There is none so blind as he who will not see
We must not close our minds, we must let our thoughts be free

https://www.songfacts.com/lyrics/ray...g-is-beautiful

Open my eyes, that I may see
Glimpses of truth Thou hast for me;
Place in my hands the wonderful key
That shall unclasp and set me free.

https://library.timelesstruths.org/m...hat_I_May_See/

NASA does show a correction page ---

https://www.grc.nasa.gov/www/k-12/airplane/wrong1.html

Note the page title --- ' Incorrect Theory #1'

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I still recall the Indian and African elephants comment, (post #27). i.e. true statements.

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Originally Posted by Tim Green

.....................

Heavier than air lift does require accelerating air downward however. Which is Newton. And ... no one has ever demonstrated otherwise.

On its own, just what's written, is a correct statement.

Or can you get lift from not accelerating air down ?

Or it isn't Newton ?

Can you demonstrate otherwise ?


Every one love to make their own interpretation of what is actually written. ?

I know not what course others may take, but as for me,
The written word always needs a second or third look.
The written word is typically nothing more than an interpretation of undocumented and or unproven thoughts.

Originally Posted by Tim Green

Heavier than air lift does require accelerating air downward however. Which is Newton. And ... no one has ever demonstrated otherwise.

That depends on where you look. In 2D there is upwash at the leading edge equal to the downwash at the trailing edge so no net downwash in 2D. A 3D wind tunnel model with its tips sealed by the tunnel walls also has no net downwash. A 3D wing in free flight appears to have more downwash than upwash immediately behind the wing but if you look outboard of the tip you'll see that there's upwash there that is equal to the additional trailing downwash. So no net downwash in 3D either.

Originally Posted by NC14310

For dynamic scaling, weight should vary as the cube of the scale ratio
Full scale aerobatic weight is 1609 lb

Therefore, a 40% scale dynamically scaled model would weigh 103 lb

And a 1/5 scale dynamically scaled model would weigh 12.9 lb

I suspect yours were quite a bit lighter, which helps explain why they didn't fly in a scale-like manner.

FYI
The 40 % typically weighed 38/40 lb dry
The 1/5 scale , 11 lbs or less
The object was never to get scale like performance
In order to fly the models, standing in one spot, you need to have relatively, far more power.
This allows you to pack the maneuvers into a smaller space.
This was all done 20 30 years ago
Today , we do the same maneuvers with 9 ounce electric models in a 50 ft box
Tumbles are impossible
Just as in nature, the aircraft performance is tied to size
If you go to indoor aerobatics, you can throw your reference books away.

Originally Posted by richard hanson

The written word is typically nothing more than an interpretation of undocumented and or unproven thoughts.

As opposed to the spoken word, which is always reliable?

Was the invention of writing a mistake?

Originally Posted by richard hanson

The object was never to get scale like performance

YOUR object. Other people might have different objectives. You seem to have trouble with that.

Originally Posted by richard hanson

If you go to indoor aerobatics, you can throw your reference books away.

Not having actually read or studied them, how do you know they're wrong?

I suspect more open-minded people involved in indoor aerobatics would disagree with you.

You got me
I have nothing to rely on but experience

For 'scale like performance' (if you mean flying), just fly on calm days ---

6 m span, 5 kg weight (some people can build very light) --

20180714212355 (2 min 6 sec)

The thread --

Douglas Globemaster C 124 Scale 8,85:1 by Thomas Maier

.

That is a very good approximation of scale like flight
The scale stuff I have flown in the past was always far too heavy and so was spooky to fly
One friend now past, built award winning scale models but they were all bricks
A couple of us would fly the models for exhibitions and it was always nerve wracking
The advent of electric power has certainly changed all this
Creating the illusion of scale flight is tricky
The huge team built models ,flown in Europe do a good job of this and now some ultra light indoor electrics can achieve the slow smooth look
Tho it all looks right, most of it is still too fast if you are a freak for textbook scale
And those critics ,typically have no experience at doing it

Originally Posted by Tim Green

... Heavier than air lift does require accelerating air downward however. Which is Newton. And ... no one has ever demonstrated otherwise.

It's been demonstrated over and over again, in test tunnels and in real life airplanes. The fact that you choose to cherry pick only what fits your narrative doesn't make the experimental results false, anymore than the ramblings of flat earthers make the earth flat.
Air has to be accelerated downwards? Nope, acceleration is not force, it's a result of the application of force. Does the plane accelerate upwards? And yet lift is applied to it. And you keep on not understanding what the third law actually says. Go and re-read Newton's principles of motion.

Me thinks Tim is having a bit of fun.

Originally Posted by ShoeDLG

Beyond not knowing of such a case, one can easily prove that a wing cannot produce lift without a pressure differential.

Originally Posted by Tim Green

Taking this old straw dog out for a walk again? Geeze! When did I ever post that? Never.

You’ve been consistently misrepresenting NASA, and now you’re misrepresenting your own initial post in this thread (or perhaps you don’t appreciate the implications of the words you posted there). You labeled the following “incorrect”:

Airplane wings are shaped to make air move faster over the top of the wing. When air moves faster, the pressure of the air decreases. So the pressure on the top of the wing is less than the pressure on the bottom of the wing. The difference in pressure creates a force on the wing that lifts the wing up into the air.

By labeling that incorrect, you’ve absolutely suggested something other than the difference in pressure is what lifts the wing up into the air.

Originally Posted by Tim Green

When did I ever post that?

In your first post of this thread.

You’re having difficulty properly interpreting words that you’ve written. Perhaps that explains your difficulty in properly interpreting the words on a K-12 web page. BTW, they’re still laughing at you.

Originally Posted by eflightray

For 'scale like performance' (if you mean flying), just fly on calm days ---
6 m span, 5 kg weight (some people can build very light) --

Depends on what you mean by "scale like", and "scale speed". Many people think "scale speed" means that a 1/4 scale model should fly 1/4 the speed of its full scale counterpart. Flying straight and level, it will cover a scaled down distance in the same amount of time as the real one.

Achieving this requires building light, slow flying models. That's perfectly all right, if realism goes no deeper than flying straight and level. The traffic pattern flown by that Globemaster model was ridiculously tight. Watching the video, it was immediately obvious that this was a model as soon as it began to turn.

"Dynamic scaling" uses a different principle. We can't scale down the Earth's gravitational field, so the idea is that the model "sees" the same acceleration as the full scale for similar maneuvers. A 2G turn, or 4G loop, will be the same for both.

This forces the design in a different direction. Keeping acceleration constant requires a 1/4 scale model to fly at 1/2 scale speed, the square root of the scale ratio. It also requires it to complete a maneuver in 1/2 the scale time. Which makes sense - everyone knows smaller models naturally respond faster, because of their lower inertia.

It turns out mathematically that "dynamic scaling" requires the model's weight to vary as the cube of the scale factor - so a 1/4 scale model would have 1/64 the full scale weight. A "scale speed" model requires weight to vary as the fourth power - so a 1/4 scale would have 1/256 the full scale weight.

Wikipedia gives the following for the full scale Globemaster:

https://en.wikipedia.org/wiki/Dougla...Globemaster_II

Span: 53 m
Weight: 45984 kg - 88220 kg

For the model in the video, the scale ratio is 53/6 = 8.83
The corresponding weight ranges are:

Dynamic scale: 66.7 lb - 128 lb
Scale speed: 7.55 kg - 14.5 kg

Looking at these results, the model is probably flying a bit slower than scale speed (traffic pattern airspeed is unfortunately not noted), but it's pretty close.

Running the calculation the other way, this model is the dynamic equivalent of a full scale Globemaster weighing only 3446 lb! Which explains why its maneuvering ability is completely different.

Which is "right"? That depends - what are you trying to do? If you just want to build the lightest possible models and fly in slow motion, no one can say you nay.

re: Poor Newton's Almanack

When folks point out to me that someone has done something not logical I tend to ask them, "How long have you been living on this planet?". We even have world leaders who to this day consistently demonstrate the effective use of non sequitur "reasoning" as applied to "What I say goes" or "Whatever I say is true" (in the moment). The ways of the French Sun King Louis XIV still lingers .... just try keep your heads on folks while things sort of work themselves out.

"A mind is a terrible thing (etc.)"



Nevermind (G. Radner as R. Roseannadanna)

Forgive me
From Poor Richards Almanac:
This being a modeling science forum, I thot I wouldst pontificate a bit on scientific changes in modeling, specifically, scale models.
My first kit was a scale model of Frank Hawks ,Time. Flies
I was 13. And had an. Atom 09 to power it with
The completed controline model taxied at a good clip but alas and alack, was never to fly.
Cut to much later, I decided my second scale model would be a P51 Top Flite kit
This one flew but my instructor snapped it on landing
I was informed that warbirds are necessarily heavy to fly scalelike
This seemed to be a generally accepted std
Further experiences in flying others scale designs, showed scale typically meant heavy
Fast forward to 1990s
Scale arfs from Japan started to arrive
These were-ply balsa designs which again, prooved to be overweight
Jump to the advent of good electric motors and li po batts then 2.4 radio
The imports became injected molded epp , which were far lighter than the wood stuff
In the space of less than 20 years, we got
Light strong foam
Very efficient electric power
Radios which were free from frequency conflicts
The current crop of foam arfs are light, strong and as far as I have see , capable of far more scale like performance than the stuff we labored over back when
A
Oddly enough, the rather rounded and blunted and strange thick airfoils worked just fine
Many times they worked better than the painstakingly built wood and silk designs
As gliders some were also quite good and some, well, not so good but all in all
Better than the scale foils and sharp trailing edges etc, we were told were important for proper flight.
So we learned, there is always room for improvement and re evaluation of accepted teaching
It has been a very interesting journey and it isn’t,over yet