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Blue on Top

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  1. Blue on Top
    @carusoam Keep your thoughts simple. It is the way Mother Nature works. As I mentioned to someone (it may have been you), it often helps to look at air flow the way it is on an airplane. The air is stagnate and the airplane passes through it. Any net results after passage is lift and drag. If one watches a tractor-trailer go by on a highway after/during a light rain, the flow is visualized (kind of … as water has more inertia). As one sees the water moving forward this is drag. Hope this helps.
  2. 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
  3. Blue on Top
    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
  4. Blue on Top
    You may want to tuft it to see what is going on. Just a thought.
  5. Blue on Top
    I’ll go through the slides tonight and make comments. I don’t think they have page numbers, though.
  6. Blue on Top
    @brndiar You can't believe everything that you find on the internet. -Abraham Lincoln
  7. Blue on Top
    @Cargil48 It's not a one or the other. It's 6 in one hand or 1/2 dozen in the other. Bernoulli and Newton are just ways that we humans try to quantify/define Mother Nature (physics, aerodynamics, fluid dynamics, etc.). An example that I use for myself is a seaplane. What keeps a seaplane up? Air and water are both fluids (both considered incompressible below M=0.3). Initially, when the airplane is static, water buoyancy keeps it in place. Displaced water weight = weight of the seaplane. As the seaplane accelerates (gains velocity), less water buoyancy is required and "lift" is produced by hull planing (one could call this Newton if they wanted to … or the pressure is greater on the bottom than on the top, too). When the seaplane gets on the step, there is now no water buoyancy, there is planing and the wing is producing some lift. When airborne, all lift is produced by the wing. So (and I apologize because I don't believe that there is a Mooney on floats) one can describe that whole sequence by physics … floatation, Newton or Bernoulli. Whether the airplane is fast or slow doesn't matter. All can be defined by pressures or Newton. The F-18 creates vortex lift at high AOA (that's what the strakes are for). Pressure above the wing is less than below the wing (or in this case, barn door (flat plate)) Blue on Top, Ron
  8. Blue on Top
    @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.
  9. Blue on Top
    Generically, there are so many incorrect statements in the video. At one point C1=C2 then later C1 does not equal C2. C1=C2 is correct (nothing is adding or subtracting energy). IOW (and this is how your altimeter and airspeed indicators work. Ptotal = Pstatic + Pdynamic. Pstatic is what your altimeter reads (and converts that pressure to altitude in feet). Ptotal is the pressure that your pitot tube takes in. rearranging the above equation Pdynamic = Ptotal - Pstatic. So, using differential pressure in the airspeed indicator, we convert Pdynamic to airspeed. Pdynamic, Qc, airspeed pressure or dynamic pressure (all of those are just different names for the same value) is 1/2 *rho*V^2. Using the above equation, wing designers trade between Pstatic and Pdynamic to shape the airfoil. In fact, some of the newer programs define a velocity gradient, and the program produces the airfoil shape.
  10. Blue on Top
    @PT20J Aman, Brother! 1) Aerodynamicists don't think that way; they simplify. We think in terms of (aircraft) AOA (1 value) that is required to stall that section of wing. It's a simple curve of stall AOA vs wing span location. Flaps (and ailerons) lower the aircraft angle of attack to stall that portion of the wing. 2) YES! And they all say, "AMEN" (note: sorry, I love my job). 3) And wing design is to tailor an elliptical lift distribution that stalls root to tip … and if you mess that up, there are stall strips and VGs to help Blue on Top, Ron
  11. Blue on Top
    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
  12. Blue on Top
    I've done a couple things with your post @carusoam to make it a little easier and shorter: I've removed text I don't reference and added numbers to your questions/my answers. 1) No; not at all. The speed brake simply adds drag (the design intent is not to lose lift/separate air flow). 2) The speed brake will cause drag. Flow separation will happen behind the speed brake and a little to the sides, depending on the hole percentage and pattern. The stall strip will separate flow at the leading edge with a triangle/wedge of separated flow behind. As AOA increases, the pattern behind the stall strip will be a triangle with the base being the stall strip and the point pointing aft. As AOA increases, the sides will spread out (get closer to being parallel to the ribs). The sides will continue to spread with increasing, making a larger and larger wedge of separated flow (and lost lift). 3) Reference 2) above. 4) As far inboard as possible without a) the wake hitting the tail (or side of fuselage) and b) losing too much lift (that's not the intent). Too far outboard and a non-symmetric deployment could get really ugly. 5) No. 6) The buffet you feel is either separated/turbulent flow hitting the wing and/or that flow hitting the horizontal stabilizer. 7) The majority of the wing is still fly through the stall (80%-ish). If it goes into a spin, you are outside of the aft CG envelope or you have enough elevator to continue (it should fall in pitch first) … I won't go there at this time. 8) It is much, much easier to talk in terms of one AOA, aircraft AOA. Pilots want to simplify the crap out of detailed engineering work, but in reality the have complicated it greatly. From an aerodynamics point of view, the airplane has 1 AOA (yes, the local AOA is different at every point on the airplane). The left and right wing have the same AOA … until the airplane is in a spin. Please simplify your life. The way aero people think about a down aileron is NOT an increase in AOA because the chord line changes (that is incorrect). We think that that portion of the wing will stall at a lower AOA (we don't change the chord line). If you want to change the chord line, also change the camber, the gaps, etc. … e.i. it's a completely different airfoil. 9) The pilot doesn't know and just continues to fly the airplane. One will feel the drag of the speed brake … not the stall strip. The second half gets letters … to be continued.
  13. Blue on Top
    Sorry, all. I haven't listened to Rod's video yet, but I am an aerodynamicist. I'll get to Rod's video later this evening. In very simple terms everyone has made true statements (and the contrary is true, too). Bernoulli cannot explain 100% of lift generation nor can Newton. They are both utilized in the Navier-Stokes equations that used to be computed by hand, but are now imbedded in CFD programs. For real CFD simulation, the boundary layer also has to be modeled. There are also good CFD programs that model well enough to run loads programs and the like. Some of the good programs will model the separation point, but programs are getting better (but not there yet) on modeling the flow (and boundary layer) after separation. Now, for popular misconceptions. #1 Air flow does not hit the physical "leading edge" of the airfoil. Remembering that the wing is twisted (every span-wise local AOA is different), we'll simplify to 2D and look at a single span-wise location (say at the stall warning switch). So, looking at a 2D airfoil, the air "hits" the airfoil below and aft of the leading edge at a point called the stagnation point. The stagnation point is where the air hits the airfoil and stops (in a perfect computer world). Air flow above the stagnation streamline (yes, there is upwash before the wing … and propeller) flows forward and around the top of the airfoil, and air flow below the stagnation streamline flows along the bottom of the airfoil. The upper surface particles don't move faster because they know it's a longer distance. They travel faster because they are pulled faster by a lower pressure. The stall warning horn activates when the stagnation point is aft of the vane, and the forward moving air flow pushes the flipper up into the contacts inside the switch. Brutally simple #2 (depending on AOA) Static air pressures on the bottom of the airfoil are not higher than ambient pressure. At low AOAs the majority of the bottom of the airfoil is also below static ambient pressure. They are higher than static pressures on the top of the airfoil, though. It is this delta P that creates lift. #3 Camber (curvature) is not required to create lift. Note: the second video has a lot of errors in it. The "curvature" (shape of the mean camber line) is a large factor in the efficiency of the airfoil. The straight slope of Cl vs. AOA curves is the flat plate lift of the airfoil. Note: airfoil design is complicated. Time to take a breath. Great thread. -Ron
  14. 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!
  15. 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.
  16. 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.
  17. Blue on Top
    @jetdriven YOU are just so freakin' cool!!!!!!!! Way cool work. I'm excited for you, and hope you find really positive results. A small note of irony (and I am sarcastically laughing about this, sorry): As one watches the video (as I did over and over), where was this airplane made?
  18. 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.
  19. 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.
  20. Blue on Top
    That's interesting. How does it compare weight-wise to copper without a fiberglass interface ply?
  21. Blue on Top
    Who uses aluminum mesh in composites? As @philiplane stated, carbon and aluminum don't work well together. Beech proved aluminum mesh didn't work back in the Starbarge days. Personally, I believe everyone is using copper mesh today … with some trying a spray on layer.
  22. Blue on Top
    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. 2) The article sounds cool, and I think I remember it now that you mention it, but it would definitely be fun to read it and learn more again. If the idea were good, it would be on every airplane made today, though. 3) A winglet doesn't have to be expensive or complex. I want to say more, but I'm guessing that Mooney won't give me access to a couple of their reports I'd need. . 4) I know the gains would be a lot more … (and this is heresy) … not everything is about top end speed Thinking out loud way too much. -Ron
  23. Blue on Top
    @cliffy I'm guessing you want me to say VGs, which I have no problem doing ... and for improved roll control. I'll also repeat that every airfoil is different. I've never worked at Lear or Bombardier (though they are on the other side of the airport and we've traded pilots and FTEs). I do know that every time a leading edge is removed (and either reinstalled or replaced) a stall series need to be completed by a factory test pilot. That tells me that although the VGs might be doing something, the LE is a much, much bigger driver of the stall characteristics. This is just aerodynamics. Learjets are good airplanes, too. I agree with you Cliffy. I know several wings on certificated airplanes that separate at the LE first. That doesn't mean stall characteristics are bad. In fact, as I say in my presentations, 2D airfoil characteristics have little or nothing to do with whole aircraft stall characteristics. To bring this back to Mooney, small, GA business jets fight for every 1/2 knot of stall speed (it determines takeoff/landing performance). Sales are won and lost over 100-200 feet of runway performance. This is not true for small, propeller-driven, GA airplanes. But, the Mooney wing is currently limiting other aspects of the aircraft because of its CLmax. A real winglet would help the M20 … in many ways. There's a big hint, Kerrville.
  24. Blue on Top
    @jetdriven Wow!!! Very cool. I’d like to know what you find. Let me know if I can help in any way. Beautiful work. Does this include removing the rumored inboard flat spot on the top of the airfoil? Dang you guys are good!
  25. Blue on Top
    @chinoguym20 From my viewpoint (which may or may not be accurate) … and I can't say everything that I would like to on MS. From what I saw, money was never a problem at either location (TX or CA) … until investor schedules/deliverables were not met. Both of those were totally unrealistic. Do I personally believe that Mooney can be turned around? YES!!! Without laying out a complete plan for them on MS, yes. A couple minor beginnings have been brought up here, along with some of their downfalls. The storied and iconic book, "Who Moved My Cheese" is the nail on the head. Mooney hasn't meaningfully looked for new cheese. I need to stop. Bottom Line: I would love, love, love to turn them around . Looking for the $100M to get us going … smartly and leanly.
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