Mooney Aerodynamics

[brndiar]

1 hour ago, Blue on Top said:

@brndiar  You can't believe everything that you find on the internet.  -Abraham Lincoln

https://docs.google.com/file/d/0B0JABuFvb_G_MkpBZHJmRGo3UkU/edit

Presentation Slides for the Lecture:

Totally agree with you.

But please, could you explain, what is incorrect there (Presentation of Holger Babinski, Dep. Engineering University of Cambridge- Journal of Phys Enducation, Vol. 38, Nov 2003) ?

PPI only.

lg.m.

Edited December 23, 2019 by brndiar

[Blue on Top]

12 minutes ago, brndiar said:

Totally agree with you.

But please, could you explain, what is incorrect there 

lg.m.

I’ll go through the slides tonight and make comments.  I don’t think they have page numbers, though.

[Nippernaper]

2 hours ago, Blue on Top said:

@Nippernaper  Yes, you can do something about it … especially if it goes the same direction every time.

1) Keep the ball centered.   No yaw --> No spin  

2) Stall strips get rid of lift, intentionally.  So … you have a little work to do.  a) How do your stall speeds compare to book?  b) Does the airplane roll the same direction all the time?  c) Does the airplane roll both with the flaps up and down?  d) Can you stop the roll with the rudder (or aileron … not recommended)?  d) Do the stall strips look like they are in the same position?  Span-wise is not as critical as up and down.

3) No VGs.  They add drag … and we don't know where to place them (they wouldn't help anyhow).  VGs may help if flow over the ailerons was separated (that should not be the case).

If you're keeping the wings level (within 15 degreed), you're meeting the certification requirements.  Keep the ball centered.  Something might be bent/twisted (aileron, flap, wing tip, etc.).  Your answers will lead us to a solution.

Ron:

1) Understood, and of course that's always the goal!

2a) I wasn't looking too closely, but from what I remembered they weren't very far off.  I'll download the flight data and check.  b)c)  Yes, always to the right, clean or dirty.  d) Yes, it does eventually stop rolling with rudder.  Interestingly, adding power before unstalling the wings did bad things; needed to release back pressure before adding power.  e) I'll take a close look today and get back to you.

Couple of other points of information; plane has damage history to wings (previous owner).  Just had the plane rigging checked at an MSC.  Right aileron is slightly up in cruise (when flying straight and level).  This would seem to jibe with right wing drop; normally at higher AOA than left (hence the need for up right aileron) therefore earlier stall.

Edited December 23, 2019 by Nippernaper
clarification

[Austintatious]

6 hours ago, ArtVandelay said:

I think meant for the first sentence to say “Incompressible” fluids?

 

 

Tom

yes, I did.  oops

[Cargil48]

3 hours ago, Blue on Top said:

@Cargil48  It's not a one or the other. 

(...)

Whether the airplane is fast or slow doesn't matter.   (...)

Blue on Top, Ron  

Hi, Ron

Thanks for the reply. We do not agree on this one, nor is it a reply to the two points I mentioned. But I do not want make this a never ending story, also (or because) you are the expert, not me, so...

Regards, Carlos

Edited December 23, 2019 by Cargil48

[Stephen]

C'mon guys, you need to get this solved! None of us can hop in and safely fly now that we've discovered the physics are not fully understood and agreed upon!

 

 

[EricJ]

6 minutes ago, Stephen said:

C'mon guys, you need to get this solved! None of us can hop in and safely fly now that we've discovered the physics are not fully understood and agreed upon!

It's a good thing we have MS to clarify things!   Oh, wait... 

 

[Cargil48]

36 minutes ago, Stephen said:

C'mon guys, you need to get this solved! None of us can hop in and safely fly now that we've discovered the physics are not fully understood and agreed upon!

This includes EricJ also... Why did I say I did not agree? Because of this phrase from @Blue on Top: "Whether the airplane is fast or slow doesn't matter." IMHO it does, because faster airplanes (with the same airfoil on the wing) get more lift than slower ones. And changing AoA, also...  Number two: I mentioned the two (for me...) different aspects making a wing getting "that up movement": the famous delta P (I think now everyone knows here what that means...) and that example Peter Garrison wrote down, the surface in the slipstream getting up or down according to the AoA (the boy's hand). For me, two different aspects, totally different! One is one aspect of physics: the delta P. The other one is another aspect of physics, the reaction of a fluid to the incidence of a given surface. Example: You deflect the rudder on your plane to one side, the tail gets to the opposite side. That has zero to do with lift but with deflection and reaction to that deflection. And the faster your airplane goes the stronger the reaction to your input will be... Did I explain myself correctly?

(I wonder what kind of lift Santa is getting in his flying sleigh...   )

Edited December 23, 2019 by Cargil48
Typo

[Stephen]

51 minutes ago, Cargil48 said:

(I wonder what kind of lift Santa is getting in his flying sleigh...   )

@Blue on Top @Cargil48

You may laugh, but actually that is being worked on as we speak , er ah.. type!

Obviously there are some issue with turbulence at the open interior and rear end...

So, thinking this:

Obviously needs to be supersonic:

And, low observability:

 

 

 

[Austintatious]

1 hour ago, Cargil48 said:

(I wonder what kind of lift Santa is getting in his flying sleigh...   )

From the documentaries I have seen, it all depends on how high The Christmas spirit meter is!

[Stephen]

15 minutes ago, Austintatious said:

From the documentaries I have seen, it all depends on how high The Christmas spirit meter is!

Sounds perfectly reasonable. 

[Blue on Top]

11 hours ago, Nippernaper said:

Couple of other points of information; plane has damage history to wings (previous owner).  Just had the plane rigging checked at an MSC.  Right aileron is slightly up in cruise (when flying straight and level).  This would seem to jibe with right wing drop; normally at higher AOA than left (hence the need for up right aileron) therefore earlier stall.

You may want to tuft it to see what is going on.  Just a thought.

[Blue on Top]

10 hours ago, Cargil48 said:

Hi, Ron

Thanks for the reply. We do not agree on this one, nor is it a reply to the two points I mentioned. But I do not want make this a never ending story, also (or because) you are the expert, not me, so...

Regards, Carlos

Depends on definition of "fast", too.  The air doesn't know if the airplane is fast or slow.  There is a bow wave ahead of a subsonic airplane.  There is a shockwave at the leading edges of everything when the airplane is supersonic.  There are also shockwaves on a lot of the airplane (including the wings) when the airplane is transonic.  All of these terms are just names for pressure variations.  Always learning, Ron

[Austintatious]

I printed and refined the experiment showing that Bernoullis principal is not the explanation to how lift is produced.   If you have a printer you cant try it out yourself!

 

https://www.thingiverse.com/thing:4063238

[Blue on Top]

@brndiar

Slide 4/5 - Picture is incorrect as the air flow doesn't contact the physical leading edge.  The stagnation point is below and aft of the highlight (leading edge).  The path above is longer across the top than the bottom.  What is more important is that there is more vertical movement of the air over the top … and therefore higher velocity.

Slide 7 (second sailboat) - The hull of the sailboat is also huge factor (but ignored in the picture).

Slide 9 - this wind tunnel test has been proven inaccurate many, many times.

Slide 13 - If pressure is lower in front and higher in back, it would be anti-drag.  We would get several long dissertations about anti-drag yearly.

Slide 16 (Bernoulli Equation) - the top line states that C is a constant (which is total pressure),  The bottom line says that C1 does not equal C2, which is contrary to C = constant.  Reality is that C is a constant.

Slide 22 - Pls > Pamb is a false statement.

Slide 23 - The fat airfoil is upside down

Slide before last - Ball lifts (and friction is required) because velocity on the right side is higher than free stream and velocity is lower than free stream on the left side due to rotation of the ball and boundary layer (friction).  

Last slide - No comment  

thanks, Ron

[carusoam]

On 12/22/2019 at 10:37 PM, Blue on Top said:

A)  Good one.  You're talking to an engineer  

b) Stall strips work by separating airflow behind them on the upper surface as AOA increases.  Airflow moving forward from the stagnation point (on the bottom of the airfoil) at some point can't make the corner around the stall strip and the flow separates.  That's why it is important that the leading edge of the stall strip be sharp.  We use stall strips to tailor the stall progression (inboard to outboard).

C) You can't … unless the wing is tufted.  It is all feel at this point.

D) Possible, but I have not seen that on a Mooney.  Citation X (with stall strips not in the certificated positions) and T-38, YES.  T-38 will do that all the way into the ground.

E) No. Reference "D)" above.  I'm kinda confused by the question.  

I love answering questions; we both become smarter.

Thanks, Ron

 

 

Thanks for the extra details...

I was thinking parts of the wing were no longer generating lift... 

I think I made it more complex than possible...

Best regards,

-a-

[bonal]

19 hours ago, Stephen said:

C'mon guys, you need to get this solved! None of us can hop in and safely fly now that we've discovered the physics are not fully understood and agreed upon!

 

 

Engineering and science still can't agree on this because they think out of the left side of the brain. Us right side folks know it's all about delta P which really means pixie dust. It's not about who makes the best wing or most powerful engine but who makes the best pixie dust. I have really enjoyed this thread.

[Ibra]

Reminds me 

1 hour ago, bonal said:

Engineering and science still can't agree on this

You can't start production unless you kick the scientist out 

You can't start flying unless you kick the engineer out 

You stop flying when you kick pilot and mechanic out 

Here is an illustration, what makes the Mooney turn? 

[0TreeLemur]

3 hours ago, bonal said:

Engineering and science still can't agree on this because they think out of the left side of the brain. Us right side folks know it's all about delta P which really means pixie dust. It's not about who makes the best wing or most powerful engine but who makes the best pixie dust. I have really enjoyed this thread.

Read this, it is the closest thing you can find to a real explanation of how wings generate lift by causing streamline curvature.  Newton's second law F=ma written normal to the streamlines shows how streamline curvature creates a pressure gradient.  The rest (wing shape, fluid compressibility, axial symmetry, angle of attack, Reynold's number, laminar/turbulent boundary layer ...) is details.

http://cribme.com/cu/data/Chemical Engineering/Fluid Mechanics/Class Notes/Lecture6.pdf

If you don't understand it, just fly.   The amount of technology that we use that non-experts don't understand is incredible.  Anyone want to develop their own GPS system?

[jlunseth]

So, what causes ground effect? If (according to Machado’s video) Newton’s law prevails on the bottom side of the wing and Bernoulli’s on top, then one would expect downwash to be reduced in ground effect, viz. the downwash would begin to bend upward and cease to be downwash. But that would reduce lift, not increase it.  The alternative is - oh lord - that there is an increase in pressure between the wing and the ground. Which implies that there was some high pressure effect under the wing to begin with, holding the plane up (lift), and now it has increased. 

[carusoam]

Ground effect...  

the ultimate initial condition / limit... of the math model.

The high pressure under the wing can dissipate... when there isn’t anything in the way... the ground keeps this from happening within a few lengths of the wing itself...

Pure speculation on my part, which seems to not work very well, often...  

It turns out, I can’t just cant make this stuff up...

what causes ground effect... the ground!   
 

When looked at under the scope of fluid flow... We can keep a plate floating on top of small spheres with the slightest AOA...

This is called the lubrication approximation... the small spheres are like oil molecules, or air molecules... the tighter the two surfaces approach together, the higher the pressure becomes....

hmmmmmm....?

PP thoughts only, not a fluid dynamicist....

Best regards,

-a-

[N201MKTurbo]

Ground effect,

It was clear in my mind once. It is a little fuzzy now. Let's see, The wing tries to force the air down under the wing but can't so the pressure under the wing increases slightly. 

Hummm… Is that right? it has to be worth a few more posts.

[0TreeLemur]

2 hours ago, jlunseth said:

So, what causes ground effect? If (according to Machado’s video) Newton’s law prevails on the bottom side of the wing and Bernoulli’s on top, then one would expect downwash to be reduced in ground effect, viz. the downwash would begin to bend upward and cease to be downwash. But that would reduce lift, not increase it.  The alternative is - oh lord - that there is an increase in pressure between the wing and the ground. Which implies that there was some high pressure effect under the wing to begin with, holding the plane up (lift), and now it has increased. 

Ok.  Work with me here.

Imagine that when you are sitting in your car waiting to turn left.   Cars are whizzing by just a few feet away.   As they pass, they don't push your car away, they pull it towards those passing cars.  You can feel the motion.   Why pull towards and not push away?   Because the air being forced around their vehicle is moving around the car, which means that their car is surrounded by a region of air that has pressure less than the static atmospheric pressure.  That causes the ambient air to move towards the vehicle, and actually fills the void left behind each car as it continuously moves.

Ever notice that the same thing happens when trains pass each other in a tunnel?   The windows/walls are pulled out when the trains pass.

Your aircraft wing does the same thing.   The static pressure both above and below the wing is depressed because of this motion.

Near the ground, within 2 wingspans is the rule of thumb I've heard, the ground partially cuts off the flow of air upward towards the moving wing.  This causes the stagnation point on the leading edge of the wing to move downward a bit, because more of the air that fills the void left by they airplane's forward motion to come from above the wing.   This increases lift.  It also impedes creation of wing tip vortices a little bit, which reduces induced drag a little.

[PT20J]

8 hours ago, bonal said:

Engineering and science still can't agree on this because they think out of the left side of the brain. Us right side folks know it's all about delta P which really means pixie dust. It's not about who makes the best wing or most powerful engine but who makes the best pixie dust. I have really enjoyed this thread.

I think you'll find the answer near the end of this:

 

[PT20J]

4 hours ago, jlunseth said:

So, what causes ground effect? If (according to Machado’s video) Newton’s law prevails on the bottom side of the wing and Bernoulli’s on top, then one would expect downwash to be reduced in ground effect, viz. the downwash would begin to bend upward and cease to be downwash. But that would reduce lift, not increase it.  The alternative is - oh lord - that there is an increase in pressure between the wing and the ground. Which implies that there was some high pressure effect under the wing to begin with, holding the plane up (lift), and now it has increased. 

Here's one way to think about it. The flow around a finite-span wing far from the ground produces wingtip vortices and a net downwash behind the wing. As the wing nears the the ground, the ground interferes with the flow in such a way that vortices and downwash are reduced. It is as if the wing gains span. The result is that the aerodynamic force vector tilts forward. If we resolve the AF vector into a vertical component (lift) and rearward component (drag) the forward tilting increases lift and reduces drag.

Skip