DEBUNKING SILLY LIFT THEORIES

[Completeaergeek]

Hi all, I am sure many of you are probably sick of this topic but I still run across far too many people who spout nonsense about how wings work and lots of them are flying instructors- some are even airline pilots..






I have spent the last 3 years lecturing Aero at University and have to take a lot of my time undoing this nonsense. Our young aviators deserve better than this. Even CASA spouts nonsense about venturis.




I would really appreciate any help in spreading the work here. We are talking physics not fairy tales. Please look a these links as circulate them for information. Incorrect Lift Theory (http://www.grc.nasa.gov/WWW/K-12/airplane/wrong1.html) How wings really work | University of Cambridge (http://www.cam.ac.uk/research/news/how-wings-really-work) DEBUNKING LIFT 'THEORIES' STILL TAUGHT | Recreational Flying (http://www.recreationalflying.com/threads/debunking-lift-theories-still-taught.123857/) We don't do ourselves or our industry any favours if we don't understand the most basic concepts of our profession. Cheers

[Whopity]

Most pilots learn theory to pass aviation exams. Over the years the content of the exams has moved further and further away from reality; everytime we change the system (about every 10 years in Europe), it just gets worse. Books have been written to help students pass nonsensical exams and then those very books become the source of further questions. Few if any of the people involved in the examination process have any relevant knowledge.

Before we can get rid of the nonsense, we have to change the system. It is time for a University to determine what a pilot needs to know and then generate a meaningfull question bank. It is very apparent that neither the industry nor the regulators are capable of performing this task.

[Lord Spandex Masher]

Lift (http://messybeast.com/dragonqueen/liftdemon.htm) - The Simple Explanation

[Big Pistons Forever]

That is a very good video which I have now saved. Below is a quote from the attached explanatory text.

Quote

“What actually causes lift is introducing a shape into the airflow, which curves the streamlines and introduces pressure changes – lower pressure on the upper surface and higher pressure on the lower surface,” clarified Babinsky, from the Department of Engineering. “This is why a flat surface like a sail is able to cause lift – here the distance on each side is the same but it is slightly curved when it is rigged and so it acts as an aerofoil. In other words, it’s the curvature that creates lift, not the distance.” - See more at: How wings really work | University of Cambridge (http://www.cam.ac.uk/research/news/how-wings-really-work#sthash.dqEZ1Rip.dpuf)

Unquote

It doesn't say why there is lower pressure on the top and higher pressure on the bottom. Of course the "correct" answer as to the why is quite complicated so this is why I believe the faster air on the top = lower pressure has been used by PPL instructors. They are looking for a fast and easy explanation. '

I used to do the same thing but I was uncomfortable because I knew it was wrong. Now I just avoid the issue entirely.

I tell PPL students they have to know 4 things about wings

1) As the wing moves through the air the airflow splits with some going around the top of the wing and some below it

2) The air above the wings will have a lower pressure than the air below the wing

3) The angle the airflow meets the wing at is important and is called AOA

4) The air is bent downwards as it flows off the back of the wing.

All of these facts have direct practical application for the pilot. Any higher level of more detailed knowledge has little practical application and detracts from all of the many other practical knowledge items that a pilot must know.

[Ascend Charlie]

Big Pistons said:
2) The air above the wings will have a higher pressure than the air below the wing

Wanna think about that one a bit?

[Big Pistons Forever]

Big Pistons said:


Wanna think about that one a bit?

Woops....... :O

[A Very Civil Pilot]

He obviously teaches his students to fly inverted!

[Duchess_Driver]

Wot.... no lift fairies or skyhooks anymore? ;)

[Lord Spandex Masher]

Post #3 :ok:

[janrein]

De Lift, 1983:
Trailer De Lift (1983) - YouTube

[+TSRA]

Unfortunately some of this comes down to the fact that we have 250 hour pilots teaching 0 hour pilots. The only way our students will change is if our instructors change. At 250 hours I was surprised I could fly straight and level...now, I'm being facetious, but...

We used to have military pilots doing the ab-initio civilian training. These were guys with thousands of hours both in class-rooms and in-flight. These guys knew the theory like the back of their hand and were able to "dumb-down" the physics in such a way that the "dumbed-down" version was still technically correct.

However, then the student becomes the instructor and takes that "dumbed-down" version and tries to dumb it down again for their students. The cycle continues until the theory no longer matches the reality (where we stand) and the student ends up having to go searching for a theory that makes sense. Like all bad science, the incorrect lift theories sound really good (and much more technical) than our current PPL-Taught theory. The newest student then takes this drivel as gospel and runs with it, soon becoming the instructor.

What we need is a strong push for back to basics right across the board (GA and Airline). We need to fail more pilots and get the word out that there is a standard to be met. It is not on the universities to come up with a new curriculum; it is on the instructor to not recommend a student for a ride if they don't know the basics - be it a PPL, CPL or Instructor Rating.

Just because they can pass a written test that has a published question and answer bank does not mean they are ready.

[BigEndBob]

The Cambridge video seems to prove the plank theory.
At greater aoa air is wedged under wing producing greater pressure because it can't escape behind quick enough.
Above the wing a void is created allowing the air to travel faster, thus lower pressure.

The aerofoil shape is just good for strength, reduce drag and produces a differential even at zero aoa.

Always wanted to try and run water over the back of a spoon in a vacuum jar, just to see what happens.
Any Uni types that can show what happens.

[pineappledaz]

I agree with Big Pistons, the theory has been simplified for easier understanding. The 4 points identified are really all that matters. It doesn't hurt to listen to the correct explanation though.

However this has nothing to do with the number of hours a person has logged. I have heard a 5000 hour pilot teach this to a class. Why do people in this industry typically assess levels of intelligence by the number of hours people have flown.

If this is the theory that gets passed down then it doesn't matter how many hours you have, this is what you know and would willingly pass onto the next generation.

[Tarq57]

Wings etc are add-ons to make people feel more normal about getting into an airliner.

Here (http://www.pprune.org/questions/204288-just-after-takeoff.html#post2295083) is the real reason they (usually) fly.

[pineappledaz]

This is what we will be teaching in 10 years time

how airplanes fly (http://www.funnyjunk.com/funny_pictures/1500036/how/)

[+TSRA]

However this has nothing to do with the number of hours a person has logged. I have heard a 5000 hour pilot teach this to a class. Why do people in this industry typically assess levels of intelligence by the number of hours people have flown.


pineappledaz,

I'm not trying to suggest that the more hours a person has makes them more intelligent by default. I too have seen 5000 and 10000 hour pilots make the same bone head mistakes that I was making at 500 hours. However, when you're talking about a brand new pilot at 250 hours teaching another brand new pilot, then yes, experience does count and a person with 5000 hours will often, not always, be able to deliver a better product.

The reason I singled out the military is they have a far more exhaustive selection process, so by the time a military pilot achieves 1,000 hours they are years ahead both in knowledge and experience of a 1,000 hour civilian pilot.

Also, keep things simple at the PPL level, but as soon as they mention a Commercial or higher, we shouldn't be keeping things simple. All that does is promote the idea that pilots are nothing more than over paid bus drivers and then we wonder why the accountants want to pay us less. We should know the theory, we should know the law, and we should know our airplanes.

[Genghis the Engineer]

Can I offer an alternative view.


I'm an aeronautical engineer in much of my working life - and as such I need a detailed understanding of aerodynamics, and some people doing more aerodynamically oriented jobs need a far greater understanding than I do.

But what does a private pilot, or even most professional pilots, need?

- Basic idea of flow around the lifting surfaces
- Effects of interfering with shape, criticality of the leading edge
- Relatonship between speed, area, coefficient, and lift
- Four main forces
- Profile and induced drag
- Bernoulli (mainly to explain how pitot and static pressures work and are used)
- Basic principles of stability and what it means.

The main issue to me is not whether the explanations are right or wrong, but whether they're necessary or not. The best thing we could reasonably do is get rid of all the "knowledge" that's of no real value to a pilot. Then they might remember stuff that's actually useful to them.

Much more than that belongs in either test pilot courses, or aeronautical engineering degrees, and not in pilot licence syllabi.

G

[thing]

Couldn't agree more with GTE. Pilots are operators, not maintainers or designers. A taxi driver doesn't need to know how a differential works or the molecular structure of his tyres.

As an ex aircraft maintainer (who did have to know how stuff worked) I'm constantly surprised at some of the banter regarding how aircraft fly/how instruments work etc etc in our crewroom. I keep my own council because no one likes a smart arse but there are a lot of strange ideas floating around. Having said that, strange ideas have no bearing really on how well a pilot flies. I might believe that there's a little guy in the engine cowling who turns a crank that spins the prop, it doesn't really have a bearing on how good or bad a pilot I am.

[stevef]

I once worked alongside a contractor who told everyone in the hangar crew-room (in all seriousness) that lift was due to air rushing over the curved upper surface of the aerofoil. It then heated up because of the increased velocity and convection gave the wing lift. :rolleyes:
No wonder he was a seat fitter...

[SpannerInTheWerks]

{Lifting airfoils are designed to have the upper surface longer than the bottom.} This is not always correct. The symmetric airfoil in our experiment generates plenty of lift and its upper surface is the same length as the lower surface. Think of a paper airplane. Its airfoil is a flat plate --> top and bottom exactly the same length and shape and yet they fly just fine.

At last.

I remember as a 10 year old boy reading the theory of lift in textbooks and not believing a word of it - for the very reason mentioned above.

All through my life I have stuck to the published theories and spouted them verbatim - still not believing a word of it.

As an aeromodeller - how did my simple glider with a flat plate section create lift, how did my aerobatic model with a fully symmetrical section fly?

Air cadet - the same.

Then as a pilot passing all my exams (with 100% - but not believing the theory to be the truth!)

Now, at last the mystery is resolved.

Nice to have a scientific answer at last.

... now haven't the 'scientists' 'proved' a bumblebee can't fly ... ?

[BigEndBob]

If a sail on ship produces 'lift', why are aircraft wings not made the same with billowing sheets of material?

Save that, just thought hang glider..duh.

[Clare Prop]

Don't forget Britten-Norman put the theory of Acoustic Lift Technology into practice....

Design documents clandestinely recovered from the Britten-Norman shredder have solved a question that has puzzled aerodynamicists and pilots for many years, disclosing that it is actually noise which causes the BN-2 to fly. The vibration set up by the engines and amplified by the airframe, in turn causes the air molecules above the wing to oscillate at atomic frequency, reducing their density and causing lift. This can be demonstrated by sudden closure of the throttles, which causes the aircraft to fall from the sky. As a result, lift is proportional to noise rather than speed, explaining amongst other things the aircraft's remarkable takeoff performance.

[Clare Prop]

3.35 onwards....

BBC - People Like Us - Pilots - Part 1 - YouTube

[ChickenHouse]

After being a professor and teaching lectures on the dynamics of compressible and incompressible media and meteorology for over 30 years, I am wondering, who believes theoretical knowledge makes a better pilot?

I have seen many great intuitive pilots, which were absolutely lousy students. I also regret to have let pass quite some great theoretical buttheads, which became the lousiest pilots ever.

There are certain parts of theory, I believe make a better pilot, if the physics and chemistry is well understood. One most prominent example is weather. If you understand the complex system of weather, it gives you opportunities for great piloting. But, apart from the very basics of lift and flying, I now believe it is much more important to focus on other things. Maybe I am getting too old, but there is not much into from the theory of flying you really need to practice flying. Or are the younger ones already overwhelmed by the simplest things?

[Ralis]

I teach that air being a fluid has viscosity and it is that property which instills a want of the air above and below the wing to meet up at the trailing edge, however never do.
As some mentioned the basics are more important as in how can i make this aerofoil work better and what will make it worse, what will happen when I do this.
my 2cents