RE: Suggestion for moderators
 

Dick,

Now that I've stopped laughing long enough retrieve my my keyboard, I'd like to put in my .10 cents. (inflation, you know). It's always real muche funn to see a very knowledgeable person "tweak noses". I thoroughly enjoyed this string
re: C.G. "Does Anyone Really Know Where It Is"??
Way to go! Now; let's start talking about "Center of Mass".

RE: basic aerodynamics
 

Dick,
You say "enlighten me," but your door often seems to be shut tight when you follow up with things like "but leave the wind tunnel at home." As I see it, the "theoretical explanations" he alludes to have already been covered, in layman's terms, in this thread several times.

-David

RE: Suggestion for moderators
 

I haven't had a chance to read the whole thread, but I am wondering: whatever happened with "nose heavy flies poorly, tail heavy flies once" ?
Luis

RE: Suggestion for moderators
 

piffle ---

RE: basic aerodynamics
 

Dick,

In point of fact, you don't explain why your stuff works. You simply say, over and over again, that you know it works because you've flown it. At no time have you explained how lower wing loading broadens the usable CG range, or why flat plates are better wings at low Reynold's numbers. Telling people to 'leave the wind tunnel at home' is perhaps the most ricidulous thing you've said. The only problem with wind tunnel results is that they are usually not performed at Reynold's numbers that are applicable to models. Wind tunnel results for the right Reynold's numbers would be very valuable to see.

banktoturn

RE: Suggestion for moderators
 

OK- you tell me why it works -using wind tunnel data .
Believe it ot not you don't need tunnel data to make something work.
Lots of stuff that was designed by wind tunnel research turned out to be a flop.
NOT because of the tunnel - simply because real world use shows up flaws that paper work and controlled enviroments don't/ can't / never will.
Tunnels beat guesswork - I am not a fool.
I never alluded to any explanation of why the stuff works - simply that it does work-
You have to do actual hands on stuff , eventually .
Where are you going to get a tunnel which runs at 10 mph airflow ?
I guess they exist - I don't kno who uses em tho -
You really don't think light weight broadens usable CG range?
Lower loadings = lower angles of attack needed to provide same amount of lift.
So the craft can maneuver at lower angles of attack and will recover to lower angles of attack that is, recover from departure conditions (stalled ) much more readily.
This is not a true statement?
Take any powered plane - fly it - now add weight - keeping speed the same - and see if you can't find the same effect.
eventually it will stall and never take off.
How does lower loading increase CG range ?
It simply reduces the critical nature of the cg --control can become pretty ham fisted in fact .
Attempts at exceeding stall angle have to be really intentional -as opposed to the typical full scale design which must be carefully kept with in the "envelope".
stability can be traded for maneuverability .

RE: Suggestion for moderators
 

Dick,

In this post, you say that 'you never alluded to any explanation of why the stuff works', but just a couple posts ago you said: "I do try to explain why my stuff works".

I don't think that low wing loading broadens the stable CG range. I have already said that it may broaden the usable CG range by making an unstable or barely stable plane flyable, due simply to the lower airspeed at which it can fly. However, your statement with which I took issue originally, and still do, is that "if a plane is light enough, CG doesn't matter". That is a different statement, and is particularly unaccaptable in a beginners' guide to aerodynamics.

Flying at a lower angle of attack does not give a broader usable range of CG locations. Nor is recovery from stall what stability is about. Is that your explanation?

banktoturn

RE: Suggestion for moderators
 

Dick, as I said, micro UAV research is quite active, but even when doing "normal" low Reynolds number research the tests are frequently done at tunnel speeds below 10 mph. The setup I have the most personal experience with usually operates between 6 and 35mph, although we have tested at even lower speeds.

RE: Suggestion for moderators
 

Great! -So - I would guess you have tested designs using very low loadings at very low speeds ?
sound like a natural for "loitering " stuff.
I have to cut and try to see what is going on.
Is there data on craft having loadings of aprox 5 oz per square ft flying at 10 mph?-20 mph?
Tunnels really don't show how wing loading enters in tho -does it ?
only angles of attack?

RE: Suggestion for moderators
 

and

Tunnels give you information on drag, lift and pitching moment coefficient. It is not dimensional, so it is valid for any wingloading as long as the Reynolds numbers tested fit into the flight envelope of the actual vehicle.

As for what are actually built for micro UAV research using the data obtained from the tunnels - loadings differ, but the very low loadings are not very interesting since, as I explained in the first post, they have a very definate size limitation. As equipment gets smaller and lighter, instead of lowering the wing loading the tendency is usually to make the aircraft even smaller. Physical sizes for those that actually fly are typically between 12" and 6" wingspan, although they are always trying to get even smaller and I wouldn't be surprised if someone such as the guys from AeroVironment have actually flown something smaller than that.

RE: Suggestion for moderators
 

I understand.

RE: Suggestion for moderators
 

Dick,
Everybody knows that by reducing the wingloading will reduce the stall speed - that's just part of the old "hard" rules, which you don't seem to appreciate so much…
But, since an airplane rotates about its centre of gravity, it either flies or dies depending on its CG location… :eek:

RE: Suggestion for moderators
 

Uh???

Luis

RE: Suggestion for moderators
 

You know -- it's one thing to know where to look up rules -
It's quite another to learn how to apply/ massage/ modify them.
Don't evaluate me .
You really don't know what I appreciate.

RE: Suggestion for moderators
 

You are unnecessarily arrogant (and WRONG)
I think I will hang around other forums and with other more open-minded and humble individuals, and not waste my time in this thread
Luis R. Urbina, MD, FCCP

RE: Suggestion for moderators
 

thank you for your unsolicited testimonial.

RE: Suggestion for moderators
 

Maelstrom,

It ain't bragging if you can do it. Dick Hanson.......arrogant? Perhaps.
Dick Hanson.......extremely knowledgable??......... undoubtedly; and he can
certainly do it, and has...... repeatedy. At times you must reach carefully past
the sharpest thorns to pick the prettiest rose.

Chuck Earnest

RE: Suggestion for moderators
 

PS:
I just hope Dick Hanson is not a commercial airline pilot, where CG does matter. He has the arrogant attitude that results in aviation fatalities. Regardless of how much he may know, he is conveying the wrong message for those who don't know as much or have his experience. For those of us who live in the real world CG is extremely important. When you are flying a model airplane you better set your CG within a range that allows you to control it properly. Sure if you have a more powerful engine you can get away with a totally unconventional CG, or if you have extremely large control surfaces (depending on which way you are moving the CG), but from there to saying that CG is irrelevant is a dangerous stretch.
And, Chuck, don't stick up for him. Arrogance is not kosher. No matter how much you know. Actually, the more you know, the more you realize how little you really know. And if that doesn't make you humble nothing will. There is something called narcissism, and it is not a flower.
Luis

RE: Suggestion for moderators
 

Luis,

With all due respect; do not set youself up as an expert as to who I should "stick up" for or who I should not. Also, I do hope you realize that there have been many lives lost in developmental aviation by those who "push the envelope". I dare say that most non-experimental aviation fatalities occur not because of unknown factors, rather know factors which are ignored. I, personally, would fly with Dick or in any aircraft of any flavor he cares to design and build. Just for the record, I was a pilot until I lost my medical cert. and have been involved in model aircraft since the middle 1950's. I am somewhat familiar with both sides of the coin. I am sure that all the advances in any endaevor one might name were not made by perfectly "balanced" (by everyone's standards) individuals. I do not think that discovery is tied to personality. If it were, we would still be sitting in caves, beating on a rock, and complaning that "we ain't never going to have television".

This thread seems to oscillate from theoretical areodynamics to the practical side of things, depending upon which sacred cow the posters are trying to worship. If one is to learn, one must look past the labels, personalities, prejudices, and any other perceived personal faults of either the student or teacher. If one digs through a pile of cow poopie, he is likely to find the seed of a tree. Years ago, I attended an event called "solo de-brief". It is held as each class of Naval Aviators at Naval Air Station, Corpus Christi, Texas, complete their solo flights. You could not, generally speaking, find a more cocky,
self-assured, and yes, some might say arrogant, group of people if you had three months to look and an unlimited expense account. Thank God for them. I only mention this to say: Do not discount self-assurance and the ability to "do it" as arrogance, which in itself is not necessarily a bad thing.

Sense of humor.......... one of the most effective offenses or defences one can possess. Hmmmm......? Narcissism; now we are branching out into psychology......... I don't think this thread is long enough. I'll just take your word for it that narcissismis not a flower. Sure sounds like one, though.

Regards to all.

RE: Suggestion for moderators
 

Interesting group of people
The point I was interested in is in CG on extremely lightly loaded airframes
My finding was that cg really is not critical on these highly powered lightly loaded models.
My statement " if it is light enough CG does not matter" really offended some
Why?
I get name calling.
I respond -
more name calling.
I really expected better .
Solch ist das leben.
This is not a good way to handle any debate or discussion - especially from those who post their "letters" after their names.
Just to put certain individuals at ease -
I have never advocated willy nilly cg placements for the conventional airframes .
Also, have models which will trim and fly as free flights (Seniorita, for one) on low power.
Spent lots of time setting up planes for those new to the hobby.
My thought was to encourage discussion on rather new approaches to models - not be condemned for scratching the sacred cows of some reader.
To the true professionals who responded - thank you .
I ain't mad - not even hurt -
just a bit disappointed.

RE: Suggestion for moderators
 

Ok Dick, maybe your intentions have been good, maybe you've just been misunderstood….
Finally, I just like to put a simple question:

Is there any case in the real world where an airplane's CG doesn't matter?

RE: Suggestion for moderators
 

Perhaps, after the crash? :)

For those of us who know Dick, we would probably characterize him as intelligent, innovative, resourceful, quick-witted, thought provoking, open minded, and fun to be around. I'm sure others that know him better than I could add even more. FWIW, I am proud to know him and consider Dick both a friend and mentor. I do not consider him arrogant, self-admiring or egotistic...I hope in time others will see him in the same light.

As for CG placement on the foamies I've found that the vertical position of the CG plays a large part of my opinion of their handing qualities. I find that making sure that the thrustline passes through the CG eliminates large pitching and yawing moments with power changes. I continually tweak the thrustline and battery position until I'm happy with it. Also I found that things we never really see on normal aerobatic models like gyroscopic precession and prop normal force have a lot to do with the stability and control (S&C) of the foamie. Originally (before good batteries light strong materials and small equipment) we had to use very large props and small airframes to obtain hovering thrust. On some of my original designs I had 14" props on 30" span models. What was funny was doing knife edge passes with zero rudder deflection because the moment generated from the prop normal force balanced the directional stability. Once the weight of the models was reduced we could run smaller props and get rid of these prop effect issues. The only other time I'd seen prop normal force be significant enough to cause real S&C problems was on flying wing UAV's. I find these models very interesting from an S&C viewpoint. I also feel like they 3-D better than my 40% aerobats but seriously lack the precision that you can obtain with a larger model...I hope to change that eventually.

All the best,

George Hicks

RE: Suggestion for moderators
 

Well --- I am not sure -
On full scale stuff like airliners absolutely CG is very important - When I started travelling a lot - we frequently had to "move to the front , please --".

But just take a real look a t a extremely lightly loaded , highly powered plane -these types act very indifferently to cg .
Why?
take the "impossible" plane which weighs nothing -bu is say - 500 sq inches--
There is no inertia if it weighs nothing - so control inputs simply have to keep it flying at angles whch do not exceed stall.
Impossible?
OK let's make it weigh a gram - now it is heavier than air .
again inertia is extremly low making it still very controllable even with the entire 1 gram situated at the rear.
I thought some guys who were into abstract thought ,would see that .
Too heavy - cg is of no value
absolutely - why bother
My point was -- fix the real problem .
I certainly did no expect some of the comments I got -
but I asked for it . Should have seen em coming.
Hving read some other threads on really odd tstuff - I thought this would be fun.

RE: Suggestion for moderators
 

And apparently it's important for reasons having nothing to do with longitudinal flying qualities...

RE: Suggestion for moderators
 

..........................and the well thought-out, informative, well-meaning comments just keep on a' commin'..........

We are amused.........


C. Earnest

RE: Suggestion for moderators
 

If one digs through a pile of cow poopie, he is likely to find the seed of a tree and may be able to build a house or just a model airplane, in case the tree is of balsa...
But CG or not CG is still the question.
Sense of humor is one of the most effective offenses or defences one can possess...:D

RE: Suggestion for moderators
 

adam_one.

aaaaaaaaaaa-men.

C. Earnest

RE: Suggestion for moderators
 

C Earnest,

What does "CV in sight" mean?

RE: Suggestion for moderators
 

Shoe,

It's a phrase near and dear to a Naval Aviator's heart:

CV (carrier) has been sighted...

BTW, are you the same "Shoe" that used to be in the JEFCO group? If so,
do you lstill have that beautiful D.F. F4 "Playboy" jet black Phantom?

C. Earnest

PS: I think that perhaps it may be time for a new tag line........

RE: Suggestion for moderators
 

That's what I thought. How many traps?

Different Shoe

RE: Suggestion for moderators
 

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

RE: Suggestion for moderators
 

You were doing really well, up to the point you said that a zero-weight airframe would have no inertia....Ouch that hurt!![:o]
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.

RE: basic
 

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.

RE: Suggestion for moderators
 

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.

RE: Suggestion for moderators
 

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

RE: Suggestion for moderators
 

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 ".

RE: Suggestion for moderators
 

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.

RE: Suggestion for moderators
 

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 ---

RE: Suggestion for moderators
 

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:D

RE: Suggestion for moderators
 

I give up -the whole thing was hypothetical.