would love to have another one. (All deference to the U.S.Air Force (my bro' was a U-2 pilot), Army, and Coast Guard pilots out there; you are all great and God Bless you one and all!!) My apologies to all for a definite off-topic post, but I did not want to leave a false impression with anyone.

C. Earnest

You were doing really well, up to the point you said that a zero-weight airframe would have no inertia....Ouch that hurt!![]
Inertia depends on mass, which is completely indenpendent from weight. Weight depends from mass, since it's a force represented by the product of mass and the gravity acceleration, but not vice-versa. See a satelitte orbiting the earth. Has it got weight?? No, otherwise it wouldn't be orbiting. Now has it got mass?? Yes, it's composed of matter, and matter has mass. Has it got inertia?? Yes!! Try imparting a rotation motion to it and see if it will stop after you quit applying the force to make it rotate. Momentum conservation law...

OK, since I don't mean any insult to you, just a constructive critic, I will try to correct that. Our hypothetical (although not that hypothetical, this is perfectly possible to be done, but not practical, there's a difference there) zero-weight airframe if had a low mass too, would have a low inertia. Zero inertia, I may be wrong but that is really impossible, even light has got it inertia (NASA is researching laser powered planes....). But I see your point. Zero weight, no center of gravity, since there's no gravity acting on it. So if there is no CG, how can it be critical?? In this situation, the center that comes into play is the center of mass, as someone has already mentioned in this thread. And it radically changes the laws governing flight, I can only thoerize about them based on my limited knowledge.

If the point people here is trying to make is that only careful designed planes will fly, they are wasting their time. Everything moving through air, by displacing it, generates lift. Everything. Now, if that lift is enough to raise the object from the ground is another story, but that lift is there. Ever seem a racing car "take-off"?? I have a pretty good video of one and I can post if anyone wants to see it. Want a more practical example, and easily done at home?? While driving your car, put your hand out of the window, like it was a wing. Go increasing the speed and when you get to somewhere around 45-50 mph, the lift generated it is enough that you don't need to force your arm to be straight. Your hand is "flying". Adjust the lift by changing your hand's AoA (Angle of Attack).

With that said, now that we know that anything will fly, we have to adjust the thing to it's mission. The 3D foamie is perfect for what it does, that is, wild, tumbling, and agile flight at low Reynolds. Try putting a super-critical, super-high Reynolds, laminar flow airfoil on it, and it will lose it's ability to perform it's mission well, because the airfoil that works better in that situation is the flat-plate, leave the super-critical airfoil to critical speeds (approaching the speed of sound) that it's designed to work at. Pick the flate-plate for critical speeds and you get the same situation, the wing won't work for what it's supposed to do. In a super-critical wing that is to create the maximum amount of lift with the minimum of drag possible (high L/D ratio). Will this wing fly in low Reynolds condition? Yes it will, but not as efficiently as it would at critical speeds. Will the flat-plate fly at critical speeds?? Yes, but again not as efficiently as it would on low Reynolds.

Dick Hanson's limit theory (as the wingloading approaches zero the CG becomes irrelevant) is true, but cannot be applied to conventional airplanes, which are subject to the earth's gravity force and always need airspeed to keep flying.
That assumption is not correct.
An airplane that weights one-gram may be lighter than the air (it depends on ratio weight/volume).
E.g. a balloon weights much more than one gram but still is lighter than the air.

Anyhow, an "airplane" that weights zero is no longer flying like a conventional one, because such an "airplane" doesn't need wings at all, it just hangs in the air like a balloon.
Such an "airplane" will never ever stall, just because - no weight - no stall.

well -an empty balloon may weigh a gram -but it can be filled with light gas to almost zero weight on any scale under conventional weighing conditions.
Not that tht matters
My point was that as we approach zero wingloading-the HARD rules soften/change -and when extremely light -the aircraft is far less critical to cg -
you can calculate till hell freezes over but in actual practice the airplane is still flyable as it moves along.
It is not a Piper Cub -or a hands off glider but it is still an airplane
maybe not one you would like .But still a powered , heavier than air machine.

An empty balloon that weights one-gram will still weight at least one-gram after it has been filled with light gas, despite the scale will show less weight due to the Archimedes' principle:
A buoyant force is exerted on an object submersed in a fluid. The pressure beneath the object is larger than the pressure above. The resultant force on the object is upward, opposing the force of gravity.
When an object is partially or fully submerged, the buoyant force, or apparent loss in weight, is equal to the weight of the fluid displaced.
That's a much less controversial assumption, which has already been addressed several times here in this thread.
Below are some of the postings:

http://www.rcuniverse.com/forum/m_11...tm.htm#1579840

http://www.rcuniverse.com/forum/m_11...tm.htm#1611105

http://www.rcuniverse.com/forum/m_11...tm.htm#1614766

http://www.rcuniverse.com/forum/m_11...tm.htm#1797383

Please - -That does not even apply --The bouyancy thing written in blue is obvious - anyone knows that a blimp or a balloon has mass -but the weight relative to the air is less.is obvious
This is just semantics -
come on I am trying to examine how light wingloading changes the generally accepted "hard and fast rules ".

I wouldn't say that there are any hard and fast rules regarding CG location.
For a conventional airplane to be positive stable in pitch, its CG most be ahead of the airplane's Neutral Point NP.
The distance between CG and NP is called static margin and is expressed as percentage of the main wing's MAC.
The static margin may be between 5% and 15% of the MAC, so there's plenty of room to play here (no hard rules).
When the static margin is zero (CG coincident with NP) the aircraft is considered
"neutrally stable".
Which means that the spot you choose for your CG within the stable range is to some extent up to your personal preference - how you want your plane to handle.

Low wingloading gives you low stall speed, but it doesn't make your plane positive stable if its CG is located aft the NP, this is a rule that applies to any airplane that's heavier than the air, including your light wingloading foamies.
Since they have low wingloading, they can fly slower without stalling, which gives you more time to react and make corrections.
Anyhow it would be much interesting to know how close your foamie's CG actually is to its NP.

I never even intimated that the planes were more stable - really -
My whole thought was that as one reaches for zero wingloading - the CG becomes less critical - I called it less important and of no importance at all in some instances.
I can't prove anything with a calculation on this -and no one has ventured a relevant calculation against the thought.
Why even bother .
I did say I thought the plane would be flyable at "zero" wingloading (weighing nothing).
It is a whimsical thought sure - but I see no reason it would not fly ---with constant corrections of course .
I see thrust becoming the all important factor in the equasion and lift reduced to zero importance. (nothing to lift.)
BUT - the surfaces would still be used --to control flight directiuon.
Now call it an airplane - call it an elephant - I don't care -
it is heavier than air (one 1/100 of a gram is till a +) and is powered.
For damn sure it is NOT a conventional airplane - I never intimated that either .
good fun tho ---

But that's nothing new, Dick.
Once upon a time there was a flying ship called Zeppelin, it carried lots of people, weighted hundreds of kilos, was controllable and still it was lighter than the air - yes it was!
Now, how can you conceive a plane weighting just 1/100 of a gram and being heavier than the air, is just beyond my wildest imagination.
But why don't you make us a surprise? - show us one

I give up -the whole thing was hypothetical.

Dick,
Can you post a scale drawing of one of your foam 3D models, with the CG labeled... just so the pencil pushers can do the math and see how things look?

thanks,
-David

Hello guys,

I see this discussion is really vivid.

Just was thinking about- if CG does not matter, does then existence of stabilisator (tail surfaces) matter? Obviously the fin is good to have for control.
But just mix the ailerons to be flaperons and you will be fine without the tail.


I am really newcomer to aerodynamics, but my gut feeling say, that very light plane with lot of thrust (twice the weight) is flying more in a way the Extra is flying the knife edge. And wingloading is not a major player there- the thrust is. I dont know if there is a defined static margin for an aeroplane to be stable in the knife edge regime. I doubt.

Given the low weight and low wingloading it actually might be of benefit to have unstable aircraft- pilot can deal with gusts and turbulence of the air with better control response. And to have stability in this size- it will only help in calm weather or indoors.

But to really answer if CG matter- why not to compare time in the air for airplanes of the same wing area and same weight, same engine and battery, one with oldfashioned CG and other with random CG. Or maximal distance flown. Perhaps also in different weather conditions (indoors vs outdoors).


I think even small size aircraft will fly more efficiently when stable.

Zero weight does not apply to aeroplanes- definition of airoplane is that it is heavier than air. And it fly only because air has mass. Go to orbit in outher space- no gravity and no air, and no thrust from propeller.
By saying zero weight- what you really mean is to have infinite thrust to weight ratio, low weight only helps to keep things slow, otherwise there is no difference with the bigger plane (except Re number and its consequences).
This beast with rocket engine will propably be stable and controllable as long center of drag is behind the center of thrust (if such thing can be defined- it is CG normally).


Once upon a time in between sessions in the school i made a paper plane (actually during the session). It happened to be precisely balanced- i could leave it in the air (without throwing) in what ever position- nose down, nose up, side up or upside down- it always returned to perfect straight gliding flight from height of less than 3 meters. It was simply beatiful- if I only could repeat this with something bigger. The plane was propably around 1-1,5 grams heavy and had approx one square decimeter of wing area, and it was delta- aspect ratio much less than one.

Hopefully we will find the thruth about the gravity and its center.

Happy flyings.

Here it is - very conventional layout -
I typically fly it with the cg at about 40% of the root - but once, when the battery pack came off -and I flew it to a normal landing - it took lots of down elevator and some aileron fussing -but it still flew.
The drawing is exactly to scale -so anyone can pick the cg which makes them comfortable - anywhere from th LE back to 40% is flyable for most people -but - you can go back further
By the way -I flew a heavy pig of a scale P51 yesterday -and the cg on that turkey was critical -
Read the prior post on eliminating the stab - and flying with flapperons only -
This is not only possible but done many times and kits were on the market .
Glad to see this guy is thinking!

Dick,
Thanks for posting that. Now that I see it, I think you posted it before... sorry for my short memory. It does look very conventional and, since the spanwise datum line for the wing is ahead of the 50% point at the root, it's not at all surprising that you can fly it well at 40% of the root chord. Eyeballing it, that will be in the 30-35% MAC range. Very normal for an aerobatic plane. And no, I'm not saying this to dispute your observations... just making an observation myself.

-David

Dick,
Could you tell us about the wingspan and the flying weight?
By the way, locating the CG at 40% from LE seems to me quite close to the NP, which would make it more neutrally stable than positive stable.
The low wingloading along with rather large control surface areas would make it flyable, but I'd not recommend more than 40% to a beginner.

34" nothing special about it - all up weight is 10-13 ounces depending on battery packs selected - wing loading is under 5 ozs/ ft
The typical popular foamie is quite a bit longer in the fuselage -to make it more of a hover forever model
This was of no interest to me - I was after a model which had instant abilities to snap and roll and turn in extremely tight ,flat circles etc.
This it does.
placed in a knife edge- one can simply do a flip -in knife edge thru 360 degrees.
OR do a pirouette.
It flies on edge very easily with virtually no couple induced - very stable
This is because the AOA of the deep/short fuselage is extremely low for level knife flight.
These types may not throw away YOUR rule book but the results are quite surprising.
And one hell of a lot of fun.

people fly capiche's at my club in the UK with the CG way back - like 55% back.

Hands off and inverted they apparently climb - wing loading I guestimate at about 15oz.

I think a lot of people thought you had your CG behind your NP.

Even paper planes set up like that tend to tumble!

One thing I would like to mention though is that if the plane's CG is behind the NP and the thrust force is greater than the weight of the airframe, then the wing isn't doing much, so perhaps CG doesn't matter then - it's effectively a helicopter

Is that what you are saying Dick? or are you making the point that perhaps birds or insects operate in a weird laminar flow low Re regime where the conventional rules do not apply?

hi again,

if you can loop those birds in knife edge- most propably you dont need wings for lift- at least not as big as they are if the flat fuselage is enough for flying. What is "wingloading" in knife edge? Instead the wings are only for drag and control. Thrust keeps it in the air, big wing creates enough drag to counteract thrust at reasonably slow speed. Make the plane bigger and heavier, put a strong engine with thrust 2x to 3x the weight and make the wing big enough to counteract thrust at 20mph. I believe it will fly the same way as the small one. And it will have low wingloading- just for drag. The problem is purely technology- such bigger plane will fail structurally. Thats why you have it small- for better structural strengh to weight ratio.


The weight does not have to be small- wing loading yes, but rather indirectly- not for lift at small speed but for large drag to counteract the thrust at slow speed. In addition big wings have big control surfaces- which is dood at low speed.

How would glider fly with weight approaching zero?


all the best
A.

sorta - --once you are able to simply vector (with thrust) - then the CG is of little importance
for some reason -this thought makes some guys crazy-
Why?
If all I was doing was flying models like the p51 I flew this weekend - which flew pretty close to upper limits of it;s lift), I would be careful to keep cg forward --and add up trim as needed
as it was the p51 was not too bad (not too good either) -but how in the world the BARF mfgr expects the novice to handle it- especially when it was suppose to have a smaller, lighter engine --is beyond me -- they say " be sure to balance". yeh, right -
This is the kind of model I used to see in this forum where the owner would ask " will flaps make my P51 fly better ?"
The answers were never the correct one .
which is:
Nothing will help it --it is too damn heavy and you haven't enough power.

thrust to weight ratio much more than one together with large drag and you should only be concerned that center of drag is behind from the center of mass.

Anyway- this kind of planes are extremes and the wings lose their meaning- wing is supposed to create lift, with vectored thrust it becomes just a control surface and may be it should not be called wing anymore.

Parashute and dart arrow might be closer to your planes in the manner they move through the air than a regular glider is.

yes - you are correct - but some of the guys did not see that - actually the drag only needs to be behind the point of thrust .
I don't think a pusher prop setup would be controllable.
as a glider this setup is worthless.
The wings still have value tho and just because it operates more like a surfboard - it still works .

DickHanson.

I got to say, I think you're nuts. You state that you balanced a pylon racer on the leading edge or very nose heavy? That's NOT how things work in racing. Most Quickie and Q40 airplanes are balanced so close to the center of lift, that full up elevator is usually about 1/8" of total throw at the trailing edge. Since the wing has to offset the downforce of the stab, having an airplane nose heavy just increases the amount of lift the wing has to generate. At one G, not much, but we pull 30-40 G's in the turns and so that extra lift the wing has to make really slows a nose heavy airplane down in the turns. Perhaps, you should stick with your flat plate knowledge and quit wasting peoples time.

High Planes,

As to whether or not you are the nutty one:-) or not will have to remain moot. You are not, however very well informed if you state that CG position has any effect on G load vs. lift requirements viv-a-vis the wing. The only thing to which you can be referring is wing loading vs. a/c mass. You are playing around with variables that you cannot play with in that fashion. Nose-heavy aircraft place a greater aerodynamic load on the elevator to obtain the same amount of elevator authority at a given airspeed. (tail-heavy lands "hot" or snaps.....nose-heavy = more stable in pitch mode; more upsetting force required on elevator to cause displacement about the lateral axis of aircraft.) There are several other confusing statements in your post, the meanings of which I will just have to guess and therefore can have no comment.

Regards

30 to 40 G's
interesting --

also moot..............