pinehilljoe
Senior Airman
- 733
- May 1, 2016
Fluids 301 was my not my favorite class in college, but I believe the effect may be caused by modial interaction of magneto-reluctance and capacitive diractance.
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Fluids 301 was my not my favorite class in college, but I believe the effect may be caused by modial interaction of magneto-reluctance and capacitive diractance.You're not drinking enough.
I have been reading Bills posts for years and he is also a qualified expert in aerodynamics. With his posts, including the one in question, I read it and then read it again and then finally read it as a series of statements which eventually I understood. Personally, I worked surrounded by many very bright people, almost all graduates, some were on the genius level and some were complete chancers. Anyone waving an MSc in my face at the first instance comes across as a chancer, it has happened a few times on these boards. Now, which part do you consider "gobbledygook" maybe I can boil it down to something someone with only an MSc can understand.Absolutely: Aerodynamics is a very complicated subject and which is why you should always be extremely vary when someone makes very detailed, complicated and assertive claims about why things "must" be in a certain way. So when you hear something like that and it makes no sense to you, you have to ask yourself does it sound like gobbledygook just because you don't understand it or simply because it actually IS gobbledygook? Personally, I find having an MSc in aerodynamics and structural engineering plus having worked in the aerospace defense industry for many years of great assistance in making such calls, and which was why I pulled the plug on the P-38 dive flap discussion.
That is where I went wrong in fluid dynamics.You're not drinking enough.
Welcome to my world.Absolutely: Aerodynamics is a very complicated subject and which is why you should always be extremely vary when someone makes very detailed, complicated and assertive claims about why things "must" be in a certain way. So when you hear something like that and it makes no sense to you, you have to ask yourself does it sound like gobbledygook just because you don't understand it or simply because it actually IS gobbledygook? Personally, I find having an MSc in aerodynamics and structural engineering plus having worked in the aerospace defense industry for many years of great assistance in making such calls, and which was why I pulled the plug on the P-38 dive flap discussion.
Must have been made out of pre-famulated amulite.Fluids 301 was my not my favorite class in college, but I believe the effect may be caused by modial interaction of magneto-reluctance and capacitive diractance.
I don't personally subscribe to the theory that the deflection of a flat plate (bottom surface) in the freestream immediately improves the lift distribution along the top of the wing- at least not until after the pitch up moment is generated. Some immediate phenomena must disrupt the shock wave before the downwash behind the wing stabilizes to re-engage elevator authority. Merely increasing local CL while the flow velocity > M=1 doesn't reduce the physics of the shock wave or flow properties aft of the shock wave.
An abrupt pitch up/increase drag/increase AoA Would affect the velocity (lower it) along the wing surface.
The explainable immediate phenomena is an instantaneous change in momentum (and force vector) of the flow from the LE along the bottom surface when the flap is deployed - causing a pitch up reaction to the change in momentum at 30% chord. The subsequent re-establishment of subsonic velocity on the top surface eliminates the shock wave and the blanketing of the horizontal stabilizer. Recall that dives are in 1G range and zero lift angle of attack, when the shock wave forms. Any pitch up 'disturbance' results in positive angle of attack, increased lift coefficient and higher drag. I'm not disputing the NACA language, just posing an incomplete explanation for the P-38 specifically.
The pressure distribution along the top surface to restore normal center of pressure is not attained, until the shock wave is eliminated. That occurred naturally as lower dive altitude increased air density and temperature to increase Mcr beyond the airflow velocity over the airfoil
I thought more about this and confess curiosity to your specific aerodynamic 'non-gobbledygook' and detailed explanation is. In detail please educate us on the following:Well in my opinion this is just aerodynamic gobbledygook with no foundation in science so this means we are done here.
As someone without an MSc it appears gobbledyook has been replaced with a picture. Is that a P-38 aerofoil and if so where is the section taken. It appears to be a 2 dimensional representation but as I understand it it was a three dimensional problem. That is, whatever the issue of compressibility was, it was made worse in the inner wing sections between the engine/boom sections and the pilots gondola.And with that my participation in this thread is done. I have no doubt that this will be met with yet another dose of impressive sounding aerodynamic word salad but I have no intention of wasting any more time on this.
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IF the drag did not increase significantly with instant increased angle of attack you would have a point. But..I was not planning to post anything more here but since this thread has gone so far south with ridicule and claims that there is no gobbledygoock to be found, here are a couple of examples:
So here we have claims that increasing the angle of attack lowers the velocity on the upper surface and re-establishes subsonic flow on the upper surface. But this is a fundamentally wrong statement. This is not how it works: The speed actually increases on the upper surface of the wing and the shock wave gets even bigger if the angle of attack is increased at a given Mach number. So totally different from what the citations above claim. And even if these ideas are cloaked in an impressive sounding aerodynamic word salad it's still fundamentally wrong: If you have a shock wave formation on the upper surface of the wing then increasing the angle of attack does NOT make the shock wave go away. Instead it's exactly the opposite: The shock wave problem actually INCREASES.
The pitch up causes the angle of attack to generate the lift/pressure distribution across the wing in front of the shock wave to a.) increase Lift, b.) negate the negative CMacFor those still in doubt, the Schlieren phots below clearly shows this. So the idea that in order to get out of the dive, the P-38 has to pitch up in order to get rid of the shock wave is wrong.
And the 'adjustable stabillzer' was not present for the P-38, and there was no other input to pitch up - due to the blanking of the elevatorHowever, you can of course still do this by using an adjustable stabilizer to pitch up. And this will increase the Cl and will get you out of the dive. But this is NOT because you have eliminated the shock wave, it's because you are using brute force. This means you have to pitch up to a slightly higher angle of attack than if no shock wave was present, because the shock wave has lowered the lift slope and you need to generate more angle of attack in order to get enough Cl to get you out of the dive.
Well, Bye then.And with that my participation in this thread is done. I have no doubt that this will be met with yet another dose of impressive sounding aerodynamic word salad but I have no intention of wasting any more time on this.
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I should have mentioned that Chaos Theory was a guiding barrier for me to not pursue a PhD.Chaos Theory was my watershed moment in my MS degree. I got through Calculus of Variations and Control Theory, but the Chaos course earned me my only B (there were no As) and the fool teaching the course flunked half the class. He shall remain nameless but forever cursed.
I still have no clue regarding how to apply the theory to the practical prediction of the formation of turbulent eddies in the transient turbulent boundary layer.
I'd even tried googling some of the wake turbulence whatever exacerbated by the venturi effect something or other and even it told me to step away from the keyboard and go play outside.Dammit, I wish you guys would speak English...
First time he made sense.'Twas brillig, and the slithy toves
Did gyre and gimble in the wabe;
All mimsy were the borogoves,
And the mome raths outgrabe.
"Beware the Jabberwock, my son
The jaws that bite, the claws that catch!
Beware the Jubjub bird, and shun
The frumious Bandersnatch!"
He took his vorpal sword in hand;
Long time the manxome foe he sought—
So rested he by the Tumtum tree,
And stood awhile in thought.
And, as in uffish thought he stood,
The Jabberwock, with eyes of flame,
Came whiffling through the tulgey wood,
And burbled as it came!
One, two! One, two! And through and through
The vorpal blade went snicker-snack!
He left it dead, and with its head
He went galumphing back.
"And hast thou slain the Jabberwock?
Come to my arms, my beamish boy!
O frabjous day! Callooh! Callay!"
He chortled in his joy.
'Twas brillig, and the slithy toves
Did gyre and gimble in the wabe;
All mimsy were the borogoves,
And the mome raths outgrabe.
OK, I laughed out loud when I read this.I'd even tried googling some of the wake turbulence whatever exacerbated by the venturi effect something or other and even it told me to step away from the keyboard and go play outside.
Hi Bill,Equally curious regarding your 'non gobbledygook' analysis why you don't believe that the alteration of the pressure distribution aft of the shock wave, and thereby the Center of Pressure of the wing, moved forward causing the Moment about the A/c to cause pitch down aerodynamic forces.