JustinG

Jef Raskin worked for Apple and he started a project that was called "Macintosh", that much is true. But the things that came to make the Macintosh a revolutionary computer in the early 80s were things that Raskin was against, mainly the use of the Motorola 68k processor and the mouse. The final product that was introduced in 1984 actually used very little of Raskin's original vision, only the Macintosh name; his ego couldn't coexist with Steve Jobs and Raskin left Apple in 1981. If you want to see Raskin's "Macintosh" then check out the Canon Cat, a computer that shipped in 1987 with no mouse and a bunch of function(leap) keys. A far, far cry from anything that could be construed as "Mac-like". It sold 20,000 units and was discontinued after 6 months in the marketplace.

Just about the only person who calls Raskin "the father of the Macintosh" is Raskin himself, and thanks to his position at Apple at the time and the rather large ego that Ben alluded to, he feels justified in repeating it. The rest of the original Mac dev team, from the accounts that I've read, don't consider him the "father" of the Mac. Andy Hertzfeld's new book on the birth of the Mac didn't sit too well with Raskin, according to Hertzfeld. Raskin has made his contributions to computer science with his work on user interface, and he's obviously a smart man with some interesting ideas, but his contributions to the Mac don't rise to the level of fatherhood IMHO. If he was the father of the Mac, then he was an absentee, deadbeat dad who abandoned it before it was even born and only came back to visit after his son grew up and became a wealthy rock star.

I had no idea Raskin was into RC until I picked up an issue of FlyRC a couple of months ago and saw his column there. To hear that he is bloviating about something and wrong at the same time only reinforces my impression of him. He appointed himself the father of the Macintosh, why can't he appoint himself the father of aerodynamics too?

rmh

Ben will hate this :
But I think it is true
Anytime you move something thru air , you change the pressure all around the object.
The lowered pressure , can be lift or drag- (a rose is a rose).
You need both - but when/how and whare is where the learnin comes in.
Look at a parachute -
It's primary job is to add drag (low pressure directly opposite the direction it is heading)-which reduces it's speed .
If we redesign the parachute to make it steerable - we can change the direction of the heading.
If we really get clever with it - we can increase speed and actually get lift.
How does that happen??
We moved the low pressure -relative to the direction the parachute is headed and turned it into lift. (way over simplified).
So what you call "lift " -----------------------is low pressure workin for you .
What you call "drag"----------------------- is usually low pressure workin against you -not always just usually.

OK -is this explaination badly flawed?

It is not complete - but let's hear another BASIC explanation .

ptulmer

My Feedback: (5)

Ben,
Well, tossing the balsa sheet is an elegant method of proving what you say. Mind if I use that in my arguments at the field? I just wonder why this argument keeps cropping up among the professionals? It was explained to me and I understood it easily... and I didn't even graduate from high school! There must be something to the downwash arguement that I'm missing. Wouldn't that only come into play during ground effect?


Man, I can't wait to use the balsa sheet method. My AE friend will think I'm smart! (unless he's lurking around here...)

Tall Paul

Referring to Martin Simons series in "R/c Soaring Digest, June '97 thur Oct '97, drag for model sections is measured using a multi-ported pressure rake which moves across the tunnel behind the model. The presssure ports on the tubes on the rake face upstream, and measure the variation of pressure from above to below the test model.
The change in flow momentum is integrated to compute drag.
Lift is measured by a force balance.

JimTrainor

Which implies one could measure change in flow momentum on the lift (vertical, perpendicular) axis and compute lift, and it should be pretty darn close to the number reported by the balance?

Siefring

Yes, but you keep making statements that don’t make physical sense. A lot of people here respect your comments and opinions., I certainly do and I’ve only been reading this forum for a few months.

Wrong. Look the streamline plots below. Where are the vertical forces acting on the air. It is where the airflow is changing direction. Seems to me it’s mostly centered right around 25% of the cord. There is only a vertical force acting where the flow changes direction (or changes velocity) in the vertical coordinate. There is almost no force at the trailing edge. You even argued that there is no force involved in the actual downwash in an earlier post. If there is no force why would it push the nose down.

If you add flaps and have a change in the flow direction near the trailing edge you do get an additional pitching moment along with additional lift.

Again, it’s both. You’ve only considered what the air does to the hood, not what the hood does to the air.

I don’t agree. If you want a good intuitive felling for something you have to try to understand all that is going on -- not just half the picture. Not only that but Conservation laws (momentum, energy, particles etc.) are at the core of fluid theory. Are you saying that fluid theory has added nothing to our understanding of aerodynamics? I seems to me that, if you want to understand aerodynamics when things get really messy (turbulent drag, bumblebees flying, etc.) you need to keep track of the momentum of all the fluid chunks.

Maybe Jef Raskin said this, but I never said pressure is meaningless. I even argued that all the aero-engineer needs to describe lift is the pressure perpendicular to the flow. Anyone who says aerodynamics is all wrong because an aero-engineer does not care how the aircraft effects the air, is just full of …

Can they do this with, one probe and turbulent flow? You say the momentum characteristics of the air are not important, but you would gladly adjust drag terms if you start uselessly stirring the air in circles, instead of creating downwash.

Carl

Oh, here is something else that I completely agree with.

britbrat

DanSavage, no one answered your question (what is the D/P between the upper & lower surfaces of a wing in flight). Assuming that you are discussing models, if you take a standard trainer with 600 sq in & 6 lb mass, the D/P needed to sustain flight would be .01 psi. For a warbird it would be ~ 50% higher. Not much, but it works.

WRT the general discussion in this thread, I'm a former military pilot & I still occasionally bumble around the sky in light aircraft. I'm also a graduate engineer (U of Western Ontario) & a fluid dynamics specialist with 37 yrs of experience, twenty of them managing a fluid dynamics engineering research lab -- I absolutely agree with Ben Lanterman.

Ben Lanterman

Justin - very interesting, I had no idea it was that way.

True Dick except unfortunately things cannot suck, they only blow. That is a basic fact of physics. Vacuum is a space where there are no molecules to bounce off a surface. Less pressure and more pressure across the parachute is just the difference in pressures, big guy against little guy in a pushing match (not a rope pulling match by the way, but pushing) . little guy loses because he can't push as hard.

Lift is indeed low pressure working for you, the closer to pure vacuum you can get the better the lift. Hence all the work on wing surfaces and contours.

Jim - if we could measure the momentum flow and apply it properly it would work - yes - but the process is not easy. It is much easier to put a force balance into the wing, model, whatever and directly read out the forces.

As a good exercise figure out how to do it and report back. I throw it out to anyoneto work out as a matter of fact. I showed lift process calculations with the F=ma in just a few steps but had no idea how to work the momentum results into lift. I would enjoy seening it done.

Ptulmer - I have no idea why a real engineer can't grab onto the notion that lift is pressure on the wing. It is what they were taught and worked with. The momentum is there but is not a good system to work with.

Bobber, there is a simple explaination, just read my comments in the thread. It is explained in one paragarph. Jeff dispels one myth and then instead of presenting good balanced information presents his view of the world which is not at all what the rest of the world presents.

Carl - My comments mostly make physical sense I think. Jeff said that the change of momentum of the air as evidenced in the downwash (look at the drawings in his article) is lift. It surely implies that the downwash is pushing on the wing. He uses the rocket anology. Downwash down and wing up. You are saying what I was trying to say. Indeed there is no pressure differential at the TE worth mentioning but a heck of a lot of downwash.

We don't care what the hood does to the air just as we aren't too bothered about where the downwash goes. Interest is put on where the work is being done, as you note on the wing and up forward.

You don't agree... (rest of statement) Have I ever said that fluid flow theory has nothing to do with aerodyanmics - lordy no. We have to understand everything and momentum is a part of the whole. If you read some past comments I have written about insect flight (the clap and flap and clap and fling are vortex methods of lift) and I embrace the whole theoretical aerodynamics field - good stuff - have never said different. But what pushes on a wing to keep it up - pressure.

Beats the heck out of me if they can do it with one probe. They seem to think they can. Paul gives the answer. We arn't taking about stirring the air in circles, we are talking about nicely working wings making lift. Nothing more.

Don't forget - the only way to move an object in the most basic way is through a Force. Then ask - where does the force come from - molecular impact? Then ask - what do we call that process - pressure.

Paul, we always measured drag on our models with a force balance too. Granted they were expensive pieces of equipment but the only way of getting really accurate data - sufficient to pickup small configuration changes. Perhaps if the tennel test rig can only measure lift and moments you have to revert to the change in flow momentum approach. Is there any chance you could copy the article and present it here. Sounds like very interesting stuff. You do have to wonder how the glider guys are getting the data from just one rake setup. Might be a lot of assumptions applied to the data.

leszek_k

Hmmmm, I am wondering why nobody tried VERY simple experiment :
- start GOOGLE
- type "theory of flight" in a search window
- click GO

I did - and just have a look of one of a results. All of those peapole say the same thing - I am not sure if Bob is going to like it

http://www.aviation-history.com/theory/lift.htm

Tall Paul

About the drag rake, Simons says ( ) that due to the full tunnel width of the models, eliminating any tip flow, creating a balance that can measure drag with this setup is expensive.
Strain gauges can measure the lifting force.
As the rake has many pressure pickups, each feeding an indicator, traversing the rake across the tunnel gives a good presentation of the forces above and below the wing, to the point that open structures can be seen to have different flow characteristics where the covering sags between the ribs.
The process is detailed in the Soartech volumes from UIUC.
A balance couldn't detect the between-the-ribs variations, it would see only the overall effect.

rmh

The only thing I was describing - was that lift - is not necessarily the exclusive property of a wing.
I think that many people get caught on "what makes a plane fly "-- with that old picture of a Clark Y airfoil and some talk about a guy named Giribaldi Brinelli or whatever. ( Take a sidewalk survey if you don't believe me .)
I was trying to (apparantly badly) illustrate that a difference in pressure - irrespective of how it occurs - CAN produce lift-----or drag.

Siefring

Oh my gosh there is all kinds of mistakes in this document.

Fig3 shows a wing that will lift but the wrong streamlines are drawn.
Somehow this is supposed to make a point!


"The lift of a wing is proportional to the amount of air diverted down times the downward velocity of that air."

This above statement is just plan wrong. If there were no other forces active you could invoke momentum balance to calculate the upward velocity of the wing.
Set MassPlane*VelocityPlane=MassAir*DeltaVelocityAir and get the new wing velocity.

However, you do not get the lift force. Force=delta_momentum/delta_time. To get the lift force you need keep track of how the air momentum is changing over time. Or as Ben says just integrate the pressure over the wing.

I stopped reading after that one.


Carl

rmh

I stopped at the picture - this old crappola simply is gibberish to the public at large and worthless to anyone with a dimes worth of common sense.

ptulmer

My Feedback: (5)

Dang, how much misinformation is out there?!

There is a pressure increase under the wing, right?(because the wing is displacing air and moving it due to the AOA) And this is what is being called "downwash", right? And the only time this effects ANYTHING is in ground effect, right?

Wait, let me try again. The pressure I'm speaking of is after the lift is generated by the pressure on the wing surface. The movement of the air is redirected down causing a pressure "bubble" in ground effect.

Some of this stuff is starting to confuse me. I thought I had a pretty good grasp on this. The 3hr round trip to the hobby shop is usually centered around politics because my friend thought I had my head on straight...little does anyone know...

Bax

My Feedback: (11)

From the pilot's point of view, the wing as a device to accelerate air downward is just fine. At any given speed, you need so much angle to keep the wing supporting the aircraft. If you go too slow, you can't move enough air no matter what the angle. If you have too much angle to the incoming air, your wing can't deflect it downward, no matter what the speed. In flight, when the wing can't deflect enough air to support the aircraft, we call it "stalled".

This idea originated with Wolfgang Langeweiche's book "Stick and Rudder", which is a practical discussion of how an airplane flies. It starts out by stating that aerodynamics is much more complex than he'll be discussing, and that he's 'way off base as far as what the air is actually doing. He's trying to help the pilot FLY the aircraft, and the visual images help the pilot a whole lot more than a knowledge of the actual dynamics involved.

As Ben states, if one's trying to teach the science of aerodynamics, then there's a whole lot more than most people imagine. And if you get the science wrong, those who DO know it will call you out.

If you're trying to teach the ART of flying, then you can simplify the science needed down to the practical visualizations needed to control the aircraft. But the visualizations now need to actually help the pilot effectively control the aircraft.

Don't think the article did either task.

rmh

Well shoot - Ulmer - I had not heard those explanations before.
But you are right
misinformation is rampant! (Not you Bax -I was typing at the same time as you) edited
In really basic English-- lift is produced when there is a pressure difference.
The shape of the wing confuses lots of people .
99% of the shapes were done to work in a specific application -be it speed / weigh lifting -etc..
For generating lift - a flat board will work (among many other shapes)
You have to move it at an angle which will get the pressure differences (top to bottom)correct.
Not enough angle or too slow = no lift.
Too much angle for the speed - = ALSO no lift.
Everybody and their dog has produced some "magic " airfoil".
The full scale pros have worked this to a science -to get the best lift for a specific job.
On models - such as we fly - you are still subject to the basic rules - but because of the size - speed and typically low weights we play with.
Well-- the finely tuned shapes just are not as necessary-
And yeh - there is more pressure somewhere under the wing and less pressure above it - but the downwash stuff - that's another story.

The "ground effect "-- is real - you are correct on that -
To put it crudely - -it is pressure between the bottom of the plane and the ground - --which can't get out of the way - so is higher than the pressure under the wings when the plane is up higher .

Ben Lanterman

You know what is funny at the beginning -

"Let us start by defining three descriptions of lift commonly used in textbooks and training manuals. The first we will call the Mathematical Aerodynamics Description which is used by aeronautical engineers. This description uses complex mathematics and/or computer simulations to calculate the lift of a wing. These are design tools which are powerful for computing lift but do not lend themselves to an intuitive understanding of flight. "

He is saying you guys reading this are too stupid to even get a clue as to what the engineers are doing with their magic boxes so don't bother.

"The second description we will call the Popular Explanation which is based on the Bernoulli principle. The primary advantage of this description is that it is easy to understand and has been taught for many years. Because of its simplicity, it is used to describe lift in most flight training manuals. The major disadvantage is that it relies on the "principle of equal transit times" which is wrong. This description focuses on the shape of the wing and prevents one from understanding such important phenomena as inverted flight, power, ground effect, and the dependence of lift on the angle of attack of the wing. "

No body has thought his way for years. Equal transit time is and has always been wrong but the rest of the things can lead one to understand such important stuff as flight. Heck look at any pressure distribution with respect to angle of attack and the corresponding lift, pitching moment and drag coefficients, and yes the upwash at the leading edge and downwash at the trailing edge and put it together into a whole and it all is quite intuitive. But if you don't show them in your discussion no one will ever understand. And indeed these guys never got around to talking about all that "hard engineering stuff". Arn't you glad they are looking out for your mental health.

"The third description, which we are advocating here, we will call the Physical Description of lift. This description is based primarily on Newton’s laws. The physical description is useful for understanding flight, and is accessible to all who are curious. Little math is needed to yield an estimate of many phenomena associated with flight. This description gives a clear, intuitive understanding of such phenomena as the power curve, ground effect, and high-speed stalls. However, unlike the mathematical aerodynamics description, the physical description has no design or simulation capabilities."

Newtons laws. Hummmm, the simplest is F=ma. mass of wing is kept in the air against 1 g of gravity. It requires a force. The only way a force can be transmitted by air is molecular motion which we have always called - pressure.
I am so glad that they have seen fit to dumb down the hard mathematical aerodynamics descriptions for one that gives no intuitive way for the force to be transmitted by air molecules.

What in the he-- do they call it when the air hits the bottom of the wing. Most guys call it pressure.

Anyone that takes the time to read that site will take the time to read a not so dumbed down version. I understood the basics when I was a young teenager. All college did was put some math to it. It embarasses me that anyone thinks their readers are that stupid.

bdavison

My Feedback: (1)

Now, maybe Im missing something here.

But you can have lift without downwash?
Downwash is just a by-product of an airfoil. Pressure is what causes lift. Even kids with a paper airplane book know that. Im on target with Ben. I thought the article was silly, almost laughable.

Its a shame.

Ben Lanterman

Guys go to this site and see some pressure distributions, the calculus challenged can just look at the pictures like I did - I didn't like calculus.

http://www.mh-aerotools.de/airfoils/...tributions.htm

The basic site in english is here

http://www.mh-aerotools.de/airfoils/index.htm

Martin Hepperle has done a tremendous amount of work in model aerodynamics and his airfoil sections are used by a large number of guys flying competition. I have a lot of respect for his work as compared to some others we have seen recently.

rmh

My favorite comment " ground effect is not air compressed between wing and ground" --then
"because the air under the wing is not circulating-in ground effect ------
Can you have your Kate and Edith too?

Ben Lanterman

Dick be sure and look at the picts on the Martin H. site.

LouW

This sums up the matter quite well. The reason that this subject comes up from time to time and elicits such strong responses is that neither side listens to what the other is saying. The fact is that both the pressure explanation and the momentum explanation of lift are correct. They are just two ways of looking at the same thing.

Suppose you suspend your airplane with a string and hold the other end in your hand. It could be argued that the string is what holds up the airplane, and so it is. On the other hand it could be said that the hand is supporting the craft since it is holding the string. The two supports must of necessity exist together. The string can’t provide any support unless the other end is held, and the hand can’t provide the support, unless it is attached to the craft by the string.

The pressure field surrounding a wing (the string) is obviously the immediate cause of lift, and is all that needs to be dealt with when designing, testing and developing them. It is OK to ignore the effect of the wing on the air through which it’s passing and only look at the effect of the pressure field as it encounters the wing. However the pressure field is bounded on all sides and where it encounters the surrounding air it causes it to be moved in response to the net pressures of the field. For a lifting wing this net deflection is downward (the hand). It always happens and is always proportional to the lift being generated, and lift could not occur without it (any more than the string could provide support if the other end was unattached).

(I will stop right here and address the “nuclear” argument that the pressure proponents always drag out. “What about the infinite span wing? A section can generate lift without making any downwash”. It is clear that if the span were infinite, so would the mass affected by its passage. The net force due to the pressure field generated by the infinite wings passage acting on an infinite mass will of course result in a zero deflection. From F=ma, the product of multiplying zero by infinity is mathematically indeterminate but can be any real number. In this case it is the section lift. For any real wing there exists an actual deflection of a mass of air proportional to the lift being generated.)

To summarize, there are two ways of looking at (explaining) lift.

1. The wing is a pressure generator. All the aero engineer needs to know to design, evaluate, and test wings is the properties of the pressure field generated by the wing’s passage. The effect of the wing on the air is of no concern to them.

2. The wing is an air deflector. A pilot operating the machine so carefully designed by the engineer can develop a real intuitive skill by seeing the wing as an air deflector. On the other hand, trying to visualize all the pressure variations changing as he yanks and banks can just confuse the issue.

In fact both a pressure field and deflection of air must take place for lift to be generated. It is not a question of one being right and the other wrong. It is only a matter of which is the more useful way of looking at lift for a given activity.

Gremlin Castle

My Feedback: (14)

I also think that Dr. Michael Selig has done some outstanding work in model airfoils. His body of work has been the basis for several others work in low speed low Reynolds numbers airfoils.

Ben Lanterman

All true Lou, except, when someone says how does the wing produce lift - not how the airplane flies or how it is a nice way of looking at it for some folks - but how does the wing produce lift? That narrows the focus down to a fairly small area around the wing doesn't it.

Why does the air above the wing move down? It is the high pressure in the far field flowing to the low pressure in the near field above the wing. In the process of trying to equalize pressures in the low pressure there is a flow setup that ends up being a strong downwash by the time it goes by the trailing edge of the wing.

OK the wing is lifting up and the flow is going downward. They are equal and opposite but are very surely not the same pheonema. Both are just trying to get into the same low pressure above the wing. The upper flow makes downwash, the wing being pushed into the void by the high pressures under it is lift.

It is hard to justify then saying that a wing liifts because the air above it is trying to get into the vacuum.

Remember the whole thing started when Jeff poopooed the "usual Bernoulli, equal transit expaination" and then threw the baby out with the bath water saying that all lift is due to momentum of downwash.

It just isn't so. Downwash and lift are equal and opposite but on opposite sides of the vacuum and not related to each other except by the vacuum. And we both know a vacuum cannot generate a force.

rmh

Nature abhors a vacuum but loves a Bissel---