New theory on how planes fly.

[djpacro]

This is one topic that annoys me a lot as an engineer.First thing I want to say to pilots is "stop trying to understand how a plane generates lift at an engineering level". What you have been taught is ********, and its not necessary.

CASA is the problem - from the new aeronautical knowledge standards in the Part 61 MOS Schedule 3 Unit 1.3.1:"2.2 Bernoulli’s theorem and Coanda theory

2.2.1 Apply Bernoulli’s theorem of constant energy flow to describe how an aerofoil produces lift, limited to the variation of kinetic energy (dynamic pressure) and potential energy (static pressure) as air flows through a venturi or over a aerofoil.

 

2.2.2 Explain Coanda theory and the effect on lift production."

 

Only CPL, aerodynamics is not required in much depth at RPL and PPL level so, I agree, pilots do not need to know much detail.

 

It wasn't quite as bad in the old Day VFR Syllabus:

 

"6.3 Bernoulli's theorem

 

6.3.1 Apply Bernoulli's theorem of constant energy flow to describe how an aerofoil

 

produces lift.

 

Note: Limited to the variation of kinetic energy (dynamic pressure) and potential

 

energy (static pressure) as air flows through a venturi or over a wing.

 

Student should also be aware that the upper surface of a wing generates the majority

 

of lift."

 

"Pre-PPL background knowledge only

 

PPL basic principles should be known

 

CPL should be known in considerable depth."

 

When I did my PPL theory, I wanted so bad to point out incorrect information that is taught and tested, but I cant, because I had to be tested on the same rubbish.

Yep, had to be tested because that is what CASA has mandated in their rules so Australian providers of pilot theory must, unfortunately, present info consistent with that.Some people read vague snippets of information with limited applicability in the good book Aerodynamics for Naval Aviators then quote it out of context as general theory. Incidentally, that book of 400+ pages is free online at the FAA website http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/00-80t-80.pdf

 

 

[bexrbetter]

The reason a wing produces lift is because its deflecting the wind downward. Stick your hand out a car window at speed and you have the perfect example.

That would mean that my hand is being deflected upward by it's motion wouldn't it, not the "wind" being deflected downwards out of the hand's way - just like a plane's wing.

 

The fact that the air (not "wind") doesn't want to be deflected because the ground creates a barrier is what causes the lift, it must compress slightly therefore raising it's pressure to greater than the top surface (flat plate) while the downslope of the upper wing causes drag, i.e. lowered pressure and there you have your increased difference over a flate plate (as you allude to).

 

 

[Pearo]

That would mean that my hand is being deflected upward by it's motion wouldn't it, not the "wind" being deflected downwards out of the hand's way - just like a plane's wing.The fact that the air (not "wind") doesn't want to be deflected because the ground creates a barrier is what causes the lift, it must compress slightly therefore raising it's pressure to greater than the top surface (flat plate) while the downslope of the upper wing causes drag, i.e. lowered pressure and there you have your increased difference over a flate plate (as you allude to).

You are overthinking it, therein lies the problem with most pilots.

 

BTW, I say wind because I am a sailor. Use air if you wish, the concept remains the same.

 

 

[spacesailor]

Another two cents worth!,

 

Negative pressure IS 29,8 inches of mercury. Try lifting a 600 kg aircraft with only that.

 

Positive pressure Is : how knows ,30,000psi, That'll push rockets upwards surly.

 

spacesailor

 

 

[djpacro]

Try lifting a 600 kg aircraft with only that.

is easy.

[facthunter]

You can find out what is happening very simply by fixing manometer tubes at various points of an aerofoil and having it in a flow of air. You can read REAL pressure changes.

 

A lifting aerofoil. (more camber on the top) will have a zero lift line at a negative AoA.

 

A straight airflow can only be turned into a curved one by having reduced pressure on the inside of the curve. ( No change of pressure it keeps going straight.) If it speeds up or slows down a force has to be applied to make that happen.

 

The wing by it's shape and angle of attack makes air go from where it is to a lower position as it moves. The reaction to this is LIFT. If a sufficient Mass of air is displaced far enough and at a good enough rate the lift will be enough to keep the plane in the air and everyone is happy, as long as it is done efficiently where it would be a bad design, otherwise..

 

A rocket engine works in a vacuum. It's unique in this respect. Is a balloon with a hole in it a rocket? Nev

 

 

[Himat]

While we are at videos on why aeroplanes fly, I do like this one:

 

 

 

[spacesailor]

Rubbish!

 

2,100 lbs. per FOOT , Compered to 11,500 lbs per INCH. (The pressure required to make "liquid oxygen").

 

Positive pressure is way greater, than the negative pressure (like the void of space).

 

AND when the "Milky way" & "Andromeda" go down the gurgler of OUR "Black hole, we will see positive pressure's that we haven't yet made tools to measure !. LoL

 

spacesqailor

 

P.S. My calculator reads 29.5 inhg = 14.49 pounds per square inch

 

 

[aro]

My calculator reads 29.5 inhg = 14.49 pounds per square inch

1 square foot is 144 square inches, so 14.49 pounds per square inch is 2087 pounds per square foot.

 

C172 wing loading is about 14 lb/square foot so we only need a difference in pressure of about 0.1 PSI or 0.7% at sea level.

 

 

[spacesailor]

OK

 

1,656,000Pounds per FOOT positive pressure is still bigger.

 

By far.

 

Have never worked with P.S.F. could it be Foot Pounds?

 

Now I've got Barr on the compressor and N.M. on the torque wrench. No idea if I'm going to blow my'self to bits with the compressor, or strip the studs with the torque wrench.

 

Is it 1.5 bar or 15 bar, for the rivet gun? (15PSI)

 

spacesailor

 

 

[eightyknots]

There are so many theories and experts including Bernouli, Newton and the bloke who lives down the road but the real answer that no-one can deny is simply MAGIC. The following highly technical high definition scale drawing created by a Magic expert proves this to be correct.[ATTACH=full]39774[/ATTACH]

 

So there you have it. A perfectly logical explanation that even the person with fewer than 2 brain cells available can understand.

Where is Bernoulli in all this theory?

 

 

[fly_tornado]

[No message]

[facthunter]

The 14.7 lbs/sq inch is sea level air pressure. (ona standard day) If you had a complete vacuum that's the maximum ever achievable. The pressure on a column of mercury can only make it rise 29.92 inches..There is never a vacuum on the top of the wing but there is a drop in pressure easily seen on a fabric wing in flight by the ballooning up of the covering between the ribs.

 

Pulsed smoke in a wind tunnel shows the speed is increased over the top curved surface also and if you get close to M crit a pressure wave quite visible and at right angles to the surface will form on the wing close to the highest camber point. The first place of supersonic flow. ( You won't observe it on a fabric covered wing).

 

There's certainly a lot of baloney going on with how this is taught. I got close to failing an interview for a job when the question was " How does an aeroplane sustain itself in flight". Having done about 2 years at University in Newtonian physics I gave the "correct" answer but noting the look of confusion and dismay on the face of the very senior airline type I quickly said "Oh do the want the one where static plus dynamic pressure is a constant?" Which if you think about it is a pretty abstract statement. If you put it over the PA it would make you seem a bit loopy. Nev

 

 

[Pearo]

While we are at videos on why aeroplanes fly, I do like this one:

That is an excellent video, well worth watching.

 

At 23:00 there is a slide that sums it up perferctly, and shows why CASA (and FAA) have it so wrong.

 

Bernoulli-versus-Newton "controversy"

 

• Some say only one or the other is right.
   
   
  
• Some say both are right
   
   
  
• Actually, each is party right but incomplete
   
   
  
• "Bernoulli" deals with flow speed and surface pressure
   
   
  
• "Newton deals with flow direction and momentum flux
   
   
  
• They're not contradictory
   
   
  

 

 

 

The problem is, as an engineer, how can you explain this to a pilot? Its nonsense that the average pilot should have to understand it at the same level. Is there an easy way to take this information and explain it to a non engineering type person?

 

 

[djpacro]

NASA does a pretty good job with their educational info online for school children.

 

 

[pylon500]

NASA does a pretty good job with their educational info online for school children.

Actually it's interesting that you say that.

I usually like watching the high tech stuff you find on the NASA website/youtube, until I came across this one, and started to think, 'Whoa, hang on a minute, what's that?';

 

<

 

Actually some of the discussion in the comments started to sound a lot like here..

 

And if you haven't/don't read the comments, my take on it all was, 'They have discovered the benefits of aspect ratio'.

 

 

[djpacro]

Ahh! Aspect ratio - one of my pet subjects. Span loading considerations have benefit. Wing loading considerations have benefit. Doesn't leave many benefits to consider for aspect ratio alone.

 

Who would've though that we'd be discussing stuff like Biot-Savart and Prandtl here.

 

 

[Guernsey]

https://www.facebook.com/video.php?v=674946289233004

Now that's a very handy explanation.

 

Alan.

 

 

[Marty_d]

Actually it's interesting that you say that.I usually like watching the high tech stuff you find on the NASA website/youtube, until I came across this one, and started to think, 'Whoa, hang on a minute, what's that?';

<

 

Ok, I'm thick. I must have missed something in the explanation of how you can flatten out a vertical winglet and not only stop tip vortices but actually gain thrust from them. Because if you flatten out a vertical winglet, don't you just get a longer wing?

 

Or are they talking about washout?

 

 

[sain]

It doesn't contribute anything but, Oblig xkcd on the topic:

 

 

 

[facthunter]

Planes with the typical lift wing, fly upside down, but not that well. Nev

 

 

[Marty_d]

When I built R/C models, if you wanted good aerobatic performance you'd build a fully symmetrical centre wing aircraft with big ailerons, long fuselage and flat tailplane & fin with big control surfaces. And overpower it to buggery.

 

 

[IBob]

OK1,656,000Pounds per FOOT positive pressure is still bigger.

By far.

 

Have never worked with P.S.F. could it be Foot Pounds?

 

Now I've got Barr on the compressor and N.M. on the torque wrench. No idea if I'm going to blow my'self to bits with the compressor, or strip the studs with the torque wrench.

 

Is it 1.5 bar or 15 bar, for the rivet gun? (15PSI)

 

spacesailor

I do refrigeration controls, amongst other things. And the industrial guys have mostly made it to kiloPascals (kPa) but the freon guys are still talking PSI.

 

I find it easiest to relate it all back to one standard atmospheric pressure, which is:

 

14.7PSI

 

1Bar

 

100kPa

 

30ft or 10metres of water

 

30cm mercury

 

Well, not exactly, but close enough for government work!

 

I also find it helps to stop talking about suction (or, worse still, 'negative pressure'). There is no such thing, there are just degrees of pressure, starting with zero at total vacuum and working on up.

 

By the same token, nothing is ever sucked, it's all blown by the great pressure on the other side.

 

Okay, this is basic practical stuff for the layman (and I don't claim to be anything else). I find it helps in my day to day practical work.

 

Oh, and while we're on it (not that we were, but I'm away now) there is no such thing as darkness, either...just different amounts of light.

 

Okay, i'll stop now..........

 

 

[Geoff13]

And does electicity flow -ve to +ve or vice versa

 

 

[jetjr]

Ok, I'm thick. I must have missed something in the explanation of how you can flatten out a vertical winglet and not only stop tip vortices but actually gain thrust from them. Because if you flatten out a vertical winglet, don't you just get a longer wing?Or are they talking about washout?

I think they mean the wing is longer yes but the outer edges dont generate lift, and therefore dont generate vorticies. ie are flat and without airfoil??

 

Vertical and horozontal winglets retain energy wasted in voticies into lift or thrust - more of an efficiency saving not generating anything.

 

Some even admit they are for looks :)