Bernoulli vs. Newton

[cliffy]

Those uncomfortable Airbus seats must have shut off blood to the brain!  :-)  Airbus has the most uncomfortable seats in any airliner.

Simplistic answer- the BIG B

Complex answer for those who need to dig deeper?  A combination of both

BTA, I'm no aerodynamic engineer either.   All I know is that if you go to slow you can die.

[Andy95W]

1 hour ago, cliffy said:

All I know is that if you go to slow you can die.

There's a different thread going where someone said if you fly by airspeed, you're an accident waiting to happen.

As for me, I'm with Cliffy: it's a combination of both.  And if you fly too slow you'll die.

[Hank]

I agree with whoever said Newton makes it fly, Bernoulli makes it fly efficiently.

[Becca]

You amateur aerospace engineers are so adorable... 

The forces acting on an object moving through a fluid are definitely more complicated than any of the simplified algebraic equations you are posting.  Most of what you are posting is simplified versions of a difficult triple integral problem that describes the conservation of momentum in a viscous compressible fluid -- if you make simplifying assumptions about shape, viscosity, and compressibility, you get to each equation you are debating.  None of which perfectly describes the forces acting on an wing, let alone the whole aircraft (see navier stokes equation) alone.  Fwiw, neither does Bernoulli, to get to his equation, you also have to make simplifying assumption that does not take into account spanwise lift, amongst other things, for instance, but it is also derived from the conservation of momentum equations.   But Bernoulli's equations are derivable form Newton's Laws, it's not either or, it's just an expression of conservation of momentum.

 So, given that and the title of the thread, I vote Newton's Laws win.

as for how to teach a student pilot without calculus, I think basic constructs of force vectors and effect of angle of attack on lift seems to do the job.  Don't change what works.  I can tell you from experience lots of pilots are startlingly bad at math.

(BS Aerospace Engineering, Georgia Tech; Masters Mechanical Engineering, Rice University.  Happy to send anyone copies of my text books and fluid dynamics notes, if anyone wants to learn the governing equations themselves.)

 

Edited September 5, 2016 by Becca

[bonal]

This is an interesting thread and I don't have a preference all I know is the damn things fly but what really amazes me is that little spinning wing acting on a fairly dense medium can accelerate a sometimes very heavy vehicle to the point that we can debate which example allows a wing to lift an airframe off the ground. As for the 2 I think Bernoulli is more interesting and eloquent Newton is more like a blunt object equivalent to a bat striking a ball.

[carusoam]

Way to go, Becca!

Equations that actually include the change of time and compressibility of fluids.  

The fun part of simplifying the equations using steady state assumptions is...  It makes it easier for a 17 year old to get a PPL.  No calculus required...

the fun part of expanding the equations using time, compressibility, and a computer is the ability to model real life with great accuracy.

Now that some people have the calculus skills, programming skills, and sensor skills and powerful computers in their pockets... Some pretty cool devices are being built and programmed in the home labs across America.

Another example of strong math skill used in every day life, is weather modeling and prediction.  Watching hurricane Hermine come through over the holiday weekend.  The weather channel was accurate enough to show their actual track vs. what they predicted.  

It is really cool when you see a family working together on some of these things.

Where is Erik today?  (School is back in session)

Best regards,

-a-

[mike20papa]

My favorite "picture" is the theory of a single vane pump, powered by either gravity or the prop, displacing air with a force equivalent to make gravity slightly less or greater than zero.  Banking induces geometric forces acting less than 100% efficient of said force.  Aggravated attitudes greater than airfoil optimum efficiency induce "PUMP CAVITATION" or airfoil flow separation - "the stall".  My other applied memory is the feeling of being in the bay area waters off the Houston ship channel, an approaching ship, perhaps a mile away, sucking/displacing water like a vacuum cleaner, actually "mounding" water around the vessel as it approaches.  When flying in the vicinity of birds, I think of them in this "field of displacement" struggling to get free.  Hence, any in the approaching field of vision, I aid them in their escape, banking hard to "overshoot" their physically limited maneuverability.  

[HRM]

Interesting thread, complete with good humor!

Take up SCUBA, it changes the way you look at flying. Both have you moving in 3D and your physics WRT how you move are coupled to the fluid dynamics of air and water, both of which you can't live without and both of which can kill you suddenly and mercilessly. I was out diving in the GOM most of last week and started musing about flying and diving during the surface intervals. In diving, you have a fixed amount of air and travel down and plan to have enough air to get back to the surface. In flying, you have a fixed amount of fuel and travel up and plan to have enough fuel to get 'back to the surface.' Bad planning leads to bad results in both activities. Both activities are dependent on technology, the more the better, and are not cheap. I could go on...

Better yet, just stick your hand out the window of a moving car. No math or physics needed, all of that gets used when you want to be efficient.

[ArtVandelay]

For those interested in aerodynamics without the calculus I highly recommend: "The Illustrated Guide to Aerodynamics" by HC Skip Smith.

[aviatoreb]

1 hour ago, Becca said:

But Bernoulli's equations are derivable form Newton's Laws, it's not either or, it's just an expression of conservation of momentum.

 So, given that and the title of the thread, I vote Newton's Laws win.

as for how to teach a student pilot without calculus, I think basic constructs of force vectors and effect of angle of attack on lift seems to do the job.  Don't change what works.  I can tell you from experience lots of pilots are startlingly bad at math.

(BS Aerospace Engineering, Georgia Tech; Masters Mechanical Engineering, Rice University.  Happy to send anyone copies of my text books and fluid dynamics notes, if anyone wants to learn the governing equations themselves.)

 

>But Bernoulli's equations are derivable form Newton's Laws, it's not either or, it's just an expression of conservation of momentum.

That's what I said.

>So, given that and the title of the thread, I vote Newton's Laws win.

I'm voting third party.  I'm voting for the Einstein platform.

>Happy to send anyone copies of my text books and fluid dynamics notes, if anyone wants to learn the governing equations themselves.)

I'll take a copy please.

[Hank]

10 minutes ago, aviatoreb said:

>But Bernoulli's equations are derivable form Newton's Laws, it's not either or, it's just an expression of conservation of momentum.

That's what I said.

>So, given that and the title of the thread, I vote Newton's Laws win.

I'm voting third party.  I'm voting for the Einstein platform.

>Happy to send anyone copies of my text books and fluid dynamics notes, if anyone wants to learn the governing equations themselves.)

I'll take a copy please.

Newton can simplify to Bernoulli, and Einstein can simplify to Newton. Big minds are trying to find what simplifies to either Einstein or Maxwell depending on assumptions made . . .

My AE classes were long ago, simple electives, and I've worked in manufacturing things without wings in the interim. Can't say I remember a whole lot of the details, but it involves temperature, density, α and a few other things, with a whole lot of integral & differential calculus. Dug out my aerodynamics book when I started flight lessons, didn't make much headway, but the little Gleim book in the "Be A Pilot" kit was all I needed. Quick, simple and much more airplane-centric than chalkboard-centric.

[Becca]

4 hours ago, aviatoreb said:

 

>So, given that and the title of the thread, I vote Newton's Laws win.

I'm voting third party.  I'm voting for the Einstein platform.

If you can get our Mooneys to speeds where Einstein matters... Well, that would be awesome.

[Hank]

47 minutes ago, Becca said:

If you can get our Mooneys to speeds where Einstein matters... Well, that would be awesome.

Dang, it sure would be hard to go for lunch the next county over! 30 miles at 186,000 miles/sec--OK, OK, 0.9c is only 167,000 miles per second.

But it would still be really cool!

[cliffy]

Lose not thine airspeed lest the earth come up and smite thee!

[HRM]

On September 5, 2016 at 2:56 PM, Hank said:

Big minds are trying to find what simplifies to either Einstein or Maxwell...

Please don't forget that it was Heaviside that pointed out, to the great relief of millions of EE students ever-after, that Maxwell's twenty-two equations could be simplified to four.

I believe this was after Routh bitch-slapped Maxwell by taking Senior Wrangler.

[bonal]

Was just mulling over this discussion as I watch NHRA and how the two, Newton vs Bernoulli relates to auto racing. Most current rules apply Newton in their wing design but if you go back some years to the ground effect designs primarily in formula one Champ car and prototype sports car the ground effect Venturi was clearly Bernoulli and was so effective it was basically outlawed because the cars generated so much downforce (opposite of lift) that when they started to go off line the Venturi began to stall and the car became un stuck with violent results. Now perhaps there can be some numbers provided from the engineering folks as to which provided more downforce the wing or the Venturi. 

[carusoam]

NHRA is cool.  Gobs of torque vs. less than rigid tube bodies + downforce of giant wings (front and back).   

The laws of physics at the undergraduate level doesn't account for the contact patch area F=uN or the fact that the contact patch is changing in dimension as a function of everything that is going on...

If you like non-steady state complexity, non-continuous acceleration is pretty cool.

 

Vacuum is a winner when it comes to holding things to the ground.  Breaking the vacuum is really like a stall close to the ground. Not enough time to restore the balance...

Jim Hall's vacuum cars of the 70’s aka chaparrals. Giant wings and the vacuum car.

https://en.m.wikipedia.org/wiki/Chaparral_Cars

Skip down to the 2J for twin fans for vacuum generation...the car had two engines one for the drive train, the other was for the vacuum system.

 

Things often get outlawed when simple contact breaks a device that then causes an accident. Or driving over something that opens the seal between the car and the surface.

 

quoting from wiki...

"Part of the danger of relying on ground effects to corner at high speeds is the possibility of the sudden removal of this force;"

 

Beroulis and Newton were brilliant.

Making some money by applying the science were guys like Al Mooney and Clyde Cessna and possibly Bill Lear.

Al was the coolest of the group.

Best regards,

-a-

[bonal]

Don't forget Colin Chapman, he applied the pressure differential with out the aid of a fan to creat vacuume and downforce. Venturi affect 

[INA201]

Ok, I'm just going to throw this video in for you guys and see what happens. 

 

[gsxrpilot]

I've actually stood on that very Dam. It's the Gordon Dam in Tasmania, Australia. We also climbed the stairs to the bottom and back up.

[Guest Mike261]

On 9/4/2016 at 9:09 PM, teejayevans said:

It will if it goes fast enough, isn't that the design of the laminar flow wing, 0 AOA results in minimum drag?

The current thinking is Newton pushes and Bernoulli pulls.

[carusoam]

In respect to Bonal's post...

Collin Chapman added lightness to his cars.   "Simplify, then add lightness..." - Lotus' Collin Chapman.

Al Mooney must have been thinking the same thing, but added cool aerodynamics to the equation.

Things get magically funner when their HP:weight ratio approaches 1:10, like Corvettes and O3s...

Best regards,

-a-