Mooney Aerodynamics

[Cargil48]

A fantastic pic about a big plane (without winglets) flying through thin cloud layers. The big vortices are the effect of the lift inducing difference of pressure between the upper and the lower parts of the wings.

[Blue on Top]

1) @Cargil48  The book looks really way cool … I'll have to checkout more of my favorite stores for it (Half Price Books).

2) @Shadrach  You're correct.  The wingtip vortices are a result of producing lift on a wing that is not infinite span.  This is why 2D CFD and wind tunnel airfoil data looks so appealing.  All those really high numbers have to be knocked down to 3D reality.  But aero folks know that. (in other words, aero folks, don't shoot me

3) Someone mentioned something earlier about getting rid of the "sheared" tips (i.e. the wingtip looks like they just ended the wing at the last rib).   This configuration is really not that bad.  The important part is that the vortex comes off the wingtip leanly.   In other words, sharp edges are actually good.

4) Winglets are better for existing designs where span cannot be grown (think airline gates and GA hangars that have 40' wide doors) and the airplane has gained weight since the original certification (ummmmm … that would be EVERY airplane in the world.

[PT20J]

Here's a description of how winglets work from Richard Whitcomb taken from patent US5407153A.

Winglets long have been used in the aircraft industry as a method for reducing drag, the retarding forces which act on an airplane as it moves through the air. Decreased drag results in increased fuel efficiency.

Winglets are small lifting surfaces attached to the outboard end of an airplane wing, commonly at or near to a vertical angle from the wing structure. Winglets function to relocate the tip vortex of an airplane wing further outboard and above the unmodified location. In flight, the substantially inward pointing load carried by the winglets relocates the wing tip vortex.

Due to pressure differentials between wing surfaces at a wing tip, air tends to flow outboard along the lower surface of a wing around the tip and inboard along the wing upper surface. When winglets are added, the relocated wing tip vortex caused by the winglets produces cross-flow at the winglets, which often are perpendicular to the flow across the wing surfaces. The side forces created by such cross-flow contain forward components which reduce drag.

[Blue on Top]

Okay, I'll put a plug in for my very good friend, Paul Bowen.  This is one of his signature shots.  His photography work is fantastic.

Note: Even with winglets, there are still wake vortices.  Horizontal wing is more efficient.  And, to answer an earlier question, yes, the wing lift distribution changes (there would be no gain if it didn't … only more drag).  As a direct result, the wing bending moment goes up, too.

[Ibra]

In gliders, some are just there because they look cool as they do reduce cruise performance but they help with climbing on thermals, they tend to be the ones on high wing span gliders with a disproportionate winglet height 

Active ones may give a decent fuel saving, the fixed ones will be a trade-off on cruise/slow speeds and also to fit structural specs: winglet behaviour is better acheived by having long wings...

[Cargil48]

5 minutes ago, PT20J said:

Here's a description of how winglets work from Richard Whitcomb taken from patent US5407153A.

(...)

Due to pressure differentials between wing surfaces at a wing tip, air tends to flow outboard along the lower surface of a wing around the tip and inboard along the wing upper surface. When winglets are added, the relocated wing tip vortex caused by the winglets produces cross-flow at the winglets, which often are perpendicular to the flow across the wing surfaces. The side forces created by such cross-flow contain forward components which reduce drag.

While you were writing this, I was drawing my idea of a possible good solution for a winglet. It is in reality a design which is not new but in the existing form it follows the contour of the wingtip, i.e. it has the same width of the tip of the wing. My idea is the other way round, making it longer, to allow a bigger separation between the lower pressure area (up side of the wing) and the high pressure area (lower part of the wing). This would allow more area for the delta P to equalize without creating these huge vortices. And since (in my idea) the upper  part of the winglet and the lower part (the fence) would be thin (sharp) but very strong (carbon fiber??) although bigger than usual, it would create low resistance to the passing air. 

Two pics: One the original, the second one my idea. Call me nuts, if you wish...  

[Blue on Top]

@Ibra  Same for the Citation X.  The wing is optimized for high speed cruise … without the winglet.  Second segment climb is better, though.

[Blue on Top]

@Cargil48  You should play with these in CFD (if you're not already).  Who knows?  Just be careful about the wing/winglet intersection interface (and drag).  There are some really, really funky things on the HondaJet winglet (there are lots of configurations, too).  Winglets, winglets with VGs up the leading edges, winglets with VGs and a monster fence in the intersection, etc.

[Cargil48]

4 minutes ago, Blue on Top said:

@Cargil48  You should play with these in CFD (if you're not already).  Who knows?  Just be careful about the wing/winglet intersection interface (and drag).  There are some really, really funky things on the HondaJet winglet (there are lots of configurations, too).  Winglets, winglets with VGs up the leading edges, winglets with VGs and a monster fence in the intersection, etc.

Thanks for the suggestion but I have only a normal laptop for my entertainment (I'm retired already) with only simple programs coming with W10... And the ideas I write down here come into my mind as I read other people's comments, here... If I still had my big scale r/c sailplanes, I might then make experiences... but now I have only one way to go: follow my logic and make you my judges... 

Regards,

Carlos

Edited December 18, 2019 by Cargil48

[PT20J]

On 12/17/2019 at 10:42 PM, Blue on Top said:

1) I think this is a rumor that was brought up again at MooneyMax.  I am (educated) guessing the stall strip locations are documented on a drawing with a small tolerance on location.

I checked with Bob Kromer and he confirmed that the stall strips are fine tuned during production flight test:

Due to variations in wing manufacture between airplanes, the stall strips are taped in place on the wing leading edges for the first production test flight.  Stall strip locations are defined spanwise.  Vertically around the leading edge radius, they are variable in location.  For first flight, they are positioned vertically at the radius center (stagnation points) of each wing leading edge radius. The production pilot then performs a variety of power-off, wing level stalls to verify the airplane meets the certification requirement of plus or minus 15 degrees roll-off during the stall maneuver.  If it does with the initial stall strip locations, they are then fixed in place and secured with screws.  However, in general those initial stalls show excessive roll-off in on direction.  In that case, the pilot returns and will adjust the stall strip on the "heavy" wing downward about 1/4" below the wing leading edge stagnation point.  Moving the stall strip downward from the leading edge stagnation point slightly delays the stall strip tripping the air flow.  This causes the "heavy" wing to maintain lift a bit longer during a stall maneuver, better matching the "airflow separation angle of attack" of the light (rising ) wing during the stall.  Both wings should now stall about the same time, reducing the wing drop or roll-off tendency previously seen.  A good production test pilot can generally set the stall strips in two flights.

Skip

[Blue on Top]

@PT20J  Interesting.  The initial chord-wise position must be conservative as it assumes that the stall strip is what is stalling the wing (which is what I saw with Scott's airplane).

On the other hand if it is rolling (left for example) due to improper wing twist in build, lowering the stall strip on that side will make it worse (or at best not change it).  The lower those stall strips are located, the lower the stall speed will be … until you get to the real aerodynamic stall … which could be hiding some bad stuff.

Thanks for the great information!

[PT20J]

59 minutes ago, Blue on Top said:

@PT20J  Interesting.  The initial chord-wise position must be conservative as it assumes that the stall strip is what is stalling the wing (which is what I saw with Scott's airplane).

On the other hand if it is rolling (left for example) due to improper wing twist in build, lowering the stall strip on that side will make it worse (or at best not change it).  The lower those stall strips are located, the lower the stall speed will be … until you get to the real aerodynamic stall … which could be hiding some bad stuff.

Thanks for the great information!

On my current ‘94 J, the stall strips appear to be at the same location vertically and it stalls wings level with very little roll off. Years ago, I owned a ‘78 J and the stall strips were obviously in different vertical locations and it had a pretty abrupt roll off. I always wondered if they were positioned at the end of the day on a Friday before beer call

Skip

[brndiar]

On 12/18/2019 at 9:05 PM, Cargil48 said:

A fantastic pic about a big plane (without winglets) flying through thin cloud layers. The big vortices are the effect of the lift inducing difference of pressure between the upper and the lower parts of the wings.

The airplane keeps itself up by beating the air down.... NEWTON.   

Nice Picture.

[carusoam]

Good Morning MS Austria!

There sure is a balance of forces there somewhere...

Something is holding hundreds of thousands of pounds of airplane up in the sky... the only thing there, is air...

That air has to supply an equal and opposite reaction (force)... or an acceleration would occur... due to gravity...

We often discuss the effects of lift on the plane... and most often ignore the effects of lift on the air around us... until we are looking at videos of wake turbulence... and how to avoid the disruptive votices that hang around the runway after heavy planes have landed, or have taken off... 

PP thoughts only, not a physicist...

Best regards,

-a-

[carusoam]

Great MSer activity Skip!

Talking to the guy who knows the most about Mooneys, that is still available to talk to...

Thank you for sharing the details!

Excellent input, Ron!

 

Let's talk stall strips for a moment, if we can...

Do they behave in a similar way, aerodynamically as speed brakes?

As in....

• when they are altering airflow About the wing....
• they disrupt the airflow about 3X the width of the strips themselves... including end effects (generally speaking)
• essentially removing that much lift that the same percentage of wing length is providing...
• briefly, a foot of mechanical disruption turns into a loss of lift for three feet of wing... (roughly speaking, end effects occur everywhere in flow challenges)
• We have four of these things, two per side...
• what defines there placement side to side?
• At a high AOA where the stall strip is above the split line... it is like deploying a speed brake...
• Lack of lift, in that section of wing is going to make that wing get proportionally heavier...
• So the buffet we are feeling... is lift from a section of wing that is getting turned off by airflow disruption locally near the stall strips...
• and... the wing is still flying, in control near, the critical AOA...
• As a pilot holding the plane’s attitude, so the stall strips are above the split line, the rest of the wing needs more AOA to maintain altitude...
• what does the pilot see, perceive, feel, when this controlled loss of lift in those sections occurs?
• Is it masked by the same feelings and observances as flying in turbulence...?

My plane is quite docile in the stall... keeping the ball centered during slow flight... intentionally raising the nose until airspeed is near Vso, (flaps and gear down stall speed) the horn is sounding...

There is so much going on at the same time... the buffet isn’t as noticeable as I was expecting it to be...

In straight flight, the AOA is a giveaway that a stall is next on the list... bumpy air will pretty much mask the buffet occurring...

Add in some bank angle... while ignoring the buffet will be the final nail in the turn to final... talk about a coffin corner... 

Briefly,

• how do those stall strips work?
• what do they do?
• how do we recognize it better?
• what do we look for the next time we are at a safe altitude practicing slow flight, to recognize the signs of stalls before they occur...

Is it possible that this is a very dynamic situation where the airflow is interrupted, restored, and interrupted again... in cycles...

• a loss of lift locally occurs,
• the AOA is improved by the loss of lift
• the airflow is re-established
• The full lift occurs again
• holding back on the yoke could potentially cause hundreds of pounds of lift to get interrupted, and then turned back, on as the AOA has the actual split line drift above and below the stall strips...

sorry for the long-winded questions... I got up early with ideas I needed to write down...   

Questions of a PP, not a test for the MS CFIs, engineers, or closet aerodynamicists... 

Best regards,

-a-

 

 

 

 

[0TreeLemur]

1 hour ago, brndiar said:

The airplane keeps itself up by beating the air down.... NEWTON.   

Nice Picture.

As you are thinking about it, Newton doesn't really work that way in the case of a flying wing.  The tip vortices are a symptom of lift, not the cause of it.   The thing that keeps a flying wing aloft is the pressure distribution, with higher average pressure below the wing than above.   This causes a flow of air from the lower surface to flow towards the upper by wrapping around the wingtip.   That creates a tip vortex.  

Theoretically, and infinitely long wing will produce lift and no tip vortices.  This truism is a useful device to help keep you thinking about lift generation correctly.

Tip vortices represent lost energy.  Minimizing them through winglets and other such devices reduces the lost energy and therefore decreases drag.  Winglets don't decrease lift.

The equation that principally describes why an airfoil generates lift is Newton's F=ma, except written to calculate the force perpendicular to the streamlines, not along them.  The radius of curvature of the streamlines appears in this equation, which shows how flow curvature created by the shape of the airfoil affects the pressure distribution on the airfoil.  Of course, the actual situation is much more complex, requiring the use of computational fluid dynamics codes, especially if compressibility effects become important, which happens above approx. Mach No. 0.2.

[brndiar]

1 hour ago, 0TreeLemur said:

As you are thinking about it, Newton doesn't really work that way in the case of a flying wing.  The tip vortices are a symptom of lift, not the cause of it.   The thing that keeps a flying wing aloft is the pressure distribution, with higher average pressure below the wing than above.   This causes a flow of air from the lower surface to flow towards the upper by wrapping around the wingtip.   That creates a tip vortex.  

Theoretically, and infinitely long wing will produce lift and no tip vortices.  This truism is a useful device to help keep you thinking about lift generation correctly.

Tip vortices represent lost energy.  Minimizing them through winglets and other such devices reduces the lost energy and therefore decreases drag.  Winglets don't decrease lift.

The equation that principally describes why an airfoil generates lift is Newton's F=ma, except written to calculate the force perpendicular to the streamlines, not along them.  The radius of curvature of the streamlines appears in this equation, which shows how flow curvature created by the shape of the airfoil affects the pressure distribution on the airfoil.  Of course, the actual situation is much more complex, requiring the use of computational fluid dynamics codes, especially if compressibility effects become important, which happens above approx. Mach No. 0.2.

Newton's third law is: For every action, there is an equal and opposite reaction.

2 tonns of air deflected with wings down = 2 tonns of aluminium up in the sky :-))))

 

 

[Ibra]

6 hours ago, 0TreeLemur said:

As you are thinking about it, Newton doesn't really work that way in the case of a flying wing.  The tip vortices are a symptom of lift, not the cause of it.   The thing that keeps a flying wing aloft is the pressure distribution, with higher average pressure below the wing than above. 

Yes, Newton laws still work by looking at how the overall airflow: is deflected by the wing, it comes in straight and goes out deflected behind and bellow the wing, the change in airflow momentum equals the drift & drag components of aerodynamic forces (some would refer to this as Lagarange descriptions) while alternatively, you can look use Bernoulli laws to get pressure distribution along the wing and calculate aerodynamic forces (some would refer to this as Euler desciptions)

The problem is that neither of these "theories" provide an accurate description of vortices in wing tips or turbulences behind a stalled wing (actually there are better theories when inertial forces dominates viscosity, RANS or K-omega, but you may not have robust solvers or enough compute power)

On a side note, the transition from laminar to turbulent has been assumed to be irreversible but recently it has been shown that you can revert to laminar flow by perturbations at least in fuel pipes, so I expect something similar for the new generation of winglets to be able to wiggle and completely cancel wing wake turbulences (on that same innovative wing, if you stall you should be able to to recover by repetitive jerky movements of the stick  )

Also there is less intuition on the relation between total drag and turbulent/laminar flow, look at golf balls and ask why they are dented?though, I don't expect a dented PA28 wing to have less drag than a clean M20J wing even at slow speeds 

https://www.sciencedaily.com/releases/2018/01/180108121612.htm?fbclid=IwAR1q6iwRsbnO7k4OIwA6tHBA7BEwF0zt3piL3fiQrYBN-Jzk56TUBfcMbj0

Edited December 22, 2019 by Ibra

[carusoam]

I would check your math, if I could, Ibra... 

I know a math guy that might be interested... in this Part of the topic...

Inviting @aviatoreb... to stop in...

Best regards,

-a-

[EricJ]

I don't think relativistic effects are keeping airplanes up in the air, or most of them, anyway, so I'm going with Newtonian physics. 

Mooneys are fast, but not that fast.

 

[PT20J]

4 hours ago, brndiar said:

Newton's third law is: For every action, there is an equal and opposite reaction.

2 tonns of air deflected with wings down = 2 tonns of aluminium up in the sky :-))))

 

 

An airfoil (2D) produces lift and drag. If you look at the airflow around it, there is an upwash ahead of the airfoil and a downwash behind it. Mathematically, half the lift comes from the upwash. 

There is a lot of confusion about lift because of the incomplete and over-simplified explanations (Bernoulli, Newton) we learned in private pilot ground school and the fact that a lot of drawings of airflow around a wing are incorrect. In order to understand lift, it's best to avoid cause and effect arguments. The wing forces the air to go around it. In so doing, there are velocity (speed and direction) and pressure changes. The velocity changes and pressure differences are part of the dynamics of fluid motion, and trouble brews when you try to figure out which causes which. My friend Rod Machado and I discussed this a while back and he ended up making a Youtube video about it. 

 

 

 

Skip

[EricJ]

32 minutes ago, PT20J said:

There is a lot of confusion about lift because of the incomplete and over-simplified explanations (Bernoulli, Newton) we learned in private pilot ground school and the fact that a lot of drawings of airflow around a wing are incorrect.

Thanks for the link.   Like most of Rod's stuff, it's very good.

I'd pick the small nit, though, that Bernoulli's principle, the Coanda effect, etc., etc., are all Newtonian physics.   They are not separate things.   Unless/until one gets to the point where relativistic or quantum effects have to be taken into account, it's all Newtonian.

 

[PT20J]

4 minutes ago, EricJ said:

Thanks for the link.   Like most of Rod's stuff, it's very good.

I'd pick the small nit, though, that Bernoulli's principle, the Coanda effect, etc., etc., are all Newtonian physics.   They are not separate things.   Unless/until one gets to the point where relativistic or quantum effects have to be taken into account, it's all Newtonian.

 

Agreed. And, I'm also not convinced that the Coanda effect applies since it refers to a jet of fluid and (as I understand it) has to do with the jet entraining adjacent fluid, so it might not work the same way with a 3D wing. http://thermofluids.co.uk/effect.php. But I understand that Rod was looking for some explanation as to why the air would follow the wing's curvature. I think it's easier to simply ponder, where else could it go?

Skip

[Ibra]

1 hour ago, EricJ said:

Unless/until one gets to the point where relativistic or quantum effects have to be taken into account, it's all Newtonian.

Yes all classical physics, it does not mean it is intuitive or simple, here is one: 

https://www.grc.nasa.gov/www/k-12/airplane/dragsphere.html

I still find it hard to explain to a PPL how a wing flies inverted flights using just Bernoulli or why a wing will never stall in low gravity, so something else may help here 

[N201MKTurbo]

1 hour ago, Ibra said:

Yes all classical physics, it does not mean it is intuitive or simple, here is one: 

https://www.grc.nasa.gov/www/k-12/airplane/dragsphere.html

I still find it hard to explain to a PPL how a wing flies inverted flights using just Bernoulli or why a wing will never stall in low gravity, so something else may help here 

Wings fly inverted the same way they fly right side up. Aerobatic planes usually have symmetrical airfoils so the wing performs the same upside down or right side up. Even though the wings are symmetrical, they have an angle of incidence that favors right side up flight. you will notice some aerobatic planes fly very nose up while inverted to compensate for this angle of incidence.